基于有限元数值模拟的地质封存CO_(2)运移行为预测方法

A Prediction Method for CO_(2)Migration Behavior in Geological Storage Based on Finite Element Numerical Simulation

针对注入咸水层CO_(2)运移特征预测的工程需求,基于COMSOL Multiphysics平台建立了矿藏尺度的咸水层CO_(2)地质封存有限元数值模型,探讨了地层孔隙度、温度及CO_(2)注入流量等因素对咸水层中CO_(2)运移行为的影响规律,开发了可移植使用的仿真软件,最终形成了一种基于有限元数值模拟的地质封存CO_(2)运移行为预测方法;以中国神华集团咸水层二氧化碳捕集与地质封存项目中的石千峰地层为例,开展了有限元数值建模、CO_(2)运移行为影响因素和影响规律研究;研究结果表明:1)在CO_(2)注入阶段的前期,CO_(2)沿着近似水平方向运移并在注入井周围形成高压区域;随着CO_(2)的持续注入,CO_(2)在咸水层中的分布区域逐渐形成上宽下窄的“舌状”,咸水层压力有所降低;在CO_(2)停注后,咸水层的压力逐渐降低至原地层压力水平,出现咸水反向驱替CO_(2)的现象;2)随着地层孔隙度的减小,CO_(2)注入咸水层后地层压力呈指数增长趋势,孔隙度的改变影响CO_(2)的运移形态;在CO_(2)停注后,随着咸水层孔隙度的增大,咸水的反向驱替现象愈加明显,咸水层顶部的CO_(2)堆积量增加;3)地层温度的升高增强了咸水的反向驱替作用,CO_(2)运移时“舌状”区域的边界倾角随之增大,咸水层顶部的CO_(2)侧向分布范围逐渐扩大;4)CO_(2)的扩散范围随注入流量的增加而扩大;注入流量相同的条件下,CO_(2)的扩散速率随时间的推移而降低;在CO_(2)停注后,注入流量越低反向驱替现象越明显;5)所开发的仿真软件具有数值模型建立、仿真数据分析等功能模块,测试结果表明了软件的可用性;研究成果可为CO_(2)地质封存点的选址、注入条件优化、泄漏监测提供理论和模型基础。

To meet the engineering requirements for predicting the migration characteristics of CO_(2)injected into saline layers,a finite element numerical model for geological storage of CO_(2)in saline layers is established based on the COMSOL Multiphysics platform.Explore the influences of factors such as formation porosity,temperature,and CO_(2)injection flow rate on CO_(2)migration behavior in saline layers,develop the portable simulation software,and achieve the finite element numerical simulation based method for predicting CO_(2)migration behavior in geological storage.By taking the Shiqianfeng Formation of China Shenhua Group's Saline Layer Carbon Dioxide Capture and Geological Storage Project as an example,study the finite element numerical modeling,influencing factors and laws of CO_(2)migration behavior.The results show that:(1)In the early stage of CO_(2)injection,CO_(2)migrates in the approximate horizontal direction and forms a high-pressure area around the injection well;With the continuous injection of CO_(2),the distribution area of CO_(2)in the saline layer gradually forms a tongue shape with a wide top and a narrow bottom,and the pressure in the saline layer decreases to some extent;After the injection of CO_(2)is stopped,the pressure of the saline water layer gradually decreases to the original formation pressure level,leading to the phenomenon of reverse displacement of CO_(2)by saline water;(2)With the desrease of the porosity of the formation,the formation pressure increases exponentially after CO_(2)is injected into the saline water layer,and the change of porosity affects the migration pattern of CO_(2);After the injection of CO_(2)is stopped,as the porosity of the saline layer increases,the reverse displacement phenomenon of saline water becomes more obvious,and the accumulation of CO_(2)at the top of the saline layer increases;(3)The increase in formation temperature enhances the reverse displacement effect of saline water,and the boundary angle of the tongue-shaped area increases duringCO_(2)migration;the lateral distribution range of CO_(2)at the top of the saline layer expands gradually;(4)The diffusion range of CO_(2)expands with the increase of the injection flow rate;Under the same injection flow rate,the diffusion rate of CO_(2)decreases with time;After the injection of CO_(2)is stopped,the lower the injection flow rate,the more obvious the reverse displacement phenomenon;(5)The simulation software developed has functional modules such as numerical model establishment and simulation data analysis,and the test results indicate the usability of the software.The research results can provide a theoretical and model basis for the selection of CO_(2)geological storage sites,optimization of injection conditions,and leakage monitoring.