Abstract:

The junction stability of multilateral well at different geometry and orientations in loose sand reservoir is very poor. Even though the production drawdown pressure is lower than 1 MPa, junctions collapse and block laterals. Consequently, there is a limited contribution of laterals to productivity. In order to enhance the stability of the multilateral well and increase the critical drawdown pressure, special treatment should be enforced to the junctions. In the normal fault in-situ stress field, regardless of the junctions, the main bore direction should be extended along with the in-situ minimum horizontal 〖JP+3〗principle stress as close as possible. Depth and width of failure area are severely influenced by the build-up rate of laterals.The relationship between the increase of build-up rate and reduction of junction plastic failure depth is found to follow the power function in the same production drawdown pressure. Provided the length and included angle of multilateral well are given, higher build-up rate is,the stability of multilateral well is much better. Another key factor of multilateral well stability is the interval between laterals. Interference could be ignored when interval is larger than 40 m if laterals arranged on different sides, otherwise, the interval should be larger than 45 m. In open hole or screen pipe completion, junction plastic failure depth and sanding swept area increase in function of exponent along with the growth of production drawdown pressure.

Key words: multilateral well configuration, loose sandstone reservoir；critical production drawdown pressure, plastic failure depth, wellbore stability

摘要：

对疏松砂岩稠油油藏，无论采用哪种构型的分支井，主分井筒接合部区域的稳定性都很差。即使生产压差低于1 MPa，该处也会发生井壁失稳垮塌，堵塞分支井眼，削弱分支对产能的贡献。因此，必须对接合部地层进行特殊处理，以提高分支井系统整体稳定性，提高生产压差。在正断型地应力场条件下，不考虑主分井筒接合部的影响，主分井筒延伸方向应尽可能沿原地最小水平主应力方向延伸。分支造斜率对接合部地层的破坏程度和破坏区域有明显影响，相同压差下，随分支造斜率增大，主、分井筒接合部塑性破坏深度呈幂函数关系减小；在主、分井筒长度及主、分井筒夹角一定时，采用较大造斜率设计的分支井系统具有更高的井眼稳定性。分支间距是影响分支井系统稳定性的另一个重要因素。当分支处于主井眼同侧时，分支间距大于45 m后分支间影响可忽略；当分支处于主井眼异侧时，分支间距大于40 m后分支间影响可忽略。在裸眼和主井筒下筛管两种完井方式下，分支接合部破坏深度、出砂波及区域随生产压差增大均呈指数增大。

关键词: 分支井构型, 疏松砂岩油藏, 临界生产压差, 塑性破坏深度, 井眼稳定性