This work presents a thermodynamic analysis of carbon dioxide (CO2) capture and reinjection processes, which have become indispensable for oil and gas production, particularly in the Brazilian offshore pre-salt fields. In comparison to the Brazilian post-salt reservoir, the petroleum from the Santos Basin pre-salt reservoir has a much larger CO2 content, which can exceed 15 percent, as opposed to less than 1 percent in the post-salt case. This peculiarity demands more complex operational equipment and processes that: (i) separate the CO2 from the produced gas; (ii) compress both the CO2 and low content CO2 natural gas streams and (iii) direct them to their subsequent destinations (reinjection, gas lift, exportation etc.). Consequently, these new capture and injection processes increase the energy demand on these production units. The present study aims to describe the processes involved in the CO2 capture and reinjection, since there is a lack of references in the literature about these new techniques and technology. Furthermore, it contributes to the evaluation of the additional energy consumption of an offshore Floating, Production, Storage and Offloading unit (FPSO), due to the inclusion of processes related to the capture and reinjection of CO2. Finally, a brief analysis is made on the environmental impact from these processes, considering the additional emission of atmospheric pollutants such as CO2 and CH4.