新井定向射孔转向压裂裂缝起裂与延伸机理研究

Study on initiation and propagation mechanism of fractures in oriented perforation of new wells

为了提高特低渗油藏新井的压裂效果,提出了采用定向射孔技术进行转向压裂从而形成双S型水力裂缝的新方法。基于有限元三维应力分析,研究了定向射孔下水力裂缝的起裂机理。考虑任意裂缝形态、地应力和缝内液体压力分布的影响,建立了任意形状裂缝应力强度因子的确定模型;同时考虑I型和II型断裂,建立了复合裂缝延伸准则。提出了定向射孔水力压裂裂缝的延伸轨迹计算模型和步骤,编制了裂缝延伸的模拟软件。采用地面微震进行了3口井的现场验证,地面微震检测结果与计算结果吻合。利用定向射孔压裂技术在单个层内可以形成双S型水力裂缝,可作为提高特低渗透油田产量的一种方式。

In order to improve fractures in new wells of low-permeability reservoirs, a new methodology to generate dual-S fractures in deflection fracturing of oriented perforation was proposed. The three-dimensional finite element method was used to study the mechanism of fracture initiation in oriented perforation. Considering the shape of arbitrary fracture, underground stress and fluid pressure distributed in fractures, a model for specifying stress intensity factor of arbitrary fracture was set up. The propagation criteria for mixed-type fracture of type Ⅰ and type Ⅱ were also presented. The models and computation procedures for determining fracture propagation path were provided, and the software for simulation of fracture propagation was developed. Surface micro-seismic technique was used in fracturing treatment of three wells to monitor fracture propagation directions. The monitoring results agreed well with the model prediction. The dual-S type fractures can be generated in a single formation by using oriented perforation fracturing technology, which may be an effective method to improve oil production in ultra-low permeability reservoir.