Chemical‐Mechanical Impacts of CO2 Intrusion Into Heterogeneous Caprock

Abstract

AbstractThe potential economic benefits offered by CO2‐enhanced oil recovery (CO2‐EOR) and storage, including increasing oil production and mitigating CO2 storage cost, make it an attractive approach for reducing CO2 emissions. Sealing formation (caprock) integrity is considered a key risk factor, because of the potential for leaked CO2 or brine migrating into shallow groundwater formations. The primary purpose of this research is to evaluate general caprock sealing efficiency and integrity under typical CO2‐EOR conditions, by assessing the influence of hydrological and mineralogical heterogeneity, possible mineralogical alteration, and potential failure of rock due to hydrological and mineralogical changes. An active CO2‐EOR project at the Farnsworth Unit (FWU) in the northern Texas is selected as a case study. A coupled reactive‐transport‐geomechanics model of the FWU caprock (the Morrow Shale and the Thirteen Fingers Limestone) was developed based on site‐specific geological data. Key results suggest that the Thirteen Fingers Limestone is an effective caprock. After 5,000 years, effectively no supercritical CO2 penetrates this formation, and the penetration depth of dissolved CO2 in aqueous phase does not exceed 10 m. Because of mineral precipitation in the Morrow Shale, maximum porosity decreases ~25% at the reservoir‐caprock interface, suggesting increased caprock sealing efficiency. Geomechanical response of the caprock due to CO2 intrusion and mineral alteration suggests low risk of induced fractures. This study provides a refined evaluation of long‐term caprock integrity as a function of coupled hydrological, chemical, and geomechanical processes and is intended to support future assessment of feasibility and safety of geologic CO2 sequestration.