Evaluation of Geo-Mechanical-Chemical Impacts of Co2 Injection to Depleted Oil Reservoirs

This paper presents a more holistic approach in evaluating the impacts of CO2 injection in CO2 sequestration operations in a depleted Morrow B sandstone of the Farnsworth Unit, Ochiltree County, Texas. The complex interactions between CO2 and the formation fluids (oil and brine) and the acidized brine interactions with formation rock when coupled with mechanical processes present an integrated and realistic effect of CO2 injection in the underground environment. In light of this, different coupled numerical simulation models were developed to investigate the various CO2 trapping mechanisms and the long-term fate of CO2 in a depleted Morrow B sandstone. The models include hydrodynamical model, coupled hydrodynamical-mechanical model, coupled hydrodynamical-chemical model, and coupled hydrodynamical-chemical-mechanical model. A WAG operation was carried out for 20 years after the history period and followed by a post-injection period of 1000 years to monitor and evaluate the effect of the injected CO2 on the underground environment. This work shows that geomechanics impacted the petrophysical properties of the reservoir and had significant impact on the injectivity of CO2. The chemical reactions had very little impact on the petrophysical properties of the reservoir. The different simulation scenarios resulted in variable amounts of storage within the partially depleted oil reservoir.