Abstract Drilling fluids perform a number of important functions during a drilling operation, including that of lifting drilled cuttings to the surface and balancing formation pressures. Drilling fluids are usually designed to be structured fluids exhibiting shear thinning and yield stress behavior, and most drilling fluids also exhibit thixotropy. Accurate modeling of drilling fluid rheology is necessary for predicting friction pressure losses in the wellbore while circulating, the pump pressure needed to resume circulation after a static period, and how the fluid rheology evolves with time while in static or near-static conditions. Although modeling the flow of thixotropic fluids in realistic geometries is still a formidable future challenge to be solved, considerable insights can still be gained by studying the viscometric flows of such fluids. We report a detailed rheological characterization of a water-based drilling fluid and an invert emulsion oilbased drilling fluid. The micro structure responsible for thixotropy is different in these fluids which results in different thixotropic responses. Measurements are primarily focused at transient responses to step changes in shear rate, but cover also steady state flow curves and stress overshoots during start-up of flow. We analyze the shear rate step change measurements using a structural kinetics thixotropy model.

中文翻译：

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钻井液流变学测量和触变行为建模

摘要 钻井液在钻井作业中发挥着许多重要的作用，包括将钻屑提升到地面和平衡地层压力。钻井液通常设计为具有剪切稀化和屈服应力行为的结构流体，大多数钻井液还具有触变性。钻井液流变学的准确建模对于预测循环时井筒中的摩擦压力损失、静止期后恢复循环所需的泵压力以及流体流变学在静态或接近静态条件下如何随时间演变是必要的。尽管在现实几何形状中模拟触变流体的流动仍然是一个艰巨的未来挑战，但通过研究此类流体的粘度流动仍然可以获得相当多的见解。我们报告了一种水基钻井液和一种反相乳液油基钻井液的详细流变特性。这些流体中引起触变性的微观结构不同，从而导致不同的触变反应。测量主要集中在对剪切速率阶跃变化的瞬态响应，但也涵盖稳态流动曲线和流动启动期间的应力超调。我们使用结构动力学触变性模型分析剪切速率阶跃变化测量值。测量主要集中在对剪切速率阶跃变化的瞬态响应，但也涵盖稳态流动曲线和流动启动期间的应力超调。我们使用结构动力学触变性模型分析剪切速率阶跃变化测量值。测量主要集中在对剪切速率阶跃变化的瞬态响应，但也涵盖稳态流动曲线和流动启动期间的应力超调。我们使用结构动力学触变性模型分析剪切速率阶跃变化测量值。