The Determination of Effective Diffusivity Coefficients in a Solvent Gas Heavy Oil System for Methane

Abstract

In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed.     

Hydrochloric acid diffusion coefficients at acid-fracturing conditions

The reaction of a 15% HCl solution with Indiana Limestone was investigated at 93 °C and 34.5 MPa using an annular flow reactor that was erected vertically. The laminar flow conditions were such that both free and forced convections contributed to the overall mass-transfer rate. The experimental results correlated well with theory when the forced and free convections were in the same direction (assisting flow) and when free-convection mass transfer dominated the mass-transfer process. Deviation from theory, however, occurred when free convection was in the opposite direction to forced convection (opposing flow). Correlating the experimental results with theory provided a method for the determination of the effective diffusion coefficient of HCl at the high temperature, pressure and acid concentrations encountered in acid-fracturing treatments. An HCl effective diffusion coefficient of 5.25 × 10⁻⁵ cm²/s was found from correlating the present experimental results with theory.Recent trend in designing acid-fracturing treatments is to use computer models to predict and optimize the etched length of the created fracture. The accuracy and reliability of such computer model predictions depend heavily on the accuracy of the values used for physical parameters such as reaction rate and diffusion coefficient of HCl. The annular flow reactor and the correlations discussed here provide a way to obtain reaction rates and diffusion coefficients at practical conditions for use in computer models and design of acid-fracturing treatments.     

Thermodynamic modeling of equilibrium conditions of CH4/CO2/N2 clathrate hydrate in presence of aqueous solution of sodium chloride inhibitor

In this work, the effect of sodium chloride (NaCl) on thermodynamic properties of CH₄+CO₂+N₂ hydrate formation and equilibrium condition has been studied. The three-phase (hydrate–liquid–gas) equilibrium calculation has been carried out using the Peng–Robinson equation of state (PR EoS) and Universal Quasi Chemical (UNIQUAC) activity coefficient models. The PR EoS coupled with classic mixing rule is applied for the vapor phase. The calculations of the gas hydrate formation pressures are performed in the absence and presence of sodium chloride inhibitor for the gas hydrate systems. The Chen–Guo model has been used for the hydrate phase and the UNIQUAC activity coefficient is applied for non-ideality of the liquid phase. To obtain higher accuracy, the solubility of the gases in the aqueous phase is also taken into account using pressure corrected Henry's law. Finally, the stepwise procedure has been followed to obtain the results and compared with the experimental results. The addition of 2% (by volume) sodium chloride to water results in large shifts in phase equilibrium boundary to increase pressure for the same temperature condition.     

Phase behavior and physical properties of CO2-saturated heavy oil and its constitutive fractions: Experimental data and correlations

An extensive set of phase behavior measurements were carried out on mixtures of carbon dioxide with a Canadian heavy oil and with its constitutive fractions. The heavy oil was divided into three fractions by asphaltene precipitation and distillation. The phase behavior data were then measured at 21°C and 140°C, and at several pressures up to 12.41 MPa, and included the mixtures' solubilities, swelling factors, densities, gas/oil ratios and viscosities. The oil samples obtained during the measurements were analyzed using gas chromatographic simulated distillation.The solubility of CO₂ increased with pressure and decreased with increasing temperature. Saturated mixture densities increased with pressure at 21°C; however, they decreased with pressure at 140°C. The extent of density change with pressure were small when compared to the changes due to temperature. A significant amount of oil swelling was also observed. An important effect of CO₂ was the large reduction in the oil viscosities. The extent of this reduction was larger at 21°C than at 140°C and was more pronounced for the more viscous oils. Simulated distillation analysis of the oil samples show the extraction of light ends into the CO₂ phase, but no deposition of heavy ends could be detected.The phase behavior data of the heavy oil and its fractions with CO₂ were correlated by the Peng-Robinson (PR) equation of state (EOS). The phase behavior data were also interpreted using binary and ternary mixtures of CO₂ with n- alkanes having the same molecular weights as the oil fractions. Mixture densities were correlated using the volume translated PR EOS and viscosities were correlated by equations proposed by Lederer.     

Phase equilibrium modeling of semi-clathrate hydrates of the CO2+H2/CH4/N2+TBAB aqueous solution system

In this study, the semi-clathrate hydrate dissociation pressure for the CO₂+N₂, CO₂+H₂, CO₂+CH₄, and pure CO₂ systems in the presence of different concentrations of TBAB aqueous solutions is predicted using a strong machine learning technique of multi-layer perceptron neural network (MLP-NN). The developed model, with an overall correlation coefficient (R²) of 0.9961 and mean square error (MSE) of 5.96E?02, presented an excellent accuracy in prognosticating experimental data. A complete statistical evaluation performed to promise the strength and generality of the multi-layer perceptron artificial neural network (MLP-ANN). In addition, the applicability of the proposed network and quality of experimental data was assessed through the Leverage approach.     

Exploitation of methane in the hydrate by use of carbon dioxide in the presence of sodium chloride

The replacement process of CH4 from CH4 hydrate formed in NaCl solution by using pressurized CO2 was investigated with a self-designed device at temperatures of 271.05,273.15 and 275.05 K and a constant pressure of 3.30 MPa.The mass fraction of the NaCl solution was either 0.5 wt% or 1.0 wt%.The effects of temperature and concentration of NaCl solution on the replacement process were investigated.Experimental results showed that high temperature was favorable to the replacement reaction but high NaCl concentration had a negative effect on the replacement process.Based on the experimental data,kinetic models of CH4 hydrate decomposition and CO2 hydrate formation in NaCl solution were established.The calculated activation energies suggested that both CH4 hydrate decomposition and CO2 hydrate formation are dominated by diffusion in the hydrate phase.     

An equation for estimating water saturation in clean formations utilizing resistivity and sonic logs: theory and application

An equation estimating water saturation values from resistivity and sonic logs, which are the common available logs in most of the wells and formations, was investigated for different lithologies. It is essentially based on the combination of Archie's and Raiga's relationships, with their respective coefficients a, m, n, and x. Application of this equation to real field data in the USA and Egypt show particularly good agreement in a variety of cases, in particular, if the formation true resistivity (R_t) is greater than 5 Ω m. In the case where R_t is less than 5 Ω m, multiplication of this equation by a certain correction factor is recommended. This factor, which can be empirically estimated, was found to be ranging numerically from 1 to 1.8 depending on the shale transit time (Δ_tsh) and cementation exponent (m). With the exception of core measurements, and where no porosity tools other than sonic logs are available, this equation can be considered as a good predictor for estimating water saturation in clean formations (non-shaly). In case of clay content, the application of the equation should include the same correction procedures of the sonic log reading those applied in usual interpretation. Worthy of remarks is that this equation gives reasonable and reliable values for rocks having transit time ranging between 40 and 150 μs/ft; above this range, the usefulness of this equation must remain in doubt. Knowledge of porosity is not necessary in such evaluation, which reflects the general usefulness of this equation. More data are needed to test the existing relation in numerous conditions.     

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.     

Modeling of CO2 capture from gas stream emissions of petrochemical industries by membrane contactor

Abstract

Process optimization of CO₂ removal from natural gas by a polyvinylidene fluoride hollow-fiber membrane contactor is a major goal of many computational fluid dynamics (CFD) simulations in this area. In this study, a 2D CFD model based on mass transfer equation inside the tube, the membrane, and the shell section of a HMFC at steady state and laminar conditions is developed and solved by COMSOL Multiphysics with finite element approach. Simulation results show an excellent agreement with experimental data. The model predicts that higher liquid velocity and membrane porosity results in higher CO₂ removal, because of enhancement of effective diffusion coefficient. Also, taller fiber length results in higher contact area and higher mass transfer of CO₂ from natural gas into distilled water. Although higher temperature will decrease the CO₂ removal.     

Sigmoidal thermal inactivation kinetics of Listeria innocua in broth: Influence of strain and growth phase

Listeria innocua inactivation was studied within the temperature range 52.5–65.0 °C, comparing two different strains (10528 and 2030c) and two growth phases (exponential and stationary). Survival curves may present a sigmoidal behaviour, with an initial shoulder (L), followed by a maximum inactivation rate (k_max) period and a final tailing tendency. A Gompertz-inspired model was used to fit experimental data, and kinetic parameters (L, k_max and tail) were estimated by non-linear regression analysis. The influence of temperature, growth phase and strain on kinetic parameters was studied using a 2³ factorial experimental design. Results showed that temperature and growth phase were the most significant variables affecting the kinetic parameters. Listeria thermal inactivation varied from a log-linear tendency till a pronounced sigmoidal behaviour, depending on the studied factors.     

Wettability/spreading of alkanes at the water–gas interface at elevated temperatures and pressures

The Hamaker–Lifshitz theory is used to calculate the spreading coefficient of alkanes on water or brine at elevated temperatures and pressures. The dielectric polarizability at elevated temperature and pressure is estimated as a function of density through the Clausius–Mosotti equation. When complete data is not available, the wetting transition can be estimated from the refractive index at elevated temperatures and pressures. The spreading of alkanes on brine can also be estimated from the refractive index of the brine as a function of electrolyte concentration. The approach used here for alkanes is also used to estimate the conditions for the spreading of H₂S between water and sulfur.     

Kinetic aspects of the effect of CO pressure and methanol concentration on cyclohexene hydrocarbomethoxylation in the presence of the Pd(PPh3)2Cl2-PPh3-p-toluenesulfonic acid catalytic system

The dependence of the rate of the cyclohexene hydrocarbomethoxylation reaction catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid system on the CO pressure and methanol concentration at temperatures varied in the range of 358–388 K has been investigated. The data are interpreted in terms of the previously proposed mechanism involving as intermediates ion pairs containing cationic hydride, alkyl, and acyl palladium complexes. By the least squares technique, apparent constants relating to the effect of CO pressure and methanol concentration have been estimated for the rate equation derived earlier. The apparent activation energies have been determined for these constants, and the following stability series of palladium complexes has been proposed on their basis: $$ Pd(PPh_3 )_2 (CO)_2 > Pd(PPh_3 )_4 > Pd(PPh_3 )_2 (CH3OH)_2 > H\mathop {Sol}\limits^ \oplus [Pd(PPh_3 )_2 (Cl)(Sol)]^ \ominus . $$      

Kinetics of cyclohexene hydrocarbalkoxylation with cyclohexanol catalyzed by the Pd(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>-PPh<Subscript>3</Subscript>-<Emphasis Type="Italic">p</Emphasis>-toluenesulfonic acid system

The reaction kinetics of cyclohexene hydrocarbalkoxylation with cyclohexanol catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid system was studied over the temperature range 363–393 K. The reaction rate was found to be a nonlinear function of the Pd(PPh₃)₂Cl₂ concentration or a nonmonotonic function of the PPh₃ and cyclohexanol concentrations or p _CO. The experimental data were interpreted in terms of a mechanism that involves ion pairs containing alkyl and acyl palladium complexes of the cationic type as intermediates. Based on the quasi-steady-state approximation, a rate equation was obtained to adequately describe the experimental data. The rate equation parameters were estimated using the least squares technique. The apparent activation energies of these parameters were determined. The heats of formation of Pd(PPh₃)₂(C₆H₁₁OH)₂, Pd(PPh₃)₂(CO)₂, and Pd(PPh₃)₄ complexes from Pd(PPh₃)₂(C₆H₅CH₃)₂ were estimated. A symbatic change in these values with the donor-acceptor properties of ligands was demonstrated.     

C8芳烃异构化催化剂内气相有效扩散系数的计算

针对C₈芳烃异构化反应中二甲苯等6种反应物在催化剂内的扩散过程,建立一种气相有效扩散系数的计算方法。根据此方法计算得到不同反应压力和温度的条件下,C₈芳烃异构化反应体系中6种气相物质在催化剂内扩散的有效扩散系数,验证了方法的可靠性,并讨论了温度和压力对分子扩散系数的影响,结果表明：随着压力增大,气体密度增大,分子间距变小,分子间作用力变大,分子扩散系数减小;而根据分子运动论,随着温度的升高,气体运动速率和扩散速率都会变大,分子扩散系数增大。     

基于CPA状态方程的高压含硫天然气压缩因子计算方法研究

对于压力高于70 MPa的含H_2S天然气,其分子之间间距缩小,极性H_2S分子之间缔合作用增强,传统SRK、PR状态方程计算高压含硫天然气的压缩因子准确性有待进一步改进。基于压力3.72～97.58 MPa、H_2S体积分数0%～70.03%的154组压缩因子修正CPA(Cubic-Plus-Association)状态方程中H_2S与CH_4、CO_2分子间二元交互作用系数,综合评价SRK、PR、CPA状态方程对压缩因子的计算精度。结果表明,对于中低压含硫天然气(p35 MPa),采用PR方程精度最高,平均相对偏差为1.12%;对于高压及超高压含硫天然气(p35 MPa),CPA方程精度最高,平均相对偏差为-1.46%。进一步采用法国ST抗硫高压PVT仪测试了4种含硫天然气在70～131 MPa条件下的138组压缩因子实测值,验证了采用CPA状态方程对于高压含硫天然气压缩因子的计算精度。     

An investigation of different gas injection scenarios as enhanced condensate recovery method in a naturally fractured gas-condensate reservoir

In gas condensate reservoirs, when the bottom hole pressure falls below the dew point pressure condensates are formed. This causes hydrocarbon liquid saturation around the well bore region. This phenomenon is called condensate blockage or condensate banking. Condensate recovery reduction due to condensate banking near the well bore region is an important problem in gas condensate reservoirs. The common method to prevent the condensate banking is gas cycling (reinjection of produced dry gas) into the reservoir that can contribute to the condensate vaporization, thus increasing the condensate recovery factor. The objective of this study was to find a suitable replacement for gas cycling. For this purpose, an investigation on the effects of injection of different types of gases (CO₂, N₂, and C₁) on enhance condensate recovery factor and pressure maintenance were performed. This research was done on one of the Iranian gas condensate reservoirs through a compositional simulator. The two-parameter Peng-Robinson equation of state (EOS) and Lohrenz-Bray-Clark correlation were used to model reservoir fluid properties through regression on the pressure-volume-temperature (PVT) experimental data. A fracture network was distributed over the reservoir, so a dual porosity/dual permeability model was selected for better evaluation of the fracture system. Then, various scenarios of natural depletion and CO₂, N₂, C₁, and gas cycling injection were studied. The results showed that CO₂ injection scenario being associated with the highest efficiency compared to that of other gases.     

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.     

Modeling of hydrogen sulfide removal from Petroleum production facilities using H2S scavenger

The scavenging of hydrogen sulfide is the preferred method for minimizing the corrosion and operational risks in oil production facilities. Hydrogen sulfide removal from multiphase produced fluids prior to phase separation and processing by injection of EPRI H₂S scavenger solution (one of the chemical products of Egyptian Petroleum Research Institute) into the gas phase by using the considered chemical system corresponds to an existing oil well in Qarun Petroleum Company was modeled. Using a kinetic model the value of H₂S in the three phases was determined along the flow path from well to separator tanks. The effect of variable parameters such as, gas flow rates, chemical injection doses, pipe diameter and length on mass transfer coefficient K_Ga, H₂S outlet concentration and H₂S scavenger efficiency has been studied. The modeling of the hydrogen sulfide concentration profiles for different conditions was performed. The results may be helpful in estimating injection rates of H₂S scavengers for similar fields and conditions.     

泥岩流-固-化耦合模型参数的蒙特卡洛估计

泥岩流-固-化耦合模型的研究与应用是正确认识泥岩井壁失稳机制的根本途径之一。化学线弹性本构方程实现了渗流、化学场作用下泥岩变形的表征,而泥岩中渗流及溶质扩散则分别满足Speigler-Kedem 模型和Fick第一定律。简化应用了泥岩的流-固-化耦合模型（包括泥岩力学平衡方程、泥岩孔隙流体及溶质质量守恒方程）,基于商业有限元软件Comsol Multiphysics,使用有限单元法求解了正向方程,并依据最小二乘准则,应用蒙特卡洛随机搜索方法,根据泥岩渗流、溶质扩散及泥岩单向扩散侧向约束膨胀实验数据,反演求解了模型参数（包括泥岩渗透率、膜效率、溶质扩散系数及膨胀系数）。理论拟合曲线与实验数据结果非常吻合,说明简化后的泥岩流-固-化耦合模型能够有效描述多场耦合环境中泥岩的性质,所建立的模型参数求解方法准确可靠,为流-固-化耦合模型在井壁稳定研究中的推广应用奠定了基础。     

Development and validation of an accurate and rapid LC-ESI-MS/MS method for the simultaneous quantification of aflatoxin B1, B2, G1 and G2 in lotus seeds

An accurate and rapid LC-ESI-MS/MS analytical method was developed and validated for the simultaneous determination of aflatoxin B₁, B₂, G₁ and G₂ in lotus seeds. The samples were firstly extracted with methanol-water solution (80:20, v/v), and then cleaned up by immunoaffinity columns. The mass spectrometer was operated in the positive ionization electrospray (ESI+) mode using multiple reaction monitoring (MRM) for analysis of four aflatoxins. The transitions of m/z 313 → 285 (AFB₁, CE 33 eV), m/z 315 → 259 (AFB₂, CE 37 eV), m/z 329 → 243 (AFG₁, CE 37 eV) and m/z 331 → 257 (AFG₂, CE 37 eV) were used to quantify these four aflatoxins, respectively. The limits of detection (LODs) of aflatoxin B₁, B₂, G₁ and G₂ were 0.007, 0.005, 0.003 and 0.005 μg kg^?1 based on a signal-to-noise ratio of 3:1, respectively. The limits of quantification (LOQs) of aflatoxin B₁, B₂, G₁ and G₂ were 0.02, 0.015, 0.01 and 0.015 μg kg^?1 based on a signal-to-noise ratio of 10:1, respectively. Recoveries for samples of spiked lotus seeds were all above 66% with relative standard deviation all below 15% for all compounds. Nineteen out of twenty batches of lotus seeds collected from different drug stores or markets in China were found to be contaminated with aflatoxins at different levels ranging from 0.02 to 688.4 μg kg^?1.