底水砂岩气藏注CO_(2)驱气提高采收率机理及埋存效果

Gas recovery enhancement and CO_(2) storage effects by CO_(2) flooding in bottom-water sandstone gas reservoir

注CO_(2)已被广泛应用于提高油气藏采收率,但有关底水砂岩气藏注CO_(2)驱及CO_(2)埋存协同开发的研究较少,气态CO_(2)和超临界态CO_(2)驱替天然气的机理和差异尚不明确。为了改善底水砂岩气藏水侵情况和明确气态与超临界态CO_(2)驱提高采收率及CO_(2)埋存机理,以X底水砂岩气藏为例,开展了注CO_(2)驱适宜度评价,提出了X气藏CO_(2)驱最优开发方案,并对比了气态和超临界态CO_(2)驱提采机理和效果,最后对注CO_(2)驱最优方案开展了生产及埋存预测。研究结果表明:①X气藏适合进行注CO_(2)驱,注CO_(2)提高采收率的最优方案即注采井网为低注高采、关井时机为采出气CO_(2)浓度达10%~20%、转注时机为地层压力7.5 MPa、压力恢复水平为地层压力7.5 MPa、注气速度为3.5×10^(4) m^(3)/d、注入量为0.25 HCPV,最优方案相对于衰竭式开发预计提高气藏采收率13.83%。②超临界CO_(2)驱抑制底水锥进效果和提高采收率效果优于气态CO_(2)驱。③注CO_(2)驱最优开发方案下,该气藏的CO_(2)总埋存量为4.7×10^(6) t,其中超临界埋存量、溶解埋存量和矿化埋存量占比分别为86.05%、11.33%和2.62%。结论认为,底水砂岩气藏在发生气井水淹后采用超临界CO_(2)驱可以有效改善储层水侵情况,提高了气藏采收率,该认识为底水砂岩气藏的高效开发提供了理论支撑。

CO_(2) flooding has been widely applied to EOR,but so far,few researches have been carried out on the collaborative development of CO_(2) flooding and storage in bottom-water sandstone gas reservoirs,and the natural gas displacement mechanisms of gaseous CO_(2) and supercritical CO_(2) and their differences have not been clarified.In order to improve water intrusion of bottom-water sandstone gas reservoirs and clarify the gas recovery enhancement and CO_(2) storage mechanisms of gaseous CO_(2) flooding and supercritical CO_(2) flooding,this paper takes X bottom-water sandstone gas reservoir as an example to evaluate the suitability of CO_(2) flooding and propose the optimal CO_(2) flooding development scheme.Then,gaseous CO_(2) flooding and supercritical CO_(2) flooding are compared in terms of EOR mechanism and effect.Finally,the production and storage capacities of the optimal CO_(2) flooding development scheme are predicted.And the following research results are obtained.First,as for X gas reservoir,CO_(2) flooding is suitable,with the optimal scheme as follows.The injection and production well pattern is in the form of low injection and high production.The well shall be shut down when the CO_(2) concentration of the produced gas reaches 10%-20%,and injection conversion shall be performed when the formation pressure is 7.5 MPa.The pressure buildup level is 7.5 MPa.0.25 HCPV CO_(2) is injected at the rate of 3.5×10^(4)m^(3)/d.The optimal scheme is expected to increase the gas recovery factor by 13.83%compared with depletion development.Second,supercritical CO_(2) flooding is superior to gaseous CO_(2) flooding in inhibiting bottom water coning and enhancing recovery factor.Third,according to the optimal CO_(2) flooding scheme,the total CO_(2) storage in this gas reservoir is 4.7×10^(6) t,among which supercritical storage,dissolved storage and mineralized storage account for 86.05%,11.33%,and 2.62%,respectively.In conclusion,supercritical CO_(2) flooding can effectively improve water intrusion and recovery factor of bottom-water sandstone gas reservoirs after the gas well is watered out.These research results provide theoretical support for the efficient development of bottom-water sandstone gas reservoirs.