昭通浅层页岩气压裂复杂裂缝扩展数值模拟研究

Numerical Simulation of Complex Fracture Propagation in Shallow Shale Gas Fracturing in Zhaotong

  • 摘要: 昭通浅层页岩气田主体埋深在1 000~2 200 m,地层压力系数低,效益开发难度较大,水力压裂是唯一增产措施,但目前国内尚无对中浅层页岩储层实施规模开发的经验可供借鉴,水力压裂工艺参数仍有优化空间。为明确目标昭通浅层页岩气田裂缝扩展主控影响因素,优化页岩气水平井压裂参数,针对该页岩气田储层天然裂缝发育、水平应力差小,主体改造工艺射孔簇较多等地质、工程特点,开展了昭通浅层页岩气压裂复杂裂缝扩展数值模拟研究。采用位移不连续法,考虑天然裂缝和水力裂缝的相互作用模式,基于压裂裂缝流动方程、裂缝宽度方程和物质平衡方程,推导了复杂裂缝扩展数学模型;针对昭通浅层页岩气实际地质特点,基于建立的数学模型优化了施工参数,明确了天然裂缝内聚力、射孔簇数是影响改造体积的主要因素。同时,通过暂堵数值模拟,明确得出:暂堵有利于提高裂缝开启效率,暂堵位置、暂堵时机及暂堵次数对暂堵效果有明显影响。通过现场试验对比模拟结果,发现采取优化后的压裂措施可使单井日产气量提高30.3%。该研究成果对昭通浅层页岩气后续压裂施工具有良好的借鉴意义。

     

    Abstract: The main burial depth of the shallow shale gas field in Zhaotong is 1000-2200 m. The formation pressure coefficient is low, making the benefit development challenging. Hydraulic fracturing technology remains the only stimulation measure. However, there is no prior experience of large-scale development of medium and shallow shale reservoirs in China for reference. Therefore, there is still room for optimizing hydraulic fracturing parameters. In consideration of the geological and engineering characteristics, such as natural fracture development, small horizontal stress differences, and large perforation cluster numbers of the main stimulation, a numerical simulation of complex fracture propagation in shallow shale gas fracturing in Zhaotong was conducted. The displacement discontinuity method was employed, with the interaction mode of natural and hydraulic fractures considered. Based on the fracture flow equation, fracture width equation, and mass balance equation, the mathematical model of complex fracture propagation was derived. Based on the model, construction parameters were optimized according to the actual geological characteristics of shallow shale gas in Zhaotong. It was determined that natural fractures and perforation cluster numbers were the main factors affecting the stimulated reservoir volume (SRV). At the same time, through the temporary plugging numerical simulation, it is clarified that temporary plugging is conducive to improving the fracture opening efficiency, and the location, timing and times for temporary plugging have obvious effects on the temporary plugging effect. The simulation results were compared with on-site test results, demonstrating that the optimized fracturing measures increased daily single gas production by 30.3%. Consequently, this study provides valuable insights for the subsequent fracturing treatment of shallow shale gas in Zhaotong.

     

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