Optimum salinity/composition for low salinity water injection in carbonate rocks: A geochemical modelling approach
Journal of Molecular Liquids
School of Engineering
European Research Council (ERC) - MILEPOST project (Grant agreement no.: 695070) under the European Union’s Horizon 2020 research and innovation program
The brine-dependent recovery process mainly known as low salinity/ smart water injection (LSWI/SWI) is of great interest to the oil industry for enhanced oil recovery (EOR), especially for carbonate reservoirs due to their complex rock properties. In-depth understanding of fluid/ carbonate rock interactions helps to better understand carbonate reservoirs’ behavior with respect to low salinity water injection. Mineral dissolution/ precipitation and multi-ion exchange (MIE) are generally known to be key factors in brine/ carbonate interactions, controlling the rock wettability and consequently the performance of low salinity water injection. However, the effect of the aforementioned mechanisms is not fully understood. In this paper we investigate the carbonate/ brine interactions, using geochemical modelling, and study the competition between all active mechanisms which results in an optimum point in water salinity. This optimum point is the best salinity of injected water, leading to the most effective alteration in the wettability towards the water-wet conditions. The simulation outputs are then validated against experimental results previously reported. Finally, a sensitivity analysis of the potential determining ions (PDIs) e.g., calcium, magnesium, and sulfate is performed to systematically understand the effect of each ion on optimum water salinity. Generally, for rocks containing anhydrite, both MIE and dissolution curves have a monotonous trend. However, for free-anhydrite rocks, MIE considered as the dominant mechanism controlling the performance of low salinity water injection. MIE mechanism mainly depends on CaSO4- surface concentration and as sulfate concentration increases a higher fold of dilution would result in a better performance of LSWI. However, calcium and magnesium have not shown significant influence on the dissolution and MIE mechanisms.