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Seismic inversion is a technique a geological surveyor can use to learn more about the properties of a formation, particularly a reservoir of oil or gas deposits under the surface of the earth. Geologists do this as part of an overall geological survey, where they collect as much information as possible about a target area. This information helps them decide if a reservoir would be profitable enough to sink development funds into, or if it should be left alone because the expense would be too high.
In a seismic inversion study, the geologist starts with a seismic survey. She transmits sound waves through the deposit of interest with the use of large vibrating devices or dynamite, and records the output. The movement of the waves through the formation can provide important information about its characteristics, and the seismic survey itself will become part of the overall report on the location. Often, raw data is included in the report for the benefit of readers.
To conduct a seismic inversion, the geologist essentially solves backward, asking what types of formations would cause that kind of output. A great deal of information about various rock types and their characteristics is available, and a computer program can run the seismic survey through some equations to generate a seismic inversion output. This process can also involve looking at similar types of formations and known data about the region to make the results as accurate as possible.
Other tools that can help with a seismic inversion include test wells and a variety of tests on samples from the area. The goal is to assemble information from multiple sources. This will allow the geologist to test the work done in the seismic inversion study. If he modeled the structure accurately, all of the data should fit the model. If he did not, there will be outliers that cannot be explained, and he must retrace the work to find out what went wrong.
Large oil and gas companies maintain their own geology teams who can conduct in-house surveys for their employers. Smaller firms may hire independent contractors to survey a site and perform tests like a seismic inversion study. The information collected is usually proprietary, although the company may discuss some of the details in annual reports to investors to justify investment decisions. Government agencies can perform similar studies on public lands, and their results are open to any member of the public who wishes to examine them.
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