| 摘要 |
<p>This invention relates to the recovery of oil from an oil-bearing formation having a natural fracture network with substantial vertical communication and wherein gravity drainage is the primary means of recovery. A downwardly inflating gas-cap is pressured up with a chase gas having a density less than that of CO2, CO2 is injected and a CO2-rich displacing slug is formed at the gas-liquid hydrocarbon contact. The chase gas is injected to facilitate displacing downwardly the CO2-rich displacing slug to recover hydrocarbon from the reservoir. CO2 is replaced in the displacing slug as the CO2 is solubilized into the oil, including matrix oil, to facilitate recovery thereof. The oil is recovered through production wells in fluid communication with the reservoir, preferably the inlet to the well is below the water-liquid hydrocarbon contactat such a level to prevent free-gas production. The chase gas has a density less than that of the CO2, abd is comprised mostly of nitrogen,however, it can contain other gases such as methane, ethane, CO2, and miscellaneous gases. Thechase gas is injected at a rate to minimize mixing of the chase gas with the CO2 and to facilitate gravity segregation of the CO2 from the chase gas. The CO2-rich displacing slug can be replenished by incorporating CO2 into the chase gas and permitting the CO2 to gravity segregate downwardly while the less dense gases move upwardly.</p> |
