Source rock

In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form 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.[1] Subsurface source rock mapping methodologies make it possible to identify likely zones of petroleum occurrence in sedimentary basins as well as shale gas plays.

Types of source rocks

Source rocks are classified from the types of kerogen that they contain, which in turn governs the type of hydrocarbons that will be generated.

  • Type I source rocks are formed from algal remains deposited under anoxic conditions in deep lakes: they tend to generate waxy crude oils when submitted to thermal stress during deep burial.
  • Type II source rocks are formed from marine planktonic and bacterial remains preserved under anoxic conditions in marine environments: they produce both oil and gas when thermally cracked during deep burial.
  • Type III source rocks are formed from terrestrial plant material that has been decomposed by bacteria and fungi under oxic or sub-oxic conditions: they tend to generate mostly gas with associated light oils when thermally cracked during deep burial. Most coals and coaly shales are generally Type III source rocks.

Maturation and expulsion

With increasing burial by later sediments and increase in temperature, the kerogen within the rock begins to break down. This thermal degradation or cracking releases shorter chain hydrocarbons from the original large and complex molecules occurring in the kerogen.

The hydrocarbons generated from thermally mature source rock are first expelled, along with other pore fluids, due to the effects of internal source rock over-pressuring caused by hydrocarbon generation as well as by compaction. Once released into porous and permeable carrier beds or into faults planes, oil and gas then move upwards towards the surface in an overall buoyancy-driven process known as secondary migration.

Mapping source rocks in sedimentary basins

Areas underlain by thermally mature generative source rocks in a sedimentary basin are called generative basins or depressions or else hydrocarbon kitchens. Mapping those regional oil and gas generative "hydrocarbon kitchens" is feasible by integrating the existing source rock data into seismic depth maps that structurally follow the source horizon(s). It has been statistically observed at a world scale [2] that zones of high success ratios in finding oil and gas generally correlate in most basin types (such as intracratonic or rift basins) with the mapped "generative depressions". Cases of long distance oil migration into shallow traps away from the "generative depressions" are usually found in foreland basins.

Besides pointing to zones of high petroleum potential within a sedimentary basin, subsurface mapping of a source rock's degree of thermal maturity is also the basic tool to identify and broadly delineate shale gas plays.

World class source rocks

Certain source rocks are referred to as "world class", meaning that they are not only of very high quality but are also thick and of wide geographical distribution. Examples include:

See also


  1. ^ Hyne N.J. (2001). Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production. PennWell Books. p. 164. ISBN 9780878148233.
  2. ^ Gerard Demaison: "The Generative Basin Concept" in: American Association of Petroleum Geologists (AAPG) Memoir #35 : "Petroleum Geochemistry and Basin Evaluation", 1984 , Edited by Gerard Demaison and Roelof J. Murris, ISBN 0-89181-312-8
  3. ^ Kimmeridgian Shales Total Petroleum System of the North Sea Graben Province – USGS Bulletin
  4. ^ James, K.H. 2000. The Venezuelan hydrocarbon habitat, Part 2: hydrocarbon occurrences and generated-accumulated volumes. Journal of Petroleum Geology, 23, 133–164
  5. ^ Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary – USGS Bulletin
  6. ^ Total Petroleum Systems of the Paleozoic and Jurassic, Greater Ghawar Uplift and Adjoining Provinces of Central Saudi Arabia and Northern Arabian-Persian Gulf – USGS Bulletin

External links

Biomarker (petroleum)

Biomarkers are any of a suite of complex organic compounds composed of carbon, hydrogen and other elements such as oxygen, nitrogen and sulfur, which are found in crude oils, bitumens, petroleum source rock and eventually show simplification in molecular structure from the parent organic molecules found in all living organisms. Essentially, they are complex carbon-based molecules derived from formerly living organisms. Biomarker compounds are typically analyzed using gas chromatography and mass spectrometry. Some examples of biomarkers found in petroleum are pristane, phytane, steranes, triterpanes and porphyrin. Geologists and Geochemists use biomarkers traces found in crude oils and their related source rock to unravel the stratigraphic origin and migration pathways of presently existing petroleum deposits.However, Biomarker analysis of untreated rock cuttings can be expected to produce misleading results. This is due to potential hydrocarbon contamination and biodegradation in the rock samples.

Cerrejón Formation

The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón sub-basin of the Cesar-Ranchería Basin of La Guajira and Cesar. The formation consists of bituminous coal fields that are an important economic resource. Coal from the Cerrejón Formation is mined extensively from the Cerrejón open-pit coal mine, one of the largest in the world. The formation also bears fossils that are the earliest record of Neotropical rainforests.

Chipaque Formation

The Chipaque Formation (Spanish: Formación Chipaque, K2cp, Kc) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The predominantly organic shale formation dates to the Late Cretaceous period; Cenomanian-Turonian epochs and has a maximum thickness of 1,700 metres (5,600 ft). The formation, rich in TOC, is an important oil and gas generating unit for the giant oilfields Cupiagua and Cusiana of the Eastern Ranges as well as in the Llanos Orientales.

Fruitland Formation

The Fruitland Formation is a sedimentary geological formation containing layers of sandstone, shale, and coal. It was laid down in marshy delta conditions, with poor drainage and frequent flooding, under a warm, humid and seasonal climate. It is found in the San Juan Basin in the states of New Mexico and Colorado, in the United States of America. The Fruitland Formation contains beds of bituminous coal that are mined in places along the outcrop. Since the 1980s, the coal beds of the Fruitland Formation have yielded large quantities of coalbed methane. The productive area for coalbed methane straddles the Colorado-New Mexico state line, and is one of the most productive areas for coalbed methane in the United States.

Fómeque Formation

The Fómeque Formation (Spanish: Formación Fómeque, Kif) is a geological formation of the Altiplano Cundiboyacense, Eastern Ranges of the Colombian Andes. The predominantly organic shale formation dates to the Early Cretaceous period; Barremian to Late Aptian epochs and has a maximum thickness of 1,200 metres (3,900 ft).

Horseshoe Canyon Formation

The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller.

The Horseshoe Canyon Formation is part of the Edmonton Group and is up to 230 metres (750 ft) thick. It is of Late Cretaceous age, Campanian to early Maastrichtian stage (Edmontonian Land-Mammal Age), and is composed of mudstone, sandstone, carbonaceous shales, and coal seams. A variety of depositional environments are represented in the succession, including floodplains, estuarine channels, and coal swamps, which have yielded a diversity of fossil material. Tidally-influenced estuarine point bar deposits are easily recognizable as Inclined Heterolithic Stratification (IHS). Brackish-water trace fossil assemblages occur within these bar deposits and demonstrate periodic incursion of marine waters into the estuaries.

The Horseshoe Canyon Formation crops out extensively in the area around Drumheller, as well as farther north along the Red Deer River near Trochu and along the North Saskatchewan River in Edmonton. It is overlain by the Battle, Whitemud, and Scollard formations. The Drumheller Coal Zone, located in the lower part of the Horseshoe Canyon Formation, was mined for sub-bituminous coal in the Drumheller area from 1911 to 1979, and the Atlas Coal Mine in Drumheller has been preserved as a National Historic Site. In more recent times, the Horseshoe Canyon Formation has become a major target for coalbed methane (CBM) production.

Dinosaurs found in the Horseshoe Canyon Formation include Albertavenator, Albertosaurus, Anchiceratops, Anodontosaurus, Arrhinoceratops, Atrociraptor, Epichirostenotes, Edmontonia, Edmontosaurus, Hypacrosaurus, Ornithomimus, Pachyrhinosaurus, Parksosaurus, Saurolophus, and Struthiomimus. Other finds have included mammals such as Didelphodon coyi, non-dinosaur reptiles, amphibians, fish, marine and terrestrial invertebrates and plant fossils. Reptiles such as turtles and crocodilians are rare in the Horseshoe Canyon Formation, and this was thought to reflect the relatively cool climate which prevailed at the time. A study by Quinney et al. (2013) however, showed that the decline in turtle diversity, which was previously attributed to climate, coincided instead with changes in soil drainage conditions, and was limited by aridity, landscape instability, and migratory barriers.

Hydrocarbon exploration

Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology.

Kimmeridge Clay

The Kimmeridge Clay is a sedimentary deposit of fossiliferous marine clay which is of Late Jurassic to lowermost Cretaceous age and occurs in southern and eastern England and in the North Sea. This rock formation is the major source rock for North Sea oil. The fossil fauna of the Kimmeridge Clay includes turtles, crocodiles, sauropods, plesiosaurs, pliosaurs and ichthyosaurs, as well as a number of invertebrate species.

Macanal Formation

The Macanal Formation or Macanal Shale (Spanish: (Formación) Lutitas de Macanal, Kilm, K1m) is a fossiliferous geological formation of the Altiplano Cundiboyacense and Tenza Valley in the Eastern Ranges of the Colombian Andes. The predominantly organic shale formation dates to the Early Cretaceous period; Berriasian to Valanginian epochs and has a maximum thickness of 2,935 metres (9,629 ft). The Macanal Formation contains numerous levels of fossiliferous abundances. Bivalves, ammonites and fossil flora have been found in the formation.

The formation is a source rock for oil and gas in the Eastern Cordillera Basin and adjacent Llanos Basin foothills and provides emeralds in the vicinity of Macanal, after which the formation is named.


Maturity may refer to:

Adulthood or age of majority

Maturity model

Capability Maturity Model, in software engineering, a model representing the degree of formality and optimization of processes in an organization

Developmental age, the age of an embryo as measured from the point of fertilization

Mature technology, a technology has been in use and development for long enough that most of its initial problems have been overcome

Maturity (finance), indicating the final date for payment of principal and interest

Maturity (geology), rock, source rock, and hydrocarbon generation

Maturity (psychological), responding to the circumstances or environment in an appropriate manner

Maturity (sedimentology), the proximity of a sedimentary deposit from its source

Sexual maturity, the stage when an organism can reproduce, though this is distinct from adulthood

Monterey Formation

The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands. The type locality is near the city of Monterey, California.

The Monterey Formation is the major source-rock for 37 to 38 billion barrels of oil in conventional traps such as sandstones. This is most of California's known oil resources. The Monterey has been extensively investigated and mapped for petroleum potential, and is of major importance for understanding the complex geological history of California. Its rocks are mostly highly siliceous strata that vary greatly in composition, stratigraphy, and tectono-stratigraphic history.

The US Energy Information Administration (EIA) estimated in 2014 that the 1,750 square mile Monterey Formation could yield about 600 million barrels of oil, from tight oil contained in the formation, down sharply from their 2011 estimate of a potential 15.4 billion barrels. An independent review by the California Council on Science and Technology found both of these estimates to be "highly uncertain." Despite intense industry efforts, there has been little success to date (2013) in producing Monterey-hosted tight oil/shale oil, except in places where it is already naturally fractured, and it may be many years, if ever, before the Monterey becomes a significant producer of shale oil.The Monterey Formation strata vary. Its lower Miocene members show indications of weak coastal upwelling, with fossil assemblages and calcareous-siliceous rocks formed from diatoms and coccolithophorids. Its middle and upper Miocene upwelling-rich assemblages, and its unique highly siliceous rocks from diatom-rich plankton, became diatomites, porcelainites, and banded cherts.

Paja Formation

The Paja Formation (Spanish: Formación Paja, K1p, Kip, Kimp, b3b6p) is an Early Cretaceous geologic formation of central Colombia. The formation extends across the northern part of the Altiplano Cundiboyacense, the Western Colombian emerald belt and surrounding areas of the Eastern Ranges of the Colombian Andes. In the subsurface, the formation is found in the Middle Magdalena Valley to the west. The Paja Formation stretches across four departments, from north to south the southernmost Bolívar Department, in Santander, Boyacá and the northern part of Cundinamarca. Well known fossiliferous outcrops of the formation occur near Villa de Leyva, also written as Villa de Leiva, and neighboring Sáchica.

The formation was named after Quebrada La Paja in Betulia, Santander, and stretches across 450 kilometres (280 mi) from northeast to southwest. The Paja Formation overlies the Ritoque and Rosablanca Formations and is overlain by the San Gil Group and the Simití and Tablazo Formations and dates from the late Hauterivian to late Aptian. The Paja Formation comprises mudstones, shales and nodules of sandstones and limestones, deposited in an anoxic environment, in the warm and shallow sea that covered large parts of the present Colombian territory during the Cretaceous.

Initially considered to host Colombian emeralds, the emerald-bearing part was redefined as a separate formation; the Muzo Formation. The Paja Formation Lagerstätte is famous for its vertebrate fossils and is the richest Mesozoic fossiliferous formation of Colombia. Several marine reptile fossils of plesiosaurs, pliosaurs, ichthyosauras and turtles have been described from the formation and it hosts the only dinosaur fossils described in the country to date; Padillasaurus. The formation also has provided many ammonites, fossil flora, decapods and the fossil shark Protolamna ricaurtei.

Petroleum geologist

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 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.

Petroleum geology

Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration).

Placer deposit

In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, and paleoplacers.

Placer materials must be both dense and resistant to weathering processes. To accumulate in placers, mineral particles must be significantly denser than quartz (whose specific gravity is 2.65), as quartz is usually the largest component of sand or gravel. Placer environments typically contain black sand, a conspicuous shiny black mixture of iron oxides, mostly magnetite with variable amounts of ilmenite and hematite. Valuable mineral components often occurring with black sands are monazite, rutile, zircon, chromite, wolframite, and cassiterite.

Posidonia Shale

The Posidonia Shale is an Early Jurassic geological formation of south-western Germany, including exceptionally well-preserved complete skeletons of fossil marine fish and reptiles. The Posidonienschiefer, as German paleontologists call it, takes its name from the ubiquitous fossils of Posidonia bronni that characterize its fauna. The formation comprises finely laminated layers of oil shales formed of fine-grained sediments intercalated with bituminous limestones and crops out in a number of locations in southwestern Germany, although most remains are from near the village of Holzmaden. The European oil shales deposited on a sea floor during the Early Toarcian in the ancient Tethys Ocean are described as being deposited in an anoxic, or oxygen-depleted, deep water environment, although the details of the depositional environment are the subject of debate by researchers of the formation.In addition to their Posidonia bronni, the shales contain some spectacularly detailed fossils of other Jurassic sea creatures—ichthyosaurs and plesiosaurs, spiral-shelled ammonites and crinoids, or sea-lilies.


Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) mineral particles or rock fragments.

Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in the Goldich dissolution series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to tectonic compression within orogenic belts.

Vaca Muerta

The Vaca Muerta Formation, commonly known as the Vaca Muerta (Spanish for Dead Cow) is a geologic formation of Late Jurassic to Early Cretaceous age, located in the Neuquén Basin in northern Patagonia, Argentina. It is well known as the host rock for major deposits of shale oil and shale gas.

The large oil discovery in the Vaca Muerta Formation was made in 2010 by the former Repsol-YPF, which announced the discovery in May 2011. The total proven reserves are around 927 million barrels (147.4×10^6 m3), and YPF's production alone is nearly 45,000 barrels per day (7,200 m3/d). In February 2012, Repsol YPF SA raised its estimate of oil reserves to 22.5 billion barrels (3.58×109 m3). The US EIA estimates total recoverable hydrocarbons from this Vaca Muerta Formation to be 16.2 billion barrels (2.58×109 m3) of oil and 308 trillion cubic feet (8.7×10^12 m3) of natural gas, more than even the Neuquén Basin's hydrocarbon-rich Middle Jurassic Los Molles Formation holds.

Villeta Group

The Villeta Group (Spanish: Grupo Villeta) is a geological group of the Eastern Ranges of the Colombian Andes, to the west of the Altiplano Cundiboyacense. The group, a sequence of shales, limestones and sandstones, is subdivided into various formations; Conejo, La Frontera, Simijaca, Hiló, Pacho, Chiquinquirá, Capotes, Socotá, El Peñón, and Trincheras, and dates to the Cretaceous period; Aptian-Coniacian epochs. The group stretches out across four departments, from Huila in the south, through Cundinamarca and Boyacá to southern Santander in the north. The upper part of the Villeta Group is time-equivalent with the La Luna Formation of the Middle Magdalena Valley (VMM) and Sierra Nevada del Cocuy, the Oliní and Güagüaquí Groups of the Guaduas-Vélez synclinal and the Chipaque Formation of the Altiplano Cundiboyacense. The lower part has been correlated with the Simití, Tablazo and Paja Formations of the VMM, the upper Tibasosa, Une and Fómeque Formations of the Altiplano Cundiboyacense and the Capacho, Aguardiente, Tibú-Mercedes and upper Río Negro Formations of the Sierra Nevada del Cocuy.


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