Gas cycling

Natural gas reservoirs often contain appreciable quantities of liquid hydrocarbons held in the gaseous state. Since these liquids are liquefied petroleum gases such as propane and butane, they are important sources of both fuel and chemical feedstocks. If the pressure in such a reservoir is allowed to decline during gas production, these liquids will condense in the reservoir and become nonrecoverable. To prevent this decline in pressure, a quantity of the produced gas from which the liquids have been removed is put back into the reservoir. This process, called gas cycling, is continued until the optimum quantity of liquids has been removed. The reservoir pressure is then allowed to decline during the production of the nearly dry gas. In effect, this process defers the use of the reinjected natural gas until after the liquids have been produced.

Overall, the production of oil and gas has become an exacting engineering job. Although new oil fields are being discovered, the huge consumption of petroleum requires that fields already in production be used more efficiently.