Wei Feng, Tang Mingguang, Deng Xuan, Zhang Yuli, Wang Fengjiao, Liu Yikun, Yan Guanli, Wu Qi
Zhanjiang Branch, CNOOC (China) Limited, Zhanjiang, Guangdong 524057, China.
Laboratory of Enhanced Oil Recovery of Education Ministry, Northeast Petroleum University, Daqing, Heilongjiang 163318, China.
ACS Omega. 2024 Dec 26;10(1):1761-1771. doi: 10.1021/acsomega.4c09893. eCollection 2025 Jan 14.
Offshore low-permeability reservoirs are mainly composed of complex fault-block structures with poor physical properties, which makes establishing an effective displacement relationship particularly challenging. Hydraulic fracturing assisted oil displacement (HFAD) can effectively increase the oil production of a single well by creating fractures to replenish the producing energy. In this study, the Khristianovich-Geertsma-de Klerk (KGD) model is used to calculate the propagation of vertical fractures, and the flow tube method is used to calculate the two-phase oil-water flow in filtration and seepage. The semianalytical mathematical model for coupling fracture propagation, filtration, and seepage of the HFAD fluid is established, followed by conducting the sensitivity analysis and the main controlling factors analysis. In contrast to conventional methods, the filtration and seepage of the HFAD fluid during the fracturing process are taken into account. Based on actual well data, the fracture half-length and the wellhead pressure are verified. The mean calculation accuracy of the fracture half-length is 88.5%, and the mean calculation accuracy of the wellhead pressure is 90.7%. The research results indicate that the fracture propagation and the filtration and seepage of the HFAD fluid occur simultaneously, including rapid propagation in the early stage, discontinuous propagation in the middle stage, and only infiltration without propagation in the later stage. Infiltration is considered a key factor in the fracture propagation of HFAD, with a higher infiltration rate leading to weaker energy storage at the fracture tip. The viscosity of the HFAD fluid significantly impacts fracture half-length and vertical infiltration distance, contributing 35% and 27%, respectively. To increase fracture half-length, select a thinner reservoir, increase HFAD fluid viscosity, and boost the injection rate. To increase the vertical infiltration distance, choose higher permeability reservoirs, reduce HFAD fluid viscosity, and increase cumulative injection volume. The results of the research study provide a valuable basis for the design of an HFAD construction scheme for offshore low-permeability reservoirs.
海上低渗透油藏主要由物性差的复杂断块构造组成，这使得建立有效的驱替关系极具挑战性。水力压裂辅助驱油（HFAD）可通过造缝补充生产能量，有效提高单井产量。本研究采用克里斯蒂安诺维奇-吉尔茨马-德克勒克（KGD）模型计算垂直裂缝扩展，采用流管法计算渗流中的油水两相流。建立了HFAD流体裂缝扩展、渗流耦合的半解析数学模型，并进行了敏感性分析和主控因素分析。与传统方法不同，该模型考虑了压裂过程中HFAD流体的渗流情况。基于实际井数据，对裂缝半长和井口压力进行了验证。裂缝半长平均计算精度为88.5%，井口压力平均计算精度为90.7%。研究结果表明，HFAD流体裂缝扩展与渗流同时发生，包括前期快速扩展、中期间断扩展、后期只渗流不扩展。渗流被认为是HFAD裂缝扩展的关键因素，渗流速率越高，裂缝尖端储能越弱。HFAD流体黏度对裂缝半长和垂直渗流距离影响显著，分别贡献35%和27%。要增加裂缝半长，选择较薄油层，提高HFAD流体黏度，增大注入排量。要增加垂直渗流距离，选择渗透率较高油层，降低HFAD流体黏度，增加累计注入量。研究结果为海上低渗透油藏HFAD施工方案设计提供了有价值的依据。
