CAUSES OF ABNORMALLY LOW PRESSURE AT BRAVO DOME AND ITS IMPLICATIONS FOR CARBON CAPTURE AND STORAGE (CCS)

The Bravo dome field in northeast New Mexico is one of the largest gas accumulations worldwide and the largest natural CO₂ accumulation in North America. The field is only 580-900 m deep and Sathaye et al. (2014) estimated that 1.3 Gt of CO₂ is stored in the reservoir. The reservoir is divided in to several compartments with near gas-static pressure. The pre-production gas pressures in the two main compartments that account for 70% of the mass of CO₂ stored at Bravo Dome are more than 6 MPa below hydrostatic pressure.

Common explanations for abnormally low pressures include erosional unloading (Neuzil and Pollock 1983), regional groundwater circulation through low permeability beds (Senger et al. 1987), and cooling (Barker 1972) cannot explain the observed low pressure. Here we introduce the dissolution of CO₂ into the brine as a new process that can reduce gas pressure in a compartmentalized reservoir. This research suggests that erosional unloading, cooling of volcanic CO₂, and dissolution of CO₂ into brine can only explain 5%±1%, 14%±4%, and 14%±3% of the total pressure drop, respectively. This suggests that CO₂ dissolution may contribute significantly to reduce the initial pressure build-up due to injection. Our results also imply that the formation was already significantly below hydrostatic pressure before the CO₂ was emplaced and that abnormally low-pressured formations should be primary targets for geological CO2 storage.