bluuebunny/crossref_metadata_2025_split huggingface dataset:
Buckley-Leverett Flow in Composite Porous Media
Authors: Wu Yu-Shu , Pruess Karsten , Chen Z. X. 
Published: June 2014

ABSTRACT
This paper presents a Buckley-Leverett-type analytical solution for one-dimensional immiscible displacement in a linear composite porous medium. The classical Buckley-Leverett theory, applicable only to flow in a homogeneous porous medium, has been extended to flow in an inhomogeneous porous medium, in which the formation system is treated as consisting of a number of flow domains with different rock properties. The analytical solution, obtained under the conditions for the Buckley-Leverett solution for each flow domain, can be used to determine the complete saturation profile in the composite system at all times. The analytical results indicate that noncapillary immiscible displacement of two fluids in a composite system is characterized by discontinuities in saturation profiles across the interfaces between adjacent flow domains.
Theory of Viscous Fingering in Two Phase, Three Component Flow
Authors: Blunt Martin , Christie Mike 
Published: June 2014

ABSTRACT
When a mobile fluid, such as gas, displaces less mobile fluids, such as oil and water, a viscous instability develops and the injected fluid fingers through the system leading to early breakthrough and poor recovery. In a WAG process (Water Alternate Gas) water and a miscible solvent (gas) are injected into a reservoir containing water and oil. Compared with a miscible flood, when only solvent is injected, fingering can be suppressed by the simultaneous injection of water, if it reduces the apparent mobility contrast between the injected and displaced fluids.
In order to understand and control this instability, it is necessary to be able to predict the expected extent of fingering. The behavior of a miscible flood, with only hydrocarbon flowing, can be modeled successfully using a Todd & Longstaff fractional flow.
We modify the Todd and Longstaff model self-consistently to account for fingering in multi-component systems. The method is verified for WAG floods. The empirical flow equations are solved analytically in one dimension and the results are in excellent agreement with the averaged saturation and concentration profiles computed using two dimensional high resolution simulation, for a variety of injected water saturations, in both secondary and tertiary displacements.
Modeling Foam Mobility at the "Limiting Capillary Pressure"
Authors: Rossen W. R. , Zhou Z. H. 
Published: June 2014

SUMMARYFoam stability depends strongly on capillary pressure. In some cases, this feedback mechanism maintains capillary pressure, and therefore liquid saturation and mobility, uniform and constant, independent of gas and liquid flow rates. This observation implies simple and powerful conclusions regarding foam behavior. Several applications of this principle are presented.
Effect of Viscous Crossflow on Miscibility Development in a Two-Layer Flow System: Part II - Ternary Condensing Gas Drives
Authors: Pande K. K. , Orr F. M. 
Published: June 2014

SUMMARY
This paper extends the analysis of a companion paper to ternary condensing gas drives. Displacement of oils, composed of butane and decane, by injection gas composed of methane and butane is described. The effects of interlayer permeability ratio and injection gas enrichment level on composition paths, composition and saturation profiles, and oil recovery are reported. The results presented lead to the conclusion that the minimum solvent enrichment level determined in one-dimensional flow experiments is not necessarily the optimum economic enrichment level for flow in heterogeneous reservoir settings.
Flux Determination of Finite Conductivity Fractures Using Higher Order Interpolation Functions
Authors: Kikani Jitendra 
Published: June 2014

SUMMARY
An efficient and accurate scheme for the determination of flux distribution along a finite conductivity fracture is proposed. Higher order interpolation functions are utilized to solve the integral equation. Use of higher order functions requires one to account for the singularities of the fracture tip and the well. The concept and use of discontinuous and partially discontinuous boundary elements is shown to account for these singularities. The proposed method can be used for other semi-analytical solution schemes.
Automated Well Test Analysis Using Robust (LAV) Nonlinear Parameter Estimation
Authors: Rosa Adalberto J. , Horne Roland N. 
Published: June 2014

ABSTRACT
Most of the nonlinear regression algorithms used in automated well test interpretation perform a minimization of an objective function formed by the sum of the squares of the differences between the data and the model values. This constitutes a typical nonlinear least-squares problem. One of the drawbacks of the least squares approach is that it is significantly affected by outliers, which are data points that can be considered bad observations. This study proposes a robust algorithm that uses the LAV (Least Absolute Value) as the criterion for the minimization.
One of the greatest advantages of the LAV approach is that it provides a smooth transition between full acceptance and total rejection of a given observation, providing a systematic way of rejecting outliers by automatically assigning them less weight in the objective function.
The technique described in this work is based on the expansion of the model function in a Taylor series up to the first order terms. This poses a new problem which is solved iteratively after being transformed into a multiple linear regression parameter estimation. The procedure becomes therefore a sequence of multiple linear regression problems, which are solved using the least absolute value criterion. Because the equations of condition are solved, instead of the so-called normal equations (as in several implementations of nonlinear parameter estimation algorithms discussed in the literature), the method avoids unnecessary exacerbation of the ill-conditioning of the design matrix.
Examples where no large errors in the data are present show that this method produces results similar to least-squares minimization. When outliers are introduced into the observations, however, the present technique yields much better estimates. Also, the least absolute value approach works better than the least-squares criterion when estimating parameters whose sensitivity is small, as in the case of obtaining the storativity ratio and the interporosity flow coefficient in a naturally fractured reservoir with double-porosity behavior.
The Laplace Transform Finite Difference (LTFD) Numerical Method for the Simulation of Compressible Liquid Flow in Reservoirs
Authors: Moridis G. J. , McVay D. A. , Reddell D. L. , Blasingame T. A. 
Published: June 2014

SUMMARY
A new numerical method, the Laplace Transform Finite Difference (LTFD) method, was developed for the simulation of single-phase compressible liquid flow through porous media. The major advantage of LTFD is that it eliminates time dependency, the need for time discretization, and the problems stemming from the treatment of the time derivative in the flow equation by employing a Laplace transform formulation. The LTFD method yields a solution semi-analytical in time and numerical in space, and renders the effects of the time derivative on accuracy and stability irrelevant because time is no longer a consideration. The method was tested against results from three test cases obtained from a standard Finite Difference (FD) simulator, as well as from analytical models. For a single timestep, LTFD requires an execution time 6 to 10 times longer than the analogous FD requirement without an increase in storage. However, this disadvantage is outweighed by the fact that LTFD allows an unlimited timestep size. Execution times may be reduced by orders of magnitude because calculations are necessary only at the desired observation times, while in a standard FD method calculations are needed at all the intermediate times of the discretized time domain. Thus, FD may require several hundred timesteps and matrix inversions to reach the desired solution time, but LTFD requires only one timestep and no more than 6 to 10 matrix inversions. Moreover, LTFD yields a stable, non-increasing material balance error in addition to a more accurate solution than FD.
Use of Voronoi Grid in Reservoir Simulation
Authors: Palagi César Luiz , Aziz Khalid 
Published: June 2014

ABSTRACTRecently, a flexible gridding technique known as Voronoi or perpendicular bisection (PEBI) grid has received some attention in the petroleum literature. The main advantage of this grid is that individual gridpoints can be specified anywhere inside the domain regardless of the position of any other points. This paper describes a practical way of using Voronoi grids for field scale simulation. Gridpoints are easily generated by using modules of known geometry which can be located, scaled or rotated in any position. Physical properties are specified at points that are independent of the computational grid. Also, a new well model for Voronoi grids is proposed.It is shown that, while the results of hybrid-Cartesian and hybrid-hexagonal grids are less sensitive to grid orientation than purely hexagonal grids or the 9-point scheme for the cases investigated, they are still dependent on the number of gridblocks.
A Novel Procedure to Increase Well Response to Matrix Acidising Treatments
Authors: Faber M. J. , Davies D. R. , Nitters G. , Ruessink B. H. 
Published: June 2014

ABSTRACT
Matrix acid treatment design in clastic formations has traditionally been based on field experience or core-flushing tests. The choice of stimulation fluid compositions has frequently been limited to full-strength (12% HCl/3% HF) or half-strength (6% HCl 1.5% HF) mud acid. These practical rules of thumb have given good results but have not always ensured an optimum acid/rock reaction, i.e. the maximum net dissolution of the rock minerals and impairment coupled with a minimum of secondary precipitate formation.
This paper shows how mathematical modelling of the chemical equilibria using a thermodynamic simulator can identify the ideal acid formulation, even when cores are not available. The input for the simulator is the mineralogical composition of the formation (from cuttings, sidewall samples or cores), the nature of the inorganic damage and the rock's porosity-permeability relationship. Chemical equilibria are calculated for different acid compositions taking into account the dynamic nature of the acidising process: the drop in acid strength during reaction with the damaged formation, and the changing rock composition due to attack by the acid. The results are translated via the porosity-permeability relationships into a theoretical well-productivity improvement factor. The acid composition which gives the highest productivity improvement is the optimum or Specially Formulated Mud Acid (SFMA) composition. It is important to note that the SFMA concept is not limited to HCl or HCl/HF acid formulations, but can also deal with other types such as Buffer Regulated HydroFluoric Acid (BRHFA).
It will be shown that different rock compositions lead to very different SFMA formulations. SFMA recipes have been tested in core-flushing experiments, and have been found to give better performance than standard mud-acid recipes. The procedure was further validated by analysing the spent fluids regained by back production after field treatment. Field case histories in which improved production results were achieved using the SFMA approach are described.
A Finite Volume Approach with Triangular Grids in Reservoir Simulation
Authors: Amado Luiz C. N. , Pedrosa Oswaldo A. 
Published: June 2014

SUMMARY
This papers describes a technique to improve the numerical modelling of fluid flow in petroleum reservoirs with complex geometries. A finite-volume formulation is applied to discretize the fluid flow equations in irregular triangular grid networks. Effect of grid orientation in multiphase flow in reservoirs with arbitrarily shaped boundaries and containing internal faults are also discussed. The proposed methodology is validated and an plausible comparison with the results obtained using a conventional Cartesian grid is shown.
Ranking Reservoirs for Carbon Dioxide Flooding Processes
Authors: Rivas O. , Embid S. , Bolívar F. 
Published: June 2014

SUMMARY
The screening of large number of reservoirs for the application of EOR processes has been generally done through "rules of thumb" which oftentimes fail to identify the most suitable reservoirs, due to their binary characteristics, which do not take into account synergistic effects on process performance. Therefore, a new screening method is developed in this work to rank reservoirs for carbon dioxide flooding which attempts to solve this shortcoming. The method is based on a parametric study, carried out systematically to determine the effect of reservoir properties on reservoir response to the gas injection. The study was done using a fully compositional simulator, a black oil model with a mixing parameter, and a semi-analytical predictive model. Results obtained with the three simulators are presented and compared in this paper.
Reservoir parameters examined were temperature, pressure, porosity, permeability, dip, API gravity, oil saturation, net oil sand thickness, minimum miscibility pressure, saturation pressure, remaining oil in place, and reservoir depth. The optimum set of parameters which gave the best average oil production rate for a base case was obtained from the simulation studies. The base case consisted of the injection of 2000 MSCF/D of carbon dioxide in a inverted five spot, 40 acres pattern. The decrease in oil production rate with departures of the characteristic parameters from the optimum values were also determined to quantify the importance or weight of each property. Actual reservoirs were ranked by an arbitrary heuristic function, called the exponentially varying function, whose value depended exponentially on the weighted differences between the properties, characteristic of the reservoir, and the optimum values obtained from the simulation studies.
Results obtained with the three simulators compare quite well and indicate that on the average, the best reservoir for carbon dioxide injection should have an oil gravity of 36°API, a temperature of 150 °F, a permeability of 300 mD, an oil saturation at the start of the injection of 60%, a reservoir pressure at the time of injection of around 200 psi over minimum miscibility pressure, a porosity of 20%, a net sand thickness of 40 ft and a reservoir dip of 20°.
Of the above parameters, those whose changes around the optimum influence the most process performance are API gravity, oil saturation and reservoir pressure. Therefore, the reservoirs with these three parameters closer to the optimum values are the best candidates for CO2 injection. This is taken adequately by the exponentially varying function defined in the paper.
The procedure was applied to rank about six hundred reservoirs in the greater Anaco and Oficina areas of Eastern Venezuela in order to identify the most suitables for a pilot test. The reservoir ranked 30th by the method hereby described was chosen to implement the pilot. This procedure could be easily extended to other EOR processes once the necessary simulations are carried out.
A Robust Algorithm for Parameter Estimation in Well Tests
Authors: Bonalde I. , Ramones M. 
Published: June 2014

ABSTRACT
A robust and efficient least-squares algorithm for parameter estimation in well tests analysis is presented. The algorithm is a Levenberg-Marquardt with a ‘trust region’" approach for global convergence along with restriction in the unknown parameters. In this approach, the selection of the step length is not independent on the choice of Marquard parameter, in contrast with linear search procedure. For a homogeneous reservoir, the algorithm converges to the same result even if each initial guess differs from the final estimates in approximately three orders of magnitude. Compared with the most robust algorithm known up to now (Watson and Lee algorithm), it usually requires about half of the iterations. On the other hand, in cases involving negative skin the convergence is slowed, due to the stronger non-linear character of the problem and the bigger residuals.
Mechanistic Design of Conventional Plunger-Lift Installation
Authors: Marcano L. , Chacín J. 
Published: June 2014

ABSTRACT
A mechanistic model for conventional plunger lift installation design is presented. This model applies to oil wells with high gas-liquid ratios and is based on the fundamental equations of momentum balance and mass conservation. The model considers that the rate of liquid fall-back produced when the plunger rises is a linear function of the average rise velocity. The obtained set of ordinary non-linear differential equations needs to be solved numerically. A Fortran computer program for both personal and mainframe based computers was implemented. This permits the calculation of fall-back losses and allows the estimation of optimum cycle time.
The model, verified with field quality data, has been shown to represent observed production trends in the wells studied, in particular the shape of the fall-back versus driving pressure ratio on the plunger is reproduced correctly. Differences between liquid/gas production and model estimations fall in the 15 to 20 percent range. This result is encouraging, considering the difficulty involved in obtaining accurate field measurements. The computer program developed can be effectively used for the design and troubleshooting of conventional plunger lift installations.
Simulation of Sand Arching Mechanics Using an Elasto-Plastic Finite Element Formulation
Authors: Polillo Adolfo , Vassilellis George D. , Graves Ramona M. , Crafton James W. 
Published: June 2014

SUMMARY
This work is a simulation of sand production mechanics using an elasto-plastic finite element formulation. An open vertical well was considered in order to simulate the performance of near-wellbore unconsolidated sand during hydrocarbon production. In the simulation procedure, the assigned values of the initial stress field around the wellbore were taken from previous sand arching experiments conducted at the Colorado School of Mines on a similar well configuration using 20/40 frac sand. The mechanical rock properties used in simulation were also taken from previous experimental work. The model did not require fluid properties such as density and viscosity be determined. The values of cohesion and pressure drop across the open well sandface were varied in the simulation of hydrocarbon production through the considered wellbore. Through multiple simulations, the effect of these variations on the stability of the sand surrounding the wellbore was observed. In this study, stability is considered to be elastic behavior and plastic behavior is assumed to indicate failure.
It is concluded that sand production from a well can be modeled using the elasto-plastic finite element formulation. The stability of the sand around the wellbore depends on the pressure-drop across the sand face and the cohesion of the sand grains. The model presented can provide information on whether a producing zone will exhibit sand production problems.
Simulation of Miscible Displacement with Interphase Mass Transfer Resistance
Authors: Embid S. , Rivas O. 
Published: June 2014

ABSTRACT
The modeling of miscible displacement processes in petroleum reservoirs, such as Carbon Dioxide Injection or Enriched Gas Drive, has been traditionally done with compositional simulators in which the distribution of the different components or pseudocomponents among the phases is given by equilibrium constants which are determined with a suitable Equation of State, or given as input to the simulator in the form of tables or correlations as function of pressure, temperature and composition.
In other words, the partial differential equations describing the flow of each phase through the reservoir are solved by finite difference techniques assuming thermodynamic equilibrium among the phases in each grid block, every time step. It is shown here that this assumption leads to large errors since at typical conditions interphase mass transfer resistances are large and thermodynamic equilibrium in not nearly reached during the time steps of interest.
In this work, a one dimensional compositional simulator is developed where mass transfer kinetics is taken into account by including equations which describe the interfacial molar flow of each component in terms of overall mass tranfer coefficients, and the difference between the actual phase concentration and that it would have at equilibrium. Sensitivity studies are carried out to determine mass transfer resistance contributions to process performance.
The simulator was validated by modeling CO2 displacement experiments carried out in a laboratory slim tube. In this case, the relative permeability curves were kept constant, and the overall mass transfer coefficient was changed to reproduce the oil production of the experiments. The experimental results were also simulated with a conventional compositional simulator, changing the relative permeability curves to adjust oil production.
Modelling Formation Damage Caused by Kaolinite from 25 to 300°C in the Oil Sand Reservoirs of Alberta
Authors: Gunter W. D. , Zhou Z. , Perkins E. H. 
Published: June 2014

SUMMARY
The oil sands of Alberta contain some of the largest deposits of bitumen in the world. In the majority of these oil sands reservoirs, the most abundant clay mineral present is kaolinite. Kaolinite has two different types of formation damage, both leading to permeability changes. At low temperatures, kaolinite contributes to fines transport; at the high temperatures accompanying steam recovery, kaolinite reacts with other minerals and condensed steam to form smectite or analcime.
Transport of kaolinite fines in the reservoir at low temperatures is dependent on both hydrodynamic and colloidal forces. Mobilization of kaolinite fines depends on the water chemistry and is favored by high pH and low salt concentration. The dependence of kaolinite mobilization on solution chemistry is modelled using surface group ionization and DLVO theory and related to produced water compositions from oil sands reservoirs.
Water-mineral reactions in oil sands reservoirs are modelled at high temperatures; and are shown to be controlled by the quality and water chemistry of the injected steam. The residual liquid phase of the injected steam can attain pH's of 12 (25°C equivalent) in the steam generator. When such a residual liquid phase contacts the oil sand reservoir, it destabilizes the 'acid' clay, kaolinite and favors the formation of zeolite over smectite.
Analytical Theory of Combined Condensing/Vaporizing Gas Drives
Authors: Johns R. T. , Dindoruk B. , Orr F. M. 
Published: June 2014

SUMMARY
Analytical solutions are presented that confirm the existence of a combined condensing and vaporizing displacement mechanism in enriched gas drives. The solutions are derived for dispersion-free, one-dimensional displacements in four-component hydrocarbon systems. A simple geometric construction is used to find a key tie line in the solution, the "crossover" tie line. This tie line is shown to control the development of miscibility in condensing/vaporizing systems, and it connects the condensing and vaporizing portions of the displacement.
Flow Regimes in Miscible Displacements in Heterogeneous Correlated Random Fields
Authors: Sorbie K. S. , Feghi Farag , Pickup G. E. , Ringrose P. S. , Jensen J. L. 
Published: June 2014

ABSTRACT
Fluid flow within a porous medium is governed by both the fluid mechanics and the rock heterogeneity level and type. Here, we model permeability heterogeneity as a random correlated field. The process is a first contact miscible viscous displacement at unit and adverse mobility ratios. We investigate the various flow regimes that are possible and discuss their significance. We point out the importance of the effective aspect ratio, which is related to vertical equilibrium, in determining the global flow regime.