The most common gas found in coal seams is methane which was formed millions of years ago as part of the breakdown and compression of peat to form coal. The gas lies in the open fractures within the coal seam and surrounding areas and also inside pores within the coal. This natural gas is almost pure methane, typically over 97%.
Coal seam gas is extracted by drilling a well vertically through rock strata until reaching the coal seam, at which point the well may also be drilled out horizontally to increase access to the methane gas.
Hydraulic fracturing, more commonly known as “fracking” is used to stimulate and accelerate the flow of coal seam gas. The process involves high pressured injection of sand, water and chemicals into the coal seam gas well. The injection causes fractures in the coal seam allowing the gas to flow to the surface of the well where it can be collected.
A significant amount of water can also be liberated as part of the gas extraction process which varies in quality, can be treated and reused in a variety of ways such as irrigation or to top-up local water supplies.
Shale gas is natural gas which is held in fractures, pore spaces and absorbed into the organic material of shale. Shale gas is generally liberated through the fracking technique.
This raw natural gas principally consists of methane from different sources and can have different impurities such as condensates, water, carbon dioxide and hydrogen sulphide that must be removed before the gas can be transported into pipelines and sent to market. In order to achieve this there is a requirement for a “scrubbing process” similar to that used for biomethane.