Petroleum geology
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Reason: Miserable translation. Anyone who translates “source” in the present context with “origin” instead of “ parent rock ” shows that he is not a subject and that he has not dealt sufficiently with the topic. With a few clicks in the Wikipedia of origin, you could have made yourself accordingly smart, but that was apparently too much to ask ... --19: 51, Feb. 12, 2019 (CET)
Petroleum geology is the study of the origin, occurrence, movement, accumulation and exploration of liquid and also gaseous hydrocarbons ( petroleum and natural gas ). It denotes a specific area of geosciences that is used in the search for hydrocarbons.
Sedimentary Basin Analyzer
Petroleum geology is mainly concerned with evaluating the seven key elements of the sedimentary basins:
- Origin : The determination of the origin uses the methods of geochemistry to quantify the nature of the rocks rich in organic material, which are the precursors of hydrocarbons; the type and quality of the leaked hydrocarbons can be assessed.
- Reservoir : The reservoir is a porous and permeable lithological unit or group of units that contains the hydrocarbon reserves. The analysis of the reservoirs in the simplest level requires the definition of the porosity (to calculate the in-situ volume of the hydrocarbons) as well as the permeability , the stratigraphy , the sedimentology and the reservoir analysis .
- Cover rock : The cover rock is a lithological unit with low permeability that prevents the hydrocarbons from flowing out of the reservoir rock. Common cap rocks are evaporites , chalk and clay rocks . The analysis of the cover rock includes the determination of the thickness and extent, as well as their effectiveness.
- Geological trap : The geological trap is a stratigraphic or structural feature that ensures the common occurrence of storage rock and cover rock in the subsurface and thus traps the hydrocarbons and prevents them from escaping (this depends on the static buoyancy of the hydrocarbons)
- Timing and Maturation : The analysis of the maturation and timing includes the determination of the thermal history of the original rock around the amount and the time of the formation and the discharge of the hydrocarbons.
- Migration : When studying migration, knowledge is gained of how hydrocarbons move from the original rock into the storage rock and helps to determine the quantity of hydrocarbons in a certain area.
In general, these parameters must be assessed through a limited “window” into the subterranean world through one or more exploration wells . These drill holes show only a one-dimensional segment of the subsurface and the ability to infer three-dimensional characteristics is one of the most important in petroleum geology. Recently, the availability of inexpensive, high quality three-dimensional seismic data (from reflection seismics ) and data from various electromagnetic geophysical measurement methods (such as magnetotellurics ) have contributed significantly to the accuracy of these inferences and interpretations.
Important stages in the exploitation of petroleum geology
Several important phases in oil production use petroleum geology to exploit the oil reserves.
Analysis of the original rock
In order to analyze the original rock, several parameters have to be determined. First, it must be determined whether there are parent rocks in the area. The representation and identification of the possible original rocks depends on the study of local stratigraphy, paleogeography and sedimentology; this also determines the likelihood of the deposition of organic matter rich sediments in the geological past.
If the probability of the presence of a source rock is high, the next goal is to determine the status and the time of maturation. The maturation of the original rock (see diagenesis and fossil energy ) strongly depends on the temperature; so the majority of crude oil is produced in a range from 60 ° C to 120 ° C. The formation of natural gas starts in a similar temperature range, but continues above it up to a range of 200 ° C. By combining the geochemical analyzes (to determine the kerogen type and its characteristics) and the modeling of the sedimentary basin, the thermal gradient in the sedimentary column is modeled.
Analysis of the sedimentary basin
A full sedimentary basin analysis is normally performed to determine the location of future boreholes in the search area. These analyzes discuss the petroleum system and study the system of origin (existence and quality) of the embedding history, maturation (time and volume), migration and enrichment as well as the potential regional cover rocks and important storage rocks and carrier rocks. All of these elements need to be investigated in order to locate the potential occurrences.
Exploration stage
Although sedimentary basin analysis is usually the first step in exploring new deposits, portions of these studies are sometimes carried out during the exploration phase. Exploration geology includes all of the activities and studies necessary to find new deposits. Usually seismic studies are made and data from old explorations (seismic lines, borehole logs, geological reports ...) are used to expand the studies. Sometimes gravimetric and geomagnetic surveys are carried out; oil seepage and spills are also mapped in the study area. As soon as a significant occurrence is found through exploration or wildcat drilling (financially risky drilling in previously non-occurrence areas), the project appraisal phase begins.
Project review phase
The project appraisal phase is used to estimate the size of the deposit. The properties, connectivity and types of hydrocarbons as well as their contact with the groundwater body are used to calculate the potential recoverable volume. This is usually done using new exploration wells around the first exploration well. Production tests provide insight into the pressure conditions and the connectivity of the deposit. Further geochemical and petrophysical analyzes provide information about the hydrocarbons (viscosity, chemistry, API, sulfur content ...) and the nature of the occurrence (porosity, permeability ...).
Production or funding phase
After a hydrocarbon resource has been discovered and the testing phase shows profitable extraction, the production phase begins. In this phase, the focus is on controlled production, with production wells being created at strategic positions. This is done with the help of target bores, which are guided to the optimal point using 3D seismics. In many cases, after the intrinsic pressure has been released, aids such as water and steam injections or pumps are used to maintain production.
literature
- Oil. In: Federal Institute for Geosciences and Raw Materials (Hrsg.): Energierohstoffe 2009 - Reserves, Resources, Availability - Oil, Natural Gas, Coal, Nuclear Fuels, Geothermal Energy. Hanover 2009, pp. 31–70.
Web links
- Oil On My Shoes - General website in English about petroleum geology and its application
- AAPG - American Association of Petroleum Geologists