Enhanced Gas Recovery (EGR) with Carbon Dioxide Sequestration: A Simulation Study of Effects of Injection Strategy and Operational Parameters

摘要

Injection of carbon dioxide into a natural gasrnreservoir is a promising technology for reducingrnanthropogenic gas emissions and increasing ultimate recoveryrnof natural gas. Computer simulation is an important,rninexpensive tool for designing pilot projects and predictingrnoptimal tradeoffs between maximum methane production andrnmaximum sequestration.rnTo investigate the amount of carbon dioxide sequestered andrnthe effect of carbon dioxide injection on gas recovery,rndifferent injection strategies were used for a thin, shalyrnsandstone reservoir situated in Northern West Virginia. Tworninjection scenarios were studied: (1) simultaneous CO_2rninjection and methane recovery from the very beginning of thernproject, and (2) primary production of natural gas to therneconomic limit, followed by injection of carbon dioxide forrnsecondary gas recovery. Horizontal injectors were used tornincrease injectivity. A 160-acre inverted 5-spot well patternrnwas studied for a pilot test.rnThe simulation results show that the highest methane recoveryrnwas obtained when the reservoir was produced under primaryrnrecovery until the economic limit, followed by CO_2 injection.rnThe maximum amount of incremental gas recovery was lessrnthan 10% of the original gas in place (OGIP). Lower recoveryrnfactors for methane were obtained in the case when CO_2rninjection was injected early. However, the early CO_2 injectionrnaccelerated methane recovery and improved CO_2 retention inrnthe reservoir. The simulations also showed that there was anrnoptimum length for the horizontal injectors to sequester thernmaximum amount of CO_2.rnBy varying operational parameters such as time of primaryrnproduction, injector length, injection pressure, injectionrntiming, and production well pressure we can evaluate differentrnproduction schemes to determine an optimum recovery ofrnmethane vs. CO_2 sequestration. The findings of this study canrnbe useful for finding tradeoffs between methane productionrnand CO_2 sequestration.