Asphaltene aggregation onset during high-salinity waterflooding of reservoirs (a molecular dynamic study)

Abstract

The primary objective of this study is to establish an understanding of the role of high-salinity brine on the intensity of asphaltene aggregation onset during waterflooding of petroleum reservoirs. We already have shown that asphaltenes have a high tendency to form aggregates during waterflooding process when pure- and low salinity-water are injected into reservoirs. To fulfill the present objective, molecular dynamic simulations are performed on asphaltenic-oil/aqueous systems at 550 K-200?bar. The oil phase consists of asphaltenes (10?wt.%) and ortho-xylene, in which asphaltene molecules are completely soluble. Our simulations results reveal that the “salt-in effect” of high-salinity brine (25 wt.% NaCl) on seven different model asphaltenic oils causes a significant reduction of the onset of asphaltene aggregation as compared with pure-water. Such “salt-in effect” is primarily due to a considerable reduction of water miscibility in the oil phase at high pressure and temperature.     

沥青质在高定向热解石墨表面络合机制的分子动力学模拟

沥青质在固体表面的络合机制是解决剩余油开采难题的重要理论基础。为了给聚集抑制剂和表面活性剂的开发提供理论依据,采用分子动力学模拟,系统研究了沥青质在高定向热解石墨表面附着、聚集的特征。通过计算表面吸附过程中沥青质的自由能变化,基于Yen-Mullins模型的定量判据,结合沥青质平均相互作用分子数和分子密度分布,定量分析了沥青质在固-液界面体系与溶液体系中聚集作用的差异。分子动力学模拟分析表明,固体表面会降低沥青质的聚集程度,加快聚集过程中的阶段分化,具体包括4个阶段的界面过程：①沥青质覆盖固体表面并逐渐铺满一层;②固体表面上形成纳米聚集体;③固体表面上纳米聚集体与溶液中的纳米聚集体通过边缘堆叠、T形堆叠形成簇状物;④固体表面的聚集体与溶液中的聚集体通过脂肪侧链接触形成絮凝物。     

Metal porphyrin occlusion: Adsorption during asphaltene aggregation

Metal compounds such as vanadyl and nickel porphyrins present in crude oils are associated to the most polar fraction defined as asphaltenes. The amount and kind of these compounds in the crude oil depend of the variations in origin, maturity, pressure, and temperature. During the asphaltene colloid formation the metal porphyrins could be trapped, occluded, or adsorbed, protecting these compounds from oxidation or chemical degradation. In this work the authors induce the aggregation of asphaltenes by changing the solubility parameter of the media in presence of metal porphyrins. UV-vis absorbance is used to monitored asphaltene aggregation at 350 nm to follow the variations in asphaltene aggregation and 405 nm to follow the porphyrin Soret band. The results showed that more than 50% of the porphyrins were trapped inside the asphaltene aggregate and posterior re-dissolution of the aggregates in toluene showed very low release of the porphyrins, demonstrating the strong interaction between the porphyrin and asphaltenes during the aggregation.     

Changing characteristics of ultralow permeability reservoirs during waterflooding operations

The characteristics of ultralow permeability reservoirs changed after waterflooding.Thin-section analysis and scanning electron microscopy(SEM) of core samples from inspection wells indicated that calcite and barite were formed in ultralow permeability reservoirs during waterflooding operations.Some asphaltene precipitates on the surface of formation rock would influence the reservoir porosity,permeability,wettability,and electrical properties.In this paper,the changes of physical,electrical,and fluid properties of ultralow permeability reservoirs during waterflooding operations were analyzed.This provides important information to improve waterflooding performance in ultralow permeability reservoirs.     

巨厚油层不同注水方式模拟研究

介绍了一种二维可视物理模型,该模型具有可视性强的特点,可直接观察到注入水在多孔介质中的流动情况.针对辽河冷家油田储层特征及原油性质的差异,在室内建立的二维可视物理模型中进行了多油层同时注水开发、上返式开采和底水托浮式开采的模拟研究,并对比研究了不同注水方式下的开发效果及其开采机理.     

塔河油田缝洞型油藏水驱后气驱提高采收率可视化实验

塔河油田缝洞型油藏注水开发后,开展单井注气提高采收率实验,注气效果显著,但油藏开发中后期逐渐出现注水、单井注气效果变差,大量水驱后剩余油未能动用。为了提高此类油藏的注气开发效果,需要针对性地开展多井单元注气提高采收率机理研究。通过设计、制作物理可视化模型进行气驱模拟实验,探讨缝洞型油藏气驱后剩余油的分布情况及其影响因素。实验结果表明,水驱后氮气驱,能有效提高驱油效率,注气方式、注入位置和模型充填等因素对气驱效果有影响,采用连续稳定注气方式,在构造高部位注气,低部位采油,可有效提高气驱效果,为类似油藏单元水驱后剩余油的开采提供借鉴。     

注水开发小型断块凝析气藏的方法及适应性

对于规模小、储量低的小型凝析气藏,枯竭式开发产量递减快,凝析油气采收率低,然而限于气藏的规模,注气开发也不经济。针对该类凝析气藏的特点,从地质特点、气藏工程、采气工艺及地面工程等角度对其实施注水开发的可行性进行了综合分析论证,同时结合具有以上特点的BG5 区块滨Ⅳ-2凝析气藏,对其注水开发的适应性进行了气藏数值模拟研究。结果表明,通过合理的注水开发能够显著提高该类气藏的凝析油气采收率,增加气田经济效益,为其他类似气藏的开发提供了借鉴。     

引入启动压力梯度计算低渗透砂岩油藏注水见效时间

用常规的压力传播的导压系数公式预测的低渗透油田注水见效时间,通常与实际情况相差很大。针对低渗透砂岩油藏存在启动压力梯度的特点,以具有启动压力梯度的渗流公式为基础,求出地层稳定生产时径向流产量公式及压力分布公式,用物质平衡法求解出低渗透油田注水见效时间与注采井距的关系。低渗透油田压力波传播时间与压力梯度关系密切,注水见效时间与启动压力梯度成正比,与井距的立方成正比。该方法用于宝中区块合理井距的确定,方案实施后,实际注水见效时间与计算值相符。     

油藏动态模型和剩余油仿真模型

以三角洲前缘低渗透砂岩储层为例,综合应用多学科理论和技术,建立了长期注水开发低渗透砂岩油藏的动态模型和剩余油仿真模型,研究了剩余油分布规律,并建立了高含水率开发阶段储层微观剩余油的三类分布模式.研究结果表明,油藏开发流体动力地质作用控制了不同含水期三角洲前缘低渗透砂岩油藏参数的演化,储层宏观物性参数及微观孔喉网络演化有利于驱油.油藏仿真模型是揭示长期注水开发油藏储层三维空间演化规律、预测和评价剩余油分布的有效技术手段.     

不稳定注水技术研究及应用

为了提高剩余油采收率,首先对用玻璃微珠填充的油藏物理模型进行了不稳定注水模拟,然后选择了一块面积为1km^2的油藏,采用VIP模拟器进行数值模拟,在模拟的基础上从理和实践2方面进行了综合分析,阐明了周期注水（包括改向注水）提高非均质油藏采收率的机理和不稳定注水工程参数的优化等问题,并在胜利油区辛109沙一段和胜索油田坨沙二段1－2砂组做了不稳定注水油矿试验,实施制定的不稳定注水方案后,取得了较好的控水稳油效果。     

中国水驱砂岩油田含水与采出程度的量化关系

分析了中国砂岩油田的地质特点和含水变化影响因素,在分析含水与可采储量采出程度关系曲线的基础上,利用中国已进入高含水阶段的15个典型注水砂岩油田开发资料,得到了代表全国注水开发水平的含水变化曲线及理论公式。对不同含水阶段下采出程度的定量分析结果表明,中国水驱砂岩油田含水变化整体呈凸型曲线特征,近70%的可采储量要在油田进入高含水阶段(含水率>60%)之后采出,其中高含水期（60%≤含水率<90%）是提高采收率最为关键的时期,约50%的可采储量要在此阶段采出。本研究成果除充分认识中国水驱砂岩含水变化规律并进行定量分析外,还可应用于油田开发指标预测、开发效果评价和开发潜力评估等方面。     

THE ROLE OF POLAR SPECIES IN THE AGGREGATION OF ASPHALTENES

Abstract

Many properties of heavy oils are Influenced by the presence of asphaltenes. According to solubility studies, asphaltenes are the most polar fraction of heavy oils, but the magnitude of the dlpole moment is not known. We quantified this parameter by applying dielectric spectroscopy to several heavy oils with different asphaitene concentrations, and the response of the permanent dlpoles was measured as a function of concentration and temperature. The asphaltenes have dielectric constants ranging from 5 to 7. Calculations Indicate more than one dlpole per asphaitene molecule. The diameter of the dlpole center was assessed to be 3 to 6 A.

The probe was extended to study the Involvement of dlpoles In asphaitene aggregation. As the concentration of asphaltenes exceeds 10%, the dielectric constant exhibits substantial negative deviation from linearity, signifying the onset of Intermolecular Interactions (the pairing of dipoles in head-to-ta1l configurations to form clusters). Raising the temperature Increases the dielectric constant. Indicating dissociation of the aggregates. Based on comparison of these results with the dielectric behavior of model compounds the role of dipoles in the process of asphaitene association has been demonstrated for the first time.     

基于流线方法的压裂水平井注水开发渗流机理研究

非常规储层采用压裂水平井技术可以获得有效的商业价值,针对低砂泥岩特低渗透油藏,通过数值模拟进行压裂水平井注水开发规律研究,运用流线方法揭示了压裂水平井注水开发渗流机理。结合数值模拟结果,根据流线形态、分布及流线与裂缝的对应关系研究了压裂水平井开发的四个流动阶段:裂缝附近线性流、垂直裂缝附近拟径向流、地层线性流和水平井拟径向流。进一步分析了不同井网形式下的压裂水平井注水开发渗流特征,为现场的开发应用提供一定的技术指导。     

氢键作用对沥青质超分子聚集的影响

对沥青质进行羧基化、磺化和甲基化反应,从加强与钝化氢键作用两个方面对比研究了不同化学处理对沥青质结构、热稳定性以及沥青质聚集的影响.研究发现:羧基、磺酸基等基团引入沥青质分子后,提高了沥青质分子的极性,增强了分子间的氢键作用,显著促进了沥青质的聚集,并且引入的基团极性越强,促进聚集效果越明显;相反,沥青质中含活泼氢官能...     

Solution techniques for population balance equation: A case study for asphaltene aggregation

Population balance equation is widely used in modeling of particulate processes. In this work, the enlargement of asphaltene particles in a synthetic heptane-toluene mixture (Heptol) was experimentally investigated in a static mode and then modeled by using PBE. Aggregation is considered as sole responsible mechanism for size evolution. Three solution methods including two discretization methods, modified Hounslow (MH) method and Kumar cell average technique (KCAT), and one moment method, quadrature method of moments (QMOM), are considered. The simulation results were compared with experimental data to evaluate each method. The results of simulations indicate that moment method offers higher accuracy and less computational expense respect to discretized methods in prediction of asphaltenes aggregation. In the case of considering fractal structure, both methods inaccurately predicted the number and average diameter of asphaltene aggregates.     

Molecular Weight Determination of Asphaltenes from Colombian Crudes by Size Exclusion Chromatography (SEC) and Vapor Pressure Osmometry (VPO)

Abstract

Characterization of Colombian asphaltenes isolated from feedstocks to refining units was carried out during this study, emphasizing the determination of their average molecular weights (MW). Experimental conditions used for vapor pressure osmometry (VPO) and size exclusion chromatography (SEC) were investigated aiming to select the most suitable set up that affords the best representative values. SEC was observed to provide the most reasonable MW values, after analysis improvements were achieved by using realistic calibration curves got with phthalocyanines, compounds that closely mimic component structures within oil and asphaltenes fractions. MWs displayed by Colombian vacuum residua asphaltenes fall within the range 1,700 ± 200 Daltons, reported previously for asphaltenes from different reservoirs worldwide.     

沈625块裂缝型低潜山油藏注水开发主要做法及效果评价

沈625块潜山油藏具有双重介质的复杂特点,开发中暴露出多种矛盾,通过注水可行性分析以及注水参数优化设计,给出了注水开发过程中的主要做法,并对措施实施后的效果进行了评价。其中,直井注水、水平井采油方式的应用对于新型注水开发模式进行了有益的探索,实施后效果明显,可为同类油藏的注水开发提供一定的借鉴。     

减氧空气吞吐技术在鲁克沁深层稠油油藏的应用

鲁克沁三叠系深层稠油油藏经过多年的注水开发,出现了含水率上升快、水驱效率低、采出程度低等问题。为了解决水驱矛盾,提高单井产量,提出了减氧空气吞吐的方案。通过室内物理模拟实验和数值模拟研究,分析了减氧空气吞吐的机理,优化了注入参数。基于理论研究结果,在鲁克沁三叠系深层稠油油藏开展了减氧空气吞吐矿场试验,结果表明：减氧空气吞吐降水增油的机理是稠油注减氧空气后存在拟泡点,形成泡沫油流分散降黏,同时封堵水流优势通道,扩大波及体积。注气量、注气速度和焖井时间对减氧空气吞吐效果影响较大,建议单井注气量40×10⁴ m³,注气速度4×10⁴ m³/d,焖井时间8~10 d。鲁克沁三叠系深层稠油油藏共实施减氧空气吞吐400余井次,有效率82%,单井平均初期日增油量4.5 t,综合含水率下降42%,有效期达168 d,有效期内单井增油量480.0 t。因此,减氧空气吞吐是深层稠油的一种有效降水增油技术,对同类型油藏注水开发后提高采收率具有重要的借鉴意义。