Hydrocarbon Generation and Migration Routes in the East Texas Basin

Abstract

The East Texas basin is a prolific, mature hydrocarbon province, producing oil and gas from several reservoirs and a variety of trap types. Many of the liquid hydrocarbons discovered in the basin are trapped in structures related to movement of the underlying Louann Salt. By determining the structural evolution of the basin, we constructed a framework to model the generation of hydrocarbons in the basin. Geochemical data indicate three major oil types: Jurassic oil, Lower Cretaceous oil, and Upper Cretaceous oil. The Jurassic source is mature throughout the basin and began to expel oil at approximately 88 Ma. The distribution of Jurassic oil in Cretaceous reservoirs shows that vertical migration routes predominated. Prospective Lower Cretaceous source rocks are only matur in the deep, central portion of the basin where expulsion began about 47 Ma. Distribution of this oil type suggests that Lower Cretaceous source rocks occur only in localized areas of the East Texas basin. Organic-rich Upper Cretaceous shales are immature in the main part of the basin, but are mature south of the Angelina-Caldwell flexure, where they reached peak generation at approximately 20 Ma. Long-distance, lateral migration routes are necessary to explain the distribution of this oil type. Migration routes to the giant East Texas field may be 100 km or more. Modeling of this basin suggests an exploration approach, in mature basins, of defining migration pathways and seeking traps astride them. Traps in this position have a better probability of being filled; and, all else being equal, are likely to be better fields than traps located away from the major migration routes.