Articolele autorului Dan Vladimir Nichita
Link la profilul stiintific al lui Dan Vladimir Nichita

Parametric construction of characteristic curves

A simple method is proposed for a parametric construction of characteristic curves using cubic equations of state. This method does not require the resolution of the equation of state for volume or compressibilty factor. For most standard alpha-function formulations, the results are totally explicit. For illustration purposes, this method is applied to the construction of Boyle, Zeno, isotherm inflection, maximum isothermal production and Joule-Thomson

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Improved delumping of compositional simulation results

A recently developed method for pseudo-component delumping is tested for delumping the results of compositional reservoir simulation. The procedure, based on the reduction concept, is analytical and consistent and it accurately takes into account non-zero binary interaction parameters in cubic equations of state. The delumping method was implemented in a postprocessor to the commercial Eclipse reservoir simulator and successfully tested on several

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Three-Phase Free-Water Flash Calculations Using a New Modified Rachford-Rice Equation

A novel Modified Rachford-Rice equation is developed for three-phase equilibrium calculations in hydrocarbon-water systems, based on the free-water assumption, i.e., the water-rich liquid phase consists of pure water only. In the inner loop of the flash algorithm, the three-phase problem (consisting in a system of two non-linear equations) is replaced by a pseudo two-phase problem (consisting in a non-linear equation). Unlike previous formulations,

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Efficient and Reliable Mixture Critical Points Calculation by Global Optimization

Multicomponent systems may exhibit several critical points or no critical point at all. Local methods can find only one critical point for a given initial guess. Recently, several global methods have been proposed for finding all the solutions of the problem. In the present work, we propose a gradient-based calculation method using global optimization, with temperature and molar volume as primary variables, and with analytical partial derivatives

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Calculation of Isentropic Compressibility and Sound Velocity in Two-Phase Fluids

Derivative properties from equations of state (EoS) are well defined for homogeneous fluid systems. However, some of these properties, such as isothermal and isentropic (or adiabatic) compressibilities and sound velocity need to be calculated at conditions for which a homogeneous fluid splits into two (or more) phases, liquid or vapor. The isentropic compressibility and sound velocity of thermodynamically-equilibrated fluids exhibit important discontinuities

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Boyle temperature and cubic equations of state

The sensitivity of Boyle temperature to changes in parameters appearing in cubic equations of state and to volume shift is analyzed. Analytical expressions for the Boyle temperature and for the dependency to the shift of the equation of state are given for the most common cases of the alpha function.

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Iterative solutions for sum(a(i)/(lambda-c(i))=1 equations

Two new methods are proposed for solving equations of the form sum(a(i)/(lambda-c(i))-1=0. Both of them are simple, easy to implement, robust and reveal a super-quadratic convergence.

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Numerical properties of equations involving high-order derivatives of pressure with respect to volume

This paper presents some unexpected features related to the solution of equations containing a high-order derivative of pressure with respect to volume equated to zero. For pure components, such equations define, in the pressure-temperature plane, nodal curves similar in shape to mixture spinodal curves. The analysis was made for a general form of two-parameter cubic equations of state and various numerical aspects for the Redlich-Kwong equation

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Isochoric Phase Stability Testing for Hydrocarbon Mixtures
Isothermal production from a supercritical gas container: A new characteristic curve

When emptying isothermally a supercritical gas container, as already well known, the cumulative production varies linearly with the pressure to compressibility factor ratio. However, the instantaneous production (that is to say, the instantaneous standard volume of the released gas) varies in a totally different manner when looked as a function of pressure; in particular, at any temperature above the critical, this production goes through a maximum

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