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Loucks, Robert1, Charles Kerans1, Xavier Janson1, Alfredo Marhx2, Carlos Reyes2 
(1) University of Texas at Austin, Austin, TX 
(2) Pemex, Pozo Rica, Mexico

ABSTRACT: Depositional Facies and Reservoir Quality of the Deep-Water, Lower Cretaceous Tamabra Carbonate Slope Reservoir in the Poza Rica Field, Mexico

The Poza Rica field in eastern Mexico is the world°¦s largest deep-water, carbonate-slope oil field. It consists of gravity-flow deposits that were sourced from the Tuxpan detached platform to the east. Water depths ranged from 3,600 to 4,000 ft. The Tamabra interval was deposited during four third-order sequences, and distribution of Tamabra rock facies reflects the sequence stratigraphic history of the area. The best reservoir quality is in the grain-rich turbidites and dolomitized grain-matrix-rich debris flows. 
Debris-flow deposits are characterized by large clasts mixed with lime mud and/or sand matrix and are internally chaotic. The clasts are derived from both the platform and the slope. The platform clasts commonly contain caprinids and are much more common than the slope clasts, indicating the bypass nature of the Tuxpan platform slope. The grain-rich debris flows are good reservoirs (ƒÖ=9.7%, k=12.54 md), especially where the grain matrix is dolomitized. 
The high-density turbidites are composed of carbonate sand and lesser lime-mud matrix. Most of the turbidites are structureless, similar to fluxoturbidites. Upward-fining sequences are present. Several sequences of distally deposited, low-density turbidites are characterized by laminated carbonate siltstones. The mud-poor turbidites are the best reservoirs (ƒÖ=12.5%, k=18.43 md). 
Suspension deposits of burrowed lime mud are interbedded among the debris flows and turbidites. They are characterized by wispy to contorted bedding. A 3-m-thick terrigenous mudstone occurs at the base of the topmost sequence. The suspension deposits may form vertical permeability barriers.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.