Shale gas reservoirs - a comparative approach

Until recently, shales were regarded by the oil industry as a setback hindering the operations while drilling to target sandstone and limestone reservoirs. Also, it was considered as the source rock for hydrocarbons migrating into conventional reservoirs and as the seal for trapping oil and gas in underlying sediments. Thanks to the “shale gas revolution” in the USA, however, it is known today that shales, as the most abundant form of sedimentary rock on Earth, can form low-permeable reservoirs containing huge quantities of hydrocarbons. Unlike the conventional reservoirs, production from shale gas resources would not be economically feasible due to the very low rates of flow of natural gas from the formation of ultra-low permeability. Yet, this is only one of the characteristics of shale gas reservoir which makes them different from conventional resources. Outlining the fundamental differences between shale gas plays and conventional gas reservoirs along with a brief description of status of shale gas development is the subject of this chapter. Furthermore, the potential of shale gas in the UK and the problems associated with its development compared to the US shale gas are presented.