Simulation of Enhanced Oil Recovery in Pre-Salt Reservoirs: The Effect of High CO2 Content on Low Salinity Water Alternating Gas Injection

Abstract

The high CO2 content of Brazil’s pre-salt fields, which may reach values from 20% to 44% molar, presents both a challenge as well as an opportunity. CO2 stripped from the produced gas cannot be released into the atmosphere due to environmental restrictions. Therefore, the whole amount of CO2 produced should be continuously reinjected into the reservoir. This work investigates the effect of CO2 content on the low salinity water alternating CO2 injection technique (CO2LSWAG) using a commercial compositional reservoir simulator. In these field-scale simulations, CO2 is stripped from the produced gas and reinjected into the reservoir. Primary oil recovery methods such as CO2 flooding and LSW flooding are also simulated. Chemical reactions between CO2 and the minerals present in the reservoir are modeled. Wettability change is assumed to be the main mechanism for improved oil recovery due to low salinity water injection. Compositional simulations of CO2 injection usually assume a constant injected gas rate. In this case, CO2 is supposed to come from an external source. In many petroleum reservoirs this assumption is true. Three factors are assessed in the present work. The first one is the natural reservoir pressure, which is the main driving force in primary production. The second factor is the amount of CO2 available for injection. The third one is the wettability change promoted by the reaction involving CO2. It is shown that in primary production, higher CO2 content leads to quicker depletion of the natural energy of the reservoir, leading to lower oil recovery. Nevertheless, higher CO2 content also means that more gas is available for reinjection, potentially leading to increased oil production. Finally, as CO2 reacts with minerals it promotes a change in wettability from an oil-wet to a water-wet state. It is shown that the CO2 content is an important variable to be assessed in a high CO2 content reservoir. Optimal injection practices must take these three aspects into consideration.

Phase Transitions and Separation Time Scales of CO2–Crude Oil Fluid Systems: Wheel Flow Loop Experiments and Modeling

“…Furthermore, CO 2 can be directly available from associated gas during production such as for the presalt reservoirs in the Santos Basin in Brazil , and in the Neuquen province in central Argentina, which contains as much as 45–75 mol % CO 2 in the produced gas. , In some Brazilian presalt fields, the approximate CO 2 molar fractions are 17.5% (associated gas) in the Sapinhoá field, 44 mol % (associated gas) in the Libra field, and 55 mol % (oil) and 79 mol % (gas cap) in the Júpiter field . Reinjection of CO 2 for EOR is considered attractive for some Brazilian presalt fields but is expected to increase the CO 2 concentration and GOR in production fluids in the future …”

“…9 Reinjection of CO 2 for EOR is considered attractive for some Brazilian presalt fields 4 but is expected to increase the CO 2 concentration and GOR in production fluids in the future. 10 1.2. Some Challenges Related to CO 2 Rich Fluids.…”

Salt Precipitation and Cement Degradation During Co2storage: A Brief Review

“…Most of these processes are very expensive, nevertheless CO2 captured by these processes can be used to recycle CO2 and produce new products that aggregate values and can be sold transforming such technologies economically feasible [7]. Whilst the aforementioned processes do not become practicable, many companies, mainly oil companies have used their own technologies to store CO2 in aquifer or depleted oil reservoirs, to recover additional oil using CO2 as a tertiary recovery method [8], or in case of unconventional scenarios, as shales gas in USA, CO2 has been used as a working fluid to efficiently fracture the reservoir [9], or in Brazil's pre-salt fields, where the content of CO2 can reach up to 44%, the produced CO2 is directed reinjected into the same reservoir to solve simultaneously two problems, CO2 releasing to atmosphere and enhanced oil recovery (EOR) [10]. Despite the oil industries have been using CO2 injection for more than 20 years, they are still facing different challenges [11].…”