Amplitude Versus Angle (AVA) Simultaneous Inversion of 3-D Partially Stacked Seismic Data for Reservoir Delineation and Lithology/Fluid Characterization in a Deepwater Gulf of Mexico Hydrocarbon Reservoir

Contreras, Arturo J., Carlos Torres-Verdin, William Galloway, The University of Texas at Austin, Austin, TX

Pre-stack seismic data and well logs have been integrated through AVA simultaneous inversion to delineate deepwater reservoirs corresponding to the Miocene “M”-series sands in the Marco Polo Field, Central Gulf of Mexico. A detailed AVA sensitivity analysis was con­ducted to assess the nature of AVA effects in the study area. Such study included cross-plot analysis, Biot-Gassmann fluid substitution, AVA reflectivity modeling, numerical simulation of synthetic gathers, and partial angle stacking. Four partial angle stacks were generated and simultaneously inverted using an AVA-adapted constrained sparse spike inversion algorithm in order to generate volumes of P-impedance, S-impedance, and Density. Subsequently, 3D models of porosity and lithology/fluid sensitive modulus attributes (RhoS and RhoF) were computed from the inversion results.

AVA analysis indicates that the shale/sand interface represented by the top of the hydro-carbon-bearing turbidite deposits clearly generate typical Class III AVA responses; and the layer-dependent Biot-Gassmann analysis shows significant sensitivity of the modulus attrib­ute RhoF to fluid substitution. Accordingly, AVA simultaneous inversion, which combines the advantages of AVA analysis with those of seismic inversion, have provided quantitative information about the dimensions, geometry, and lateral continuity of the turbidite reservoir sands which have been interpreted as stacked depositional lobes. Finally, the spatial distri­bution of economically viable areas has been obtained from interpretation of lithology/fluid sensitive modulus attributes and porosity volumes, thereby significantly reducing explo­ration and development risk.