基于高密度钻井液的高温涡轮取心钻进模型研究

The ultra-deep-hole project over ten thousand meters is the main part of the deep exploration program of the Earth in china. It faces the complicated conditions such as high temperature, high pressure and large stress. In order to balance formation pressure in high temperature condition, the turbodill coring system driven by the ultra-high density drilling fluid (≥2.0g/cm3) will be used. At present, the design theory of turbine blades based on high-density and high-viscosity drilling fluid is still and the research on high-temperature turbodrill coring technology still haven’t effective implemented. Based on the design method of non-Newtonian, the turbodrill model is put forward to improve the drilling speed and core quality. Firstly, the fluid-solid coupling model between high-temperature drilling fluid and single blade was established by unsteady flow continuity equation, multi-phase flow basic equation and viscous fluid N-S equation. Secondly, taking into account the blade thickness and the input differences of turbine-stages, the momentum equation of multi-stage turbine output is established based on the theory of flow field around the turbine blade. The relationship between flow field and main controlling factors such as blade structure and drilling fluid properties is studied. Then, considering the hydrodynamic load and the mechanical load, the coring drilling model of turbodrill with coring assembly was established to simulate the coring process，and it is modificated by indoor drilling experiments in hard strata. Finally, the structure of blade, coreing assembly and drilling parameters are optimized by the drilling model according to the drilling speed and coring quality. In addition, an effective drilling method and coring technology that can be used in typical hard rock formations in high temperture conditions will be developed.

万米超深孔工程是地球深部探测计划的主要部分，其面临着高温硬岩大应力等井下复杂工况，抗高温超高密度（≥2.0g/cm3）钻井液驱动的全金属涡轮钻具将是取心作业主要形式。当前，基于高密度介质的涡轮叶片设计理论尚处空白，硬岩涡轮取心工艺研究匮缺。课题基于非牛顿流体基本理论，创新高温涡轮叶片设计理论，建立涡轮取心模型，以提高钻进速度和取心效果。首先，利用非定常粘性流动基本方程建立起高温钻井液与叶片之间流-固耦合模型。随后，考虑叶片厚度和涡轮级副差异，基于叶栅绕流理论，开展涡轮输出特性与叶片结构、钻井液特性等关系研究；考虑取心钻具水力负载和破岩机械负载，针对硬脆和硬塑性地层，建立高温高密度钻井液驱动的涡轮钻具-取心钻具-地层为一体的取心钻进模型，并利用多级仿真和实钻实验进行修正。最后，利用该模型对涡轮叶片结构、钻具结构和钻进参数等进行优化，进而为创新涡轮钻具设计和超深孔涡轮取心工艺提供参考依据。

我国即将启动的万米深孔钻探工程面临着孔底高温、高压环境，细长钻柱与井壁巨大摩阻损耗等带来钻机地表驱动差、钻杆强度不足等问题，采用孔底动力钻具驱动是必然选择，而全金属的涡轮钻具具有耐高温、耐腐蚀等优点，是当前唯一能在超过250℃高温高压环境下钻进的动力钻具。课题在开展高温高密度钻井液流变性研究的基础上，提出非定常流动条件下涡轮叶片设计方法，建立高温涡轮钻具取心钻进模型，进而提高涡轮钻进效率和改进钻进工艺。..首先，本项目考虑涡轮流场，基于固液两相流基本方程以及修正的伯努利方程，建立了两相流粘性流动与涡轮叶片耦合作用的数学模型，提出了单级涡轮定转子性能预测模型，推导出两相流情况下涡轮扭矩、功率、压降的计算公式，定性分析了两相流、流体密度、流体粘度对涡轮输出性能的影响。研究结果表明：粘度对涡轮的扭矩和功率影响不大，但会大幅增加涡轮消耗的压降，降低效率；密度的增加可明显提高扭矩和功率，提升钻具性能，但同时也会增加压降。..随后，建立叶栅绕流的单涡轮级设计模型，推到了三维叶片的水力性能理论，探究了涡轮副的结构对水力性能的影响规律和机理，并通过计算流体动力学仿真分析进行验证；建立了多级多叶片设计模型，开展了全涡轮级工作特性预测研究，优化设计涡轮基本叶型和结构；建立涡轮钻具-取心结构-岩心结构水力负载模型，揭示涡轮钻具出口流动对流场的作用机理，并开展涡轮取心系统仿真研究；提出涡轮叶片新的三维成型方法，推导了其三维叶片水力性能的表达式，通过理论分析、仿真分析和试验验证了三维叶型优化设计能够提高涡轮钻进效率，优化钻进工艺，为提高地球深部探测高温取心效果和钻具优化提供参考依据。