The Effective Diffusion/Dispersion Coefficient in Vapor Extraction of Heavy Oil

Abstract

In this study, a new correlation for determination of effective diffusion/dispersion coefficients in the vapor extraction of heavy oil/bitumen (VAPEX) is introduced. This model takes into account the solvent concentration as well as the drainage height and permeability dependency of these coefficients. The concentration dependency in this model stems from the mixture viscosity changes, while the height dependency appears directly in the correlation. The correlation was obtained using the experimental results of the VAPEX experiments that were conducted with physical models of varying sizes and different permeability sand-packs. Estimation of a proper mass transfer coefficient has been a challenging issue for the analytical and numerical simulation of the VAPEX and other similar processes. Incorporating the effect of drainage height on dispersion with a concentration-dependent diffusivity model enables one to estimate the dispersion coefficient values involved in this process.     

Multilateral Analysis of Pressure and Temperature Effects on Steam Methane Reforming Reaction

Abstract

Pressure and temperature effects on steam methane reforming (SMR) process in porous media and at equilibrium conditions of the reaction were investigated. The investigation was carried out by developing of a computer program to check the simultaneous effects of pressure and temperature on the extent of the reaction. Two methods for estimation of the effective diffusivity coefficients through porous catalysts were applied: (a) simplified method and (b) a new method based on more realistic conditions of the reaction. The results obtained based on this study would be useful for optimizing of pressure and temperature of SMR reaction.     

Prediction of Diffusion Coefficients for Binary Gas System

Abstract

A new formula has been developed to estimate diffusion coefficients for a binary system for some gases dependent on temperature, pressure, molecular weight, and a Pitzer acentric factor in a different range of temperatures. In this work, an introduction of the available observed data develops a new correlation for the effect of these parameters on the prediction of diffusion coefficients.     

Mass Transfer of CO2 Into Water and Surfactant Solutions

Abstract

The mass transfer of CO₂ into water and aqueous solutions of sodium dodecyl sulphate (SDS) is experimentally studied using a pressure, volume, temperature (PVT) cell at different initial pressures and a constant temperature (T = 25°C). It is observed that the transfer rate is initially much larger than expected from a diffusion process alone. The model equations describing the experiments are based on Fick's Law and Henry's Law. The experiments are interpreted in terms of two effective diffusion coefficients—one for the early-stages of the experiments and the other one for the later stages. The results show that at the early stages, the effective diffusion coefficients are one order of magnitude larger than the molecular diffusivity of CO₂ in water. Nevertheless, in the later stages the extracted diffusion coefficients are close to literature values. It is asserted that at the early stages, density-driven natural convection enhances the mass transfer. A similar mass transfer enhancement was observed for the mass transfer between a gaseous CO₂ rich phase with an oil (n-decane) phase. It is also found that at the experimental conditions studied addition of pure SDS does not have a significant effect on the mass transfer rate of CO₂ in water.     

Measurement of gas diffusivity in heavy oils

Molecular diffusion of gases in oil plays a role in several heavy oil recovery processes. In solution gas drive, the gas diffusion coefficient has a direct impact on the amount of gas that is released and the level of supersaturation that exists during pressure depletion. In the Vapex process, molecular diffusion controls the rate at which the solvent vapour is absorbed by the oil. Molecular diffusion is also important in supercritical fluid extraction of heavy oils and in recovery of residual oil by miscible displacement. Unfortunately experimental data on gas diffusion coefficient in heavy oils are relatively scarce due to the tedious nature of diffusivity measurements. The main objective of this work was to develop a simple experimental technique for measuring gas diffusion coefficients in heavy oils. Diffusion coefficients of carbon dioxide and methane were measured by measuring the rate of gas absorption in a high-pressure windowed cell. The diffusion equation, coupled with the gas material balance equation, was used to history match the gas absorption data using the diffusion coefficient as an adjustable parameter. The diffusion coefficients calculated by this history match technique are compared with the reported values of diffusion coefficients in similar systems.     

Analytical Modeling of Gas Diffusivity Into Oil Through a Film of Water

Abstract

The authors aimed to determine diffusion coefficient of gas in oil when there is a water-blocking film between them. Dealing with this purpose, a new technique based on analytical modeling was developed to measure the diffusivity and solubility of gas into oil and water. The system that was described is solved analytically and numerically. The result of analytical solution is presented as different type curves, which are very simple to use. To generate data, a numerical scheme was employed. The determination of gas diffusivity and solubility emerged from matching concentration data with the type curves.     

Diffusion Coefficient of a Binary Liquid System

Abstract

A generalized diffusion coefficient correlation for a binary system of liquids has been developed to represent the data for a wide range of temperatures. Detailed analysis shows that the proposed correlation fits the experimental measurements of diffusivity with the corresponding calculated values with an acceptable percentage error.     

Wax Diffusivity: Is It a Physical Property or a Pivotable Parameter?

Abstract

In order to predict wax deposition problems the key parameter is the wax diffusion coefficient. While it is quite easy to find measured diffusivity values for well-defined compounds at quite low concentrations, very few experimental data are available for wax diffusivity in oil. Most of the literature data are estimated by interpolating experimental data obtained by loop tests and then they are affected by a noticeable uncertainty. In fact this parameter collects the whole uncertainty of the test and the paradoxical situation is that the key parameter ends to be the most error-affected or to be used as a pivotable parameter in “predictive” models. This article describes an experimental procedure to determine the overall diffusivity coefficient of waxes into the oil; the main advantage of this technique is that it allows the direct measure of diffusivity on the oil. Besides it is a very simple and straightforward technique. Results obtained were used to gain insight into the deposition process; the conclusion was that, due to the counter-intuitive diffusivity dependence on temperature, it is likely that noncompositional models available at present are structurally incorrect.     

多孔介质高温高压多组分气体-原油分子扩散系数研究

目前气体-原油分子扩散系数的研究对象多为单组分气体-原油体系,而且多在低温或者低压下在 PVT 筒中进行实验,与实际的注气过程相差较大。在这种情况下,研究了多孔介质中高温高压下多组分气 体-原油的扩散系数,测试了全直径岩心中多组分气体-凝析油、多组分气体-重质原油在60 ℃,20 MPa 条 件下的扩散系数。研究结果表明：原油组分对扩散有一定影响,但对于最终扩散程度影响不大;气体在凝析 油中的扩散系数高于其在重质原油中的扩散系数;扩散系数以幂函数形式逐渐增加,最终逐渐趋于平缓。     

STUDIES ON LARGE CRUDE OIL ALKANES. I. HIGH TEMPERATURE LIQUID CHROMATOGRAPHY

Abstract

Isolation of very large alkane components from heavy oil fractions and solid deposits was achieved by high temperature medium pressure liquid chromatography (MPLC–. n-Heptane and silicagel were the selected solvent and adsorbent employed for routine analysis. Preadsorption of the sample proved to be the most convenient injection technique. Porosity of adsorbents and stepwise temperature gradients were assessed to influence the generation of diverse-multimodal solid phases. Total elution of complex mixtures was possible if high temperature was adopted during the entire experiment and, this behavior was rationalized on the basis of mutual cosolvency of very broad alkane distributions.

Isolated fractions were characterized by high temperature size exclusion chromatography (SEC), technique that allowed to detect very large alkanes preconcentrated during the stepwise separations. Porosity of solid asphaltenes was inferred and diffusional plus crystallization effects were proposed to explain all these findings.     

New Proposals of Theoretical Models for Oil Dispersion Concentration in Flow Through a Packed Bed

Abstract

When a fluid flows through a packed bed, dispersion of fluid occurs as a result of the combined effects of molecular diffusion and mixing in the voids. Thus, in using a packed bed as a coalescer, allowance must be made for the fact that the flow deviates somewhat from plug flow. In general, the dispersion coefficient in the longitudinal direction is greater than in the radial direction. New proposals for theoretical models for dispersion concentration in the packed bed were derived using an analogy between molecular diffusion and flow of secondary dispersion inside the packed bed. A general differential equation has been solved in two directions, the axial and the radial directions, under both unsteady and steady-state conditions.     

The Impact of Pore Pressure on CO2-Methane Displacement

Abstract

The intricate behavior of carbon dioxide at supercritical conditions is considered to influence the ultimate recovery of additional hydrocarbon reserves through the application of CO₂-enhanced gas recovery projects. Mixing in such a system is a diffusion-like process, which definitely depends on the physical properties of the displacing and displaced phases and the heterogeneity of the medium. The authors' aim was to experimentally investigate the consequence of pore pressure on the recovery efficiency and multiphase gas flow in a reservoirs porous medium. The displacement tests were carried out at five different pore pressures ranging from 10.34 to 40.68 MPa, temperature of 433.15 K, and displacement rate of 10 cm/hr. Results determined that improved recovery by approximately 40% can be obtained by applying the highest pore pressure in comparison with the test conducted at low pore pressure.     

WASHABILITY CURVES FOR PYRITE REMOVAL IN COAL USING PERCHLOROETHYLENE AS HEAVY MEDIUM

Abstract

Pyritic sulfur is removed from raw, high sulfur coal by gravitational separation using a suitable solvent, or heavy medium. This is possible due to the inherent difference in the specific gravity of clean coal and the mineral matter in it. The effectiveness of perchloroethylene (PCE) as a heavy medium was experimentally evaluated. The most important factors governing the efficiency of this process are the quantity of clean coal yield and depyriting efficiency. It was found that the pyritic sulfur removal efficiency as well as the clean coal yield depended strongly on its particle size distribution and mineral matter content. This paper presents valuable data on the effect of particle size of coal on clean coal yield as well as pyritic sulfur removal efficiency. A “master” curve is obtained to determine a workable size range which gives the most optimal yield of clean and depyrited coal.     

An Experimental and Numerical Investigation of Solvent Injection to Heavy Oil in Fractured Five-Spot Micromodels

Abstract

In this work a series of solvent injection experiments was conducted on horizontal glass micromodels at several fixed flow rate conditions. The micromodels were initially saturated with heavy crude oil. The produced oil as a function of injected volume of solvents was measured using image analysis of the continuously provided pictures. In order to investigate the macroscopic behavior of the process in different media, several fractured, with constant width, and nonfractured five-spot micromodels were designed and used. The measured data have also been used for verifying and developing a simulation model that was later used for sensitivity analysis of some parameters that affect oil recovery. The results show that when the fracture spacing increased, the oil recovery decreased. In contrast, as the fracture orientation angle (the angle with the mean flow direction) or solvent viscosity increased, the oil recovery increased. A critical value for the ratio of connate water saturation to the oil volume has been found that, beyond that the solvent injection process, loses its efficiency. The final recovery of a water alternating solvent (WAS) injection process in fractured medium in the presence/absence of connate water saturation was considerably greater than that obtained either by continuous solvent injection or water injection alone. Good agreement was observed between experimental and simulation results when a dual permeability model was used in our simulation.     

STRUCTURE,INTERACTION AND PHASE TRANSITION OF VACUUM RESIDUE IN APOLAR SOLVENTS

ABSTRACT

Structure, Interaction, and phase transition of a vacuum residue fractions In various apolar solvents were Investigated, using viscosity measurements and small angle neutron scattering. Both light and heavy ended fractions form colloidal particles of spherical shape with average sizes of -40 and -60 A respectively. The size distributions follow a Schultz distribution function approximately. Rheological studies of these fractions indicated significant particle solvation. The solvation mechanism is through association of the solvent molecules with individual VR colloids, instead of through solvent entrapment between agglomerated colloids. The viscosity, as a function of temperature, suggested a glass-like transition at approximately 254?K for the heavy ended fraction at 0.5 volume fraction. The small angle neutron scattering measurements confirmed the colloidal structure determined from rheological study. It also provided the information about the total colloids/solvent Interfacial area, from which we found that VR colloids have a rough surface     

Liquid-phase Mutual Diffusion Coefficients for Heavy Oil + Light Hydrocarbon Mixtures

Abstract:

Liquid-phase mutual diffusion coefficients are a key parameter in reservoir simulation models related to both primary production and envisioned secondary recovery processes for heavy oil and bitumen. The measurement of liquid-phase mutual diffusion coefficients in bitumen and heavy oil + light hydrocarbon or gas mixtures present numerous experimental and data analysis challenges due to the viscosity and opacity of the mixtures, the variability of density, viscosity and mutual diffusion coefficient with composition, and the multi-phase nature of these mixtures. Data analysis challenges are particularly acute. For example, recently reported mutual diffusion coefficient values for liquid mixtures of bitumen + carbon dioxide vary over three orders of magnitude when different analysis methods are applied to the same experimental data. In this contribution, we illustrate the importance of measuring composition profiles within liquids as a function of time, as a basis for mutual diffusion coefficient computation, and for allowing explicitly for the variation of diffusion coefficient and liquid density with composition in the analysis of composition profile data. Such inclusions eliminate apparent temporal variations of mutual diffusion coefficients and yield values consistent with relevant theories and exogenous data sets. Liquid-phase mutual diffusion coefficients computed for the mixtures Athabasca Bitumen + pentane and Cold Lake Bitumen + heptane exemplify the experimental and data analysis approaches.     

THE COLLOIDAL STRUCTURE OF CRUDE OILS AND SUSPENSIONS OF ASPHALTENES AND RESINS

ABSTRACT

A better understanding of colloidal macrostructure of the heavy petroleum products and their complex fractions is of great importance in the context of industrial problems that arise during the crude oil production, refining and transport. Much effort has been devoted to the chemical structure studies, but there is a need for more precise data regarding parameters that characterize those complex systems. For instance, the molecular weight of heavy molecules, the composition and size of aggregates formed during the industrial processing and their evolution upon the variation of temperature, pressure and with the addition of solvent have not been well known. In this paper we present new results obtained using several powerful techniques. Scattering methods (using X-rays and neutrons) are applied to study both the fractionated products (asphaltene and resin solutions in more or less good solvents) and the real systems (Safaniya vacuum residue). The lamellar structural model for asphaltenes and resins is confirmed and the molecular weight of these species determined using a polydisperse size distribution. Discussion is presented concerning the specificity of X-ray and neutron scattering : X-ray experiments are more sensitive to the aromatic-rich regions, whereas the neutron scattering data provide information about all the particle volume. Viscosimetry measurements provide information on the molecular shape of asphaltene and confirm the disk-like model. Critical micellar concentration has been obtained using Vapour Pressure Osmometry (VPO) for asphaltene suspensions in toluene and in pyridine. The resin molecules are smaller than asphaltenes, and appear to be a good solvent for asphaltenes. One of the major conclusions of this work is the wide-spread presence of density heterogeneities in diluted solutions of asphaltenes and resins as well as in the pure product (Safaniya vacuum residue). This was deduced from the scattering experiments and cryo-scanning electron microscopy data. The heating effects. were studied: a temperature increase leads to the decrease of molecular weight, but heterogeneities remain present. The structure of vacuum residue exhibits large density fluctuations which are thermally stable. These dense regions remain connected into a network up to 393°K and determine the yield value of the rheological behaviour.     

连续重整催化剂固定床内气体径向扩散规律的研究

在直径约为φ816mm的固定床中填充国产3861催化剂担体,以氢气为示踪气体,采用稳态有限源示踪技术,测定了不同操作气速下床层内部不同截面上示踪气体的浓度分布实验数据,通过求解固定床二维扩散模型,获得了不同操作气速下的径向扩散系数。结果表明,在本文的实验条件范围内,轴向扩散系数值对径向扩散系数的计算结果影响不大。随着Re数增加,径向扩散系数逐渐增大,表明操作气速是影响气体在固定床内扩散行为的主要因素。Rer与Re的关系可用准数关联式表示为：Per=2.7476InRe-5．3161。     

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.     

重质油大分子在模型催化剂中扩散行为的研究

采用F127为模板剂、正硅酸四乙酯为硅源,经水热法合成了FDU-12介孔分子筛, 将其作为模型孔道催化剂用于沥青质的扩散研究。通过N2吸附-脱附、XRD、TEM、SEM等对FDU-12进行表征。结果表明：升高晶化温度能够增大催化剂孔道的入口孔径,而笼孔径不变;降低组装温度能够增大分子筛的笼孔径,而入口孔径不变。运用吸附扩散法测定了沥青质在模型孔道催化剂中的有效扩散系数,结果表明：增加模型催化剂的入口孔径和笼孔径在一定范围内能够提高有效扩散系数,但是孔径过大会导致载体的比表面积下降,使有效扩散系数降低。