Geology of Southwest Texas

Oil Recovery Symposium on Southwest Texas, 29–30 October, Corpus Christi, Texas Introduction Since the problems mutually faced by both petroleum geologists and engineers are exploration, development and production of oil and gas, various aspects of the geology of Southwest Texas pertinent to these problems are presented in this paper. Southwest Texas is considered geographically to occupy Railroad Commission Districts 2 and 4 and the southeastern portion of District 1.Structure, stratigraphy and sedimentation are of critical interest to petroleum geologists and petroleum engineers. These will be sketched in broad outline so as to provide a framework and pertinent detail then added. Structure Fig. 1 is an outline map of Southwest Texas on which the following data are noted:Railroad Commission Districts 2 and 4 and part of 1.The paths of four cross sections.The producing trends.The Vicksburg Flexure. To understand the structure and stratigraphy of Southwest Texas a series of cross sections are most helpful. Fig. 2 through 7 are regional cross sections approximately normal to the coast and to the strike. They show coastward dip and coastward thickening of the formations. Fig. 8 is approximately a strike section along the lower coast showing thickening into the Rio Grande Embayment. In a larger context, Southwest Texas is situated on the southwestern flank of a large basin, the central part of which is now occupied by the Gulf of Mexico. The long axis of this basin is near the shore of and parallel with the present Texas coast line. Strikewise along this southwest flank there are alternating areas that have received a preponderance of sediments, having had a relative subsidence to accommodate them and intervening areas of relative stability which have generally thinner sedimentary sections The Rio Grande Embayment, with the present day Rio Grande River being near or shortly to the south of its axis, has received an added thickness of sediments. During times of advance of the sea it was deeper than the adjacent areas, so that rivers brought more sediments into it and deposited them farther inland. During times of recession the area remained relatively low and the rivers continued to flow into and across it, depositing great quantities of sediments.