CO₂ huff-n-puff process appears to be important to unlock hydrocarbon resources from shale oil reservoirs after multi-stage hydraulic fracturing. While existing literature shows that CO₂ diffusion plays a significant role in kinetics of oil recovery, few studies have been able to draw on any systematic research into fluid-fluid-shale interaction due to water uptake of CO₂ in connate water (water carbonation), which governs fluids flow in fractures thus CO₂ huff-n-puff performance. We therefore hypothesized that water carbonation would depress ion exchange process between oil and organic matter (OM) thus forming a more water-wet system. Moreover, water carbonation would also decrease the electrostatic forces between oil and edge charge on OM, thereby further promoting water-wet system. To test the hypothesis, we measured contact angles in non‑carbonated high salinity brine (HS), carbonated high salinity brine (CO₂ HS) and carbonated low salinity brine (CO₂ LS) at temperature of 25 °C and under pressure of 3000 psi. Moreover, a geochemical modelling was conducted to evaluate ion exchange and surface complexation reactions in three different brines.

Our contact angle measurements showed that HS gave a contact angle of 130°, while CO₂ HS and CO₂ LS resulted a contact angle of 23.5° and 23.0°, suggesting a more water-wet system. Geochemical modelling shows that ion exchange reactions between oil and shale surfaces are dramatically depressed in carbonated brine. In particular, the bridges number between oil and shale surfaces decreases from 5.2 × 10⁻⁴ μmol/m² to 5.3 × 10⁻⁶ μmol/m² in carbonated brines, supporting the contact angle measurements. Moreover, the computed surface potential at oil and rock surfaces increases from around −40 mV to 150 mV, suggesting more repulsive forces in the presence of carbonated brine, further supporting contact angle results. This work reveals for the first time that water carbonation during CO₂ huff-n-puff process likely triggers a hydrophilic shale surface, which may significantly affects multiphase flow in natural and hydraulic fractures in particular.

在多级水力压裂之后，CO ₂吞吐正压过程对于从页岩油储层中释放碳氢化合物资源似乎很重要。现有文献表明，CO ₂扩散在采油动力学中起着重要作用，但由于原生水吸收了CO ₂（水碳酸化），很少有研究能够对流体-页岩相互作用进行任何系统的研究。，它控制裂缝中的流体流动，从而控制CO ₂吹牛性能。因此，我们假设水的碳酸化会抑制油与有机物（OM）之间的离子交换过程，从而形成一个更加水湿的系统。此外，水的碳酸化作用还将降低油与OM上边缘电荷之间的静电力，从而进一步促进水湿系统。为了验证该假设，我们在25°C的温度和3000的压力下测量了非碳酸高盐度盐水（HS），碳酸高盐度盐水（CO ₂ HS）和碳酸低盐度盐水（CO ₂ LS）的接触角磅/平方英寸 此外，进行了地球化学建模以评估三种不同盐水中的离子交换和表面络合反应。

我们的接触角测量结果表明，HS的接触角为130°，而CO ₂ HS和CO ₂ LS的接触角分别为23.5°和23.0°，这表明系统更湿润。地球化学模型表明，在碳酸盐水中，油和页岩表面之间的离子交换反应被大大抑制。特别地，油和之间的桥数页岩表面减小从5.2×10 ^-4 微摩尔/米²至5.3×10 ^-6 微摩尔/米²在碳酸盐水中，支持接触角测量。此外，计算得出的在石油和岩石表面的表面电势从大约-40 mV增加到150 mV，这表明在存在碳酸盐盐水的情况下有更多的排斥力，从而进一步支持了接触角。这项工作首次揭示，CO ₂吞吐－正吹过程中的水碳化可能会触发亲水性页岩表面，这可能会显着影响尤其是天然裂缝和水力裂缝中的多相流。