Regional Geology of the Delaware Basin

Abstract

Abstract The Delaware basin of West Texas has a long, complex history and the events that occurred during this great period of time are related to the present economic conditions of West Texas. Geological history in the area presently occupied by the Permian Basin began with gentle tectonic movements and shallow seas during Cambrian and Lower Ordovician time and reached a peak of activity during late Pennsylvanian and early Wolfcampian time. Following this period of pronounced activity, the area became relatively quiet; reefing, along with associated back- and fore-reef deposits, came into prominence. In the Delaware basin vicinity, oil acid gas accumulation has been influenced by the environment of deposition of the rocks comprising the geological column and by tectonic movements that have modified sedimentary framework. Faulting and folding are the principal mechanisms for trapping hydrocarbons in the deeper fields of the basin. Shallow accumulations are often controlled by stratigraphic traps. In addition to a trap, a source of hydrocarbons and presence of rock porosity are necessary for the existence of a reservoir. Gas reservoirs in the Devonian and Ellenburger of the Delaware basin are found primarily in fracture porosity while the Wolfcampian and Pennsylvanian conglomerate reservoirs and middle Permian sand accumulations are characterized by intergranular porosity. The true source of hydrocarbons found in these fields is unknown. Possible sources include origin within the reservoir rock and migration from adjacent shale sections. Introduction The Delaware basin of West Texas and southeast New Mexico covers an area about 200 miles long and 100 miles wide. It is a prime example of a large sedimentary basin in which vast amounts Of rock have been deposited. As sedimentary basins in general are important to the petroleum industry of the world, so is the Delaware basin important to the industry of the West Texas-New Mexico area. This prominent geological feature can be expected to attain even greater importance in the future as the quest for oil and gas continues. The growing importance of this significant area is emphasized frequently, especially when the industry notes the ever-increasing number of deep tests announced for the basin and vicinity. The index map of regional structure (Fig. 1) shows the major features that make up the Permian Basin of the southwest United States. The Midland basin on the east and the Delaware basin on the west are separated by the Central basin platform. Both of these basins were areas of deep water during most of Permian time; because of this, they were filled with shales and sandstones deposited in a marine environment. The Central basin platform is an area of Permian reefing that grew over an older structural feature - the West Texas structural platform. South of the Central basin platform is an elongated east-west sedimentary feature called the Sheffield Channel. JPT P. 1260ˆ