Petrophysical Analysis of Fluid Substitution in Gas Bearing 在气体轴承替代流体物性分析.ppt
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1、Petrophysical Analysis of Fluid Substitution in Gas Bearing Reservoirs to Define Velocity Profiles Application of Gassmann and Krief Models,Digital Formation, Inc. November 2003,Title,Contents,Benefits Introduction Gassmann Equation in Shaley Formation Wyllie Time Series Equation Linking Gassmann to
2、 Wyllie Adding a gas term to Wyllie Equation Krief Equation Examples Conclusions,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, V
3、p/Vs ratios. Reliable synthetics. Does not involve neural network or empirical correlations.,Benefits Petrophysics,Verifies consistency of petrophysical model. Ability to create reconstructed porosity logs using deterministic approaches.,Benefits Engineering,Reliable mechanical property profiles for
4、 drilling and stimulation design. Does not rely on empirical correlations, or neural network curve generation, for mechanical properties.,Introduction,A critical link between petrophysics and seismic interpretation is the influence of fluid content on acoustic and density properties. Presented are t
5、wo techniques which rigorously solve compressional and shear acoustic responses in the entire range of rock types, and assuming different fluid contents.,Gassmann Equation in Shaley Formation I,The Gassmann equation accounts for the slowing of acoustic compressional energy in the formation in the pr
6、esence of gas. There is no standard petrophysical analysis 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 rock Merf = Elastic modulus of the empty rock
7、 frame Berf = Bulk modulus of the empty rock frame Bsolid = Bulk modulus of the rock matrix and shale Bfl = Bulk modulus of the fluid in pores and in clay porosity FT = Total Porosity rB = Bulk density of the rock fluid and shale combination Vp = Compressional wave velocity,Gassmann Equation in Shal
8、ey Formation II,In shaley formation, adjustments need to be made to several 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 m
9、ade using a Krief model analogy.,Wyllie Time Series Equation,In the 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:,Dt = Travel time = 1/V
10、 Dtma = Travel time in matrix Dtfl = Travel time in fluid,Matrix Contribution,Fluid Contribution,Linking Gassmann to Wyllie,Calculate Dt 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 co
11、nstant Sg of 80% From Dt values, calculate effective fluid travel times (Dtfl) Knowing mix of water and gas, determine effective travel time of gas (Dtgas) Relate Dt values to gas saturation, bulk volume gas,Gassmann Sg vs. Ratio of Dtgas to Dtwet,Color coding refers to porosity bins,Gassmann Bulk V
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