裂缝闭合临界流体压力对油气田开发的影响

裂缝在低渗透致密砂岩油气藏、碳酸盐岩油气藏、变质岩类油气藏中广泛发育和存在，一方面影响油气的聚集与分布，另一方面裂缝的动态变化特征又将极大地影响到油气藏的开发方式和油气的采收率。因此，针对裂缝性油气藏开采过程中裂缝的动态行为开展研究，对高效开发该类油气藏具有重要的指导性意义。文章在裂缝及裂缝面微凸体受力分析的基础上，结合Druck-Prager方程对裂缝表面微凸体的屈服进行了研究。结果表明，裂缝微凸起的屈服与裂缝的闭合存在一个临界的裂缝内流体压力，该压力由裂缝地层所处的原地应力状态、裂缝的倾角和倾斜方位角，以及岩石的屈服强度决定；屈服强度越高的岩石，其临界裂缝闭合流体压力越低，即高屈服强度岩石中的裂缝即使裂缝内流体压力处于较低水平，裂缝也不会发生闭合。

Effects of Critical Fluid Pressure of Fracture Closure on Oil/Gas Exploitation

Fractures grow and exist widely in tight sand reservoirs with low permeability, carbonate reservoirs and metamorphic reservoirs. On one hand, fractures will affect the accumulation and distribution of oil and gas. On the other hand, the performance of the fractures will also greatly affect the development mode of reservoirs and the oil/gas recovery factor. So studying the performance of the fractures in the exploitation process of reservoirs has important guiding significance to develop this kind of reservoirs efficiently. Based on force analysis of the fractures and the mini-protuberances spreading on the fracture faces, with Druck-Prager equation, the critical yielding of the mini-protuberances spreading on the fracture faces is studied. The results show there is a critical fluid pressure within the fractures resulting in the yielding of the mini-protuberances and the closure of the fractures. The critical pressure depends on the original earth stress of the fractured reservoir, the dip angle and azimuth of fractures, and the yield strength of rocks. The higher the yield strength of rocks is, the lower the critical fluid pressure of fracture closure. That means the fractures in the rocks with high yield strength will not close even though the fluid pressure within the fractures is low.