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BASIC THEORY
CARBONATE RESERVOIR CHARACTERIZATION
STATIC AND DYNAMIC RESERVOIRCHARACTERIZATION
Static Properties :StratigraphyGeometry of reservoir and component faciesLithologyPorosity and permeabilityOther petrophysical propertiesStructure
TemperatureFluid compositions ?
Dynamic Properties :SaturationsPressureFluid contactsProduction and flow ratesRock/fluid impedances (and seismic amplitudes)Fluid compositions ?
Others ???
OVERVIEWTHE IMPORTANCE AND IMPLICAT IONS
OF RESERVOIR HETEROGENEITY
• The rationale for characterization of heterogeneous reservoirs is one offundamental economic
• Recent geological analyses indicate that most reservoirs display significantgeologic variation and compartementalization
• Reserve and distribution of mobile oil is very much a function of reservoirheterogeneity at meso- and macroscopic scales
• Designing a reliable reservoir model is a function of tectonic complexity , depositional environment , well spacing and the available cores and logs
• Reservoir heterogeneity in carbonate rocks is much complicated than insiliciclastic rocks due to its different origin and diagenetic process
HETEROGENEITY OF CARBONATE RESERVOIR
DEPOSITIONAL PROCESS
DIAGENESIS
PORE GEOMETRYSHAPE ; SIZE ; INTERCONNCTIVITY
CLASTICSCARBONATES
CARBONATESCLASTICS
POSITION INHYDROCARBON COLUMN
RESERVOIR QUALITYPOR ; PERM ; Sw ; So ; Rel.Perm; Po
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CHANGE PROPERTIES
DIAGENESIS and SECONDARY POROSITY
RESERVOIR QUALITY IN CARBONATE ROCKS
• IS A FUNCTION OF :- DEPOSITIONAL TEXTURES- ORIGINAL MINERALOGY- DIAGENESIS
• CAN BE PREDICTED THROUGH DEPOSITIONALFACIES ANALYSIS AND DIAGENETIC ANALYSIS( by applying sequence stratigraphy approach )
BASIC IDEA ……………………
POTENTIAL CARBONATE RESERVOIRS PASS THROUGH SEVERAL DIAGENETIC ENVIRONMENT
AFTER DEPOSITION
• EACH DIAGENETIC ENVIRONMENT LEAVES ANIMPRINT ON THE ROCK
• THE FINAL PORE NETWORK IS A RESULT OF THE DIAGENETIC PATHWAY EXPERIENCED BY THE RESERVOIR
• ALL CARBONATE DEPOSITIONAL TEXTURE MAY DEVELOPECONOMIC PORE NETWORKS THROUGH FAVORABLE DIAGENESIS
BASIC IDEA ……………………
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Dunham’s Classification of Limestone
REEFLIMESTONE
JAMES & BOURQUE,1992FLOATSTONE RUDSTONE
BAFFLESTONE BINDSTONE FRAMESTONE
CARBONATE FACIES BELTS
a. Mechanical breakdown ofHalimeda and Acropora
coral skeletonsb. Biological Breakdown of
massive corrals by sponges,fish , and urchins
( after Folk and Robles , 1964 )
PROCESS CONTROLLING DOMINANT GRAIN-SIZE FRACTIONS IN CARBONATE ROCKS :
PROCESS CONTROLLINGDOMINANT GRAIN-SIZE
FRACTIONSIN CARBONATE ROCKS :
a. Mechanical breakdown ofHalimeda and Acropora
coral skeletonsb. Biological Breakdown of
massive corrals by sponges,fish , and urchins
( after Folk and Robles , 1964 )
HYDRAULIC BEHAVIOUR OF GRAINS
- THRESHOLD VELOCITY- SETTLING VELOCITY- HJULSTROM’S DIAGRAM
Quartz
Problem mixed siliciclastic-carbonate sediments :Specific gravity of : Quartz – 2.65 Aragonite – 2.94
Calcite – 2.71
Bulk density + intraporousityCoral fragments e.g. Porites 1.2 (porous)
Agaricia 2.0 (compact)Mollusc + 2.0
Carbonate particle
Grains of similar size and shape will behave differently ina fluid due to their different bulk densities. Conversely ,grains of different shapes and sizes may be hydraulicallyequivalent.
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Cation Ionic Radii and Common Carbonate Minerals(after Speer, in Reeder (eds.) 1983)
Cation Ionic radius(nm) Minerals Crystal habit
Ni 0.069 Gaspeite NiCO3Mg 0.072 Magnesite MgCO3Zn 0.072 Smithsonite ZnCO3Co 0.075 Sphaerocobalite CoCO3 RhombohedralFe 0.078 Siderite FeCO3 (trigonal system)Mn 0.083 Rhodochrosite MnCO3Ca 0.100 Calcite CaC03
Ca 0.118 Aragonite CaCO3Sr 0.131 Strontianite SrCO3 OrthorhombicPb 0.135 Cerussite PbCO3Ba 0.147 Witherite BaCO3
CaCO3Three common polymorphs
1) Lo-Mg Calcite- most abundant sedimentary carbonate mineral- primary constituent of limestone- dissolves in acidic water- contains mol 1 – 4 mol % Mg
2) Hi-Mg Calcite- more soluble than calcite- contains 4 – 20+ mol % Mg- common in modern sediments, rare in limestone
3) Aragonite- highly soluble- same composition as Lo-Mg calcite, but with
different crystallinity- common in modern sediments, rare in limestone
Aragonite : Present-day coralsSome mollusks
Low-Mg calcite :Some mollusksSome foraminifera (including all deep-sea sp.)BrachiopodsUnicellular plant family(Coccolithophoridae deep-sea sediments & chalk)
High-Mg calcite :EchinodermsSome large foraminifera
DEPOSITION OF THE CARBONATE MINERALS DUE TO THE ACTION OF ORGANISMS
ORGANISMS AND MINERALOGYCalcareous Green Algae Aragonite
Sponges Mg-CalciteCoelenterates (Modern) AragoniteCoelenterates (Ancient ) Aragonite & CalciteBryozoans Calcite & Mg-CalciteBrachiopods CalciteMolluscs Aragonite & Calcite-
Mg-Calcite
Echinoderms Mg-Calcite
Calcareous Red Algae MgCalciteCoccolith CalciteForaminifera Calcite & Mg-Calcite
3. Aragonite grains either dissolve to form moldic pores or recrystallize to a coarser crystalline calcite that preserves grain texture but develops no porosity (Loucks and Brown, 1988).
1. Grains that are originallycalcite show little macroscopicevidence of alteration.
2. Mg-calcite grains commonlyconvert to calcite with no associate porosity developed.
In a few areas (e.g Jurassic and Lower Cretaceous of the Gulf Coast), Mg calcite grains have recrystallized to microrhombiccalcite, producing microporositybetween the rhombs.
In rare cases Mg-calcite dissolves Completely to yield moldic porosity.
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( Loucks and Brown , 1988 )
DIAGENETIC ENVIRONMENTS AND PRODUCT
SL1
MP
BZ
SL2
MTV
MTP
MP
BZ
SL3
MP
U
BZ
MP : Marine pure-atic zone
MTV : Meteoric va-doose zone
MTP : Meteoric pure-atic zone
BZ : Burial zoneU : UnconformitySL : Sea Level
DEVELOPMENT OF DIAGENESIS
INITIALLY POROUS& PERMEABLE
RQ poor RQ good RQ moderate RQ moderate RQ moderate - good
MARINE DIAGENESISCementation / No dissolution
EXPOSED
no yes
no
COMPACTIONLIMITED ?yes no
CLOSE TOUNCONFORMITY
yes
no
METEORIC PHREATICLimited dissolution
CementationPoro/Perm decrease
METEORIC VADOSE
yes
Extensive dissolutionLimited cementation
Porosity increase
DIAGENESIS
EFFECT OF DIAGANESIS ON RESERVOIR QUALITY HETEROGENEITY OF CARBONATE RESERVOIR
DEPOSITIONAL PROCESS
DIAGENESIS
PORE GEOMETRYSHAPE ; SIZE ; INTERCONNCTIVITY
CLASTICSCARBONATES
CARBONATESCLASTICS
POSITION INHYDROCARBON COLUMN
RESERVOIR QUALITYPOR ; PERM ; Sw ; So ; Rel.Perm; Po
( L k d B 1988
RELATIONSHIP BETWEEN FACIES, DIAGENESISAND POROSITY IN CARBONATE RESERVOIRS
PRIMARYPOROSITY
SECONDARYPOROSITY
1. INSIGNIFICANTDIAGENESIS
2. FABRIC SELECTIVEDIAGENESISEg. Biomoldic porosity
3. ENVIRONMENT RELATEDEg. ‘Beach rock’ cement
4. DATUM RELATEDEg. parallel to water tableor unconformityor petroleum /water contact
5. STRUCTURE RELATEDEg. fractures over salt domes,
dolomitization adjacent to faults
DECREASINGAPPLICATION
OFFACIES ANALYSIS
TO RESERVOIRPREDICTION
CARBONATE ROCKS TEXTURES AND COMMON POROSITY TYPES( Loucks and Brown , 1988 )
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CARTOON OF PORE GEOMETRIES IN CARBONATE ROCKS
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( After Esteban and Klappa , 1983 )
Examples of Characteristics of GR and Sonic Log of Paleokarst Development
IN MESOZOIC CARBONATES,OFFSHORE NORTHERN SPAIN
MODEL………………….
DIAGENETIC ENVIRONMENTSCARBONATE DIAGENETIC ENVIRONMENTS
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SIZE and SORTING
SILICICLASTIC
1. Provide a criterion for interpreting transportation, depositionand textural maturity
2. Relate to porosity, permeability and pore size3. After diagenesis : porosity and permeability ~ initial depositional
texture
CARBONATE
1. Depend on both hydraulic condition and organic productivity atthe site of deposition
2. Carbonate grains have a wide variety of size and shape difficult to relate size and sorting with porosity and permeability
3. Degree of diagenetic modification is more intensive lack of relatedevidence between observable texture and depositional texture