Resolving the K-2 Salt Structure in the Gulf of Mexico: An Integrated Approach Using Full Tensor Gravity Gradiometry and Pre-Stack Depth Imaging

John O'Brien¹, Arnold Rodriguez¹, David Sixta¹, Mark Davies², and Phill Houghton^2
1 Anadarko Petroleum Corporation, Woodlands, TX
² ARKeX Ltd, Cambridge, United Kingdom

K-2 is a subsalt field underlying a massive salt body in the deepwater Gulf of Mexico. Prestack depth migration has played a vital role in exploring and appraising this field. The technique however is not without problems and fails to image the Base of Salt and subsalt section in an area where the Top of Salt has a pronounced structural peak; as a result seismic data is unable to determine the updip extent of the field.

To locate the Base of Salt in the seismic “no-data” zone we performed an inversion of Full Tensor Gravity Gradiometry data (FTG) constrained with well information and Prestack Depth Migration results, where these provide a reliable image. FTG is a powerful geophysical technique that provides a superior measurement of the earth's gravitational field compared to that obtained with conventional gravity surveys. This integrated analysis proved to be a potent technique capable of discriminating between the initial candidate interpretations for the Base of Salt configuration, even at subsea depths greater than 20,000 ft. It indicates that the salt has an asymmetric keel that is approximately 6,000 ft. deep and that the termination of the sedimentary subsalt reflections delineates the truncation of the pay sands against the salt keel.

These results have major implications for the field appraisal program. They indicate that we can confidently identify the updip extent of the pay sands and they also resolve the need for further delineation drilling in this part of the field.

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