X区块注CO2和N2提高反凝析油采收率机理研究

通过对X区块原始地层流体的相态分析,确定了该区块为近临界凝析气藏。该区块一直采用衰竭式开采方式,气藏原始地层压力为27MPa,自开采以来至2012年8月地层压力下降为10MPa,已低于露点压力,反凝析加剧,地层污染加重,并造成大量的凝析油损失。利用该凝析气田附近所具有的高纯CO2气藏气,探索注CO2气开发方式改善和提高凝析油气的采收率具有技术进步意义。通过对CO2和N2两种注入气与地层流体膨胀实验数据的对比研究,得到CO2与地层流体的增溶膨胀能力、混相能力等相态配伍性较好且优于N2。在CO2与目前地层凝析油混相能力研究中发现在19.3MPa下CO2能与目前凝析油达到混相,CO2与目前地层凝析油容易达到混相,故开采时只要通过先期注CO2把目前地层压力提高至19.3MPa以上,就可实现混相驱提高凝析油的采收率。

Study on mechanisms of enhanced condensate oil by CO2 and N2 gas injection in Block X

According to phase analysis of initial reservoir fluid collected from block X, it is confirmed that reservoirs in the block are near- critical condensate gas reservoirs. Depletion development is always used in the block. By the end of August 2012, the formation pressure decreased from initial reservoir pressure of 27 MPa to 10 MPa which is lower than dew point pressure. This condition results in increasing retrograde condensation and formation pollution, and loss of condensate oil. Therefore, it is necessary to enhance condensate oil recovery by using high - purity CO2 from gas reservoir in the vicini- ty of the block. By compared with CO2 and N2 swelling experiments, the capability of solubilization and swelling of CO2 is better than that of N2, and CO2 is easier to mix with formation fluid. For the target condensate oil, CO2 minimum miscible pressure is 19.3 MPa. Therefore,as long as the present formation pressure is increased to more than 19.3MPa by CO2 injection, CO2 miscible flooding can be reached to enhance condensate oil recovery.