Application of Drilling Performance Data to Overpressure Detection

8/9/2019 Application of Drilling Performance Data to Overpressure Detection

1/8

RILLIN

pplication of rilling Performance ata to Overpressure etection

J JOR EN

MEMBER A/ME

O J. SHIRLEY

bstract

Th e previously recognized effects of pressure on rateof penetr ation have been adapted to an overpressuredetection technique for the Texas-Louis iana u lf Coast.It is postulated that, under specified conditions, a plotof incremental rate of penetration vs de pt h will definean ever-decreasing trend in the normal pressure sectionan d that this tr end will reverse w hen overpressures areencounte red, thus permi tt ing the de tect ion of overpressures from drilling performance data. t also is postulated tha t a relationship between rate of penetration andd iffe renti al pressure exists. Relat ionships between pressure an d rate of penetration as developed by several investigators are reviewed. Methods are developed to normalize rate of pene trat ion data with respect to some ofthe more significant dri lling variables bi t weight, rotaryspeed and bi t diameter . Using these m et hods , drillingperformance data are analyzed to determine if the postulated correlations mentioned can be recogn ized from actual field data, an d results of these analyses are presented.

Introduction

Th e presence of overpressured formations formationswith abnormally high fluid pressure) is a significantcharacteristic of the Texas-Louisiana Gulf Coast geologicprovince. Dickinson originally outlined the occurrenceof overpressured format ions in this province, and bothDickinson and Hubbert and Rubey presented theorieson the origin of these high-pressure zones. Subsequently,dril ling pract ices and mud and casing programs have

been developed which per mi t the detection and controlof overpressures, thus enhancing the chances of successfully drilling these zones. Many of these techniques,which are not in the l itera ture , have been used extensively by various operators in the Gulf C oa st f or severalyears. Recently, log analysis methods have been reportedby Hottman and Johnson using the transit time and

Original manuscript r ec ei ve d i n Society of Petroleum Engineers officeMarch 31. 1966. Revised manuscript received Sept . 13, 1966. Paper S PE 1407) wa s presented S P E Symposium on Offshore Technology

an d Operations held i n N ew O rl ea ns . La • Ma y 23-24. 1966; an d at SP E41st Annual F a ll M e et i ng h eld i n Da lla s. Te x • Oct. 2-5 . 1966. ©Copy-r ight 1966 A me ri ca n I n st it u te o f Mining. Metallurgical an d PetroleumEngineers Inc

l R ef e re n ce s g i ve n at end of paper

N O V E M B E R 9

SHELL DEVELOPMENT COHOUSTON TEXSHELL OIL C OMETA/R/E L

resistivity of shales to 1) ident ify the first occurrence

of overpressures, an d 2) estimate formati on pressuregradients.T hi s p ap er presents a technique developed f or identi

fying the first occurr ence of overpressured formationsfrom interpretation of drilling performance data. Specifically, rate of penet ra tion data, by vi rtue of its dependence on differential pressure the bottom-hole pressuredifference between the mud column and the format ion),can be used to identify overpressures. Data from thistechnique are immediately available as a well is drilledwhich is a n obvious operational advantage over t he loganalYsis methods reported earlier.

Studies·-· in the indus try have shown tha t rate of penetration is considerably reduced by an increased mudcolumn pressure. Assuming an inversely proport ional relat ionship between rate of penetration and differentialpressure, consider dril ling under constant conditions) agiven rock in the normal pressure sect ion at ever-increasing depths. Th e total differential pressure will increasewith depth, and rate of penetration should decrease.Consider drilling the same rock under the same conditions as the overpressure section is entered. As t he formation pressure gradient increases, the differential pressure decreases and the rate of penetration should improve.

Thus, for constan t rock proper ties and dril ling conditions, it is postulated that a plot of incrementa l rate ofpenetrati on vs dept h should define a n ever-decreasingtrend in the nor mal pressure section, and that the t rendshould reverse when drilling into overpressures Fig.1 Such a plot would show character is tics similar to theshale resistivity and shale transit time plots currentlyused for overpressure detect ion, and would be a valuable supplement to these log analysis methods because itwould be available as a well is drilled.

Fur ther mor e, there should b e a relationship betweenincremental rate of penetration and the differential pressure exist ing between the mud column and the formation.Knowledge of such a re la tionship would provide a method to 1) maintain minimum differential pressures andthus improve dril ling efficiency, and 2) predict formation pressures while drilling.

I f rate of penetration is proportionally related to pres-

1 3 8 7


2/8

125

STRENGTHEFFECT

25 50 75 100MUD PRESSURES k g m

32 RPM ATMOSPHERIC PORE PRESSUREo OBERNKIRCHENER SANDSTONE BIT LOAD 30 0 kg.X VAURION LIMESTONE BIT LOAD 50 0 kg. BELGIAN LIMESTONE BIT LOAD 70 0 kg.

O - - - - . . . - - - - - - - - - - - r - - - : - - - r - - - -- -o

Ee

zoI

~I -wZWD..

Applieation of Drilling Fundamentals

they affect rate of penetration. These data indicate thatch ip hold-down affects rate of penetration more significantly than does rock strengthening.

Most of th e wor k cited suggests that a relat ionshipdoes exist between differential pressure an d rate of penetrati on. Howev er, th e w or k of Bingham has shown arelationship between rate of penetration an d pressure,but not necessarily a proport iona l relat ionsh ip betweenrate of penetration and differential pressure. Bingham sfindings imply that drilling under laboratory conditionsmay

be directly influenced by differential pressure,but

drilling under field conditions is not necessarily influencedby differential pressure in the same manner.

In summary, all investigators recognize a s trong relat ion between rate of penetration an d pressure, differentialor hydrostatic; however, definition of the exact nature ofth e relation has not y et been made. I t was the originalpremise of the p resen t st udy that overpressures can bedetected in a well by a change in penetration rate andit is implicit that a relat ionsh ip between rate of penetration and differential pressure mus t exist for this premise to be valid. Therefore , this investigation is directedt ow ar d developing a reasonable means to represent theeffect of differential pressure, recognizing that it mayormay not be the only physical phenomenon involved.

TheoryThis investigation is to relate rate of penetration be-

havior to differential pressure behavior and thus developa tool to detect overpressures. I t has been shown byseveral investigators that a recognizable relationship between differential pressure an d rate of penetration shouldobtain under constan t drilling condit ions. An equationof the general form R N =a W / d has been shown torelate penetration rate to bit weight, rot ary speed an db it size, pro vided that all o ther drilling variables are

Fig. 2 - P e n e t r a t i o n ra te as a funct ion o f m ud pressure a tatmospher ic pore pressure af ter Garn ie r and va n Lingen 4 .

R AT E O F PENETRATION d EXPONENTOG 6tsh PREssuRE tiP

GRADIENT

\ \ \ \ >:;i \ ~

( :ORMAL COMPACTION

TR N

LOG Rsh

Fig. I S c h e m a t i c comparison b et we en s ha le resistivityshale transit time differential pressure an d rate

o f p e ne tr a ti o n.

sure differential, the foregoing postu lat ions are valid inthe ideal case where all o th er drilling variables are constant . However, the rate of penetration-different ial pressure relationship is obscure, and actual field condi tionsnecessarily include variations in rock properties and drilling mechanics. Therefore, i t is the purpose of this studyto examine actual field data to determine i f these postulated correlations are recognizable and, if so, to establishmeans of applying these relationships to improve current overpressure detection and drilling techniques.

Influence of Differential PressureOn Drilling Performance

Th e influence of pressure, either differential or hydrostatic, on drilling p erf orman ce has n ot b een clearly defined. Murray and Cunningham concluded from laborat ory experiments t hat r at e of penetration is decreasedby an increased confining pressure in most formations,and suggested this decrease is caused by rock strengthening due to the confining pressure. They further concludedfrom field data t hat ra te of penetration is decreased byan increased mud column pressure, and t ha t m ud columnpressure affects rate of penet ra tion in the field approximately the same as confining pressure in the laboratory.

Subsequently, Eckel reported laboratory work on limestones which indicated the pressure differential betweenthe mud column and formation is the only pressureparameter which affects rate of penetration.

Further l ab orat ory wo rk b y C un nin gh am a nd Eenin kshowed that overburden pressure has prac tical ly no effect on rate of penetration and confirmed that rate ofpenetration is dependent on the difference between mu dcolumn and formation pressures. These authors foundthat rate of penetration decreased when mu d column pressure was greater than formation pressure. They attributedth e decrease pri mari ly to th e redrilling of a layer ofcuttings and mud particles held to the hole bottom bythe difference in pressure, an d secondarily to the strengthening of the rock by the differential pressure.

Garnier an d van Lingen found that differential pressure affects both rock strength and chip hold-down. Fig.2 shows an example of the relative influence of differential pressure on rock strength an d chip hold-down as

1388 J O U R N A L OF P E T R O LE U M T E C HN O L O G Y


3/8

2

4

6

20

3

8

fO

30

40

50

BI T WEIGHT

W IOOO LB

66 /i8 /i9 7/8

~

\\

BIT SIZED INCHES

12W106D

\

\\

010

.050

.040

006

00 3

.020

.004

d 20 0

RATE OF PENETRATIONlL FT PER H OUR EXAMPLE60N Ro20

N°OO25 0 W=25 OOO

D=97/8

200d=1 64

001150

100

.002

ROTARY SPEEDN REV PER MIN

50 25 0

20 0 .004

1 5 9 /

/ 006

/50

.008

30 01020

10 10 R

8 .020 6 0 Nd=

12 W6

10 6 D03 05

Fig. 3 - N o m o g r a m fo r exponen t de termina t ion .

constant an d certain other ideal conditions are met. I thas also been shown that this e qua ti on does no t describe drilling performance under field conditions. However, as an empirical approximation, it is suggested thata recognizable relat ionship between different ial pressureand exponent (exponent of the genera l dr illing equa-

2000

1600 / J

0

Wa::

1200

w0::a. J


4/8

DEPTHflUID PRESSURE AUXILIARY DATA

SHALE RESISTIVITY SHALE TRANSIT d EXPONENT DIFFERENTIAL PRESSURE GRADIENTFEET TIME M UD FORMATION CASING POINTS, K CKS, ETC

X MEASURED P G

1\ I . H AD D RL G. B REAK 13205 '-10 ' , STARTE£I

~ GAINING MUD VOLUME WHILE CIRC.6(l(X)

OUT. WELL FLOWED W/PUMPS OFF

CLOSED HYDRIL. INCR. Wl. I N P IT S\

\I TO IZ.O. CIRCULATED ON CHOKE

~ I 7 H RS . a RETURNS STABILIZED AT8000 IL8. 'BOTTOMS

U P H AD BEEN SALT-

\ \ IWATER-CUT TO 9.8 MIN. OPENED

I HYDRIL. INCREASEO WT. IN PITS TOI 12.5. CIRCULATED 6 H RS . a RETURNS

STABILIZED AT 12.5. M AD E S H ORT10,000

\TRIP O.K.I

~I

\2. INCREASED WT. FROM 12.5 TO 13.0

, I AT 1 32 32 ' T O CONTROL CAVING12,000 -lLHOLE a EXCESS SHALE.

TOP \VERPRESSURES~ ~ - -1/ -. ) \

14,000 9 5

\.

~ 14157

/ 1\ ,_..._

~ 3 INCREASED WT FROM 10.0 TO 17.016.000

£ \ ? 'iAT 15066' TO CONTROL CAVING

I HOLE 6 E XC ES S SHALE.

I 000 I \ 05 0 70 100 150 1 2 ° '000 2000 .4 06 'O B 1RSh, ohm-m l i . t . , a S ~ ( : / f l 'd d p , p s i FP.G. , p s i . l f t

Fig. 5 -0ve rp re s su re data sheet, Well A

FLUID PRESSURE AUXILIARY DATADEPTH SHALE RESISTIVITYSHALE TRANSIT

d EXPONENT DIFFERENTIAL PRESSURE GRADIENTFEET TIME M UD fORMATION CASING POIN TS, KICKS, ETC

X MEASURED fPC>

\1:\ 1,

I I 250u 'I I

l. HAD EXCESS SHALE AT 12035:4000

1 \ I 2 , H AD GAS-CUT MUD AT 12160:I AfTER LOG AT 1 21 60 ' H ADMOOERATE GAS-CUT MUD6000~ \ \

WHILE R E AM IN G B A CK T O

I BOTTOM 1

3 . AFTER T RI PS AT 13202 :13325 '

8000 6 13436 ' , RETURNS CUT fROM

~ s I 165 TO 154 MIN.I 4. AFTER TRIP AT 13718: RETURNSI C UT F RO M \6.5 TO ] L ---- l__) AFTER LOG AT 13718, RETURNSw ~ C UT F RO M 1 6. 5 T O 1 5. 5 MIN. V f l P ~ ~ S 1P- ~ i ; ~ ~12,000 \ .. 1

~ , /} 1< ,

J12176'

\ L ' < ;,- 14,000

I ? \ rr- 1 W l F T : 0 6 8 ~ P S i ~ tAT 1 I 1 ~

514S09'

16000 iZ I S H p : 0 1 9 2

1

p . i / F l , AT 1 ~ 6 8 0

05 0 0 '00 150 , 2 ° '000 20000,4 0.6 °, , 0Fish, ohm-m J . 1 . , a S t c - / f t d Ii ,ps, F P C ; , ps,/FI

Fig. 6--0verpressure data s h ee t , We ll B.

flUID PRESSURE AUXILIARY DATADEPTHSHALE RESISTIVITY SHALE TRANSIT d EXPONENT DIFFERENTIAL PRESSURE GRADIENT

FEET TIME M UD FORMATION CASING P OINTS, KICKS, ETCX M EA SU RE D f.PC;

~ T455\ ' _ •• ' . ' =' I000 I THROUGHOUT INTERVAL 10355 '-11420'

\ < / \ I2. CEASED DRILLING AT 118 60 ' D UE T O

R AT E O F PENETRATION INCREASE.

/ > i BOTTOMS uP CUT FROM 12.0 TO 11.86000

J \I FO R 4 H RS . I NC R. WT. TO 12.3 . MADEI

SHORT TRIP O.K. LOGGED WELL.

~ ~ I 3 WHILE DRLC>. AT 11948'.W 12 3

MUD,WELL lOCKED. CLOSED HYDRIL WI8000

\ ~ If ~ \ I 300p, i SIOPP. INCfl. WT. I N P IT S TOI 14 . 0 . CIR CULATED 3.5 HRS. ON CHOICE} I l H RS , O PE N 6 RETURNS STABILIZED10,000

i LJAT 4 . 0, R ES UM ED D RL G .

TOP

- ~ i \ 1--'O V E ~ P ~ E S S U E S 7 ~ ·- l: L_ / HB60'12.000 ~ \ I ) :3- . / . ~ \ 4 . H OL E S WA BB ED ON TRIP AT 12.015./ P , ~ - = : 5 . H AD INTERMITTENT M IL D G AS C UTTING THROUG HOUT INTERVAL14.000I \

, L 14013'-14355'.hlFPG AT II 'UTO.6$3 e ~ E OON

~ i \ 12.3 PPG jUO a :soo r SIOPP0 05 0 20 0 '00 '50 , 2 0 '000 20 0 4 0.6 °, 10RtM, ohm-m l 1 t . , A , S t ( : , / F l d Ii , j : l ' F f ' G , ·ps i /F

Fig. 7-0verpressure data shee t , Wel l C.

l i l 9 0 J O U R N A L O F P E T R O L E U M T E C H N O L O G Y


5/8

* T hi s e q ua ti o n is no t a r i go r ou s s ol ut io n of the equation R N =a W / D in t ha t th e d e x po n en t a s used h e re a c tu a ll y represents d

]oga

RWhen 60 N is less than unity, t he a bso lu te va lue of log

Rate 1 Penetration

During the collection an d analysis of exponent datai t was re co gn iz ed that another approach, possibly betterthan normalizing drilling data, would be to maintain alldrilling variables constant an d simply record uncorrectedrate of penet ra tion . S ince this p ract ice cannot prudent lybe followed over the ent ir e hole due to ch an ge s i n formation characteristics with dep th , the fol lowing methodwas developed.

1 Preselect an interval of 1,000 to 1,500 ft immediately above the expected top of overpressures based on available data in t he area of the well of interest.

d EXPONENT MUD WT ppg..0 2 0 3 0 1 12 14 16

C/

w~

\ z«

t: :r

\u

q c::;

t : : :

~

l

cC

j~ 1

~~ -

\c

c r .\t:

{ 1

=

oI - - - = = ~ - ~g

S PH ~ 2 M V g

~ - - - r - . . . . - - 40o

ool L J . _ 0C\J

2 When the well reaches this preselected depth, increase mu d weight sufficiently u p to 12.0 Ib / gal toavo id a kick at the top of overpressures.

3 Ma in ta in a s nearly as practical constant rotaryspeed, weight on bit, bit size an d type, pump pressure,etc., throughout the selected interval. Th e rotary speed,weight on bit , et c., should be optimum based on experience in the well of interest or nearby wells.

I )log [ ~] [12W]log lO D

d=

~ varies inversely with R; therefore, the d exponent

varies inversely with rate of penetration. Calculations ofthe d e xp on en t we re fac ili ta ted by use of the nomogramshown in Fig. 3.

exponents an d differen ti al p ressure between themu d column an d t he f or ma ti on were plotted vs depthfo r each bi t ru n Figs. 5 through 7 . To calculate thedifferent ia l pressure, a constant for rgat ion pressure gradient of 0.465 psi/ ft was used in the k no wn n or ma lpressured section, an d the formation pressure gradient inthe overpressured sec tion was est imated from s ha le resistivity-formation pressure gradient relationships developedby H ott ma n a nd J oh ns on : Recorded mu d density datawere assumed to occur at the lowes t depth of each bitru n an d an y c ha ng es i n mu d density were a ssumed tooccur l inea rly between these depth point s, un less o therwise noted.

5. To evaluate the reliability of exponent plots asan overpressure detection method, these plots were thencompared with shale resi st ivi ty an d shale transit timeplots an d the known drilling history of the wells understudy. To obtain a relationship between d an d differentialpressure, d exponent data for each bi t ru n were plottedvs the average d iffe rent ia l p ressure occur ring during thebit run.

6. Addit iona lly, a program of data col lect ion was under taken on then-current offshore exploratory wells. Datacol lect ion methods were s imilar to those previously outl ined except that rate of penetration, bi t weight, rotaryspeed, mu d weight an d circulation rate were recorded

f or s ho rt intervals some ev er y 30 ft an d some every 10ft dri lled . These data were then ana lyzed as previouslydescribed. Th e exponents in shale sections were selectedan d plotted fo r comparison with the sha le resis tivity an dt rans it t ime p lo ts and drilling history. Short interval datawere available from two wells, an d the analysis of oneis discussed herein.

Fig. 3 - d exponent vs depth compared with S P l og ,Well C

N O V E M B E R , 1 9 6 6 1 ~ 9 1


6/8

4. Record an d p lo t r at e of penet ra tion in lO-ft increments throughout the interval unt il overpressures ar e indicated by the plot.

5. Log to confi rm o v e r p ~ e s s u r e sby shale resistivity ortransit time plots.

Evaluation of Results

Normalized Rate o f P en e tr at io nResults of the original s tu dy s how that definite corre

lations between d exponent an d differential pressure ca nbe recognized f rom field da ta . Of the 7 original casesstudied, four showed a very consi sten t d exponent trendin the normal pressure section, nine showed a reasonably cons istent tr en d a nd f ou r s howed a poor trend. Th etwo wells for which closely spaced data were availableclearly s howed the t op of overpressures. Of the wellswhich dri lled deep into overpressures , nine showed a defini te decrease in d exponent. Several of the wells s tudiedshowed an excellent correlation between d an d differential pressure. in cases where the differential pressurechanged abruptly due to abrupt changes in mu d weight.These correlations were noted in both the normal an doverpressure sections. Fig. 4 shows a differential pressure d exponen t relat ionship obtained as previously described. Although a trend is ind icated, the sca tt er ofdata is too great for a quantitat ive field application ofthis relationship. To note in some detail the c ha ra ct eristics an d limitations of drilling performance data as anoverpressure detection technique, a discussion of representative well studies follows.

Well A Offshore S t. M ar y Parish La.

A very consi sten t d exponent trend occurs in the normal pressure section of this well, wit h the to p of theoverpressures indicated at 12,450 ft (Fig. 5). Shale resistivity d ata a re difficult to analyze in this well w it h t wopossible interpretations of the overpr ess ur e top; i.e., at12,200 an d 14,000 ft. Th e preferred interpretation placesoverpressures at 12,200 ft which seems to be confirmedby d exponent data an d the well behavior. There areexcellent indications of a decreasing pressure different ialbelow 15,300 ft. As the mu d weight was held constantthrough this interval, d exponent data give a direct indication of the increasing formation pressure gradient,which is confirmed by shale resistivity data.

Note that the d ex pon ent is higher between 13,000to 14,000 ft (in the overpressure section) than anywhere in the normal pr ess ure section. E ve n t ho ugh theformation pressure gradient is higher in the overpressureinterval than in the normal pressure interval, the respective mu d column pressures ar e such that a higherdifferent ial pressure occurs in the overpressure section.This emphasizes the belief that dri ll ing performance isdependent upon differential pressure, and that d exponentdata must be interpreted in thc light . of existing mu dcolumn pressures.

Well B Terrebonne Parish La.

Th e d exponent data form a poor tr end in the nor malpressure section of this well (Fig. 6). Th e sharp increase in d at 10,450 f t appears related to the significantincrease in differential pressure at about the same depth.Below protect ive casing there is an outstanding correlat ion between d exponent an d differential pressure. Notethat shale resistivity data show an increasing formationpressure gr adient f rom 11,450 to 12,700 it and then adecreasing formation pressure gradien t be low 12,700 ft.Th e resulting differential pressure is clearly ref lected bythe d exponent.

Well C, Offshore Iberia Parish LaConsiderable scatter of d exponent data is evident in

the normal pressure section of this well (Figs. 7 and 8).Much of this sca tt er is undoubted ly due to varying too thwear whic h becomes a m aj or var iable affecting drillingper formance when several data points are taken fr omone bit run. A series of individual trends ar e apparentin the individual bit runs. However, the over-al l t rendis one of consistent increase with depth in the normalpressure section. Note the abrupt shift in the trend atabout 10,400 ft due to the abrupt increase in diffe rentialpressure. This was the first well in which overpressureswere detected from drilling performance data before experiencing a kick.

Between 10,000 and 10,400 ft the mu d weight was in

creased rapidly from 10.3 to 2 lb l gal an d held at thatvalue t o 11,860 ft. Drilling p er fo rm anc e data were recorded at lO-ft intervals. Fig. 8 shows a plot of d exponent vs depth o n an expanded depth scale. Based onth e slow, consistent decrease in d exponent between11,730 an d 11,860 ft, the decision was made to stop

FLUID PRESSUREDEPTH

SHALE RESISTIVITYSHALE TRANSIT RATE OF DIFFERENTIAL GffADIENT AUXILIARY DATA

FF: ET TIME PENETRATION PRESSURE M U O - - - F OM IATI C* CASING ~ O I H T SI(I(:KS, (TC.X MI SUltED ~

, 0 > } 4. 0 0 0

4000

B>T \ N S I I6000

t J \ I8000 I WELl. KICkEO WHILE P EPARING TO\ I {-- I IUI ( [ TIltP AT 9610 ' INCIt. MUD ---- - - - - ~ - - -- - -- l FROM 10.0 TO l l 7 P P G L O GG E D10000

[;:., S£T 1 5/S C S 6 . H8r OVl __ 55

12000

14000

16000 o os D 2 70 100 LSO 0 100 .0 00 1000 200


7/8

FLUID PRESSUREDEPTH

S H AL E R E S IS T IV I TYSHALE TRANSIT RATE OF DIFFERENTIAL GRADIENT AUXILIARY DATA

FEET TIME PENETRAflON PRESSURE - - M U D - - -FQltMATlOM CASING POINTS, K I C KS . E T CX MEASURED F. .G.

~ . l O 3 / 4TI48

4 0 0 0

l 1I60 00~ ~ \ III80 00 ( I1I

10000M UD GA S C UT W HI LE D RL G 12030 INCR

~POSSIBLE if ( ~ ~

I J OM : 0 0 .• ,eo , c o m~ O V E R P R E S U R E ~ I, 1 2 2 8 7 - L O G G E D l l i SET CSG12000

,I f ~ ~ l2:

12287D AL D O UT W 11 4. 0 PPG MUD, I NC R T O

\ I ~ O PPG WHILE DRLG.

\ I DEFINITE14000 ,OVERTEssur s

16000

0 .0 w w 00 0 0 0 000 200 < 0.0 0. O

A s ~ o ~ 0 . 1 , Sec : . /F I F t / H , .I l .P,I i F P G . , l s ; F l

Fig. I O - O v e r p r e s s u r e data s he et , We ll E.

RATE OF PENETRATION

FTiHOUR

150 100 50 0

. .B IT C HA NG E - -Z


8/8

from an a ut om at ic r at e of pene t ra t ion recorder on anoffshore exploratory test. Comparison with the inductionelectric log s ho ws v ery good correlation with sands encountered in th e interval. T hi s e xa mp le al so s how s th eeffect of bi t we ar on rate of penetration. (Note th e sawtooth profi le with continually decreasing average penetration rate with depth.) Overpressures ar e c lear ly ind icated by continuous increase in penetration rate below11,750 ft. Note that the penetration rate reaches 25ft /hour near t ot al dep th , being approximately eight timesgreater than expected f rom ext rapo la t ion of the expectedrate of penetration.

Conclusions

Based on t he or igi na l study from whi ch this new techn ique was developed an d over two ye ar s of subsequentexper ience in field application, th e following conclusionsca n be made relative to the Texas-Louisiana Gulf Coast.

Drilling p er fo rm an ce d at a can be used to detectth e top of overp ressured sed imen ts in a reas where t heapprox imate dep th of overpressuring is known. A plotof normalized rate of penetration will show a trend ofcontinually decreasing penetration r at es wi th depth an da reversal in this trend as overpressures ar e penetratedby th e dri ll bit. This technique can be used as a means

to avoid t ak ing a kick an d to identify overpressures priorto logging.

2. Rate of penetration data ca n be n or ma li ze d b y atleast two methods with sufficient val idity fo r use withthis technique: a) by using a general drilling equation exponent method), or b) by maintai ning all drillingvariables constant in the field. Experience has shown thelatter method to be pre fe rable. Exper ience has a lso shownthat analysis of short foo tage inc rement s gives morediagnostic results.

3 A c or re la ti on bet wee n n or ma li ze d r at e of penetration an d differential pressure is recognizable from theavailable da ta. Although a trend is indicated in the dexpone nt-di ffe rent ia l pres sure cu rv e s ho wn in Fig. 4, t hescatter of data is too great for quantitative application.However, results are sufficiently encouraging to merit further investigation under controlled drilling conditions specifically designed to investigate this relat ion.

Nomenclature

a constant in general dri ll ing equationD bit diameter, in.d exponent in general dri ll ing equation

N = rotary speed, rp m6.p different ia l pressure between mud column and

formation, psi

1 3 9 4

R = penetration rate, ft / hrR h = shale resistivity, ohm-m /m

6.t h = shale transit time, microsec/ftW bi t l oad, Ib

References

Dickinson , G.: Geo logic Aspec ts of Abnormal Reservoir Pressures in the Gulf Coast Region of Louisiana, U.S.A. , Pro cThird World Petroleum Congress, Th e Hague , Netherlands 1951)

2 Hubbert, M. K in g a nd Rubey, W. W. : R ol e of Fluid Pressurein Mechanics of Over thrus t Faul t ing . Part I , Bull GSA F eb ., 1959) 70.

3 Hottman, C an d Johnson, R K . : E st im at io n of FormationPressures from Log-Derived Shale Properties , lour. Pet . Tech. J une, 1965) 717-722.

4 Garnier, A. J. an d van Lingen, N H. : Phenomena AffectingDril l ing Rates at Depth , Trans. AIME 1959) 216, 232-239.

5 Murray, A S. an d Cunningham, R A.: Ef fe ct o f Mud Column Pressure on D ri ll in g R at es , Trans. AIME 1955) 204,196-204.

6 Eckel , J . R.: E ffec t of Pressure on Rock Dri ll ab il ity , Trans.AIME 1958) 213, 1-6.

7 Cunningham, R A. a nd E en in k, J. G.: Laboratory Study ofErrec t of Overburden. Formation and Mud Column Pressureson Drilling Rates of Permeable Formations , Trans. AIME 1959) 216,9-17.

8 Bingham, M. G.: A New A pp ro ac h to Interpreting RockDrillability , Oil Gas IOllr. Nov. 2, 1964-Apri l 5 , 1965) .

J. R. JORDEN left) is a s en io r p etr op hy si ca l en gi neer

with She ll Development Co. Houston. He r eceived a BSdegree with honors in petroleum engineering from the Uof Tu lsa in 1957. Since retu rning to Shell in 1960 frommilitary duty, he held var ious eng inee ring pos it ions inSouth Louisiana prior to hi s present assignment. O. J.SHIRLEY r ig ht ) h ol ds a BS degree in petroleum engineer-ing from Th e U of Oklahoma. He j oi ne d S hel l in 1948as an exploitat ion engineer and has held various engineer-ing ass ignments for Sh el l O il an d Shell Development inCorpus Christi Houston an d Ne w Orleans. He is current-ly assigned to Shell s Offshore West Div. as staff petro-physical engineer.

.1011 II : iA I O F P T R O l W M T E C H N O L O G Y

Application of Drilling Performance Data to Overpressure Detection

Documents

Transcript of Application of Drilling Performance Data to Overpressure Detection