1

FDP-PETROPHYSICS

BYDr. Gamal Ragab Gaafar

(PCSB/PE/PETROPHYSICS)

2

Objective• The main objective of this module is how

to characterize reservoir quality andfluids contained.

• Determine the size of a reservoir, thequantity of hydrocarbons in place, andthe reservoir's producing capabilities.

3

PETROPHYSICS ROLE AND RESPONSIBILITY

- Synthetic Seismogram- Rock Physics- Seismic Inversion

GEOPHYSICS

PETROPHYSICS(FORMATION

EVALUATION, FE)

- HCIIP

RESOURCE ASSESSMENT

- Well correlation panel- 3D static model

GEOLOGY

- Reservoir monitoring- Production logging- Opportunities behind Casing

Production operation (SSI)

- Well completion- Sand control- Borehole stability- Geomechanics

PROD. TECH. / DRILLING

- Dynamic Model- Recovery Factor

RESERVOIR ENGINEERING-N

/G-P

hi-S

hc

-ElasticM

odulus-C

ementand

casingeval.log

-Perf.Intervals

4

THE ROLE OF FORMATION EVALUATION in the LOF Processes

ACQUISITION

- Petrophysical inputs for CBDprojects -Data room exercise- Resource Assessment for potentialasset- Technical inputs for biddingproposals

The FE Section, responsible for petrophysical data acquisition, evaluation and interpretation of well data,plays a very important role in all stages in the Life of a Field, starting from the Asset Acquisition phase tothe End of Life and Abandonment of a Field.

EXPLORATION

- Petrophysical parameters for explorationproposal -Design, coordination, implementation, supervisionand quality control of well log data acquisition- Well log evaluation- Resource Assessment for future fielddevelopment - Manage contract

DEVELOPMENT

- Formulating FDP (petrophysicalinputs) -Design, coordination, implementation,supervision and quality control of welllog data acquisition- Provide quick petrophysical resultsfor consequences development wellsplan -Petrophysical analysis for PDR- Manage Contract

ABANDOMENT

- Identify candidate wells forabandonment- Coordinate with service contractorsto ensure abandonment activitiessafely and efficiently

PRODUCTION

- Identify further opportunities behid casing, bypassed hc zones, reservoir performance- Design, coordination, implementation,supervision and quality control of well log dataacquisition of cased hole- Full field review exercise- IOR and EOR exercise

5

PETROPHYSICIST

•Rock property and fluid type identifier.•Petrophysical data are derived mostly from indirect measurements.

Example:Hydrocarbon intervals are related to high formation resistivity measured by logging tools.Oil is differentiated from gas based from neutron response and neutron respond is related to

hydrogen counts in the formationProductive rocks are differentiated from non-productive rocks based from a number of different

log data like gamma ray, density and neutron.

•Thus, due to indirect measurements, petrophysics requires interpretation ofthe data available to arrive at defining the reservoir properties and the typesof fluid in the borehole drilled.

Interpreted LogBedding scaleSlab core scale CuttingPore scale

6

OWC

GOC

Abu Kecil-1 I-55 Sand

8.9m NGPAve Por 29.0%,Ave Sw 36.4%

6.5m NOPAve Por 31.5%,Ave Sw 44.7%

Example of Typical Open Hole Logs

7

To derive input parameters for calculatinghydrocarbon volumes as follows:

HCIIP = GRV x N/G x x Sh x 1/FVF

GRV = Gross Rock VolumeN/G = Net to Gross Ratio

= Formation PorositySh = Hydrocarbon SaturationFVF = Formation Volume Factor (shrinkage factor)

HCIIP

8

Porosity Definition

9

Effect of Packing on Porosity

Governing Factors:Rate of compactional porosity loss

controlled by ductiles (clays, ductilegrains) fractionCementation can be environment or

temperature (e.g. quartz at T > 120degC)Overpressure can reduce compactionMovement of cementing fluids e.g. from

shales, hydrothermal fluids

Random 36% Rhomb 25.9%Cubic 47.6%

Depositional/initial porosity - controlled by grain packing –most natural grain packs, such as sands have close to random packing

Porosity modification during burial:CompactionCementationDiagenetic AlterationDissolution – esp. in carbonatesFracturing

10

Effect of Sorting on Porosity

11

12

Porosity Types of different Rocks

13

Measuring Permeability from Core

Henry D’Arcy derived the following fluid flow equation:

Q = flow rate of fluid, cm3/seck = permeability, Darcy (0.986923 m2)A = cross-sectional area, cm2

= fluid viscosity, centipoise (cP)L = length, cmp1,p2 = pressures at inlet and outlet of the sample, atm

LAk 21 ppQ

A

Length= L

Permeability DefinitionPermeability is the intrinsic characteristic of a material thatdetermines how easily a fluid can pass through it.

14

Permeability Classification in conventional reservoirs:

Poor (tight) = k < 1 mDFair = 1 < k < 10mDModerate = 10 < k < 50mDGood = 50 < k < 250mDVery good = k > 250mD

15

Factors ControllingPermeability:

• Grain size• Shape of sand

grains• Sorting• Lamination• Cementation• Fracturing• Fine migration

16

Pore Perm Relationship

17

18

Saturation Definition

• The Water saturation Sw is the fraction or percentage of thepore volume in the rock which is occupied by formationwater:

Sw = Vw / Vpor

• Sw can be calculated from Resistivity logs with the

“Archie equation’

Sw = (a x Rw/ m Rt)1/n

19

20

21

Petrophysical Definitions• Gross Interval Thickness

Base of Interval minus Top of Interval

• Gross Sand ThicknessThe sum of all thicknesses in the Sand Unit , meeting acertain clay volume Vcl cutoff criterion

• Net Sand ThicknessThe sum of all thicknesses in the Gross Sand,meeting a certain porosity cutoff criterion

• Net Pay ThicknessThe sum of all thicknesses in the Net Sand, meetinga certain water saturation Sw cutoff criterion

22

23

Data Acquisition1. Direct

1. Coring

2. Side wall coring

3. Mud logging

4. Formation pressure testing

5. Fluid sampling

2. Indirect1. Wireline logging

2. Logging while drilling

3. Seismic

24

WHY CORE ?????

FOR GEOLOGIST

HYDROCARBON PRESENCE FRACTURE STUDYPOROSITY AND PERMEABILITYSEDIMENTOLOGY AND DEPOSITIONAL ENVIRONMENT

FOR ENGINEER

POROSITY AND PERMEABILITY DISTRIBUTIONCAPILLARY PRESSURE AND PORE GEOMETRYWETTABILITYRELATIVE PERMEABILITY AND END POINTS

FOR PETROPHYSICIST

GAMMA RADIATION MINERALOGYPOROSITY AND GRAIN DENSITYELECTRICAL PROPERTIESACOUSTIC PROPERTIES

APPLICATIONS OF CORES

25

26

· Porosity· Fluid saturation· Permeability· Relative permeability· Wettability· Capillary pressure· Pore throat distribution· Grain size distribution· Grain density· Mineral composition· Electrical properties· Effects of overburden stress· Sensitivity to fluids· Hydrocarbon analysis

Core Analysis

27

28

Mud Logs

Mud logs are veryuseful in fluididentification.

Gas and oil showsare used tocorroborate fluididentification fromwell logs.

Mud logs are alsovery useful in rocktyping and matrixidentification.

29

Well Logging• What are well logs

• Why do we run logs

• The essential logs– Gamma Ray Log– Porosity Log– Resistivity Log

• Water saturation calculation

• Summary

• Conclusions

30

WELL LOGGING DATA ACQUISITION

• Data recordings of formation rock properties

• Continuously recorded versus well depth

• Measured by logging tools lowered into the well

• Conveyed by electric cable (called Wireline Logging)

• Conveyed by drill pipes (TLC/PCL Logs)

• Recorded during drilling (called Logging WhileDrilling).

• Recorded by means of resistivity, nuclear, acousticor magnetic measuring devices

31

Types of Well Logs

Two main types of well logs

• Open hole logs

• Well logs run inside a well while the formation isstill exposed or open

• Cased hole logs

• Well logs run inside a casing or tubing, mainly forproduction/injection profiling and reservoirmonitoring purposes

• Casing and cement evaluation logs, corrosionmonitoring logs

32

Typical Logging Tools

Comparison between thestandard supercombo(triple combo) logging toolsand the PEX (PlatformExpress) logging tools

Shorter tool length meansless rat hole required

Less tool componentsmeans shorter rig up andrig down time

33

Methods of Tool Conveyance

• Wireline conveyed logging

• Drill pipe conveyed logging(TLC/PCL)

• Logging While Drilling (LWD)

• Coiled tubing conveyed logging

• Slick line (piano wire) conveyedlogging

34

Wireline Logging

Well logging tools are loweredinto the well by means of anelectric cable attached tothe head of the tool string.

Power and tool commands aresent downwards and data istransmitted upwards, by meansof a telemetry tool.

IDW (Integrated Depth Wheel)measures the length of cablelowered into the well, thusproviding depth measurement

35

Pipe Conveyed Logging System

Normal wireline logging tools areattached to the drill pipe by meansof a “side-entry sub” and loweredinto the well.

Pipe Conveyed Logging System isused in wells where the loggingtools cannot be lowered into thewell using a logging cable, due tohole conditions.

36

Logging While Drilling LWD

37

Coiled Tubing Logging

Logging tools, usually casedhole logging tools, can beattached to the end of a coiledtubing and lowered into the well.

A special coiled tubing, with anelectric cable inside, is requiredto transmit power and data toand from the logging tools.

38

Essential Types of Well Logs

Gamma Ray logs: todifferentiate reservoir rockfrom non-reservoir rock

Porosity logs: to determinenet reservoir rock withpotential to storehydrocarbons

Resistivity logs: to calculatewater saturation, which inturn provides hydrocarbonsaturation

39

Gamma Ray Log

40

Uses of Gamma Ray Logs

1. Discrimination between reservoir and non-reservoir rocks

2. Computation of clay content in reservoir rocks

3. Well to well correlation in a field

4. Identification of reservoir characteristics

5. Determination of depositional environment

41

Gamma Ray Log

GR Log measures natural Gamma Rays and is used todifferentiate between reservoir and non-reservoir rock

42

Vsh calculation from Gamma Ray Log

Gamma Ray Log is used to discriminate reservoirrock (sandstone) from non-reservoir rock (shales).

A cutoff value of 105 API has been imposed on theGR log to differentiate sands from shales.

Based on this cutoff criteria:

Net Sand Thickness : 65 meters

Shale volume calculation:

Vsh = (GR – GRmin)/(GRmax – GRmin)

GR Gamma Ray for the interested zoneGR min Minimum Gamma RayGR max Maximum Gamma Ray

43

GR

44

45

Litho Density Tool

46

Litho Density Log Application1. Calculate porosity from measured bulk

density.2. Lithology identification.3. Gas detection in reservoirs when used in

combination with the neutron log4. When combined with sonic travel times, the

density data gives the acoustic impedance,which is important for calibration of seismicdata.

47

Example Porosity Calculation from LithoDensity Log

Litho density log provides bulk densityof the formation and PEF (photo electricabsorption factor)

Bulk density log ( b) is used to computeformation porosity if grain density maand fluid density are f known

PEF is used to identify the rock matrix

flma

bma

SS 2.65 FRESH 1.0

LST 2.71 SALT 1.1

DOL 2.87

48

Neutron Log Principle• Neutron log determine porosity by measuring hydrogen indexbased on elastic interaction of neutrons with hydrogen atoms(protons) in the pores.

49

Neutron Logs Application

• porosity, usually in combination with thedensity tool

• shale volume determination, in combinationwith the density tool

• gas detection, usually in combination with thedensity tool, but also with a sonic tool

• lithology indication, again in combination withthe density log and/or sonic log

50

Example of Fluid Identification from Neutron-Density log

51

Sonic Log Principle• Sonic tools measure the speed of sound waves in subsurface formations

52

Sonic Log Applications• Evaluate porosity from travel time ( T)• Indicating lithology (using the ratio of compressional velocity over

shear velocity),• Determining integrated travel time (an important tool for

seismic/wellbore correlation),• Correlation with other wells• Detecting fractures and evaluating secondary porosity,• Evaluating cement bonds between casing, and formation,• Detecting over-pressure,• Determining mechanical properties (in combination with the density

log), and• Determining acoustic impedance (in combination with the density log).

53

Example of Porosity Computationfrom Sonic Log

Formation porosity can becalculated as follows:Wyllie’s equation:

fresh 189 ss 55.5 us/ftsalt 185 lst 47.6

dol 43.5

cpmaf

mas B

1tttt

54

Summary of Porosity Logs

1. Computation of formation porosity using variousporosity logs

2. Three main types of porosity logsBulk Density LogNeutron Porosity LogSonic Porosity Log

3. Determination of Net Porous Reservoir Thickness

4. Identification of hydrocarbon type based on thecombination of various porosity logs

55

56

Resistivity Log Applications1. Calculation of hydrocarbon saturation2. Identification of hydrocarbon bearing reservoirs

(net pay) and fluid contacts3. Identification of formation permeability /

productive reservoirs

57

Example of Resistivity Log

Resistivity logs are used to differentiatehydrocarbon bearing zones from thewater bearing intervals.

Hydrocarbon bearing zones usually havehigh resistivites accompanied by high ormedium porosities.

Water bearing intervals usually have lowresistivities accompanied by high ormedium porosities.

Tight or non-permeable zones have highresistivities accompanied by lowporosities.

58

Water Saturation Calculation

Archie’s equation may be used to compute watersaturation:

Sw2 = aRw/( 2 * Rt)

This can be modified as follows:

Sw2 = Ro/Rt

Where: Ro = resistivity in the water bearing intervalRt = resistivity in the hydrocarbon bearing

zoneRw = resistivity of formation water

59

Raw Open Hole Logs

• Gamma Ray

• Caliper

• True Resistivity

• Bulk Density

• Neutron Porosity

60

Interpreted OH Logs

• Hydrocarbon zones identified

• Gas-oil contact identified

• Porosity, water saturation androck volumes computed

• Reservoir sums and averagescomputed for volumetrics

61

Wireline Formation Tester

MDT (Modular Dynamics Tester) toolfrom Schlumberger

This wireline formation testing toolcan take an unlimited number ofpressure measurements

Depending on the tool configurationseveral formation fluid samples canbe taken during one trip in the well

This tool is used for identification offormation fluids (from pressuregradient) and fluid contacts

62

63

64

Pressure Plot

Fluid type and fluid contactscan be determined by usingformation pressure andfluid sampling tools.

The intersection betweenthe different fluid gradientlines indicates fluid contact.

Fluid type and fluid contactinterpreted from well logscan be confirmed by usingformation tester tools

65

Gradients and Phase Contacts

66

Fluid Identification From Open Hole Log andPressure Gradient

67

Log to Core Calibration

Illustration of calibration of log-derived porosity with measured coreporosity.

Whenever available, log derivedporosity and permeability shouldbe calibrated with measured coreporosity and permeability.

Replace with a better example

68

Log - Core Calibration

D-55

• Illustration of calibration of log-derived porosity/permeability withmeasured core porosity/permeability.

69

70

Summary

• Well logs acquired in oil and gas wells play a crucial role inassessment of hydrocarbon resources

• The parameters used in hydrocarbon volume calculationare derived from well logs

• Minimum three types of well logs, namely Gamma Ray log,porosity log and resistivity logs, are required to deriveformation rock parameters.

71

• Gamma Ray log can be used to distinguishreservoir rock from non-reservoir by imposinga certain cutoff value on the log

• In a porous rock formation, hydrocarbonbearing zones will have higher resistivityvalues compared to the water bearing zones

• High resistivity accompanied by high porosityindicates hydrocarbon

• Low resistivity accompanied by high porosityindicates water

Conclusions

72

73

Definitions of Petrophysical Parameters

• Net to Gross = Net Thickness/Gross Thickness

• Porosity = (Total Pore Volume)/(Total Rock Volume)

• Sw = (Water filled porosity)/(Total porosity)

74

Petrophysical Definitions• Gross Interval Thickness

Base of Interval minus Top of Interval

• Gross Sand ThicknessThe sum of all thicknesses in the Sand Unit , meeting acertain clay volume Vcl cutoff criterion

• Net Sand ThicknessThe sum of all thicknesses in the Gross Sand,meeting a certain porosity cutoff criterion

• Net Pay ThicknessThe sum of all thicknesses in the Net Sand, meetinga certain water saturation Sw cutoff criterion

75

Petrophysical Dependencies

• Gross Sand thickness is dependent onclay volume Vcl cutoff

• Net Sand thickness is dependent on clayvolume Vcl and porosity cutoffs

• Net Pay thickness is dependent on clayvolume Vcl , porosity and watersaturation Sw cutoffs