煤岩水力压裂裂缝扩展物理模拟实验

探讨煤岩水压裂缝扩展规律是提高煤层气开采效率，降低开采安全风险及成本的重要课题。采用原煤试样，参照煤层气井水力压裂工程制定了“三轴向施加围压-顶部钻孔-下射流管注水”的煤岩水力压裂裂缝扩展物理模拟实验方案，根据实验方案结合现有实验条件开展了煤岩水力压裂物理模拟实验及煤岩裂缝检测实验。实验结果表明：煤岩沿层理面方向裂缝的发育程度要高于垂直层理面方向的裂缝；煤岩水压裂缝扩展形式以注水孔壁原生横向裂缝扩展为主，纵向裂缝扩展为辅，且裂缝呈直线形、跳跃性扩展。同时，根据实验结果分析提出：实际煤储层水力压裂工程中，射流孔应尽量布置在井壁含有较多横向原生裂缝的位置，提高煤层气井水力压裂质量；对于井壁同时含有较多横向裂缝和纵向裂缝的储层，采用“控压”压裂方式提高造缝质量；对于厚储层，采用“分段-分压”压裂方式构造横纵交织的裂缝网，提高煤层气的开采效率；尽量避免在含较多纵向原生裂缝及较大断层的井壁位置布置射流孔，以免引起煤储层顶板、底板失稳破坏，造成安全事故。

A physical simulation experiment on fracture propagation of coalpetrography in hydraulic fracturing

It is an important subject worthy of probing into fracture propagation laws of coal petrography in hydraulic fracturing as to how to improve the efficiency of coal-bed methane and reduce the safety risk of mining.According to practical engineering applications,the physical simulation experiment program-“exerting confining pressure on triaxial-drilling hole on the top-injecting water through the down jet pipe”-on fracture propagation of coal petrography in hydraulic fracturing was established using raw coal samples.Based on the program above combining the existing experimental conditions,this paper performed physical simulation experiments and fracture detection experiments.The experimental results show that the development degree of fractures is higher on the direction along the bedding plane of coal petrography than on the direction vertical to the bedding plane,and presents that the fracture propagation is a primary waterflooding original transverse form of hole wall with rectilinear-figure and jumping-characteristics extension and a subordinate waterflooding original longitudinal form.And according to the analysis of experimental results,the paper presents that in practical engineering applications jet holes should be placed in waterflooding hole wall with transverse original fractures around,which can help improve the hydraulic-fracturing quality of CBM well.For the borehole wall of reservoir containing many transverse and longitudinal fractures,the fracturing way of “pressure-control” should be used to improve the fracture-making quality.For thick reservoir,the fracturing way of “multi stage-multi pressure”,structuring the transverse and longitudinal staggered fracture network,should be used to improve the efficiency of the CBM mining.And jet holes should not be placed at those borehole walls with more vertical original fractures and lager fault for avoiding the unstable failure of coal reservoir roof and bottom to cause safety accidents.