超低渗油藏CO_2吞吐室内评价及参数优化

Laboratory Evaluation and Parameter Optimization of CO_2 Huff-n-puff in Ultra-low Permeability Reservoirs

针对鄂尔多斯盆地某超低渗透油藏注水开发矛盾突出、水驱动用程度差和原油采收率低等问题,基于超低渗透油藏特征及国外CO_2驱的成功案例,提出了CO_2吞吐提高采收率的开发思路。通过长岩心驱替实验,结合换油率和驱油效率来综合评价CO_2吞吐在超低渗透油藏的开发效果,并进行了CO_2吞吐注采参数的优化。研究结果表明,当油藏压力大于最小混相压力(20.78 MPa)时CO_2吞吐能获得较高的采收率;当CO_2吞吐段塞大小为0.1 PV、焖井时间为24 h,吞吐3轮次时的CO_2吞吐的开发效果最佳,驱油效率为56.39%,平均换油率为0.454。

The ultra-low permeability reservoirs in Ordos Basin face serious problems of water injection difficulty, poor flooding results and low oil recovery. In order to improve the oil recovery of ultra-low permeability reservoir, the development idea of CO2 huff-n-puff was proposed based on the characteristics of ultra-low permeability reservoirs and the successful cases of CO2 flooding in abroad. Long core flooding experiment were done in laboratory, and the effect of CO2 huff-n-puff were evaluated combining the oil change rate and displacement efficiency, meanwhile, the injection parameters were optimized. The experiment result showed that CO2 huff-n-puff had higher oil recovery when reservoirs pressure was greater than the minimum miscible pressure（MMP）, being of 20.78 MPa. The optimum operation strategy was 0.1 PV for slug size, the soaking time of 24 h and three-cycle huff-n-puff. CO2 huff-n-puff provided an effective method for ultra-low permeability reservoir, the oil displacement efficiency was 56.39%, the average oil exchange ratio was 0.454.