An Investigation to Document Morrow Reservoirs That Can Be Better Detected with Seismic Shear (S) Waves Than With Compressional (P) Waves

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2001

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Abstract

Pennsylvanian-age Morrow reservoirs are a key component of a large fluvial-deltaic system that extends across portions of Colorado, Kansas, Oklahoma, and Texas. A problem that operators have to solve in some Morrow plays in this multi-state area is that many of the fluvial channels within the Morrow interval are invisible to seismic compressional (P) waves. This P-wave imaging problem forces operators in such situations to site infill, field-extension, and exploration wells without the aid of 3-D seismic technology.

The objective of this project was to develop and demonstrate seismic technology that can improve drilling success in Morrow plays. Current P-wave technology commonly results in 8 percent of Morrow exploration wells not penetrating economic reservoir facies. Studies at Colorado School of Mines have shown that some of the Morrow channels that are elusive as P wave targets create robust shear (S) wave reflections (Rampton, 1995). These findings caused Isos Energy to conclude that exploration and field development of Morrow prospects should be done by a combination of P-wave and S-wave seismic imaging.

To obtain expanded information about the P and S reflectivity of Morrow facies, 9-component vertical seismic profile (9-C VSP) data were recorded at three locations along the Morrow trend. These data were processed to create P and S images of Morrow stratigraphy. These images were then analyzed to determine if S waves offer an alternative to P waves, or perhaps even an advantage over P waves, in imaging Morrow reservoir targets. The study areas where these field demonstrations were done are defined in Figure 1. Well A was in Sherman County, Texas; well B in Clark County, Kansas; and well C in Cheyenne County, Colorado.

Technology demonstrated at these sites can be applied over a wide geographical area and influence operators across the multi-state region spanned by Morrow channel plays. The scope of the investigation described here is significant on the basis of the geographical extent of Morrow reservoirs, the number of operators that can be affected, and the importance of Morrow hydrocarbon reserves to the nation's economy.

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