碳封存区块内弃置井泄露机制及控制方法模拟

Simulation Study of Sealing Integrity in Abandoned Wells Within CO_(2) Sequestration Block

弃置井筒作为CO_(2)地质封存中的主要泄露途径,其密封完整性直接关乎封存效果。为此,针对弃置井筒泄露问题,基于耦合孔隙压力的Cohesive单元法,建立了三维水泥塞-地层有限元模型,模拟了CO_(2)沿弃置井筒运移过程,分析了水泥浆体系、胶结质量对泄露风险的影响。模拟结果表明:CO_(2)聚积会诱发水泥塞-地层界面微环隙,形成泄露通道,且微环隙倾向于轴向发育;选择高模量、高泊松比、微膨胀性水泥密封井筒时,井筒泄露风险低;微环隙对胶结质量极为敏感,密封井筒时应重点控制胶结质量。研究结果对指导碳封存区块内井筒弃置具有重要意义。

As the main leakage pathway in CO_(2) sequestration,the sealing integrity of the abandoned wellbore is directly related to the sequestration effect.To this end,for the abandoned wellbore leakage problem,a three-dimensional finite element model of cement plug-formation is developed based on the cohesive zone method coupled pore pressure.In this paper,we simulated the CO_(2) transport process along the abandoned wellbore and analyzed the influence of cement slurry system and bonding quality on the risk of leakage.The simulation results show that:CO_(2) accumulation induces micro-annulus at the plug-formation interface,forming a leakage channel,and the micro-annulus tends to develop axially;the risk of wellbore leakage is lower when choosing higher modulus,higher Poisson's ratio,and micro-expansion cement to seal the wellbore;the micro-annulus is extremely sensitive to the poor bonding zone,and the control of bonding quality should be focused when sealing the wellbore.The results of this study have important implications for guiding wellbore abandonment within the CO_(2) sequestration block.