Mohammad R. Riazi

A new method for experimental measurement of diffusion coefficients in reservoir fluids

Abstract A simple method is presented for determining diffusion coefficients of dense gases in liquids using a PVT cell. When a non-equilibrium gas is brought into contact with a liquid in a sealed container at a constant temperature, the final state is determined by thermodynamic equilibrium. However, the time which is required to reach the final state is determined from the diffusion process in each phase. At the gas-liquid interface, thermodynamic equilibrium exists between the two phases at all times, but the position of the interface as well as the pressure may change with time. The rate of change of pressure and the interface position as a function of time depends on the rate of diffusion in each phase and therefore on the diffusion coefficients. No compositional measurements are necessary for this method of measuring diffusion coefficients; hence, it is less expensive than conventional methods. Results obtained by this method for the binary system of methane and n -pentane at 311 K and 70 bar yielded diffusion coefficients within ± 5% of literature values. The technique can be easily applied to multicomponent systems for measurement of effective diffusion coefficients in reservoir fluids.

Physical properties of heavy petroleum fractions and crude oils

Abstract Equations are provided for calculating boiling point, density, refractive index, critical temperature, pressure and density, acentric factor, surface tension and solubility parameter of single carbon number (SCN) hydrocarbon groups for C 6 -C 50 existing in crude oils and hydrocarbon-plus fractions. Results show good consistency among various properties and improvement over the values previously reported. These methods should enhance equation-of-state (EOS) predictions when experimental data are lacking.

Estimation of viscosity of liquid hydrocarbon systems

Based on the principle of intermolecular forces for non-polar compounds, a simple relation is proposed for the estimation of viscosity of liquid hydrocarbons and petroleum mixtures at various temperatures from the knowledge of refractive index. Also some experimental data on the viscosity of some Kuwaiti light and medium petroleum fractions are reported. Evaluation of the proposed method shows that while it is simple it is comparable with other methods available in the literature.

MODELLING OF FALLING FILM REACTORS

An improved mathematical model for falling film reactors is presented. Effects of liquid film turbulence, gas phase heat and mass transfer resistances, gas-liquid interfacial drag, exothermic chemical reaction and heat transfer within the system, as well as volatility of liquid film are considered. The model predicts liquid phase chemical conversions and the interfacial temperatures along the reactor length. Model predictions agreed well with data from both laboratory and industrial scale reactors.

Modelling of the rate of oil spill disappearance from seawater for Kuwaiti crude and its products

Abstract In this paper a semi-analytical model has been developed to estimate the amount of oil disappeared from an oil spill floating on seawater surface. The model considers evaporation, dissolution and sedimentation of oil components. Crude oil and wide boiling range fractions are divided into several pseudocomponents using distribution model developed by Riazi (Ind. Eng. Chem. Res., 36 (10) (1997) 4299–4307). Heavy components with densities above density of water, sink to the bottom of sea while light components vaporize or dissolve into water. In the model, oil spill thickness is considered variable versus time. The input data for the model are distillation data (or composition) for oil, API gravity of oil, initial volume of oil spill, initial area of oil spill, air temperature, wind speed and water surface velocity. The only adjustable parameter is a constant in the relation for the mass transfer coefficient for evaporation. The model estimates area, volume and composition of oil spill versus time. It also calculates the amount of oil vaporized, dissolved or sunk into water versus time. Three sets of experiments were conducted for a Kuwaiti export crude oil and four different Kuwaiti petroleum products also used for export to determine the rate of oil disappearance at ambient temperature. Data obtained in these experiments were used to determine the model parameter as well as evaluation of the proposed model.

Improving cubic equations of state for heavy reservoir fluids and critical region

Abstract It is shown that by considering the “b” parameter in a cubic equation of state (EOS) as acentric factor/temperature-dependent, liquid densities especially for heavy compounds and the region near the critical point can be estimated more accurately. The proposed equation can also be used for accurate estimation of critical compressibility factors of different compounds, Although the method is applied to Peng-Robinson equation of state (PR-EOS), it can be used for any other cubic equation of state. The proposed method is particularly useful for phase equilibrium calculations of reservoir fluids. The proposed equation requires critical temperature, critical pressure and acentric factor as the input parameters. The proposed equation of stale estimates properties of liquids, vapor-pressure and critical compressibility factors with greater accuracy for pure compounds and mixtures as well as light and heavy compounds found in reservoir fluids.

A thermodynamic model for liquid adsorption isotherms

Based on the principle of solution thermodynamics for liquid–solid equilibrium, a simple mathematical expression has been developed to express liquid adsorption isotherms. A weight fraction based activity coefficient model has been derived for the solid phase nonideality. The proposed model has been evaluated and compared with four other models commonly used for liquid adsorption isotherms in the literature. Systems used in this study are solute adsorption from dilute aqueous solution on various activated carbon or molecular sieve. For 14 systems at various isotherms for the temperature range 0.1–75°C and the solute concentration range of 5–26540 g/m3 for 382 data points, the proposed model predicts equilibrium concentration with an average deviation of 6%. The proposed model clearly outperforms other available methods such as vacancy solution theory, exponential model and various other modified forms of the Freundlich isotherm. The unique features of the proposed model are its simplicity, generality and accuracy over the entrie experimental concentration and temperature ranges.

Prediction of the rate of oil removal from seawater by evaporation and dissolution

Abstract A mathematical model is presented to predict the rates of vaporization and dissolution for an oil spill floating on the sea surface. Laboratory experiments were conducted on two oil samples, a crude oil from Ahwaz oil fields in Iran and a home kerosene produced at Tehran Refinary. Effects of temperature and salt concentration on the rate of oil disappearance were studied and the rates of oil disappearance by evaporation and dissolution were determined. It was found that the rate of dissolution under normal sea surface conditions is ~ 0.1 % of the rate of evaporation.

A generalized method for estimation of critical constants

Abstract A generalized and simple method is proposed to estimate critical temperature, pressure and volume of both polar and non-polar compounds. The input parameters are normal boiling point, density and relative molar mass. The proposed procedure was used to estimate critical properties of more than 250 compounds including hydrocarbons (C1–C18), acids, sulfur compounds, nitriles, oxide gases, alcohols, halogenated compounds, ethers, amines and water. Average absolute deviations for estimation of critical temperature, pressure and volume for the proposed method are 0.9, 2.8 and 1.8%, respectively.

Use of the velocity of sound in predicting the PVT relations

Thermodynamic properties of fluids are generally calculated from the PVT relations through equations of state. The majority of existing equations of state require the critical properties or intermolecular potential energy parameters as their input data. In many cases, such properties are neither available nor they can be accurately estimated. One accessible and accurately measurable property of substances is the velocity of sound. In this report a method is introduced through which one can predict the PVT behavior of fluids using the velocity of sound data. A general mathematical relationship,