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Ernesto Caballero-Garcia1, Angel Francisco Callejon2, Noel Holguin-Quiñones3, Louis W. Elrod2, K.K. Bissada2
(1) PEMEX, Villahermosa, Mexico
(2) Houston Advanced Research Center, The Woodlands, TX
(3) PEMEX, Mexico City, Mexico

Abstract: Exploration and reservoir heterogeneity implications of the composition of natural gases in the Macuspana Basin, Southern Gulf of Mexico

A geochemical study of the occurrence and distribution of natural gases in the Macuspana Basin, Mexico, was carried out jointly by Petroleos Mexicanos (PEMEX) and HARC’s Geochemistry Unit. The study entailed molecular and isotopic characterization of 113 gas samples from 12 fields in the basin, in order to identify reservoir heterogeneities in the fields.

The study revealed that the gas accumulations in the Macuspana Basin owe their origin to two distinct processes, microbial and thermal. Gases of purely thermal origin are restricted to Miocene reservoirs, exception are the Pliocene reservoirs in Jose Colomo. The mixed biogenic/thermogenic accumulations are pervasive throughout the basin in Pliocene reservoirs. The thermogenic contribution to each reservoir was estimated.

Most gases from the Jose Colomo, Chilapilla and Fortuna Nacional fields are similar in composition, suggesting that, in general, the reservoir system inside each field is in fluid communication. However, some samples are isotopically, and molecular distinct from the others (and one another) suggesting the presence of isolated reservoir compartments, vertically and laterally separated.

Samples from the Hormiguero field are virtually identical, and appear to be mixtures of thermogenic and biogenic gases, produced from individual compartments, indicating the presence of permeability barriers.

The widespread occurrence of commercial gas accumulations in the basin suggests that additional untapped reserves remain to be discovered and exploited. Based on the stratigraphic segregation of the thermal and biogenic gases, it is likely that one would find wet gas in the Miocene reservoirs and dry gas in the Pliocene reservoirs.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana