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 geologists make the decision of where to drill for petroleum. This is done by locating prospects within a sedimentary basin. Petroleum geologists determine a prospect's viability looking at seven main aspects:
- Source – The presence of an organic-rich source rock capable of generating hydrocarbons during deep burial.
- Reservoir – The usually porous rock 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 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 surveys show the seismology 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.