A petroleum geologist is an earth scientist who works in the field of

petroleum geology Petroleum geology is the study of the origins, 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). ...

, 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

geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...

s look at the structural and

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

ary aspects of the

stratum In geology and related fields, a stratum (: strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ...

/strata to identify possible oil traps or tight shale plays.

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Petroleum geologists make the decision of where to drill for petroleum. This is done by locating prospects within a

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

. Petroleum geologists determine a prospect's viability looking at seven main aspects in conventional petroleum geology: * Source: the presence of an organic-rich source rock capable of generating

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

s during deep burial. * Reservoir: the usually porous rock and permeable unit that collects the hydrocarbons expelled from the source rock and holds them inside a trap. * Seal: the rock unit that inhibits the oil or gas from escaping from a hydrocarbon-bearing reservoir rock. * Trap: structural or stratigraphic feature that captures migrating hydrocarbons into an economically producible accumulation. * Timing: geologic events must occur in a certain order, e.g. that the trap formed before migration rather than after. * Maturation: the process of alteration of a source rock under heat and pressure, leading to the cracking of its organic matter into oil and gas. * Migration: the movement of the (less dense) oil or gas from the source rock into a reservoir rock and then into a trap. These seven key aspects require the petroleum geologist to obtain a 4-dimensional idea of the subsurface (the three spatial dimensions, plus time). Data may be obtained via geophysical methods.

Geophysical survey Geophysical survey is the systematic collection of geophysical data for spatial studies. Detection and analysis of the geophysical signals forms the core of Geophysical signal processing. The magnetic and gravitational fields emanating from the ...

s show the

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

data of elastic waves, mainly seismic reflection. This provides a 3-dimensional look of the trap, and source rock. More data may be obtained from the mudlogger, who analyzes the drill cuttings and the rock formation thicknesses. Today, there are also unconventional tight plays. Petroleum geologists for these plays work with petroleum engineers and other specialists to make decisions of where to drill for oil. Data is also obtained via geophysical methods (the same as conventional plays, plus fracture data), but these are modernly analyzed with various statistical methods. The geological analysis is done by looking at a combination of geological aspects, with completion analogs. The geological aspects are as follows: *Source: the presence of an organic-rich source rock. Unlike conventional plays, where the source rock typically underlays the reservoir rock and the oil/gas migrates into the reservoir, tight shale plays can be their own source rock. *Reservoir: the usually porous rock with lower permeability rock. This rock could have collected hydrocarbons expelled from a source rock, or be its own source rock. *Seal: often, due to the low permeability, oil/gas is unable to migrate out of this rock, but it is common to also have a sealing rock above the reservoir rock that inhibits further migration of oil or gas. *Timing: geologic events must occur in a certain order, e.g. a seal to trap gas must be in place before kerogen cracking. *Maturation: the process of alteration of a source rock under head and pressure, leading to the cracking of its organic matter into oil and gas. *Migration: the movement of the (less dense) oil or gas from the source rock into a reservoir rock and then into a trap. The 'trap' aspect is absent. Tight shale plays, or unconventional plays, do not require a trap to contain hydrocarbons due to the low permeability preventing further migration.

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See also