Analytical approach for estimating CO₂ storage capacity of produced gas reservoirs with or without a water drive.

摘要

An analytical CO₂ injection equation for estimating effective CO₂ storage capacity is derived and verified for a gas reservoir producing gas, followed by injecting CO₂ into the reservoir with a water drive. The equation can be expressed in the forms of an injection-production-ratio (IPR) equation and the p/z equation. An effective capacity coefficient can be obtained either from the ratio of effective CO₂ storage capacity and theoretical CO₂ storage capacity, or from the IPR and z-factors. In a gas reservoir with a water drive, the CO₂ injected to increase the pressure from the abandonment pressure to the initial pressure is less than the gas produced. The single effective capacity coefficient is less than one depending on the strength of the water drive. In a gas reservoir with no water drive, the CO₂ injected to increase the pressure from the abandonment pressure to the initial pressure is more than the gas produced. The single effective capacity coefficient is 1. The discussion includes examples of using the CO₂ injection equation and IPR type curves to estimate effective CO₂ storage capacity, and pressure behaviors in p/z plots [p/z versus (G_phc - G_inj)] during gas production and CO₂ injection.