On the integration of calcite scale management and operational optimisation of CCUS in Pre-salt carbonate reservoirs

In this thesis, we describe a simulation-based reactive transport workflow to optimise Carbon Capture Utilization and Storage (CCUS) in carbonate reservoirs. Although CCUS may play a crucial role in reducing greenhouse gas emissions, it does not come short of challenges. Here we focus on three of them: i) the economics, ii) carbon footprint and iii) inorganic scale, the latter being crucial when carbon dioxide (CO2) water-alternating-gas (WAG) is performed in reactive carbonate rocks. Our objective is to integrate reservoir engineering calculations, cash flow projections, carbon accounting and production chemistry to support field operational decisions. The analysis is made in the context of the Brazilian Pre-salt oilfields that have been pioneering deep-water CO2 utilization for Enhanced Oil Recovery (EOR) to avoid flaring. We used well-established optimisation techniques - statistical sampling and evolutionary algorithms - to identify CO2-EOR strategies with the highest potential to co-optimise profitability and CO2 storage, without triggering calcite deposition to the point of permanent jeopardy of production wells and facilities. Based on the production brine chemistry and flow rate forecasts, we assessed calcite scale risk and designed damage prevention strategies with the lowest cost of scale inhibitor “squeeze” treatment deployment. The methodology is presented through synthetic sector models and then applied to a field case for validation. We used deterministic models, but the impact of geological uncertainties on the outcomes is demonstrated using a set of representative models of the field case. The optimized CCUS strategies showed the potential to enhance profitability and offset operational emissions through adjustments of well operations, with limited additional investment. In addition, the mineral scaling assessment revealed how applying WAG schemes in carbonate reservoirs with considerable initial CO2 content will result in a lower calcite deposition risk compared to waterflooding. The proposed workflow provides valuable insights into the simulation and optimisation of CCUS projects with high calcite scaling risk. Its application demonstrated the importance of an integrated analysis that seeks to improve economic returns in a sustainable manner, with reduced production damage caused by CO2 speciation