A High Resolution 3-D Marine Gravity Gradiometry Survey Over a Gulf of Mexico Deepwater Subsalt Prospect in the Mississippi Canyon Area

L. Pratson, R. Bell, R. Anderson, C. Affleck, D. Dosch, A. Grierson, J. White, B. Korn, R. Phair, E. Biegert, P. Gale

In April 1994, a proof-of-concept survey was conducted over a deepwater subsalt prospect in the Gulf of Mexico Mississippi Canyon Area using the Bell Aerospace gravity gradiometry survey system, which utilizes the world's only operational moving base gradiometer. This system was originally designed for military applications. The purpose of the April survey was to assess the resolution of the system for geological and geophysical applications, and to evaluate the potential of gradiometry data for use in subsalt exploration. While a conventional gravimeter measures only the vertical component of gravity acceleration (Tz), the Bell system additionally measures five gradients of the gravity vector (Txx, Txy, Tzx, Tzy, Tzz). These five gradients, which are the independent grad ents in the gravitational potential curvature tensor, describe the 3-D spatial variation of the gravity field. They are useful in constraining the edges of buried causative mass anomalies and can be used in a 3-D inversion to model subsurface structures. Preliminary assessment of the data indicates that: 1) Measured gradients compare favorably with those computed from a realistic, 3-D-seismic-based model of the prospect, which includes a complex salt tongue; and 2) The Txx and Txy gradient measurements appear to provide geologic information about the prospect area that has not previously applied in oil and gas marine exploration. Estimation of the salt tongue structure derived from Bell's proprietary gradiometry inversion algorithm will be shown.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995