The Brown Dense limestone is an informal name used by petroleum geologists for a layer of rock that lies beneath large parts of southern Arkansas and northwest Louisiana. The Brown Dense is a 300- to 500-foot thick interval within organic-rich, fine-grained carbonate rock that comprise the Lower Member of the Smackover Formation. [1] [2] Within this area, the Lower Smackover Member lies at depths of 8,000 to 10,000 feet beneath the land surface. [3] [4]
The term “Brown Dense” possibly came from a description of the Lower Member of the Smackover Formation by W. B. Weeks. [5] He described it as “gray to brown, dense, cryptocrystalline limestone.” This description incorrectly implied a nonporous, non-permeable unit that lacks any potential for oil and gas production, which has discouraged until recently the exploration for oil and gas in this unit. [6]
The Lower Member of the Smackover Formation, of which the Brown Dense is a part, consists of organic-rich limestone, which in places contains as much as 50 feet of sandstone and 100 feet of dolomite with excellent porosity and permeability beneath parts of southern Arkansas and northern Louisiana. Typically, the Lower Member of the Smackover consists of limestone composed of a sequence, from bottom to top, of laminated mudstone, thin-bedded mudstone, burrowed mudstone, and wackestone. The Brown Dense consists of the thin-bedded and burrowed mudstone. [6] [7] These mudstones were a prolific source of oil and gas for a significant amount of the oil and gas found in reservoirs in this part of the Gulf of Mexico. [7] [8]
The Brown Dense accumulated on the bottom of a prehistoric stratified Gulf of Mexico. The upper part of the water column was well-oxygenated and subject to frequent algal blooms. Underlying these oxygenated waters and separated by a pycnocline, were anoxic and hypersaline bottom waters, which preserved organic matter as it accumulated. The organic matter consisted of algal material that fell downward from the overlying oxygenated waters. [7] [9]
As part of the Smackover Formation, the Brown Dense is Oxfordian in age, 161 to 156 million years ago. [10]
Estimates for the total amount of reserves of oil and natural gas in the Brown Dense (limestone) are unavailable. However, various organizations, i.e. the Louisiana Natural Resources Department and Louisiana Oil and Gas Association, argue that it is a very promising new source of significant economic reserves of oil and natural gas. Petroleum companies, i.e. the Oklahoma City-based Devon Energy and Southwestern Energy have leased land in both Arkansas and Louisiana for drilling for oil and natural gas within the Brown Dense. [2] [11]
Haynesville is a town in northern Claiborne Parish, Louisiana, United States, located just south of the Arkansas border. The population was 2,327 at the 2010 census.
Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation, transport, deposition and diagenesis. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures.
Hydrocarbon exploration is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology.
Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than 1⁄16 mm and are too small to study readily in the field. At first sight, the rock types appear quite similar; however, there are important differences in composition and nomenclature.
A petroleum geologist is an earth scientist who works in the field of petroleum geology, which involves all aspects of oil discovery and production. Petroleum geologists are usually linked to the actual discovery of oil and the identification of possible oil deposits, gas caps, or leads. It can be a very labor-intensive task involving several different fields of science and elaborate equipment. Petroleum geologists look at the structural and sedimentary aspects of the stratum/strata to identify possible oil traps or tight shale plays.
The Bend Arch–Fort Worth Basin Province is a major petroleum producing geological system which is primarily located in North Central Texas and southwestern Oklahoma. It is officially designated by the United States Geological Survey (USGS) as Province 045 and classified as the Barnett-Paleozoic Total Petroleum System (TPS).
In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including deep water marine, lacustrine and deltaic. Oil shale can be regarded as an organic-rich but immature source rock from which little or no oil has been generated and expelled. Subsurface source rock mapping methodologies make it possible to identify likely zones of petroleum occurrence in sedimentary basins as well as shale gas plays.
The Haynesville Shale is an informal, popular name for a Jurassic Period rock formation that underlies large parts of southwestern Arkansas, northwest Louisiana, and East Texas. It lies at depths of 10,500 to 13,000 feet below the land’s surface. It is part of a large rock formation which is known by geologists as the Haynesville Formation. The Haynesville Shale underlies an area of about 9,000 square miles and averages about 200 to 300 feet thick. The Haynesville Shale is overlain by sandstone of the Cotton Valley Group and underlain by limestone of the Smackover Formation.
Shale gas in the United States is an available source of unconventional natural gas. Led by new applications of hydraulic fracturing technology and horizontal drilling, development of new sources of shale gas has offset declines in production from conventional gas reservoirs, and has led to major increases in reserves of U.S. natural gas. Largely due to shale gas discoveries, estimated reserves of natural gas in the United States in 2008 were 35% higher than in 2006.
The Duvernay Formation is a stratigraphical unit of Frasnian age in the Western Canadian Sedimentary Basin.
Safaniya Oil Field, operated and owned by Saudi Aramco, is the largest offshore oil field in the world. It is located about 265 kilometres (165 mi) north of the company headquarters in Dhahran on the coast of the Persian Gulf, Saudi Arabia. Measuring 50 by 15 kilometres, the field has a producing capability of more than 1.2 million barrels per day.
The Smackover Formation is a geologic formation in Arkansas. It preserves fossils dating back to the Jurassic period.
The Eagle Ford Group is a sedimentary rock formation deposited during the Cenomanian and Turonian ages of the Late Cretaceous over much of the modern-day state of Texas. The Eagle Ford is predominantly composed of organic matter-rich fossiliferous marine shales and marls with interbedded thin limestones. It derives its name from outcrops on the banks of the West Fork of the Trinity River near the old community of Eagle Ford, which is now a neighborhood within the city of Dallas. The Eagle Ford outcrop belt trends from the Oklahoma-Texas border southward to San Antonio, westward to the Rio Grande, Big Bend National Park, and the Quitman Mountains of West Texas. It also occurs in the subsurface of East Texas and South Texas, where it is the source rock for oil found in the Woodbine, Austin Chalk, and the Buda Limestone, and is produced unconventionally in South Texas and the "Eaglebine" play of East Texas. The Eagle Ford was one of the most actively drilled targets for unconventional oil and gas in the United States in 2010, but its output had dropped sharply by 2015. By the summer of 2016, Eagle Ford spending had dropped by two-thirds from $30 billion in 2014 to $10 billion, according to an analysis from the research firm Wood Mackenzie. This strike has been the hardest hit of any oil fields in the world. The spending was, however, expected to increase to $11.6 billion in 2017. A full recovery is not expected any time soon.
The Albert Formation is a stratigraphic unit of Early Mississippian (Tournaisian) age in the Moncton Subbasin of southeastern New Brunswick. It was deposited in a lacustrine environment and includes fossils of fish and land plants, as well as trace fossils. It also includes significant deposits of oil shale. The oil shale beds are the source rocks for the petroleum and natural gas that has been produced from Albert Formation reservoirs at the Stoney Creek and McCully fields. In addition, the solid asphalt-like hydrocarbon albertite was mined from the Albert Formation at Albert Mines between 1854 and 1884.
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The geology of Alaska includes Precambrian igneous and metamorphic rocks formed in offshore terranes and added to the western margin of North America from the Paleozoic through modern times. The region was submerged for much of the Paleozoic and Mesozoic and formed extensive oil and gas reserves due to tectonic activity in the Arctic Ocean. Alaska was largely ice free during the Pleistocene, allowing humans to migrate into the Americas.