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Micromodel Investigation of the Non-Monotonic Effect of Injection Water Salinity on Wettability and Oil Recovery

Karimpour Khamaneh, Mehran | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55130 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan
  7. Abstract:
  8. Based on numerous laboratory and field evidence, low-salinity waterflooding or engineered salinity waterflooding can lead to enhanced oil production. According to the literature, the mechanisms involved in this process can be divided into two general categories: fluid-fluid interactions and solid-liquid interactions. These mechanisms are caused by intermolecular and electrostatic forces at the rock and fluid interfaces. The most important controlling factor of the electrostatic forces is the concentration of ions at/near fluids-rock interface. Therefore, improving the concentration of ions causes a shift in wettability toward a more water-wetting state, eventually leading to increased oil recovery. Recent studies have focused more on the fluid-fluid interface and suggested that in the presence of low-salinity water, the oil-brine interface becomes more elastic.For deeper understanding of the effect of fluid-rock and fluid-fluid interactions, and their time-scale of action, in this thesis, the behavior and trend of some important and effective phenomena in low salinity EOR have been thoroughly investigated as a function of salinity or salt concentration in the brine. These phenomena include wettability, oil-water interfacial tension (IFT), and the coalescence behavior and time of oil droplets. The collective or resultant effect of these phenomena on the efficiency of oil recovery by low-salinity water was studied using microfluidics technique. The micromodels were made of glass and initialized with oil and brine. Four different salts, sodium chloride, magnesium chloride, calcium chloride, and sodium sulfate were used in the experiment. Synthetic brines were made from each of the salts at different salinities. Low-salinity waterflooding was performed in secondary and tertiary mode.According to the results of the microfluidic experiments, the amount of oil recovery by injection of brine containing sodium chloride has a nonmonotonic behavior and the maximum oil recovery is obtained at the ionic strength of 0.5 molar sodium chloride. To justify this behavior, the results of the oil-brine interfacial tension tests, the contact angle, and the coalescence of the oil drops as a function of ion strength were evaluated. It is observed that the interfacial tension of oil-brine has a nonmonotonic behavior with salt concentration, and at the ionic strength of 1 molar sodium chloride reaches its minimum value. According to the results obtained from the contact angle tests on a glass substrate and under dynamic salinity alteration, the contact angle trend with salinity is nonmonotonic and at the ionic strength of 0.1 molar sodium chloride reaches the lowest value. Moreover, the results of the coalescence experiments indicate that the time of coalescence of two oil droplets follow a nonmonotonic behavior with brine salinity, and at the ionic strength of 0.5 molar of sodium chloride the maximum time is obtained. A larger coalescence time implies a more elastic interface which then causes the oil phase not to break-up into smaller droplets when passing through a narrow throat. These results confirm that each of these phenomena has the best performance in a particular salinity range, which is important in choosing the optimal salinity for the whole system.It was also observed that after the injection of low-salinity water to the micromodel, it is important to add a shut-in period. After this period, the amount of oil recovery from the porous medium increased significantly, which confirms the importance of time-effect or low salinity kinetics. In fact, different mechanisms of low-salinity water have a different time-scale. In order to observe the full effect of low-salinity, especially related to the phenomenon of wettability change, the system must be given enough time about a few days to a few weeks for all mechanisms to complete. Otherwise, the oil recovery may be underestimated
  9. Keywords:
  10. Low Salinity Water Flooding ; Wettability Alteration ; Enhanced Oil Recovery ; Glass Micromodel ; Microfluidic System ; Fluid-Rock Ineraction

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