Wettability of an oil/brine/rock system is a critical petrophysical parameter, which governs subsurface multiphase flow behavior, thus hydrocarbon recovery. While the mechanisms of CO₂-assisted enhanced oil recovery (EOR) techniques have been extensively investigated in carbonate reservoirs, few have been done to identify the controlling factor of CO₂-induced wettability alteration, and fewer have looked beyond the implications for CO₂-assisted EOR. We thus hypothesize that CO₂-assisted EOR techniques cause a more hydrophilic system due to H⁺ adsorption on the interface of oil/brine and brine/carbonate as a result of CO₂ dissolution. To test this hypothesis, we measured contact angles of two oils with different acid and base numbers in the presence of 1 M Na₂SO₄ at pH either 3 or 8. Moreover, we performed a geochemical study to identify the controlling factor of wettability alteration. Contact angle results support the hypothesis, showing that the oil/brine/rock system shifts toward more water-wet because of less bonds between oil/brine and brine/carbonate due to H⁺ adsorption on the interface of oil/brine and brine/carbonate. Our results also suggest that CO₂-assisted EOR techniques likely shift relative permeability curves toward a lower residual oil saturation due to wettability alteration. We argue that geochemical reactions may need to be incorporated into a reservoir numerical model, thus better managing and predicting the performance of CO₂-assisted EOR.

中文翻译：

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pH值解决的润湿性变化：对碳酸盐岩储层中CO ₂辅助EOR的影响

石油/盐水/岩石系统的可湿性是关键的岩石物理参数，它决定着地下多相流动行为，从而决定了油气的采收率。尽管在碳酸盐岩储层中广泛研究了CO ₂辅助提高采收率（EOR）技术的机理，但很少能确定CO ₂引起的润湿性变化的控制因素，并且很少有人关注CO ₂的影响。辅助的EOR。因此，我们假设，CO ₂ -assisted EOR技术导致更亲水的系统由于ħ ⁺油/盐水和盐水/碳酸酯的界面作为CO的结果上吸附₂解散。为了验证这一假设，我们在pH 1为3或8的情况下，在存在1 M Na ₂ SO ₄的情况下，测量了两种具有不同酸和碱值的油的接触角。此外，我们进行了地球化学研究，确定了润湿性改变的控制因素。 。接触角结果支持该假设，表明油/盐水/岩石系统朝着更多水润湿的方向移动，这是由于油/盐水与盐水/碳酸盐界面上的H ⁺吸附导致油/盐水与盐水/碳酸盐之间的键合较少。我们的结果还表明，CO ₂辅助的EOR技术可能会由于润湿性改变而使相对渗透率曲线向较低的剩余油饱和度方向移动。我们认为地球化学反应可能需要纳入储层数值模型中，从而更好地管理和预测CO ₂辅助EOR的性能。