Applying low-salinity water to alter wettability in carbonate oil reservoirs: an experimental study
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Applying low‑salinity water to alter wettability in carbonate oil reservoirs: an experimental study Erfan Hosseini1 · Zhongwei Chen2 · Mohammad Sarmadivaleh3 · Dana Mohammadnazar4 Received: 13 April 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract Seawater has been widely used as an injection fluid for maintaining pressure in sandstone and carbonate reservoirs. In the literature related to EOR research, it was noted that diluted seawater (low-salinity water) can highly improve recovery due to the specific ions (such as Ca2+, Mg2+, and S O42−). Such conclusions lead to the application of “Smart Water” in which changing the ion composition of injected water alters wettability and enhances recovery. Although many theories have been established to explain the mechanism of this phenomenon, almost all of them are limited to sandstone rocks, and the impact of smart water on carbonated reservoirs has rarely been explored. This study experimentally investigates the impact of the injection of high- and low-salinity and smart water on the change of wettability and recovery improvement in an Iranian South oil reservoir. Two different sets of experimental work were conducted. In the first set of experiments, the effect of formation water, diluted formation water (from 223,969 to 5000 ppm and 2000 ppm), seawater (initially 51,400 ppm), and diluted seawater on wettability alteration is investigated by monitoring the contact angle and relative permeability variation. The results showed that dilution of seawater to 2000 ppm has the most impact on wettability alteration. The relative permeability changed, and the contact angle decreased by a significant value of 100°, and recovery increased by about 71%. In the second set, the effect of ion change on the result was studied. For this purpose, the sulfate ion of diluted seawater (2000 ppm) is substituted by phosphate ion (H2PO4−). The results show the wettability alteration similar to the sulfate one. This study sheds light on the possible mechanism of wettability alteration in the carbonate reservoir, and the result will help to design a better low-salinity injection scenario. Keywords Wettability alteration · Contact angle · Relative permeability · Low salinity · Recovery Abbreviations FW Formation water SW Seawater TDS Total dissolved solids (mg/l) LowSal Low-salinity water SW5000 Seawater diluted to TDS = 5000 mg/l
* Erfan Hosseini [email protected] 1
Department of Petroleum Engineering, Sarvak Azar Engineering, and Development (SAED) Company, Oil Industries Engineering and Construction (OIEC) Group, Tehran, Iran
2
School of Mechanical and Mining Engineering, Queensland University (UQ), Brisbane, Australia
3
Department of Petroleum Engineering, Curtin University, Perth, Australia
4
Department of Polymer Chemistry, Islamic Azad University, Shahreza, Iran
SW2000 Seawater diluted to TDS = 2000 mg/l FW5000 Formation water diluted to TDS = 5000 mg/l FW2000 Formation water diluted to TDS = 2
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