螺旋射孔条件下水平缝起裂延伸规律

LAWS OF HORIZONTAL FRACTURAL INITIATION AND EXTENSION UNDER THE CONDITION OF THE HELICAL PERFORATION

通过物理实验和数值模拟相结合的方式，研究了水平缝螺旋射孔条件下的裂缝起裂、扩展规律。根据大庆油田形成水平缝地层的地应力大小和实验条件的相似准则确定物理实验方案，利用大尺寸真三轴实验装置对水平缝的起裂、延伸进行物理模拟；依据损伤力学原理，利用有限元法对部分实验的裂缝起裂、扩展进行数值模拟。结果表明：60°相位角、高密度射孔可以小范围降低水平缝的破裂压力；压裂过程中，井简附近可能产生多点起裂，但是随着压裂过程的进行，只有最上面射孔位置或者最下面射孔位置的1条裂缝能继续向前延伸形成主裂缝，其他裂缝止裂。数值模拟结果与实验结果相一致，证明实验结果合理。

By mean of the integrating method of the physical experiment and numerical simulation, the laws of the fractural initiation and propagation for the horizontal fractures are searched under the condition of helix perforation. According to the magnitudes of the in-situ stresses and the similarity principles for the horizontally fractured forma- tions in Daqing Oilfield, the physical experimental program is established： numerically simulates horizontal fractu- ring initiation and propagation with the help of large-size tri-axial testing instruments; numerically models the frac- turing initiation and propagation of the partial experi.ment by virtue of the principles of the damage mechanics and fi- nite element method. The results show that 60~ phase angle and high-density perforation can decrease the break- down pressure of the horizontal fractures in small size ; in the course of the fracturing, multi-point fracturing initia- tions may be happened nearby the boreholes, but with the proceeding of the fracturing, only one fracture at the top or bottom of the perforated location can be further extended and become maintain fracture, the rest is stopped frac- turing. The consistence of the numerical simulation results with those of the experiments prove that the results of the experiments are rational and reasonable.