致密低渗透气藏注CO_2提高采收率潜力评价

CO_2驱替天然气气藏是将CO_2以超临界相态形式驱替天然气,在实现提高天然气气藏采收率的同时也达到将CO_2地质封存的目的。注CO_2提高气藏采收率仍处于探索阶段,目前CO_2驱气提高采收率程度不清楚、适合开展CO_2驱气提高采收率的地质条件不明确、CO_2驱替的合理工作制度也不明确。为此,首先开展长岩心驱替实验,以明确低渗透储层是否能通过注入CO_2提高采收率及提高采收率的程度,实验结果表明,当出口端CO_2含量为10%时,CO_2可提高气藏采收率12%;其次建立超临界CO_2驱替天然气多组分渗流数学模型,通过实验数据验证模型的准确性;然后应用该数学模型,开展超临界CO_2驱替天然气影响因素分析,明确选区条件;最后,以鄂尔多斯盆地大牛地气田为例,优选出DK13井区作为CO_2驱替天然气评价区,并开展注CO_2提高采收率潜力的评价研究。数值模拟计算结果表明:当DK13井区生产井CO_2含量为10%(防腐成本较低)时,CO_2可提高气藏采收率介于8.0%~9.5%,同时可实现31.1%HCPV的CO_2封存量。结论认为,此举既提高了气藏采收率,又能实现对CO_2的地下有效封存,可实现社会效益与经济效益的双赢。

Potential evaluation on CO2-EGR in tight and low-permeability reservoirs

CO₂-EGR, i.e. enhanced gas recovery by injectingCO₂, is to displace natural gas by injectingCO₂ in the supercritical phase. It can both enhance the recovery of gas reservoirs and realizeCO₂ storage. Currently, this technique is still at its exploring stage. The effect of CO2-EGR is not clarified, the geologic conditions forCO₂-EGR are not definite, and the rational working system forCO₂-EGR is not available. In this paper, the long-core experiment was conducted to determine whether and how much the recovery of low-permeability reservoirs can be enhanced by injectingCO₂ According to the experimental results, the recovery can be enhanced by 12% whenCO₂ content in produced gas is more than 10%. Moreover, the multi-component seepage mathematical model was built for displacing natural gas by injecting supercriticalCO₂, and the model accuracy was verified using laboratory data. With this mathematical model, the influence factors for displacing natural gas by injecting supercriticalCO₂ were analyzed in order to define the conditions for selecting favorable zones. The Well DK13 area in the Daniudi gas field, Ordos Basin, was selected for potential evaluation ofCO₂-EGR. As indicated by the numerical simulation results, whenCO₂ content of producing wells in the Well DK13 area is 10% (with lower cost for corrosion prevention), the ratio ofCO₂-EGR is 8.0–9.5%, and 31.1% HCPVCO₂ storage can be realized. It is thus concluded that theCO₂-EGR technique can enhance the recovery of gas reservoirs and also storeCO₂ underground, contributing to the increase of both social and economic benefits.