ABSTRACT

The East Texas basin is a prolific mature hydrocarbon province, producing oil and gas from several reservoirs and a variety of trap types. Much 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, a framework was constructed to model the generation of hydrocarbons in the basin. Geochemical data indicate that there are three major source horizons; the Smackover Formation (Jurassic oil), shales in the Pearsal Group (Lower Cretaceous oil), and the Eagleford Shale (Upper Cretaceous oil). The Jurassic source is mature throughout the basin and began to expel oil approximately 88 ma. The distribution of Jurassic oil in Cretaceous reservoirs shows that vertical migration routes predominated. Lower Cretaceous source rocks are only mature in the deep, central portion of the basin where expulsion commenced around 47 ma. Distribution of this oil type suggests that Lower Cretaceous source rocks occur only in localized areas of the East Texas Basin. The Eagleford Shale is immature in the main part of the basin, but it is mature south of the Angelina-Caldwell flexure where it reached peak oil generation approximately 20 ma. Lateral migration explains the distribution of this oil type. Migration routes to the giant East Texas Field may be 60 miles or more.