Traditionally, most extraction of natural gas has been from so called “conventional” sources, where natural gas has accumulated within a trap or reservoir within the rock which can be drilled and extracted. “Unconventional” gas resources refer to gas that has not accumulated within a reservoir and remains within the impermeable source rock. Types of unconventional gas include coal seam gas (CSG), found in coal beds; shale gas; and tight gas, which is found in sandstone or limestone, and has extremely low permeability.
Unconventional gas is typically widespread throughout the rock, and occurs in much lower concentrations compared to conventional gas. Due to the nature of unconventional gas, the process of extraction is more difficult than for conventional gas, requiring special extraction methods. Unconventional gas development generally creates a much larger environmental footprint, and poses major environmental and health risks.
In particular, the use of hydraulic fracturing, or “fracking”, can cause serious hazards. Fracking is the process of shooting water, chemicals and sand into the ground to create cracks in underground rock formations and increase the flow of gas for extraction. Unconventional gas extraction generally requires this procedure in order to generate adequate flow rates, and it is particularly essential for tight gas and shale gas developments. The process also involves injecting large quantities of toxic chemicals, typically including hazardous BTEX chemicals (benzene, toluene, ethylbenzene and xylene). Fracking has caused many environmental and health problems, particularly water contamination from leaking of methane and fracking fluids.
The process of CSG production also involves the extraction of large quantities of water from the coal bed. The contaminated waste-water often contains high levels of salt and other contaminants from the coal seam, including heavy metals such as mercury, cadmium, arsenic and other elements in harmful quantities. There is no safe way of disposing of this water.