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FDP-PETROPHYSICS
BYDr. Gamal Ragab Gaafar
(PCSB/PE/PETROPHYSICS)
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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.
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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
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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
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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
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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
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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
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Porosity Definition
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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
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Effect of Sorting on Porosity
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Porosity Types of different Rocks
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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.
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Permeability Classification in conventional reservoirs:
Poor (tight) = k < 1 mDFair = 1 < k < 10mDModerate = 10 < k < 50mDGood = 50 < k < 250mDVery good = k > 250mD
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Factors ControllingPermeability:
• Grain size• Shape of sand
grains• Sorting• Lamination• Cementation• Fracturing• Fine migration
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Pore Perm Relationship
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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
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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
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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
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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
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· 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
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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.
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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
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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
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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
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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
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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
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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
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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.
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Logging While Drilling LWD
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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.
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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
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Gamma Ray Log
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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
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Gamma Ray Log
GR Log measures natural Gamma Rays and is used todifferentiate between reservoir and non-reservoir rock
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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
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GR
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Litho Density Tool
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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.
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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
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Neutron Log Principle• Neutron log determine porosity by measuring hydrogen indexbased on elastic interaction of neutrons with hydrogen atoms(protons) in the pores.
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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
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Example of Fluid Identification from Neutron-Density log
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Sonic Log Principle• Sonic tools measure the speed of sound waves in subsurface formations
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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).
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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
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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
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Resistivity Log Applications1. Calculation of hydrocarbon saturation2. Identification of hydrocarbon bearing reservoirs
(net pay) and fluid contacts3. Identification of formation permeability /
productive reservoirs
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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.
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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
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Raw Open Hole Logs
• Gamma Ray
• Caliper
• True Resistivity
• Bulk Density
• Neutron Porosity
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Interpreted OH Logs
• Hydrocarbon zones identified
• Gas-oil contact identified
• Porosity, water saturation androck volumes computed
• Reservoir sums and averagescomputed for volumetrics
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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
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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
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Gradients and Phase Contacts
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Fluid Identification From Open Hole Log andPressure Gradient
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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
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Log - Core Calibration
D-55
• Illustration of calibration of log-derived porosity/permeability withmeasured core porosity/permeability.
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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.
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• 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
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Definitions of Petrophysical Parameters
• Net to Gross = Net Thickness/Gross Thickness
• Porosity = (Total Pore Volume)/(Total Rock Volume)
• Sw = (Water filled porosity)/(Total porosity)
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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
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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