Using Seismic Inversion Methods to Characterize the Extents of Gas Hydrate Traps in Northwest Walker Ridge—Deepwater Gulf of Mexico

Daniel R. McConnell¹, Zijian Zhang¹, and Beth A. Kendall^2
1 AOA Geophysics, Houston, TX
² Kerr-McGee Oil and Gas Corp, Houston,

In this poster, inversion methods are applied to image the lateral and vertical extents of the gas hydrate traps identified by McConnell and Kendall (2002) in northwest Walker Ridge in the deepwater Gulf of Mexico. In the prior work, McConnell and Kendall identified a series of gas accumulations without structural or stratigraphic control that were suspected to be trapped by gas hydrate at the base of gas hydrate stability. After the exploration well was drilled, the checkshot survey (for depth/pressure control) and analysis of well logs (for gas composition) established that the distribution of gassy sediments in the area is consistent with gas hydrate prediction theory. Seismic amplitude data in this area show the base of gas hydrate stability by proxy, but do not image the inferred gas hydrate deposits updip from the base of gas hydrate stability. A critical question that this paper intends to address is the lateral and vertical extent of the gas hydrate traps near the base of gas hydrate stability in the northwest Walker Ridge area.

Inversion results in the Walker Ridge area show high-impedance interpreted gas hydrate deposits updip from the trapped gas consistent with the interpreted gas hydrate distribution model. The lateral distribution of gas hydrate and gas hydrate saturation are also presented. Because of the regular distribution of gas traps across the uplifted mini-basin and well data (even though not specifically acquired to test the presence of gas hydrate), the Northwest Walker Ridge example is an excellent setting in which to test the ability of inversion methods to characterize the extents of gas hydrate traps using typically available data.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005