水平井体积改造多裂缝扩展形态算法——不同布缝模式的研究

为了探索不同布缝模式的水平井体积改造多裂缝扩展形态,基于位移不连续边界元法,建立了三维非平面裂缝应力干扰计算模型,并根据亚临界裂缝扩展模型和最大周向应力准则,提出了多裂缝扩展形态算法。根据该算法,编程求解了不同布缝模式的裂缝扩展形态,研究发现:(1)多簇压裂模式外侧裂缝为主扩展裂缝,内侧裂缝扩展变短且发生非平面扩展,有利于产生复杂裂缝,单簇压裂有利于单簇缝长的有效延伸;(2)应力干扰只作用于发生交叠的裂缝,并不作用于对称分布的未交叠裂缝;(3)在交错布缝模式下,后续压裂缝与邻近裂缝发生交叠时会向邻近裂缝靠近,偏转角度为5°~6°;交错布缝同步压裂时,井间裂缝以9°~10°的偏转角相互靠近,不利于远井的储层改造,而交错布缝拉链式压裂可提高裂缝延伸长度,增大远井改造体积;(4)多井间隔布缝模式增大了施工缝间距,可减小裂缝偏转幅度,而采用先压裂一段中间井,后在邻井围绕该段压裂的布缝顺序,能够增大裂缝复杂度,提高改造体积。

Algorithm for multi-fracture propagation morphology in horizontal well volume fracturing: Investigation on different fracture distribution patterns

For the probe of multi-fracture propagation geometry induced by horizontal-well volume stimulation in different fracture distribution patterns, a 3D non-areal fracture stress interference calculation model was established by means of the displacement discontinuity boundary element method. Then, a new algorithm for multi-fracture propagation geometry was proposed according to the subcritical fracture propagation model and the maximum circumferential stress criterion. And finally, the fracture propagation morphology in different fracture distribution patterns were programmed and solved on the basis of this algorithm. The results show that in the mode of multi-cluster fracturing, the exterior fractures are main propagation fractures and the interior fractures present non-areal propagation with short length. This multi-cluster fracturing is favorable for the formation of complex fractures while the single-cluster fracturing is favorable for the effective extension of a single-cluster fracture length. Besides, stress interference has effect only on interlaced fractures instead of uninterlaced fractures which are symmetrically distributed. Moreover, in the pattern of interlaced fracture distribution, the subsequent hydraulic fractures approach to their adjacent fractures when they are interlaced, with a deflection angle of 5°–6°. When the simultaneous fracturing with interlaced fracture distribution is conducted, the fractures between wells get close to each other with a deflection angle of 9°–10°, which is unfavorable for the reservoir stimulation far away from the wells. However, the zip-like fracturing with interlaced fracture distribution can increase the fracture propagation length and improve the stimulated volume far away from the wells. Finally, multi- well gap fracture distribution mode can increase the space of construction fractures and decrease the deflection amplitude of fractures. If the fracturing is performed first at the well in the center and then at its neighboring wells, the fracture complexity will be enhanced and the stimulated volume be increased.