为研究常规压裂与多级压裂两种不同改造方式下的裂缝扩展规律及增产机理,制备力学参数接近真实地层的人造岩心,采用真三轴加载方式模拟地层真实三向地应力环境,自主设计并开展了常规射孔压裂与多级射孔压裂物理模拟实验。研究结果表明:多级射孔笼统压裂时纵向应力均质情况下,岩石在射孔位置同时起裂,产生的多条裂缝在垂直方向同时扩展,扩展的裂缝会在裂缝尖端周围产生局部应力,从而彼此干扰,出现复杂裂缝情况。多级射孔分段压裂当第一条裂缝存在时,缝内的压力会改变周围的应力场,进而改变局部最大和最小主应力的方向,进行第二次压裂时,新的裂缝会受到第一条裂缝的局部应力场影响,沿着新的应力方向扩展,并不会与第一条裂缝重合,从而引起空间裂缝的形态变化。相同条件下多级射孔压裂比集中射孔笼统压裂的裂缝面积大,相同施工规模条件下射孔分段数目越多裂缝越复杂,裂缝与储层接触面积越大。针对低渗透非均质厚储层而言,推荐采用多级射孔、分段注入方式进行压裂。

To compare the crack propagation law and production increase mechanism under conventional perforated fracturing and multi-stage perforated fracturing,the physical simulation experiments are independently designed and conducted by preparing artificial cores whose mechanical parameters are close to the real strata, the true triaxial loading method is used to simulate the true three-dimensional ground stress environment.The results of the study indicate that in the case of homogeneous stress in the longitudinal fracturing, the rock starts to crack at the same time as the perforation.The multiple cracks produced expand in the vertical direction simultaneously.The extended cracks will generate local stress around the crack tip and thus interfere with each other.So there will be complex cracks.In the case of multi-stage perforated fracturing, when the first crack exists, the pressure in the seam will change the surrounding stress field,and then change the direction of the local maximum and minimum principal stress.During the second fracturing, the new crack will be affected by the local stress field of the first crack,spread along the new stress direction,and will not coincide with the first crack,causing the trajectory of the space crack to change.Under the same conditions, multi-stage perforated fracturing has a larger crack area than centralized perforation general fracturing.Under the condition of the same construction scale, the more number of perforation subdivisions, the more complex the cracks and the greater the contact area between fractures and reservoirs.For the heterogeneous and low permeability reservoir, multi-stage perforated segmented fracturing technology is recommended.