WAX DEPOSITION IN HORIZONTAL WELLS

ABSTRACT

In this research, wax deposition in horizontal well bores was studied. In a horizontal well, the main mechanism for wax appearance is the pressure change rather than the temperature change. Six different thermodynamic models were improved for horizontal wells by adding a pressure function, and a computer program was developed to simulate the precipitation phenomena in horizontal wells. Solid-liquid equilibrium constants for each pseudo-component were calculated. Critical pressures and overall solid mole fractions of the crude oil at different error ranges are determined. In addition to these, the changes in productivity index due to wax deposition for steady state and pseudo-steady state conditions were examined by the addition of a “wax factor”. It was observed that pressure change was slightly effective on wax appearance in horizontal wells.     

WAX DEPOSITION IN HORIZONTAL WELLS

In this research, wax deposition in horizontal well bores was studied. In a horizontal well, the main mechanism for wax appearance is the pressure change rather than the temperature change. Six different thermodynamic models were improved for horizontal wells by adding a pressure function, and a computer program was developed to simulate the precipitation phenomena in horizontal wells. Solid-liquid equilibrium constants for each pseudo-component were calculated. Critical pressures and overall solid mole fractions of the crude oil at different error ranges are determined. In addition to these, the changes in productivity index due to wax deposition for steady state and pseudo-steady state conditions were examined by the addition of a “wax factor”. It was observed that pressure change was slightly effective on wax appearance in horizontal wells.     

输油管道蜡沉积试验新技术及装备

介绍了输油管道蜡沉积试验的一些新技术和装备。在析蜡点测量方面,主要介绍了旋转黏度计法、偏光显微镜法和差示扫描量热法;在蜡沉积量测定方面,主要介绍了清管法、拆管法、压降法、传热法、液体置换与检测法、超声波法和激光测厚法;在蜡沉积物组分测定方面,主要介绍了气相色谱法和气相色谱-质谱联用技术。这些新技术和装备为解决蜡沉积试验和工程中的问题提供有效手段。     

Studies of Wax Deposition Onset in the Case of Indian Crude Oil

Abstract

Before taking any decision regarding strategies for prevention and remediation of wax deposition problems in the production tubing, pipeline, and process equipment, it is essential to identify the conditions of wax deposition and to predict wax deposition rates. In this article a study on the prediction of wax deposition, different factors affecting the deposition, and the practical applications of laboratory results obtained for characterization of the Indian crude oils have been presented. The waxy crude characterization study was performed on both stock tank crude oil and recombined integrated crude oil. The results of it exemplify the influence of composition, temperature, and pressure on the solid behavior of Indian paraffinic crudes.     

高凝原油析蜡点的不同确定方法与应用

高凝原油析蜡点不仅是地面工程设计中的重要参数,也是油藏工程应用中确定合理注水温度的关键指标.文中列举了国内外8种析蜡点测试方法在海外某高凝油田A中的应用,分别筛选出满足地面管输工程和油藏工程应用的析蜡点.结果表明,显微观测法的测试结果最高,在地面管输工程应用中最为保守;地层条件下含气原油析蜡点明显低于地面原油析蜡点,应作为合理注水温度的确定标准.     

SPECTROSCOPIC DETERMINATION OF CARBON IN AROMATIC RINGS IN PETROLEUM KEROSENES

ABSTRACT

On the basis of the composition of aromatic carbon in the petroleum kerosenes being exclusively mono and di-ring systems; which absorb UV light in a distinct region; the slope of the plot of the total absorbance in the region 250 to 290 nm Vs known concentration of authentic model kerosene mixture, may be utilized to determine the percentage of carbon in aromatic rings in a sample kerosene.

The area under the aromatic envelope curve ; whether expressed as a function of direct instrumental measurements of the total absorbance at = 250, 260,270,280 and 290 nm, or actually traced and evaluated; of a 1 ml kerosene sample dissolved in 500 ml iso- propyl alcohol, enables the estimation of the percentage of carbon in aromatic rings ( %CA ) using a mathematically derived expression for this purpose. This spectroscopic method was applied to determine % CA in Libyan kerosene samples, sequentially subjected to aromatic carbon depletion by adsorbents.     

The Limitations of the Cloud Point Measurement Techniques and the Influence of the Oil Composition on Its Detection

In the petroleum industry, cloud points are one of the main guides to evaluate the wax precipitation potential of a fluid. The planning of the exploration of a reservoir or the design of its pipelines are based on the measured cloud points for the reservoir oil. It is known that each measuring technique will provide a different cloud point temperature, yet although some of these techniques seem to be more accurate than others, no definite conclusion was established on how cloud points should be measured.

On this work, several cloud point measurement techniques are discussed and compared. It will be shown that some of these techniques, such as viscosity, filter plugging, and differential scanning calorimetry (DSC) can only be used under very favorable circumstances, but it will be argued that because every technique requires some finite, often large, amount of solid to detect the presence of a new phase, the cloud point, defined as the temperature for which the first solid appears in the oil, is not accessible experimentally, and unless a very detailed compositional analysis is available, it is also impossible to predict it accurately with a thermodynamic model. The effect of the paraffin distribution in the oils on the cloud point detection will be discussed, and it will be shown how the compositional information can be used to assess the uncertainty of the measured cloud points.     

高含蜡原油生产中析蜡和熔蜡规律实验研究

运用激光测试高压原油析蜡点的最新方法,对井筒中原油的析蜡规律和地层中原油的熔蜡规律进行了研究。研究结果表明：含气原油比脱气原油的析蜡点温度低;井筒中压力高于泡点压力时,原油析蜡点随压力下降而下降;压力低于泡点压力时,原油析蜡点随压力下降而升高;地层条件下熔蜡温度比析蜡温度高。     

哈萨克斯坦PKKR原油特性及HS防蜡剂的研究

 采用气相色谱、核磁共振和DSC热分析等方法,分析了哈萨克斯坦PKKR原油的组成和结构。采用显微镜和接触角仪研究了HS防蜡剂对哈萨克斯坦PKKR原油的防蜡机理。结果表明,哈萨克斯坦PKKR油井结蜡严重的主要原因是原油中沥青质+胶质与蜡的质量比低、采出液含水量低、原油中溶解气量较多、原油含高碳蜡且蜡的支链度低和井口温度低于析蜡点。HS防蜡剂对PKKR原油的防蜡率大于60%（部分油井防蜡率大于90%）。HS防蜡剂通过改变原油中蜡晶的结构,抑制其形成三维网状结构;改变蜡沉积表面的水润湿性能,形成不利于蜡沉积的表面,从而达到降低结蜡的目的。     

MATHEMATICAL MODELLING OF WAX DEPOSITION IN CRUDE OIL PIPELINES (COMPARATIVE STUDY)

ABSTRACT

In this research, wax deposition in different crude oil pipeline systems was studied. In oil pipelines, the main mechanism for wax appearance is the temperature change along the pipeline. A computer program was developed to simulate the wax precipitation phenomena. Temperature profile along the pipeline was determined and solid liquid equilibrium constant, wax mole fraction and wax thickness along the pipeline were calculated. This computer program was applied to different crude oil pipeline systems in Iraq (Baiji-Daura, Rumaila-Zubair-Fao and Hadttha-Rumailia). In Haditha-Rumaila crude oil pipeline system, it was observed that wax thickness after a year is approximately 0.1 mm and temperature declined from 303 K to around 300.5 K. The wax mole fraction after a year is approximately 0.2. The solid-liquid equilibrium constant for the first component around 0.228 and around 165 for the second component after a year. Similar results were observed in other crude oil pipeline systems studied.     

MATHEMATICAL MODELLING OF WAX DEPOSITION IN CRUDE OIL PIPELINES (COMPARATIVE STUDY)

In this research, wax deposition in different crude oil pipeline systems was studied. In oil pipelines, the main mechanism for wax appearance is the temperature change along the pipeline. A computer program was developed to simulate the wax precipitation phenomena. Temperature profile along the pipeline was determined and solid liquid equilibrium constant, wax mole fraction and wax thickness along the pipeline were calculated. This computer program was applied to different crude oil pipeline systems in Iraq (Baiji-Daura, Rumaila-Zubair-Fao and Hadttha-Rumailia). In Haditha-Rumaila crude oil pipeline system, it was observed that wax thickness after a year is approximately 0.1 mm and temperature declined from 303 K to around 300.5 K. The wax mole fraction after a year is approximately 0.2. The solid-liquid equilibrium constant for the first component around 0.228 and around 165 for the second component after a year. Similar results were observed in other crude oil pipeline systems studied.     

高压含气条件下含蜡原油析蜡点测量方法

针对常规方法只能测量地面脱气油的析蜡点,不能测量高压含气条件(油藏条件)下含蜡原油析蜡点的不足,提出了以Arrhenius方程为理论基础,利用高压毛细管黏度计测量高压含气条件下含蜡原油析蜡点的方法。实验结果表明,实验油样地面脱气后析蜡点为63.74℃,油藏条件下析蜡点为59.73℃,含蜡原油地面脱气后更容易析蜡。建议采用油藏条件下的析蜡点作为注水设计参数。     

石油流体析蜡特性检测技术

石油流体中蜡组分的析出会导致原油流动性的恶化和蜡沉积问题,降低管输经济性,威胁石油生产安全。析蜡特性是开发流动改性剂和防蜡剂以及科学制定原油输送和清蜡方案的基础。目前,石油流体析蜡特性检测技术的发展十分多样化,涵盖了分析化学、光谱学、流变学、量热学等多个学科领域。不同的析蜡信号检测方法决定了各检测技术在灵敏度、可靠性、适用性等方面的差异,有时测试结果相差较大。综述了现有石油流体析蜡特性各检测技术的原理和测试装置,以及国内外的应用现状,从灵敏度、可靠性、测试效率等方面分析了各自的优缺点,评价了各检测技术的适用性和发展前景,以期为石油化工行业工作者提供借鉴。     

普适性结蜡模型研究

根据原油在管道内流动特性及析蜡规律,提出了有效析蜡量的计算方法.利用F检验法筛选了原油结蜡的主要影响因素,包括原油黏度、管壁处剪切应力、温度梯度及管壁处蜡晶溶解度系数.利用9种原油室内环道结蜡实验数据,按照逐步线性回归的方法,得到了含蜡原油的普适性结蜡模型.该模型不需进行结蜡模拟实验,只需根据原油的黏度、析蜡特性及密度等物性参数就可预测原油的结蜡规律.在未进行室内结蜡模拟实验的情况下,利用普适性结蜡模型预测了中宁-银川输油管道不同工况下沿线结蜡分布,并和现场运行参数进行了对比,平均误差为6.32%,最大误差为20%,预测结果为现场清管作业提供了依据.     

大庆原油蜡沉积规律研究

在理论分析及室内试验的基础上,系统研究了油温、流速、管壁处温度梯度等参数对大庆原油蜡沉积的影响.在原油与管壁温差相同时,不同温度段蜡沉积速率并不相同,存在蜡沉积高峰区.在壁温相同时,随油温升高,蜡沉积速率逐渐增加.在油温、壁温相同的条件下,随流速增加,蜡沉积速率下降.建立了大庆原油蜡沉积模型,并利用该模型预测了铁岭-秦皇岛输油管线不同季节、不同时间沿线蜡沉积分布.铁-秦线冬季存在蜡沉积高峰区;春、秋季出站时蜡沉积最严重,下一站进站时蜡沉积最轻;夏季蜡沉积速率更小,且沿线变化不大.     

任京线正反输运行长期不清管条件下的结蜡规律

针对任京输油管道正反输运行长期不清管的情况,通过比较现有结蜡模型的优缺点．建立了适用于大庆冀东混合原油的结蜡模型;考虑结蜡过程的周期性和时效性,研究了任京线的结蜡规律;利用两次任京线改线工程的现场实测结蜡厚度进行了验证,实测值与预测值的最大相对误差为15．8％;分析了任京线管壁蜡沉积物的基本物性和结构强度。研究成果为任京线安全清管提供了理论依据。     

考虑剪切弥散效应的结蜡厚度

在分析热原油管道结蜡机理的基础上，给出了考虑分子扩散与剪切散共同作用下的结蜡厚度公式，可计算给定时间内热油管道的结蜡厚度及形成某一结蜡厚度的时间。     

DETERMINATION OF ORGANIC SULFUR COMPOUND TYPES IN VACUUM GAS OILS USING GC-FID-SCD METHOD

The analyses of individual organic sulfur compounds in petroleum distillates are the key to understanding the kinetics of the chemistry involved in hydrodesulfurization, HDS. A sample of vacuum gas oil (VGO) produced commercially by distillation of treated atmospheric residue was analyzed by GC-FID-SCD method for individual organic sulfur compounds characterization and quantification. Dibenzothiophene and benzonaphthothiophene and their alkyl derivatives were found to constitute almost the entire organic sulfur compound range present in the VGO. Using a relationship between the total sulfur determined by “X-ray” and “Coulomax” methods and the composition of individual sulfur compounds determined by SCD, the quantity of those organic sulfur compounds present in VGO was estimated. Despite the limit in temperature raise (325°C) in the capillary column and that the range studied (346-555°C) is higher than those limits, optimum conditions were chosen to overcome those obstacles. From the analyses the behavior of refractory and unrefractory sulfur compounds in the VGO region can now be followed easily.