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Poisson impedance inversion for characterization of sandstone reservoirs

Summary We demonstrate the application of Poisson impedance (PI) inversion for characterizing sandstone reservoir encased in shale, when the impedance contrast between them is very small. Poisson Impedance is defined as the difference between the P-impedance (IP) and a scaled version of the Simpedance (I S), where the scalar (c) can be determined from the slope of the regression line between IP and IS. Using well data, if the PI curve is correlated with the Gamma Ray (GR) curve, the porosity (ϕ) curve, or the water saturation curve for different values of c, it is possible to determine the maximum correlation coefficient in each case. The c value corresponding to the maximum correlation coefficient for GR is used to compute another attribute called lithology impedance (LI). Similarly, fluid impedance (FI) can be computed using the c value that corresponds to the maximum correlation coefficient for the porosity (ϕ) curve. The crossplot between LI and GR shows the advantages of LI in distinguishing sandstone from shale. Pore content is predicted using the linear relationship exhibited on the cross-plot of FI versus ϕ.