AAPG Annual Convention and Exhibition

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Poststack, Prestack and Joint Inversion of P- and S-Wave Data at Postle Field, Oklahoma


Postle Field in Panhandle Oklahoma is undergoing CO2 flooding and it is important to understand the characteristics of the Morrow A sandstone reservoir for successful flood management. Prestack P- and S-wave amplitude versus angle (AVA) inversion and joint P- and S-wave inversion provide density estimates along with the P- and S-impedance for better characterization of the Morrow A sandstone. We will discuss the poststack, prestack and joint inversion methods applied to the Postle field data. Fluid substitution modeling is done to prepare the logs for seismic data inversion by replacing the original fluid properties when the well was logged with those present during seismic data acquisition. The single link existing between well data and seismic data is the wavelet, therefore, it should be carefully estimated. The well to seismic calibration is divided into two main stages: the first one uses seismic data only and evaluates a preliminary zero-phase wavelet whose amplitude spectrum is representative of the signal in the seismic data. The second main stage tries to globally conciliate the seismic data and the well data to derive a unique wavelet for the whole field. This two stage analysis is performed for all P, SV and SH stacks. After performing poststack and prestack P- and S-wave inversion, the joint P- and S-wave inversion is performed in a way that the density, P- and S-impedance can be interpreted in the same PP time. The SS to PP time correspondence is achieved using a warping method which minimizes the difference between the S-impedance obtained from prestack P inversion in PP time and the S-impedance obtained from prestack S inversion transformed in PP time using initial Vs/Vp model. One way of analyzing the results is by visually comparing the bandpass filtered well logs and bandpass filtered inversion results. Another way of finding the quality of inversion results is to high-cut filter the logs to inversion bandwidth and cross correlate it with the inversion results. Cross correlation of seismic inversion results with well log data and visual comparison of inverted volumes show that the P-impedance is well estimated from prestack inversion of P data and the S-impedance and density are well estimated from prestack inversion of SV data.