水平井射孔压裂完井下控制近井筒裂缝复杂度的参数优化

Parameter optimization for controlling the complexity of near-wellbore fractures for perforated fracturing of horizontal wells

水平井射孔压裂完井是开发非常规油气储层的关键手段,但水力裂缝在射孔孔眼的竞争起裂与近井筒的非平面扩展行为仍不明确。为此,以某页岩油储层HX井为例,结合离散格子方法建立三维全耦合螺旋射孔压裂数值模型,精细描述多孔眼裂缝竞争扩展中的相互干扰行为以及空间演化,系统研究水平主应力差、射孔密度和射孔相位角等关键因素影响下的水平井近井筒裂缝起裂与扩展行为,提出控制近井筒裂缝复杂度的工程措施建议。结果表明,在压裂初期,各射孔孔眼根部存在径向和横向的“十”型裂缝;随后在地应力的控制下,各孔眼的横向裂缝发生优势扩展而纵向裂缝扩展受到抑制;最后在相邻孔眼裂缝发生不同程度的沟通与连接下,在远井端形成了垂直于最小水平主应力方位的横向主裂缝。当水平井筒沿着最小水平主应力方位时,低水平主应力差、高射孔密度和低相位角有利于在近井筒形成简单连续的横向主裂缝,而高水平主应力差、低射孔密度和高相位角下由于各孔眼裂缝之间沟通困难,导致形成含多条分支缝的复杂裂缝。提出的三维全耦合射孔压裂数值模型有效地描述了多孔眼裂缝起裂与扩展行为,同时研究成果为通过优化射孔完井参数以降低近井筒裂缝复杂度提供了理论指导。

Perforated fracturing of horizontal wells is a key measure to exploit unconventional oil and gas reservoirs,but the competitive initiation of hydraulic fractures from perforation tunnels and the non-planar propagation near the wellbore are still unclear. Therefore,taking the well HX of shale oil reservoir as an example,a three-dimensional fully-coupled fracturing model with helical perforation is established by using the discrete lattice method. The interaction behavior and propagation evolution of multi-tunnel fractures for helical perforation are described in detail. The impacts of controlling factors such as horizontal stress difference,perforation density and phase angle on the propagation of near-wellbore fractures are systematically studied,and several engineering measures to control the complexity of near-wellbore fractures are put forward. The results show that there are longitudinal fractures and transverse fractures at the bottom of perforation tunnels in the initial stage of fracturing,then,transverse fractures propagate predominantly while longitudinal fractures are restrained due to the influence of in-situ stresses,and finally,a dominant transverse-fracture perpendicular to the direction of the minimum horizontal principal stress is formed at the far end after different communication between fractures initiated from adjacent tunnels. When the horizontal wellbore is oriented along the direction of the minimum horizontal stress,the low horizontal stress difference,high perforation density and low phase angle are beneficial to the creation of simple and continuous transverse-fractures near the wellbore. However,under the conditions of high horizontal stress difference,low perforation density and high phase angle,complex fractures with multiple branches are generated due to the difficulty in communication between fractures initiated from adjacent tunnels. The proposed three-dimensional fully-coupled model of perforated fracturing effectively describes the initiation and propagation of multiple-tunnel fractures,and the research results provide theoretical guidance for controlling the complexity of near-wellbore fractures by optimizing perforation completion.