【作者】 王志华；

【导师】 刘扬；

【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】 在原油紧缺和低碳经济背景下，油气集输工艺的优化简化已经在油田高效开发中发挥着举足轻重的作用，低温集输工艺作为降投资控成本的有效途径，近年来在油田地面工程方案中得到了广泛的研究、设计和推广应用，并取得了明显的成效。但以单管串接通球为代表的简化集油工艺，在运行实践中暴露出集输管道发生淤积、堵塞、井口回压升高、管理缺乏科学性等一系列制约正常生产的问题，含水原油作为一种热力学不稳定的复杂混合体系，这些问题在严寒地区及多种开发方式并存的油田中表现更为突出。为此，本文对非牛顿含水原油体系的胶凝特征温度及胶凝结构强度进行了流变测量，基于热力学倾向系数和动力学扩散系数理论方法及室内模拟试验，对含水原油体系低温管输过程的淤积规律进行了系统研究和预测，同时从能量转化的角度解释了考虑剪切流场中含水原油体系乳化成核机制的低温胶凝淤积行为与机理，最后通过单管集油工艺现场试验研究，对含水原油低温集输胶凝淤积行为所带来油井高回压的问题进行了全面系统的分析，并研究提出了胶凝淤积行为及其所致高回压井的治理技术措施与方案。通过对含水原油体系降温胶凝过程特性的研究发现，流变测量技术仍适用于对不同含水原油体系降温胶凝过程特性的描述与解释，基于温降过程中不同含水原油体系粘弹性参数的变化规律，可确定其相应的胶凝特征温度与胶凝结构强度。含水原油体系的胶凝温度要低于原油本身的凝固点，且含水率升高，体系的胶凝特征温度进一步降低，相应胶凝过程中的受力稳定性及其抵抗剪切变形的能力变弱，胶凝强度减小。同时在恒应力作用下，降温速率增大，任一相同含水原油体系的胶凝特征温度值均升高，但体系的胶凝强度却减弱。原油含水率和降温速率对含水原油体系胶凝过程特性影响的研究认识，对于在新的节能形势下，高寒地区和低产液量油井进行地面低温集输工艺设计、参数优化及集输系统的安全运行保障具有重要参考价值。在管输模拟试验研究中，考虑流场畸变对压降测试的影响，针对非牛顿型油-水两相水平管流，改进了差压法试验确定结蜡淤积厚度的方法，研究了含水原油体系温度、含水率、含聚浓度、流速及系统压力对淤积规律的影响。考虑到单相油流关于蜡沉积问题研究的主要方法和目标是构建准确的热力学或动力学模型来描述蜡沉积过程、预测蜡沉积规律，从而以典型单相流的蜡沉积理论模型为出发点，将两相混合体系相关物性及流动特征参数作为含水率的函数，回归建立了描述油-水两相流动结蜡淤积的热力学倾向系数模型和动力学扩散系数模型，并分别对非牛顿含水原油体系低温管输过程的淤积行为进行了预测。不同工况下含水原油体系淤积行为的模拟试验和预测结果均具有相似的变化规律，体系胶凝温度附近的淤积速率相对最大、转相点附近是淤积行为发生明显变化的含水区间、流速增大时淤积速率减小、体系中的含聚浓度上升时淤积加快、管输系统压力升高时淤积行为则在一定程度上减缓。与热力学倾向系数回归模型相比，综合了扩散效应、剪切剥落效应及沉积老化作用，同时考虑了沉积过程中的动力学行为而引入扩散系数反映油-水两相体系中蜡分子从液流到沉积界面扩散机制的动力学扩散系数回归模型，对油-水两相流结蜡淤积的预测具有更好的适用性，其厚度淤积速率预测值与试验结果的平均相对偏差在10%左右。由于体系组成的多样性，水力、热力工况的不稳定性及乳化条件的存在，含水原油低温集输的胶凝淤积行为较含蜡原油管输结蜡更为复杂。通过显微观察认为，胶凝、聚集成核是淤积物表现最为突出的物理状态；胶凝淤积物的熔点温度高达60℃以上，析蜡热焓超过80J/g，且在流场突变区域，DSC曲线上的特征温度值更高；形貌学所分析固相组分中的砂质、成垢与腐蚀产物，又为淤积在规模上的增多、变大提供了晶核。同时，低温流动结构的研究反映出剪切流场中必然存在着乳化成核效应，在特定流场区域内，定义剪切能为沿该区域某一特征长度的圆管流动时所存在压降的函数，也就是剪切应力在流场中剪切做功所产生的能量，则依据能量守恒方程，当含水原油体系处于剪切流场中有动能存在时，剪切能是体现含水原油体系动能对乳化成核过程油水界面Gibbs自由能贡献的一种有效形式。通过对典型节点区域流动压降与剪切能的关联，运用剪切能分析法定量描述了集输系统流场剪切作用对油水乳化成核的贡献及区别，实例计算分析结果表明，对于同一含水原油体系，在相同温度条件下，同一系统中沿程弯头及阀组位置的剪切能明显要高于正常集油管道内的剪切能，表明在流场突变区域，对于油水乳化所需克服的界面Gibbs自由能要相对减少，低温环境下含水原油体系的乳化聚集、成核几率也更大，从而对胶凝淤积行为的作用机制更为显现，且主要发挥于局部区域。低温集输的胶凝淤积物结构充满孔隙，密度和粘度大，除了40%以上的蜡质含量外，胶质、沥青质及固相杂质等重组分的含量也较多，水分则以少量游离水、毛细水、吸附水和内部乳化水为主要存在形式，同时滋生有大量的细菌，呈具有一定强度的海绵状弹性凝胶态特征，属于温降过程中含水原油介质结蜡与乳化成核共同作用的结果。基于单管集油适应性现场试验，多尺度分析了集油工艺井口高回压的形成原因及相应油井生产特征，认为单管串接集油工艺中含水原油体系的沿程温降胶凝过程特性是高回压形成的内在机理，含水率低、产液量小于集输管道最小安全流量界限、井口出油温度低于管输起点最低温度界限则是高回压形成的外部表现；提出了低温集输中将井口回压按A类＞1.5MPa、B类0.8～1.5MPa、C类0.5～0.8MPa、D类＜0.5MPa进行分级分类控制与治理的思想。现场试验结果表明，多数高含水、大液量生产井对单管串接集油工艺具有较好的适应性，但对于部分低液量、大集油半径、特别是端点井液量远小于串接井的井组，胶凝、淤积严重，回压上升快，表现出其地面控制与有效治理的必要性；同时，现场试验在凝油形成规律、油水流型及其过渡上与室内实验及理论研究认识具有较好的符合性。通过对单管集油工艺高回压井治理技术的系统研究，建立了胶凝温度附近集油清管周期随管输液量、含聚浓度变化的关系；考察了井口安装电加热器对胶凝结构形成时间延长、凝油速率减缓、井口回压控制的效果；提出了包括健全通球配套设施、井口安装定压调节阀、更换管道材质及扩建辅助掺水流程等在内的集输工艺改造措施；研究了含水原油体系低温降粘减阻输送的可行性，结果表明，有效的表面活性剂类减阻剂能够适应于对已发生淤积阀组间汇管干线的溶淤、清淤及其摩阻压降的减小，更适应于保障阀组间汇管干线清管后的含水原油转输，延长汇管干线的冲洗周期，控制所辖单井井口回压的上升，减阻率可达到20%以上。另外，针对高含水期油气集输系统简化优化设计与低能耗运行的背景，对各种治理技术的投资和操作成本进行了比较，以技术性和经济性相结合为实际工程应用方案的选择提供了充分依据。综合实验及理论研究认为，低温集输工艺中，含水原油体系的降温胶凝过程特性是淤积行为发生的条件基础，多相体系的形成及相间作用是胶凝淤积过程发生的关键，而含水原油体系温降过程中结蜡与乳化成核的共同作用机制则是胶凝淤积过程发生的根本，这种胶凝淤积行为导致了集输管道局部（或整体）有效流通截面减小，流动阻力增加，井口回压升高。研究结果与认识对于更加深入地掌握含水原油胶凝淤积机理、油井高回压成因及集输系统节能降耗潜力均具有重要价值，同时能够为集油工艺及其运行参数的进一步优化简化提供实验与理论支持，也为维持油田地面工程系统的高效、低耗、安全、协调与平稳运行状态提供技术保障方案。更多还原

【Abstract】 Under the background of crude oil shortage and low-carbon economy, optimization andsimplification of oil-gas gathering&transportation plays a significant role in efficientdevelopment of oilfield. Recently, cooling gathering&transportation has been widely studied,designed, popularized and applied in oilfield surface engineering projects, as a effective wayto reduce investment and control cost, it has achieved obvious effects. However, thesimplified oil gathering processes represented by single-pipe concatenation process expose aseries of problems, which restrict normal production in the operation practice, such asdeposition in pipelines, blocking, high wellhead pressure and lack of scientific management.These problems are presented more seriously in severe cold areas and oilfields with variesdevelopment methods, as the oil-water two-phase system is a complex mixed system withunstable thermodynamics. Therefore, gelling characteristic temperature and gelling structuralstrength of non-Newtonian oil-water two-phase system are rheological measured in this article.Based on theoretical methods and laboratory simulation tests of thermodynamics tendencycoefficient and dynamics diffusion coefficient, the gelling law of oil-water two-phase systemcooling transportation is systematic studied and predicted. From energy transformationviewpoint, gelling deposition behavior and mechanism of oil-water two-phase systememulsification nucleation in low temperature in shear flow is also explained. Then, accordingto the study of single-pipe gathering process field tests, the problem of high wellhead pressurecaused by oil-water two-phase system cooling gathering gelling deposition behavior issystematic analyzed, and the control methods and schemes are proposed.By studying oil-water two-phase system gelling characteristic, it shows that rheologicalmeasurement technique is still suitable for description and explanation of gellingcharacteristic of crude oil with different water cuts. Based on the change law of viscoelasticityparameter, the gelling characteristic temperature and gelling structural strength can bemeasured correspondingly. Gelling temperature of oil-water two-phase system is lower thanfreezing point of crude oil, and the temperature would be further decreased as water cut rises,correspondingly, stress stability and the resistance to shear deformation in gelling areweakened and gelling strength is decreased. Under the constant stress, gelling characteristictemperature of crude oil with same water cut rises as the temperature drop rate increases, butthe gelling strength is weakened. Study of the effects of crude oil water cut and temperaturedrop rate on oil-water two-phase system gelling characteristic has important reference valueon surface cooling gathering design, parameter optimization and gathering&transportation safe operation of alpine region and low production wells under the new energy conservationsituation.In the study of pipeline transportation simulation tests, the effect of flow distortion onpressure drop test is considered. And aiming at non-Newtonian oil-water two-phase horizontalflow, differential pressure method to measure wax deposition thickness is improved, theeffects of oil-water two-phase system temperature, water cut, polymer containedconcentration, flow rate and system pressure on gelling law are studied. The main method andtarget in studying wax deposition of single-phase oil flow is to establish accuratethermodynamics or dynamics models to describe wax deposition process and to predict waxdeposition law. Therefore, based on typical single-phase flow wax deposition theoreticalmodel, relevant properties and flow characteristic parameters of two-phase system are asfunctions of water cut, thermodynamics tendency coefficient model and dynamics diffusioncoefficient model of describing oil-water two-phase flow wax deposition are regressiveestablished, and the deposition behavior of non-Newtonian oil-water two-phase system incooling transportation is predicted respectively. Under different working conditions, thechange rules of simulation tests are similar with the predict results of oil-water two-phasesystem deposition behavior, relative maximum deposition rate is achieved near the gellingtemperature and significant change in deposition behavior is happened near the phaseinversion point. Furthermore, deposition rate decreases as flow rate increases and depositionrate increases as polymer contained concentration of the system increases, and the depositionbehavior slows down in a certain degree when the pipeline transportation pressure rises up.Comparing with the thermodynamics tendency coefficient regression model, the dynamicsdiffusion coefficient regression model has better applicability to predict wax deposition inoil-water two-phase system, which combined diffusing effect, shear effect and depositionaging effect, and the average relative deviation is near10%between predicted values of rateof deposition thickness and test results. The dynamic behavior in deposition process isconsidered in the dynamics diffusion coefficient regression model and a diffusion coefficientis introduced to reflect the diffusion mechanism of wax molecule from flow to depositinterface in oil-water two-phase system.Due to the variety of system composition, instability of hydraulic and thermal workingconditions and the exist of emulsification conditions, the gelling deposition behavior ofoil-water two-phase system during cooling gathering&transportation is more complex thanthe wax deposition of crude oil. Through microscopic observation, gelling and aggregativenucleation are the most prominent physical states of the deposition. Melting temperature ofthe gelling deposition reaches more than60℃, wax crystallization enthalpy is more than80J/g, and in the flow field mutational area, characteristic temperature value on DSC curve ismuch higher. Sand, scale and corrosion products of solid phase components analyzed bymorphology provide crystal nucleus for increase and growth of the deposition. At the sametime, the study of cooling flow structure reflect that the emulsification nucleation effect mustexist in shear flow field, and in the specific flow field area, shearing energy is defined as a function of pressure drop of circle pipe flow along with one characteristic length, which is theenergy produced by shearing stress working in the flow field. Then, according to the energyconservation equation, when there is kinetic energy in oil-water two-phase system in shearingflow field, shearing energy is an effective form to reflect the contribution of kinetic energy ofoil-water two-phase system to oil-water interface Gibbs free energy during emulsificationnucleation. By the correlation between flow pressure drop and shearing energy in typicalpoints, shearing energy analytical approach is used to quantitatively describe the contributionand distinction of flow field shearing action in gathering&transportation system on oil-wateremulsification nucleation. The instance calculation and analysis results show that in the sameoil-water two-phase system, shearing energy of elbow and valve bank are obviously higherthan that of common gathering pipeline under the same temperature, this indicates in flowfield mutational area, Gibbs free energy which the oil-water system required to overcomeduring emulsification at interface is relative lower, the probability of oil-water two-phasesystem emulsification aggregation and nucleation is higher in low temperature, then, it ismore obvious to action mechanism of gelling deposition behavior and it is mainly in localarea. Pores are filled with gelling deposition structure in cooling gathering&transportation,the deposit is with high density and viscosity, and except for the more than40%wax content,there are also lots of heavy constituents such as colloid, asphaltene and solid impurities. Themain existence forms of water phase in deposit are free water, capillary water, absorbed waterand internal emulsification water, it also propagates large amount of bacteria, and presentsspongy elastic gelling state characteristic in certain strength. The deposit is the result of thejoint effect of wax deposition and emulsification nucleation during temperature drop process.According to single-pipe oil gathering adaptation field tests, forming reasons of highwellhead pressure and production characteristics of corresponding wells in oil gatheringprocess are analyzed. It is considered that gelling process characteristic of oil-water two-phasesystem is the internal mechanism for forming high wellhead pressure in single-pipeconcatenation oil gathering process. Low water cut, production is less than minimum securityflow limit of gathering&transportation pipeline and wellhead temperature is below minimumtemperature limit of pipeline origin are the external performances of the formation of highwellhead pressure. Classification and management thought of wellhead pressure in coolinggathering&transportation is proposed, as level A:>1.5MPa, level B:0.8～1.5MPa, level C:0.5～0.8MPa, level D:＜0.5MPa. Field test results indicate that majority wells with highwater cut and production are better adapted to single-pipe concatenation oil gathering process.However, to some well groups with low production and long oil gathering radius, especiallythe production of terminal well is far lower than concatenation well’s, the gelling anddeposition are serious and the wellhead pressure are rising fast, it is necessary to combineother field controls and effective managements. Besides, there are better conformances ofsolidification oil formation law, oil-water flow pattern and the transition in field tests,laboratory experiments and theoretical studies. By systematic study of high wellhead pressurecontrol in single-pipe oil gathering process, the correlation of pigging period varied with transportation volume and polymer contained concentration near the gelling temperature isestablished. The effects of electric heater installed at wellhead on gelling structure formingtime extension, oil solidification rate mitigation and wellhead pressure control areinvestigated. The improvements of gathering&transportation process are proposed such asperfect pigging supporting facility, install constant pressure regulating valve at wellhead,change pipe material and extend assistant water mixing process. The study of feasibility ofoil-water two-phase system cooling transportation with low viscosity shows that effectivesurfactant type viscosity reducer could adapt to deposit dissolution, deposit elimination andfrictional pressure drop reduction. And it is more applicable to guarantee the transportation ofoil-water two-phase system in main pipe of valve group room after pigging, extend washperiod of the main pipe, and control the rise of wellhead pressure, the drag reductionefficiency achieve more than20%. In addition, considered the background of gathering&transportation system optimization design and low-energy operation during high water cutstage, investment and operation cost of various management technologies are compared,sufficient bases are provided to select practical engineering application scheme in thecombination of technicality and economy.Combined experiments and theoretical study we found that, in cooling gathering&transportation process, basic condition of deposition behavior occurred in oil-water two-phasesystem is the gelling characteristic and keys of gelling are formation of heterogeneous systemand effects in phases. Besides, fundamental of gelling in the system is the combined actionmechanism of wax deposition and emulsification nucleation during temperature drop. Andthis deposition behavior leads to part (or whole) effective flow area of gathering&transportation pipeline decrease, flow resistance increase and wellhead pressure rise. Thestudy has significant value on mastering gelling mechanism in oil-water two-phase system,the cause of high wellhead pressure and potential of energy-saving and cost-reducing ingathering&transportation system. In addition, it will provide experimental and theoreticalsupport for further optimization and simplification of oil gathering process and operatingparameters, and it can also supply technical support scheme for maintaining the efficient, lowconsumption, security, coordination and stable operating status in oilfield surface engineering.更多还原