A Future Pathway for CO2 Geological Storage (CCS) in the Offshore Pre-Salt of Santos Basin

Abstract

Abstract Carbon Capture Utilization and Storage (CCUS) operations in the Pre-salt Santos basin oil fields should injected, by 2025, a total of 80 million tons of CO2, as additional production units enter operation. This stands as one of the largest CCUS projects in the world, since the CO2 originally dissolved in the oil is reinjected as an Enhanced Oil Recovery method. The infrastructure already placed in the Pre-salt, the characteristics of the reservoirs, the continuous technological advances and the acquired experience, allow us to glimpse a future scenario in which current CCUS operations will open opportunities for strict CCS (Carbon Capture and Storage) projects disposing of anthropogenic CO2. This paper aims to discuss the long-term perspectives for CCS projects in Brazil taking as a case study a hypothetical Pre-salt field, inspired on a real one, resulting in a preliminary estimate of CO2 storage capacity. The text encompasses an overview of the CO2 sources in Brazil, a review of the main mechanisms of CO2 entrapment in porous media and a summary of the technical requirements for proper injection and permanent CO2 underground storage. Sound reasons may justify the future exhausted/depleted Pre-salt fields as a scenario for CCS projects: reservoirs with large storage and sealing capacity, good injectivity, presence of infrastructure of wells and pipelines (production units will probably need to be replaced in the long term), among others. We propose a workflow, based on material balance, to reach a preliminary estimate of the CO2 mass that could be stored in the field case study. The adopted procedure uses publicly available data and assumes parameters for total reservoir compressibility, reservoir pressure and CO2 water solubility in formation brine. The exercise carried out for the case study, admitting the field at the end of its producing stage, pointed to a CO2 storage capacity of around 26 million tons trapped under the mechanisms of structural imprisonment in porous medium and dissolution of CO2 in brine. The obtained results highlight the vocation of the present Pre-salt oil fields as an important player for future CCS initiatives.