ABSTRACT
Deep-marine bottom-current reworked sands (sandy contourites) have been recognized in hydrocarbon-bearing sands of the Gulf of Mexico. A distinctive attribute of these sands is their traction bed forms, which occur in discrete units. Common sedimentary features of traction currents include cross-bedding, current ripples, horizontal lamination, sharp upper contacts, and inverse size grading. These sands also exhibit internal erosional surfaces and mud offshoots, indicating oscillating current energy conditions.
The Pliocene-Pleistocene sequence cored in the Ewing Bank Block 826 field in the Gulf of Mexico provides an example of sand distribution and reservoir quality of deep-marine bottom-current reworked sands. Presumably, the Loop Current, a strong wind-driven surface current in the Gulf of Mexico, impinged on the sea bottom, as it does today, and resulted in bottom-current reworked sands. A depositional model based on the integration of well (core and log) and three-dimensional seismic data suggests that the reworked sediment package may be thick and continuous, but individual sand layers within the package may be thin and discontinuous. This unconventional model, which depicts the distribution of bottom-current reworked sands in interchannel slope areas as a distinctly different facies from channellevee facies, has the potential for general application to other slope plays outside the study area. In the Ewing Bank Block 826 field, the type 1 (L-1) reservoir with 80% sand exhibits higher permeability values (100–1800 md). than the type 2(N-1) reservoir with 26% sand (50–800md). The increased permeability in the type 1 sand has been attributed to high sand content, vigorous reworking, and microfractures. The clean, porous, and well-sorted type 1 sands with good communication between sand layers have produced at higher rates and recovery efficiencies than the type 2 sands with numerous interbedded mud layers.
