摘要
碳酸盐岩储层天然裂缝发育,当水力压裂人造裂缝与天然裂缝相遇时,裂缝扩展方向可能发生改变,而常规裂缝扩展仿真中裂缝扩展多基于平面扩展,无法研究裂缝转向问题。针对碳酸盐岩储层压裂过程中主裂缝遇到天然裂缝后的裂缝扩展方向问题,利用扩展有限元和常规有限元的接触算法,编制扩展有限元的UEL用户子程序嵌入ABAQUS平台,并结合塔河碳酸盐岩储层参数,进行碳酸盐岩储层的方向预测仿真。仿真结果表明,水力裂缝遇到天然裂缝后是否转向取决于水平主应力差值的大小,存在一个发生转向的极限值。对于塔河储层算例,极限值为8MPa,当储层水平主应力差高于8MPa时,水力裂缝直接穿过天然裂缝,不发生转向;当低于8MPa时,水力裂缝遇天然裂缝后发生转向,沿天然裂缝扩展,且缝宽减小。水力裂缝沿天然裂缝扩展后是否发生二次转向取决于水平主应力差与极限值差值的大小。当水平主应力差较大时(5MPa),在天然裂缝尖端将发生二次转向,裂缝宽度进一步降低;当水平主应力差较小时(2MPa),将不发生二次转向,裂缝沿天然裂缝方向继续扩展。研究结果为解决裂缝的非平面扩展做出了有益探索,为裂缝性油藏的水力裂缝扩展仿真提供了支撑。
Nature fractures are highly developed in carbonate reservoirs,when fracturing this type of reservoir,the fracture path is hard to be predicted because that the hydraulic fracture may change direction when encounters with nature fracture,and traditional models are based on planar fracture which cannot simulate complex fracture. The concern of the paper is to simulate the interaction between hydraulic fracture and nature fracture in carbonate reservoirs. In this paper,we embedded the UEL subroutine to the extendible software ABAQUS combining the theory of Extended Finite Element method and contact algorithm of tradition Finite Element method. Ta He carbonate reservoir parameters were used as input data,and the new model was used to simulate fracture growth when the hydraulic fracture met the nature fracture; Fracture expansion path and geometry were analyzed. According to the simulation results,following conclusions can be drawn：（ 1） Whether fracture growing path will change direction when it meets nature fracture depends on the horizontal in-situ stress difference,there is a limiting value of changing direction.For the Ta He reservoir case in this paper,the limiting value is 8MPa,when the reservoir in-situ stress difference is higher than 8MPa,the hydraulic fracture will cross the nature fracture without changing direction; when the stress difference is lower than 8MPa,hydraulic fracture will expand along the nature fracture,and the fracture width reduce.（ 2） Whether fracture path will be redirected for a second time depends on the gap between the absolute in-situ stress difference and the limiting value. With a relatively lager in-situ stress difference 5MPa,fracture will change its direction at the tip of the nature fracture with smaller fracture width; while the in-situ stress difference is2 MPa,fracture will continue its path along the nature fracture without redirection. This paper makes some contribution to solving the fracture non-planar propagation,and provides a new method to simulate fracture p
出处
《计算机仿真》
CSCD
北大核心
2016年第8期105-110,共6页
Computer Simulation
关键词
扩展有限元法
裂缝扩展
天然裂缝
裂缝转向
Extended finite element method
Fracture propagation
Nature fracture
Fracture redirection
