A comprehensive study of near-wall turbulence for developing effective hole cleaning strategies

水平井钻井成功的关键是钻井液固体的有效运移。岩屑清除不充分会导致代价高昂的问题，如卡钻、扭矩和阻力过大、套管/固井和测井困难。管道和环空中固体运移的研究也有助于其他现场作业的设计，如：水力压裂中支撑剂的运移；清理生产井出砂；以及油砂的管道输送。在固体输运理论中，一个长期占据中心地位的理论假设，临界床层剪切应力引发了沉积物床上颗粒的运动。然而，最近的研究表明，近床湍流波动和固体颗粒对流动的随机暴露使颗粒有可能移动-即使在非常低的平均床剪切应力值下也是如此。其他研究表明，在固体输运过程中，纵向和垂直方向的动量通量可能比剪切应力更重要。因此，固体在管道和环空中的输运模型不应该像目前大多数输运模型那样仅仅基于剪切应力来建立。本研究的主要目标是进行实验和理论研究：i-)确定局部湍流爆发/横扫作用（主导近壁区域）对颗粒沉积和/或再夹带的影响；Ii -)观察和量化发生在床浆界面的颗粒沉积/去除过程；Iii -)分析控制力量，并提供一个全面的（机理）模型，可用于开发有效的管道和环空固体输送策略。固体输送过程的任何改进都将特别有利于加拿大西部的重油生产，该地区广泛使用水平井。这些储层主要是松散的；因此，钻井、完井和采收作业往往容易在长水平井段产生过多的出砂、沉积和堆积。本研究中提出的全面实验研究将极大地提高工业在此类水库中安全、经济运行的能力。

Effective transport of drilled solids is essential for the successful drilling of horizontal wells. Insufficient cuttings removal causes costly problems such as pipe sticking, excessive torque and drag, difficulties in casing/cementing and logging. The study of solids transport in pipes and annulus is also pertinent to the designing of other field operations such as: proppant transport in hydraulic fracturing; cleaning of sand from production wells; and pipeline transport of oil sands. A long occupied central position in solids transport theory assumes that critical bed shear stress initiates the motion of a particle lying on a bed of sediments. However, recent studies have shown that near bed turbulent fluctuations and the random exposure of solid particles to the flow make it possible for particles to move - even at very low values of the mean bed shear stress. Other studies indicate that the momentum fluxes in longitudinal and vertical direction may be more important in solids transport than the shear stress. Therefore, models for solids transport in pipes and annuli should not be developed based on shear stress alone, as most of the current transport models generally are.The main objectives of this research are to conduct experimental and theoretical studies: i-) to determine the effect of local turbulent burst/ sweep actions (dominating the near wall regions) on the particle deposition and/or re-entrainment; ii-) to observe and quantify the particle deposition/removal process occurring at the bed-slurry interface; iii-) to analyze the controlling forces and offer a comprehensive (mechanistic) model which can be used for the development of effective solids transport strategies in pipes and annuli. Any improvement in solids transport process could particularly benefit Western Canadian heavy-oil production, which extensively uses horizontal wells. These reservoirs are predominantly unconsolidated; as a result, drilling, completion and recovery operations are often prone to excessive sand production, deposition and accumulation along the long horizontal wellbore sections. Industry's capacity to operate safely and economically in such reservoirs will benefit tremendously from a full-scale experimental research such as the one proposed in this study.