Investigation of asphaltene deposition under dynamic flow conditions

Asphaltene deposition is one of the most serious problems, which usually occurs in oil wells, petroleum production, oil processing, and transportation facilities. Deposition of heavy organic components, especially asphaltene, can lead to wellbore blockage and impacts well economics due to reduction in oil production. Therefore, it is necessary to pay more attention to finding some solution to overcome this problem. In this study, a pipe-loop apparatus for investigation of oil stability was employed to measure deposition thickness using a thermal method. The effects of many factors such as oil type, oil temperature, oil velocity, inhibitors, and solvents on asphaltene deposition were investigated. The results showed that the deposition increased with the increasing value of the colloidal instability index. Besides, the deposition thickness increased with the decreasing velocity of oil, but did not change with oil temperature. In addition, n-heptane could result in more deposition; however, toluene had no effect on the deposition. Branched dodecyl benzene sulfonic acid (Branched DBSA) and Linear DBSA as inhibitors decreased the rate of asphaltene deposition.     

Challenges Inherent in the Development of Predictive Deposition Tools for Asphaltene Containing Hydrocarbon Fluids

The correlation and prediction of deposit formation are at the core of flow assurance, risk assessment, and other reservoir fluid management issues and are equally important for heavy oil or bitumen partitioning and upgrading. Asphaltene deposition in particular is a key topic in both sectors. Hydrocarbons from condensate-rich reservoir fluids to bitumen + diluent mixtures share constituents, from asphaltenes and resins to pentane, and can all be classified as asymmetric from a phase behavior perspective. The phase dia-grams for these asymmetric fluids are characterized by zone of four-phase behavior surrounded by three-phase and two-phase regions in both pressure-composition at constant temperature, and pressure-temperature at constant composition diagrams. Adherent asphaltenic solid and liquid deposits only arise within some multiphase zones. Zones such as the SL1, SL1V, L1L2V, and L1L2 are prone to the production of adherent asphaltenic deposits particularly when combined with intermittent or laminar flow. By incorporating incomplete approaches prevalent in both sectors into qualitative four component phase diagrams, one can illustrate key aspects of the phase diagrams for the entire range of fluids, as well as the challenges faced with respect to the prediction of specific phase behaviors. In this article we present and illustrate some of these challenges and propose a path toward their resolution.     

An experimental study on the effects of temperature and asphaltene content on the rheological behavior of vacuum residues

In this study, the rheological behavior of five types of Iranian vacuum residues (VRs) containing different values of asphaltene content is investigated under the effects of a wide range of temperature and shear rate. Rheological tests showed that the asphaltene content of VRs plays an important role on the viscosity of these fluids. The samples with higher content of asphaltene have higher values of viscosity and also higher yield point. The Bingham plastic and Herschel–Bulkley models were successfully used to model the rheology and yield behavior of VR samples at a wide range of shear rate and temperature.     

A new technique for treatment of permeability damage due to asphaltene deposition using laser technology

This study proposes a new technique for cleaning deposited asphaltenes using laser energy. Two series of experiments were carried out to achieve this objective. In the first one, one-inch column of bitumen mixed with limestone was placed above powdered limestone column in a flow cell. In the second series of experiments, actual consolidated limestone cores were subjected to flow of asphaltenic crude oil to simulate the damage process (i.e. permeability reduction). Both unconsolidated and consolidated limestone samples were subjected to a laser energy using laboratory diode modules at various laser intensity and treatment time intervals.Experimental results indicated that exposure of the above-mentioned permeability damaged limestone samples to laser energy caused asphaltene disruption and resulted in recovery of damaged permeability. The increase of laser intensity increased the recovered permeability and the optimum time duration is measured to be 1 h at laser intensity of 19 mW/h. Simultaneous pumping is required during the laser treatment to avoid the re-precipitation of the disrupted asphaltene.     

A new dynamic model for accurate prediction of asphaltene precipitation process in petroleum reservoirs

A novel dynamic model for accurate evaluation of the effects of different process variables on the asphaltene precipitation process in petroleum reservoirs is presented. Different deposition mechanisms such as surface deposition, pore throat plugging, deposits entrainment, and asphaltene adsorption are properly incorporated in the proposed multiphase model. The variations of porosity, permeability, and pressure profiles are in good agreement with the available experimental data. The presented approach can have potential application for evaluation of the asphaltene precipitation process in petroleum reservoirs at different operating conditions.     

油气层录井综合评价概论

针对华北油田油气勘探复杂程度逐年增加,寻找油气藏的难度越来越大的现状,为提高油气层录井综合评价符合率,该文对华北油田储集层热解气相色谱录井技术、快速色谱录井技术、荧光显微图像分析技术、地化录井评价技术、气测图版评价技术等多项油气层录井单项评价技术进行了概要介绍;详细阐述了油气层综合评价方法的流程与步骤,并用实例进行了说明;提出了:①影响油气层评价的主要因素有油气丰度、油气性质、储集层物性及其相互关系;②单一录井项目不能完成储集层各项参数定性定量描述,必须充分发挥各项录井的优势,进行综合评价的观点。为如何合理利用各项录井资料,进行综合解释提供了经验。     

就地CO_2技术油藏条件下性能评价

就地CO_2技术是一种提高原油采收率的有效手段,在油藏条件下,通过实验,对就地CO_2技术的性能(原油膨胀能力、原油降粘能力、结垢、地层伤害)以及驱油效率进行了评价。实验结果表明,在油藏条件下,就地CO_2技术具有良好的膨胀原油体积、降低原油粘度能力,并且具有良好的驱油效果。当原油粘度为12904．1 mPa·s,温度70℃,压力6 MPa时,就地CO_2技术可以使原油体积膨胀32．5%;可以使原油粘度降低52．69%,能够提高原油采收率6．40%～17．06%。就地CO_2技术对地层不会造成伤害。     

页岩气储层品质测井综合评价

页岩气储层品质对压裂改造至关重要,直接影响到试油层位的优选和压裂施工的效果,进而影响页岩气产能的高低。为此,针对四川盆地南部地区海相页岩储层开展综合评价研究:首先,通过岩心实验数据与测井曲线相关性分析,优选铀含量、密度计算有机碳含量,优选声波、密度、铀含量计算储层孔隙度和有机孔隙度,建立多参数计算页岩储层参数模型,参数精度高;其次,利用页岩气水平井单段测试产量与储层参数开展主成分方法分析,优选页岩孔隙度、有机碳含量、脆性指数、总含气量,建立页岩气水平井储层品质综合评价模型,形成了页岩气水平井储层品质测井综合评价方法,评价结果与生产测井测试成果有着较好的对应性。研究结果表明:①声波能较好地表征无机孔隙度,铀含量能较好地表征页岩有机孔隙度;②水平井靶体应尽量控制在页岩储层品质好、脆性矿物含量高、脆性指数高的小层内,易于被压裂,形成的压裂缝网复杂,测试产气量贡献大。结论认为,页岩气水平井储层品质测井评价方法对水平井储层品质级别具有较好的指示性,为现场水平井靶体优化和优质页岩储层压裂分段优选提供了技术支撑,可以有效地指导现场生产。     

A new rigorous two-phase kinetic model for accurate prediction of the asphaltene deposition rate during the oil flow in porous media of petroleum reservoirs

Asphaltene formation and deposition in oil reservoirs are the most important problems in petroleum industry. A new rigorous two-phase kinetic model for simulation of flow behavior considering the asphaltene deposition process is presented in this work. All governing equations considering the proposed new adsorption kinetic model are solved by finite difference method. The presented model is validated using the most accurate available data and different oil samples. The proposed approach can be used for accurate evaluation of the effect of asphaltene deposition on the oil flowing condition in porous media of petroleum reservoirs.     

低渗透油田储层连通关系动静态综合评价方法

葡西油田G137区块水驱控制程度达79%,而油田却有50%以上油井因注水不受效关井,说明仅用水驱控制程度评价注采系统的适应性已经不能满足油田开发的需求。将注采系统研究中连通关系细分为静态连通和动态连通,并提出有效连通系数概念,即注水受效厚度与砂体静态连通厚度的比值;将常用的真水驱控制程度定义为视水驱控制程度和有效连通系数的乘积。该方法实现了静态连通和动态连通的分阶段评价。应用该方法分析了葡西油田试验区和G137区块注水受效差的本质区别,前者是由于砂体规模小、静态不连通所致,后者则是因为储层物性差、动态不连通所致。因此,对于低渗透油田,将油田开发的水驱控制程度考核指标分解为视水驱控制程度和有效连通系数进行考核更为合理。     

凝析气藏注CO2提高采收率机理物理模拟

为深入研究凝析气藏注CO₂提高采收率机理,应用室内实验手段开展了CO₂对凝析气藏流体物性的影响实验。结果表明：注CO₂降低了凝析气的露点压力,降低幅度随注入量增加越来越大,注入0.4倍时的下降幅度达到了15.42%;CO₂注入倍数较小时,对凝析油以溶解、降黏、膨胀作用为主,凝析油膨胀体积的增量是萃取产出凝析油体积的9倍以上,溶解气油比和相对密度随注入倍数增加而增加;CO₂注入倍数较高时以萃取作用为主,生产气油比迅速增加,凝析油相对密度越来越大,采出程度达83%以上。在实际地层条件下,注CO₂开发,在远井区主要发挥降低露点压力的作用,并将露点线向产出井推移;在过渡带初期以溶解膨胀为主,压缩了该区带范围,后期主要为萃取作用,将液动线向产出井推进,缩小了近井带范围;在近井带初期主要为驱替作用形成气流通道,中后期主要为溶解、膨胀、携带和萃取作用。综合以上,凝析气藏注CO₂开发压缩了气液两相区,可大幅提高凝析气藏采收率。研究成果为凝析气藏的注CO₂开发和技术推广提供了重要的技术支撑。     

低渗气层损害评价室内试验条件的研究

在进行储层损害室内评价时，选择和明确规定合适的试验条件，是正确认识储层损害机理 和针对给定的储层优选出合适的，双储层损害较小钻井液的关键，亦有利于对不同来源岩样或相同岩样在不同时间及不同试验室所做结果进行对比。目前国内外已制定的标准，均没有结合所用试验装置明确规定出合适的试验条件。在对低渗气层岩样进行室内试验研究的基础上，提出了气层岩样气相渗透率测定条件和钻井液损害岩样条件，供室内进行地层损害评价     

南海西部海域复杂条件下PVT取样技术对策

南海西部海域新发现的含油气构造探井、评价井数量少,获取PVT样品成本高昂,且面临易脱气、易挥发、易凝析、组分缺失、样品污染、样品少和含水量高等诸多难题。在南海西部海域PVT取样统计分析的基础上,总结出了复杂条件下PVT取样的经验和适合海上油气藏PVT取样的技术对策。     

A Novel ANFIS-PSO Network for forecasting oil flocculated asphaltene weight percentage at wide range of operation conditions

Asphaltene precipitation is known as one of the challenging problems in petroleum industries which have significant effects on production such as formation damage and wellbore plugging, that consequently impose a serious restriction on production and in turn increases total cost of entire operation. Through decades an extensive research has been performed in order to identify asphaltene molecular structure, its behavior at different condition, and its departure mechanism from oil. One of most critical parameter associated with asphaltene precipitation modeling is flocculated asphaltene weight percentage in oil at given operation condition. In this investigation, to eliminate cost and time related with experimental procedure that concern with determining this critical parameter, a novel hybrid structure of ANN and FIS with the help of Genetic algorithm has been developed, which trained and tested by over 350 experimental data. The constructed network show good performance regarding flocculated weight percentage forecasting, and therefore can be used as a universal tool in order to provide input for any asphaltene-related modeling, with assurance.     

多油层油藏分层注水稳产条件与井网加密调整

实现注水开发油田的稳产,须提高产液量,以弥补产油量的下降。当现有的井网适应性变差,提高产液量受到限制时,就应该进行井网加密调整以增加井点数改善油层动用状况,来提高产液量。提高产液量是实现油田稳产的基本条件,井网加密调整,提高水驱控制程度,增加可采储量则是实现油田稳产的必要条件。油田稳产的5个要素包括含水率、产液量、井网密度、注水量及注水时机。以含水率与产液量关系建立了油田稳产方程,表述了不同含水阶段实现油田稳产的技术界限。根据统计规律提出了井网密度与可采储量增长率表达式,该计算式可用于预测不同开发阶段井网加密调整可采储量的增幅。对保持产液量稳定增长的宏观注水原则进行了论述。     

红山嘴齐古组浅层稠油油藏注汽参数研究与效果评价

红山嘴浅层稠油齐古组油藏原油粘度高，注汽参数不合理，在投产初期吞吐效果较差，周期生产指标与方案设计值差距也较大。针对这种情况，在重新确定地层参数和建立油层地质模型的基础上，进行了二次热采参数的数值模拟，其结果作为理论依据，在生产中针对不同类别的油层，设计多种不同的注汽参数进行现场试验，并以此对数模结果加以验证，确定出本油藏吞吐期合理的注气参数。     

特低渗储层润湿性评价新方法研究

对储层润湿性评价实验各种方法进行了对比,特别是特低渗储层,分析了自吸法实验中计量存在的问题,提出新的计量方法,并对这种实验方法进行了测试结果的比对,发现该方法可行,简单实用,同时可以节约大量的实验成本,降低劳动强度,提高工作效率.     

基于模糊综合评判与层次分析的储层定量评价——以包界地区须家河组为例

储层的分类与评价是储层研究的重点,也是气藏描述的基础.基于以往的评价方法存在多解性及相互矛盾等问题,提出了模糊综合评判与层次分析相结合的储层定量评价方法,并建立了定量评价模型.该模型将2种系统评价方法有机结合,优势互补.将该方法运用于包界地区须家河组储层的定量评价,选取储层的平均孔隙度、平均渗透率、有效厚度、砂地比、泥质含量建立评价集,确定了参数分类的隶属函数及隶属度,并尝试应用层次分析法确定了参数的权重,经计算可得研究区储层的平均孔隙度、平均渗透率、有效厚度、砂地比、泥质含量的权重分别为0.194 8,0.405 2,0.203 4,0.098 1,0.098 5.通过试采资料检验,该方法的评价结果与试采结果吻合程度很高.     

一种碳酸盐岩凝析气藏储量的计算方法

碳酸盐岩凝析气藏地层压力下降到露点压力以下时,凝析油在地层及井筒内析出,井口产气量、产油量与井底产气量、产油量之间存在差异,导致储量计算存在困难。通过经验公式拟合得到露点压力,当地层压力大于露点压力时,将井口产油折成气,按单相气求取凝析气储量,再通过气油比折算凝析油储量和干气储量;当地层压力小于露点压力时,地层出现多相流,分别计算干气储量和凝析油储量;实例对比分析表明,该方法的计算结果准确可靠。     

钻井液除硫剂除硫效果的静态评价实验及认识

目前室内评价出的钻井液硫化氢吸收液除硫效果与现场使用时的效果差异较大。为此,通过在水基钻井液中加入除硫剂制作成吸收液进行室内静态实验,考察了吸收液在改变温度、膨润土含量、无水碳酸钠含量、基浆水化时间、吸收液pH值后的除硫（使用）效果,得到了温度、硫化氢气体发生装置的稳定性、膨润土加量、无水碳酸钠加量、基浆水化时间、吸收液的pH值、碘量法中标准溶液的配制,操作误差以及滴定终点的判断等因素对测定钻井液除硫剂除硫效果影响的认识。研究结果认为,室内评价钻井液除硫剂的除硫效果的最佳实验条件如下：温度40 ℃、膨润土加量为4%、无水碳酸钠加量为0.5%、基浆水化时间为2 d、钻井液pH值大于11、碘量法滴定前调节吸收液的pH值大于11。