bluuebunny/crossref_metadata_2025 huggingface dataset:
Representation of Reservoir Geometry for Numerical Simulation
Authors: Hirasaki G.J. , O'Dell P.M.
Published: December 2007

For most reservoirs the reservoir thickness and dip vary with position. For such reservoirs, the use of a Cartesian coordinate system is awkward as the coordinate surfaces are planes and the finite-difference grid elements are rectangular parallepipeds. However, these reservoirs may be efficiently parallepipeds. However, these reservoirs may be efficiently modeled with a curvilinear coordinate system that has coordinate surfaces that coincide with the reservoir surfaces. A procedure is presented that may be used to determine a curvilinear coordinate system that will conform with the geometry of the reservoir. The reservoir geometry is described by the depth of the top of the reservoir and the thickness. The mass conservation equations are presented in curvilinear coordinates. The finite-difference equations differ from the usual Cartesian coordinate formulation by a factor multiplying the pore volume and transmissibilities. A numerical example is presented to illustrate the magnitude of the error that may occur in the computed oil recovery if the Cartesian coordinate system is simply modified to yield the correct depth and pore volumes.

Introduction

Many reservoirs have a shape that is inconvenient and possibly inaccurate to model with Cartesian coordinates. The use of a curvilinear coordinate system that follows the shape of the reservoir can be advantageous for such reservoirs. The formulation discussed here will have the greatest advantage in modeling thin reservoirs but will have little advantage in modeling a reservoir whose thickness is greater than its radius of curvature, such as a pinnacle reef. pinnacle reef. In this paper the reader is introduced to various grid systems used to model reservoirs. A brief discussion of some concepts of differential geometry contrasts differences between Cartesian coordinates and curvilinear coordinates. A curvilinear coordinate system for modeling reservoir geometry is presented. Formulation of the conservation equations in curvilinear coordinates and the necessary modifications to pore volume and transmissibility are discussed. A numerical example illustrates the magnitude of the error that may result from some coordinate systems.
Evolution of Analyzing Reservoir Simulation Data
Authors: Phelps R. E. , Huang A. Y.
Published: December 2007

Petroleum-producing companies world-wide routinely use numerical reservoir simulation as an engineering tool to manage their hydrocarbon reservoirs efficiently. The task of building models with a large number of gridblocks is not easy, and analyzing the voluminous results produced by such models is even more difficult. This paper discusses the historical evolution of techniques used to analyze reservoir simulation data over the past decade. It outlines how the advancement of workstation technology and the introduction of an X-Window system opened up an entirely new way of using mainframe computing power and workstation graphical display capabilities simultaneously. The paper also discusses Saudi Aramco's experience in the development of sophisticated reservoir simulation postprocessing packages. We emphasize the need for direct communication between the programmer and end users to facilitate a userfriendly package.

We present a practical example illustrating the benefit of these postprocessing packages in the construction and history matching of a large model with approximately 52,000 cells. We estimate savings in manpower and computer resources using current technology.
Scanned Well-Log Image and Digital Data Management
Authors: Zainalabedin K. A. , Derr M. E. , Fenn C. J.
Published: December 2007

As part of a comprehensive, multidisciplinary data-management project, libraries of computer-archived well logs that provide access to both scanned-image and digitized-curve data are under development. A comprehensive set of retrieval and management tools facilitates log-image and digitized-curve access and use.

Images are accessible for viewing on Unix workstation and mainframe terminals at all office locations and also may be plotted as hard-copy paper prints. Network connectivity and file sharing also facilitate transfer to workstation analytical software.

By using the central mainframe as a library and catalog manager, mass storage and database-intensive management tasks are handled outside of the Unix networks. Independence from the rapidly developing workstation network environment reduces database maintenance and permits longer-term data management planning than would otherwise be practical.

Image libraries are a developmental step in a trend toward an imagebased work environment in which well-log and other geotechnical image data are expected to become primary analytical resources.
An Integrated Deterministic/Probabilistic Approach to Reserve Estimations(includes associated papers 31056 and 35248 )
Authors: Patricelli J.A. , McMichael C.L.
Published: December 2007

Mobil Oil Exploration and Producing Corporation utilizes a unique methodology for reserve and resource evaluation. The approach integrates both deterministic and probabilistic methods to evaluate externally reported reserves and establish the full hydrocarbon potential of our projects. There are three basic classifications for hydrocarbons in our reserve/resource system; Reserves (appropriated projects that are economic at today's prices), Contingent Resources (projects being appraised or not viable with today's prices and technology), and Speculative Potential (yet to be drilled). In addition, the Reserves and Contingent Resources classifications each have three categories: Proved, Probable, and Possible. Proved and Probable are calculated deterministically utilizing in house definitions which conform to SEC and SPE guidelines.

Monte-Carlo simulation is then run to establish the cumulative probability distribution for recoverable hydrocarbons. This distribution and the deterministic results are used to define the possible category and to establish the project expected value. Average risk factors are calculated for each of the categories to ensure they meet Mobil guidelines. These average risk factors (truly confidence factors) are reported in association with their category value. The ultimate or EV is then used for economic assessment of the field and equals the projected ultimate recovered amount.
Screening of Geostatistical Reservoir Models With Pressure Transients
Authors: Herweijer J.C. , Dubrule O.R.F.
Published: December 2007

A geostatistical reservoir study provides an ensemble of possible reservoir models, with a variability reflecting the uncertainty of the geology and fluid-flow properties. A production test links the static geostatistical model with dynamic fluid-flow data and thus provides possible means of validation and selection. We used a highly efficient 3D single-phase simulator to simulate pressure transients without compromising the fine-grid resolution typical for geostatistical models. This simulator was applied to Boolean and Gaussian geostatistical models that represent reservoirs consisting of heterogeneous fluviodeltaic deposits. Simulated buildup and interference tests were analyzed and related to 3D permeability and connectivity patterns. Effective well-test permeability was compared with 3D averages obtained from different volumes within the geostatistical model. The cases studied show that combining geostatistical models and well tests can reduce uncertainty with respect to geometric connections and the permeability distribution. However, the study also confirms that well tests have a limited capability to assess lateral continuity precisely and uniquely. Simulation of an interference test has the potential to screen the geostatistical model for high-permeability connections between wells. This pragmatic integration of pressure transients and detailed heterogeneous reservoir models through forward simulation provides a simple means to evaluate these models. It allows testing a model based on small-scale (core-plug) permeabilities and qualitative geologic information vs. routine field measurements representing large-scale hydraulic behavior of a reservoir.

Introduction

During the early stage of field development, production tests are the only data providing information about fluid flow in oil reservoirs and about permeability in the wider volume surrounding a well. At the same stage, construction of a geostatistical reservoir model is now a viable option. The main purpose of this model is to assess the uncertainty of reservoir performance resulting from incomplete knowledge of the heterogeneous reservoir. Geologic data and core measurements are honored at the wells, and models are created between wells that are statistically similar to those inferred from geologic analogs. These are static data, and subjecting the geostatistical model to verification on the basis of dynamic fluid-flow data (i.e., pressure-transient production tests) is a logical step. The pressure transient reaches faraway boundaries in a relatively short time.
Operating Experience With ESP's and Permanent Downhole Flowmeters in Wytch Farm Extended-Reach Wells
Authors: Brodie Alan , Allan Joe
Published: December 2007

One-third of the recoverable reserves in British Petroleum CO.'s U.K. onshore oil field, Wytch Farm, lie in an offshore extension of the field. These reserves, which have been undeveloped until recently, are now being exploited with electric submersible pumps (ESP's) in extended-reach wells drilled from onshore wellsites. The relatively high productivities achieved as a result of successful horizontal completions have pushed ESP technology to the limits in terms of capacity and power requirements. This paper presents a case history of the unique set of problems encountered during and subsequent to startup of the ESP's in the first three wells. The problems, in particular pump-suction-blockage problems, were directly attributable to the position of the ESP's in the near-horizontal section (82 to 85°) of the wells.

The paper also describes the innovative permanent downhole flowmeter system incorporated in the completion. The system measures and logs flow-rate data, pump-suction and -discharge pressures, and temperature. Examples are presented that clearly demonstrate how these data have been invaluable in understanding the problems encountered in the initial extended-reach wells and the role the system has played in extending ESP run lives. Finally, completion-equipment modifications and operating-procedure changes, successfully introduced to resolve the problems encountered in the first two wells and to avoid them in subsequent wells, are described.

Introduction

Wytch Farm, on the southern coast of England ˜100 miles southwest of London (Fig. 1), is the largest onshore oil field in western Europe. The main reservoir lies under Poole Harbor and extends offshore under Poole Bay. Poole Harbor has been designated as an area of outstanding natural beauty, with sites of special scientific interest and special protection areas, and is noted for its landscape, ecology, and amenity value.
Relative Permeability Hysteresis: Laboratory Measurements and a Conceptual Model
Authors: Braun E. M. , Holland R. F.
Published: December 2007

Relative permeability hysteresis has been measured for a water-wet outcrop rock sample and a mixed-wet reservoir core. For the oil phase, imbibition and drainage relative permeability curves differed significantly. The difference was much less pronounced for the water phase. Scanning curves, which characterize transitions between imbibition and drainage curves, were also measured. A notable characteristic of the oil relative permeability scanning curves is their reversibility; along most of the length of a scanning curve, oil relative permeability exhibits no hysteresis. A proposed mechanism for the reversible behavior is pinning of water/oil interfaces on surfaces of rock grains. Pinned interfaces remain anchored at fixed positions on grains despite changes in interface curvature and contact angle. In water-wet samples, pinning can occur as a result of contact-angle hysteresis. In mixed-wet rock, pinning can occur at the boundaries between water- and oil-wet grain surfaces. As long as interfaces remain pinned, pore-level fluid geometry is a function of saturation only and does not depend on the direction of saturation change.
Effect of Injectant Composition and Pressure on Displacement of Oil by Enriched Hydrocarbon Gases
Authors: Shyeh-Yung J. Jane , Stadler Maurice P.
Published: December 2007

Reservoir-condition phase-behavior and tertiary-gasflood studies have been conducted in the laboratory to investigate the effect of hydrocarbon-injectant composition and pressure on oil-displacement efficiency. Lower oil-recovery efficiencies and lower injectant mobilities have been observed at lower enrichment levels and/or at lower pressures. Coreflood oil recoveries, however, remained high for gas injectants that are below multiple-contact miscible (MCM) with the oil. These results suggest that near-miscible hydrocarbon-gas-injection processes show promise and that there may be a tradeoff between local oil-displacement efficiency and gas-sweep efficiency in near-miscible displacements in the field.
Evaluating Deepwater Development Concepts
Authors: Abbott P.A. , D'Souza R.B. , Solberg I.C. , Eriksen Knut
Published: December 2007

This paper provides an overview of the current state of deepwater technology. It discusses the major factors that must be considered when evaluating potential deepwater development concepts, presents proven deepwater development concepts, and provides insight into the applicability of each. Two unproven "dry tree" concepts are presented to illustrate proposed new concepts. Approximate costs are included, leading up to general conclusions with respect to the evaluation process. The focus is primarily on the Gulf of Mexico.

The Deepwater Market

The incentives for developing deepwater fields are clear. World oil demand is expected to rise annually by an average of 890,000 B/D between 1993 and 1995. The U.S. has a serious balance of payments problem that is aggravated by the fact that it is importing more than half of its oil. The east and west coasts of the U.S., plus the section of the Gulf of Mexico east of Alabama, are restricted from drilling. Total deepwater discovered and potential reserves in the Gulf of Mexico are estimated to be 2 to 4 billion bbl and 10 to 12 billion bbl, respectively. More than 20 undeveloped discoveries exist in the Gulf of Mexico in water depths ranging from 2,400 to 7,520 ft.

Development Options and Critical Issues

Development Options. Deepwater fields can sometimes be developed with subsea tieback techniques without requiring a deepwater platform at the field itself. If a deepwater platform at the field is required, a wide choice of type exists. The list of proven and unproven (but highly developed) deepwater platform concepts includes (1) steel and concrete tension leg platforms (TLP's); (2) semi- and monohull, steel and concrete floating production systems (FPS's); (3) steel and concrete spars; (4) concrete deep draft floaters (DDF's); and (5) compliant towers (primarily steel).

Some critical issues to consider when selecting concepts to include in a detailed evaluation study will be presented before describing the various deepwater development concepts and discussing the pros and cons of each. The pros and cons of the use of DDF's will not be included because the 45-ft draft limitation along the U.S. gulf coast will probably prohibit their use unless and until suitable techniques for mating an integrated deck to an already-moored hull are developed.
Gas and Water Permeability Data for Some Common Oilwell Cements
Authors: Goode John M.
Published: December 2007

Permeabilities of cementing compositions have become of increasing interest during the last few years due to the growing use of underground reservoirs for gas storage. This paper presents data on water permeabilities and limited data on gas permeabilities for some of the more common oilwell cementing compositions. These data were obtained in the laboratory using both water and air permeameters with Hassler-sleeve specimen cells. The liquid permeameter was designed to operate at pressures up to 100 psi; the air permeameter was designed to operate at a maximum pressure of 3,000 psi. The study was made at the temperature range normally encountered in gas-storage reservoirs. Results obtained in this study indicate that, in obtaining permeability data on cements, liquid permeability tests should be run instead of gas. Also, permeability of any sort is probably not of significant importance when planning a cementing program of a low-temperature gas-storage reservoir since there is little to choose among cements as to permeability after seven days' curing time.

Introduction

Due to the growth in the number of underground gas-storage reservoirs in recent years, an increased interest in permeabilities of oilwell cementing compositions has been shown. When leakage of gas in storage wells is discussed, the question of permeability of cements always seems to arise. Therefore, the purpose of this study was to obtain these data. Some previous work has been done by Morgan and Dumbauld on water permeabilities of cements, but very little information could be found on gas permeabilities. This is particularly true for the wide range of cementing compositions available to the oil industry today. Questions have also arisen as to bonding of the cement to pipe and formation, and what practices should be observed in order to obtain a good bond for sealing wells in LPG-storage reservoirs. Bonding of cement to pipe has been discussed at length by Winn, Anderson and Carter in their paper. A survey of cementing practices among the companies utilizing underground storage for natural gas indicated that two types of reservoirs are being usedaquifers, or formations that originally contained water; andformations that originally contained oil and gas as well as water.

In multiple-zone storage some small leaks have occurred, but investigations indicate these are located between the mud cake-cement interface where poor bonding occurs and are not due to the permeability of the cement. Nevertheless, a comprehensive permeability study of a variety of cements has been made.

Experimental Determinations

The two instruments used in obtaining permeability data were an air permeameter (Fig. 1) and a liquid permeameter (Fig. 2).

JPT

P. 851^
Filtration From Mud During Drilling
Authors: Ferguson C.K. , Klotz J.A.
Published: December 2007

This paper describes experimental investigations conducted at the California Research Corporation's model oil well.

The first part describes filter loss from several drilling muds through bore hole walls during mud circulation and drill string rotation. The effect of mud properties and drill string rotation with mud circulation is described. Filtration from a bore hole full of drilling mud, not circulating, but under pressure for extended time periods, is also discussed.

The second part describes filter loss to permeable formations from beneath a drilling bit where filter cake has no opportunity to develop appreciable thickness. If potential flow theory is applied to predict filtrate invasion from this hole bottom, large invasions are calculated. But model well experimentation shows that filtrate invasion from the hole bottom is controlled by mud particles that penetrate the formation ahead of the bit. This experimentation provides data to estimate the effect of mud particle penetration on fluid loss to formation.

The third part presents an estimate of mud filtration during drilling of a well.

Introduction

As oil wells are drilled by the rotary method, drilling mud circulates up the annulus between drill pipe and well wall. Drillers adjust mud density so that the pressure at the bottom of the mud column is several hundred psi greater than the pressure of reservoir fluid. As a result of this pressure difference, the liquid part of the mud filters into the rock around the bore and mud solids deposit as a filter cake on the well wall. For many reasons the petroleum industry, within the past 20 years, has spent much money and energy to determine the volume of mud filtrate that enters rock around the well bore and dedicated much research effort to reduce this volume.

Among the reasons for attempts to determine the volume of mud filtrate and to reduce this volume are the following:If filtrate damages the permeability of oil sand, the resultant damage to oil well productivity will depend on the distance that the filtrate invades the oil sand; reduction of filtrate volume may, therefore, increase well productivity.Filtrate that penetrates shale sections may cause the shale to swell and to slough into the well bore. Uncontrolled sloughing may stick drill pipe. Reduction in filtrate volume may reduce drilling trouble.Electric log resistivity curves are changed by invasion of a mud filtrate; the change depends on the depth to which filtrate invades. Knowledge of this depth is necessary before resistivity logs can be interpreted accurately.
Parallel Reservoir Simulator Computations
Authors: Hemanth-Kumar Kesavalu , Young L. C.
Published: December 2007

We describe the adaptation of a reservoir simulator for parallel computations. The simulator was originally designed for vector processors. It performs approximately 99% of its calculations in vector/ parallel mode, and, relative to scalar calculations, it achieves speedups of 65 and 81 for black oil and EOS simulations, respectively, on the CRAY C-90. This work also shows that it is easy to adapt a simulator designed for vector processing to parallel processing on shared memory parallel machines.
The Use of Wavelet Transforms in the Solution of Two-Phase Flow Problems
Authors: Moridis G. J. , Nikolaou M. , You Y.
Published: December 2007

In this paper we present the use of wavelets to solve the nonlinear Partial Differential Equation (PDE) of two-phase flow in one dimension. The wavelet transforms allow a drastically different approach in the discretization of space. In contrast to the traditional trigonometric basis functions, wavelets approximate a function not by cancellation but by placement of wavelets at appropriate locations. When an abrupt change, such as a shock wave or a spike, occurs in a function, only local coefficients in a wavelet approximation will be affected. The unique feature of wavelets is their Multi-Resolution Analysis (MRA) property, which allows seamless investigation at any spatial resolution. The use of wavelets is tested in the solution of the one-dimensional Buckley-Leverett problem against analytical solutions and solutions obtained from standard numerical models, Two classes of wavelet bases (Daubechies and Chui-Wang) and two methods (Galerkin and collocation) are investigated. We determine that the Chui-Wang wavelets and a collocation method provide the optimum wavelet solution for this type of problem. Increasing the resolution level improves the accuracy of the solution, but the order of the basis function seems to be less important. Our results indicate that wavelet transforms are an effective and accurate method which does not suffer from oscillations or numerical smearing in the presence of steep fronts.
A One-Dimensional Analytical Technique for Predicting Oil Recovery by Steamflooding
Authors: Shutler N.D. , Boberg T.C.
Published: December 2007

This paper describes a graphical method for calculating oil recovery by steamflooding that permits accurate prediction of fluid saturation permits accurate prediction of fluid saturation profiles and oil bank formation. profiles and oil bank formation. The oil displacement calculation is based on the Buckley-Leverett method for isothermal, two-phase flow in porous media. The fluid-flow theory is used with the Marx and Langenheim method to predict the size of a steam zone from energy balance and beat transfer considerations. The method is more complex than previous simplified methods, but permits band calculations of fluid saturation profiles and the delay of oil bank, arrival in producing wells for partially depleted oil reservoirs. These computations are in excellent agreement with those calculated numerically. Since uniform vertical displacement is assumed this method is suggested for use only for thin sands.

Introduction

The model for steamflooding described in this paper is based on the physical system illustrated paper is based on the physical system illustrated in Fig. 1. The reservoir is considered in vertical cross-section and is bounded above and below by impermeable strata. Heat losses to adjacent strata are accounted for by the method of Marx and Langenheim to describe the rate of steam front advance. This paper is concerned primarily with the prediction of linear fluid-flow behavior in the presence of temperature distributions that are time presence of temperature distributions that are time and distance dependent. The method may also be applied m hot waterflooding. In order to use the isothermal two-phase flow theory of Buckley and Leverett, the temperature distribution T(x, t) is represented by a series of n + 1 moving isothermal zones separated by discontinuities or "shocks" in temperature (Fig. 2a). The Marx-Langenheim method assumes only two isothermal zones (n = 1 in Fig. 2) -- one at injection temperature and the other at initial reservoir temperature - separated by a single shock. Since piston-like flow through the reservoir is assumed, the Marx-Langenheim method is not recommended for thick sands where gravity segregation would greatly reduce vertical sweep. A two-dimensional numerical method as described in Ref. 10 should be used in such a case.

SPEJ

P. 489
Accounting for Local Probabilities in Stochastic Modeling of Facies Data
Authors: Goovaerts Pierre , Journel Andre G.
Published: December 2007

This paper proposes an annealing-type algorithm for generating multiple realizations of facies distributions that: (i) honor the facies data at well locations, (ii) match global proportions of facies, (iii) reproduce spatial continuity and transition probabilities between facies, (iiii) account for prior information such as trend or gradient in facies proportions or the absence of a facies in any particular area. A case-study shows the realizations to reproduce important features of the reference categorical map. A waterflood simulation indicates that the algorithm allows a reduction of the space of uncertainty of flow response values.
A Battery-Operated, Electro-Mechanical Setting Tool for Use With Bridge Plugs and Similar Wellbore Tools
Authors: Gazda I. I. , Goiffon J. J.
Published: December 2007

Traditionally, the method of choice for setting packers, bridge plugs, and similar wellbore tools has consisted of running an electrically activated explosive-charge setting tool to the required setting depth on electric line and activating the tool by an explosive charge. Although this method requires an electric line truck and an operator who is licensed to handle the explosives, it is more cost efficient and faster than other mechanical or hydraulic alternatives. Recently, however, new completion technologies with wellbore configurations in which the explosive-type setting method is not desirable have been introduced to the oilfield.

This paper will discuss the design and operational advantages of a new slickline service tool, the downhole power unit (DPU), which has the capability to set wellbore devices without the use of explosives, and thus can comply with the needs of the new completion technologies. Its gradual setting motion allows the slips and sealing elements of packer and bridge plugs to expand and conform uniformly against the tubing/casing wall, thus decreasing the chance of a misrun. The gradual setting motion also eliminates the high-impact stresses that are imposed upon downhole devices when using an explosive-charge setting tool.

The DPU uses an electric gear motor and linear drive mechanism to generate forces of up to 60,000 lbf, and the design is inherently safer than equipment requiring an explosive charge because the power to operate the tool is provided by standard alkaline batteries. Its specially developed circuitry also increases assurance that the tool will be activated at the proper depth.

The tool can be redressed quickly at the wellsite, and routine maintenance involves only lubrication and battery replacement. The combination of simple maintenance, safety-enhanced operation through the elimination of explosives, deployment with slick-line, and the capability to reduce high-impact stresses and misruns has provided the service industry with a cost-efficient, state-of-the-art setting tool that can be used in applications for which traditional methods have not been satisfactory.
Viscosity of Hydrocarbon Gases Under Pressure
Authors: Carr Norman L. , Kobayashi Riki , Burrows David B.
Published: December 2007

The viscosity of hydrocarbon mixtures, whether in the gas or liquid phase, is a function of pressure, temperature, and phase composition. This paper presents methods for the prediction of the viscosity of the gas or less dense fluid phase over the practical range of pressure, temperature, and phase compositions encountered in surface and subsurface petroleum production operations. The correlation necessary to predict the effect of pressure on viscosities is presented in Part I. Serious discrepancies in high pressure gas viscosity data in the literature are discussed.

The application of the correlation to predict absolute viscosities is discussed in Part II. Auxiliary correlations are presented to enable calculations of viscosities from a knowledge of the pressure, temperature, and gravity of the gas phase.

Introduction

A knowledge of the viscosity of hydrocarbon fluids is needed to study the dynamical or flow behavior of these mixtures through pipes, porous media, or more generally wherever transport of momentum occurs in fluid motion. Since flow is predominantly in the laminar region in petroleum reservoirs, the influence of fluid viscosity on this flow is especially important.

As early as 1894, Onnes and Onnes and de Haas noted that the viscosities of homologs under corresponding states could be correlated. The theorem of corresponding states has been further developed and applied to the viscosity of pure, nonpolar gases under pressure by Comings, Mayland, and Egly.

Serious discrepancies in the viscosity of pure hydrocarbon gases at high pressures have been called to our attention by Comings, Mayland, and Egly. They made a careful analysis of the following methods commonly used to measure gas viscosities:Oscillating disc viscometer.Rolling ball viscometer.Capillary tube viscometer
Tests of the Stability and Time-Step Sensitivity of Semi-Implicit Reservoir Stimulation Techniques
Authors: Nolen James S. , Berry D.W.
Published: December 2007

A reservoir simulation technique that employs semi-implicit approximations to relative permeabilities exhibits excellent stability and permeabilities exhibits excellent stability and convergence characteristics when applied to water- or gas-coning problems. Recent workers in this area have made a simplifying assumption in order to linearize the flow terms of the semi-implicit finite-difference equations. This paper describes a method of solving efficiently paper describes a method of solving efficiently the nonlinear form of the equations and demonstrates that time-step sensitivity is reduced by iterating on the nonlinear terms. In addition, it addresses the problem of allocating a well's production among multiple grid blocks. Example problems include both water-coning and gas-percolation applications.

Introduction

Multiphase reservoir simulators traditionally have employed finite-difference approximations in which relative permeabilities are evaluated explicitly at the beginning of each time step. Simulators of this type are capable of handling many reservoir studies in a perfectly satisfactory fashion, but they are incapable of solving economically problems characterized by high flow velocities. Included in this category are the studies of such phenomena as well coning and gas percolation. The difficulty in such problems is a stability limitation imposed by the use of explicit relative permeabilities. In an attempt to overcome this permeabilities. In an attempt to overcome this limitation, Blair and Weinaug developed a simulator that employed implicitly evaluated relative permeabilities. The increased stability of their permeabilities. The increased stability of their equations allowed the use of time steps much larger than previously possible, but this was counteracted by an increase in the computational work per time step and an increased difficulty in the iterative solution of the difference equations. While the net result was a significant advance in the solution of coning problems, improvements still were needed to increase the dependability and decrease the cost of obtaining solutions for such problems. More recently, two papers were published describing a method that employs semi-implicit relative permeabilities. This method is greatly superior to the fully implicit method, both in computational effort and maximum time-step size. In developing this method, the previous workers made a simplifying assumption to obtain linear finite-difference equations. We have developed a reservoir simulator based on the nonlinear form of the semi-implicit finite-difference equations. This paper describes the techniques used in the simulator and presents the results of some tests conducted with it. These include time-step sensitivity studies and tests of alternate production allocation methods. Some of these tests compare the nonlinear form of the semi-implicit method with the linear form.

SPEJ

P. 253
Fracture Initiation from Inclined Wellbores in Anisotropic Formations
Authors: Ong See Hong , Roegiers Jean-Claude
Published: December 2007

This paper presents a wellbore stability design code that can be used to optimally drill, complete and stimulate inclined wells. The design code was developed for the most general case where the borehole, in-situ stress, and rock property coordinate frames are totally independent of each other. It essentially consists of a three-dimensional linear elastic stress analysis in anisotropic formations. Although this particular paper is only limited to tensile failure, based on the minimum normal stress theory, the numerical model is also able to consider shear failure by involving a generalized three-dimensional anisotropic yield criterion. The design code enables the selection of the most optimum borehole orientation and wellbore fluid gradient to avoid fracture initiation. It is also useful in conducting sensitivity studies, particularly when the data is scanty. A remarkable finding by exercising such code was that fracture initiation is strongly dependent on the formation anisotropy; a contradiction to the current industry thinking.
A Numerical Study of Diphasic Multicomponent Flow
Authors: Van-Quy N. , Simandoux P. , Corteville J.
Published: December 2007

This paper describes a general multicomponent two-phase flow model, taking into account convection, diffusion and thermodynamic exchange between phases. The main assumptions are: isothermal one-dimensional flow; two-phase flow (gas and liquid); each phase may be represented by a mixture of three components or groups of components. Actually, a great many recovery problems cannot be pictured by usual models because the oil and, in many cases, the injected fluid are not simple fluids and may bring about exchanges of components that considerably modify their characteristics. This is why efforts are now being made to develop "compositional" or "multicomponent" models capable of solving such situations. Generalization of the model to more complex systems can be considered. Cases treated may be any type of single- and two-phase flow, in particular any miscible process (e. g., high-pressure gas drive, condensing gas drive, slug displacement) and any diphasic processes with high mass exchange (e.g., displacement by carbon dioxide or flue gas). This model is working and has been successfully checked by experiments.

Introduction

Many investigations, broth experimental and theoretical, have been made on the recovery of oil from reservoirs. With regard to mathematical models, most of those conceived up to now have dealt with oil recovery by the injection of a fluid that is miscible or immiscible with the oil. For miscible drives, single-phase flow with a binary mixture and miscibility in all proportions is involved. In such an ideal situation oil recovery is theoretically total. For immiscible displacements flow is diphasic. Capillary pressure and relative permeability play a preponderant role. Since irreducible oil saturation preponderant role. Since irreducible oil saturation is inevitable, oil recovery can never be total. Actually, a great many recovery problems cannot be pictured by such models because the oil and, in many cases, the injected fluid are not simple fluids and may bring about exchanges of components that considerably modify their characteristics. This is why efforts are now being made to develop "compositional" or "multicomponent" models capable of solving such situations. Such a model is described here. It is designed to handle the most general case of the displacement of one fluid by another. This model offers the following possibilities.
A General Pressure Buildup Theory for a Well in a Closed Drainage Area (includes associated paper 6563 )
Authors: Ramey H.J. , Cobb William M.
Published: December 2007

Pressure buildup analysis, when properly done, yields the same results nomatter which of the conventional methods is used. As illustrated here with aclosed square, general interpretation equations may be derived that are correctfor closed drainage regions of any shape.

Introduction

In 1935, Theis1 showed that buildup pressures in a shut-in waterwell should be a linear function of the logarithm of the time ratio(t+?t)/?t, and that the slope of the line is inverselyproportional to the mean formation effective permeability. Muskat discussedpressure buildup in oil wells in 1937, and proposed determination of staticpressure by a semilog trial-and-error plot that has been found to be applicableto a variety of buildup cases. In the late 1940's, van Everdingen presented aseries of lectures on well test analysis in the U.S. that related to aclassical study of unsteady flow by van Everdingen and Hurst.3 In1951, Horner4 presented a study of pressure buildup that appears tohave summarized fundamental efforts of a number of pioneering researchers inthe Shell companies. Horner also recommended a semilog buildup curve identicalwith the Theis curve, and presented a method for extrapolation to fully builtup static pressure for a closed circular reservoir. This sort of semilogpressure buildup plot is often referred to in the oil industry as a Hornerplot. About the same time, Miller-Dyes-Hutchinson5 presented ananalysis for buildup when the well had been produced long enough to reachpseudosteady, or true steady state prior to shut-in. Their work indicated thatbuildup pressures should plot as a linear function of the logarithm of shut-intime. As in the Horner plot, the slope of the straight line was shown to beinversely proportional to the permeability to the flowing fluid. It isinteresting that about the same time Jacob6 presented a similarapproach to determine aquifer transmissibility for a water well productiontest. Miller-Dyes-Hutchinson presented several important extensions of builduptheory. One was an initial attempt to apply buildup theory to multiphase flow. This problem was later resolved by Perrine.7 More important to thisstudy, an approach to extrapolation to fully built-up static pressure waspresented for outer boundary conditions of either no flow (closed), or constantpressure (water drive).

Thus, by the early 1950's, both Horner and Miller-Dyes-Hutchinson hadpresented methods for determining permeability and static pressure from buildupdata. Although there were similaries - both involved semilog plotting - therewere confusing differences between the methods. Perrine7 presented an excellentreview of this theory in 1956 that clearly indicates the state of understandingat that time. He stated that Horner-type plot (which he referred to as the vanEverdingen-Hurst method) was valid for a new well in a large reservoir, butthat the Miller-Dyes-Hutchinson approach was best for older wells in fullydeveloped fields. The latter is a widely held misconception.
A Coupled Rod and Fluid Dynamic Model for Predicting the Behavior of Sucker-Rod Pumping Systems—Part 2: Parametric Study and Demonstration of Model Capabilities
Authors: Lekia S. D. , Evans R. D.
Published: December 2007

Equations for predicting the behavior of sucker-rod pumping systems including the coupled dynamic effects of rod and fluid motion and kinematics of the surface pumping unit which were presented in Part I of this two-part paper series. These equations are used together with complementary sucker-rod system predictive formulas for parametric studies in this paper. Example problems are used to investigate the effects of well and fluid parameters on sucker-rod design parameters and the results are compared against calculations using the API Bulletin 11L3.
Building an Internet World Wide Web Server
Authors: Barnett A. A. , Bates F. G. , Russell J. E.
Published: December 2007

The World Wide Web (WWW) is the fastest growing client/server environment on the Internet. This environment consists of a group of software products and a set of protocols and conventions. The WWW environment, based on hypertext and hypermedia technology, allows intuitive, seamless, "point and click" access to and interaction with information distributed across the Internet. Many think of the WWW as solely responsible for transforming the way the Internet is accessed and used by millions of users worldwide.

Although the use of WWW "clients" is intuitive and seamless, the building and deploying of WWW "servers" is more complex and time-consuming. Both commercial and shareware/freeware WWW server software is available for most hardware and operating system configurations. Choosing the right server depends on your objectives. A Windows/DOS server is sufficient for providing access to small amounts of information to a small number of users. A commercial server with user authentication and encryption capability is required to provide wide area access to mission critical information residing in distributed databases.

This paper discusses WWW technology and describes how to choose and obtain a WWW server. We include many references to online resources and documentation, and we also discuss authoring tools.
An Experimental Investigation of the S.P. and Resistivity Phenomena in Dirty Sands
Authors: Wyllie M.R.J. , Southwick P.F.
Published: December 2007

The importance of the so-called "dirty sand" or "conductive solids" problem in electric log interpretation was first stressed in a paper presented in 1949. Since that time the problem has been generally recognized as a most serious one. Several research papers bearing on the theory of the effects of clay contaminants on reservoir rock resistivities have appeared. These papers, while contributing to the theory of the problem, have not offered any practical solution.

In the present paper an experimental investigation has been made of the effects of ion-exchange materials on the electrical properties of natural and synthetic porous media. The method used to make synthetic dirty sands is entirely novel and has proved a valuable guide to a better understanding of the properties of dirty sands generally. The effects of ion-exchange materials on both the resistivity and self potential (S.P.) logs have been examined. From the data obtained it has been possible to formulate a simple, practical method whereby electrical logs of dirty sands can be qualitatively interpreted. The method is in all essentials identical to that presently in use for interpreting clean sands. New light has also been thrown on the significance of the term formation factor when it is applied to dirty sands.

Introduction

In 1949 a paper was presented which showed that the presence of so-called "conductive solids" introduced considerable complexities into the analysis of the resistivities of dirty sands, i.e., permeable formations containing clay. The reduction of the self potential (S.P.) resulting from the presence of interlaminated shale or interstitial clay in permeable formations has been discussed by Doll.

Noteworthy papers which dilate further upon the effects of shale and clay on the resistivity of permeable formations are those of deWitte, Berg, Wyllie, and most recently, Winsauer and McCardell. The last authors have endeavored to elucidate the chemistry of the resistivity phenomena in dirty sands in terms of an adsorption hypothesis. Specifically, they attribute the electrolytic conductivity of shales and clays within a permeable formation to an ionic double-layer effect and, for this reason, regard the term "conductive solids" as a misleading one.

Some consideration has been given to the effect of dirty sands on the S.P. by Wyllie and by McCardell, Winsauer and Williams.
Leveraging Software Investment: Designing and Building Quality Software Products
Authors: Meikle D. E. , Campkin Michael , Grimley Brendan
Published: December 2007

Software investments represent a significant, if not dominant, proportion of the information technology cost within an oil and gas operating company. Technical software costs are particularly high because companies value specialized applications that have high development costs. Training and support for these applications drive up costs even more, especially if an application has not had rigorous quality control applied during its development process. Oil and gas operators then must dedicate additional internal resources for product support, which increases the product's real cost even further.

This paper shows the rigorous methods of quality control and assurance techniques involved in software development and testing and the benefits of these methods to the oil and gas technical applications’ investor. Our paper also illustrates how technical applications’ support cost may be reduced by designing quality and stability into the software through the application of quality control techniques during the specification, design, implementation, documentation, and testing phases. Lastly, we discuss the metrics we used to measure the quality of the software's performance.
Implementation of a World Wide Web Server for the Oil and Gas Industry
Authors: Blaylock R. E. , Martin F. D. , Emery Robert
Published: December 2007

The Gas and Oil Technology Exchange and Communication Highway (GO-TECH) provides an electronic information system for the petroleum community for exchanging ideas, data, and technology The PC-based system fosters communication and discussion by linking the oil and gas producers with resource centers, government agencies, consulting firms, service companies, national laboratories, academic research groups, and universities throughout the world. The oil and gas producers can access the GO-TECH World Wide Web (WWW) home page through modem links, as well as through the Internet. Future GO-TECH applications will include the establishment of "virtual corporations" consisting of consortia of small companies, consultants, and service companies linked by electronic information systems. These virtual corporations will have the resources and expertise previously found only in major corporations.