L. Liro, M. Kadri, P. Montecchi, N. Weber, S. O’Hara, M. Etemadi, S. L. Williams, and M. Cubanski

Veritas Exploration Services, Houston, TX USA

ABSTRACT: Subsalt Exploration Potential, Walker Ridge and Keathley Canyon Areas, Deepwater Gulf of Mexico

We describe the major exploration plays associated with the salt nappe, salt canopy, and salt massif systems of Walker Ridge and Keathley Canyon areas in the deepwater Gulf of Mexico. 3D prestack depth imaging of seismic volumes over this region allows explicit definition of the salt emplacement and deformation history, and the associated subsalt structural trap styles.

Salt emplacement in the region follows a simple history: a series of relatively evenly spaced inferred paleo salt stocks have fed salt canopy, nappe, and massif systems. In this region, salt is likely emanating directly from the original Jurassic Louann layer, rather than from intervening salt layers. A pronounced bend in the salt trend is related to a regional fracture zone. Detailed mapping of the salt masses allows division of the present–day salt masses into discrete salt ‘cells’. Emplacement and lateral extrusion occurred in a series of low-angle and high-angle surfaces, dominantly lateral in the salt canopy and salt nappe systems, and dominantly vertical in the salt massif system. Deformation of the upper surface of the salt masses is relatively mild, and is marked by the development of sedimentary mini-basins, localized compressional thrust regions, and salt deflation surfaces.

Subsalt structural traps can be divided into three major types, listed from deepest to shallowest: (1) Simple anticlinal salt–cored folds of Mesozoic and Paleogene strata; (2) Salt stock–related structural inversions (“turtles”) of Paleogene and Neogene strata; and (3) Subtle counterregional dip and truncation of Neogene strata against the vertical salt emplacement to lateral salt emplacement transition.

Most of the deep salt-cored anticlines are located basinward of a regional low in the Mid Cretaceous sequence boundary (MCSB). The basinward edge of this low effectively separates the region of isolated allochthonous salt paleo-sources from downslope nappe development. Although these structures are associated basinward of a regional ramp in the salt nappe system, we believe they are fully detached from the lateral salt emplacement events. In depth slice, these deep structures have a roughly circular outline, and structural risk and closure definition are easily addressed. Structural relief on individual features appears to diminish southwestward, defining the terminus of the Mississippi Fan Foldbelt. These structures are on–trend with recent significant discoveries in shallower waters, and likely represent the lowest exploration risk. Due to proximity to mature Mesozoic organic source rocks, early trap creation, and ready structural definition, the poorest understood risk component in this trap type is likely reservoir presence and quality.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado