PERMIAN BASIN. The Permian Basin is located in West Texas and the adjoining area of southeastern New Mexico. It underlies an area approximately 250 miles wide and 300 miles long and includes the Texas counties of Andrews, Borden, Crane, Dawson, Ector, Gaines, Glasscock, Howard, Loving, Martin, Midland, Pecos, Reeves, Terrell, Upton, Ward, and Winkler. The name derives from the fact that the area was downwarped before being covered by the Permian sea and the subsidence continued through much of the Permian period; consequently, it contains one of the thickest deposits of Permian rocks found anywhere. Although it is structurally a basin in the subsurface, much of the basin lies under the Llano Estacado^qv and the northwestern portion of the Edwards Plateau,^qv which are topographically high. On the west and south it extends across the Pecos River valley to mountain ranges in both New Mexico and West Texas.

The presence of rocks of Permian age was first reported by George G. and Benjamin F. Shumard^qv in 1858 after a study of outcrops in the Guadalupe Mountains. Later work in West Texas by Johan August Udden^qv and his associates in the Bureau of Economic Geology at the University of Texas contributed to knowledge of the age, structure, and stratigraphy of sediments found in outcrops around its Texas margin. When the Permian sea retreated southward, it left the Permian Basin area with a restricted outlet. This resulted in an inland sea where evaporation greatly exceeded fluid intake, and a great thickness of "evaporite" sediments was deposited; one of these was potash, a critical commodity during World War I,^qv until then a product obtained from Germany. Udden's early investigations led the United States Geological Survey^qv to concentrate much of its early effort in the search for potash in this area. The first commercial deposit was found in New Mexico in 1925. Up to 1967 all seven of the potash companies operating in the Permian Basin, representing an investment of some $200 million, were located in New Mexico. Texas deposits have not been developed because of the more expensive processes involved.

Much of the Permian Basin was home to the Comanche Indians until they were finally forced out by the United States Army in 1875. Because of good grasslands, most of the area was inviting to both ranchers and farmers. Since surface water was almost nonexistent, ranchers and farmers drilled water wells to sustain themselves and their livestock, and they often found evidence of oil or gas. The first commercial oil well in the Permian Basin was completed in 1921 in Mitchell County, on the east side of the basin; completed at a total depth of 2,498 feet, it was the discovery well of the Westbrook field. Early oil prospecting was started in southeastern New Mexico about the same time as in West Texas. By 1923 it was presumed that the Permian Basin was in the form of an elliptical bowl, the subsurface strata dipping from the rim to a maximum depth in the middle. Because of this and the lack of suitable rock outcrops in the interior during the early search for oil, geological survey crews looked for surface anticlines in the Edwards Plateau and the rock outcrop areas west and south of the Pecos River. This method resulted in the discovery of several good oilfields, notably the World field in Crockett County, the McCamey field in Upton and Crane counties (1925), and the Yates oilfield^qv in Pecos County (1926). Prior to the Hobbs field discovery in 1928, all discoveries were made as a result of random drilling or surface and subsurface mapping. The Hobbs field discovery was made after magnetometer and torsion balance surveys both showed the area to be anomalous. From that time on geophysics, particularly the seismograph, was used as an exploratory tool. By 1929 a sufficient number of oil tests had been drilled to give sketchy control for a subsurface map of the Permian Basin. Its outline was fairly well defined, and oil discoveries within the basin suggested the probability of interior folds. In 1930 Lon D. Cartwright published a report with a cross section and map, showing a large positive area located in the approximate middle of the basin, which he named the Central Basin Platform. The map showed the platform trending north­northwest across the Texas-New Mexico line into Lea County. By this time a sufficient number of wells had been drilled to show that the Central Basin Platform was a structural feature common to both states.

Because of the great distances to the markets and the lack of pipelines through which to move the oil, deep tests were not economically justified. Consequently, all oilfields discovered before 1928 were producing from Permian dolomite or sand, from depths less than 4,500 feet. A deep test was started in the Big Lake oil field^qv in Reagan County, and in 1928 a large flow of oil and gas was encountered at 8,525 feet. Fossil evidence showed the producing section to be of Ordovician age. This discovery greatly expanded the prospects for the Permian Basin's becoming a major oil and gas producing area; however, because of the Great Depression^qv in the early 1930s few locations for deep tests were made prior to 1936. With the coming of World War II^qv the need for oil was urgent, and it became economically justified to drill more and deeper tests. During the war many new oil and gas zones were found not only in rocks of Permian and Ordovician age but also from zones in each geologic system from Permian through Cambrian and from practically every known type of subsurface trap. Two of the largest accumulations were the Horseshoe Atoll and the Spraberry trend area. Horseshoe Atoll is a subsurface accumulation of fossiliferous limestone, as much as 3,000 feet thick, deposited during Pennsylvanian and early Permian time in the northern part of the Midland basin in West Texas. It is a horseshoe­shaped mass about ninety miles across and seventy miles from north to south. The crest of the atoll is a series of irregular hills and depressions. Oil migrated to many of these buried hills and was trapped in the porous rock, resulting in a line of oilfields nearly 200 miles in length. The Spraberry trend area is located in the region between the south end of the Llano Estacado and the north part of the Edwards Plateau (see SPRABERRY-DEAN SANDSTONE FIELDS). The producing structure here is basically a fractured permeability trap on a homoclinal fold about 150 miles in length. Oil production is practically continuous along its entire length; its maximum width is thirty­five miles.

The entire Permian Basin during 1966 produced a total of 607 million barrels of oil and 2.3 trillion cubic feet of gas for a total of $2 billion. A cumulative total of 11.3 billion barrels of oil had been produced. Intrastate and interstate gas pipeline systems were expanded throughout the area, and Midland­Odessa was the headquarters for the oil and gas industry^qv in the Permian Basin area. Hundreds of millions of dollars have been spent on petrochemical refineries and supplemental construction work in the Permian Basin, which was rated the largest inland petrochemical complex in the United States. Some of the more commonly known Permian Basin petrochemical products were synthetic rubber, plastics, emulsion paints, solvents, food wrappers, nylon, ammonia, nitric acid, hydrogen, and fertilizer. In 1992 the Texas counties of the Permian basin produced over 217 million barrels of oil. Total production for that region up to the beginning of 1993 was over 14.9 billion barrels. See also PETROCHEMICAL INDUSTRY.

BIBLIOGRAPHY: Lon D. Cartwright, Jr., "Transverse Section of Permian Basin, West Texas and Southeast New Mexico," Bulletin of the American Association of Petroleum Geologists 14 (1930). J. E. Flis and R. C. Price, eds., Permian Basin Oil and Gas Fields: Innovative Ideas in Exploration and Development (West Texas Geological Society Symposium, November 1-2, 1990). Frank A. Herald, Occurrence of Oil and Gas in West Texas (Austin: University of Texas Bureau of Economic Geology, 1957). Samuel D. Myres, The Permian Basin: Petroleum Empire of the Southwest (2 vols., El Paso: Permian, 1973, 1977). Johan August Udden, Review of the Geology of Texas (University of Texas Bulletin 44, Austin, 1916).

Charles D. Vertrees