中高渗倾斜地层与水平地层中CO2地质封存的差异性对比

CO2地质封存是减少CO2向大气排放,缓解温室效应的有效手段之一。由于构造和成岩作用,倾斜地层在自然界中普遍存在,研究倾斜地层对CO2封存量及安全性的影响具有实际意义。依托新疆准噶尔盆地阜康凹陷某CO2地质封存示范工程,采用数值模拟方法,分析了中高渗CO2储层地层倾角变化对CO2地质封存过程的影响。结果表明:CO2注入将导致近井区域地层压力显著升高;中高渗倾斜地层与水平地层相比,在地层压力分布、CO2侧向运移距离、CO2注入速率和总封存量等方面均存在明显差异。相比于水平地层,由于地层倾角的存在,倾斜地层压力呈不对称分布,CO2侧向运移距离显著加大。倾斜地层中压力传递和消散过程与水平地层差异显著,受此影响,倾斜地层与水平地层CO2的总注入量差值随时间呈非单调性变化。在注入初期,倾斜地层CO2的总注入量小于水平地层,随着注入时间延长,倾斜地层CO2的总注入量逐渐接近并超过水平地层;注入20年后,相较于水平地层,倾斜地层倾角越大越有助于增加CO2的总注入量,这一研究结果与前人基于低渗倾斜地层的研究结论正好相反。地层倾角的存在会促进CO2向浅部运移,倾角越大,CO2向浅部含水层和大气泄露的风险越大。因此,在CO2地质封存场地选址中,应充分考虑倾斜地层对封存效率及安全性的影响。

Comparison on the Difference of CO2 Geological Storage Between Sloping and Horizontal Strata with Mid-high Permeability

CO2 geological storage is an effective means to reduce CO2 emission into the atmosphere and alleviate the dangers of greenhouse effect.The sloping strata are common in nature due to tectonic and diagenetic effects,which have practical significance to study the effect of sloping strata on CO2 storage amount and security.Based on a demonstration project in Fukang sag of Junggar Basin,Xinjiang,the influence of the variation of stratigraphic dip angle of CO2 reservoirs with mid-high permeability on the process of CO2 geological storage was studied by means of numerical simulation.The results show that the injection of CO2 leads to a significant increase in the stratigraphic pressure near the well;compared with horizontal strata,the sloping strata have a significant difference on pressure distribution,CO2 migration distance,CO2 injection rate and storage amount.CO2 lateral migration distance of sloping strata is significantly larger than that of horizontal strata under the action of asymmetric stratigraphic pressure.The pressure distribution and dissipation process in sloping strata are quite different from that in horizontal strata;as a result,the influence of sloping strata on CO2 total injection amount presents a non-monotonic change.At the initial stage of injection,the CO2 total injection amount in sloping strata is less than that in horizontal strata,and with the injection time extension,the CO2 total injection amount in sloping strata gradually approaches and exceeds that in horizontal strata.After injection for 20 years,the larger the dip angle of sloping strata is,the more helpful to the increase of CO2 total injection amount,which is contrary to the conclusion of sloping strata with low permeability by previous studies.The existence of stratigraphic dip angles can promote CO2 migration to the shallow part,the larger dip angle can greatly increase the risk of CO2 leakage to the shallow aquifer or atmosphere.Therefore,the influence of sloping strata on the storage efficiency and security should be fully considered in the site selection of CO2 geological storage.