Structural and Sedimentological Evolution of the Ultra-Deep Gas Play Fairway – Gulf of Mexico Shelf, Texas and Louisiana

Farmer, Cathy L.¹, Debra H. Phillips², R. H. Benthien², D. V. Dailey², B. W. Horn², D. G. Derbecker² (1) BP America Inc, Houston, TX (2) BP America Inc,

Ultra-deep drilling activity on the Gulf of Mexico shelf is targeting a new deep gas play fairway below established older production. The fairway extends from the Mississippi delta across the Texas shelf in the section below 25,000 feet. Large relatively simple anticlines with inverted Paleogene and Cretaceous sediment packages have been identified. These packages have been mapped regionally and locally to identify isopach thicks that should be favorable for accumulation of reservoir sandstone. The main exploration risks identified for the ultra-deep fairway are reservoir presence and quality.

The targeted deep structures contain sediments that exhibit internal ponded geometries with thickening axes coincident with present day anticlinal axes. Closure on many of the deep inversion anticlines formed very early as a result of initial autochthonous salt withdrawal. The deep structures are de-coupled from the shallower growth faulted section. Restoration of the structures through geological time indicates a complex interaction between salt thickness, depositional thickening and structural geometry.

Comparison of structures across the ultra-deep trend reveals important differences in the depositional and structural evolution of the anticlines. Three-dimensional seismic data is being used to interpret some of the differences in depositional and structural history. Internal geometries of sediment packages are identified in their current structural setting as well as in their original depositional setting by flattening on major time horizons. Viewing seismic data in this manner assists in understanding inversion history related to evacuation of the underlying autochthonous salt.