'''Gas reinjection''' is the reinjection of
natural gas into an underground
reservoir, typically one already containing both natural gas and
crude oil, in order to increase the pressure within the reservoir and thus induce the flow of crude oil. After the crude has been pumped out, the natural gas is once again recovered. Since many of the wells found around the world contain heavy crude, this process increases their production. The basic difference between
light crude and
heavy crude is its viscosity and pumpability - the lighter the crude the easier it is to pump. Recovery of
hydrocarbons in a well is generally limited to 50% (heavy crudes) and 75-80% (light crudes).
Recycling of natural gas or other inert gases causes the pressure to rise in the well, thus causing more gas molecules to dissolve in the oil lowering its viscosity and thereby increasing the well's output. Air is not suitable for
repressuring wells because it tends to cause deterioration of the oil, thus carbon dioxide or natural gas is used to repressure the well. The term
gas-reinjection is also sometimes referred to as repressuring--the term being used only to imply that the pressure inside the well is being increased to aid recovery.