注入速率对CO_2地质储存封存潜力的影响分析

Analysis of Impacts of Variation in Injection Rate on the Potential of Proposed Reservoir for CO_2 Geological Sequestration

国内某著名煤炭企业计划实施每年10万吨的CO2地质储存（CCS）项目,拟选了5组地层做为目标储层。但所选封存层平均渗透率在0.15~0.6mD,平均孔隙度在2~6%,属于低渗低孔地层,如不进行人工压裂提高注入层渗透率,要实现预定存储目标尚有一些困难。笔者在研究中发现,除对目标层进行一定的水裂酸化处理提高地层渗透特性可以显著提高注入性和存储能力外,CO2注入速率的变化对地层的封存能力和注入性也有明显影响。运用TOUGH2-ECO2N软件分别模拟了无水裂及水裂情况下8种不同注入速率下这些目标存储层的压力变化及CO2封存状态比例及理论最大封存能力。模拟结果表明使用水裂酸化方法对储层进行处理后,不仅可以使注入总量达到项目要求,还可使系统理论最大储存能力提高55%;并且在灌注过程中采用变速灌注方式,可以有效控制系统压力积聚,对将来实际灌注压力控制具有重要意义。

A well-known China-based coal group planned to implement a CCS（Carbon Capture and Sequestration） project in which 100000 tons of supercritical CO2 would be injected into 5 formations underground.However,the proposed reservoir has average permeability in 0.15~0.6mD,and average porosity in 2~6%,belonging to a low permeable strata with poor pore space.Capacity of the proposed reservoir will be unlikely to satisfy the volume requirement of the CCS project unless it is fractured artificially.It was found in the research that not only the fracturing approach can greatly increase the injectivity and capacity of the reservoir also the selection of injection rate.8 scenarios under natural and fractured conditions were modeled by TOUGH2-ECO2N,respectively,to access the increased pressure caused by injection,phase proportions of CO2 in the reservoir and the theoretical capacity potential.Modeling results showed that fracturing is capable to make the reservoir meet the volume requirement,and increase the theoretical capacity by 55%;moreover,injection with inconstant rate could effectively control the pressure buildup in the reservoir,which is of interest for operation pressure control in the future injection practice.