Name: RAFAEL DE PAULA COSMO
Publication date: 21/11/2022
Advisor:
Name |
Role |
|---|---|
| EDSON JOSE SOARES | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| EDSON JOSE SOARES | Advisor * |
| FABIO DE ASSIS RESSEL PEREIRA | Co advisor * |
| RENATO DO NASCIMENTO SIQUEIRA | Internal Examiner * |
Summary: Precipitation and scaling are recurring problems in many water-handling processes. In oil production, particularly, such occurrences are critical due to the unfeasibility or extreme difficulty of remediating precipitation or removing scale. This is due to adverse operating conditions: high pressures and temperatures, the action of corrosive gases such as CO2 and H2S, high salinity, and confined system in a rocky medium. Pre-Salt carbonate reservoirs are notable for the high CO2 content in their fluids, with this acid gas being a variable that affects several stages of the exploration process. The relationship between CO2 and calcium carbonate (CaCO3) is evident in the reaction Ca2+(aq) + 2 HCO3(aq) ⇆ H2O + CaCO3(s) + CO2(aq). The pressure drop inherent to the production degass the CO2 (CO2(aq) → CO2(g)), which shifts the equilibrium to the right and implies the formation of CaCO3(s). An applied review of the role of CO2 in precipitation, considering the water, oil and gas phases, was carried out with field data from the Pre-Salt. Likewise for the aqueous, the oily CO2 degass (CO2(o) → CO2(g)) and also implies more CaCO3, with the partitioning of the CO2 between phases governing the phenomenon. An experimental procedure was developed to quantify the CaCO3 that precipitates directly due to pressure and temperature variation and that which precipitates indirectly due to the escape of CO2(aq), allowing the estimation of the weight of the CO2 degassing in the CaCO3 precipitation. An experimental prototype was designed and built so that this procedure can, in the near future, be actually investigated. In addition, the unit will allow the research of several other phenomena related to flow assurance. Simulations of the procedure were carried out with a thermodynamic software for an H2OCO2CaCO3 system, indicating that the CO2 escape contributes with 55% to 93% of the precipitation. The software includes, in addition to the thermodynamics of aqueous solution, the interaction with oil, gases and several other solids, which allows simulating real cases. Five geothermal energy production assets around the world that report problems with carbonate precipitation have been investigated. As a result, the CO2 flash contributes 66% to 93% of the CaCO3 precipitation. In simulations with real data from a Pre-Salt field the results were similar, but indicated sui generis behaviors of the influence of the CO2 with the variation of the BSW. Such discoveries correspond to operational problems faced in many oilfields and may help to explain their still unknown causes. In order to validate the experimental prototype, some qualitative experiments were carried out, including the precipitation of the CaCO3 in the presence of CO2 and oil from the Pre-Salt of 29 °API, with the capture of in situ photomicrographs of the crystals and oil drops, at 60 °C and 50 bar.
