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Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Any further oil migrating in from the source will escape to the surface and seep. These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology.
The following section discusses these elements in brief. For a more in-depth treatise, see the second half of this article below.
Evaluation of the source uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed. The reservoir is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. Some of the key disciplines used in reservoir analysis are the fields of structural analysis, stratigraphy, sedimentology, and reservoir engineering.
The seal, or cap rock, is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock. Common seals include evaporites, chalks and shales. Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified. Analysis of maturation involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.
Mud log in process, a common way to study the lithology when drilling oil wells. Several major subdisciplines exist in petroleum geology specifically to study the seven key elements discussed above. In terms of source rock analysis, several facts need to be established.
Firstly, the question of whether there actually is any source rock in the area must be answered. Delineation and identification of potential source rocks depends on studies of the local stratigraphy, palaeogeography and sedimentology to determine the likelihood of organic-rich sediments having been deposited in the past. If the likelihood of there being a source rock is thought to be high, the next matter to address is the state of thermal maturity of the source, and the timing of maturation.