Safe and permanent carbon geological storages require an elaborate analysis of geomechanical stability. Subsurface injection of CO₂ changes the local temperature and pore pressure and, further, alters the stress due to thermo-poro-elastic responses.

A permanent CO₂ storage testing was conducted in the water leg of Cranfield reservoir in Mississippi, USA, where hosted CO₂ enhanced-oil recovery activities. During CO₂ injection, the injection rate was ramped up twice but the bottom-hole pressure did not increase with the imposed injection rates as expected. This unexpected field observation suggests the possibility of an open-mode fracture development at the injector. However, the injector response and potential fracture development have not been rigorously interpreted with detailed near-wellbore temperature and pore pressure change upon the CO₂ injection.

In this study, we performed history matching of CO₂ injection using coupled thermo-poro-elastic reservoir simulation to examine the possibility of fracturing. We built a reservoir model including vertical heterogeneity in both petrophysical and geomechanical properties estimated from well-logging analysis and laboratory experiments.

The simulation results show that CO₂ injection changes stresses and support the hypothesis of development of an open-mode fracture at the injector during the Cranfield test. The near-injector region exhibits a large temperature reduction up to 55 °C with ensuing effective horizontal stress reduction up to 9.1 MPa. However, a caprock integrity issue is unlikely because of the horizontal stress contrast within layers and low hydraulic communication with the injection zone.

This study indicates that the injectant temperature should be considered in the design of high-rate CO₂ injector.

安全和永久的碳地质储藏需要对地质力学稳定性进行详尽的分析。地下注入CO _2会改变局部温度和孔隙压力，并进一步改变由于热-孔隙-弹性反应引起的应力。

在美国密西西比州克兰菲尔德水库的水段进行了永久性的CO ₂储存测试，在该处进行了CO ₂强化采油活动。在注入CO ₂期间，注入速率增加了两倍，但井底压力并未随预期注入速率的增加而增加。这种出乎意料的现场观察表明，在注入器处可能发生开模裂缝。然而，在详细的近井眼温度和CO ₂注入时的孔隙压力变化方面，尚未严格解释注入器的响应和潜在的裂缝发展。

在这项研究中，我们使用耦合的热-孔隙-弹性储层模拟进行了CO ₂注入的历史匹配，以检查压裂的可能性。我们建立了一个储层模型，包括通过测井分析和实验室实验估算的岩石物理和地质力学特性的垂直非均质性。

模拟结果表明，在Cranfield测试期间，CO ₂注入改变了应力并支持了在注入器处发生开式裂缝的假设。靠近喷油嘴区域的温度下降幅度最大，可达55°C，而有效的水平应力减小幅度高达9.1 MPa。但是，由于层内的水平应力对比以及与注入区的低水力连通，盖层完整性问题不太可能出现。

这项研究表明，在设计高速率CO ₂喷射器时应考虑喷射温度。