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Prashant Modi Guides: Methane reservoirs underneath the earth’s surface
Although methane can form in many different locations, it is most often found beneath the earth’s surface. Because this gas has a low density, after it has formed it will always rise towards the surface, through the cracks and crevices of shale-type rock and other natural materials. Some of this methane will naturally make it out of the earth and simply dissipate into the air. However Prashant Modi explains that the majority of methane located under the surface will rise up until it reaches a geological formation which traps it, and prevents it from reaching the air. These formations consist of layers of sedimentary, highly porous rock, which serves as a sponge for the methane gas, which are then covered with an impermeable, denser rock layer on top.According to Prashant Modi, if the formation is large enough, it will be able to trap huge quantities of methane underground – in this case, it is referred to as a reservoir. There are many different kinds of formations like this; however, the most frequently found formation of this type is dome shaped, and serves as an umbrella, which captures and holds on to all of the methane which is making its way to the surface. There are several different ways in which this dome formation can develop. For example, ‘faults’ are a common location for methane and oil deposits.
A ‘fault’ is a term used to describe what occurs when normal sediment layers crack vertically, so that the impermeable layer at the top falls downwards over time and traps the methane gas in the permeable layers of sandstone or limestone. This formation, which takes on a dome shape, has the potential to trap a large quantity of methane and in such a case, is called an anti-clinal formation. Prashant Modi says that when an energy company wishes to extract methane from this type of rock, a hole has to be drilled through the tough layers of impermeable boulders, so as to release the gas. The methane beneath this type of rock will be under a great deal of pressure, and once this pressure it released by the drilling process, the methane naturally rises to the surface..
