Summary

This case history demonstrates the use of AVO inversion to help find commercial quantities of hydrocarbons in a multizone carbonate and clastic reservoir environment. The study area is close to Oyen, Alberta, Canada where a small 3D was acquired to help delineate gas in the Viking and Mannville sands, and heavy oil in a porous Banff carbonate. The seismic data were processed with a controlled amplitude processing sequence resulting in prestack migrated gathers. From this, P-wave and S-wave impedance volumes along with ?p, and µp volumes were generated for cross-plot analysis. Based on this analysis an step-out well was subsequently drilled which encountered four pay zones totaling 15 meters of gross pay.

Introduction

The Oyen 3D seismic survey is located in southeast part of the Western Canadian Sedimentary Basin (WCSB). This area has proven reserves from both clastic and carbonate reservoirs. The 7-12 well penetrated Viking gas sands and Banff heavy oil reservoirs. In an adjacent area, wells also encountered gas in the Glauconitic and Detrital clastics above the Paleozoic unconformity. Before the acquisition of the 3D seismic survey, there existed only one 2D seismic line in the study area. On this 2D line it was impossible to differentiate changes in any of the reservoir units seismically. In order to understand the structure of the Banff reservoir, a 3D seismic survey was acquired. Further, based on successful AVO case histories on these particular reservoir units (Goodway et al., 1997, Downton et al., 1999, and Li et al., 2003) it was decided to perform AVO inversion to help determine the best location for an step-out well.

Geological Setting
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