CalculationModelforAdhesionResistanceinDifferential Pressure Sticking of Downhole String

Zhou Yuting1Zhang Hui1Yang Boyuan1Wang Peng1.2.3Yu Qing4Liu Kerou1Lu Kunhong1 （1.ColegeofPetrolemEngneeing，China Uniersityofetrole（Beiing）;2.CNCEngineingTeoogyRamp;DCni ited;3.NationalEngineeingResechenteofOilamp;GasDrilingandCompletionTecolog；4JinghanMacnryReeaIst tute Limited Company of CNPC）

Abstract： Diffrential pressure sticking is one of the main causes for significantly increased non-production time and cost.The existing research on diferential presure sticking often relies onempirical summaries offield data or laboratory tests，while the current theoretical model research also fails to consider the stress on pipe string， wellboreconditionand mudcake strength.In this paper，considering the length，force and area of contact between the pipe string and the wellore wall，a calculation model for theadhesion resistance in diferential pressure stickingofdownhole string was built.Then，the model was used forsensitivityanalysis ontheaxialforceofthe string，the wellbore parameters（welldiameter，hole angle，dogleg）and the mud cake parameters（mud cake thickness，elastic modulus，Poisson'sratio，permeability），to understand how these factors affecttheadhesion resistane.Finally，the model was verified through exampleapplication.Theresults show that fortheaxial force of the string，theadhesion resistancedecreases withthe increase of tensionand increases with the increase of pressure.Forthe main wellbore parameters，the adhesion resistance decreases with the increase of welldiameterand increases with the increase of holeangleanddogleg.For the main mud cakeparameters，theadhesion resistance decreases with the increase of the elastic modulusof the mud cake，slightlydecreases with the increase ofthe Poisson’sratio of the mud cake， and first increases and then tends tobe smooth with the increase of the mud cake permeability；and the maximum adhesion resistance increases with the increase of the mud cake thickness.The research results provide a theoretical basis forthefurtherresearchondiferential pressure sticking andatheoretical guidanceforthefield pre-vention of sticking accidents.

Keywords：downhole string;diferential pressure sticking；adhesion resistance；frictional torque；axial force： wellbore pa-rameter；contact mechanics

0 引言

压差卡钻是显著延长非生产时间、增加成本的主要原因之一[1]。统计数据表明，在2016年发生的管柱阻卡事故中， 32% 为压差卡钻。在管柱下人过程中，管柱受自身重力、轴向力及弯矩影响易与井壁发生接触[3-4]。由于井下地层岩性和实际井眼轨迹复杂，管柱下入阻力大，管柱静止情况频繁，若管柱停靠在砂岩、泥页岩等易形成泥饼的地层，环空与地层间存在正压差，管柱会受到井壁泥饼的黏附力，严重时将引发压差卡钻事故。压差卡钻处理工艺烦琐[5-9]，不但会造成时间和经济成本的严重损失，处理不当还可能导致埋钻具甚至井眼报废等事故[10-11]。因此，研究井下管串黏附阻力并分析其影响规律具有重要意义。

程忠等[2基于现场压差卡钻事故进行了分析总结，认为管柱静止时间、压差、井斜角及狗腿度为管柱压差卡钻主要原因。王世越等[13对南海西部电缆测井作业数据进行分析和总结，建立了基于监督学习的电缆测井压差卡钻概率预测模型，分析了该区块不同井斜角、狗腿度、钻井液体系等因素与压差卡钻概率的关系。M.R.ANNIS等[14]通过试验研究了泥饼组分、接触时间对泥饼摩擦因数的影响，研究结果表明，泥饼摩擦因数随泥饼中重晶石含量及接触时间的延长而增大。张坤等[15]针对水平段压差卡钻情况研制了SPJ解卡液并进行了现场应用。汤明等[6基于室内试验数据，拟合了泥饼厚度和摩擦因数随盐水体积分数及时间的变化规律方程，建立了泥饼厚度随时间变化的压差卡钻模型，研究了钻柱静止时间、盐水体积分数及压差对黏附卡钻的影响规律。……