斜井水力压裂三维裂缝动态扩展数值模拟

 斜井的近井筒效应较为复杂，若存在射孔相位误差，极易在地层和水泥环交界面处产生微环隙，引起较高的近井压降，甚至在微环隙内产生砂堵，造成压裂施工失败。对于斜井水力压裂裂缝三维几何形态的预测，一直是水力压裂领域的难题。本文采用黏弹性损伤cohesive孔压单元，考虑套管、水泥环、地层、射孔孔眼和微环隙对水力压裂的影响，建立了斜井的水力压裂三维裂缝形态的有限元模型。同时，考虑水力压裂过程中储层岩石渗透率和孔隙度的动态演变，对渤海湾地区20°井斜角的C5井开展了水力压裂裂缝动态扩展的数值模拟研究，计算得到的井底压力曲线与现场施工曲线一致。研究了斜井水力裂缝和微环隙的起裂和扩展机理。微环隙在水力压裂的初始阶段沿井眼周向和轴向同时起裂并扩展，随着水力裂缝的扩展而逐渐闭合，对于具有较复杂近井筒效应的硬地层大斜度井而言，微环隙的起裂和多条裂缝的产生，极易导致压裂失败。斜井水力裂缝近似两翼对称，易向地应力较小的盖层扩展，缝高较难控制。数值模拟结果为现场水力压裂的设计提供理论指导。

Three-dimensional Numerical Simulation of Hydraulic Fracture Dynamic Propagation of Deviated Well

The near wellbore fractures are very complex in deviated well. If the perforations are not along with the maximum principal stress direction, a micro-annulus between the cement sheath and rock formation interface is likely to generate. For a long time, it has been difficult to simulate the three-dimensional geometries of hydraulic fracture in deviated well. In this paper, using viscoelastic continuum damage pore pressure cohesive elements and considering casing, cement, formation, perforation and the micro annulus, a three-dimensional numerical simulation model of hydraulic fracture dynamic propagation of deviated well is established. Then, considering the dynamic evolution of permeability and porosity of the pay zone, the hydraulic fracture dynamic propagation of a 20° deviated well in the Bohai Basin oilfield is calculated, and the calculated well bottom-hole pressure curve is consistent with the field hydraulic fracturing treatment curve. The hydraulic fracture and micro annulus initiation and propagation mechanism are analyzed. The micro annulus initiates and propagates simultaneously alone the well axial and circumferential directions at the initial stage of hydraulic fracturing, and then it closes with the propagation of the hydraulic fracture. The two hydraulic fracture wings of the deviated well are almost symmetrical, and easily propagate into the caprocks where the in-situ stress is smaller, that is, the fracture height of the deviated well is hard to control.