Gas venting
Gas venting is the intentional safe release, without combustion, into the earth's atmosphere of gases that cannot be readily recycled into a production process, are surplus to requirements and have no export route or market value. As an industry practice, it has been criticized for its environmental impact and is being phased out in favor of gas recompression/injection or gas flaring. Controlled gas venting should not be confused with
- gas leaks which are unintentional and must be eliminated as a risk to safe operations,
- emergency pressure relief of last resort to safeguard human life and prevent equipment from exploding, or confused with
- uncontrolled and/or undetected gas seepage from the earth or oceans, naturally or due to human activity.
Oil field practice relating to unwanted gas
An example of gas venting from the oil industry is the atmospheric release of low pressure natural gas or contaminated gas to a safe location and at a concentration that avoids creation of a flammable or explosive mixture, or one that directly affects human health. Venting smaller volumes of low pressure gas can be the lowest cost and sometimes the only practicable option, particularly for limited durations and exceptional activities. Today, it is generally considered unacceptable in normal operations due to its environmental impact: natural gas has far greater global warming potential before than after combustion to CO2 and often contains harmful contaminants prior to processing.
Historical context
Natural gas was sometimes considered troublesome, dangerous, low value: a "free" by-product associated with financially more lucrative coal or liquid hydrocarbon recovery that has to be dealt with. The growth of international gas markets, infrastructure and supply chains have done much to change this. It has become standard practice to
- capture and use associated gas to provide local power and to
- reinject re-compressed gas for secondary recovery, reservoir pressure maintenance and potential later reservoir depressurization once hydrocarbon liquids recovery has been maximized and a gas export infrastructure and market access have been established.
Today, it is financially viable to develop even relatively small hydrocarbon reservoirs containing unassociated gas (i.e. with little or no oil) close to a market or export route, as well as large, remote accumulations.
Gas seepage as a result of human activity
Human activity has increased the number of potential sources and pathways for natural gas to escape from the earth.[1] Activities include not only hydrocarbon extraction, but also
- inadequate abandonment and decommissioning practices,
- insufficiently controlled burial of decomposing rubbish and
- water wells into subsurface aquifers.
Measures to minimize environmental impact include complete hydrocarbon reservoir depressurization, and capture or controlled combustion of gases from coal mining and of so-called biogases.
Other sources of gas release
In practice, it is impossible or impractical to capture and filter the air from coal mining (esp open-cast) and to completely degas hydrocarbon product and/or water produced from the ground which in some cases may be disposed at surface for and used after treatment. Melting of methane hydrates in the world's oceans or sea ice would also constitute uncontrolled gas leakage to atmosphere.