Enhanced Gas Recovery (EGR) in Shale Gas Reservoirs

The generation of energy in the United States is considerably aided by the country’s abundant shale gas resources. Combustion of fossil fuels is the source of greenhouse gas emissions. Potential sources of greenhouse gas emissions include power plants, oil refineries, and flaring or venting of generated gas (mainly methane) in oilfields. Not only can the commercial usage of greenhouse gases in shale reservoirs lead to an improvement in oil or gas recovery, but it also helps to contribute to the sequestration of carbon dioxide. Because of the enormous gas reserves that are believed to exist around the globe, shale gas is currently being extracted in various nations and is therefore regarded as one of the most reliable sources of energy. Shale reservoirs are naturally fractured, and for this reason, it is necessary to consider two separate systems: the matrix and the fracture. Implementation of improved recovery techniques is required in order to make the production of gas from shale reservoirs economically viable. This chapter’s primary objective is to provide an overview of improved gas recovery methods applicable to shale reservoirs. In the first portion, it gives a detailed explanation on shale and enhanced gas recovery (EGR), and then it discusses the characteristics and flow behaviour of shale gas in the second section. Both the continuous CO2 injection approach and the huff-n-puff CO2 injection technique are reviewed in relation to the mechanism of enhanced gas recovery as well as the problems that were faced during the process of gas recovery.