Abstract
Tuning the salinity and concentration of potential-determining ions, such as Mg2+, Ca2+, and SO42−, could alter the wettability toward a more water-wet state. The rate of alteration in carbonate rock wettability is a critical parameter to design the duration of the ion-engineered water flooding. Characteristic experiments, such as dynamic contact angle and pH measurements, ion chromatography, and spontaneous imbibition, are applied to study the rate of wettability alteration using different samples of ion-engineered water. Our study shows that the Caspian Sea water (CSW) with a salinity of 15,000 ppm is an efficient displacing fluid as it can initiate the multi-ion exchange (MIE) mechanism and alter the wettability from 86° to 35° within 2 d. The adjustment of salinity and active ion concentration makes the MIE mechanism much faster. For example, with five times diluted CSW, the same change in wettability is only achieved only within 9 h. Spiking the concentration of Ca2+ and SO42− ions is used to further shift the contact angle to 22° within 9 h. Spontaneous imbibition tests demonstrate that the rate of oil production doubles as a result of the ion-engineered brine due to the faster MIE process. The results obtained from this research work suggest that even a short period of interaction with optimized engineered water can affect the brine, oil, and carbonates interactions and change the reservoir rock initial wettability from neutral to strongly water-wet state. This allows to efficiently design engineered water flooding based on CSW in the field scale and make such projects more profitable.
Highlights
The availability of formation brine, its nonnegative impact on the reservoir, ease of injection, and small capital and operational costs make water flooding projects attractive to be applied for many years as secondary recovery methods
The development of low-salinity water flooding (LSW) methods by altering the salinity of the injected water became attractive for carbonates when the first unexpected high oil recovery from the chalk reservoir at the Ekofisk field in the North Sea was produced (Al-Shalabi and Sepehrnoori 2016)
The impact of the adjustment of potential-determining ions (PDIs) ( SO24−, Ca2+, and Mg2+ ) in Caspian Sea injection water to develop an optimized ion-engineered brine and water to affect the rate of wettability alteration in carbonate formations was studied
Summary
The availability of formation brine, its nonnegative impact on the reservoir, ease of injection, and small capital and operational costs make water flooding projects attractive to be applied for many years as secondary recovery methods. The development of low-salinity water flooding (LSW) methods by altering the salinity of the injected water became attractive for carbonates when the first unexpected high oil recovery from the chalk reservoir at the Ekofisk field in the North Sea was produced (Al-Shalabi and Sepehrnoori 2016) Another term frequently used in LSW methods is ion-engineered brine, a brine in which the ion composition is changed by adding different salts. One of the best examples of utilizing low-salinity water was a study carried out by Webb et al (2005) They observed a reduction in residual oil saturation from 0.14 to 0.10 by increasing the concentration of sulfate ions in the injection brine. They observed incremental 9% and 5.1% oil recovery with spiked concentration of sulfate in the dolomite and limestone cores, respectively
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