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Smart Water Optimal Injection Policy in Fractured Carbonate Reservoirs, Using Laboratory Data

Madadi Mogharrab, Javad | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57509 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ayatollahi, Shahaboddin; Pishvaie, Mahmood Reza
  7. Abstract:
  8. Wettability alteration is the main mechanism for enhancing oil recovery in carbonate reservoirs during low salinity or engineered water flooding (LS/EWF), though it is a complex process due to the high heterogeneity of rock. During LS/EWF, wettability alteration occurs as a result of electrochemical interactions at the interface between carbonate rock and brine. One of the most critical factors affecting these interactions, and the wettability alteration process, is the presence of anhydrite impurities in the carbonate rock. Therefore, the success of LS/EWF in carbonate reservoirs lies on understanding the role of impurities like anhydrite from both geochemical and dissolution perspectives. However, modeling and quantifying wettability alteration remained a challenging issue. Several methods have been employed to quantify wettability, including zeta potential, disjoining pressure, surface complexation modeling (SCM), mineral dissolution, and contact angle measurement. Yet, in complex systems like those involving impurities in carbonate rocks, traditional methods have shown poor performance. This study is divided into three main sections: laboratory experiments, core-scale modeling and simulations, and field-scale optimization of well placement and injection rate. In the laboratory section, tests such as modified flotation (MFT), zeta potential, core flooding, and effluent ion analysis were performed on two rock samples, pure calcite and a mixture of calcite and 10wt% of anhydrite. The results showed non-monotonic wettability and oil recovery in response to brine salinity. The presence of anhydrite reduced the optimal salinity range from 10 times diluted seawater to 25 times diluted seawater. However, mineral dissolution and zeta potential measurements did not comprehensively correlate with the wettability states observed in flotation tests or the oil recovery seen in core flooding experiments. In the core-scale modeling and simulation section, a surface complexation model (diffuse double layer based SCM) was developed using the geochemical software PHREEQC to clarify the role of anhydrite in desorbing acidic oil components from the rock surface. This model, validated by measured zeta potential values, accurately predicted flotation test results, showing a strong correlation between the amount of oil acid adsorbed onto the carbonate rock surface and the wettability conditions observed in the experiments. The SCM also identified an anhydrite dominant range, where anhydrite dissolution and the released SO42- ions lead to a shift in wettability toward more water wetness. For core flooding simulations, the MATLAB Reservoir Simulation Toolbox (MRST) was coupled with PHREEQC and SCM to model LS/EWF as a reactive transport phenomenon. The experimental core flooding results were successfully matched using this integrated software. An interpolation factor, based on carboxylic acids adsorbed onto the rock surface, demonstrated reasonable performance in matching oil recovery and effluent ion concentrations, both in the presence and absence of anhydrite. In contrast, traditional methods were unable to reproduce the flotation and core flooding results in the presence of anhydrite. A comprehensive approach was also introduced to model LS/EWF in both static and dynamic phases, taking mineral heterogeneities into account. In the field-scale optimization section, CMG software and the CMOST-DECE optimizer engine were used to investigate the optimal placement of injection and production wells, as well as the smart water injection rate, to maximize oil recovery in the presence of geological uncertainties such as anhydrite distribution. The well placement results revealed that the optimal locations for injection and production wells responded to the distribution of anhydrite in the reservoir, with wells being placed in regions with higher percentages of anhydrite. Furthermore, robust optimization provided more comprehensive results under geological uncertainty compared to nominal model optimization. The optimization of injection rates in both models also showed that after water breakthrough at production wells, the smart water injection rate should be reduced to avoid well shut-in. This study underscores the significant impact of anhydrite impurities on the performance of low-salinity water injection, using experimental data and SCM. While simpler techniques like rock dissolution and zeta potential measurements fail to explain the non-monotonic wettability behavior, this approach introduces a new quantitative parameter for wettability, based on carboxylic acids adsorbed onto calcite surfaces as reported by SCM
  9. Keywords:
  10. Low Salinity Water Flooding ; Smart Water ; Surface Complexation Reactions ; PHREEQC Software ; MATLAB Reservoir Simulation Toolbox (MRST) ; Non-Monotonic Wettability ; Anhydrite

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