SOLID ORGANIC DEPOSITION DURING GAS INJECTION STUDIES

Recently a series of first contact miscibility (swelling) experiments have been performed on undersaturated light and heavy oils using LPG rich and methane rich injection gases, in which solid organic deposition was observed. A compositional gradient in the oils during the gas injection process was also evident as oil fractions expelled from the top to bottom of the PVT cell were observed to vary in density, molecular weight, as well as darkness of color. The change in stability of the oil samples before and after the contact with gas was analyzed using flocculation threshold titration. The asphaltene content of the different oil samples were determined by the IP 143 method. The standard asphaltenes and the solid organic deposit recovered from the swelling tests were analyzed using FTIR, HPLC-SEC and ¹H NMR. The aim of these analyses is to reveal the molecular nature of the deposits formed during the gas injection process in comparison with the standard asphaltenes in order to understand the mechanisms involved in asphaltene deposition.     

The Effects of Asphaltene Deposition on Unconsolidated Porous Media Properties during Miscible Natural Gas Flooding

Abstract

The deposition of asphaltenes in porous media is a complex phenomenon, which needs to be investigated under dynamic flowing conditions. Here, the likelihood of asphaltene deposition problems during dynamic displacement of dead oil by natural gas in unconsolidated porous media is experimentally inspected. Dynamic experiments showed a considerable increase in asphaltene deposition in the unconsolidated matrix during natural gas injection. The results show that increase in asphaltene deposition leads to pore plugging, porosity, and absolute permeability reduction of the porous media. Irreducible water measurements show that natural gas-induced asphaltenes change the sandstone wettability to oil-wet.     

Test Methods for Determining Asphaltene Stability in Crude Oils

Abstract

The high cost of remediating asphaltene deposition in crude oil production and processing has necessitated the development of test methods for determining the stability of asphaltenes in crude oils. In the current work, the stability of asphaltenes in crude oils of varying API gravity is predicted using the Oliensis Spot Test, the Colloidal Instability Index, the Asphaltene–Resin ratio, and a solvent titration method with NIR solids detection. The test methods are described in detail and experimental data from them presented. The experimental stability data were validated via correlation with field deposition data. The effectiveness of the various tests as predictors of the stability of asphaltenes in oils is discussed. The Colloidal Instability Index and the solvent titration method were found to predict a crude oil's propensity towards asphaltene precipitation better than both the Asphaltene–Resin ratio and the Oliensis Spot Test. For oils with low asphaltene content where most stability tests fail, live oil depressurization is proposed as the test for predicting the stability of asphaltenes.     

Polydispersity of heavy organics in crude oils and their role in oil well fouling

In this report, the polydisperse data of heavy organic fractions of crude oil and solid deposit were produced to investigate the causes of deposition in oil wells. The oilfields of the study have experienced, for several years, shutdowns and decrease in the production ratios due to heavy organics deposition. Several measures such as mechanical cleaning and periodic aromatic washes have been adopted to maintain the production level; nevertheless the costs associated with these procedures are very high.The SARA method was employed to separate the samples into four distinct fractions, namely Saturates, Aromatics, Resins and Asphaltenes. The total asphaltene content of the crude oil samples was determined using n-pentane, n-heptane, and n-nonuse as the precipitating solvents. Polydispersity and molecular weight of each fraction have been further characterized by Gel Permeation Chromatography (GPC). The presence of diamondoids in the solid deposits was also investigated by GC-MS. This technique has been carried out on various crude oil samples collected from an oil field.The results provided useful information on the interaction between the various heavy organic species responsible for the deposition phenomena. Solid samples from different wells resulted in similar composition concluding that these crude oils undergo similar deposition mechanisms. These studies showed that the crude oils produced from different wells in this oilfield are very similar in nature. The asphaltenes contained in some of the crude oil samples displayed a rather strong tendency to self-associate; they also render the highest amounts of precipitation. While diamondoids and alkyl-substituted diamondoids were confirmed to be present in the crude oils produced no evidence was found of their occurrence in the deposits.The polydispersity analysis procedure presented here provides a good understanding of the overall behavior of the species that precipitate and also of the interactions among these species. It is concluded that while most of the heavy organics contained in these crude oils may produce precipitates, asphaltene is the major cause of flocculation of the precipitates, which may result in deposition and plugging of oil-producing wells.     

Simulation of Natural Depletion and Miscible Gas Injection Effects on Asphaltene Stability in Petroleum Reservoir Fluids

Abstract

Natural depletion of petroleum reservoirs as well as gas injection for enhance oil recovery, are unavoidable processes in the oil industry. Foremost, prediction of the problems due to these two processes is very necessary and important. So many field and experimental experiences have shown that heavy organic depositions, especially asphaltene deposition, are principal results during these processes. Results of laboratory simulation of asphaltene deposition during the natural depletion of petroleum reservoirs and also during gas injection and enhanced oil recovery (EOR) processes are reported here. This is achieved through the design of a new experimental setup for the investigation of pressure and composition effects on asphaltene deposition in petroleum fluids at high pressure and high temperature conditions. In this work, asphaltene deposition during decreasing pressure, from pressures greater than reservoir pressure to pressures below the bubble point pressure (natural depletion) and also asphaltene deposition during natural gas injection in reservoir conditions, are studied for three samples—one recombined sample and two bottomhole samples. All of the obtained results from this work conform to theoretical and other experimental works.     

Modeling of Asphaltene Phase Behavior with the SAFT Equation of State

Abstract

The SAFT equation of state was used to model asphaltene phase behavior in a model live oil and a recombined oil under reservoir conditions. The equation of state parameters for the asphaltenes were fit to precipitation data from oil titrations with n-alkanes at ambient conditions. The SAFT model was then used to predict the asphaltene stability boundaries in the live oils. A lumping scheme that divides the recombined oil into six pseudo-components based on composition, saturates–aromatics–resins–asphaltenes fractionation, and gas–oil-ratio data was introduced. Using this lumping scheme, SAFT predicted stock-tank oil and recombined oil densities that are in excellent agreement with experiment data. For both the model and the recombined oil systems, SAFT predicted asphaltene instability and bubble points agree well with experimental measurements.     

Study of Asphaltene Precipitation Using Refractive Index Measurement

Abstract

The measurements of the refractive index of crude oils were utilized in this work to enhance the understanding of the behavior of asphaltenes in crude oil, specifically, their tendency to precipitate from crude oil. The onset of asphaltene precipitation was measured in eight crude oil samples, which were titrated with either heptane or pentane in order to induce precipitation of the asphaltenes. The refractive index of each sample was measured to find its relationship to asphaltene precipitation. The assumption that refractive index of a mixture is a linear combination of the refractive indexes of the individual components was verified. It was also found that mixtures of heptane or pentane and crude oil also followed this same behavior. However, as asphaltenes began to precipitate from the solution, the refractive index no longer followed this linear mixing rule. Careful analysis of the refractive index data for each of the crude oil samples revealed many interesting relationships between the refractive index data and the content of the different polar asphaltene fractions present. The refractive index of asphaltenes was predicted from the refractive index data of crude oils. The results suggest the possibility predicting the properties and characteristics of the asphaltenes contained in a crude oil simply by measuring the refractive index.     

注天然气油井沥青质析出规律研究

目的 解决东河区块原油在注气开采过程中沥青质沉积堵塞井筒问题。方法 采用高温高压固相沉积规律测试装置,基于光散射理论,研究了温度、压力、气油比等因素对沥青质析出特征的影响。结果 温度升高会增加沥青质在原油中的溶解度,促进原油稳定;等温降压过程中,沥青质随着压力降低逐渐析出,在泡点压力附近达到最大析出量,发生沥青质沉积堵塞油井的风险最大。DH-1井泡点压力对应井深2 140 m,与油井生产实际遇阻位置1 969 m接近,泡点压力可初步用于预测油井堵塞位置;溶解注气量越大,沥青质初始析出压力越大,沥青质析出压力区间也增大,沥青质沉积位置向油井深度下移。结论 研究揭示了注气过程沥青质的析出规律,对注天然气油井沥青质析出防治具有重要指导作用。     

REVERSIBILITY AND INHIBITION OF ASPHALTENE PRECIPITATION IN BRAZILIAN CRUDE OILS

ABSTRACT

A fundamental understanding of the aggregation and precipitation of asphaltenes in petroleum crudes is important for the development of preventive and curative measures for the potential problem of asphaltene deposition occurring during production, transport and refining operations. The question of reversibility of asphaltene precipitation, yet a controversial issue, is crucial for a clear and unequivocal understanding of the precipitation phenomenon, development of mathematical models that describe the behavior of asphaltenes in petroleum fluids, and the design of inhibitors. In this work, the behavior of precipitated asphaltenes in Brazilian crude tank oil samples following flocculant removal and gradual addition of fresh oil was investigated. The results obtained revealed a re-dissolution of precipitated asphaltene particles following flocculant removal and oil addition. On the inhibition of asphaltene precipitation, the capacity of a number of surfactants and block copolymers to inhibit asphaltene precipitation and deposition was also examined. Ethoxylated Nonylphenols and Hexadecyl Trimethyl Ammonium Bromide displayed highest capacity in the inhibition of asphaltene deposition.     

注气对固溶物沉淀影响的研究与应用

注气采油是提高原油采收率的主要方式之一,在此过程中准确描述含有沥青质等高分子有机固相物质的油气体系相平衡十分必要。为此,将沉淀的沥青质视为固相,假设标准状态下必须有沥青质沉淀,将标准状态压力和温度引入沥青质固相逸度计算,并同时考虑了标准状态压力和温度对沥青质固相逸度的影响,建立了能模拟沥青质沉淀的气、液、固三相相平衡热力学模型。据该模型计算的结果表明:①能通过比较液相沥青质逸度和固相沥青质逸度大小来判断固相沥青质沉淀的出现。②当注入某油的气体为烃类混合气体时,烃类混合气体的添加使得含沥青质原油的组分发生变化;温度相同时,注气浓度越高,沉淀的压力越大;浓度相同时,温度越低,沉淀的压力越大;当沉淀量一定时,随着注气浓度增加,油品的饱和压力随之增大;相同注气浓度下,当压力高于饱和压力时,随着压力增大,沉淀量减少。③在温度不变的情况下,注入某油的气体为CO2时,其沥青质沉淀量是注CO2浓度的函数且随着CO2浓度的增加,固相(沥青质)的沉淀量不断增大。④在注气驱油过程中,气体的注入极易引发含沥青质原油中沥青质等重质有机物的沉积。     

Characterization of Asphaltenes and Resins Separated from Water-in-Oil Emulsions

Abstract

Knowledge of the properties and behavior of asphaltenes and resins is indispensable for the design of preventive and curative measure for emulsion problems created by the presence of asphaltene, resins, and other organic and inorganic solids. In order to understand the phenomena of water-oil emulsions formed in Kuwaiti oil fields and determine the factors involved in the stabilization of these emulsions, the role of asphaltenes, resins and wax separated from various samples of oil field emulsions formed in Burgan oil field have been evaluated. Physicochemical properties of asphaltenes, resins, wax, and de-asphalted de-resined (DADR) oil samples have been studied via FT-IR, ¹H, and ¹³C NMR, elemental analysis, and differential scanning calorimetry (DSC). These emulsion samples contain different amounts of water ranges from 24 to 35%, asphaltene content ranges from 0.9 to 1.7%, and resin content from 3.7 to 4.6%. IR-FT spectra were performed to identify the various functional groups which have an effect on the stability of water-oil emulsions. The freezing behavior of an emulsion was characterized by differential scanning calorimetry to determine whether the water in the emulsion is free water or emulsified water.     

Changes in Asphaltenes Properties Modified with Fe in Hydrotreating Reactions

Abstract

The properties of the Hamaca of asphaltenes extra-heavy crude oil (AsfH) of Petroliferous Orinoco Belt can be modified for evaluating the changes produced with hydrotreating (HDT). One characterized the solid modified by means of UV-visible spectroscopy and nuclear magnetic proton resonance (NMR ¹H). The samples were put under hydrotreating to 200°C to avoid thermal cracking, atmospheric pressure, and a flow of feeding of 10.5 mL/hr in a fixed-bed reactor in the presence of H₂S generated in situ. The reactivity was followed by gas chromatography (GC). All the samples were evaluated before and after being hydrotreated by ¹H NMR, total sulfur analysis, and determination of molecular weight average by vapor pressure osmometry (VPO). The obtained results suggest the iron possibly is inserted in the structure of the asphaltene forming a new active phase catalytically, presumably a mixed sulfide (pyrrotite type) of iron-metal of transition (V and Ni) present in the asphaltene.     

Hydrotreating of Furrial Crude Oil Using NiMoS Supported on Alumina: Study of the Asphaltene and Their Fractions in Cyclohexane

Abstract

The Furrial crude oil originated in northern Monagas State. This shows problems such as the colloidal instability of the asphaltenes fraction present in them, causing its precipitation. This work is oriented to achieve an interpretation of the colloidal behavior of the asphaltenes through the study of the effect of the hydrotreating reactions (HDT) on the asphaltenes of the Furrial crude oil, using NiMoS/γ-Al₂O₃ as a catalyst. The results obtained after HDT reactions were analyzed to know the percentage of asphaltene and their fractions in cyclohexane, the measurement of flocculation thresholds and molecular weights by the VPO technique, and ¹³C NMR as well as the determination of the total sulfur content. Appreciable changes on the asphaltene of the Furrial crude oil and its fractions in cyclohexane after HDT, under conditions used, were observed. In general terms, the amount of asphaltene diminished and the percentage of distribution for insoluble fraction in cyclohexane (IFC) and for soluble fraction in cyclohexane (SFC) was affected causing an increase in the stability of the asphaltene. The asphaltene and IFC were observed to be a pronounced variation of the molecular weight average in number, in comparison with SFC. ¹³C NMR spectra indicate that the hydrotreated asphaltene shows structural change, and IFC presents a variation of the percentage of sulfur minor in comparison to SFC.     

Preparative Subfractionation of Petroleum Resins and Asphaltenes. II. Characterization of Size Exclusion Chromatography Isolated Fractions

Abstract

In the first study of this series, resins and asphaltenes from stable and unstable crude oils have been separated by size exclusion chromatography in three molecular mass ranges (MM: high, medium, and low). In the present study, the isolated fractions were further characterized in order to correlate several of their structural properties with crude oil tendency to solid deposition. Elemental analysis (C, H, S, N), infrared spectrophotometry (IR), and proton nuclear magnetic resonance (¹H NMR) were the characterization techniques performed in order to meet the objective. Hydrogen deficiency and aromaticity appear to be the main parameters governing the intrinsic stability for the studied samples. Oxygen compounds were observed to be more abundant within fractions isolated from unstable oils, particularly in resins and in the low MM range fractions both from resins and asphaltenes. However, causes for the presence of these oxygenates remain open to further study. Experimental evidence gathered during this work suggest the possibility of small compounds acting like natural dispersants of the larger components present in complex mixtures like asphaltenes.     

CHANGE OF PHYSICAL AND THERMAL DECOMPOSITION PROPERTIES OF IN SITU HEAVY OIL WITH STEAM TEMPERATURE

ABSTRACT

Ikiztepe crude oil was subjected to four different steam temperatures during steam injection which was applied as an enhanced oil recovery process on a linear limestone model saturated with oil. Produced oils were characterized using density, viscosity measurements, pyrolysis experiments utilizing TGA and elemental analysis runs. Results showed that produced crude oils change in measured characteristics as compared to the original oil. These changes include an increase in H/C, and cracking activation energy, decrease in density, viscosity and amount of residue remaining after cracking (coke). Also, decrease in asphaltene amount, changes in the elemental composition of asphaltenes and increase in the cracking activation energies were observed at 225 °C run. These measurements show that the produced oils get lighter and differ compositionally from the original oil as steam temperature increases. Decrease in elemental sulphur amount is one of the major changes when environmental considerations are concerned. Residual oil left in the limestone pack on the other hand shows an increase in the low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO) activation energies as determined from TGA combustion experiments on the samples taken from the pack after steam injection experiments.     

The Effects of Asphaltene Deposition on Unconsolidated Porous Media Properties during Miscible Natural Gas Flooding

The deposition of asphaltenes in porous media is a complex phenomenon, which needs to be investigated under dynamic flowing conditions. Here, the likelihood of asphaltene deposition problems during dynamic displacement of dead oil by natural gas in unconsolidated porous media is experimentally inspected. Dynamic experiments showed a considerable increase in asphaltene deposition in the unconsolidated matrix during natural gas injection. The results show that increase in asphaltene deposition leads to pore plugging, porosity, and absolute permeability reduction of the porous media. Irreducible water measurements show that natural gas-induced asphaltenes change the sandstone wettability to oil-wet.     

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.     

Comparisons Between Asphaltenes from the Dead and Live-Oil Samples of the Same Crude Oils

Abstract

Asphaltenes precipitated from pressure-preserve bottomhole oil samples have been obtained for three oils at different pressures, using a bulk high-pressure filtration apparatus. The precipitates captured on the filter were recovered, the asphaltenes defined by the n-heptane insolubility were extracted and analyzed. These pressure-driven asphaltenes found on the filter were found to make up in the range between 50 and 100 ppm of the whole crude oil. Opening of the cell did not reveal asphaltenes retained due to wall adhesion. Size exclusion chromatography tests performed on both the live-oil-derived asphaltenes and the standard asphaltenes as precipitated by atmospheric titration on the same crude oil, revealed that the live-oil asphaltenes had apparent smaller hydrodynamic volume and narrower distributions than the standard asphaltenes for two oils. Further FTIR tests also showed large differences between standard asphaltenes and the asphaltenes obtained at high pressure filter. The latter appeared to contain more functional groups and be less saturated. Implication of these structural differences on precipitation modeling is discussed.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

ABSTRACT

Improved prediction of the onset of asphaltene precipitation may be achieved using refractive index (RI) to characterize crude oils and their mixtures with precipitants and solvents. Experimental measurements of RI for mixtures of several crude oils with the precipitant n-heptane, are reported at ambient conditions. Theoretical developments are described that will permit extension of these observations to reservoir conditions

Measurements of RJ at the onset of precipitation have shown that the onset occurs at a characteristic RI for each oil/ precipitant combination, supporting the premise that precipitation is dominated by London dispersion interactions and thus, that RI can be used to predict the onset of precipitation. Reports in the literature showing that the onset of precipitation occurs at constant solvent-to-precipitant ratios provide additional confirmation

The theory is developed on the assumption that London dispersion forces dominate aggregation and precipitation of asphaltenes. The interaction energy of asphaltene molecules or aggregates in a medium of oil can be expressed as a function of the difference between the RI of asphaltene and oil. The RI of live crude oil during pressure depletion can be calculated from the RI of the stock tank oil, the molar refraction of the separator gas, the formation volume factor B_o and the solution gas/ oil ratio R_s     

CHARACTERIZATION OF ASPHALTENES AND RESINS FROM PROBLEMATIC MEXICAN CRUDE OILS

Asphaltenes and resins have been separated from four mexican oils suffering from the deposition of asphaltenic material during recovery operations. A SARA separation of the oils was performed and the resins and asphaltenes further analyzed. Characterization methods employed were FTIR, elemental composition both of CHNSO, and trace metals and molecular weight determination using size exclusion chromatography. NMR techniques were applied to two asphaltene samples. The overall scope of the work was to get a better understanding of the nature of the asphaltene stability at a molecular level in these problematic oils. Separation of resin in two fractions indicates that there is no long alkyl chains in these as given by FTIR, which may be the cause of the lack of stability along with the large difference in bubble point and reservoir pressure.