bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Viscous Fingering in Two Phase, Three Component Flow
Authors: Blunt Martin , Christie Mike
Published: June 2014

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

Foam 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

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

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

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

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

Recently, 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

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

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

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

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

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

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

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

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

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

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.
Polymer Adsorption/Retention in Porous Media: Effects of Core Wettability and Residual Oil
Authors: Broseta D. , Medjahed F. , Lecourtier J. , Robin M.
Published: June 2014

Low polymer retention in the reservoir is essential to the success of a polymer EOR operation. It is usually estimated from laboratory core flood experiments conducted under conditions as close as possible to those prevailing in the field. This paper addresses the effects of core wettability and oil saturation on polymer adsorption/retention.

Adsorption of EOR water-soluble polymers onto oil or, more generally, hydrophobic substrates was estimated from a series of core flood experiments on alkane-coated (silane-treated) substrates and compared to adsorption on the bare siliceous substrates. A significant adsorption onto hydrophobic surfaces was found, the effect being stronger for nonionic Polyacrylamide and polysaccharides (scleroglucan and xanthan) than for anionic (hydrolyzed) Polyacrylamides.

In a second series of core flood experiments, Polyacrylamide adsorption/retention in cores under residual oil saturation was measured and compared to the adsorption/retention in similar oil-free, 100% brine saturated, cores. In oil-wet cores, retention decreased considerably in the presence of oil, while it increased slightly in water-wet systems.

These effects may be explained in terms of water/rock and water/oil interfacial area distribution within the pore space, which is governed by wettability. In water-wet cores, droplets of residual oil offer an additional adsorbing surface to the polymer, whereas in oil-wet cores the oil wetting film offers the polymer an adsorbing surface much smaller than the (no longer accessible) rock surface.
Applying Fractional-Flow Theory to Foam Processes at the "Limiting Capillary Pressure"
Authors: Zhou Z. H. , Rossen W. R.
Published: June 2014

A fractional-flow analysis is extrapolated from laboratory data for foams at the "limiting capillary pressure." This analysis suggests that for continuous-injection foam processes, the best surfactant should drive water saturation to the lowest possible value and be sensitive to permeability. For WAG processes, the best surfactant should cause foam to degrade over a range of water saturations.
Effect of Conductivity on Horizontal-Well Pressure-Behavior
Authors: Ozkan E. , Sarica C. , Haciislamoglu M. , Raghavan R.
Published: June 2014

This study investigates the effect of pressure drop within the horizontal section on horizontal-well responses. A general, semi-analytical model that couples wellbore and reservoir hydraulics is presented. Dimensionless groups are defined to correlate the effect of wellbore hydraulics on horizontal-well responses. Flux and pressure distributions along the length of the well are investigated and the validity of the infinite-conductivity assumption is discussed. Short- and long-term characteristics of pressure responses along with asymptotic expressions are documented.
Interpretation of Oil-Water Relative Permeabilities from Centrifuge Experiments
Authors: Hirasaki G. J. , Rohan J. A. , Dudley J. W.
Published: June 2014

Collection of production data from centrifuge displacement with a time resolution of seconds and volume resolution of 4 µl provides the precision for interpreting the transient data for the displaced phase relative permeability curve. Interpretation for the relative permeability requires a simulation model that includes all relevant phenomena that affects the displacement. This includes the variation of the centrifugal force within the sample and during the centrifuge start-up period. Capillary pressure is a significant factor in both the initiation and cessation of production and thus must also be included in the analysis. The finite mobility of the invading phase places limitations on the portion of the relative permeability curve that is in the region of the shock. In addition, the finite mobility of the invading phase reduces the sensitivity to the initial (end ppinf) relative permeability of the displaced phase. The design of experiments in mixed wet systems require a balance between the Brownell-Katz (or Bond) number criteria for displacement of a disconnected phase and retention due to a capillary end effect.
Effect of Gas Enrichment and Dispersion on Nearly Miscible Displacements in Condensing/Vaporizing Drives
Authors: Johns R. T. , Fayers F. J. , Orr F. M.
Published: June 2014

Compositional simulation and analytical solutions are presented that model enriched gas drive processes using only four pseudocomponents. A four-component model is used and compared to a more detailed 12-component model to examine the effects of dispersion, gas enrichment and pressure on oil recovery.

We show that a simple four-component lumping method can give a model with acceptable average front velocities that exhibits features of both condensing and vaporizing displacements. Furthermore, we show that a four-component model can achieve a nearly exact match to the 12-component model if the four-component enrichment level is adjusted. We also compare the dispersion-free analytical four-component solution with a dispersive four-component compositional simulation to demonstrate that dispersion causes some two-phase flow in a displacement that would otherwise be multicontact miscible (MCM). As dispersion increases in both the four and 12-component models, the oil recovery is reduced, especially near the minimum enrichment for miscibility (MME).
The Validation of Horizontal Well Models Using a Physical Model of Heat Flow in Anisotropic Conductor
Authors: Sabeh Michael A. , Enick Robert M.
Published: June 2014

Two recently proposed models of fluid flow in anisotropic media yield different expressions for horizontal well productivity due to their representation of the wellbore. The model developed by Babu and Odeh used a point source/sink for the wellbore, while Peaceman's model implemented an isobaric boundary along the surface of the wellbore. Babu and Odeh's model predicted elliptical isobars, even in the immediate vicinity of the wellbore. Peaceman's model predicted a rapid transition from circular to elliptical isobars as the distance from the wellbore increased. Both models were mathematically correct and seemed plausible, but only one could have been accurate with respect to the actual system. Therefore the more appropriate model to use in reservoir simulation was determined experimentally.

The temperature-induced flow of heat from an anisotropic conductor into a circular heat sink is analogous to the pressure-induced flow of fluids from an anisotropic porous medium into a circular wellbore since the governing differential equations for both processes are identical in form. Heat transfer experiments were therefore used to model this fluid flow problem. The position and shape of isotherms in an anisotropic conductor corresponded to the position and shape of an isobar in a porous medium.

The results clearly indicated that a transition from circular to elliptical isopotentials occurred, in agreement with Peaceman's model. It is therefore more appropriate to model a wellbore as an isopotential of finite diameter when studying near-wellbore problems, such as the calculation of well productivity. If one desires to use the point representation, the modifications suggested by Brigham and Peaceman should be employed.
Component Partitioning in CO2/Crude Oil Systems: Effects of Oil Composition on CO2 Displacement Performance
Authors: Hagedorn K. D. , Orr F. M.
Published: June 2014

Gas chromatography/mass spectrometry (GC/MS) was used to analyze equilibrium phase samples from CO2/crude oil mixtures. K-values, or partitioning coefficients, are presented for over 250 individual components in these CO2/crude oil mixtures. The data show that both molecular size and structure affect the way a molecule partitions into a CO2-rich phase. Multi-ring aromatic compounds partition much less favorably into the CO2-rich phase than other components with similar molecular size or similar GC elution time.

Two crude oils which have similar carbon number distributions, but different slim tube displacement behavior, were analyzed by GC/MS. The oil containing a significant quantity of multi-ring aromatics produced a much lower slim tube recovery at given pressure, and had a correspondingly higher minimum miscibility pressure (MMP).

Equation of state (EOS) flash calculations and compositional simulations indicate that inclusion of the properties of the multi-ring aromatic compounds in an oil characterization is required if the types of behavior observed experimentally in both the single contact partitioning experiments and in slim tube experiments are to be reproduced numerically for oils containing significant quantities of multi-ring aromatic compounds.
The Transformational Decomposition (TD) Method for Compressible Fluid Flow Simulations
Authors: Moridis G. J.
Published: June 2014

A new method, the Transformational Decomposition (TD) method, is developed for the solution of the Partial Differential Equations (PDE's) of single-phase, compressible liquid flow through porous media. The major advantage of the TD method is that it eliminates the need for time discretization, and significantly reduces space discretization. There are two stages in the TD method: a Decomposition stage and a Reconstitution stage. In the Decomposition stage the original PDE is decomposed by using a Laplace transform for time, and successive levels of finite integral transforms for space. Each level of finite integral transform eliminates one active dimension, until a small set of algebraic equations remain. The original PDE is thus decomposed into much simpler algebraic equations, for which solutions are obtained in the transformed space. In the Reconstitution stage, solutions in space and time are obtained by applying succesive levels of inverse transforms. In contrast to traditional numerical techniques, the TD method requires no discretization of time and only a very coarse space discretization. The TD method is tested against results from one- and two-dimensional test cases obtained from a Finite Difference (FD) simulator, as well as from analytical models. The TD method may significantly reduce memory requirements because discretization in time is not needed, and a very coarse grid suffices for the space discretization. Execution times may be substantially reduced because smaller matrices are inverted and solutions are obtained at the desired points in space and time only.
Nuclear Magnetic Resonance Measurements of Wettability and Fluid Saturations in Chalk
Authors: Howard J. J. , Spinier E. A.
Published: June 2014

Laboratory Nuclear Magnetic Resonance (NMR) measurements on chalk cores are used for a rapid and accurate determination of fluid saturations and a qualitative estimate of wettability. Relaxation-time populations generated by a non-linear optimization technique clearly distinguish between the water and hydrocarbon phases in pores at various water-saturation states. Shifts of these relaxation time populations are interpreted as indicators of pore-wall wettability. These relaxation time shifts also correlate with changes in saturation exponents determined from resistivity measurements at initial water saturation, Swi. Quantitative estimates of water saturation in these predominantly water-wet chalks at both initial irreducible water and after spontaneous water imbibition are in excellent agreement with more conventional core analyses.
Scaling Fluid Flow Through Heterogeneous Permeable Media
Authors: Li Dachang , Lake Larry W.
Published: June 2014

Despite several decades of study, there is no rigorous method for scaling flow through heterogeneous permeable media. Existing methods neglect heterogeneity and spatial correlation, which we now know to be of fundamental importance in many processes. On the basis of statistical techniques and inspectional analysis, we present a general method to scale flow through heterogeneous permeable media for an immiscible displacement of oil by water in a two-dimensional, anisotropic, heterogeneous cross section with statistically stationary properties.

Our results illustrate the interplay among local heterogeneity (the variance at a lower cutoff in a power-law variogram), global heterogeneity (the variance at an upper cutoff) and zonal heterogeneity (the power-law upper cutoff and exponent). The effects of the scaling groups obtained from the method have been examined in detail, and some important flow characteristics, which were unknown or poorly understood before, have been revealed.
Safety Management Systems: Questioning Some Fundamentals
Authors: KEARNS JOHN , SHARP LAN , TAYLOR DONALD
Published: June 2014

1.0 Abstract

The Gullen Enquiry into the Piper Alpha disaster emphasised the importance of work practices as well as equipment hardware in ensuring safety offshore. In the complex offshore environment, the need to dovetail the various work practices and safety initiatives is paramount. The resulting integrated corpus is termed a Safety Management System (SMS). Many SMS concepts have been borrowed from the related discipline of Quality Management. Sometimes these concepts are used without thought as to what specific benefits they bring to safety.

The authors believe that the industry is beginning to loose sight of utility when putting in place certain elements of SMS. Some work practices and initiatives are instigated because they are expected to be there rather than because of need. In three specific areas, BHP Petroleum has developed novel elements of their Safety Management System for North Sea Production operations in order to satisfy specific needs.

The first element is Safety Auditing. BHP has developed a custom designed auditing system which focuses on the offshore installation rather than the overall Safety Management System. This auditing system takes as its point of departure the specific hazards that exist on the installation in question.

The second element relates to safety responsibilities. In defining safety responsibilities, it is very easy to give individual members of the workforce too much direction. The result can be an overly proceduralised and rigid organisation. BHP are in the process of developing a system for delineating safety responsibilities in order to support training goals. This allows members of the workforce scope to apply good judgement in a goal setting way.

The third element concerns the management of safety in contractors operations. Rather than requiring a contractor to import the Operators SMS, BHP has developed a mechanism for using and enhancing the Contractors existing Safety Management System.

This paper provides a description of how these systems work.
A Model for the Production Interference of Multiple Reservoirs Sharing a Common Aquifer
Authors: Rodriguez F. , Samaniego-V F. , Cinco-Ley H.
Published: June 2014

A semi-analytical model for the production interference of multiple reservoirs sharing a common aquifer is presented in this work. A two dimensional finite aquifer is considered, with nr reservoirs located across the aquifer domain. Water injection is allowed through nw arbitrarily located injection wells. The solution to this problem provides the pressure distribution in the aquifer and the average pressure and water influx for each of the reservoirs, as a function of time.

The flow behavior in a given aquifer-reservoirs system was found to be governed by the hydraulic diffusivity of the aquifer, ηα, the pore volume-total compressibility of the aquifer, (Vpct)a, and of the reservoirs, (Vpct)r, r = 1,2,…,nr the aquifer dimensions, xe,ye, and the location of the reservoirs within the aquifer. These parameters can be estimated through the model by history matching the average pressure of the reservoirs; the estimation of the water influx in each reservoir is obtained through the matching process.

A field application of the model is presented, which consists of the characterization of a system of three naturally fractured reservoirs sharing a common aquifer in the Gulf of México. Parameters estimated through the model were found most valuable as input data for numerical reservoir simulation of the system.
A Horizontal Well in a Depleted Reservoir in Lake Maracaibo: A Case Study
Authors: Suarez Tony
Published: June 2014

This paper describes an integrated reservoir study performed to select a location for Maraven's first horizontal well in Lake Maracaibo, Venezuela. A depleted reservoir producing for 40 years, and with over 80 % of its recoverable book reserves produced, was selected to place the horizontal drainhole. The field has been yielding high water cuts since 1975, ranging from 85 to 95 %, and vertical new wells would water out within weeks. The reservoir study used a synergetic approach from a team composed of Petrophysicists, Geologists, Sedimentologists and reservoir engineers, from both the operator and the service company, aimed at choosing the reservoir and the best location within it. The selected reservoir has a dip of 30 degrees and leans against one of the major faults defined in the Lake Maracaibo basin.
Field Cases for Permeability Determination from Minifracs
Authors: Mayerhofer M. J. , Economides M. J.
Published: June 2014

The estimation of the reservoir permeability, a variable of great importance in hydraulic fracture design, is frequently inaccessible because candidate wells either do not flow or a pretreatment pressure transient test would be inordinately long (and expensive). A methodology for the interpretation of a fracture calibration treatment has been developed that allows the calculation of the permeability in addition to the traditional results of the "leakoff coefficient", closure pressure and fluid efficiency. Here, gas reservoir field cases are presented and interpreted with this method. A log-log diagnostic plot of the rate-normalized pressure and its derivative was employed to account for a multi-rate injection (fluid leakoff) and it is used to identify the transient reservoir response during fracture closing. The reservoir permeability can then be estimated from a specialized plot. This procedure is verified by a pressure match.
Transport Phenomena in Chemical Flooding
Authors: Porcelli P. C. , Bidner M. S.
Published: June 2014

A chemical flood simulator of a three-component, two phase system has been extended to include concentration dependent functions: phase behavior, relative permeabilities, capillary pressure, interfacial tension, residual saturations, phase viscosities, wettability, etc.. Their influence on concentration profiles and on oil recovery is analyzed hereupon.
Enhanced Oil Recovery by Means of Microorganisms: Pilot Test
Authors: Buciak J. , Vazquez A. , Frydman R. , Mediavilla J. , Bryant Rebecca
Published: June 2014

The paper presents the design, implementation and results of a microbial single-well stimulation test performed at the Diadema field in Argentina. The purpose of the test was to achieve increased production by injecting a microbial formulation and nutrients, and to gain experience with this procedure under actual field conditions. Two out of five treated wells showed excellent oil production response to the microbial stimulation.

The results suggest that a microbial-enhanced waterflood could be implemented successfully at the Diadema field.
Impact of Asphaltene Presence in Some Rock Properties
Authors: de Pedroza T. M. , Calderon G. , Rico A.
Published: June 2014

Several studies have shown that asphaltene precipitation at porous medium level leads to changes in some of its properties, such as wettability and hydraulic conductivity. This work shows the results obtained in a study aimed at assessing the effect of asphaltenes and its occasional precipitation on wettability and permeability of rocks found in Venezuelan oil reservoirs. Fluids and cores from five crude reservoirs having different asphaltene contents and Berea cores plugs were used. Wettability measurements were performed by using a variation of Amott method. Similarly, measurements were effected on cores in which precipitation was induced by n-pentane injection. Permeability reduction was evaluated by carrying out displacements tests before and after the precipitation induction.

All cases indicated the presence of changes in wettability. Such changes depend on the specific crude asphaltene content and always tend to an intermediate or preferential oil wettability condition, which does not increase during asphaltene precipitation.

Mean hydraulic radius reductions in tests where the precipitation was induced were in the range of 93.3 – 47%, which corresponded to asphaltene retention values of 19 and 3.6 %PV, respectively. These reductions depend on the rock nature and the core properties: permeability, porosity and pore size distribution.
Effects on the Marine Environment of Produced Formation Water Discharges from Offshore Development in Bass Strait, Australia
Authors: Terrens G. W. , Tait R. D.
Published: June 2014

An environmental effects study was undertaken to assess the potential environmental effects of discharged produced formation water from offshore oil and gas platforms in Bass Strait, Australia. The focus was on potential effects on the fisheries of Bass Strait. Produced formation water discharged to the ocean from the Halibut platform, one of the largest Australian oil fields and now the most prolific produced formation water field, was modelled for dilution versus distance from the platform. Characterisation of produced formation water from 10 Bass Strait platforms for chemical constituents and toxicity to local marine organisms was performed.

It was found that produced formation water discharged into Bass Strait presents a very low risk to marine organisms due to very low toxicity and very high dilution rates. For the Halibut platform, acceptable acute toxicity concentration of produced formation water can be obtained with dilution of less than 2:1. Actual dilution rates are approximately 30:1 within 10m of the discharge point, and concentrations reach an indicative "no chronic" toxicity effect level within 25m of the discharge point. The discharge plume is also spatially limited and mobile and any organism would be exposed to potentially lethal concentrations of produced formation water for the order of less than 30 seconds for median current conditions.
Remediation of Ponds and Landfills at a Gas Plant in Alberta
Authors: Kent R. P. , Beresford C. R.
Published: June 2014

Work is in progress on the remediation of contaminated ponds and landfills at a gas plant in central Alberta. Previous experience in the excavation and disposal of large quantities of heterogeneous, contaminated industrial wastes is limited. Through studies, investigations and pilot work a cost effective strategy for remediation has been developed.
High-Permeability Fracturing: The Evolution of a Technology
Authors: Smith M.B. , Hannah R.R.
Published: June 2014

Since its introduction almost 50 years ago, hydraulic fracturing has been the prime engineering tool for improving well productivity, either bypassing near wellbore damage or actually stimulating performance. Historically (and in many instances erroneously) the emphasis for propped fracturing was on fracture penetration or length, culminating in massive treatments for tight gas sands using several million pounds of proppant with design 1/2 lengths in excess of 1500 feet (460 m). More recently, the importance of fracture conductivity has become appreciated. This has led to exciting "new" applications of propped fractures in better quality reservoirs as illustrated by North Sea wells, stimulations in Prudhoe Bay, and "frac-pack" operations in the Gulf of Mexico and Indonesia.

While better understanding and new technologies are being used today, the actual application of fracturing to higher permeability formations is not new. During early development of fracturing, nearly all applications were for moderate to high permeability zones (since low permeability rock was of little interest at oil prices of $3/BBL).

While tremendously successful at increasing PI, these early high permeability treatments were doing little more than bypassing damage. More recent development of improved, artificial proppant, cleaner fluid systems, and new technologies have changed this, making it possible to truly alter reservoir flow and stimulate production from moderate to high permeability reservoirs. The primary new tool in the engineers arsenal is the development of "tip screenout" fracturing. While higher permeability formations provide the "new" applications, the actual philosophy shift for fracturing occurred with the massive, tight gas stimulations. while outwardly a traditional, straight forward, application of fracturing to poor quality reservoirs, in actual fact these treatments represented the first engineering attempts to alter reservoir flow in the horizontal plane.