多煤层压裂裂纹竞争起裂扩展特征分析

Characteristics of fracture propagation caused by fracture competition in multi-seam fracturing

针对多煤层压裂裂纹竞争起裂扩展特征认识不清的这一难题,采用真三轴水力压裂试验系统,分析了煤层强度比和厚度比对于联合压裂过程中裂纹的萌生和扩展的影响。结果表明:对于不同强度比的两个煤层,声发射定位信号首先在软煤层中被监测到,且主要分布在软煤层中,这表明裂纹优先在软煤层中扩展。切开试样后,分析示踪剂的分布也进一步证明了上述结论。对于不同厚度比的煤层,两个煤层之间同样存在裂纹扩展的竞争关系。较薄煤层的示踪剂面积大于较厚煤层的示踪剂面积,表明较薄煤层在裂纹竞争扩展中占据优势。因此,对于煤层强度比和厚度比差异不大的煤层群,推荐使用联合压裂技术,其具有“工程量少、一孔多用”优势。

In order to clarify unclear understanding of characteristics of fracture propagation caused by fracture competition in multi-seam fracturing,the effect of coal seam strength ratio and thickness ratio on fracture initiation and propagation in joint fracturing process was analyzed with true triaxial hydraulic fracturing system.The results have shown that for two coal seams with different strength ratios,acoustic emission location signals are first detected and mainly distributed in the soft coal seam,which indicates that fractures preferentially propagate in the soft coal seam.Distribution of tracers as shown in the cut samples also proves the above conclusion.For coal seams with different thickness ratios,a competitive relationship of fracture propagation exists between two coal seams.The tracer area of the thinner coal seam is larger than that of the thicker one,indicating that the thinner coal seam has an advantage in fracture propagation.Therefore,for coal seam groups with little difference in coal seam strength ratio and thickness ratio,multi-seam fracturing technology is recommended for the advantage of“less engineering amount and multi-purpose in one hole”.