A Comprehensive Study of the Combined Effects of Drilling Fluid Rheological Properties and Near Wall Turbulence on the Particle Removal From Bed Deposits in Horizontal Wells

当钻长水平井时，钻出的固体倾向于在井筒的低侧下沉并形成一个固定的床。固定岩屑床的存在给施工带来了困难，如封堵、扭矩和阻力过大、钻井速度慢，严重时会卡住油管、井漏，甚至失去井控。偶尔，钻探必须停下来清理固定床，这是一个昂贵的过程，必须及时完成。尽管在钻井液、工具和现场实践方面取得了重大进展，加上大学和行业50多年的研究，但现场经验表明，井眼清洁仍然是大多数水平井的主要问题。这项研究的主要动机是缺乏一个可靠的模型来优化清孔工艺。 作为建立统一的井眼清洗理论的系统努力的一部分，本文提出了一个全面的研究计划，该计划要求对以下方面进行实验研究：i)近床湍流及其与床层颗粒去除的关系；ii)床层颗粒去除的临界流量和床层冲蚀率如何随钻井液剪切粘度、凝胶强度、弹性应力和其他粘弹性性质的变化而变化。 孔清洗实验将使用9米长的同心环形几何形状的水平流动回路(外管内径=95 mm，内管外径=38 mm)进行。最先进的流动可视化技术，粒子图像测速仪和粒子跟踪测速仪，将被用于确定局部流体和固体颗粒的速度。 此外，还将进行计算流体力学(CFD)模拟研究，以模拟岩屑从床上沉积的过程。这种情况下的具体目标是：i)开发水平井多相固/液流动的CFD模型；ii)将CFD模型用作将结果从实验室提升到现场规模的工具；iii)使用CFD模型预测在给定操作条件下的井眼清洗所需时间，并确定钻井液流量和流变性的最佳组合，以实现最小的井眼清洗时间。 在过去的几十年里，钻井的水平井数量急剧增加，然而，井眼清洁仍然是一个挑战，特别是在钻井长水平段时。需要开发有效的井眼清理策略，以减少与井眼清理相关的时间。井眼清洗时间越短，用于实际钻井的时间就越多，从而可以显著降低钻井成本。以较低的成本交付油井对于确保储量的可获得性至关重要，否则开采这些储量在经济上是不合理的。工业安全和经济运行的能力将极大地受益于一项全面的实验和数值研究，如本研究中提出的那样。

When drilling long horizontal wells, drilled solids tend to settle down on the low side of the wellbore and form a stationary bed. Presence of stationary cuttings bed causes operational difficulties such as pack-off, excessive torque and drag, slow drilling rate, and in severe cases, stuck pipe, lost circulation, and even loss of the well control. Occasionally, drilling must stop to clean the stationary bed, which is an expensive process and must be done in a timely manner. Despite significant progress made in drilling fluids, tools, and field practices, along with more than 50 years of university and industry research, field experience indicates that hole cleaning is still a major problem in most horizontal wells. The primary motivation of this study is the lack of a reliable model for optimizing hole cleaning process. As part of the systematic efforts to develop a unified theory of hole cleaning, a comprehensive research plan is proposed here, which calls for experimental investigation of: i-) the near bed turbulence and how it relates to particle removal from bed deposits ; ii-) how the critical flow rate for the particle removal from bed deposits and bed erosion rate change with drilling fluid shear viscosity, gel strength, elastic stresses and other viscoelastic properties. Hole cleaning experiments will be conducted using a 9m long horizontal flow loop with concentric annular geometry (Outer Pipe ID= 95 mm, Inner Pipe OD= 38 mm). State of the art flow visualization techniques, Particle Image Velocimetry and Particle Tracking Velocimetry, will be used to determine local fluid and solid particle velocities. In addition, a Computational Fluid Dynamic (CFD) simulation study will be conducted to model the cuttings removal from the bed deposits. Specific objectives in this case are to: i-) Develop a CFD model of multiphase solid/liquid flow in horizontal well; ii-) Use the CFD model as a tool for upscaling results from lab to field scale; iii-) Use the CFD model for predicting time required for hole cleaning under given operational conditions and determine best combination of drilling fluid flow rate and rheological properties for minimum hole cleaning time. The number of horizontal wells drilled has dramatically increased over the past decades, however, hole cleaning still remains a challenge especially when drilling long horizontal sections. Efficient hole cleaning strategies need to be developed to reduce time associated with well cleaning. The shorter the hole cleaning time, the more time can be spent on actual drilling and, as a result, the drilling cost can be reduced significantly. Delivering an oil well at lower costs is essential in ensuring accessibility of reserves, which otherwise are not economically sound to exploit. Industry's capacity to operate safely and economically will benefit tremendously from a full-scale experimental and numerical research such as the one proposed in this study.