SHELL - Well Planning
Transcript of SHELL - Well Planning
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Pr&@ntly,he is a full-time contractkafeeor
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ON
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. - ~ ' \ , L W . ~ t d ~SHORT NOTES. C/--T;t, ~
~ 3~ " " - ~ - - - -
WELL PLANNING
AND
PROPOSAL FOR
PRODUCTION GEOLOGISTS
IN THE
PETROLEUM INDUSTRY
P.O.Okeke
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1\11 Ilgllls reserved. No part of this publication
111ily 1)(' reproduced. stored in ' a retrievalsyl'l ( ' I I I or l ransmit led in any form or by any
11H'r1llh. eleclronic. me.cl18nica l. photocopying, 9n'('C)J(\Il1i!, or otherWise wlthoul the pnor
pernJiI'lHIOl1 of' the Publisher.
I-F ',
1\
FII : ' ( Publi.shed 2006
DulllCS Publishing Co. Ltd.
J \/'!.7 ('111111(' Avenue, New I-Iaven. Enugu.
'1\'1: 011·2 310903, 0803-955-5253
(0 P.O. Okeke, 2006
ISI3N 978-32:327 - 1-1
CONDITIONS OF SALES
Published and Printed in Ni/4eria by
Dulacs Publishing an d Printing Press Ltd.
ii
~
J
PREFACE
The ability of the geologists in handling
seismic and well log data will either lead
positively or mislead later well 'jJlanners
(geophysicists, petrophysicists and reservoir
engineers) and drillers. This is th e bottomline. Everything must be done in o rder to dril la successful well. Nobody would like to be
heJd responsiblc for any failure. The entir e
approach must be interactive.
What you will read in this text book ar e
short notes that could enable a potential
production geologist contribute meaningfully
so that a good result is achieved. Petroleumexploitation and development remain a very
expensive bus iness, and mistakes must be
reduced as much as humanly possible.The book is divided into five chapters:-
(i) Chapier I - Usefulness of production
Geology in Well Planning and
Proposal,
(ii) Chapter 2 - Log Correlation
techniques. Deviated/Directionally
drilled wells and Mul1Jlaterals,(iii) Chapter 3 - Well Log Evaluation.
(iv) Chapter 4 - Well Planning and
Proposal (A Summary), and
ii i
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CONTENTS Mature ~ i t ~ l d e.g NigerDelta.'.Ni.geria': 'I : :.... i, ' 8Oil in Agbada Formation . . ,
(Niger Delta. Nip:eria) .. 8True Verlical Thickness
(TVT)I) f
Expected Grq§E! sandThiclcness., .. ft·· 8. Deviation Data . } . . ! J ~ .. -.,,:: 11
Q r q ~ $ - s e c t i Q n S n , . . .. 12
l ) a t a r e q l l i t e ~ f ' Q ~ W : e l 1 , P l ~ n ~ ~and ProPQsa] '" , __« •• 15
G e o p h y ~ i c a i p i . : o ~ p e ; C t i n g in 'the search, for Petroleum
,Aswmmaxy. . . . . 16 :
Ba.siC Materials needed in the ...
detennination of the b Y d r o c a . r b ~ , ~ ·potentiql Qf ClJly ,reservoir level
q ~ Q Q ~ _ . .",': ",. .. 24
: ~ d r " g c . a r b : a n migration the
Jlfage.r D e l ! a . ~ . , " ,( " ., -2@Seals in t.he NJger ,Diclta' .. 25Reservoir i c l ~ , t l i j f i q a . t i o n . "Structures and· B:YR-r9carbon , .accumulation ..,.' ( ~ $
1.19
1.17
1.18
1.20
1.21
1.22
1.24
1.25
1.26
1.27
1.28
7
67
2
4
4
1
1
1
tanning And Proposal
Major objective ..Planning a well ..\Vell types (Definit.ions)Well ,lrajectories (Planning
and Advice)Well path or Trajectory.
Horizontal Sidetrack.. ..International Geological Data
base (I.;PB)t . . . ~ , ~ r · 4Detern:ttnation of fluid ontacts 5JuxtapositionI COffirllunjcation INon-sealing between two (2)
sand units 5Why inject water into wells? 5
1d ntification of Hydrocarbon
h 'aring intervals ., .. 6I) t rm in lion of Hydrocarbon
tvp '(s)1.1 ti v sand
I I teroliLic lay r(s)
on1partruentalization and
HOlnogeneity of reservoirs ., 7
Net and Gross sand 7
1.1.
1.1
1.1;'>
1. I'
1.16
\.10
1. I I
1.8
I.
1. I\ .')
1 . : ~I,
Preface
D die tion
CHAPTER ONE
U fulness Of Production Geology In
Wll
v i vii
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CHAPTER TWO
Log Corelatio:J} Techniques. Deviated!
Directionally Drilled Wells. And Multi
Laterals
ix
54
47
55
56
56
58
58
58
59
65
66
I f )
Hi
CHAPTER THREE
Well Log Evaluation
3.1 What is the role of a Petrophysicist
in tJle Oil and Gas industIy? 45
Net-lo-Gross ratio N/G). .. 47
Discrimination between sand
and shale .Discrimination amongst Hydro-
carbons. Fresh water and saline
water sands (brackish watersands).48
Inlerpretation of well logs- ."'"
Qualitative and Quantitative
QU[llita1.ive Evaluation of porosityvalues
Porosily. & Permeability values
in Ihc Niger Delta. . . . . 55
Radioactive sand. oil. water and gas.55Lithofacies scheme for th e NigerDelta.
Well Evaluation at a glance
Sand correlation across wells in atypical hydrocarbon field ...Gas or oil column ..
Isopach maps
Wire Line Logs, logs from
Measuremcnt while Drilling(MWD) and Core Analysis..
DetenTlination ofSaturation (S)
Qualitative and Quantitative
EVrlluation orWell Data
3.2
3.3
3.4
3.5
3.6
3.7
3.83.9
3.10
11
:1.12:1.13:1. 14
viii
'hicf objeclives of LogC o r r e l a t io n . . 29
Factors that can complicate
correlation .. 29
Log correlation Techniques/Tips 30
Faults. Fault cuts. Variation
Slratigraphy. and Unconformities 34
Faults vs. Variations in Stratigraphy
Pault cut determination 34
True stratigraphic thickness 35
Unconformities. . .. 37
Some checks .. .. .. 37
Relationship between structuredirection and stratigraphic
lhickpess . . . . 38
Deviation/Directionally dirlledwells. 38
llorizontal wells 40
Multilaterals.. 41
Applicat.ions of directional
drJIling 43
/I .,.o l
2. J
fl ()
..,n.n
,,,: \
:VI.: Ir1 • i 1••1
:l./I. IIJ.t! ,I
I' ,Hn,O
1\. I ()
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x
CHAP'fERFIVE
Questions And Answers Useful In Well
Planning. Proposal And Drilling.
5.1 Why do you construct structural
and sediment.ological sections? 93
5.2 Projection of Well in the cross
section is along stril<e. How done? 94
5.3 In the horizon map. why are some
wells proposed and drilled within the
boundary fault? 95
5.4 What is the basis for any cluster? 95
5.5 Distinguish between the Ol;ginalan d present flUid contacts.
WhClt are the ir implications? 97
5.6 What is BS & W? 98
5.7 What is the least separation
distance between two wells (allowable)
in a given reservoir? 98
5.8 Define the follOWing Drilling/
driller's terms usually seen on the
Driller's Planning report: - TFO:Turn; Build: DLS. VS? 98
"'.9 Gainma - ray logs for the
structural/sedimentalogical cross-
section give TVD and not
FTAH. Why? 99
b10
What are single. dual or multiplecompletions? 99
I I I Choice of drainage area.
I!orizontal well ranges between
91
79
8687
88
89
90
77
77
71
71
73
4.104. I I
4.12
4. 1:1
4.14
4. \ ()
4.84.n
4. 34.4
4.5'l.G4.7
CHAPTER FOUR
Well Planning And Proposal (Summary)
4. J Relationship between pilot holeand development well 69
Environmental Impact Assessment
(EIA) 70
Reservoir Management 70Advantages of horizont.aI wells,
over vertical onesUseful terms in proposing a well
Terminal dept.hs (TD)
Increase of Production/
development of reserves
SidetracksDefinition of some terms used
in Well Proposal
ToleranceWhy deviate?
ndrained oil/Attic oil
Commingle
S Ismic SupportTipS on the Production of Cross-
RCct.ions from Top structure
horizon map.
4.2
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..I
(i I) Exploration/Pilot:
The e ar e w e ~ s drilled in a proven orr ognized firld. They e oft n of
g ological int ires t. and th obj iv L
1
C ~ T E R NE
USEFULNEsl OF PRODUCTION
GEOLOGY WELL P:L.ANNING
AND rROPOSAL
Major O b j e c t i ~ e :The main o b j e ~ t i v e . in SUlnmary. is lhedeveloprn nt air the reserve(s).
Planning a wJl1:Two onditio?-s lTIUst be looked at
namely: I(a) The type of well. Well types ar eWild at I D viated. V rtica!,Exploratioh/Pilo. Appraisal or
Deve1oprn¢nt. .(b) Often sOfe information on th e
enVisaged complet ion is mcblded,e.g.. i n g l ~ . multiple zone. or dualstring etc. I
1.3 Well types (Definitions)
(i) Wildcat: IThese are first wells in a virgin
rea.
1.2
1.1
105
105
105
104
105105
103
103
104
99
100
100100
101102
y.1000ft a 1
5 . 1 2 ~ What i s DFE?5.13 What is Deviation/Build up
rate? How:is the c.a1culation
done? ~ " ' f "' ... ..5.14 What ~ f l e t J { O P and EOB?
,5.15 W h a t j ~ ~ S T I ..5.16 S e i S ( J l l ~ 0 : , s U p p o r t - why?17 Whal.are th e implications of
1 shaliow hydrocarbons? 102
:18 What is collision risk? 103
).19 What is a n ( ) v e r p r e s s u r c . ~problem? ," .... 103
. .20 What Is the problem of shales, '1n tn t borehole stability?5.211 U n c ~ r t a t n t i e s ..
5 ~ 2 ~ Name th e mud logging types•.!1;' In the prognosis.. what does. 11569ftss or 11580. ftss.~ for example. mean? ..
What is plug b a ~ k ? ... What is inclination? ..
e seme well data for th e
u1 lecUve sand?5.27 I I do )O U detect thin
r H rvoirs?
5';2 are sandstone teservoirchar c-t ~ h s t l c s typical of the p I i J ; ' \ ~ ~ p a 1depositional environments?,
xi i
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(Iv)
3.
~ l i ) :Depth map(stntctural map.
ifhls is a sub-surface map of the
.ireservoir of interest.
NB: In order Lo say co t . plan your
surface well location in th e already
acquired space.
(ti}lIorlzontal
Section:Draw your proposed horizontal section
where and how you want your well to
go,' bu t consider th e contacts. faults.
contours, th e drainage area for your
proposed well, an d th e adjoinin . well
(whi 'h should serv (' th conLrol).
NB: Mal e sur your horizon al section
land inside th e reservoir.
( ) Cross-Section:Draw your cross-section. (structural
and sedimentological) llsln;g 1VD .(Tr,ueVertical Depth) and not AHD (AlongHole bepth) from the Gamma-ray lqgs.
!'Insert the follOWing: ,(i} The wells (whether projected
(along th e strike' or not -Unto th e
cross-section).(ii) The contacts (GOe (gas-oil
contact. owe (oil-water-contact)etc.(Hi} The well trajectory and i n c l u d ~
the Heel and Toe (see later).
(ii i)
2
10 It" l 1b c lr ad . availabl
Pt OpllY. 'jea! da a and in t 11)r la ions.
ppraisal:'I Ill' > (3) or four (4-) wells are drilled in
n 'lei in order to appraise th following:
(:\) Number of reservoir sand ..
(1 ) Lateral e t nt ofth
hydrocarbOI.bemin ) sands, and
(c) Estimate of ih hydrocarbon in
place in that f luid.
evelopment:'[ 11 e ar wells d ri lle d in order toxLrac the availabl hydro arbons in
II I fi ld.
I . Well t rajectories (Planning and
Advice):n iUlportant que lion that fiU t be
:\11 w red is: Has the re s Ivoir b en
t l l ' in d at all and/or before? If lh
t i l l . wer is positive, then i t is necessary
I ( on ider if it is vii e econon1ical ly to
(I n in fu rth r. If COlltinuati n is valid.
II '1 planning will invol e th e follo"ving
II lJHl l :
( .I) M erials required
(II Lo(" lion Inap (surface filap)'Il< k if Lhe area of interest has
1)(' ' t l 'lcquired by th e Company.
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(d) Co '":' ordinates:Determine the co-ordinates' of surface
location. pt'Oposed Heel (landing point).propOsed (Final point).
'- '
( ) Well path or Trajectory.
Finally, th e geologists will submit the
'o-ordinat s to the R e s e . I ; V 9 J ~ Dn ing
Engineers who will" use an adequate'omputer program to detenfiine the
I. J H e e l ~ the T o ~ , the KOP (Kick Off Point),
and "theBuild up angle HPJ, Some ofthese tenus used. in deviated wells willbe ~ l a i n e d ' l a t ~ r i.n the textbook as
t h e ~ t . · needs arise,f.t,Jr'H6rlzontal'Sic\etrac.k:.. . T h i ~ :is dr il ling a horizoritalhole from
an wexisting well into ane'xisting•. r e s ~ r v o i r where the 'oil is collected.. \see
" j'J' ~ e c t i o n 4:8 for mbre 'details).
l . ~ ' , J n t e r n a t i o n a l Geologi'eal riata BaseJi(lGDB):
t' . ~ ( i \ This is a Sands File storing suchI .. J.\4I- d' t Tihfor,mation, as co-or Ina es, ops
I'and Bottoms of sands. Fluid
.. l contacts, Deviation.. TVDss (True J
Vel1ttcal Depth sub-seal] TV ] ) (True iVertical Depthl,AHD (Along 01
Depth). etc, They are details of thstrat.a.
4
~(11) I t is stored in one server and data
can be migrated to another server
(software) using ASCII fonnat.
NB: 1VD = ftss + DFE (Derrick FloorElevation)
Ftss = Feet sub-sea
Ftab = Feet along hole.
1.8 Determination ·of fluid contacts:Original fluid contact can be
determined usmg Densi ty or Neu tron
Logs, while the present fluid contact is
determined by RST logging or MaterialBalance.
1.9 J11Xtapo$ition/Communication/Non
sealing between two (2) sand units:
Evidences are(i) $ame original owe value/S i .e
OOWC (Original O i l - W ~ t e rContact). .
(ti) Intervenitlg ' shale is no t sealing.(iii) Check'on the GST results for
POWC ( p r e s e n ~ Oil-Water Contact),
I. 0 Why inject water into wells?:This -. is done either for pressure
maintenance or for disposal intoshallow aqUifers.
5
.;r.1
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1.14
1.13·.11 Identification of Hydrocarbon'; V ,' , bearing intervals:·
This can 00 -' achieved using amhina(ion of lh e following:
(i) Shallow and de p resisUvily l o , g ~ .and
(ii) An overlay of tIl compu ted R 1 g
(from a porosity d _vi.c and tht:
estimated 'true' formationesistivity) ,and a RI\" curve
comput d from th SP uev aflercorrecting baseline drifl.
I.12 Deterntination of the Hydrocarbontype(s):
This can be done based on:
nOl' (1) The· t t ~ s u 1 t 8 o f side wall :sample::f' a n a l ~ s ' '·(m.arked ort -the-: PDLS
(Petrophysical Data Logs)" ' , I.(ii) WLFf (Wireliae:, Formation Tester)formation litessureS' 'and! samplesdata. j ' - ' ,- : ,Y, •
(Ut) The density"'rieu'trron overlay'. ,and-flv) Neutron count rate:: idVerlays for
gas - oil differentiation. '
NB: . Units. of - e a s u r e r n ~ e r i t forhydrogcarbons:
Gas-) nunscf (milli0rls standard
cubi fe [)
Oil ~ stock t ank ba rr I (3tb)
6
1.J5
1.16
I
Objective ~ a n d :This is sirrtPly the target sand or thereservoir interest.
HeterolitiJ layer(s):
Simpl , . sh ~ e s . usually charact riz cI by:(i] low pern7eability. and
(ti) llnes lIlat will reduce verti al
permeabrlity and impairproduction I.e. ct as baffles tovertical ~ o w _
C o m p a r t m ~ n t a l i z a t i o n andHomogeneIty of reservoirs:
(i) Camp r t nenta lj za tion
Simply, Fault blocks or faultcompart$ents.
(ti) Hornoge1eity
Almost homogeneous, implying
that we1l6 in th reservoir are incomn1uni ation.
N.B Fo r any comlTIunication between
fields. c h ~ c k th e followin6:(i) Well prodpction data,
(ti) Bottom Hole ternperatures andp r e s s u r e ~ .
Evidence: sinj1ilar or same results in
th e wells being considered.
Net and G r ~ s s SandGross ~ Totfll Le. and and ShaJ
Net ~ only ~ a n dI
I 7
I
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N.B From the above. Net-to-Gross
ratio can be calculated. ifnecessary.
1. i 7 Mature Fields e.g. Niger Delta,
Nigeria.
With time and drilling activities insome fields, wells start pmducmg
excess water. This excess water iseither used for pressure maintenanceor disposed of by:
(i) Re-injection into shallow aquifersor
(ii) Channeling into the se a or ocean.
These happen in a typical maturefield.
1.18 Oil in Agbada Formation (Niger Delta):
The characteristics are:(il Paraffin type.(ii) Very low sulphur,
(iii) Very low asphaltene, and(iv) CAP!, 15°- 50".
1. 19 True Vertical Thickness (TVT) or
Expected Gross Sand Thickness.
This can be determined using any of
the following three (3) methods:
(i) Structural Cross Section.
(ti) Sands File (IGOB) or
(iii) FOP (Field Development Plan)
Update Reservoir Top Structure
8
map based on 3-D Seismic and
well data).
Method (i) - Structural Cross S clion
X Proposed/Planned- - - - - - ~ ~ = = - - - \Iv'ell path /Tra1"ctory
-TIl r·· ...."
Objl'Cli\ e S"nd or T"rget San
Iqg. 1. I Construction of Slructural Cross-section
using thicknesses (Ta, Tb, and Tc).
Prol(';edure:
Til. Tb and Tc are the gross sand
Il1fcl nesses a5 determined at the
Inte:I'sections of the well p.'lth with the
, \rious reservoir lOpS (X.Y.2).
NB: Often these values differ significantly
f'mm those calculated from the sands
!l
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10
which
File
J I
(i) 7. 9 anel ] 2 are cxist ing well
had proper IGDS/Sandsinformation.
(ii) This is done for c\'ery reservoi,·.
Procedure:
1. Read off the Horizontal Section (Z)
for the reservoir from th e Deviation
Data Sheet.
2. With appropJiate Sca le ( that o f th e
Top structure map) measu re out
the reading of (1) above I.edetermine T (rnd o[ horizontalsection).
3. 1\rt [o r this reservoir falls between
that of well 7 and that of well 9
obtained [rom the Sands File.4. Inlerpolate (depending on where T
falls nearest (i.e (0 7 or 9).
This is th e proposed Tvt. This value
must be a whole number (i.e. not afraction).
I .20 Deviation Data:
These include the following:
[i) Target co-ordinates (Easting and
North ing) [or each well (surfaceand sub-sUlfacc).
(ii) Horizontal drift
(iii) Depth (nss an d Ilah)
Piss = feet sul>-:,ea
that pass
/)n)p()sL'd \ \'-l'I 1
Limitof thl' hydro('ilri"IHl
column/arcd foJ' thIs 1"t,:.''''L'nUlr
'9' 0 ' ~ " " " . ' . ,\ .V \:../ . . . . _. . )1 '
X ;<. _. .• . . _. \' ..:..\..>(.1;;\,,"... .. ' \t' ... , ·.,of\• t\-0\:\
oT
@,
Fil /IGDB [or lhe wellsthrough lhese reservoirs.
Method (ii) - Sands File (IGDB).f"W(.1J rrunn Top
Base ! GrossSand Iode AHBOF AJ-IBOF 'Thickness I(Reservoir)J !
X y I V-X lor each I,1 reScryoir
Jnd well..
Pig. l. 2 Construction of Cross Sec tion usingPDP update.
NB: AHBDI" means Along Hole bel,Q::I",
Derrick F l o ~ ~ F- ~ ~ ('''''''Method (iii) - FOP Update.
(a) Data Needed
1. Top structure map showing the
proposed well pos it ion. hor izon ta l
section along the well path. anel
Deviation e1ata.
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J1)
\
k
Ftah = feet along hole(iv) DFE (Derrick Floor Elevation)(v) Build up rate
(vi) Maximum deviation. and(vii) Azimuth
1.21 Cross-Sections (X-Sections):
Basically, the aim of constructing across-section is to produce a 2-D viewof the sub-surface through line ordirection of interest.
Types of cross-sections are:(i) Dip - always advised and strongly
favoured.
(iil Strike - structureless. and
therefore no t recommended.
(iii) Stratigraphic - very useful.
For the purposes of this textbook. materials
needed for successful construction of across-section are listed below:
Protractor set square. Divider (forhorizontal scale). Ruler, GeologicalTemplate (1 :5.000 or 1: 10.000 scales).FleXible curves or French curves.
Structural/Horizon map showing the line of
the proposed section. transparencies,
leaner/Eraser. Masking tape. and Pencil(HB; 28 preferred).
The cross-section should contain thefollowing:
12
Fault(s) (boundary or any other). Verticalscale. 1-1Ol-izon tal Scale. Fluid contacts,
Azimuth. Wells. Horizon/Sand tops. Intra
Shales. TD of the proposed well. wcllTrajectory/ Path (proposed), Gamma-ray
signatures for adjoining wells. thicknesses
of th e sands and shales. legend. key mapand title.
NB: The following well data must be
included because a stratigraphic
(structure and sedimentology) X-
section is normally reqUired in
planning and proposing any well:
• Top of reservoir (ftss)• Expected hydrocarbon column
(ftah)• Maximum inclination (degrees)• OGOe (ftss) from density/neutron
logs
• PGOe (ftss) from RSTImaterial
balance calculations
• oowe (ftss) fromdensity/Neutron logs
• powe (ftss) from RST/Material
balance calculations.
Explanations:
RST means Reservoir Saturation ToolPGOe means Present Gas-oil-contact
co e means Original Gas-oi!'colliat'l
13
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GOC
Wilter
~ ~ , , ~-_ fa
+
I_ Proposed ,veil
1\
TVSS
'depthi
15
o
1.22 DATA REGUIRED FOR WELL
PLANNING AND PROPOSAL
a) Minimum:
LSite Visit
ranput from T e c h n o l o , ~ & Petrophysics
:Horizon maps (structural with co-ordinates)
:Stratigraphic/sedimentological
sec·tion/structural section
I Location map/surface with coordinates
Scismic section with support
Section A'
"=snft' gnp (2/3)
b = safe g"p II ;, )
Fig. 1 .3 Conslruction of a Horizontal Section
fa met'e sketch)
~ W v " -. . .
1\'
0-- Pn ' r H ) ~ I . . ' d wL'l1A . / \ 1_ - I I ( ) r i / ( ) n t ~ l l Sl'Ctidl1 to d r ~ l i n
the oil tro1110
CD-- Q ) an.' vvL'lI:-..
OOWC means Original Oil-Water-contact
POWC means Present Oil-Water-contact
14
A
1.21.1 HORIZONTAL SECTION
The length of the Horizontal section isgUided by the following:
a) The potential Le. the reserve to develop
e.g. long section (higher potential[arguable) and more production).
(bl The structure and the sedimentology:
Choice of horizontal seclion
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DWell data
[]nput from rese rvoir Engineers and
operations (drillers)
b) Others:
[Devialion calculations (for deviated weIll
[[Pressure prognosisJProvisional status diagram
1.23 GEOPHYSICAL PRO SPEC TIN G IN
THE SEARCH FOR PETROLEUM _A SUMMARY.
OUTLNE
(1) Introduction
(2) The accumulation of oil & gas
(3) Geophysical methods of prospecting:
(i) Gravitational methods
(ii) Magnetic methods
(iii) Seismic methods
(4) Application of GeophySics to PetroleumExploration
(5) Cost of GeophYSical Surveys.
1.23. I: INTRODUCTION
Geophysical prospecting ha s pro\'edvaluable in the search for oil and is almost
certain to be relied upon more and more to
find the oil and gas for the ever increaSing
energy reqUired for the transportation.
16
power, heat, and chemiral activit lcs of thepeople of the world.
1.23,2 (1) THE ACCUMULATION OF OIL& GAS
Accumulation of oil and gas occurs under
certain, rather restricted, underground
conditions.
Note the [allowing terms:-
(i) Oil '1'001'
Not an open underground lake bu t
a porous rock. more or less
saturated with oil.
(ii) Reservoir rock
, Usua lly a porous sandstone or
limestone.(iii) Source rock
Oil will no t accumulate unles s
there is a place for it to come from.Hence, there must be 'source'
rocks', usually shale beds
containing organic matter,
(iv) Cap rock
Oil would no t be held in a
particular place unless there wassomething to prevent it s further
migration from that place, Heney,there mllst be an impervious '('ap
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GEOPHYSICAL METHODS OF
PROSPECTING
1.23.3
I,)
Any conceivable p ro perty or p ro cess
which can be measured or carried out
at or above the sur face and which is
affe ted by the nature or a tt it ude o f
rocks (or by oil itseH) through a cover
of hundreds of many thousands of feet
of intervenincr rock s may be made th eba is of a method of geophysical
prospec mg. Many principles have been
S1.l crested and tried but practically allthe geophysical search fo r oil dependson a very few basic physical principlesnamely:
(Al· Gravitational methods:
Measurement at! the':l$,urface: . o f ~ · s m a l l• variations' in .:the:;j ~ a Y i ~ t i O f l a 1 !lleld.
Tl1 refore, i f geoloo'ical movements
i valve rock s of diH ring densi-ty. th
r ulting irregularity in m . .
eli. tnbutjon Will mal< a carre. pan lit I
(vii) Traps
Thes'€.; are;- ·due· ')1fOL vnrf ty of
!Cj.,· I ge010gic ' p r o c e s s ~ ~ " , " ' t J r ('k
defonnations. Such d r n 11nll )11,are usual ly caJJed 'StruClllr s' . Toserve as a trap it is essenli 1 tl tthe structure be closed.
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rock' or other trapping conditionabove or adjacent to th e reservoirrock.
(v) Migration
The oil indigenous to the SOurcerock is no t sufficiently-concentrated to make an oil pool.The required accumulation
necessitates 'migration of oilthrough porous. rocks and some
irregu1anty. of the rocks which willarrest· th e migration in acomparatively local area. .
, ., I
(vi) V o i d s / S p a c e S / P ( ) r ~ s J t y :Th.e spaces between the' grains of
porous rocks ar e almost never vJi dbut ar e filled with flUid which may
be 'oil, gas or water- either separate
·Or·-miXed. As, the flUids migrate
thr0ugh' tnep())rous rocks, the
lighter ones tend to rise through
an d float on the heavier ones. If atrap of some kind exists within
.which the migrating flUidsaccumulat e, they will tend to
e a i
densities, th e lightest (gas) at th etop, t.he oil next, and the heaviest(water) below.
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pro 1 ing
II ('11 'ug(l l n bl
( I
surfac apalJl n-
8t ru tural reI'e[ jilt JI(
s-dimcnb whi h -'ouldfor th a cumulation of il.
(C) Seismic Methods: Ba I 11 tlw
mea 'uremenl of travel time rartificially indue d elastic waves. Such
way s. e up y explosives or by othersour or pub or continuous
aCOLl li" n rgy at or near th e surface.
trav 1 in L 11 directions from th e
saure =>s. Wa s having paths in cer ta in
dir ' ions ar r [rae I d or reDected so
th a hey OIne back to th e surface.
A senes of sensitive s e t s U 1 ~ d e t e ~ t o r s , .at the surface and at. vart01J1,$ distanGes
from th e sou rc e : c ~ n n e 9 t e d through
suitable . filters and ,amp lifi ers to arecorder. The resulting seismic record,
which may be visual. or on m a ~ t i ctape or both. proVides .th€ ' : < d a t a j ~ f o rdetermination of th e depth and form of
certain r e f l ~ c t l l 1 g .. or r ~ f t a c t i n g'horizons' in th e unde.rlipg rock .. s e r i ~ ' ,Under favourable conditions:, & ( i } ' i ~ i n i cmethods ma$' give information that can
be i n t e r p r e ~ d qUite s;imply and dttectlyin turns of geologiccQpditions" . .' I. I
v ri tion, in t he int ensi ty of gravity.Th measured variations are
I' • I interpreted in terms of probable
I " II subsurface mass distributions, which
in tum are the basis for references
about probable geologic conditions and
the presence o r ' absence of trc:psfavourable for th e accumulation of oilor gas.
(BJ Magnetic Methods:
Based on th e mea su rement o f small
var ia tions in t he magne ti c field. This
field is affected by any var ia tion in the
distribution of magnetized (orpolarized). rocks. Most sedimentary
rocks are near ly non-magnetic. but th e
u n d e ~ l in igneous or basemen r
usualIy flTe slightly magnetic. AsensItive magnetometer is used to
m'easure the re1alive o'r'absolute values
of magnetiC i n . t ~ n ~ i t y . T l i . ~ . s e · variation
may .b e measu re d at the surface or
more commonly, by suitable
lnstnunents 'carried in an aircraft. Aucost important result of th e
~ j J J l n . t e r p r e t a t 1 o m is the determination of
'l(depth r td the basement .rocks .and
thete.fore th e thickness of sedimentapres nL Also, i t is possible to'determin local rel ie f of th e basement
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1.23.4 APPLICATION OF GEOPHYSICS
TO PETROLEUM EXPLORATION
The cliiTerent geophysical methods may
serve qUite different purposes in ageneral geophysical campaign for the
exploration of a large area.
E.g (i) General preliminary or
reconnaissance survey:
~ Gravity or Magnetic methods or both.(H) 'P'irsllook' at any large and relativE:y
t1111<1l0Wll area:
) Aeromagnetic melhod:
(iv) The interes ting indicat ions lhen
can be selectively tested by lhe
much more expensive. but
usually more certain. seimic
method or, in favourable
circllmstances. directly by
drilling.
N.B:
(i) There have been great changes ininstrumentation and advances in
interpretation, but the same (3) three
physical principles (graVity, magnetic.
lravel times) are still employed.
(ii) Inspile of many attempts to us e other
principles, especially electrical, none hasever allalned extensive field use.
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1.23.5 COST OF GEOPHYSICALSURVEYS. (Econoniics of Petroleum
Exploration)I
(a) As a very crucle o r d e r - o f - m a ~ n l l l Hie
rule of thumb. the cost s per ml1e of
line of magnetic, gravity and seismic
exploration slanel in ratios of
1': 10: 100(e) The relative simplicity of its basic
concepts and it s a lmos t 'p ic ture
book' results in many applications,
have made the, seismic method
much t he mos t common petroleum
exploration method.
(d) Because of this and it s much
greater cost. seismic operations use
over 95% of the geophysical budget
for oil exploration.,(e) The potential field methods (graVity
and magnetic methods) depends on
forces acting at. a dis tan ce in amanner defined by the mathematics
of potential fields. (indirect/remote
sensing approach). This background
makes th ese method s much moreobscure and difficult than the
seismic methods to relate to geology.
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·1.24 BASIC MATERIALS NEEDED IN
THE DETERMINATION OF THE
HYDROCARBON POTENTIAL OF
ANY RESERVOIR LEVEL.
0) Grain size motifs an d porositydata
(ji) Isopach (equal thickness) maps(iii) Iso-poroSity maps
(iv) Profile directions and weils(v) I ohath ( C]lIal depth maps)(vi) St ruet ural ll1:l{lS
(vii) Logs-Sonic. DCIlSily. Resistiviry-.Gamma-ray. SP etc
(Viii) Plots - Neutron p o r o ~ i t y- Formation denSity an d
Compensated
- Neutron Log- PoroSity VS. Bulk density
- Porosity Evaluation [rom
Sonic Log.(ix) Volumetrics
1.25 GEOCAP
This is a software package usefu l in the
p lann ing o f wells. It is . particularly.
u ~ e d in th e determination of R e a l i ~ U cl ~ l U Its (in effect. no fault is vertical).
24
1.26 H y d r o ~ a ; : b o n Migration in th e Niger
Delta of Nigeria
(i) Es ential ly Ver tical migration up
d ip alo ng fau lts from the kitchen
ar .as. an d
(ii) Lateral migration from t h ( ~ kJtehenarcas.
1.27 Seals in th e Niger Delta
Generallv. 2 types or se::lls/bc niers
exist in ihe Nigeria Dell a. na r lely:-(::l) Regional shales commonl. I referred
to as shale markers. T 1 , ~ higher
th e shale percentage. the better
th e tr·.:lpping potential :;. \150. the
t h i c k ~ r t he sha le s, th e hJgher th e
smear (greasy/sticky) potential
and. therefore. the ~ e ( ' tel' is th e
seal'ing capaci.ty.
(b) Fau. ts ( these display gr:lwth). But
fau li s with growth may seal If there
is !1Ufficient clay smear or i frese:voirs ar e j ux taposed aga in st
shales.
N.B: Oil trapped by faults. I t is
always advisable to drill behind t h ~ m .
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(3) (Sedirnentary/Pinch out)
Unconformity
- -
Fig. 1 .4 Structures and O il accumulation
xXX
(2) (F,ulting)
N.B. 1.2 & 3 show different ways in which
struC":ure may control oilaccunlulation.
(Ii) Traps due to a variety of geologicp r o c e s s · ~ s and rock defolmations.
Such ddormalions are usually called·structures·. To serve as a trap it. is
(' sential tha t the s t r u c t u r ~ ' be clos-ecl.
---
---
___ Direction of General- - - '.."Migration
26
IMPERMEAI;I.1: ClIP
1.28 Reservoir Identification. Structures
and Hydrocarbon accumulationW l g ~ . 1.4 and 1.5)
(i) RED (Seed Grid (High amplitude
in Landmark Seisworks).
(ii) Remember to drill at the crest of
the structure (ie top of t h ; - structure/anticiline)
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LOG CORRELATION T E C H N Q ~ ; . ' , t , ..DEVIATED /DIRECTIONALLV
DRILLED WELLS AND MULTILATERALS.
2; 1 LOG CORRELATION TECHIl'lQUES.
Chief objectives of the log correlation
are:
D ~ l i n e a t e sand' tops a.J?d bottoms
Delineate shale and sand units
Interpolate and fix faults (tnorethan 1aOOft throw is no t
sio'niilcant)Correlate th e s and and shale
units a ross wells and later close
Ifeltls in order'to build upstratigraphic hi tory/sequence.
FACTORS THAT C;\..N
~ O M f L I C ) \ . T $ > C O ~ L A T ~ O N , '"
Stratigraphic · t h ~ , o . i n g i
Beddipl, " I , . " "
Faulting
Unconformities
Lateral facies changes
- I Poor log q u a l ~ t y . {llldDirectionally drilled W ~ U & "
' .2
2
' + - 00 - -+ - - :\ I1licli 1L'
. I II ' .g. 1.5 Dtflflng the c r e $ t ~ r a 1 ? c: icline
(iii) Relnember that your stru ture must l e
amplitude supported (seismic).
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\
NB: Closely spaced correlations generally
• Improve the accuracy of thecorrelation
• Help differentiate between faultcuts and stratigraphic variations.and
• Improve the estimate of the size(lnd depth of identified faull cuts.
2.,1 LOG CORRELATION TECHNIQUES/TIPS
orrelallon is dcfjlJ{'cl. as the
delermination of strvctural Qr
stratigraphic uni ts tha t ar e eguivale!lt
in time, age of stratigraphic position. ,for the purpose qf preparing sub
surface maps and crQSs section, the
two general sources of correlation dataare:
• Elect ric wirel ine logs. and
• Seismic Sections.
- No geologic interpretation can be
prepared without detailed elect ric logcorrelations. Accurate correlations ar e
paramount for reliable geologicinterpretations
- Electric Log correlation is patternrccognition.
- When geologists correlate one log toanother , they are attempting to match
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the pattern of curves on on(' log to the
pattern of curves on the second lop;.
- Higher degree of correlation is ;lCill<'vccIwhen there are very similar pa It (,J'1lS
amongst the correlated logs.
- A correlated log prOVides infornlaUonon the sub-surface, such as:
• Formation tops and bases
• Depth and size of faults
• Lithology• Depth to and thickness of the
Hydrocarbon (H,J bearing zones
• Porosity• Permeability of production zones,
and
• Depth to unconformities.
- An incorrect correlation can be costly
in terms of a dry hole or an
unsuccessful worker or recompilation;therefore, it is essential that extreme
care be taken in correlating well logs.
- GUIDELINES - which improve the
correlation efficiency and minimize
correlation problems are:
• QUick - Log correlation i.e reviewmajor sands/sandstones using thc
SP or Gamma-ray curves.
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• I,'m dl'lnllcd corrcln! 1011 work. firsl
('Ol'relale shale scct Ions
• Initially. use lhe amplified short
normal resistivity CUI\lC. whichusually provides the most. reliable
shale correlations
• Use Coloured penci ls to identityspecific correlation points
• Always begin correlation at th e topof the log. no t th e middle.
• Do no t force a correlation
• In highly faulted zones. I" correlatedown the log llrst and t hen correlate
up the log.
_The correlation patterns might be
peaks. valleys or groups of wiggles thatare recognizable in many or all of the
well logs being correlated._In highly faulted areas it is
advantageous to approach a recognized
fault cut from two directions:
• I 'l._ correlate down the log to the
fault. and
• 2'''' - correlate up the log to the fault.• l3y taking this approach.
dt'lprmination of the size and dep th of
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t.he fault in the correlaled well will bemore accurate
- Log correlation Plan - Ask y011 n'll ,If 01]( '
of the several questions like
• Where do I start?
• Which log do [correI8te. 1".2"" and 3'" etc,'?- A good correlation plan involves thecorrel8Uon of each well with aminimum of two other wells (as closeas possible in the first place).
- Continue log correlation progressing
Ii'om wells in a dow;-.- structure positionto wells in an up - struclure position.
- Generally, corrclate wells located nearesteach other. In mosl cases. ' Closelyspaced wells should have a similar
stratigraphic section and so correlation
is usually easier.
- Initial QUicklook can be made byreviewing major sands. Sands are the
dominant and most obvious feature seenon the SP or Gamma ray curves. andserve as good quick - look cor re lat ions . .Because major sand beds frequently
exhibit Significant variation in thicknessand character from well to well and areoftcn laterally discontinuous. however,
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For a fault-cut. there are 3important pieces of data:the size of the fault I' 'fthe log depth of the fault cut. andthe well or wells correlated toobtain -the fault cut.
• Fault size
This is expressed as th e vertical. 'thickness of missing or repeated
section
In. a vertical well. the logthickness and vertical thickness
are th e same.
Can be determined for horizontalbeds, dipping dipping beds and
deviated wells (see below).
2.4.3. True Stratigraphic ThicknessTST = TVTCoS(I)
• Where- TST = Tru e stratigraphic
Thickness
- TVT = True VerticalThickness of the section as
seen in a vertical well, and
W ::: True bed dip. " r
(a) F ~ u ; ; Size for h O r i z ~ p t ~ l r b < f d s- .l v J = J'Cep- Where
I ' •
34
they are no t recommendeCl for detailedelectric log correlations. Detailed electriclog correlation can be undertaken by
concentratingon SHALE SECTIONS.
2.4 FAULTS. FAULT CUTS &: VA;RIATIONSTAATIGRAPttr tJNcONFb1tMITIES
(FACtEs ~ ~ G ~ ) : ' , .2.4.1 Faults verSus,yadations in Stratigraphy
• The' differentiation between fault
cuts and variations in
stratigraphic thickness in wellLog correlation is very'important.
I. 1, If. a stratigraphically t h ~ n section1s correlated incorrectly as a fa111t
cut, this erroneous fault data Will
be incorporated into theconst ruct ion of a fault surface
map and later integrated Into th e
structural interpretation.
2. 4:.2 F ~ y 1 ~ Cu*. D e ~ e r m i n a t i o , n :By measu ring the amount ofsectiOn misswg in a ,well" on,e ,candeteimine the size of the fau lt by
CQrrelatjqn with another (nearby,if available).. well. This recognized
fault jn .a well is called a Fault
cut.
..
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3T
w w 'It hOI" d viatio~ , ) j t ~ " l ' . '
I '. ,I I . t "'"'
." I j • . l,·r I "
where (<1» i th n
angle.
2.4.4 Unconormities
• S teeply dippiJig structures such
·as salt domes
• Excellent hydrocarbon ·traps
• Versions are:- Primary erosional., ", ..:.
'- Sonle D e p . o S i i t i o n J t l · ~ ... '- Qtl1er Qon1bjnatiqp. of both
• Appear as missing . s ~ c t i 9 n s on an .Electric Log. Therefore.' can bemistaken for a normal fault..
2.5 .sOME CHECKS .. ",
Structural dIp 9tty.O Q i t f ~ r ~ r i r ,above and below an un<;orifo.rmity.Dipmeter data can be used toindicate this cha.ng.e in dip. The dip
below an t:tncohfonnlty· is usually
steeper.
- If th e missing section is recogniZedin two or mote wells at. the saine ornearly the same c o n - e l ~ t i ~ e I depth,
an unconformity should besuspected.
- The amount of missing' sectionresulting' from an unconform i t
36
TVT = Tru· Vertical Thiel ne s
f a u l t s i ze )
MLT :::: Measured La f Thickness
in devial dwell
(I) == Angle of well boredeviation from vertical
• (b) Fault Size for DippinO" bee:,
- Depends n if this is requir dfor we drilled Updip ai
Downdipt.·- Whatever. you requir. pieces
data:-)1 The wellbor de\ iati n angle
(<j)) which can b obtained
from th e directional survey
[ th w II.
l( 1h rInation dip (»
obtain d from lhstructural map, and
» The il l asured Lo['"
Thickness (MLT) in ell.
that is equivalenl to th
mis ing section in Well Y.
Therefore
Cos(f) - (,) I) (U d' )TVT (Fault Size) =MLT . 0 P lp
Cos 1
CosCO 1 -
0 1)
TVT (Fault Size) = MLT (downdip)Cos
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(ii) Common TYpes IMany complex I(a 'Iors go inlo lh e
design of a directionally d rl ll 'd w 'l l.
Most deviated w ~ l l s rail inlo Olle r twotypes:-
(a) 'L' shaped h<i>le (drilled vertically [0
a predelerrr¥nec1 depth and Ulen
deviated to aI certain angel which is
usually ~ constant to a total
depth (TO) of th e well. (FigS.2.1 or
2.2). I(b) 'S' shaped hple - With this, begins
as a v e r t i c a ~ hole and then builds
to a ptedeLermined angle,
maintains [lhiS angle to a
designated depl h and then th e
angle is l o w ~ r e d aga in , often goingback to vertiFal.
N.B Deviated \fells ca n also be
classified in10 three groups:-
(I) Wells dril led down-dip(ii) Wells dr i led along strike. and
(iii) Wells dli led up-dip
II
I
J9lI
111\' LI p-sl ructu rcncreases in
direction.
DEVIATEDjDlRECTIONALLY
DRILLED WELLSDefinition
A directionally drilled/deviated well is
defined as a well drilled at an angle
less than 90" to Ule horizontal. W ll s
are normally deviated intentional ly in
response to a predetermined plan.
Straight holes often devia te from t; ,e
vertical due to
(a) 8 ft rolation, and(b) Natural deviation tendencies
of sub-surface formations.
- The stratigraphic !:Jcquence g e l ~older in the up - structure direction.
_ The sedimentary sequencc just
above the unconformily is younger
in th e up-structure direeLion
RELATIONSHIP BETWEEN
STRUCTURE DIRECTION AND
STRATIGRAPHIC THICKNESS
• Up Structure Direr-lion ...... Constant or
Reduced Thieknes
• Down Structure Direclion ~ Increased
TI,rrkn 55
(i)
2.7
2.6
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...;, I rl<1t.'('
Dcrl\'atil!rl
t \ n ~ k '
Fi,t(. 2.1 (.1) l ) ( , I ' ! n k t l / f ) i r ~ I ' t i o n n l l y c1riil<.:d IITIl
CALCULATION OF TVD FROM AHD IN
DEVIATED WELLS (Fig. 2. 1(b)
<D
AHTva
TVD =AHD Cosine <I) \\'Ill'ft. til::: dt'\ i,\I,on.H
TVD =AI-ID COSillt: (1
wiler· 4'= cI vial ion angle
2.8 HORIZONTAL WELLS
'I 'll ' ~ ; ( ' also belong to th e class of
c1('vialccl/directionally drilled wells.(Figs. 2. I., 2.2 , and 2.3)
40
I ' ~ ~ I -+-11,"17<'lnt"I-+s.....liull
2.2: f-!ol 'iwnlal well
2.9 MULTILATERALS
(13) One vert ical and two horizontal wells/arIJIs.
The vert ical can be deviated also.
fig. 2.4[a) - MullilaLerals showing various [11111
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li'ig. 2.4(c) Multilaterals (Contd.)
WELL LOG EVALUATION
4!1
CHAPTER THREE
What is the role of a Petrophysicist
in the Oil and Gas industry?
The objectives depend on differenttasks in the different stages of the
reservoir life cycle, but at. the
exploration and appraisal stages, t.hemain job is the quantif icat ion of the
volume of !he hydrocarbon in place.However, tJ I·j,.; is done in conjunction
wi th the geophysicists and geologists.Logs which are used to quant ify the
hydrocarbon in place, can be classifiedinto three ramilies:-
Reservoir Thickness (Gamma Ray,Spontaneous Potential). These logsdiscriminate reservoir from on
reservoiL(8) Porosity (Density, Neutron, Sonic).
These logs are used to calculat.eporosit.y. identif'y lithologies, and
differential oil [rom gas.(Cl Resistivity (Lateralog, Inductiol1,
Microresistivity). These logs . toge! IW I
with pOl'osHy logs. are lIscd II I
calculate hydmcarbon ;saluralionf-!,
::
,I 3.1; I j I"
":
I :l:1 ,.......... .;
r:J ~
:' }.
::-: .
I 1,1(A)
;
'""."
E:t c;.'"
0be .D ...
t E c g o ~g u: r- N U>"'S: (f) '" !'J
N _: 2 u. - "S:- .2: :r a ;;;, '" I ';: ~ - , " , ~ ":e-;c: , '-'' " :J.: C: I B -. , .L..""Q.J.. ._a ::e::e l:-;c: 0 ::e ... ml../)
", c .!:j C :J;:'" N
1; 0:J .;:;r: 0 0 I 0
l: I
m 'v 11.1 t
j <3 H:"'
J \\IIH ".'", 1: t' .
";
:: -
0 0
'l; "-:'
-.-, 1 I
.J/ i - I i.:,
11;
;;,;
:;,
f
>LJ
-I I I f--I--z
<;;0,;
o
ZI.c \ ', T
o.,
c:::
Q.o7,
-r.'J )
'"
-Gwr->lJ.'/.
...U-'...
...VZov
9' .
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I hi" ,,(oJ • n,..J !>(';l" .,,111<-
1"'"lull) ... ~ " h . · . 1 1
\ , , \ '!!I.t. h-,t ".1,111,1. ,J
Tru(' (onn,'1lil'lI pr of ile------ log response
- - - - - Blocks u s ed f o r evaluatiOIl
Ot.hcr ly p 's orWireJine lools a n ~ : -(i) Siele Wall Sampler -
Takcs sma ll rock samples. which are
used for lithology and I luid type
confirmations
(ii) Formation Tes te r -
Measures fon11alion pressure!:> and can
ret.rieve fluid samples.
(iii) Dipme te r -
Measures dip and Azimuth 01" the layers.
(iv) Well shoot & VSP -
Used to calibrate seismic
N.B: Large and irregular boreholes (;an
adversely affect the accuracy of the
measurements. The log correclion needed in
these cases can be quantified using
approprial e charis.
3. I. I Jad ing Log Responses
1\11 lools hew a l imiled vertical
I l ~ s o h II ion. los to ii I hology boundaries,
11)(' II I ':11")111'('111 'n(s will be affect.ed by
nd.lil{'('111 beds. In very thin beds this could
I 'ad 10 lool responses which d c v i a t ~ from
Ill(' I rue forma ti on profile. Fig. 3./ is a
lccl1lliflllC useful fo r reading log values of
acll 'constant' formation bed. These values
can b ' used to calculate the petrophysical
parameters of each bed.
4 6
Fig. 3.1 Reading Lo,£( responses.
3.2 Net - to - Gross mlio (N/G).
Gross means total thickness of the
reservoir ie inclUding shale while Net
refers to the sand/reservoir only. (see
Fig 3.2, Gamma-Ray log and Tab le 3, I- Tops and Bottoms).
3.3 Discrimination between sand clncl sll:II ..
(see Figs. 3.2 and 3.3)
47
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2 I X 12 62 3.3 12653.3 13 0 I 173 I X I 2591.4 I 2616.4 I 2; ' I I I
.- SW I I X I 2691.0 I 2722.5 I 31 I 2 I
H
Gil (MI)o'\11 20 JfJ -10 ;(1 I>lI 711 'III 11111
1800 J ~ _ J __ . L J ~ r -[LI ..(:.... _.! iii j (
! ; $11 ;
, : 'I, " .,);: ' ' ! , j'-- ;.-.- ...;...,.. - _., .. y ' .- -.-
j ~ ~ ~ ; : - .
J - · i ' - - ; ( i J , · t ~ ~ D ! · _ · ; - - - : - - t - · - l i\ ' • I , ( • I'h
-to_or t ~ : - t - j - - ~ · - - ~ - - r l ...: ' r ~ { .1 ••
-\ .. " ' ' f : - : ~ : . . r . · , · , \".' ...., i ( i j
; J ; : j : _ > ~ ; \ U ~ O ; I I ! r. _ ~ - h . ; __ •. i._ - , l . - - ~ - - 1 · " ' ' ' ' ~ .. '.i ~ ~ ' j ~ J I ;: ; : l (. I
· · i · · · ~ · · ~ - + · · r · · · ; · · - < : · · · ~ · · ~ · · ·, I"'". SAND
...h·
'T":' -: .. .. ·i: " i - ' ~ - ' - ~ l - r - "I \ I < ,. J
1810 f - · ~ __ ·L - "' - -, • •,---;-_, • __ ..
I ~ . _ ~ - _ . ; •• ~ ~ ••
i ' ! \ ' I" - ; - - " - - c r r l , - ~ .. _._._, .. - ·... _L .D il\L.U: ~ . ;
; \ ! i i. j. I I •_ . ~ _ . i . . ___ ~ , _ . : . . . . - . : , - ' ._L....::c....-.J
~..cE 1805~
49
..c
0...OJ
Cl
Shale H,lSl' I.in" (50 API .. Mid-wav)
I··ig. 3.2 Discrimination between Sand and ShnJe.and relationship between Nei and Gross
thickness using Gamma.. ray Log.
- -
lEVELELL NI\ME ABSOLUTE DEI'TH ' TliICKNESS I THICKNESS:
TOI' 1m) Iml I ImIINET) I1 - _ ~ _ - - l - __ + ~ _ ~ + B : : : O : : . : n . : . . : : O : . : . M + (GROSS) I --J013AGI I 2609.2 2631.7 22 ~ I
17 I " I 2656.0 I 2666.0 I 10 10
3.4 Discrimination fo r various combinations
of rock types and containe>c! Ollicls (see
Pig 3.4)
Table 3. 1 TOPS AND BOTTOMS OF RESERVOIRS
AND THEIR RESPECTIVE THICKNESSES
48
.. 19" 2073.8 2707 .7 , )4 24~ 20" 2615.5 2040.1 12
.. ~ : I ' 12.7_ ~ 1 J . : 1 2H 18
1 -.. X 2lillH.a 271 :l.1I :! I 7
- --. <:11 X <:0:32.:1 2G47.2 15 2
.. :31 .. 2U<iO.O 2677.0 17 6 I
~:1'1" 2G0:2.H 2627 .S . 2S I j I ,
.. : la" 2671.9 26RII.9 17 16 I
, , ~ O " 2607.7 2626.9 lH ! ? I--<013AGISI X 2616.9 2641 .925 11 6 I
.. 4 X 2585.5 2510.5 12 5 I 16
.. 5 .. 2609.0 2G21i.7 lit< 14 -
I" 6 .. 2606.3 :263•. 3 -2 8 I 14 I
I" 7 " 2581.5 2606.H, :2S ,1;< -j
8 " 2660.R 269·1.1 I :J :J i 23 :
I .. 13 " 264.6.2 2674.2 T:2H I 13 , ~'.. 14 " 2057.8 2690. IT :n j-;;; II OBACI 15" 2622.7 2652.9 I :30 1:20 --1
.. 16 " '2650.6 2672.G I 22 t 6 I
N.B: Net - to - Gmss can be determined anclthe n:sel"oir appraised properly/correctly.
Exercise:
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"
\
J
...
_-...
;'::": 1
I
"
\
)...., - -!I
~ D
. ::..'.1'~ i = : : : ~ - ; , ",. I"':: " , , I "" " :i r ~ ~ MI t,]:::,:.:·, ~ ' ,.!," l j '-·, :..7.: .?ij}' I (. I,_,'r -- rr.=':::::-'" I ' - - - .~ ; f ; " J J"'"b : ' ; ; 2 ~ ", I J ,--\:",.,0'/:\.: (-f' 1\~ ' i ; , t ; : ¥ l ' " I -; i ~ ~ ~ ~ ! ; : i \ -H I1-':.':':" I : ': ~ ~ ; - : ~ I \ . , . I I~ - - . . ; : : : : : [_+. I
'- ' 1; - ~ < i i ; (". I I /:=. c··A ~ Ir£" -
I
I.I
I
\11:IIe ..
\h;d.\ ~ : ~ : = I\;1·,<1 C:'
\h.11e ~ : ~ ; ; ; 1.==- ..
I , t ' ~ h ~ . ,\\.';lltT ~ _ ~ i- ..__ ::::::::.--",I -= ; . . - ~ .
)ddk ~ - - - - -t . f , ~ ; ; ; ' ~~ , l ' :::;v.'.. f . > d . I ' \ j ~ 1
Oil !(d·,,\!J\,'\1";','4! f ~ ! : I . : , I " L ,;\ ; ; , i , , ! j , ~ ! '
\11;1/(' i ; ; ~ - :; . : . . - r
~ ; d tW ; r ' l T ~~\halc ..::. : : . ~ _ .
.....:.. .:..:
I
I
51
I,
.- ":: . . : ~,halc ..:'" j
"'ig. 3.4 U ~ i n g R e s i s t i ~ i t y an d (Spontaneous
r 'otential Logs) to identify O il Fr esh watcr ancl
Saline watel ' sands. an d Irock types.
( ,r:-.h,dL'
Sh.lk,
-
( . , IJlll l l , l-r.l \
Cr",,, nd
50
Poro ... ity
r 'ig. :J.3 Saml/Shrl lr discrimination using
porosity an d Gammrl-RrlY d>1trl.
(i) Calculate the fraction of th c reservoir
within the total sand sequcnee (ie.
Net/Gross) given as Ij{; = (!I, + !I,Xt )(ii) Determine
(a) Tops an d bottoms of the sand (reservoir
sections)
(b) Thicknesses of the individurll sand
layers (Ii, an d h,)
(el Total th ic k nc s s of sand (= Nct reservoir)
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(12 n".I.u ....l l' I l l" '" touo
'illl4d'ltllili' JJIDi-'l'" 1: 1II lIlW!!.'"111 ,- .1!1ihf , !
j 1.1111 'I--- <'u· .,I t !TiT I : - ' . ' ~ , I Jh II ..
11 '1 i;;'" '" JJ.!1 I • I rF.T1"j
I 11
111 t i t ' l l,mll I·q: 1
mill ljll! !I i l l l l l ' ) :III ' 'I i 1 I' 1 I" ! 1
I " * ~ I 1\11 i ~ , , . . , ~ ~ ~fi 1111 I t ' : I ~ :II II " i ~ _ h ; ' ~ t l : ~
III 1 ,I ~ ' ~ " 1 < ' ~I 111 Hg.;,; ( ' l ! ~'I I II I ,II l li,l. i
I dill III r 1/ lid; ;n lit I III i 1I11l: 1,:11
11111 :iill :111111 11'llI II Il i l i I II ; l:'ll
11111 I ill I IIILilllIl :
~ 1 1 . 1 I 1 1 1 1 l ~ 1 1I" II!!I ; l I 1 f f i T T ~ ~ ;
Will ! lIBI dltlm 11::l!l I
Hllll '!Hi 'I i !Ill' I , , ! ~ r .
I iiII 1 l 1 ~ II I II! II ;rfiififl Ifill 1111 mI tr:HU
r r W ~ l l l i ll I l lt i ll . I li' liTiIlilll ' Ill ' ' 11 11 Ul I 1'111
f t i 1 ~ i l ~ ~ ; i j ~ ~ ;ttUfflr i J i j I I - - : - r i i j [ f n ~TTTTJ
TTI : l
,I
-++1.,,
!I!:. : ~ . 6 Ii) DiscTiminal10n as in (Fig. 3.5),bu l further [or cvalu<llion. Density
10.;( is included.
53
, ; : : : ' . ~ ? ' ~ - , ~ ; t ' !~ ~ e ; ' ' ' ' ; ~ , , ,
_ ~ , [ ; ' . ; . ~ : ~ >1' I i
. ''<:1''$:' d - ~ - = S . -\ 9 ; ~ 1 I ! I I i I 1'"(
I J l -LL 1± ' 1 ,~ L _ I I I .J ~_.1' U ~ I " I_ I T J ' ' ! I J IS' .L.L.l '1'1"~ -l±J ' I. , .. ~
J; -l I
{." f+Jffi1820 I . 1 1
m'.'··\''.:t±iTIJ, ~ m
G>.."TTi1 l ! It ! t
fEW!S 3 C b ~ 1I I I gl I; i I .J.J
. ' - I-'-ttt ItI::I: J
52
_:', (",\: O ~ " I I .. . ' , ~ ' w - " j r ~ ~ c ; ~ l ; ' ; ~ ' i i : ! : ' : V : 7 ; ' :".1" ; l : : > J · : ~ j . V .• •
, l I ''. I ;5·S") 1 )
- - ~ ~ i l ! ~ ~' , I 1 '. , ,
r : I -' '· 5 JL__!.,... 1 \ __ : , ( I l (
( I '. ~ - U'I" , t,; /' t . ' lh · 1- LIII1[I1( '
(I! \
" . I ' ' ) I........ , ' , ,), - I") ,I '
! . i ' •
c.;'-1 -J-_---L- _. ( - O..!VC: i I\ lll)il -\'Volt',- C"nt.le:)
I : I r ,.' I,. . I I(Sf" _.' ! c.; :. ~ - . ; - )
- ~ [ r-I I~ " l (. \, Ik·o I \
IFig. 3.5 (il Discrimination between Gas. oil.
salt water using Gamma-ray.
Spontaneous PotenLial RcsisUvity and
Neutron Logs.(iil For oil. gas. and W<lter and·their
contacts, ResisLivity and Neutron Logs
are ideal.
QUALITATIVE EVALUATION OF3.0) " ~ ~ •..!•....;:lL'.. •. ;-,"";"__1'1. _. ~ , .. ~ : , - 1"""';
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54
Qualitative evaluation
Nea:JigiblePoor
Fair
GonclVerv Good
Excellent
POROSITY VALUES
% POROSITY
0 -5
5 - 10lO - 15
1!'i-20
Ovcr 20 - 25
More than 30
55
3.7 POROSITY AND PERMEABILITY
VALUES IN THE NIGER DELTA
(Omatsola, 1982), lor reservoir sands
of [h e Della.
•r ~ e s i s l i v i L y
of radioactive sand isapproXimately equal to that of shale .
so there is [hat problem of
.. Poorly (,oIlso!id,lteci
• Porosities as high as 40 1% in the oilbearing sanus
• PoroSity reduction with dcpth is
p:radual because compaction increases
wi t h depth (i.e density increase),• Shallow sands less than (300m) have
porosity greater than 15%.
• PermealJi li lies --_ .. I - 2 darcy range inth e I-fydro('arbon rcservoirs.
3. 8 RECOGNITION OF RADIOACTIVE
SAND, OIL, WATER AND GAS.
t;.';,"
··W'I ,
71:: ' i+-u
';'iTJ-".
•/k-Li-+--"rJ
ualitative
...!
I Quantitative rlI
Use 01' 11l'1thelll<ltil'alIllodc:j,; Irl'1aLions LO
. I
1o(('t values for th e I
I()rlllat ion paramt ' l tT " r
(pclropllvsiCfI!):- I----porosit\l I
---pernlcability I---saturatJoll.
I INote: Sec Section 3.15 3ncl3.16 fo r morc delails.
Fig. 3.7. Straligraphic CorrelatioIl of \ V e l ! ~ i i '
Niger Dclta oil fielci. lEI u-Efeotor. 19871
~ , : : ' : . . b ~ · 1 . . .
\ :( ..j
} I j ~ : . ] ! , - i v , ,<C
Visual icielltificaLion.
classlficatioll ilncl('onlparlsoll 01' sal Ids.
silnit's. I'nvinlllllll' lll ofdl'pllHi lion [1I1t1 nI lid
1'11[1 mell ' rH/ responses/
('OIIIHl'ls based 011
similarlog signat ures.
3.5 INTERPRETATION OF WELL LOGS
disl inguishing bCtWCCII shale and
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sllch a sand.
• I ~ c s i s l i v i t y , Density al1Cl NCLItron
Porosity logs arc rcqll ircd all to.L(cl!1cr.
• Thc best way or !·cco.L(1l i Sill,!!;
radioac liv c s ands is Ih< lISC or
Spectral Gall1Il1,1-ray lo.t':s.
3. 9 LITHOFACIES SCHEME FOR THENIGER DELTA
011111
Or
Ohm 1(-("
Volts.
I ~1----1
__-.1 I
Electric';11
n·:-.b/:IIlC·I·.
n· ... i ~ ' i v i ' . Y
V l l l t l l ~ C '
Wh:lI Is lJllih
tllt',IHlll""d of
111(' rorrll;,1 i l l l !
N;l1ltr'Oil 1\1 'I 1ttlils
t!H It 1I1t;1
r;l( li;11 io n
I 1·:lt'I'lroll (;111/('('
Ikllsilv
f'
IJ r y d r o ~ ( ' 1 trkll:-.itv
•
r d ~ ' 1 1 1 i fyll II-!
: - ' V l l l h o J ~
' -I '
[.1,1) Ik"p
I IW; I ...III 't·ltlC'lll
l (:NI.
L
I,',c
In general. lor Ilydro('arilolis (oil i l i id
gas), rcsislivily and dens ity I ( ) , ~ s ;11111
correlatc.
Logs, identifying symbols. What is
measured of the Formation. and
units of measurement
0) ( i ; lI l l 1 ll ,1 r; l ) ' I ( i l ~
1 . J ~ l . ) Shallow
111l': 1"'11 n 'JlIt'1l1
P>7
nj) IIl 'n ... iIV 1 VI l( :
(iv) HI'..,'...,1 iVll.Y I M ~ F L MifTII
tlll·;I ...lll ' l · llll·ll!
IvlSP'Hlllltll·IJlI ...
pOII'111 i:d
\ kn l ri l l I
(2)
(.I) The dceper readin,1..( lo ols arc L1sed (0
inclicate il' a ~ o n c is waler (l 1
hyd rocarhOll I)C81"in,l..(.
N ,B;f)"IJI i ls o f IIIV",,1 i . ~ ; 1 1 I o n vis· i1-vis Hcsisl iVily L o . ~ s
C(HTe It II (.
Pore Ph I ids
I)vllsily-)
kh'C'lnlll
( h · l l ~ i t . v l
;1I1<l
56
) Iit-slsl iVily "11(1 1 J ~ l I s l l yIl ' I I ' i ' I l 'OII
clt ·t I . il vi
---? dose: 1I1e!
sindln,-
I { ) g ~ ill
,il<lpe _
O p p o s i l ~ 01'111) N"l I lml l "m l I ) ~ f l s i l ylogs; l l l l i - ('oITcI.li ('
l.illlOl:H'it's S:lllrl 'HI SIJ;lI{' 1M. '('utaloJi)
COlli Ill ''Ill: Ii(IknillllwltI:llllJlt) (YO 10 100
Trn nsil iOIl<l t HO 20 100
P<tr;llic
ll\gllad:l FOl'tltalllH1) GO 40 100
Mnrillc
1"1\:11:1 FOI'Ill:LlhllJ! 20 HO lOO
WELL EVALUATION AT A G LA NC EUSING DIFFERENT LOGS
Uscl'ul Discrimination be(wecn
( f o \ ~ s . 3.!'5 & 3.6).
(III Oi l N('\iI mil
III) W"I,"
((') C"s
3.10
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58
It can thcn be deducted as foll()ws:-
59
TI,c downhole mC'asuremenLs are
perfo rmed with logging tools. The arephySical devices [sondes). working withvarious principles (or nuclear.electrical. acoustical). lowered in the
borehole via wireline (wireline logging)or as part of the dr! II string (measuring
while dri lling (MMTD). logging while
drilling (LWD). aI' formation evaluation
whHe drilling (FEWI)) . In some casesWh{,ll wireline l o g g i n ~ is difflclIlt e.g isstrongly deviatf'd holes, the tools C<l11
be lowered (aftel' drilling) wi lilt'
sclccted silml unils in dil'Jerl'l1l wells,OJl a bl a n l( n1<1 p.
:1.14 Wire Line Logs. Logs from
Measurement while D r ~ I l i n g (MWD)
and core Analysis.
LOl!;S or any (ypes scan be measu red
after l l1e drillml!; (\Vire Line Logs) (see
belowl ancl rllIrin.!.\ the drilling exercise(measlIrement while DrllJingl. These
days allrl in oroer to save costs , MWDis standard. Typical MWD Tools are
(j) Fnrm;;dio!1 Density Tool
(ii) Ncu Iroll Log Tool
(iii) Sunic Log Tool, or
[iv) Dipl1leter Tool.
best responds III
resistivity rind denSity
logs.
---tiii) Waf"r
(i) Saline' water zone'o> - ) Low r lsistiv iLy or
l l igh l ')llcluclivity
(il) Oi l f\l, I Gas --t best \ 'eSpllllci to neLit ronand dl'nsity LO!l;s, hu t
(b) In general. resistivily is high inhydrocarbon zones, and 10\\ in water
zones. and(c) Formatioll water saliniLy and porosity
influence the readings. and fresh water
zones can resemble hydrocC1rb011
l'I:i>ervoin, .
3.11 SAN') COR.RELATION ACR.OSSWELLS IN A TYPICAL
HYDROCARBON FIE·LD (FIC. 37).
0.12 Oil/Gas Column
f'dl11ply l prod1\e( of Th iekness (Net)
"ncl nvcnI/!,c porosity. WiGS. 3.5 and 3.G).
:3,13 Isopach Maps
T11('sc ::;how the lbjclt'lf;SS of sand :.milsit l different wells and a re used to study
:->lructum.1 g;rowl.h. They are preparedby con1::Jurlng the I.hickness of th e
I
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connccled 10 drill pipe. 1)1' coiled lubin,g,
This is somc( imcs Tnlle;11 LO,l",gi n,l(
condilions (TLCJ.
al len togging is curried oul by
contraclors. Thc rn,lin Ioggin,g
conlraclors arc Sehlumber, l(eL Western
Atlas (WALS). and Halliburton (I-I LS) ,
Important LWD Conlra('[ors ~ r ( 'Anadril l (a Schomber,ger company).
Spcny Sun an<l Tdeco. Ev,l!vat ion ~ l r cc;lrried out by in-house by the main
company like Shell, which has its
pctrophysical so!lw8re package
(LOGIC).
Core Analysis measurcments (porosity.
permeabil i ty, grain density) can be
carried out correctly by most scor('analysis contractors c.,g Corelab hu !
dala are always aud il ec l/cl1cckcd by
main company that has the contract in
her own laboralies,
I';ssenlially Win' l ine I>ogs ar c used 10
<l1'll'Il1lll1(' lh e reservo ir par8meters.
r';xalllplc's arc Sponlaneous Potential
(SI'), GWl1ll1a I ~ D Y (GR). Df'n!-'ity (POC).
NClI lo rn Log and Dipll1cter t o , ~ s . The
potenlial and procllleibilily or a
n ~ s e r v o i r dcpend on certain
characteristics and propertics which
60
include porosity, pCI'Ill<'a!>illly, gr;111l
size. grain shapc, ,gra in ('Olllp;1('11011,
malr ix and cemcnt compOIl('lll o( III('
sand body. Thc logs arc 1)/ Idly
explained bclow:-
3,14. I Spontaneous Potential (SP) Log
The curve records the electricalpolenlial (voltage) produccd by thc
inleraclion or rormalion conna le water.
conduelive drill ing fluid and certain
ion-selec li ve rock (shale), The shale
basc l ine rrom which the Sf> deflcclions
8rc l11easurcd is lIsllally fairly del'ined
on the SP IO,t(. Thc SP CUI-VC has a
nUI11:Jer or usefJl! ru nct ion s which
include correlation lit hology. porosily
and pcrmcilhility indications 8nd ameLlSIm.:menl or (form8Uon walersalinity).
1\ Iypical Sf> log s llows deparlures to
th e Icn rrom a base-line or shalc-l ine
reading on the right, to a sand l ine on
thc Icl l in the 'cleanest: non-shale
zones. SP defleclions a lso respond 10
depositional sequenccs where sorling.
grain size or cement at.ion chanc;es wi l hdepth. The shapes ar c also callcd /)ells
or run nels.
6]
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3.14.2 Gamma Ray (GR) Log
This is a measurement of tile natu ralradioactivity of the formations. [nsedimentation formations. the lognormally reflects the shales. Clean
fomlations usually have very low !evclof radioactivity, unless radioactive
contaminant such as volcanic ash or
granite wash is present or the
formation wat.er cont.ain dissolved
radioactive saU s.
Gan:llna Ray (GR) Logs me used for 4main purposes:-
(a) Correlation and bed boundary
determination.
(b) Eva luat ion of the shale content ofa formation.
(c) Mineral analysis, and
(d) Perforating depth control and the
tracing of the radioactive fluidmovement.
3.14.3 Density Log
This is t.he pr imary ind icato r of
porosity. In combination with other
mcasurement, it may also be used to
Indicate lithology. formation lluid type.evaluation of shaly s a n d ~ .
62
identificat.ion of minerals ill l'v;lporilcdeposits. detection of g;I.."
determination of oil-sl1ai<' .I'11'llI,
c alcula tion o f overbu rden pr('SS\lI<',and rock mechanical p r o p c r t i e ~ .
3.14.4 Neutron Log
This nleasures the amount of nitrogen
in the lorllmtion. The neutron and
density l o ~ s have Ilrst order
dependencc on l i t h o l o , ~ , porosity and
flufd contcnt. of the formation. The
presence of shales/siltstones in the
matrix has a partic!i1arly strong effecton the signals because clay minerals
integra te valuable amoLlIlts of water
with smeclil es (swelling clays) thathave important volume variations
depending on thei r wat er con tent . The
neutron tool detecls all water in the
form8tion, including bounding water
associated with shales.
:U4.5 Dipmeter Log
Dipmcter logs record ways in which
subsurface layers of rock have been
depos ited and su bsequenlly movC'( 1.
The raw data consists of orient<lfhJIIinformation an d corre];\ 111111
63
presence of .!.(8S
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J,
11111111'I1CC or
Water
&11 IIr:11lO ll
ClIVi! Ollll l( 'nl ;1i
COl I (.(., lOllS.
Secolle! Arehic
cqU<11 iOIl ( I I)
65
J,
Plrsl Arch if '
eqllatiol1 (I)
Influence or
I'orosily
Determination of Saturation (5)
(i) Defined as the rraction of porc
volumc
, . s". =I -S"
Where S,,,=hydrocarbon s;lluration
and S,,= waleI' saturation
(ii) Use Archie f lo r waleI' bearing
rocl(, and
(iii) Use Archie II lo r hydrocarborn
beahng rock.
conditions and .!.(8S
tempera t ure and pressure.
But consider the followin,!.(:
PoroSity.Resistivity of the formation brine.
Water content. and
Amount and type of shale.
N.B. Archie equations combined.
I ~ e s i s l ivity (H,J
Measured by
lAJggi 11'(( Tool
3 15
/\ numbc,' of ways of rep,-escnl in./..(
dipmeter resul ts is available e ..l.(
information used to determine the
al t itudc of the bedclin.l.( planes.
Dipmetcr logs have ;1 variety 01'
applications. Compu 1cd dipl11et er
results can be used to determine (i) the
gross geologic struet.ur<ll JCillllr('.c;
crossed by the well bore (iii
sedimentary deta i ls with simd bodies
(iii) t.he depositional environments. ;Ind
(iv)sl rn l igraph ie am i vertic;lI
(Itieknesscs.
64
-+ Tad pole or arrow plots lFi,/..(. 5.8(a) I
-+ SODA (Separation of Dip ancl
Azimith) plots-+ Listings
-+ Azimuth frequency plols
-+ Histograms,
-+ Polar plots,
-+ Stick plots, and
-+ Stratigraphic plols
N.B. Other factors that a ffec t w ire line
log signals include the distr ibution or
shales ( laminated. nodular, or cliperscd).M(';lSurements are also allecleel hv
l)orcllOle conditions, especially washoll ts
1'01' (he I leutron porosily tool and (11('
0= ( I / I / I - f "where R, '= R " , q ) - " ' S , ~ "
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66
where:
1'",,, = rock malrix density (assullle
2.65gll1/cc for sand)
I,. '= bulk density as measured
by th e tool
I , '= fluid density in th e invaded
ZOne (assume 1.0 gm/cc).
N.B. In ga s bearin,£( sands. make a '
qUick correction for t he gas effect on th e
density Jog by reading a densi ty value,
approXimately ;.. across the FDC-CNL3 .
sepami ion distance.
07'
I' '/1(1 - / ,
(b) Caculation of the waterresistivity (R'£l
Determine th e value of formation water
resistivity (Rw) in the water bea ring
sands from th e calculated porosity and
the resistivity log using Archie formula
simplified for S" '= 1.0 ie.N =R
II / I fIwhere
1\, '= resistivity of the fonnaUon water.l ~ , . = resistivity of kno\vn water bearing
rock (use the deep reading LLD C'lIJ'VI'j
Qualitative and Quantit ative
Evaluation of wel l data
Qualitative Quick look
Evaluation ..
Use your knowledge of log response in
a sandstone/shale environment. and
establish the folJowing:-
(i) the locat ion of the reservoir sand
zones.
(ii) th e location of the shale zones.(iii) th e primary fluid contacts . and
(iv) th e primary fluid contents (gas.oil and water) for th e reservoir sand zones.
In = cementation faclor (Llssume 2.0) andn = Saturation exponenl[LlgLlin assume 2.0)R, = Resistivity measured by til(' LOt;,l1ing TnoJR" = Resistivity of the formation hrine!wale,-
resistivity
3.16.2 Quantitative Quick Look
Evaluation.
(a) Calculation of porosity (0 )
Calculate a typical average
porosity in the sand containingeach fluid type using th e formula:
3.16
3.16.1
...
0= porosity calculated in the water CHAPTER FOUR
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zone (in fraclions)111 = cementation faclor (assume 2.0 in
this case).WELL PLANNING AND PROPOSAL
(A SUMMARY)
Note: Use the a v c l - a . ~ e valuc of the
formation water resislivities found
for the vanous water zones.
4. I RELATIONSHIP BETWEEN PILOT
HOLE AND DEVELOPMENTWELL:
Calculation of water saturation (Sw)
69
i. Pilot Hole: (Remember --7 An Exploratory
Hole).
1. Well/ Hole drilled for gUidance.2. Essentially of geological input
and interest.
3. Basically to appraise the objectivesand/garget aimed at understanding
properly the nuid contacts, structure,
and lateral extent of the hydrocarbon
column. and
4. Dl'ilIed vertically.
BEFORE
ii. Development well: (Remember --7 Drilledin order to extract the available
Hydrocarbon in that field).
1. Can be vertical. deviated or horizontal
(Conventional)
2. Drill vert ical ly to target. and then.cement back (bottom to depth frolllwhen you now deviated) in order II I
•
68
1\\kc one average value for R, foreach zone.
Determine th e R, value that wouldrepresent each zone best.
where
R, = resistivity of hydrocarban bearing
formation (again use (he LLD)
R = formation water rcsistivitvw
(assullled ('ons(;l11l <1S e<1 I('u 18lerl above)
0= porosity re-caleulaled in the
<Ippropriatc Z011e
n = sa(\lrntion exponent (again assume
.0 In IlJis case).
Using the porosities an d calculated
abovc. thc' water saturation in th e
hydrocarbon bearing zones can be
calculated with Archie fOl-mula
RS =(-"-)"" /) III
\, v'
Note:
(I l(I I)
(cl
. !
achieve th e desir'ed tmjectory/welJ
I
INB . DPR stipulatets rnll11llllJIlJ ( l I s t a n c ~
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r .
.'
path
3. Essentially for Reservoir Engineers.Well Engineers (driJlers) working incollabomtion with geologists.
4. 2 EIA (Environmental Impact
Assessment)
Thl': following Environmental issues
Illllst be considered when planning andproposing a well:
1. Water/River pollution
2. Air pollution (flares. exhaust emissions)3 . Noise pollution
4. Impact on inland water ways (marinetraffic
5. Solid/Domestic waste proposal
.6. Managing dredging spoils7. Emuent quality monitoring
Plus '
LARS (Location Area Reports)
4.3 RESERVOIR MANAGEMENT
Mllst consider the follOWing factors:-
I. r·'ltlfd contracts
2. Drainage distance, distribution andin ted'erence
3. Reselvcs to develop.
70
between producing wells from r1 rnwrvoiI'to be 800m. Cotlld be less blli Ihisrequest/change mbt be backed Lip willifacts and appropri4te permission.
4.3.1 EVIDENCE OF JUXTAPOSITION OR
COMMUNICATIbN OR NON-SEALING
BETWEEN Twd SAND UNITS.
1. Same original I 1 U i ~ contacts (values)obtained from Sary.d files
2. Intervening shale is not sealing
3. GST results for present fluid contacts
or RST I
4.4 ADVANTAGES q F HORIZONTAL
WELLS OVER VERTICAL ONES
1. Less problem of draw down
2. Penetration ratr is more gradual3. Negative poroSitY eflect is Reduced
4. Marc hydrocarqon
5. Reduced ElA prpblems
6. Vfore coverage qf the proposedhydrocarbon reservoir. ,
7. Though expensive. the over-all cost
is eventua lIy chf8 per.
I.f) USEFUL TERMS IN DISCUSSING
RESERVOIRSII
(Vis-a.-vis Well Plaqning & Proposal)
III
71 IIII
.. 'INB:
4.5.1 (i) Drilling:
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. "
(1) - (5) - 7 Vertical w e l l ~ ..
GUT -7 Gas Up'to_
GOT ~ Gas Downto
OPT -7 Oil Down to
0UT -7 Oil Up to"GOC -7 Gas-ail-contact
owe -7 Oil-Water-contact
WUT ~ Water Up'to
73
1.6 TERMINAL DEPTHS (TD)VERTICAL WELL, DEVIATED WELL
AND DEVIATED iDATA
4.5.3 UP-TO & DOWN-TO
The realjactual fluid contact but not
yet seen in the well. E.g. oil-up-to -7 oil
occurs to lhe topmost part of the sandbefore the shale above it.Pil-down.,.to -7 oil occurs To-the bottom
60st part .of the sand before the' shale
below it. Table 4.1 Shows examples
from CPS-3.
," I (, i' IJ: .. , r
(2)
72
• Best done at the c rest and no t at th eflanks (un le s fluid conta t a r e
obvious)
(ii) Types of wells
a) Exploration/Exploratory -7 Pilot/testwell. . . , l : · ' ....
bJAppraisal -t Actual hydrocarbon I
column detennined.c) Development ~ recovery of the
hYdrocarb9ll aVailable.
( I)
Fi'g.4.1 .Ulustratton shOWing different fluid contaot .
E08= End of Build4.6.1 (Al . VERTICAL WELL
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Bull.1 'I ..... IW.f1
- ,- -
I II I
I IA)\ I n c l i n ~ t i o l lI ' ' ' 'II
TVpBDFI
I i " '- FlnhIIIII
j - - - - - - b - - - - - ~ ~ ~ - - - - - - - - - - - = ~ l D
VerlicOl \ Secllon MII(lrinmtal di"pl;h.cnwnt
75
TD (along hole - flah) = DF'E + (a+b) whcr('DFE = Denick Floor Elevation and
(a+b) is the well trajectory.
Fig. 4.3(a) Illustration showing the estimat iOIl of
TO fo r a deviated well.
Note:
i. At th e Landing point (Heel). the drilling
continues at th e ma,'Cimum inclination
(tangent section) until th e TO is reached.
ii. As much as it is possible to determine
th e Vertical Section and the Tangent
section. i t is not easy to do same for the
Build -up secLion since the build up
angle rate is not constant .
4.6.3 (el DEVIATION DATA (Drilling Engineers)
1'1/0(. 4.3(b) Illustration showi.ng basic deviaLion df l i l l
JV!)';o.; I \ I \ I ) I H ~ I 1)1 1
,\ }
U•"rrl,h.l'lnil,
DH D·rr;I"'llt'lIlI.lI'I,llipnn1 1 . , l u l ~ ; ' : hult'l .... r \ , l ) B [ ) ! ~tl.'l,,1 \,·r!'I.lll)"llth t',WI
IJ\'rn, h I" .. ,r'
\,lll'!'I'IVDS:-: L11".,llltll' ,.1 ;"
r [) "lib ",',I
r - " I . t " " ' ~ " , . K I ·~
x
1
\lntll.:.,1 "I('CIItHl
'tlMI,·'Ullild
"01'
/ f - - - - ~ " ; - - - - - - - ; r - - - - _10 6 t t "' ,.,.
Lmdlll).; ' ~ I m l r . I l 1 J - : ~ ...1 ... ·.-1'''11
(ht't.'lt
- h ./
74
C::r-ti: D e n ' l < ' ~ FI
J' i I '"
J
=1 j Cround ~ l l r l. . .kl '
r v D S ~ '
IFt"1Tn
Pig. 4.2 Illustration showing TVD fot, vertical well
4.6.2 (El DEVIATED WELL
S. '" dnli111 ...v=-- /
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Flail
Tall'!' = drijiTVDBDF
CJ" driji
(),\o.v =--F/{{II
... TVDBDF = {!J'i/i
T{/II<!'... TVDSS =TVDBDF - DFE
Other deviation data include:
• D e p ~ h of target
• Horizontal displacement/vertical
• section/drift to target
• Build up rate
• DFE
• Maximum Deviation
• Azimuth (Direction)
• Inclination or Hole angle (</».
4.6.4 Drift
Diagmm (Vert ical ity is very important
and should be maintained as much aspossible.)
I II I III h.l!l!,
l"tt,
i ! -- OrifJ
76
DEVELOPMENT OF RESERVES
• Production Engineers
• Can be thmugh
(iJ Water injection.(ii) Gas injection. or
(iii) Gas liftThe objective: drive/increase the aquifer
pressure and move the oil (strong water
drive/strong acquifer support and this iscommon in th e Niger Delta (DriveMechanism)
Result - Improve recovery/productivity.
N.D. Weak Aquiler drive ---7 Recovery isnever 100%.
4.8 SIDE TRACKS
i. What is a side-track?
Answer:Drill ing a well from an already
existing one. Reason: possibly abandoned
[or some genuine reasons.
• F'or example. a horizontal side-track isdrilling a horizontal hole from an
existing well into the reservoir wherthe oil is collected. You can also have
vertical side-track or deviated sidc'
track depending on the circumstan '(. )
77
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z
Sl
... ... ... ... ... ... ... ... ... ... ... Ii0 0 0 0 0 0? '" § '"
.... '" .... .... '" "... g ...'" §
..... .'" '"
In S 0
'"
;;:n.. .... ... ..... '" ...
" ~ F . !"... .... .... .... "... .... .... .... .... .... .... .... .... .... .... n - '1('" ... '" i w
:§ ll:
*6! g: :1'" '"
.... !:::::::; ", en w :a0 N
'" '" '" '"N .... W
" ;j5DII
130
"... ,:. II Z l . ~.. ....h :8 :80 0 0 0 s f:
0 §uN 8 N0 ... ... '" g:.. .... ...
'"0' '" ..... '" '" '"
..... .....
II p-I, , ,, "... ...
51 § :5 - II i l . ~0 0 130 0 s S II
'"... w w r:; N
:e '"... 00 w l!l :c II... w co ... .... .... ...
l-N G'l"
"VI !'• '0
§ .h § :8,:..91<'
0 0"00 "6'.... N In
C> 0 C> ...'" 0 co ... C> C> C> C> co
I: 6;'t:J§ "0. 0
S S"O '" 0 0"0 0 0 0 0 0 '" 0 0 0 0 00
" Q". ,' " .! '... ... II C:N
0..
"0 s s s 0 0 0 0 OnS....
t::i t8 2 :0 '" ::0 II
'"00
'"0
0 '"0 N 0' 0 N 0 N 0
'"1-
" 0... ,:. :: 6:;>
0 S II g0 0"
0 0 0 0 0 0 0 0 0 0 0 0 0 0 w
•"II t,:.
:5II
0 ::; ... :;o
0 0 0 0
t :::! w w W '" :: '"0 <;; ;;; 0 0'"w 0 0 0 0
'"
" l§
N:0 '" 15
... r..... \II W .....
'"... :g ....
0 00 0 ...
'"
0
'" '"
0 00 0
'" ""
8 fi w ... ... II
:l!...
t;; N0 0
:;:j II0 , 0 In N 0 ..
"IIII8"I
";. ::;; .. - ::: ..oD 0> .... '" '"
... w ..... II... .... 0
i& - L A ~ ~ I 0;
IIII
'" g; 8l 8l 2l '" g; g; g;1I'"
00
'"
2: Z
o 1.0
= '"I
z Z'o 10Ul CIl
6 ) f ~ B J lll+ 8JB lBqM on1',' [HjlIO'l,!J q JO
(JO:pBJ AI A O J 8 ~ ) dH
[Xl8AOJ8J 8 ~ B U I r l l n ] ClD = dIlOJ.,S •
8JBId U1 ATI"Brll1.h no ) f U B ~ } { J O ~ S •
I:iIIO-LS
I dIIOLS I '6 °
ONI'I'IIHG 'lVSOdOHd
'ONImIVId ' I ' Ih NI 03S11S W H ~ J , ID\IOS .!IO ~ O I J , I N I . i l ~ O 6"17
0 ( S 8 ~ S B M . UJIIPb) 1JBdUl!
I B ~ U 8 U I U O J 1 A U 8 sS8I ~ iU8WUO.IJAU3 (p
S ~ d S S B ~ d n ~ r x 8 8lfl~ U 1 Z J i l l q d o ~ 1 U 8 W 8 . o B L f W -l8S V (J
"uoqJnpo.Id P d ~ B . l 18 JV "N
on d 91 » l lMOP MjlP .ldM.0'1 On!
°.101 BJ
iU8Ul8A0.1dUlJ AlJAJ1Jnpqld
818qM (9L -dId) AlJA!1JnpOfd J8H8H on.°8Ioq UJB.Ip rBiuOZ110H OJ
'SiY8udq u9H npoJd (q
jp;;>.I1nb8.IliOQJ8 8I0L{ ~ i B T P ; ; > W J d ~ q ! / d o l oN "n
u qBJol M.8U JO UOnTstnbJB oN OJ
°fU8f q oJ (B
: . l3mSUV
= Initial oil Ion alion v 1 1111 fa r
E, = Gas expan ion -[ ct rOR
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Up Ihll1l1'11 ,,,1<- (1111'1'" 1'''';,lbl,,)
/
, tl\l 'll thl'O\l'1l
~ I d c /unrL'lJ.ih'l')
'-/1-"-./1. 'J ' - J ' - . - __<j_. _.
!
F = Net-to-Gros ratio or fra lion
of the total sand volum Ib'lt i.considered to be poro'll
4.9.5 Ultin1ate Recovery (UR)
DR = STOUP
RF(See 4.9. Labove)
4.9.6 Mapping Across Faults
• Use the Upthrown side (more reliable)
• Down thrown side is unreliable.
Fig:.4.4 MapPing across Faults with referenceto th e throw.
4.9.7 Well Numbering
\VeU Numbering
E.er UVLW/-l
Real well name bas ed on gridrl
= first wrell but if 2. for exampl
it implies econd well with th e fir t
already existing in that field.
8180
• Unit measurement for oil
• Stock tank barrel
4.9.4 Scf
4.9.2 mmscf
Unit of measurement for gas
• Million standard cubic feet
4.9.3Stb
xFx¢x(J - S"'r
• Unitmeasurement for gas• Standard e'ubic f ~ e t . II: ..); ; # · f \ ' , ' j t. 1 I t INote; (Compare 4.9:.4 and 4.9.2)
4. 9 . . 4 ! ( ~ J 1 .1 ' ~ t n t t u n 1 I 1 g I g ~ ~ ~ ' t V § I :. c' ir- I ',; '" lJlt"( ' j . ' 1 '11/
Remaini ng r eserve ---7 undeveloped
reserve or Developable reserve minus (-)
Net production from existing wells.
4.9.4(b) FGIIP
Free Gas iniUally in place.FGIIP = VI'. x F x <p x(l-SIV)xE,
V l! = Gross bulk volume ([romgeological map).
<p.= Porosity from (Petrophysics)IV<'- Conate water saturation
(P lrophysicsJ
II
4.9.10 Oil Clolwnn -4 Acceplable/4.9.8 Naming a field
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Commercial interest
• 30ft; depending on drilling style andsuch petropbysical features as:
• porosity, I• permeability,
• saturation I
• lateral e A 1 : e I 1 , ~I
NB: The petrojJhysical features should
account for reservoir properties Vis-avis sand qualit)1.
4.9.11 Reservoir Dtive Mechanism:
i. Dissolved g a ~ ,ii. Water, Iiii. Gas cap, or I
iv. A c o m b i n a t i ~ n drive.4.9.12 Scales (maps land X-sections) - 7
Standard: setiTemplates)
• Most horiZ?,ll maps - 4 1.25,000
• Most X - s e c ~ i o l l acrossconventiollfl wells (deViated orvertical. -4 t 10,000 or 1:5000
• For horiZOlltal weIls,
• Vertical sCClfe -7 .1: 1000• Horizntal s9ale -4 1:5000
I
II
83
III
AZ -+F:l
..l l l l ~ "Ell -+ Nnl'lhlll.\;'<
1 -+ Fi"'l \\(']1 In til_ I,,· ,jI' I I
! l ul l I ",
". -
--
r -__2..'uh
IUIUI ,h , ~ ! o 'I"'!.""'''/
,/
A
Fig: 4.6 In fl l l Faull
82
[I IB-+ AZE8·1
i'il(, ,1.5 Nanling a field ( " ' ~ I\ZEll-l
tNnrthlll';":
,
• Use grid name; not n u m b e r ~• Use co-ordinates-Eastings and Northin,e;s
Note:
El.O and E3.0 are key faults. while
E2.0 is an in fill fault.
4.9.9 Interpolation (In fill)
4.9.13 Dog Leg Severity:i. With very low permeability,
ji That produce flnes which could
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High Dog
leg ~ e ~ l ' f i t y ,{ : Wl,ll p,llh.Wl'llp.Hh
reduce vertical penneabilily and
impair production, and
iii. Can act as baffles to vertical now.
NB: (i). (U) and (iii) definitely impair
production.
85
What are Compartmentalization
and Homogeneity of reservoirs?
Answer: Location (Land)
Answer:
il Compartmen1illization -4 Pault.blocks/compart.ments
ii) Homogeneity ---? Almost
homogeneous: Wells in the
reservoir ar e in communication.
4.9.17
4.9.18 EOR& GOR
ERO ---? Enhanced oil recoveryGOR ---? Gas oil ratio
4.9.19 What is Ullage? Or (space)
Answer: Plow station capacity: say 40.000 6pdE.g. gross liqUid ---? 6pd (barTe! pe r day)
Net oit ---? 60 pd (barrel oil pe r day)
-1.9.20 What is Cellar?
Fig: 4.7 Dog Leg severity
Answer:
Shales
4.9.14 Draw downs (measured in psi):
Down-down simply means waler
encroachment or water break through
i) Conventional well (vertical & devialed) ---?
fast water encroachmenl higher drawdown
ii) Horizontal wells ---? slow water break
through. and therefore lower draw-down(can' be managed).
4.9.15 Why do you inject water into wells?
Answer: Either for pressure maintenance
or roi- disposal into shallow
aquifers.
84
4.9.16 What are Heterolithics or
Heterolithic layers?
Circle and Cylinder Tol r' n 'i.
1
4.10 TOLEAANCE
What is it ?
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1I
(6)
•IJ
I -,I'I"" . ~ .. _..•(/\) I 5'
A=Cir" Tolc'rallce B = ylinderToleran e s
Fig. 4.9 Cir I and Cylinder Tolerance
87
• N w Technology
• Increase productivity e.g. horizontalw 11 have longer complete intervals
and there10re better oil recover (e.g.Att ic oil)
• Can be used in built up areas.
• Optimal penetration of reservoir
• EnVironmental preservation (Ie snumber of wells)
4.11 WHY DEVIATE
NB: The oil accumulates behind th e fault
as expected. Therefor . dr il l there and not
across th e fault (fault scoopersl
"
Reservoir
I
86
Fl . 4.8 Square box Tolerance
Allowable l imit (about 25 ' away from
OWC but within th e reservoir.
owe
Permissible limit on eithe- ofhorizontal section/path. ..~ r n p rp box. circle or cylfnder
i. Square Box Tolerance;
Horizontal Section
"
NB:
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• Production from 2 more reservoirs
usin th e same tUbing (or string)
• at allowed by NNPC.
• Nonnally 2 strings (short an dlong) are used
But there is a prob! i l l ' see questionbelow:-
89
•When a well is drilled close tq a fault.it is placed at least 100111 way t
account for uncertainty in IIIpositioning. Surely some atti oi l I
left between lh e well and fault.
How substantia:! the attic accumulationWill be . depends on th e shape of thstructure.
i. How do you account for th e production?
Le. with the drainage point (perforation
a indicat d the production is col lec tiv .
4.13 COMMINGLE
1) What is it about?Answer:
8
4.12UNDRAINED OIL (Attic oil) (Fig. 4.12)
i. Background:
• I t is becoming i n ~ r e . a s i n g l y costly andmore difficult to find new oil.
• U'ndrained oil n eds to b tapped.
• UndrainedaU
i an accmulati nwhich cannot b drained by th
exi ting drainage at a par ti u la r
time due to Some constraint .
ii. Classification of undrained oil (onbasis of occurrence)
• Attic accumulations
• StartigraphicaJl by pass d oil
• Trun bedded intervals
• Small accumulations
• Low reservoir energy accumulations.
• Accumulations
() -VI, lkJ I \dl
(I',llIlt <'((1°1"''')
F i . ~ . 4.10 hHlIt .' 'oop'r (D viA.l dwell)
4.15 TIP ON THE PRODUCTION OF
X-SECTIONS FROM TOP
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91
STRUCTURE/HORIZON MAPS
o Geological Template for the X-sectionuseful in th e control of scales (Vertical& Horizontal) -,
o Choose appr(}priate Scales:• Vertical scale --tis vis-a.-vis the
Template
.. Horizontal Bcale -7 nOImally providedbut select w-r'lich can be
accoffirnodated in your final section.(Use th e V ~ · r n i e r ) .
'-"'.'J vertiCal._:.scale -7 startwith th e lowystt4.la..-;'. Canton ..
a Respect al l faults. centaurs and wellswhict, your section Jlasses in the block.
'0'''' Nu;m] :,er of c o n t o u r ~ ~ . between 2imIDedfate control ~ j . o i n t s isappn.;dmately
:::: .Difference in e l ~ ~ v a t i c ~ n (tops}Contour : n t e r n ~ t l
This value m u ~ r be a whole
number (i.E' nct.
a fral:tion).
Fig. 4.11 Commingl
• Required after well proposal
• Involves appraisal of seismic data i-a-vis Well proposal
• Check co-ordina tes of the drill points
proposed
• Check on amplitJude maps and seismic
sectj,on, (DHIS) I where DHIS means
DirectHydrocarbon I n d i c a t o r ~ ..
• See how the de-ta from th e anlplitude
maps relate to ' ~ h e faults, Confinn any
closures ..
• Relate this infr)ffilation Lo the finaldepth Inaps of th e objective level with
contou:s using Lhe actual fluidontacts as prop.:>sed [rOll1 th e log data.
4.14 SEISMIC SUPPORT
CHAPTER FIVE
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(2)
_I
TO- . 1hlni' l l l l l . l I : - " ~ t l l l '
f
I'
"
~ HORIZONTAL SCALEFig 5.1 Construction of structural and
Sedimentological section.
QUESTIONS AND ANSWERS USEFUL IN
WELL PLANNING. PROPOSAL AND
DRILLING
93
1,2 ~ drilled wells: Pw ~ proposed well
TD '" Terminal depth within the Objectivesand/Target
oF· ~ Symbol means additional depthinformation no t accommodated in thesection.
5. ] Why do you construct Structural &
Sedimentological Sections?
•
o·ui' t
f'I
.!'lL
92
i'M,
;f1!nswer: -;.'!, __ i a 1 ! t ~ i J :in order to~ h o w , a t € ~ I " i . ; S ~ ' ¢ a l r e a d y drilled Vis-a 5.3' In th e Hbrizori<map ~ why are some
wen p ~ o p o s e d and d r i 1 1 ~ d within the
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,. :iVis the, 'tW'Q · ; w : e l l ~ ; · : ~ ~ f X J fN:>w far you :havegone q i r e ~ l.·e:. 'the,weU ..has been drilledfrom the sittfaee.i ;I \ '. :
5.2\ Pr.ojeclion af'wetl ' 1 . : . J t - i l e : c ~ i a n along'strike - How d O J l ~ ' " t . ,i . ,; :" ,
o......... Producing well (control)
+-- Projection to section
Line of se tion
Proposed well
Fig. 5.2'Well projection with reference to th .line of section.
Answer.: I Put a r u l ~ r : parallel to lit);e ofsection and· with _a setsquare placed
perpendicular to ·tt. measure the
projection d i ~ t a n c e : and read of f the. scale
and calculate the result. This is the
projected distance for tl:1e p r o ~ u C i n g wellunto the line of section.
94
boundary fault?
Answer:
Check the sand file. and you will see thatthe fault did not penetrate' the objective
zone.Also check if
completelyfaulted (eF)
or partly faulted ou t (PF) is the situation.
5.4 What is the Basis for any cluster?
Answer.The main aim is increase inUltimate Recovery and there must beoptional productivity.
The gUides are:
I
• Structure; . e ~ e r V o i r management.
• Fluid contacts (away frOID' gas avf<twater (safe distance}.
·f I' r. ,. I
• D . n . l i p a g ~ 9 J s . t ~ u c ~ . h ; f i ~ t r i b ; u t i o n , '(there should.be n Q . i l l t e r f ~ I : ' e p c e J n o ttoo close wells).
I ,
• There must be r:eserves to develop.
95
5.5 WIt t t e Basis r any cluster;?,.Co:ntd.x y Z f
(b) In horizon map -1 OWC/GOC
(original) are or-en us d unless
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there ar e updates. The v lu an
be obtained fron1 the Sand fil ( ).
+-1-- Cluc,kr 'x \\ "II - Ipr0posed
I'rodlllil1g \\Ie III~ \ " 1 t f ( l l l i l 1 g well
- - - .....-- roweFl,n Oil
(Ilelcrolithic inlr,l-
SI iA LE r<'servo;r shnl '/L'nfflc)
_ .!!,(l c".=:... __+-- OGoc
I (I Oil/Gi\S- - - - - - - -+- - I 'GOC
FlO Oil/IV,ller
n n n I IT IT I ITITIT -+-- )OW(
97
O"plh
(iI1Cr(','$e)
Fl.O is the target/objective reServoir sand.
, 'Pig.'S.4 Fi4id contacts "
N.B.: In the above diagram, th original
gas /oil contact has dropped to PGOC(deeper) while original OWC came up
shallow to powe. Th refore, oil column
is reduced while th e gas column
increased. 'T ~ ~ ~ e ' .
,wd!caUeJ theneed/encouragement: ' t@f qrtU ~proposed Well-I,., . , " J -ok
96
A n s ~ ' .J ; P ~ ~ ~ ¢ n t .-;: saturation'tools are usecj'
RST (less. ~ p . e n s i v e wireline tubing,
GST (Rig; mGre e x p ~ n s i v e ) , and
Material Balance calculations
N.6 x, y, z , F, are proposed wells in tbe c J l 1 ~ t e r .,Ad
Fig. 5.3 Cluster
N.B, x,y,z,f .are proposed wells in c 1 u ~ t ~ r , " A ".Cellar -4 Land LocatJ,tm I ' •
.Slot -4 SW8mp..u>cation.. "
N .B.: Cluster is very good for offshor
drilling operations. So many wells can be
drilled from one spot.
5.5: Distinguish between the original and
present fluid contacts; what are
their implications?
Gamma Ray Logs for the structural!sedimentological cross-section:
a .5.H".' ..6 What is BS:$: W?
Answer: ca,lled Basjc Sediment and Water
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99
Single completion -7 1 ' s a h d / i r i t e ~ lD ~ a l '
completion -) 2 sands/intervalsstrings (1 s}iort and 1 l<!>hg), and'
Multiple completion-7 2Q r 3 -moresands/inteIVals. .-
Answer: Reservoir Management.
TVD not FTAH. Why?
Answer: The Cross-section ha s to be in
1VD so that we work on the correctthickness of the reservoir.
Note; +/-65ft; +/-50ft e.g as seen on
structural/sedimento-logtea-r·cross-section.Why?
Answer: These aTe r a n g ~ s of.'uncertainties of depllis that shOUld be
so indicated on the cross-section.' .
5.10 What ar e single, dual and multiple
completions.
5.11 Choice of drainage area: Horizontal
well range; 1,OOOft- 1.500ft. Why?
98
or simplywater production.
5.7 What is t he l east separation distance
between 2 -wells (allowable in a given
reservoir? I.e proximity to other wells
from the planned/proposed one!
Answer. Producing wells from areservoir have statuary approvedrequirement by DPR (Department of
Petroleum Resources) of 800m unless
otherwise discussed and approved!Adequate data must J : : > ~ available.
-- -- -' I· -. -- - - ,
5.B-Define tbe:- following t.erms i t s u ~ l 1 yseen in th e Drillers planning reports.
-7TFO -7 Tool face orientation (bit)--+Turn -4 R ~ l a . t e mbre to direction ( A z i m u t h ~ !-7 Build ~ Relates mar La inclination
-7 DLS-7Dog leg severity (approximately
equal to build up rate)
-7 VS -7 V rtical se tion or drifL or
horizar tal d ispla ement .
N .B. Directional Drilling Engineers
(Good ones)
(i) Baker Hughes(ii) Anadrill
(iii) Petrodynarnfcs:
•:" __ Vl·I'I,•. 11X fleh
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101
A.,... d;""
. "or
Build ul Drift
t .... , holt ..._ •
"'/ .
wn;!'I U n ~ I ' n ! /:"\.'\.-11«'1:,....-
.L.. ~ J r i n l ..... _ . . ''I'
Fig 5.6 Kick off point (KOPl an d
End of BUild (EOB).
Answer: Gas Saturation Tool which is a
Petrophysical instrument for pressuremeasurement.
N.B If the pressures from twowells/reservoirs are close or behaving
:tIikf'. i[ means there is interference i.ethere is communication.
Best eVidence of communication between
two wel ls is presSure data using RFT.
5.15 GST?
Y fl
L.,nding point (Ileel)
,.
-n- / TO
'/
5 )2
Fig. 5.5 HorIzontal well r a n ~ e
DFE: What is it?
Answer: Derrick Floor Elevation.
Determined during the well flx bysurveyo rs when the rig is brought tothe site.
5.13 What is deviation/build up rate?
How is the calculation done?
100
Answer: Done by well Engineers with
the co-ordinates (surface and
subsurlacel supplied by th e geologists.Build up rate can be
• Close co-ordinates (fast!. or
• Too far (slow).
5.14 KOP and EOB?
Answer: KOP ~ Kick off point
EOB ~ End of Build
Done by well Engineers during theirprogram calculations.
NB: You do no t kick off from the
surface (usually) (see Fig. 4.3).
5.16 Seismic Support - Why?
Answer:
. (il Check seismic quality i.e check faults.
5.18 Collision Risk?
With respect to th e surrounding wells.
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DHls, Amplitudes. nlld how the well is
planned.
(iii) As part of ( I l l ' seismic support,
always ensure' lhnl the horizontal
seclibn is fixed within the
objcCiivc/target.l81.0 sand).
Wl'1!
lr,ljL'C!III'\ 1'1
/)1'111 p.lth--+
SH.\LE
Hl !Ql . :;;';! , : ! . ! , , : : ' : , ~ : : ' ~ ' : '. ..... :....... , . : . ~ : : : i : : : ' : : ' ~ ; : " ~ ' · ; ,orL.lndlng , : ; . ~ ::'l ,1)',1 . ~ : : •• I.EJ.O SAND ·Il .......\ .. ,. , ~ ; ,Point : . : !.;. ': ;: J.:' .,' ...: :' 'I . i : . i ' ~ · : :: :,: ,;: :.: , ; , ; ' ~ ' . : . ~ : . : , : ' ,
: > : : ~ . ;/!UV .. : ; / y ~ y : · : ~ i : . ~ · : ; i ; L ~ ~ I / { ~ i : / . ~ \DFig. 5.7 Landing point (Heel) and Horizontalsection.
5.17 Shallow Hydrocarbons; implications?
Answer. If' seen -i > Problematic -i> blowout (if gas). Normally no t antiCipated i.e.not expected. But i f there is.cementation of the a nn ulu s must be
done in order to isolate these unwanted
Hydrocarbon zones.
102
these must no t be too close. (remember
th e DPR stal:utory requirement)
5.19 Overpressure problem?
(it Result -i> blow-out
(iiJ Remedv -i> mud sYstem (increase or- .reduce as appropriate)
5.20 What is the Problem o f shal es i n the
borehole stability?
Answer: Usually hard, fissile shale;
therefore use of pseudo-oil-base mud isrecommended for drilling. This problem
is related Lo overpressures and is
commonil l
shales. as some of them areexpandable or reactive (depending on
the mineralogy).
).21 Uncertainties?
Answer: can be due to
(i) Structure -i> dep th uncer ta in ty
especially where U1ere is
insufficient well control (± 30ft ispermissible)
(ii) Sedimentology (i.e sand developlllt'lll)
103
ll"-
(iii) Fluid contacts & types: original is
.no problem. But present can be
I
I
I5.24 What i s p lug back?
Answer: Aftbr drill ing. cement is
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5.22. Name th e mud logging types
5.23
unknown/uncertain.
Therefore, . pilot hole is recommended
and drilled in order to reduce these
uncertainties.
Answer:
(il RFf ~ Repeat Formation Test for
Hydrocarbon pressure.
(ii) MWD ~ Measurement while
drilling (e.g deviation etc)
(iii) GR/CDR ~ Logs. which are not
the conventional wire-line logs
NB. The three (3) are done whiledrilling instead of the conventional
wire-line (clone after).
In the prognosis, what does 11569
ftss or 11580 ftss for example,
mean?
Answer: Estimate of the landing point(Forecast)
104
used as a pluk back. Do no t leave the
well open b e f o ~ e continuing to dri ll the
horizontal secdon.
5.25 What is I n C l i n ~ t i o n ?Answer: can IJe measured, planned,
MWD or Gyrg. These are deviations
and Log rne¥urements done whiledrilling But G ~ r o is done after drilling(wire linejuslCjs a deviation survey)
5.26 Name some wel l data for th e
objective sandi
Answer: I(i) Expected Top of sand (ftss/ftah)
(il) Expected Grassl Hydrocarbon column
(ft gas / oil) I(iii) Horizontal Displacement or drift (ft).
5.27 How do you detect thin reservoirs?
Answer: SUmm¥ilY, [or the problems/
difficulties and ~ o l u U o n s . see Fig. 5.8
for a possible a ~ p r o a c h .fl.28 What are f>andstone Reservoir
characteristics Itypical of th e principal
depositional enrironments?
Answer: See examples in Fig. 5.9 (a & b).
II
1?5II
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THE AUTHOR
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] 1
For th pa t tw ) ,ca :Ies, at least, rof.
Pius Ositadinma k 'k , ha remain a a
strong acad mic, nnd, pra lisi g ologi :. t in
the oil, gas co, I ,1n J VI .. l('\" upstr am sector.
P r e s ~ n t l y , h> is , full-l im' c nt\"act PIofe'sor
of Geolog n l l hl ' Imtl lJ • Lat U n i v e r s i ~ y of
Sciene and ,hnolog (Ii 1'), Enugu where
heteach II'. ' [nil w i n g ! ' l I b j ~ c t s : -(a) Expl r, lion drilling,
(b) ExpJ l 'i lt il ln , l' ( 1 It 'ics, and
(c) P lm l 'LIm 1, pi nlion Methods.
Prof. k 'k L ,) [,('llnw f lh G ological
Society of LonL!\)Il, and a Fellow of the
Nig0rian Minin > 'I gine and eoscientisl.
FU1'therm re, h '-ved lh nation (Nigeria) as
the Managing ir l)1" of the Nigerian Coal
C .rpOl'ali n, 1.1I1' of th arastatals in the
F dcral Mini. lr f Solid Mineralso wi pm nl (200 I 2003).
THE AUTHOR
For tile past two d ~ a d e s : at least, rof.
Pius Ositadinma. Okeke, has remaifte a
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I ".strong academic, and a practising geologist'
tIlE! oil, gas coal and water upstream sector.
P r ~ ~ n t l y , he is a full-time contract ProfessOr
of G ~ o g y at the Enugu State Univ.ersit}r of
Science andT.echnology (ESUT),Enuguwhere
he teaches'the fa.llowing subjects:- i'(a) ' Explorationdrllling,
'-(b) ExploranonGeophysics, and' :
-"{£)." Petroleum ExplQ'ratiCljl Metho.ds. ,, -
Prof. Okel<e is a Fel low of the Geological'
Society of L I don, and a Fellow of the
Nigerian Mining Engineersand G oscientist .
Furthermore, he s' l"ved the nation (Ni.g ria) as
the Managin Dir ctor of.the Nigerian Coal
I CorporatiOJ1, one of the parastatals in the
F d er al M in is tr y of Solid Mineral
D veJopment (2001 2003).