Shale gas is natural gas which is trapped tightly in dense rock as opposed to existing natural gas resources which flow freely from drilled rock formations. Supplies of this easy-to-access gas are declining so most of the remaining gas resources in the world are shale. The gas is processed and separated into Natural Gas Liquids (NGLs), the main one of which is ethane.

There are vast reserves of shale gas in the United States, therefore Shell is constructing its polyethylene complex in Pennsylvania, which is located in the Appalachian Basin, one of the main shale gas areas. Shale gas in this area is predominantly ‘wet’ which means it contains a higher percentage of ethane and ultimately ethylene for polyethylene.

A technique known as hydraulic fracturing (‘fracking’) is used to break open rock and release the natural gas. Fluid (99% sand & water) is pumped into the well bore at high pressure to form the fractures. Fracturing typically occurs at least a kilometre below drinking water supplies and barriers are also inserted into the wells to prevent fluids entering local water supplies. To minimise the surface footprint of the process, long horizontal wells are drilled, meaning more production from a single well.