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Ricardo Alcántara-Garcia1, Héctor Solís-Muñóz1, R Michael Lloyd2, John C. Webb3, Robert M. Cluff4

(1) Pemex Exploracion y Produccion, Macuspana, Tabasco, Mexico
(2) Roxanna Oil Company, Houston, TX
(3) Consulting Geologist/Petrologist, Louisville, CO
(4) The Discovery Group, Inc, Denver, CO

ABSTRACT: The relationship of depositional and diagenetic history to reservoir distribution and quality in the Muspac and Catedral Fields, Reforma Area, Chiapas, Mexico

Gas and condensate are produced from Middle and Upper Cretaceous carbonates in complex faulted domal traps. The Middle Cretaceous is characterized by stacked shallowing upward cycles (< 20m thick), grading upward from tight subtidal mudstones at the base to porous packstones/grainstones that constitute the reservoir. Porosity is interparticle and intraparticle with minor vugs and fractures. The depositional environment was shallow subtidal platform, with local buildups of tidal flat islands.

The Upper Cretaceous is characterized by thick (>50m) coarsening upward cycles, capped by massive porous (>15%) rudist skeletal grainstone/packstone units that are the dominant reservoir. Fracturing contributes to the high flow capacity and excellent interconnection of reservoir layers. The fracture porosity is small in comparison to the high interparticle porosity, however, so that fractures are only a minor part of the reservoir storage.

The Muspac-Catedral area resides near the southern edge of an extensive carbonate shelf. The Middle Cretaceous represents simple aggradation on a subsiding shallow platform. The Upper Cretaceous is characterized by major flooding events followed by rapid progradation of the thick grainstone/packstone units. This depositional model contrasts with the slope breccia model, which has been applied to reservoir sections elsewhere in the Reforma Area. Locally extensive subaerial exposure, related to sea level low-stands, has resulted in the formation of karstic solution collapse breccias in low energy intertidal facies and the development of moldic and secondary interparticle porosity in higher energy grainstones and packstones. Karstic breccias have low matrix porosity (i.e. storage capacity), but typically retain fracture porosity (high flow capacity).

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