INFLUENCE OF GEOCHEMICAL PROCESSES ON THE GEOMECHANICAL RESPONSE OF THE OVERBURDEN DUE TO CO2 STORAGE IN SALINE AQUIFERS
咸水层是适合大量储存二氧化碳的理想地质构造。虽然上覆的非渗透盖层为注入的二氧化碳实现了主要构造捕集，但其他捕集方式，如溶解捕集、残余气捕集、离子或矿物捕集，也是封存二氧化碳重要机制。地球化学反应改变了目标储层的岩石物理性质，如孔隙度，并可能影响储层的储集能力。当长时间注入CO2时，它会改变流体压力和覆盖层的地质力学响应。时间相关地球化学反应与地质力学响应相关联，并可能影响盖层的完整性和长期注入的注入CO2分布。
本文研究了长期（1000年）向深层含水层大量注入二氧化碳（每年高达1000万吨）的多相流动、地球化学反应及地质力学多场耦合模拟。主要目的是研究长期CO2注入期间地球化学反应对覆盖层地质力学响应的影响。地球化学模拟结果表明，矿物溶解和沉淀等地球化学反应对储层岩石孔隙度没有显著影响（减少约2%）。然而，矿物反应速率常数的增加导致岩石孔隙度降低约35%。
模拟结果表明，地质力学模型中的地球化学反应对注入期间和注入后期计算的地面位移没有显著影响。然而，盐水矿化度和CO2溶解度对CO2注入期间计算的压力累积和地面位移有影响。在文研究了井筒周围垂向渗透带（伤害带）对长期CO2注入过程中CO2泄漏的影响。模拟结果表明，伤害区渗透率和伤害区的垂向范围对CO2泄漏量有显著影响。模拟结果还表明，伤害区的垂直范围对计算的地面位移没有显著影响。因此，计算的地面位移可能不是井筒周围伤害区范围的良好指标。
西弗吉尼亚大学 博士论文
Modeling results show that the inclusion of geochemical reactions in the geomechanical models does not have a significant influence on the computed ground displacements during the injection and post-injection periods. However, brine salinity and CO2 solubility have an influence on the computed pressure buildup and ground displacements during CO2 injection. In this study, the influence of a vertical permeable zone (damage zone) around the wellbore on CO2 leakage during long-term CO2 injection was investigated. Modeling results show that the damage zone permeability and the vertical extent of the damage zone have a significant influence on the amount of CO2 leakage. Modeling results also show that the vertical extent of the damage zone does not have a significant influence on the computed ground displacements. Therefore, the computed ground displacements may not be a good indicator of the extent of damage zone around the wellbore.
Saline aquifers have been identified as desirable geologic formations, suitable for the storage of carbon dioxide (CO2) in large amounts. While the impermeable caprock layer(s) in the overburden provide(s) the primary trap for injected carbon dioxide, other trapping mechanisms, such as solubility, residual, ionic or mineral trapping, help contribute to CO2 storage. Geochemical reactions alter the petrophysical properties such as porosity in the target reservoir, and may have an influence on the reservoir storage capacity. When CO2 is injected for long periods of time, it changes the fluid pressures and the overburden geomechanical response. The geomechanical response associated with time-dependent geochemical reactions may also influence the integrity of the caprock layer and the long-term fate of injected CO2.
In the current study, coupled multiphase fluid flow and geomechanical modeling with geochemical reactions was performed to simulate the long-term (1,000 years), large-scale injection of CO2 (up to10 million metric tons per year) into a deep saline aquifer. The primary objective of the study is to investigate the influence of geochemical reactions on the geomechanical response of the overburden during long-term CO2 injection. The geochemical modeling results show that geochemical reactions, such as mineral dissolution and precipitation, do not have a significant influence on reservoir rock porosity (about 2% reduction). However, an increase in the mineral reaction rate constants resulted in a reduction of about 35% in rock porosity. Modeling results show that the inclusion of geochemical reactions in the geomechanical models does not have a significant influence on the computed ground displacements during the injection and post-injection periods. However, brine salinity and CO2 solubility have an influence on the computed pressure buildup and ground displacements during CO2 injection. In this study, the influence of a vertical permeable zone (damage zone) around the wellbore on CO2 leakage during long-term CO2 injection was investigated. Modeling results show that the damage zone permeability and the vertical extent of the damage zone have a significant influence on the amount of CO2 leakage. Modeling results also show that the vertical extent of the damage zone does not have a significant influence on the computed ground displacements. Therefore, the computed ground displacements may not be a good indicator of the extent of damage zone around the wellbore.
