Mechanical Modeling and Analysis of Stability Deterioration of Production Well During Marine Hydrate Depressurization Production

Different from oil and gas production,hydrate reservoirs are shallow and unconsolidated,whose mechanical properties deteriorate with hydrate decomposition.Therefore,the formations will undergo significant subsidence during depressurization,which will destroy the original force state of the production well.However,existing research on the stability of oil and gas production wells assumes the formation to be stable,and lacks consideration of the force exerted on the hydrate production well by formation subsidence caused by hydrate decomposition during production.To fill this gap,this paper proposes an analytical method for the dynamic evolution of the stability of hydrate production well considering the effects of hydrate decomposition.Based on the mechanical model of the production well,the basis for stability analysis has been proposed.A multi-field coupling model of the force state of the production well considering the effect of hydrate decomposition and formation subsidence is established,and a solver is developed.The analytical approach is verified by its good agreement with the results from the numerical method.A case study found that the decomposition of hydrate will increase the pulling-down force and reduce the supporting force,which is the main reason for the stability deterioration.The higher the initial hydrate saturation,the larger the reservoir thickness,and the lower the production pressure,the worse the stability or even instability.This work can provide a theoretical reference for the stability maintaining of the production well.

对分课堂在流体力学教学中的实践

针对流体力学教学内容与特点,应用对分课堂教学模式,进行对分模式整体的课程设计、知识点对分教学设计以及三分钟对分设计,并对课后学习环节和课堂讨论环节进行设计,对流体力学对分教学实践进行反思与总结,为其他课程提供借鉴与参考。

顶部压井法最小泵排量实验及其计算方法

顶部压井法作为一种非常规压井方法,能够有效应对钻头不在井底、无法关井、井内喷空等复杂条件下的井喷。但是,目前该技术尚不成熟,其压井机理研究较少,参数计算方法也有待进一步完善。本文根据自行设计的可视化实验平台,模拟井内喷空状态下顶部压井实验。实验结果表明:顶部压井过程中,在气体压力一定的情况下,最小泵排量随注入管下入深度的增加而减小,随气体流量的增加而小幅度增加。同时,本文根据顶部压井过程中井筒流型变化,探究了顶部压井法压井机理,在考虑井筒流动及地层渗流的基础上,提出了顶部压井法最小泵排量参数计算模型。

置换法液相沉降规律及井筒压力变化研究

深水井控有时会遇到无法建立正常压井循环通道的情况,而置换法压井技术可以较好地解决这一问题,但目前对压井液沉降以及井筒压力变化规律的研究较少,所以对此进行深入研究具有重要的意义。本文通过置换法实验研究了液相沉降规律,从受力角度建立了液相沉降速度模型,并在此基础上分三个阶段:压井液注入阶段、压井液沉降阶段以及静液柱建立阶段,推导得到了井筒中的压力变化模型,最后通过实验数据对模型精度进行了验证。结果表明:液相沉降速度随着压井液排量的增大而增大;在第一阶段,井口与井底压力均增大,在第二阶段,井筒压力保持不变,在第三阶段,井口压力不变,井底压力继续增大。对比实验结果发现,本文模型的相对误差为5.53%,具有较高的精度,对现场作业具有一定的指导意义。

Numerical Investigation on Dynamic Characteristics of Casing Deformation During Marine Hydrate Production

Formation subsidence is inevitable during marine hydrate decomposition,and the consequent casing deformation seriously threatens the security of sustainable hydrate production.Owing to insufficient observed data of formation subsidence in field,displacement boundary condition of casing is undetermined.Thus the conventional static methods are inapplicable for the calculation of casing deformation in hydrate production well.The present work aims at proposing an approach to investigate dynamic deformation of the casing during hydrate production.In the proposed methodology,based on the movement theory of hydrate decomposition front,hydrate decomposition process can be simulated,in which hydrate reservoir strength formation subsidence showed time-dependent characteristics.By considering the actual interactions among casing,cement and formation,three models of hydrate production well are developed to reveal the static and dynamic deformation mechanisms of the casing.The application of the proposed methodology is demonstrated through a case study.Results show that buckling deformation and bending deformation of casing reduce the passing ability of downhole tools in deformed casing by 4.2%and 7.5%,respectively.With the progress of hydrate production,buckling deformation will increase obviously,while a little increase of bending deformation will occur,as the formation slippage induced by formation inclination is much larger than that caused by hydrate decomposition.The proposed approach can provide theoretical reference for improving casing integrity of marine hydrate production.

Nonlinear Dynamics of Viscoelastic Pipe Conveying Pulsating Fluid Subjected to Base Excitation

Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governing partial differential equation is transformed into a nonlinear system of fourth-order ordinary differential equations by using the generalized integral transform technique(GITT).The effects of the combined excitation of base motion and pulsating internal flow on the nonlinear dynamic behavior of the pipe are investigated using a bifurcation diagram,phase trajectory diagram,power spectrum diagram,time-domain diagram,and Poincare map.The results show that the base excitation amplitude and frequency significantly affect the dynamic behavior of the pipe system.Some new resonance phenomena can be observed,such as the period-1 motion under the base excitation or the pulsating internal flow alone becomes the multi-periodic motion,quasi-periodic motion or even chaotic motion due to the combined excitation action.

基于等效系统假定的变厚度板弯曲广义积分变换解

针对等厚度薄板的弯曲问题,研究人员已给出了基于不同数值算法的经典数值解。针对变厚度薄板弯曲问题的解答较少,且以有限元数值模拟计算为主,计算耗时较大。本文基于广义积分变换原理建立了求解变厚度等效系统的广义积分变换算法,分析了线性和二次变化的变厚度板在多种边界条件下的弯曲问题,利用文献已发表结果同本文建立的广义积分变换解进行验证。计算结果表明,本文建立的基于广义积分变换的变厚度板弯曲求解方法具有较高准确性。同时,通过参数化分析手段,分别利用广义积分变换方法和有限元数值模拟方法讨论了不同边界约束和长宽比等条件对中心点处挠度的影响,计算结果具有较好的一致性,证明本文建立的广义积分变换方法可用于求解变厚度板弯曲问题,且具有较高的准确性。

基于CFD-DEM耦合模型的深水钻屑返出运移沉积规律研究

国内外深水油气田开发过程多次遇到因海床不平导致的生产管汇水下安装不能满足要求的问题,因此,获悉岩屑运移沉积情况的信息就显得尤为必要。相关研究人员对携岩规律的研究工作大多停留在井筒内,对于泥沙输移的研究主要是在浅滩,对深水钻屑运移沉积研究成果较少。为了揭示深水钻屑运移规律,本文采用CFD-DEM耦合计算模型,利用EDEM软件建立岩屑颗粒的离散元模型,与FLUENT软件实现耦合并行计算,流场计算采用Realizable k-ε模型、SIMPLE算法,颗粒间相互作用采用Hertz-Mindlin弹性接触模型,对岩屑颗粒在海底的运移沉积进行了数值计算。通过实验验证,本研究采用的CFD-DEM固液两相流耦合模型计算结果相对误差低于10%,吻合度较高。模拟了洋流速度、岩屑返速、岩屑粒径、机械钻速等参数对其运移沉积的影响规律。结果表明:随着洋流速度和岩屑返出速度的增大,岩屑运移距离增加;增大颗粒粒径和提高机械钻速,岩屑沉积高度增加。本文研究可为深水钻屑沉积问题的研究提供一定的参考价值。

CO2在钻井液中的溶解度实验及规律研究

深水钻井气侵期间,受大温度差环境的影响,井筒内钻井液流动过程中会发生气体的溶解与脱溶,对于溶解度较大的CO 2气体更是如此。准确预测钻井液体系中CO 2的溶解规律,是井筒多相流动计算、溢流早期监测以及井筒压力控制等关键问题的基础内容。本文以溶解度实验为基础,构建了高温高压气体溶解度测量实验系统,在25~84℃、5~45 MPa温度压力范围内,对CO 2在水基钻井液体系内的溶解度进行了测量,结果表明:①温度一定时,随着压力的升高,溶解度逐渐变大,但变化趋势逐渐变缓;②一定的温度压力下,CO 2在KCl、NaCl水溶液中的溶解度随着离子浓度的增加,溶解度逐渐降低;③聚合物处理剂对CO 2的溶解度影响不大;④对于钻井液这一复杂体系而言,CO 2的溶解度主要受到无机盐的影响,较高的无机盐浓度导致CO 2的溶解度比在纯水中的小。