PetrophysicalAnalysisofFluidSubstitutioninGasBearing在氣體軸承替代流體物性分析PPT課件

1、Benefits Seismic Reliable compressional and shear curves even if no acoustic data exists. Quantify velocity slowing due to presence of gas. Full spectrum of fluid substitution analysis. Reliable mechanical properties, Vp/Vs ratios. Reliable synthetics. Does not involve neural network or empirical co

2、rrelations.第1頁(yè)/共27頁(yè)Benefits Petrophysics Verifies consistency of petrophysical model. Ability to create reconstructed porosity logs using deterministic approaches.第2頁(yè)/共27頁(yè)Benefits Engineering Reliable mechanical property profiles for drilling and stimulation design. Does not rely on empirical correl

3、ations, or neural network curve generation, for mechanical properties.第3頁(yè)/共27頁(yè)Introduction A critical link between petrophysics and seismic interpretation is the influence of fluid content on acoustic and density properties. Presented are two techniques which rigorously solve compressional and shear

4、 acoustic responses in the entire range of rock types, and assuming different fluid contents.第4頁(yè)/共27頁(yè)Gassmann Equation inShaley Formation I The Gassmann equation accounts for the slowing of acoustic compressional energy in the formation in the presence of gas. There is no standard petrophysical anal

5、ysis that accounts for the Gassmann response and incorporates the effect in acoustic equations (e.g. Wyllie Time-Series). Terms in the Gassmann equation:M=Elastic modulus of the porous fluid filled rockMerf=Elastic modulus of the empty rock frameBerf=Bulk modulus of the empty rock frameBsolid=Bulk m

6、odulus of the rock matrix and shaleBfl=Bulk modulus of the fluid in pores and in clay porosityFT=Total PorosityrB=Bulk density of the rock fluid and shale combinationVp=Compressional wave velocity第5頁(yè)/共27頁(yè)Gassmann Equation inShaley Formation II In shaley formation, adjustments need to be made to seve

7、ral of the Gassmann equation terms, including porosity and bulk modulus of the solid components. This allows a rigorous solution to Gassmann through the full range of shaley formations. Estimates of shear acoustic response are made using a Krief model analogy.第6頁(yè)/共27頁(yè)Wyllie Time Series Equation In t

8、he approach presented here, we have solved the Gassmann equation in petrophysical terms, and defined a gas term for the Wyllie Time-Series equation that rigorously accounts for gas. Original Time-Series equation:flemaetttFF1t=Travel time = 1/Vtma=Travel time in matrixtfl=Travel time in fluidMatrixCo

9、ntributionFluidContribution第7頁(yè)/共27頁(yè)Linking Gassmann to Wyllie Calculate t values from Gassmann using fluid substitution Liquid filled i.e. Gas saturation Sg=0 Gas filled assuming remote (far from wellbore) gas Sg Gas filled assuming a constant Sg of 80% From t values, calculate effective fluid trave

10、l times (tfl) Knowing mix of water and gas, determine effective travel time of gas (tgas) Relate t values to gas saturation, bulk volume gas第8頁(yè)/共27頁(yè)Gassmann Sg vs. Ratio of Dtgas to DtwetColor coding refers to porosity bins第9頁(yè)/共27頁(yè)Gassmann Bulk Volume Gas vs. Ratio Dtgas to DtwetColor coding refers

11、to porosity bins第10頁(yè)/共27頁(yè)Gassmann Bulk Volume Gas vs. DtgasC1Hyperbola = C3C2第11頁(yè)/共27頁(yè)Adding a Gas Term to Wyllie Equation Gas term involves C1, C2 and C3 (constants) Equation reduces to traditional Wyllie equation when Sg=0 If gas is present, but has not been determined from other logs, the acousti

12、c cannot be used to determine reliable porosity values.maemawaterwettGas TermttS F FGasContributionMatrixContributionWaterContribution第12頁(yè)/共27頁(yè)Krief Equation Part I Krief has developed a model that is analogous to Gassmann, but also extends interpretations into the shear realm. We have similarly ada

13、pted these equations to petrophysics.Vp=Compressional wave velocityVS=Shear wave velocityrB=Bulk density of the rock fluids and matrix and shalem=Shear modulusK=Elastic modulus of the shaley porous fluid filled rockKS=Elastic modulus of the shaley formationKf=Elastic modulus of the fluid in poresbb=

14、Biot compressibility constantMb=Biot coefficientFT=Total Porosity第13頁(yè)/共27頁(yè)Krief Equation Part II The Krief analysis gives significantly different results from Gassmann, in fast velocity systems (less change in velocity in the presence of gas as compared with Gassmann). In slow velocity systems (high

15、 porosity, unconsolidated rocks), the two models give closely comparable results.第14頁(yè)/共27頁(yè)Examples Slow Rocks Gassmann DTP Krief DTP Krief DTP & DTS Fast Rocks Gassmann DTP Krief DTP Carbonates Gassmann DTP Krief DTP Fast Rocks Gassmann DTP & DTS Krief DTP & DTSIn all of these examples,

16、the pseudo acoustic logs are derived from a reservoir model of porosity, matrix, clay and fluids.There is no information from existing acoustic logs in these calculations.On all plots, porosity scale is 0 to 40%, increasing right to left.第15頁(yè)/共27頁(yè)Slow Rocks Gassmann DTPCompressional showssignificant

17、slowing due to gas第16頁(yè)/共27頁(yè)Slow Rocks Krief DTPCompressional showssignificantslowing due to gas第17頁(yè)/共27頁(yè)Slow Rocks Krief DTP & DTSCompressional showsvery good comparisonRatio and Shearshows fair togood comparison第18頁(yè)/共27頁(yè)Fast Rocks Gassmann DTPActual compressionalmeanders betweenwet and remoteNo

18、ticeableslowing due to gas第19頁(yè)/共27頁(yè)Fast Rocks Krief DTPActual compressionalsuperimposes on both wet andremoteNegligibleslowing due to gas第20頁(yè)/共27頁(yè)Carbonates Gassmann DTPCompressionalshows slightslowing due to gas第21頁(yè)/共27頁(yè)Carbonates Krief DTPCompressional showsnegligibleslowing due to gas第22頁(yè)/共27頁(yè)Fas

19、t Rocks Gassmann DTP/DTSGood comparison with actual ShearRatio showsslight slowingdue to gas第23頁(yè)/共27頁(yè)Fast Rocks Krief DTP/DTSGood comparison with actual ShearRatio showsnegligibleslowing due to gas第24頁(yè)/共27頁(yè)Conclusions Part I Pseudo acoustic logs (both compressional and shear) can be created using an

20、y combination of water, oil and gas, using either Gassmanns or Kriefs equations for clean and the full range of shaley formations. Comparison with actual acoustic log will show whether or not the acoustic log “sees” gas or not gives information on invasion profile. Pseudo acoustic logs can be created even if no source acoustic log is available. Data from either model can