大倾角煤层水力裂缝扩展物理模拟实验

Physical simutation experiment investigation on hydraulic fracture propagation in high-dip coal seam

为研究大倾角煤层水力压裂裂缝扩展形态,采用大尺寸真三轴压裂模拟系统,分别开展最大水平主应力沿地层走向和沿地层倾向的60°倾角煤层水力裂缝扩展物理模拟实验。结果表明:最大主应力方向沿地层走向时,裂缝起裂容易,缝高受限,裂缝连通性好,裂缝的开启主要沿层理和天然裂缝,形成垂直缝形态,地层倾角对压裂施工影响相对较小,建议进行大规模压裂以充分改造煤储层;最大主应力方向沿地层倾向时,裂缝起裂困难,前期缝高受限,后期缝高失控,裂缝连通性差,受节理影响,不易形成主缝,所以裂缝扩展困难,转向及多级破裂较多,此类煤层建议进行多级小规模压裂改造。实验结果对新疆等地区大倾角煤层的改造模式和改造规模具有指导作用。

In order to study the hydraulic fracture geometry in high-dip coal seam,a large-scale true triaxial fracturing simulation system was used to carry out physical simulation experiments,and the hydraulic fracture geometry of the maximum horizontal principal stress along the strike direction and along the dip direction-in 60°dip coal seam were investigated respectively.Experimental results of the maximum principal stress direction along the strike direction show that:hydraulic fracture initiation is easily;fracture height is limited in the whole time;fracture connectivity is good;fracture propagates mainly along bedding and natural fracture,vertical fracture is formed;the influence of high-dip on stimulation is relatively small;massive volume stimulation is needed.Experimental results of the maximum principal stress direction along the dip direction show that:hydraulic fracture initiation is hard;fracture height is limited in the early time and out of control in the later period;fracture connectivity is poor;fracture is not easy to form influenced by joint,and hydraulic fracture propagates difficultly;fracture diversion and multi-stage breakdown can be observed in the fracturing curve;small volume but multi-stage stimulation is needed.The experimental results have a good guiding effect on the stimulation model and scale determination of the high-dip coal seam in Xinjiang and other regions.