Geochemical evolution of the Eagle Ford Formation and its role as source rocks for gas and oil in Coahuila, NE Mexico

Abstract

To determine the quality of the Eagle Ford Formation, on the Burro-Picachos platform, as a hydrocarbon generating rock and its implication in the context of an unconventional type of deposit (shale gas), they were analyzed with the adaptation of the method Dykstra-Parson for permeability, the average values weighted to the thickness of COT, Tmax, S2 / S3 and PP 1.42 to 6.1) of four wells located in the southeast portion of the border line of the state of Coahuila, in the range of 1410 m 2460 m deep. Thanks to the COT content (1.05 to 2.44%), present in the study area, the Eagle Ford Formation can be classified as a hydrocarbon generator, with a regular to excellent quality. The Tmax data (443 ° C at 484 ° C), locate the generating rock in a phase of early to late thermal maturity, with the exception of the Habano-1 well that reached over maturity. The potential producer (PP) of the area is between weak to medium and the calculation of the type of hydrocarbon generated (S2 / S3) indicates the presence of oil and gas in the formation. This could limit the existence of oil at maximum depths of 1820 m in the northern portion of the studied area, if the hydrogen index (IH) is observed. Oxygen index (IO), its evolution indicates that the predominant is a mixture formed mainly of type III and II which can be interpreted as the precursors of the gas and oil found Of four exploratory wells analyzed, only one presents geochemical characteristics with cutoff values similar to those proposed in shale gas development in the Barnett Basin.