AN IMPROVED INHIBITION OF PARAFFIN DEPOSITION FROM WAXY CRUDES

ABSTRACT

A series of cold spot tests of progressively increasing complexity was employed to evaluate the potential of several chemical additives for inhibiting paraffin deposition from waxy crudes. Test data revealed that trichloroethylene-xylene (TEX) binary system has a unique ability to effect substantial pour point depression and improved transport properties for a wide range of waxy crudes. This led to improved inhibition of paraffin deposition by TEX additive in comparison with the perfonnance of some tested, commercial anti-paraffin chemical products.     

Understanding wax appearance temperature in light crude oils by DSC,NMR, and HT-GC

The wax precipitated from oil mixtures primarily consists of C18 to C36 (macro crystalline waxes) or C30 to C60 (micro crystalline waxes), both made of aligned paraffinic and naphthenic molecules. Paraffins have significant impact on wax deposition characteristics as paraffin waxes react and respond easily to temperature changes due to its straight chain structure. In this paper, 12 light crudes of different origin were analyzed by DSC. Method was standardized for the determination of WAT in light crudes and these were found to have WAT ranging from 10 to 30°C. Wax content is proportional to enthalpy of crystallization (ΔH) and the ΔH ranges from 3 to 9 J/g. WAT and wax content do not follow the same trend which is understandable as these parameters depends not only on the concentration and molecular weight of the waxes but also on the chemical nature of both waxy and non waxy part of the crude oil. To understand the trend in WAT, these crudes were also analyzed for paraffinic carbon (Cp), Saturates and CH₂/CH₃ ratio by NMR spectroscopy and carbon number distribution by HT-GC. It was observed that WAT correlates fairly well with CH₂/CH₃ ratio which is in an indicator of normal paraffin content as WAT depends primarily on the nature / type of paraffins. The anomalies can be explained through carbon–wise n-paraffin content by HT-GC.     

An Evaluation of the Performance of Selected Wax Inhibitors on Paraffin Deposition of Nigerian Crude Oils

Paraffin deposition in oil production constitutes a critical and difficult to control problem, in terms of productivity and production operation costs, going from the reservoir to surface facilities. In Nigeria, operators spend millions of dollars each year to control the deposition of paraffin and to deal with other paraffin deposition related problems. Expenditures of this magnitude obviously have a significant impact on profits. The main purpose of this work is to assess the net effect of many commercial wax inhibitors on paraffin deposition from a wide range of waxy crude oil systems in Nigeria for the selection of an efficient additive. Deposition from a wide range of waxy crude oil systems from Nigerian oilfields were examined with and without chemical wax deposition inhibitors. The devices used to produce the deposits investigated were cold spot and dynamic flow wax deposition apparatus capable of producing field-like deposits with relatively small volumes of oil in minutes. Results show that most of the commercial wax inhibitors tested could decrease the deposition of wax, but none has the economical capability to solve the paraffin deposition problem for an extended period of time. One intriguing result was that the addition of xylene improved the performance of three wax inhibitors tested. It was also observed that there are subtle differences in inhibitor performance depending on deposition tendencies of crude oil.     

微生物对含蜡原油的除蜡降黏效果

为提高含蜡原油的开采与运输效率,挖掘高效嗜蜡菌,笔者以石蜡为唯一碳源,从石油污染土壤中分离出一株嗜蜡菌,对其进行优化培养后,考察了该嗜蜡菌对大庆含蜡原油的除蜡降黏效果,并对其代谢产生的生物表面活性剂性能进行测定。结果表明：该嗜蜡菌能代谢产生脂肽类表面活性剂,具有较强的疏水性及乳化性能;其与含蜡原油作用7 d后,含蜡原油蜡质量分数降低43%、黏度下降18%。该嗜蜡菌对含蜡原油具有一定除蜡降黏作用,可以提高原油流动性能。     

Correlations Between the Pour Point/Gel Point and the Amount of Precipitated Wax for Waxy Crudes

The amount of precipitated wax is one of the key factors that governs the flow properties of waxy crudes. Experimental results of 24 crudes have shown that approximately 2 wt% precipitated wax is sufficient to cause a virgin waxy crude gelling. Accordingly, a correlation between the pour point and the temperature at which 2 wt% of wax has precipitated out from a crude oil; i.e., T_c(2 wt%), and a correlation between the gel point and T_c(2 wt%) have been developed. The proposed correlation of the pour point is in accordance with the correlation developed by Letoffe et al. (1995) on the basis of 14 crudes from eight countries. The development of the gel point correlation and further verification of the pour point correlation indicate that there is a relationship between the gelling of virgin waxy crudes and the amount of precipitated wax. According to these correlations and the amount of precipitated wax, which can be determined only with a little sample by thermodynamic models or Differential Scanning Calorimetry (DSC) experiment, the gel point and pour point of virgin waxy crude can be predicted even if the oil sample is very limited. Heat treatment and chemical treatment can greatly improve flow behavior of waxy crudes, and more precipitated wax is present when the beneficiated (thermally beneficiated or PPD-beneficiated) crude oils gel. Experimental results showed that approximately two or three times the amount of precipitated wax presents at the gelling temperature when the oils were in their beneficiated (thermally beneficiated or PPD-beneficiated) conditions.     

含蜡原油热处理过程中若干组分的作用

本文研究了大庆、南阳原油中的胶质—沥青质,石蜡—正构烷烃和微晶等组分在含蜡原油热处理过程中的作用,从而指出:(1)只有当原油中含有石蜡和适量的胶质—沥青质时,才具备用热处理方法来改善其低温流动性能的可能性。(2)胶质—沥青质在含蜡原油中具有非常显著的分散作用增粘作用。它们通过吸附、共晶等作用改变原池中石蜡的结晶习性、形态及结构强度,从而取得降凝、降粘等效果。(3)各种原油中胶与正构烷烃之比在0.43～5.2之间,经过最佳条件热处理就可显示出热处理效果。胶—正烷烃比在0.6～3.0之间热处理效果最佳。(4)微晶蜡在含蜡原油热处理过程中,其本身不能显示热处理效果,当加热温度高达微晶蜡能在原油中大量溶解的温度时,在降温重结晶过程中,微晶蜡的析出将恶化热处理效果。     

Influencing factors governing paraffin wax deposition of heavy oil and research on wellbore paraffin remover

Abstract

Wax deposition is harmful to oil wells, especially for waxy heavy oils at low temperature. The influencing factors on wax deposition of heavy oil were studied and a kind of O/W emulsion type wellbore wax remover was investigated. The results showed that the wax deposition rate of Jinghe heavy oil increased with the increasing wax content and asphaltenes content but decreased with the increasing water content. The oil in water emulsion type paraffin remover was prepared and it showed both good wax dissolution and paraffin prevention ability and can save large quantities of solvent. The results of this study provides a possible way for waxy heavy oils to dissolve wax, to prevent wax deposition and reduce the viscosity of heavy oils by emulsification together, which is helpful to reduce the frequency of hot washing and enhance oil recovery for waxy heavy oils.     

A comparative analysis of two methods of wax treatment for a waxy oil in Southwest Trinidad

When oil flows into the wellbore, pressure, and temperature decreases. This causes paraffin (wax) to precipitate into the oil and to deposit in production tubings, which negatively affect oil production. Wax deposition can be mitigated by the application of passive energy waves or chemical solvents. In this study, both methods of wax treatment were tested on a waxy oil well in Trinidad. Production outputs and economics showed that chemical solvent injection was the more feasible method. However, passive energy wave application enhanced oil properties, oil-water separation and showed notable success in preventing wax deposition.     

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.     

An Experimental Study of Rheological Properties of Nigerian Waxy Crude Oil

Abstract

Nigerian crude oils are known for their good quality (low sulfur, high American Petroleum Institute gravity). However, similar to any other paraffinic-based crudes, most Nigerian crudes contain moderate to high contents of paraffinic waxes. These waxy crudes exhibit non-Newtonian flow behavior at temperatures below the cloud point because of wax crystallization. In order to accurately predict flowing and static temperature profiles, design waxy crude oil pipelines, evaluate flow interruption scenarios, and start up requirements in the handling of waxy crude oils, the effect of temperature and shear rate on the rheology of crude oils must be determined. This work presented some experimental results on the rheology of two waxy crude oils produced from different Nigerian oil fields. A Brookfield DV-III ultraprogrammable rheometer (Brookfield Engineering Laboratories, Middleboro, MA) was utilized. The temperature dependence of rheological properties and thixotropy of these crudes were investigated. The influence of some petroleum-based diluents to depress the wax appearance temperature (WAT), their effect on the thixotropic/yield pseudoplastic behavior of two Nigerian crudes were studied and it was observed that lower wax content crude has higher tendency to regain its cohesive lattice bonding (yield strength) when left undisturbed for some days at its gel point after agitation. The experimental results showed that the addition of petroleum-based diluents to the lower wax content crude oil leads to its lost some of its yield strength regaining capacity.     

PARAFFIN DEPOSITION IN OIL PRODUCTION. OIL COMPOSITION AND PARAFFIN INHIBITORS ACTIVITY

Several commercial paraffin inhibitors were evaluated with highly paraffinic crudes. Pour point depression was observed in some of the studied crudes in the presence of any product, while others showed insignificant changes in this parameter. Crudes characterization was achieved with physico-chemical analysis (pour point, cloud point and API gravity) and hydrocarbon analysis (thin layer chromatography with flame ionization detection, wax content, gel permeation chromatography and high temperature simulated distillation). A correlation between crude oil composition and paraffin inhibitors activity was found. The normal / cyclo+iso-paraffins ratio of the crudes that were not affected by the paraffin inhibitors was found higher compared to the others. The molecular weight distribution of the crudes which responded to modifiers, showed a bimodal character and a concentration of components with more than 24 carbon atoms lower than 39 % wt. On the other hand, the crudes insensitive to the action of the inhibitors displayed monomodal molecular weight distributions with larger contributions of heavy components (more than 52 % wt). Doping experiments supporting the former findings, permitted to asses the inefficiency of commercial paraffin inhibitors for crudes rich in C24+ alkanes.     

Advances in rheology and flow assurance studies of waxy crude

Flow assurance is one of the core issues in safe and economical operation of waxy crude pipelines.Its essence lies in flow and heat transfer of the crude.In the past 10 years,the authors’ team has achieved a lot of innovative results in aspects of waxy crude rheology,flow assurance assessment,and pipelining technologies on the basis of decades of studies.The rheological characteristics of waxy crude are much better understood,and a method for quantitatively simulating the effect of flow shear was developed based on some theoretical breakthroughs.Studies of the mechanism of waxy crude rheology have been deepened to the quantitative level.After successful development of efficient numericalalgorithms,accurate simulations have been achieved for various complex flow and heat transfer situations in waxy crude pipelining,and a reliability-based approach to flow assurance assessment has been set up.New pipelining technologies have been developed such as batching pour-point depressant-(PPD-) treated multiple-waxy-crudes,intermittent transport of waxy crudes through long-distance pipelines,and batching hot and cold crudes.By their application,a series of problems hindering safe,efficient and flexible operation of waxy crude pipelines were tackled,demonstrating that transportation technologies for waxy crude have advanced to a new and high level.     

PARAFFIN DEPOSITION IN OIL PRODUCTION. OIL COMPOSITION AND PARAFFIN INHIBITORS ACTIVITY

ABSTRACT

Several commercial paraffin inhibitors were evaluated with highly paraffinic crudes. Pour point depression was observed in some of the studied crudes in the presence of any product, while others showed insignificant changes in this parameter. Crudes characterization was achieved with physico-chemical analysis (pour point, cloud point and API gravity) and hydrocarbon analysis (thin layer chromatography with flame ionization detection, wax content, gel permeation chromatography and high temperature simulated distillation). A correlation between crude oil composition and paraffin inhibitors activity was found. The normal / cyclo+iso-paraffins ratio of the crudes that were not affected by the paraffin inhibitors was found higher compared to the others. The molecular weight distribution of the crudes which responded to modifiers, showed a bimodal character and a concentration of components with more than 24 carbon atoms lower than 39 % wt. On the other hand, the crudes insensitive to the action of the inhibitors displayed monomodal molecular weight distributions with larger contributions of heavy components (more than 52 % wt). Doping experiments supporting the former findings, permitted to asses the inefficiency of commercial paraffin inhibitors for crudes rich in C24+ alkanes.     

探求石油勘探地球化学新参数的尝试

本文主要对澳大利亚高含量蜡和正烷烃的陆源原油的成因及生成潜量进行研究.研究中作者发现,采用目前已有的地球化学方法难以解释其成因及生成潜量.为此,作者通过水热解和氢化反应试验,提出把化学结构作为一种控制因素,以源岩中热稳定的长链和正烷基组份作为该原油的预测和评价标准.      

输油工艺现状及其发展预测

本文简要综述国内外在含蜡粘性原油输送工艺方面的研究和实施情况,在此基础上,针对我国原油特性和管道输送需要,预测其研究发展方向,以期对创立具有我国特色的输油工艺技术体系有所裨益。在世界范围内,输油工艺日趋新型化、多样化,而输油工艺化学化则是新型化的主要内容。为了解决我国重质高粘易凝原油的输送问题,重点研究课题应该是化学化和生物化学工艺。     

Viscosity Prediction of Non-Newtonian Waxy Crude Heated at Various Temperatures

Viscosities are important parameters for design and operation of crude pipelines. The heating temperature is the major factor affecting viscosities of waxy crude below the wax appearance temperature. Below the abnormal point, waxy crude exhibits non-Newtonian flow behavior with the viscosity dependent on the shear rate. Both of these make determination of the non-Newtonian viscosities of waxy crude a very time-consuming job. On the basis of the model for predicting non-Newtonian viscosity of waxy crudes as a function of temperature and precipitated wax, an approach to predict non-Newtonian viscosity of waxy crude heated to various temperatures has been developed only based on a few measurements. The accuracy of prediction by this approach has been verified by 468 viscosity data from the Daqing crude heated at various temperatures. The totally average relative deviation between the measured and predicted viscosity is 9.42%.     

宁东油田清蜡、防蜡技术分析

在原油开采过程中,随着温度、压力的降低和气体的析出,溶解的石蜡便以结晶体析出、逐渐长大聚集最终沉积在管壁等固相表面上,即出现所谓的结蜡现象.结蜡会堵塞产油层,降低油井产量,同时也会增大油井负荷,造成生产事故.油井结蜡是影响油井高产、稳产的主要因素之一,清蜡和防蜡是高含蜡油井常规管理的重要内容.通过收集整理现场资料、分析原油性质和综合评价不同清防蜡技术的经济效果,确定宁东油田采用热力清蜡和化学防蜡技术较为合适.     

Methods of Analysis of High-Wax Crude Oils. Resins,Asphaltenes, Paraffin Waxes

Methods of determining the content of resins, asphaltenes, and paraffin waxes and distillation of the waxes applied to high-wax crudes are reported. The method is based on the experience from many years of research on ozocerites, minerals of petroleum origin that primarily consist of paraffin waxes, and crudes with a high wax content.__________Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 3, pp. 48 –50, May – June, 2005.     

Microbial treatment of waxy crude oil for mitigating wax precipitation and improving liquidity

The wax deposition of crude oil during transportation reduces the inner diameter, blocks the pipeline, and eventually increases the cost of petroleum production. This study reports a paraffin-degrading bacterial strain DG2 isolated from petroleum-contaminated soil. The effect of this strain on the removal of paraffin in crude oil was investigated. DG2, identified as Pseudomonas, produced biosurfactant that reduced the surface tension to 35.7?mN/m^?1 and exhibited high emulsification activity. Results of gas chromatography–mass spectrometry analysis of the waxy crude oil treated by DG2 showed decreased heavy hydrocarbon fractions (C25 and C32). The degradation test revealed that DG2 reduced the wax appearance temperature by 4.16?°C and the viscosity by 23% of the waxy crude oil. These findings indicate that paraffin-degradation strain DG2 may be used for effective paraffin biodegradation.     

海上高含蜡油田井筒清蜡周期预测图版建立及应用

渤海部分高含蜡油井投产后面临比较严重的井筒结蜡问题,现场作业人员一般根据生产经验确定清蜡周期,导致准确度低、清蜡作业成功率有限。根据海上油井生产管柱特征,以Ramey温度场计算数学模型为基础,结合井筒结蜡速率模型计算得到了井筒结蜡剖面,推导建立了电潜泵井清蜡周期预测方法,并进一步绘制了某油田A区块清蜡周期和清蜡深度预测图版。结果表明,清蜡周期随产液量的下降呈幂函数形式变短,随含水率增加呈指数函数形式增加。根据清蜡周期预测图版,预测3口井的清蜡周期分别为11 d、15 d、46 d,实际清蜡周期分别为8 d、12 d、39 d,预测结果与实际基本吻合。该方法同样适用于陆地油田自喷井确定清蜡周期和清蜡深度,对高含蜡电潜泵井、自喷井及时制定清防蜡措施具有借鉴意义。