(147c) Chemical Impacts of CO2 Intrusion into Heterogeneous Caprock

Carbon capture, utilization, and storage (CCUS) is considered one of the most practical options for reducing CO₂ emissions from stationary sources. Particularly, CO₂-enhanced oil recovery (CO₂-EOR) with CO₂ injected into oil reservoirs is a well-established and relatively mature technology that offers potential economic benefits of increasing oil production and reducing costs of CO₂ storage. Sealing formation (caprock) integrity is considered as a key risk factor, because of the potential for leaked CO₂ or brine to migrate into shallow groundwater formations. The purpose of this work is to evaluate the long-term caprock sealing capacity and effects of caprock hydrological heterogeneities on CO₂ migration. The Farnsworth Unit (FWU), an oilfield in the northern Anadarko Basin in Texas undergoing active CO₂ enhanced oil recovery (EOR) is selected as a case study. A two-dimensional reactive transport model of the caprock (Morrow Shale and Thirteen Fingers) of the FWU was developed based on the site geological model. Specific objectives of this study include: (1) to understand how CO₂ is likely to influence the caprock integrity; and (2) to analyze the effects of caprock heterogeneity that control CO₂ migration and CO₂-water-rock interactions.

Heterogeneities in permeability and porosity could significantly affect containment of intruded CO₂ within the caprock. Key results of analysis include forecasted spatial and temporal CO₂ distribution in caprock near injection wells, because the pressure and CO₂ saturation tend to be the highest over the reservoir. The risk of CO₂ leakage through the caprock is evaluated, and mineral alteration of the caprock and self-sealing effects are assessed.