The Permian Basin is a large sedimentary basin in the southwestern part of the United States. It is the highest-producing oil field in the US, producing an average of 4.2 million barrels of crude oil per day in 2019. This sedimentary basin is located in western Texas and far-southeastern New Mexico.
It is named after the Permian geologic period, the final period of the Paleozoic era, as it contains some of the world's thickest deposits of rocks from the period.
The Permian Basin comprises several component basins, including the Midland Basin, which is the largest; Delaware Basin, the second largest; and Marfa Basin, the smallest. The Permian Basin covers more than , and extends about wide and long.
The Texas cities of Midland, Odessa, and San Angelo serve as headquarters for some of the oil production activities in the basin.
The Permian Basin is also a major source of potassium salts (potash). Potash mines are located in Lea and Eddy counties, New Mexico, and are operated by the room and pillar method. Halite (rock salt) is produced as a byproduct of potash mining.), Leonardian (Avalon Shale), and early Guadalupian times.
Midland Basin
thumb|upright=1.2|Figure 4
<!-- Deleted image removed: thumb|upright=1.3|Figure 5: Midland Basin Stratigraphy -->
The westward-dipping Midland Basin is subdivided into several formations (figure 4) and is composed of laminated siltstone and sandstone. The Midland Basin was filled by a large subaqueous delta that deposited clastic sediment into the basin. Aside from clastic sediment, the Midland Basin also contains carbonate deposits originating from the Guadalupian times when the Hovey Channel allowed access from the sea into the basin. and was the main source of sea water for the Delaware Basin. The closing of the Hovey Channel towards the end of the Permian Period eventually caused the death of the Permian Reef, as without water being brought in through the Channel, salinity levels rose drastically in the Delaware Basin and the reef could not survive.
Horseshoe Atoll
The Horseshoe Atoll is a westward-tilting arcuate chain of reef mounds long located in the Midland Basin, consisting of of limestone accumulated in the Pennsylvanian and in the Permian, with 15 significant petroleum reservoirs from to in depth.
The reef complex consists of Upper Pennsylvanian Strawn, Canyon and Cisco limestones, overlain by Lower Permian Wolfcamp sandstones and shales of terrigenous origin prograding northeast to southwest. The first production well, Seabird Oil Company of Delaware No.1-B J.C. Caldwell, was completed in 1948.
Depositional history
The Permian Basin is the thickest deposit of Permian-aged rocks on Earth; they were rapidly deposited during the collision of North America and Gondwana (South America and Africa) between the late Mississippian through the Permian. The Permian Basin also includes formations that date back to the Ordovician Period, 445 million years ago (mya).
Proterozoic
Before the breakup of the Precambrian supercontinent and the formation of the modern Permian Basin geometry, shallow marine sedimentation onto the ancestral Tobosa Basin characterized the passive margin, shallow marine environment. The Tobosa Basin also contains basement rock that dates back to 1,330 million years ago (mya), and that is still visible in the present-day Guadalupe Mountains. The basement rock contains biotite-quartz granite, discovered at a depth of . and extends into the southern US. It has been dated to 1,163 mya.
Early to mid-Paleozoic (Late Cambrian to Mississippian)
thumb|400px|Permian Basin stratigraphic column
Ordovician Period (485.4–443.8 mya)
Each period from the Paleozoic Era has contributed a specific lithology to the Tobosa Basin, accumulating into almost of sediment at the start of the Pennsylvanian Period (323.2–298.9 mya).
The Morrow Formation
The Early Pennsylvanian Morrow Formation underlies the Atoka Formation. The Morrow is an important reservoir consisting of clastic sediments, sandstones and shales, deposited in a deltaic environment.
Permian Period (298.9–251 mya)
The Permian Period was a time of major reef building to transform the Permian Reef Complex into a major reef system, with Permian-aged rock formations making up 95% of the present-day outcrops in the Permian Basin. When considering any type of reef building that occurred in the Permian, it is important to keep in mind that tectonics played a major part. During this period, the supercontinent of Pangaea, which lasted from 335 to 175 mya, started undergoing breakup. Pangea was clustered together near the equator and surrounded by the superocean Panthalassa, with the Permian Basin located on its western edge within 5–10 degrees of the equator.
Any reef building environment would need a source of water, and the Delaware Basin was located near a marginal sea. Thanks to the Hovey Channel, this sea transported water into the Delaware Basin. Global temperatures during this time were warm, as the world climate was changing from icehouse to greenhouse. This rise in global temperatures also led to the melting of ice masses located towards the South Pole, which then led to a rise in sea levels.
Cisuralian Epoch (298.9–272.3 mya)
thumb|350px|Climatic zones of the Carboniferous–Permian boundary
The Cisuralian Epoch contained two ages, the Wolfcampian and the Leonardian, both of which have a geological formation in the Permian Basin named after them.
The Wolfcampian Formation lies conformably on top of the Pennsylvanian Formation and is the first formation from the Permian Period. Its composition varies depending on its location in the Basin, with the northernmost part being more rich in shale. The thickness of this formation also varies, reaching a maximum of . The Wolfcampian is made up primarily of grey to brown shale and fine-grained, chert-dominated, brown limestone. There are also interbedded layers of fine-grained sandstone found within the formation.
The Bone Spring Limestone consists of several fossils, such as bryozoans, crinoids, and spirifers, but lack algae and sponges that are plentiful in the rest of the Permian Reef Complex. Rocks from the Bone Spring Limestone are predominantly found in the Delaware Basin, but the Victorio Peak Member extends into the shelf margin area.
Guadalupian Epoch (272.3–259.8 mya)
The Guadalupian Epoch was named after the Guadalupe Mountains, since this epoch in the Permian is when reef building was at its most efficient. Lasting from approximately 272–260 mya, this epoch was dominated by the Delaware Mountain Group, which can be further subdivided into rock divisions based on location in the Permian Reef Complex.
The basin water provided plenty of nutrients, since there was continuous upwelling of water that mixed newly brought marine water with anoxic water from the basin floor. The makeup of the reef is described as being built primarily from erect sponges, which have large, rigid skeletons, and abundant red algae, microbial micrite, and inorganic cement. The microbial micrite worked to trap sediment.
One of the most prominent sponges that made up the Capitan Reef was the sponge family Guadalupiidae, a sponge that first appeared on Glass Mountains in the mid-Permian and had spread into the Delaware Basin by the late Permian.
There were more environmental changes to mark the second stage of the formation of the Capitan Reef. This period of growth was marked by eustatic changes in global sea levels, due to frequent glaciations. The reef experienced major growth vertically at this stage and grew at a rapid enough pace to keep up with rising sea levels. The Capitan Reef also found a stable foundation on the reef debris and talus that rested on its slopes, and this foundation allowed the reef to grow outward. In some locations, nutrients and minerals were so abundant that the Capitan Reef grew out almost 50 km from the starting point.
Reef death during the Late Permian
The third stage of the Capitan Reef is the death of the reef system. Ocean currents in the Permian played a huge role in setting up the climate of the region and for aiding in the growth and death of the Capitan Reef. The climate of the basin region was hot and arid, which is shown in the evaporite deposits that can be found in the back reef region.
The end in growth and accumulation of the Permian Reef Complex was influenced by tectonics. During the end of the Permian Period, the supercontinent of Pangaea was beginning its break up, which drastically changed the conditions that were previously favourable for reef growth. Change in tectonics limited the exchange of sea water in the Hovey Channel, which then led to a salinity increase in the Permian Basin. The reef could not survive this drastic change in water salinity, and was therefore destroyed. The growing temperatures in the late Permian combined with the increase in salinity caused the extinction of the Capitan Reef, as well as the formation of evaporites with the basin.
The layers of evaporites that formed as a result of increased salinity is called the Castile Formation. This formation consists of alternating layers of gypsum/anhydrite and limestone, as well as massive beds of gypsum/anhydrite, salt, and some limestone. The unit measures almost in total and was formed during the Lopingian Epoch. The individual layers (laminae) of gypsum/anhydrite are between and in thickness, which is thought to correlate with the basin salinity on a year-by-year basis.
The Capitan Reef had been altered diagenetically early on in its history, especially after the deposition of the Castile Formation. There is evidence of fabric alteration throughout this formation, which is thought to indicate the dehydration and rehydration process of the gypsum and anhydrites. There is also evidence of evaporite calcitization. The reef system was buried until it was exposed in the Mesozoic era as a result of tectonic activity by the Laramide orogeny.
Tectonic history
During the Cambrian–Mississippian, the ancestral Permian Basin was the broad marine passive margin Tobosa Basin containing deposits of carbonates and clastics. In the early Pennsylvanian–early Permian the collision of North American and Gondwana Land (South America and Africa) caused the Hercynian orogeny. The Hercynian orogeny resulted in the Tobosa basin being differentiated into two deep basins (the Delaware and the Midland Basins) surrounded by shallow shelves. During the Permian, the basin became structurally stable and filled with clastics in the basin and carbonates on the shelves.
Lower Paleozoic passive margin phase (late Precambrian–Mississippian, 850–310 mya)
This passive margin succession is present throughout the southwestern US and is up to thick. The ancestral Permian basin is characterized by weak crustal extension and low subsidence in which the Tobosa basin developed. The Tobosa basin contained shelf carbonates and shales.
Collision phase (late Mississippian–Pennsylvanian, 310–265 mya)
The two lobed geometry of the Permian basin separated by a platform was the result of the Hercynian collisional orogeny during the collision of North America and Gondwana Land (South America and Africa). This collision uplifted the Ouachita-Marathon fold belt and deformed the Tobosa Basin. The Delaware Basin resulted from tilting along areas of Proterozoic weakness in Tobosa basin. Southwestern compression reactivated steeply dipping thrust faults and uplifted the Central Basin ridge. Folding of the basement terrane split the basin into the Delaware basin to the west and the Midland Basin to the east.
Permian Basin phase (Permian, 265–230 mya)
Rapid sedimentation of clastics, carbonate platforms and shelves, and evaporites proceeded synorogenically. Bursts of orogenic activity are divided by three angular unconformities in basin strata. Evaporite deposits in the small remnant basin mark the final stage of sedimentation as the basin became restricted from the sea during sea level fall.
Hydrocarbon production and reserves
thumb|upright=1.3|Figure 9: Significant [[hydrocarbon plays within the Permian Basin]]
The Permian Basin is the largest petroleum-producing basin in the United States and has produced a cumulative 28.9billion barrels of oil and 75trillion cubic feet of gas. In early 2020, over 4 million barrels of oil a day were being pumped from the basin. Eighty percent of estimated reserves are located at less than depth. Ten percent of the oil recovered from the Permian Basin has come from Pennsylvanian carbonates.
History of resources
thumb|300px|Santa Rita No. 1 rig, used in the discovery of the Big Lake Oil Field in 1923
In 1917, J.A. Udden, a University of Texas geology professor, speculated that the Marathon Fold, associated with the Marathon Mountains, may extend northward. This fold theory was further elaborated on in 1918 by geologists R.A. Liddle and J.W. Beede. The potential structure was thought to be a potential trap for oil. Based on this Marathon Fold theory, and known oil seeps, test drilling commenced in the eastern Permian Basin.
Oil reserves in the Permian Basin were first documented by W.H. Abrams in Mitchell County, West Texas in 1920. The first commercial well was opened in 1921, in the newly discovered Westbrook Oil Field in Mitchell County, at a depth of . Initially, the Permian Basin was thought to have a bowl-like shape, with geological survey crews unable to study the inside of the basin due to a lack of outcrops.
By 1924, companies establishing regional geological offices in the basin included the California Company (Standard Oil of California), Gulf Oil, Humble (Standard Oil of New Jersey), Roxana (Shell Oil Company), Dixie Oil (Standard Oil of Indiana), Midwest Exploration (Standard Oil of Indiana), and The Texas Company.
Current production
, the Permian Basin has produced more than 33 billion barrels of oil, along with 118 trillion cubic feet of natural gas. This production accounts for 20% of US crude oil production and 7% of US dry natural gas production. While the production was thought to have peaked in the early 1970s, new technologies for oil extraction, such as hydraulic fracturing and horizontal drilling, have increased production dramatically. Estimates from the Energy Information Administration have predicted that proven reserves in the Permian Basin still hold 5 billion barrels of oil and approximately 19 trillion cubic feet of natural gas.
Environmental concerns
By October 2019, the fossil-fuel executives said that until recently they had been making progress in cutting back on flaring, which is to burn natural gas. Drilling companies focus on drilling and pumping oil, which is highly lucrative, but the less-valuable gas which is pumped along with the oil is considered to be a "byproduct". Satellite data show that 3.7% of gas produced from the Permian Basin is lost in leaks, equivalent to the consumption of 7 million Texas homes. The price of natural gas was so cheap that smaller companies that have the pipeline capacity are choosing to flare rather than pay pipeline costs.