Abstract Spontaneous imbibition has become a role on the development of tight oil reservoirs. Many oilfield cases have confirmed the validity of soaking to produce oil depending on imbibition. Considerable yield has been recovered from soaking for a period of time after hydraulic fracturing by fracturing fluid. In order to study the spontaneous imbibition and its influencing factors in tight oil reservoir with stimulated reservoir volume (SRV), we first conducted wettability and imbibition experiments with/without surfactant treatment using different tight cores. Then, we established a mechanism model of imbibition including the influencing factors in tight oil reservoirs based on the experiments. The model was also validated using the published results. After that, numerical simulation was employed to study the impacts of some essential factors on the effects of spontaneous imbibition. The results indicate that no matter mixed-wet or water-wet tight cores, water can be spontaneously imbibed into the tight cores, and consequently expel the oil. The wettability alteration agent has slight influence on contact angle and imbibition recovery for the water-wet core, but it has a distinct influence on those of the mixed-wet or oil-wet core. Natural fractures in tight rock can promote the imbibition. The size of the tight rock after hydraulic fracturing is a significant factor of imbibition recovery. Interfacial tension is crucial to imbibition in tight reservoir because capillary force becomes more significant in tight rocks than that in conventional reservoirs. Wettability intensely decides the imbibition recovery, and it is indispensable to add modifying agents to enhance imbibition for mix-wet or oil-wet rocks. The reduction of temperature in tight oil reservoir due to fracturing and huff-n-puff may decrease the recovery by more than 1% after 5–6 cycles.

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致密油藏自吸及其影响因素研究

摘要 自吸已成为致密油藏开发的重要因素。许多油田案例已经证实了浸渗取油的有效性。压裂液进行水力压裂后，经过一段时间的浸泡，已经恢复了可观的产量。为了研究模拟储层体积（SRV）致密油储层的自吸作用及其影响因素，我们首先使用不同的致密岩心进行了表面活性剂处理和非表面活性剂处理的润湿性和渗吸实验。在此基础上，我们建立了包括致密油藏影响因素在内的渗吸机理模型。该模型还使用已发布的结果进行了验证。之后，数值模拟被用来研究一些基本因素对自吸效应的影响。结果表明，无论是混湿还是水湿致密岩心，水都可以自发地吸进致密岩心，从而驱油。润湿性改变剂对水湿岩心的接触角和渗吸回收率影响不大，但对混湿岩心和油湿岩心的影响明显。致密岩石中的天然裂缝可以促进渗吸。水力压裂后致密岩石的尺寸是渗吸恢复的重要因素。界面张力对致密油藏的渗吸至关重要，因为在致密岩石中毛细管力比在常规油藏中更为显着。润湿性在很大程度上决定了渗吸采收率，对于混湿或油湿岩石，必须添加改性剂来增强渗吸能力。由于压裂和吞吐导致致密油储层温度降低，5-6 个循环后采收率可能会降低 1% 以上。