【作者】 孙晓峰；

【导师】 闫铁；

【作者基本信息】 东北石油大学 ， 石油与天然气工程， 2014， 博士

【摘要】 现场实践和室内实验研究均表明水平井、大位移井、多分支井的大斜度井段在钻井过程中，岩屑易堆积形成岩屑床，导致钻杆出现高摩阻、高扭矩、拖压等现象，严重时造成卡钻、钻具断落等井下安全事故。因此研究如何提高岩屑运移效率，抑制岩屑床生成的方法和相关机理十分必要。论文重点研究了直井段岩屑在钻井液中的沉降速度，大斜度井段岩屑的启动速度和岩屑悬浮速度等岩屑运移问题。根据前人研究成果总结了不同岩性、不同钻头类型和岩石埋深对岩屑颗粒粒径的影响，通过室内实验数据回归得到了不同粒径岩屑颗粒在幂律流体中的阻力系数表达式，从而建立了适用于幂律流体的岩屑沉降速度模型。提出了岩屑床休止角的概念，并通过室内实验，测定了岩屑休止角数值。根据岩屑床休止角的定义和力学平衡关系可以求得岩屑颗粒之间滑动运移时的摩擦系数，同时根据岩屑床休止角数值确定大斜度井段起始井斜角。根据岩屑力学平衡关系建立了岩屑床床面颗粒滑动运移、滚动运移和举升运移三种形式的岩屑启动速度模型。根据直井段岩屑沉降速度模型和已发表的实验数据，建立了考虑钻杆旋转、岩屑粒径等因素影响的小斜度、中斜度和大斜度井段岩屑悬浮速度模型。模型数值模拟分析结果表明井斜角、机械钻速、钻井液有效粘度对水平井段岩屑运移影响较大，而岩屑粒径和钻杆转速主要影响大斜度井段，流性指数和岩屑密度则影响小斜度井段。通过CFD数值模拟方法定量评价了钻杆旋转对岩屑床的抑制作用效果，根据数值模拟结果回归出了岩屑床比面积和压耗计算模型。模拟表明钻杆旋转作用使岩屑在井眼环空内沿周向非对称状分布，能够显著增加钻井液切向速度，由此产生的切向拖拽力能够在一定程度上抑制岩屑床的形成。当钻井液在中低排量下，提高钻杆转速能够显著提高携岩效率，有效提高井眼清洁程度。而在高排量下，钻柱转速达到160RPM以上时对提高携岩效率影响不再显著。提出了机械法井眼清洁工具的基本叶片类型，通过数值模拟分析得到了不同类型叶片的旋转辅助清洁岩屑作用机理。由CFD数值模拟可知螺旋形-V形复合型叶片井眼清洁工具有较高岩屑床清洁效率。基于螺旋工具面上岩屑颗粒的力学平衡，可对岩屑通过螺旋式工具后的运动规律进行定量的描述。讨论了基于叶元法井眼清洁工具叶片的水力结构设计方法，为这类工具的设计提供参考依据。更多还原

【Abstract】 It has been shown by field practice and laboratory experiments that during the drillingoperation of highly-deviated interval of horizontal wells, extended reach wells, multilateralwells, cuttings are likely to accumulate and form cuttings bed, which leads to the phenomenonof high drag, high torque and drag slide of the drill bit, even downhole safety accidents, e.g.,sticking and broken off of the drilling pipe. So we can reach a conclusion that it is necessary toresearch on methods and mechanism of enhancing the hole cleaning efficiency and inhibitingthe formation of cuttings bed. This study is focused on terms of cutting settling velocity indrilling fluids in vertical well interval, cuttings incipient velocity and cuttings suspensionvelocity in highly-deviated interval, etc.In this study, how lithology, bit types and the burial depth of the rock influence the rangeof particle size have been summarized based on previous research achievements. The range ofparticle size, in which the cutting is likely to lead to the formation of cuttings bed in the annulus,have been defined. Based on laboratory experiments, a formula of drag coefficient of thecuttings in different particle size in power-low fluid has been introduced, and a model appliedfor cuttings settling velocity in power-low fluid has been established.In the study, the concept of cuttings bed repose angle has been proposed.The values ofcuttings bed repose angle of different sort of cuttings have been measured during the laboratoryexperiment of cuttings bed repose angle. The friction coefficient of cuttings during the processof slip transport could be obtained by concept of cuttings bed repose angle mechanical balancerelation. Also, initial deviation angle in highly-deviated interval can be obtained by the valueof cuttings bed repose angle. Based on cuttings mechanical balance relationship, three forms ofcuttings incipient velocity model, e.t., cuttings slip transport，rolling transport，lift transporton the surface of cuttings bed, have been built. Numerical analysis of the model showed thatthe critical slip transport and rolling transport incipient velocities exceed0.6m/s generally forcuttings whose diameter range from1mm to3mm.Based on the model of cuttings settling velocity in vertical well section and publishedexperimental data, cuttings suspension velocity models in low, medium and highly deviatedinterval have been built considering impact factors, e.g., rotational speed of drill pipe, cuttingsdiameter, etc.The result of numerical simulation and analysis proves that drilling operation ofhorizontal interval is greatly impacted by deviated angle, rotational speed and effectiveviscosity of drilling fluid. Cuttings diameter and rotational speed of drill pipe impact mainly onhighly-deviated well intervals drilling operation, and flow index and cuttings density influenceon drilling operation in low-deviated well intervals.CFD numerical simulation has been applied to quantitatively evaluate the inhibition effectof drill pipe rotation on cuttings bed. Also, according to numerical simulation regression, the specific area of cuttings bed and a model for pressure loss calculation have been obtained. Thesimulation shows cuttings distribute along the circumferential direction asymmetrically in theannulus owing to the rotation of drill pipe, and thus the tangential velocity of drilling fluidincreases significantly. Then the formation of cuttings bed is inhibited to some extent by thetangent drag force caused by the rotation of drill pipe. As a consequence, increasing rotationalspeed could remarkably enhance the cuttings transport efficiency and hole cleaning efficiencyat medium or low pump rate. However, when drill pipe exceed160RPM at high pump rate, theinhabitation of rotation velocity on cuttings transport efficiency is no longer significant.In this study, basic blade types of mechanism hole cleaning tools are proposed.Rotationhole cleaning assisted mechanisms of different type of blades are obtained according tonumerical simulation and numerical analysis. Based on CFD numerical simulation, it is provedthat spiral-V shaped hybrid hole cleaning tools has a higher efficiency in hole cleaning in theannulus According to mechanical balance of cuttings on the tool face, the motion law of cuttingswhich pass the spiral tool can be evaluated quantitatively, and tangent velocity and axialvelocity can be calculated separately in particular, providing a reference for the design of thissort of tools.更多还原