裂缝性地层固化类堵漏材料井下运移仿真模拟研究

固化类堵漏材料常用于裂缝性地层恶性漏失堵漏，在裂缝近井壁处形成完整的固结段塞，是堵漏成功的前提。固化类材料进入井筒后难免会与地层流体发生共混，堵漏浆-地层流体两相体积分布随着空间和时间变化，与流体理化性质、施工参数、裂缝几何形貌等有密切关系。为此，采用CFD仿真模拟方法，研究了固化堵漏浆密度和流变参数对堵漏浆裂缝体积分布及流速的影响规律，几何模型选择三维井筒-垂直裂缝模型，模拟压差为1.9 MPa，堵漏浆入口流速为2.5 m/s，两相流模型为VOF模型，井筒和裂缝中原始流体为水基钻井液。模拟结果表明，堵漏浆密度和动切力对其在井筒和裂缝中运移影响少，稠度系数和流性指数对堵漏浆裂缝驻留性能影响显著。稠度系数或流性指数越高，堵漏浆裂缝中流速越小，体积分数越高，低于临界值后，裂缝中将一直以堵漏浆-钻井液共混流体存在。流性指数相比稠度系数对于堵漏浆裂缝驻留能力影响更为显著，牛顿流体和剪切增稠型堵漏浆更利于在裂缝中形成完整段塞。该仿真模拟工作为固化堵漏浆流变性优化提供一定理论基础，有利于提升固化堵漏技术一次成功率。 

Simulation Study on Movement of Solidifying LCMs for Controlling Mud Losses into Fracturing Formations

Solidifying lost circulation materials (LCMs) are always used to control severe mud losses into fractured formations, they control mud losses by forming whole plugs near the borehole wall in the fractures. The solidifying LCMs entering the wellbore often inevitably are mixed with formation fluids. The volume distribution of the LCM slurry and the formation fluids changes with time and location, and is closely related to the physical-chemical properties of the formation fluids, the operation parameters and the geometry of the fractures. Using the computational fluid dynamics (CFD) method, the effects of the density and rheology of solidifying LCM slurries on the volume distribution of the LCM slurry and the formation fluids in the fractures and the flow velocity of the fluids were studied. In this study a 3D wellbore-vertical fracture model was used, the pressure differential used in the simulation was 1.9 MPa, the flow rate of the LCM slurry at the entry of the fractures was 2.5 m/s, the two-phase model was a VOF model, and the in-situ fluids in the wellbore and the fractures were a water based drilling fluid. The simulation results showed that the density and the yield point of the LCM slurry have little effect on the movement of the LCM slurry in the wellbore and the fractures, while the consistency index and the flow index significantly affected the residency of the LCM slurry in the fractures; the higher the consistency index and/or flow index, the lower the flow rate of the LCM slurry inside the fractures, and the higher the volume fraction of the LCM slurry inside the fractures. When the flow rate of the LCM slurry is less than the critical flow rate, the fractures will always be filled with the mixture of the LCM slurry and the drilling fluid. Compared with consistency index, flow index plays a more important role in affecting the residency of LCM slurries in formation fractures. LCM slurries of the Newtonian fluids and the shear-thickening fluids more easily form whole plugs in a fracture. This CFD simulation provides a theoretical basis for the optimization of the rheology of solidifying LCM slurries and is beneficial to the success rate at first try of controlling mud losses with the solidifying LCM slurries.