Fan Pingtian, Liu Yuetian, He Yuting, Hu Yuanping, Chao Leihui, Wang Yapeng, Liu Lang, Li Jingpeng
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China.
Nanniwan Oil Production Plant, Yanchang Oilfield Co., Ltd., Yan'an 716000, China.
ACS Omega. 2024 Mar 5;9(11):12665-12675. doi: 10.1021/acsomega.3c07960. eCollection 2024 Mar 19.
Currently, research surrounding low-salinity water flooding predominantly focuses on medium- to high-permeability sandstone reservoirs. Nevertheless, further investigation is necessary to implement this technique with regard to tight sandstone reservoirs. The present study comprises a series of experiments conducted on the crude oil and core of the Ordos Chang 6 reservoir to investigate the influence of ionic composition on low-salinity water flooding in tight oil reservoirs. The change in wettability on the rock surface was analyzed by using the contact angle experiment. The change in recovery rate was analyzed using a core displacement experiment. The reaction between rock fluids was analyzed using an ion chromatography experiment. Additionally, a nuclear magnetic resonance (NMR) experiment was used to analyze the mobilization law of crude oil and the change in wettability on the scale of the rock core. This led to a comprehensive discussion of the law and mechanism of enhancing the recovery rate via low-salinity water flooding from various perspectives. Experiments show that low-salinity water flooding is an effective technique for enhancing recovery in tight sandstone reservoirs. Altering the ionic composition of injected water can improve the water wettability of the rock surface and enhance recovery. Decreasing the mass concentration of Ca or increasing the mass concentration of SO can prompt the ion-exchange reaction on the rock surface and detachment of polar components from the surface. Consequently, the wettability of the rock surface strengthens, augmenting the recovery process. Nuclear magnetic resonance experiments evidence that low-salinity water injection, with ion adjustment, significantly alters the interactions between the rock and fluid in tight sandstone reservoirs. As a result, the signal amplitude decreases significantly, residual oil saturation reduces considerably, and the hydrophilic nature of the rock surface increases.
目前，围绕低盐水驱油的研究主要集中在中高渗透率砂岩油藏。然而，对于致密砂岩油藏实施该技术仍需进一步研究。本研究对鄂尔多斯长6油藏的原油和岩心进行了一系列实验，以研究离子组成对致密油藏低盐水驱油的影响。通过接触角实验分析岩石表面润湿性的变化。利用岩心驱替实验分析采收率的变化。通过离子色谱实验分析岩石流体之间的反应。此外，还利用核磁共振（NMR）实验分析了岩心尺度上原油的动用规律和润湿性变化。从而从多个角度对低盐水驱油提高采收率的规律和机理进行了全面探讨。实验表明，低盐水驱油是提高致密砂岩油藏采收率的有效技术。改变注入水的离子组成可以改善岩石表面的水润湿性并提高采收率。降低Ca的质量浓度或提高SO的质量浓度可促使岩石表面的离子交换反应以及极性组分从表面脱离。因此，岩石表面的润湿性增强，采收过程得到强化。核磁共振实验证明，通过离子调整的低盐水注入显著改变了致密砂岩油藏中岩石与流体之间的相互作用。结果，信号幅度显著降低，残余油饱和度大幅降低，岩石表面的亲水性增加。
