基于数值模拟的CO_(2)地质封存项目井筒泄漏风险定量化评价方法

Quantitative Evaluation Method of Wellbore Leakage Risk of CO_(2) Geological Storage Project Based on Numerical Simulation

为评估CO_(2)地质封存场地的CO_(2)沿井筒泄漏风险,介绍了自主研发的可对CO_(2)井筒泄漏风险进行定量化评价的数值模拟WellRisk软件,将软件应用于实际CO_(2)地质封存场地--神华鄂尔多斯CO_(2)咸水层封存示范工程,定量评估该场地CO_(2)沿注入井和监测井的泄漏量,并将软件模拟结果与美国能源部开发的NRAP–IAM–CS(The national risk assessment partnership–integrated assessment model–carbon storage)软件模拟结果进行对比,实现了CO_(2)沿井筒泄漏风险的定量化评价。定义了井筒泄漏系数,即井筒发生泄漏的有效截面积和井筒总截面积的比值,并将井筒泄漏系数作为量化表征井筒固井质量的重要参数。当泄漏系数取值为10^(–6)时,神华CO_(2)地质封存场地在1000 a内的总泄漏量为720 tCO_(2),占总注入量的0.24%,小于IPCC的风险阈值1%。因此,泄漏系数为10^(–6)或更低的井筒是低风险泄漏井,具有良好的固井质量,对应于NRAP–IAM–CS软件中井筒渗透率低于10^(–12)m^(2)的情况。泄漏系数为10–5或更高的井筒是高风险泄漏井,具有较差的固井质量。WellRisk和NRAP–IAM–CS的计算结果均表明,当注入井和监测井的固井质量良好时,神华CO_(2)地质封存场地基本不存在CO_(2)泄漏风险。

To evaluate the CO_(2) leakage risk through wellbores in CO_(2) geological storage sites,a self-developed numerical simulation code—WellRisk is introduced.The WellRisk could quantitatively evaluate the CO_(2) wellbore leakage risk,and it was applied to an actual CO_(2) geological storage site—Shenhua Ordos saline aquifer CO_(2) storage demonstration project.The leakage of CO_(2) along the injection wells and monitoring wells at the site was quantitatively evaluated by WellRisk,and the results were compared against the simulation results of NRAP–IAM–CS(The National Risk Assessment Partnership–Integrated Assessment Model–Carbon Storage)developed by the US Department of Energy,demonstrating a reliable quantitative assessment of CO_(2) leakage risk by WellRisk.This paper defines the wellbore leakage coefficient(the ratio of the effective sectional area of the wellbore where leakage occurs to the total sectional area of the wellbore)and takes the wellbore leakage coefficient as an important parameter to quantitatively characterize the quality of wellbore cementing.When the leakage coefficient is 10^(–6),the total CO_(2) leakage of the Shenhua storage site in 1000 years is 720 tons,accounting for 0.24%of the total injection,which is less than the IPCC CO_(2) leakage risk threshold of 1%.Therefore,wellbores with leakage coefficients of 10^(–6) or lower are low-risk leakage wells with good cementing,corresponding to wellbore permeability below 10^(–12)m^(2) in the NRAP–IAM–CS software.Wellbores with leakage coefficients of 10–5 or higher are high-risk leakage wells with poor cementing.The results of WellRisk and NRAP–IAM–CS both show that when the quality of wellbore cementing in injection wells and monitoring wells is good,there is almost no risk of CO_(2) leakage at the Shenhua CO_(2) storage site.