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Zeta potential measurements and microscopic surface characterization and imaging were conducted on calcite and dolomite crystals aged in stearic acid model oil and exposed to different synthetic brines representing different potential scenarios of injected seawater from the Arabian Gulf. Calcite particles were negatively charged in deionized water and maintained negative surface charges in all tested brines, except in diluted Arabian Gulf seawater that contained higher concentration of Ca2+ and Mg2+ ions. Dolomite particles were positively charged in deionized water as well as in all tested brines, except in diluted Arabian Gulf seawater that contained four times higher concentration of SO4 2– ions. Scanning electron microscopy and atomic force microscopy experiments on cleaved calcite and dolomite chips showed different morphological changes when both samples were aged in model oil and then treated with brines. Calcite surface dissolution was observed in addition to stearic acid deposition. Surface elemental analysis using energy-dispersive spectroscopy showed Mg2+ and SO4 2– ions adsorb preferably on locations where stearic acid is deposited. The finding that stearic acid was adsorbing more strongly on dolomite than on calcite could indicate why the tested brines were less efficient to change the zeta potential of the dolomite systems. The current study concludes that manipulating the concentration of potential-determining ions present in the Arabian Gulf seawater, especially Mg2+ and SO4 2– ions, will alter the surface charges of aged calcite and dolomite samples as well as their surface morphology.

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Chelating agent solutions have been proposed as effective fluids for enhancing oil production. Different recovery mechanisms are reported for increasing the oil recovery during chelating agent flooding. The aims of this work are to identify the possible recovery mechanisms during chelating agent flooding in carbonate reservoirs and to investigate the in situ CO2 generation as a potential recovery mechanism during the injection of chelating agent solutions into carbonate reservoirs. The contribution of CO2 on enhancing the oil recovery was determined using experimental measurements and analytical calculations. Several measurements were conducted to study the contribution of each mechanism on enhancing the oil recovery. Coreflooding tests, zeta potential measurements, CO2 generation, and interfacial tension (IFT) experiments were carried out. Also, analytical models were utilized to determine the impact of the injected chemicals on reducing the capillary pressure and improving the flow conditions. In flooding tests, two chemicals (EDTA and GLDA) were injected in a sequential mode and the chemical concentration was increased gradually. In addition, a comparative study was performed to evaluate the effectiveness of EDTA and GLDA solutions to enhance oil recovery. Several parameters were investigated in this paper including incremental oil recovery, in situ CO2 generation, hydrocarbon swelling, IFT, wettability alteration, permeability enhancement, productivity index, and chemical cost. The obtained results show that GLDA chelating agent has better performance than EDTA solutions for enhancing the oil recovery when the same concentrations are used. Also, the in situ generation of CO2 shows a significant impact on improving the oil recovery from carbonate reservoirs during chelating agent flooding. In the literature, the reported recovery mechanisms of using chelating agents are the IFT reduction, wettability alteration, and rock dissolution. Based on this work, injecting chelating agent solutions at low pH can lead to involve additional recovery mechanisms due to the CO2 generation, the additional mechanisms are hydrocarbon swelling, viscosity and density reduction, and oil vaporization.