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Pore pressure influence on rock property and reflectivity modeling

Diamond Geoscience Research Corporation, Tulsa, Oklahoma, U.S.

Bill Towner

Vintage Petroleum, Tulsa, Oklahoma, U.S.

Corresponding author: R. Lindsay, ROLindsay@dgrc.com

The first 20% of the full text of this article appears below.

Explorationists use rock property and reflectivity modeling to understand the frequently ambiguous amplitude and AVO signatures in seismic data. In that quest, great effort is placed on understanding the elastic reservoir properties and their dependence on pore fluid. Yet seismic reflection data measure changes in elastic rock properties across interfaces. It then necessarily follows that the elastic properties of the sealing cap rock are as important to the reflectivity solution as are those of the reservoir.

Pore pressure has greater influence on the elastic properties of shale than it has on the properties of sand. This phenomenon occurs primarily because of the influence of the adsorbed water on the clay particles. And because pore pressure is related to shale dewatering, at least in Tertiary sand-shale sequences, the amount of adsorbed water correlates with pressure. Pore pressure then is a critical parameter in rock property and reflectivity models because of its disproportionate influence on the elastic properties of the shale cap rock. The ultimate result is that essentially identical reservoir sands with similar pore fluids may have dramatically different amplitude and AVO signatures simply as a consequence of their pore pressure environment (Figure 1).

View larger version (80K): [in this window] [in a new window]   Figure 1. Similarly scaled AVO strength maps of reservoir sands in the control and prospect areas. Warm colors represent increases in absolute amplitude. Cool colors . . . [Full Text of this Article]