Tight gas is natural gas which is difficult to access because of the nature of the rock and sand surrounding the deposit. Because this gas is so much more difficult to extract than natural gas from other sources, companies require a large financial incentive to go after it; as energy prices rise, so does interest in extracting tight gas. Several global oil and gas companies control significant tight gas reserves, including BP, which has also sunk substantial resources into learning more about extracting tight gas.

Normally, natural gas is fairly easy to access. When a deposit is identified, a well can be sunk, and the gas naturally flows into the well, making it easy to pump the gas to the surface and to distribute it from there. This is because natural gas is normally surrounded by deposits of porous rock, with lots of small holes for the gas to seep through. Sometimes, the gas literally pumps itself.

In the case of tight gas, the surrounding sandstone, shale, or other rock is not so permeable, looking much denser in cross-section. The lack of permeability locks the tight gas up underground, making it difficult to drill a profitable well. Tight gas is also found trapped in coal deposits. In order to get at the tight gas, it is necessary to find a “sweet spot” where a large amount of gas is accessible, and sometimes to use various means to create a pressure vacuum in the well which sucks gas out of the surrounding rock.

Historically, such deposits were written off as “unrecoverable.” However, as the demand for natural gas has grown, many companies have rethought this assessment, pushing to see if tight gas deposits could be accessed. While tight gas is costly to extract, higher gas prices can make the cost worth it, especially if the gas has a composition which is favorable to distillation, allowing the company to extract several valuable fractions from a single well.

Most tight gas deposits date to the Paleozoic era, which means that these deposits are at least 251 million years old. The advanced age of such deposits is presumably responsible for their inaccessibility; tight gas is tight, in other words, because the rock around it has had more time to become dense. These deposits may also be deeper than ordinary gas deposits, posing additional challenges. Companies which work with tight gas use a variety of survey tactics to identify potential sources of gas, and to target the best spots for drilling.