Abstract

Pre-existing faults cross-cutting caprock formations constitute potential leakage pathways during geological CO₂ sequestration. When the fault filling material is calcite-rich, dissolution of the fault minerals is expected to occur causing the mechanical weakening of the fault or, even worse, its reactivation. In turn, these chemical-mechanical processes influence the distribution of pore pressure in the vicinity of the fault. Hence, a fully coupled approach including the chemically-induced alteration is necessary while investigating fault’s mechanical stability.

In this paper, we present a simplified set of equations that allows the resolution of the coupled hydro-chemo-mechanical problem of reactive fluid flow inside a fault. Empirical relationships are used to describe the change of the fault’s material mechanical properties with porosity. The derived model was used to simulate the evolution of the hydro-chemo-mechanical behavior of a fault following an expected leakage scenario during CO₂ storage in the Dogger formation in the Paris Basin.

The simulation results showed that under normal conditions, fault reactivation is unlikely to happen even in the long term (∼100 years). Nevertheless, the proposed model is capable of capturing the evolution of fault reactivation and has the potential to become a useful element of the toolbox for assessing the risks related to fault reactivation and leakage for CO₂ storage projects.

摘要

先前存在的断层横穿盖层地层构成了地质CO ₂固存过程中的潜在泄漏途径。当断层填充材料富含方解石时，预计会发生断层矿物的溶解，从而导致断层的机械弱化，或更糟糕的是其再活化。反过来，这些化学-机械过程会影响断层附近孔隙压力的分布。因此，在研究断层的机械稳定性时，必须采用包括化学诱导变化的完全耦合方法。

在本文中，我们提出了一组简化的方程组，该方程组可以解决故障内部反应流体的耦合水-化学-机械问题。经验关系用来描述断层的材料机械性能随孔隙度的变化。派生模型用于模拟在巴黎盆地Dogger地层中CO ₂封存过程中，在预期的泄漏情况之后，断层的水化学力学行为的演变。

仿真结果表明，在正常条件下，即使在长期（约100年）内也不太可能发生故障重新激活。然而，所提出的模型能够捕获故障再激活的演变，并有可能成为评估与CO ₂储存项目的故障再激活和泄漏相关的风险的工具箱的有用元素。