Debottlenecking a Compression System, Handling CO2-Rich Stream, to Increase CCUS and Reduce GHG Emissions

Floating Production, Storage, and Offloading units (FPSOs) play a crucial role in offshore Oil & gas production. Among the various systems that may compose an FPSO Gas Plant, the CO₂ compression system holds a vital importance, both from an operational and environmental standpoint, by enabling CO2 to be reinjected into reservoir instead of releasing it to atmosphere. This reinjected CO2 helps on reservoir pressure support, which enhances long term oil production. A disadvantage of this strategy would be an eventual return of CO2 through production fluids in case CO2 migrates within reservoir and reaches out to production wells. In Brazil’s pre-salt area, FPSOs have been deployed in deep water region, above 2000 meters of water depth. A FPSO, deployed in such area and pioneer in Carbon Capture and Utilization (CUUS), is expected to gradually handle more CO2 content from production fluids following a long period of CO2 reinjection. There is an opportunity to Debottlenecking CO2 Compression System, allowing more CO2-rich stream to be reinjected. Originally, the CO₂ compression system was designed for a capacity of 0.5 MMSm3/d, 308bar.g discharge pressure and an original [CO₂] range between 83.2% and 90.4%. Considering that compressor is centrifugal-type, heavier gas will allow achieving higher compression ratios and flow rates with existing impellers Thus, to enhance CCUS capacity, it is possible to increase the flow rate of the CO₂ Compression System, if the gas molecular weight (MW) can be kept at heavier range. An additional capacity increase can be achieved by reducing discharge pressure. This improvement is feasible when higher MW (which is consistent with higher [CO2]) is kept and taking advantage of reduced top-of-riser pressure. This paper will address the challenges and solutions related to increasing the capacity of centrifugal compression system handling CO2-rich streams. The reliability of such compression system is critical for reducing Greenhouse Gas (GHG) emissions, while prolonging Oil & Gas production in this field.