Well-Based Seismic Lithoiogy Inversion for Porosity and Pay Thickness
David W. Burge, Dennis B. Neff, and Scott A. Runnestrand
Well log and 3D seismic data were integrated in a Gulf of Mexico field study to determine the distribution of hydrocarbon bearing sands, reservoir porosity, and to estimate the volume of hydrocarbons in-place. Problematic to this study were the highly variable petrophysical characteristics of the reservoir sands, and low saturation gas which caused seismic bright spots in some zones with non-commercial hydrocarbon.
The inversion scheme used here employed a technique in which thousands of synthetic seismic traces are generated using petrophysical logs (porosity, water saturation, shale volume), geologic models, and other apriori information. Comparison of these synthetic traces to the 3D seismic traces was made during the inversion process which created reservoir maps for predefined geologic layers. Also produced were three-dimensional pseudo log volumes which are used for trend mapping and volumetric calculations.
The inversion method successfully addressed the effect of vertical variation in rock petrophysics on the seismic response, and accounted for the lateral variation in depositional environment. Three-dimensional visualization of the pay flag, pseudo log was used to differentiate commercial from non-commercial contacts. A comparison of 3D AVO amplitude maps to the porosity and pay thickness was made to map the lateral extent of the reserves. These results were then used to determine the most-likely volume of reserves in-place as well as a low-side and high-side value for use in economic analysis.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California