压裂过程中水力裂缝动态宽度实验研究

 裂缝宽度及其变化规律对验证水力压裂模型及指导压裂施工设计具有重要意义。由于水力裂缝宽度比其长度和高度小3～4个量级，且储层埋藏较深，目前尚无法直接测量实际地层中的水力裂缝宽度，仅能大致通过模型估算或数值模拟获得。通过在室内压裂试件中布置单根或多根布拉格光纤光栅(FBG)应变传感器，对类混凝土材料的水力裂缝宽度进行多点同步动态监测，得到不同时刻多点水力裂缝宽度的变化，并依据裂缝宽度变化得到了裂缝扩展速度，从而对水力压裂裂缝扩展中的尺度变化进行了过程描述。实验研究表明，室内水力压裂模拟实验中水力裂缝的宽度为微米级别，裂缝扩展速度为0.1 mm/s量级；在水力压裂过程中，裂缝宽度随裂缝扩展呈现波动式变化，并非随着裂缝扩展单调增加。研究结果对认识水力压裂裂缝的扩展及提升压裂工艺技术具有重要参考价值。

Experimental research on the variation of fracture width in hydraulic fracturing process

Fracture width and its variation are of great significance to verify the hydraulic fracture model and to guide the fracturing treatment in oil field. Because that the width of hydraulic fracture is 3–4 magnitude orders smaller than its length or height and the reservoir is deeply buried underground，there is no direct method of measurement regarding the width. The width can only be approximately obtained through the estimation of mathematical models and numerical simulations at present. In order to investigate hydraulic fracture width，the transient changes of the width of concrete fracture were monitored by embedding the strain sensors Fiber Bragg Grating(FBG) along the expected path of fracture propagation during the laboratory hydraulic fracturing experiments. The average velocity of fracture propagation and fracture morphology in different moments of time were also obtained with the multiple FBG strain sensors. The fracture propagation process of hydraulic fracturing was described. The research indicated that the width of hydraulic fracture in laboratory experiment reached micron-scale and the velocity reached 0.1 mm/s scale. The fracture width does not increase monotonously along with the expansion of the hydraulic fracture，but fluctuates within a certain range with the intermittent extension of the hydraulic fracture.