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ABSTRACT: Hydrocarbon prospectivity in the Sierra Madre Oriental, Mexico: Integrated fluid inclusion and thermochronology results

Gray, Gary G.1, Robert J. Pottorf2, Donald A. Yurewicz3, Keith I. Mahon1, Mark Richardson1, David R. Pevear1, and Maxim O. Vityk1
(1) Exxonmobil Upstream Research Company, Houston, TX 
(2) Exxonmobil Upstream Research Company 
(3) Exxonmobil Exploration Company, Houston, TX

Maximum aqueous fluid inclusion homogenization temperatures and reset apatite fission track ages indicate that a 4-7 km thick foreland basin formed on the leading edge of the Sierra Madre Oriental (SMO) foldbelt during the late stages of the Laramide Orogeny. K/Ar dating of bentonites interbedded with late Cretaceous pelagic carbonates suggests that portions of this region had up to 5 km of overburden by the end of the Laramide at 50-45 Ma. Nearly all traces of this basin have been removed by Neogene erosion.

Estimates of maximum burial depths are derived from homogenization temperatures of aqueous fluid inclusion assemblages. In blind tests this technique generally predicts true maximum burial temperatures within 5-10 °C. In the SMO, maximum temperatures post-date folding, and are greatest along the frontal edge of the foldbelt. Although data are limited, contours of the temperature data suggest that this basin had a classic foreland basin asymmetry, with a steep flank adjacent to the foldbelt on the west, and a gentle flank on the east.

Oil migration occurred into this region prior to maximum burial. These in-migrated oils were thermally degraded to high-gravity liquids, gas, and pyrobitumen by burial beneath the axis of the foreland basin. A later migration of low-maturity oils into the foreland basin section occurred during uplift and erosion at about 20Ma. Away from the axis of this basin, oil gravities measured on the fluid inclusions decrease, as do the maximum temperatures of the associated aqueous inclusions. These relationships suggest that reservoirs and traps beneath the central portion of this foreland basin are now prospective only for gas, while the regions peripheral to the basin may still be prospective for oil. This prospective area may include a considerable portion of the foldbelt to the west.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia