Gas-Assisted Gravity Drainage - A New Process for CO_2 Sequestration and Enhanced Oil Recovery

摘要

The current commercial practice of gas-based enhanced oil recovery processes involves either continuous gas injection (CGI) or Water-Alternating-Gas (WAG) injection. Over 60 commercial projects in West Texas and other parts of the world have amply demonstrated that these CGI and WAG processes have been technically successful and commercially profitable. However, the oil recoveries from the CGI and WAG processes fall in the range of 5-15% of the remaining oil. The Gas-Assisted Gravity Drainage (GAGD) process, invented and patented at LSU, has yielded oil recoveries in the range of 65 - 95% in laboratory experiments conducted at realistic reservoir conditions. The GAGD process involves utilizing several vertical wells for injection of CO_2 in addition to drilling long horizontal wells for production. Injected CO_2 accumulates at the top of the payzone due to gravity segregation and displaces oil, which drains to the horizontal producer. This maximizes the volumetric sweep efficiency. The gravity segregation of CO_2 also helps in delaying, or even eliminating, CO_2 breakthrough to the producer as well as preventing the gas phase from competing for flow with oil. Thus GAGD enables sequestering injected CO_2 in addition to yielding much higher recoveries of trapped oil from depleted reservoirs.