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Michael O. Maler1, Neil R. Braunsdorf1, Mark G. Kittridge1
(1) Shell International EP, Inc. - Technology Applications and Research, Houston, TX

Abstract: 3-D Stress and Pressure Prediction in the Deep Water Setting

As industry progressively moves into deeper water, they are encountering a range of high over pressure / low effective stress environments. The ability to predict and safely drill such environments becomes paramount in the current environment of cost minimization.

By applying a variation on the Eaton equation (Eaton, 1975) to seismically derived interval velocities, we have had reasonable success at predicting pore pressure for Gulf of Mexico deep water wildcat wells. This has had a significant impact on well planning and seal capacity prediction for deep water prospects. The success stems from two improvements: development of a set of non-linear, pressure-dependent compaction curves to use with Eaton, and improved seismic velocity data due to careful interpretation combined with more widely available 3D data.

Pitfalls occur where the assumptions of the Eaton equation are no longer valid, for example the sediments are currently not at their greatest depth of burial. Additional errors result from improper handling of the velocity data or the anisotropy correction.

Understanding the stress magnitudes is equally important, as they are key to pore pressure prediction and seal capacity analyses. Shell has developed an overburden pressure function for the GOM deep water trend that works well as a first approximation for the vertical stress. The minimum horizontal stress can be calculated from predicted overburden and pore pressures. Leak-off test data provide both an independent check on these calculations and a regional look at stress variations.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana