新井定向射孔转向压裂裂缝起裂与延伸机理研究

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。

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

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.