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Haghighi E.,ETH Zurich | Shahraeeni E.,Reservoir Engineering Research Institute RERI | Shahraeeni E.,Jülich Research Center | Lehmann P.,ETH Zurich | Or D.,ETH Zurich
Water Resources Research | Year: 2013

The relative contributions of advection and diffusion to isothermal mass transfer from drying porous surfaces across a constant air boundary layer have been quantified. Analysis has shown that neglecting diffusion in longitudinal direction (often justified by large Peclet number) may lead to underestimation of evaporative mass losses from porous surfaces. Considering diffusion only from individual pores across a constant boundary layer accounts for most of the evaporation rates predicted by the full advection-diffusion equation (ADE). The apparent decoupling between diffusion and advection, and the relatively small role of advection in flux generation (other than defining boundary layer thickness) greatly simplifies analytical description of drying surfaces. Consequently, evaporation rates from porous surfaces may be represented by superposition of readily-available analytical diffusion solutions from discrete pores considering different patterns and spacing between surface pores. Results have been used to formulate a generalized top boundary condition for effective resistance to evaporation linking soil type, surface water content and boundary layer characteristic into a simple and physically based analytical expression. ©2013. American Geophysical Union. All Rights Reserved.


Wu S.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Reservoir Engineering Research Institute RERI
Energy and Fuels | Year: 2011

The alteration of the wettability from liquid-wetting to intermediate gas-wetting has great potential in improving gas well productivity, from mitigating water blocking to condensate banking in gas reservoirs. Even a small quantity of salt ions (such as Na +) in the initial saturation in rock has a detrimental effect on the alteration of the wettability by chemical treatments. The initial salt ions may cause clay release and permeability reduction. Berea cores are usually used in laboratory flow studies, including wettability alterations. In this work, we present a comprehensive study on the use of Berea, both unfired and fired, in single- and two-phase flows, with a focus on the salt and firing effect on the chemical treatment. Three fluoropolymeric surfactants are used. We find that one of the three, a nonionic surfactant, is effective in the alteration of wettability in the fired Berea (with and without salt in the initial saturation). The treatment efficiency of ionic surfactants is reduced in the presence of the initial salt. © 2010 American Chemical Society.


Ahmed T.,Texas A&M University at Qatar | Nasrabadi H.,Texas A&M University at Qatar | Firoozabadi A.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Yale University
Energy and Fuels | Year: 2012

CO 2 injection has been used to improve oil recovery for the last 4 decades. In recent years, CO 2 injection has become more attractive because of the dual effect: injection in the subsurface (1) allows for reduction of the CO 2 concentration in the atmosphere to reduce global warming and (2) improves the oil recovery. One of the screening criteria for CO 2 injection as an enhanced oil recovery method is based on the measurement of CO 2 minimum miscibility pressure (MMP) in a slim tube. The slim tube data are used for the purpose of field evaluation and for the tuning of the equations of state. The slim tube represents one-dimensional (1D) horizontal flow. When CO 2 dissolves in the oil, the density may increase. The effect of the density increase in high-permeability reservoirs when CO 2 is injected from the top has not been modeled in the past. The increase in density changes the flow path from 1D to two-dimensional (2D) and three-dimensional (3D) (downward flow). As a result of this density effect, the compositional path in a reservoir can be radically different from the flow path in a slim tube. In this work, we study the density effect from CO 2 dissolution in modeling of CO 2 injection. We account for the increase in oil density with CO 2 dissolution using the Peng-Robinson equation of state. The viscosity is modeled based on the Pedersen-Fredenslund viscosity correlation. We perform compositional simulation of CO 2 injection in a 2D vertical cross-section with the density effect. Our results show that the density increase from CO 2 dissolution may have a drastic effect on the CO 2 flow path and recovery performance. One conclusion from this work is that there is a need to have accurate density data for CO 2/oil mixtures at different CO 2 concentrations to model properly CO 2 injection studies. Our main conclusion is that the downward flow of the CO 2 and oil mixture may not be gravity-stable, despite the widespread assumption in the literature. © 2012 American Chemical Society.


Haugen K.B.,Yale University | Firoozabadi A.,Yale University | Sun L.,Reservoir Engineering Research Institute RERI
AIChE Journal | Year: 2011

The combination of successive substitution and the Newton method provides a robust and efficient algorithm to solve the nonlinear isofugacity and mass balance equations for two-phase split computations. The two-phase Rachford-Rice equation may sometimes introduce complexity, but the Newton and bisection methods provide a robust solution algorithm. For three-phase split calculations, the literature shows that the computed three-phase region is smaller than measured data indicate. We suggest that an improved solution algorithm for the three-phase Rachford-Rice equations can address the problem. Our proposal is to use a two-dimensional bisection method to provide good initial guesses for the Newton algorithm used to solve the three-phase Rachford-Rice equations. In this work, we present examples of various degree of complexity to demonstrate powerful features of the combined bisection-Newton method in three-phase split calculations. To the best of our knowledge, the use of the bisection method in two variables has not been used to solve the three-phase Rachford-Rice equations in the past. © 2010 American Institute of Chemical Engineers (AIChE).


Mikyska J.,Czech Technical University | Firoozabadi A.,Reservoir Engineering Research Institute RERI
Energy and Fuels | Year: 2016

The Peng-Robinson (PR) and cubic-plus-association (CPA) equations of state are used to predict the phase behavior and solubility of CO2 and normal alkanes from C1 to nC10 in several bitumens. Both of the equations of state are investigated over wide ranges of temperature and pressure. The results show that the PR-EOS describes mixure of bitumens with CO2 and alkanes when there is no second liquid phase or when the asphaltene content in the second liquid phase is not high. The CPA-EOS describes the phase behavior of mixtures of bitumens and CO2 and alkanes in liquid-liquid states even when the asphaltene content of one of the phases is high. High asphaltene content results in significant association and cross-association where the CPA-EOS is a natural choice. In this work the only adjustable parameter in the CPA-EOS is the cross-association energy parameter, and we show that the solubility of CO2 and alkanes in bitumens is usually not sensitive to this parameter. However, in two-phase liquid-liquid and three-phase liquid-liquid-vapor states with one phase having a high concentration of asphaltenes, the results become sensitive to the cross-association energy parameter. © 2015 American Chemical Society.


Li Z.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Reservoir Engineering Research Institute RERI
Fluid Phase Equilibria | Year: 2012

A key element of efficient and robust three-phase split calculation is the initialization of phase mole fractions. While the initial guess of equilibrium ratios is made from two-phase split calculation and two-phase stability testing, initializing phase fractions through solving three-phase Rachford-Rice equations can be a challenge especially close to the bicritical points and phase boundaries. In this research, we examine three different methods: the improved two-dimensional bisection method, the minimization method, and the direct Newton method. We present a large number of three-phase examples of various degrees of complexity to demonstrate both robustness and efficiency of all these methods. The direct Newton method combined with the starting guess of phase fractions from two-phase split calculation and two-phase stability testing is the most efficient approach. © 2012 Elsevier B.V.


Li Z.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Reservoir Engineering Research Institute RERI
Energy and Fuels | Year: 2010

We apply a cubic-plus-association equation of state to study the asphaltene precipitation from n-alkane diluted model solutions (asphaltene+toluene), and heavy oils and bitumens. Heavy oils and bitumens are characterized in terms of saturates, aromatics/resins, and asphaltenes; n-alkanes are treated independently. The asphaltene precipitation is modeled as liquid-liquid phase equilibrium. The self-association between asphaltene molecules and the cross-association between asphaltene and aromatics/resins (or toluene) molecules are explicitly taken into account. There is no self-association between aromatics/resins (or toluene) molecules. Our model contains only one adjustable parameter, the cross-association energy between asphaltene and aromatics/resins (or toluene) molecules, which depends on the types of asphaltene and n-alkane, and possibly temperature but is independent of pressure and concentration. We successfully predict the amount of asphaltene precipitation over a broad range of compositions, temperatures, and pressures for n-alkane diluted model solutions, heavy oils, and bitumens Copyright © 2010 American Chemical Society.


Wu S.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Reservoir Engineering Research Institute RERI
SPE Reservoir Evaluation and Engineering | Year: 2010

The effect of salinity on the alteration of wettability from water-wetting to intermediate gas-wetting is studied in this work. We find that NaCl salinity increases water-wetting when a core is saturated with brine. NaCl also reduces gas absolute permeability, as reported in the literature. CaCl2 salinity effect is dramatically different from that of NaCl brine and has a minor effect on permeability. The NaCl, KC1, and CaCl2 brines have an adverse effect on wettability alteration. To alleviate the effect of salt on chemical treatment, we suggest pretreatment by displacement of brine with water and subsequent drainage by nitrogen. © 2010 Society of Petroleum Engineers.


Li Z.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Reservoir Engineering Research Institute RERI
Energy and Fuels | Year: 2010

We apply a cubic-plus-association equation of state (CPA-EOS) to study the asphaltene precipitation in live oils from temperature, pressure, and composition effects. The live oils are characterized by considering the pure components, the pseudo-hydrocarbon components, and the hydrocarbon residue. The hydrocarbon residue is further divided into the "heavy" component and asphaltenes. The asphaltene precipitation is modeled as liquid-liquid equilibrium between the upper onset and bubble point pressures and as gas-liquid-liquid equilibrium between the bubble point and lower onset pressures. In our work, the self-association between asphaltene molecules and the cross-association between asphaltene and "heavy" molecules are taken into account. The EOS parameters are either directly available, from our recent work, or from fitting the bubble point pressure. The cross-association energy between asphaltene and "heavy" molecules depends upon the temperature but is independent of the pressure. We reproduce the experiments of the amount and onset pressures of asphaltene precipitation in several live oils over a broad range of composition, temperature, and pressure conditions. © 2010 American Chemical Society.


Bestehorn M.,TU Brandenburg | Firoozabadi A.,Reservoir Engineering Research Institute RERI | Firoozabadi A.,Yale University
Physics of Fluids | Year: 2012

We study the dissolution of CO2 in saline aquifers. The long diffusion times can be accelerated by orders of magnitude from mass transfer that origins from convection. Convection occurs at a critical time via a phase transition from the horizontally homogeneous diffusion state. To start the instability, perturbations that break the horizontal translation symmetry are necessary. We start with the basic equations and the boundary conditions, examine the linearized equations around the diffusive time and z-dependent base state and compare different definitions of the critical time found in the literature. Taking a simple model we show the role of fluctuations for delayed instabilities if the control parameter is slowly swept through the bifurcation point. Apart from the critical time we use a "visible" time where convection is manifested in the vertical CO2 transport. We specify the perturbations with respect to their strength and length scale, and compute the critical times for various cases by numerical integration of the basic equations in two spatial dimensions. Fluctuating concentration at the upper boundary, fluctuating porosity as well fluctuating permeability are studied in detail. For the permeability fluctuation, the compressibility of the fluid becomes important and the velocity field cannot be derived from a stream function. Our work also includes non-isothermal conditions with a prescribed vertical geothermal gradient and space dependent thermal conductivity. Temperature fields for different standard configurations are computed numerically and serve as starting condition for density-driven convection. Based on our work, we conclude that the visible time is much larger than the critical time. The visible time is a strong function of strength and length scale of the perturbations. © 2012 American Institute of Physics.

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