泡沫钻井全过程井筒-地层耦合瞬态传热机理研究

The distribution of the borehole temperature plays a very important role during foam drilling process, which has influence on multiple key factors, such as the distribution of the borehole pressure, the rheological behavior of the drilling fluid, the frictional resistance and the borehole stability. For a safer and faster drilling, it's crucial to understand the rule of the borehole temperature distribution during foam drilling. However, the present computational models about the distribution of the borehole temperature during foam drilling have the following problems: neglect of the influence by the major thermal effects including simple fluid or single condition; apply the overall heat transfer coefficient as the local convective heat transfer coefficient. For the lack of research that exist at present, the project on the basis of different conditions between the wellbore and the formation mechanism of energy exchange on the analysis, considering the influence of the well borehole temperature of the main heat source term, the establishment of the whole process of foam drilling borehole - formation coupling instant state heat transfer model, and through field tests to validate and drilling optimization model can systematically solve cyclic pressure and flow analysis of foam drilling fluid during the drilling process, temperature and static temperature and circulation during drilling and formation of the wellbore temperature distribution calculation to obtain a number of fluid temperature in the wellbore tool joints, drill eccentric, different speed and tripping drill pipe and other different conditions, pressure and velocity variation for the realization of the wellbore pressure control, wellbore stability prediction and foam drilling parameter optimization procedure to provide a theoretical basis.

泡沫钻井过程中，井下温度分布是影响井下压力平衡及控制、钻井液的流变性能、摩阻压力、井壁稳定等方面的重要因素，掌握其分布规律对钻井作业安全、快速地进行具有极其重要的意义。现有传热模型多数基于简单流体、单一工况或稳定流动状态条件下，且未充分考虑井筒热源项的影响，导致计算结果与实际工况差别较大。针对目前研究中存在的不足，本项目在分析不同工况下井筒与地层之间能量交换机制的基础上，综合考虑井内主要热源项对井筒温度的影响，建立泡沫钻井全过程井筒-地层耦合瞬态传热模型，并通过现场钻井试验来验证和优化模型，能够较系统地解决泡沫钻井过程中钻井液的循环压力和流速分析、循环温度和静止温度以及钻井过程中井筒和地层的温度分布的计算问题，得到井筒内多项流体在钻具接头、钻杆偏心、不同钻杆转速和起下钻等不同工况下的温度、压力和速度变化规律，为实现井筒压力控制、井壁稳定性预测和泡沫钻井规程参数优选提供理论基础。

泡沫钻井过程中，井下温度分布是影响井下压力平衡及控制、钻井液的流变性能、摩阻压力、井壁稳定等方面的重要因素，掌握其分布规律对钻井作业安全、快速地进行具有极其重要的意义。本项目在分析不同工况下井筒与地层之间热交换机制的基础上，建立了钻头钻进岩石的三维模型，利用有限元软件对钻头破碎岩石过程进行热-结构耦合仿真模拟，分析了钻进过程中钻头切削齿温度场、应力场的分布规律；建立了泡沫钻井循环期间和静止期间井筒-地层的物理模型和数学模型，模拟分析了泡沫温度、泡沫密度、泡沫流速等因素对井筒-地层温度场的影响规律；建立泡沫钻井多相流的压力和速度模型，分析井筒内多项流体在不同工况下的压力和速度变化规律；搭建了泡沫钻井实验平台，进行泡沫钻井全过程试验，通过正交实验的方法，研究了泡沫钻井液在循环和静止工况下，不同泡沫初始温度、不同泡沫上返流速和不同泡沫密度等因素对井筒-地层温度场规律的影响，验证了数值模拟结果的准确性，得出了适合冻土地层钻进的泡沫钻井液相关参数，为冻土地区泡沫钻进规程参数优选提供了理论基础。