The use of adjusted/optimized saline water categorized into two different classes namely smart water (SW) and low salinity (LoSal) water injection has been proposed for more oil recovery from specific types of oil reservoirs. There are possible mechanisms concerning SW flooding that have been proposed in the literature, some of them are still subject to more examination. In this study, an experimental investigation is performed to determine the influence of type and amount of salt to the surface properties including interfacial tension (IFT) and contact angle (CA) of aqueous solution + acidic and asphaltenic crude oil + carbonate rock systems. For this purpose, the concentration of different salts including NaCl, KCl, Na2SO4, MgSO4, CaSO4, CaCl2, and MgCl2 are examined in a wide range of concentrations. The measurements revealed that salinity has dual impacts on the CA of water wet surfaces of carbonate rock. That is, CA could remain unchanged or increase as a function of brine salinity, though the increase was still within the strongly water-wet region of wettability with high film stability. The results of IFT measurements show that using ions especially divalent cations in the presence of chloride anion could substantially decrease the IFT values. The results show that the lowest IFT values are obtained at high salinity conditions (above 0.053 mol·kg–1) especially if divalent ions of MgCl2 are utilized. High values of IFT are obtained if monovalent salts such as NaCl and KCl are used.

It has been already well established that adjusting the salinity of displacing fluid critically affects the oil recovery efficiency during secondary and tertiary oil recovery processes. In this investigation, systematic experiments are designed and conducted to find the effects of both low and high salinity water on the surface properties of crude oil−brine/solid surfaces. In this respect, the effects of the major salts including NaCl, CaCl 2 , and MgCl 2 are tested in the concentration range of 0−45 000 ppm on fluid/solid and fluid/fluid interactions for a crude oil/water/rock system. Two main surface properties including contact angle and interfacial tension (IFT) are measured using a pendant drop apparatus. The obtained results demonstrate the critical effects of heavy oil components on the interfacial properties. High film stability in some cases resulted in small contact angle changes, mostly in the range of the strongly water wet condition, for different brine salinity.

Carbon dioxide (CO 2 ) injection is a well-established method for increasing recovery from oil reservoirs. However, poor sweep efficiency has been reported in many CO 2 injection projects due to the high mobility contrast between CO 2 and oil and water. Various injection strategies including gravity stable, WAG and SWAG have been suggested and, to some extent, applied in the field to alleviate this problem. An alternative injection strategy is carbonated water injection (CWI). In CWI, CO 2 is delivered to a much larger part of the reservoir compared to direct CO 2 injection due to a much improved sweep efficiency. In CWI, CO 2 is used efficiently and much less CO 2 is required compared to conventional CO 2 flooding, and hence the process is particularly attractive for reservoirs with limited access to large quantities of CO 2 (offshore reservoirs or reservoirs far away from inexpensive natural CO 2 resources). This article describes the results of a pore-scale study of the process of CWI by performing high-pressure visualisation flow experiments. The experimental results show that CWI, compared to unadulterated (conventional) water injection, improves oil recovery as both a secondary (before water flooding) and a tertiary (after water flooding) recovery method. The mechanisms of oil recovery by CWI include oil swelling, coalescence of the isolated oil ganglia and flow diversion due to flow restriction in some of the pores as a result of oil swelling and the resultant fluid redistribution. In this article the potential benefit of a subsequent depressurisation period on oil recovery after the CWI period is also investigated.

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