Multiphase flows of high CO2 content fluids in the production stream of a Brazilian presalt field are analyzed during a transient (shut-in/restart) operation. Simulations were performed using the 1D gas-liquid module of LedaFlow®. PVT tables were generated for mixtures of 20–50% (molar) of CO2 and 300–600 Sm3/Sm3 of GOR through Multiflash® and an in-house routine. A validation against field data is made for the results regarding the 20% of CO2 and 500 Sm3/Sm3 of GOR mixture. Lastly, the effects of CO2 content for fixed GOR values on several important parameters, such as the upstream conditions of the choke valve, are presented and discussed.
The offshore exploitation of the pre-salt oil fields is one of the greatest technological challenges currently addressed by the Oil & Gas industry in Brazil. The ultra-deep waters, very deep reservoir layers, high pressures, high Gas-Oil Ratios (GOR) along with various flow assurance concerns represent major challenges for the transport of crude oils from the reservoirs to the platforms through production pipelines in the pre-salt fields (4,5). Furthermore, the produced crudes and gases present unusual high CO2 contents in their composition compared to oil fields from other locations (5). The following pre-salt fields from the Santos basin and their respective CO2 molar fractions confirm the previous statement: Sapinhoá (up to 17.5%) (14), Lula (up to 20%) (5), Libra (up to 44%) (1) and Júpiter (up to 79%) (7). Besides the high CO2 content, the Libra field, for example, also has a GOR of approximately 420 Sm3/Sm3. Both the CO2 content and the GORs are expected to increase with the reinjection of gas into the reservoir (as an Enhanced Oil Recovery, EOR, measure) (13).