Oil and Gas Reservoirs

Mature oil and gas reservoirs have held crude oil and natural gas over millions of years. They consist of a layer of permeable rock with a layer of nonpermeable rock (caprock) above, such that the nonpermeable layer forms a trap that holds the hydrocarbons in place. Oil and gas fields have many characteristics that make them excellent target locations for geologic storage of CO₂. The geologic conditions that trap oil and gas are also the conditions that are conducive to CO₂ sequestration.

As a value-added benefit, CO₂ injected into a mature oil reservoir can enable incremental oil to be recovered. A small amount of CO₂ will dissolve in the oil, increasing the bulk volume and decreasing the viscosity, thereby facilitating flow to the wellbore. Typically, primary oil recovery and secondary recovery via a water flood produce 30-40 percent of a reservoir's original oil in place (OOIP). A CO₂ flood allows recovery of an additional 10-15 percent of the OOIP. NETL's work in this area is focused on increasing the amount of CO₂ that remains in the ground as part of CO₂ EOR injection.

While not all potential mature oil and gas reservoirs have been examined, the RCSPs have documented the location of more than 82.4 billion metric tons (90.8 billion tons) of sequestration potential in mature oil and gas reservoirs.

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