The Thunder Horse discovery is an accumulation of over one billion barrels of oil in the deepwater Gulf of Mexico. This test led to the discovery of a new play and challenged traditional exploration philosophies in the GOM. After early success in the amplitude-driven deepwater play, pool sizes were declining, and the success rate was flat at best. After multiple exploration failures in the conventional attribute-driven play, we adopted a "back to basics" exploration philosophy, focused on the geologic elements of the basin, while ignoring seismic attributes. We also focused on exploring from the source rock up. These concepts changed the way we viewed prospectivity in the GOM, and steered us toward targeting older stratigraphy in previously untested deeper structures.

Regional work indicated that the Mississippi Canyon protraction area was a top place to focus our exploration efforts. Existing discoveries highlighted the presence of a world-class petroleum system, and large structures with significant fetch areas were present. Our subregional analysis focused on high-grading structural accumulations with the best fetch areas and well-developed reservoir, which led us to focus on Mississippi Canyon. Analysis indicated that south central Mississippi Canyon held promise as a top area to test this new play concept, and two structures were prepared for testing. Both prospects were turtle structures with primary targets in Miocene strata.

Before we could drill, several major hurdles had to be overcome. The acreage position had to be secured, and rigs with the ability to drill in these water depths had to be accessed. Three-D seismic surveys and depth-imaging breakthroughs were required to describe the prospect elements and position a well. Depth imaging was especially important, as it provided a much better structural image for prospect description and well positioning. When we finally tested the two top prospects in the play, one (Thunder Horse) was successful, and one (MC 911-1) was a. failure. Post-appraisal of these wells helped us understand the potential and risks of this new play, although each new well in the play continues to teach us new lessons and keep us humble.

The process of continued focus has led us to this success. In building a regional framework for the northern Gulf of Mexico basin, then focusing our subregional analysis and prospect in the interpreted sweet spots, we were constantly high-grading. While the regional and subregional work were very efficient in terms of cost and time, prospect maturation and drilling were extremely cost and team intensive.

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