A petroleum geologist is an

earth scientist Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres, ...

who works in the field of petroleum geology, which involves all aspects of oil discovery and

production Production may refer to: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in the outline of industrial organization, the act of making products (goods and services) * Production as a stati ...

. 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 solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

s look at the structural and

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

ary aspects of the stratum/strata to identify possible oil traps or tight shale plays.

Profile

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 subside ...

. 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 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 depo ...

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 hydrophobic, and their odors are usually weak or ...

s during deep burial. * Reservoir: the usually

porous rock Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

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 Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

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 E ...

s show the

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

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 Mud logging is the creation of a detailed record ( well log) of a borehole by examining the cuttings of rock brought to the surface by the circulating drilling medium (most commonly drilling mud). Mud logging is usually performed by a third-part ...

, 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

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.

Profile

See also