bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of Changing Backpressure Test Curves From Some Gulf Coast Area Gas Wells
Authors: Graham J.R. , Boyd W.E.
Published: December 2007

Estimates of gas well deliverability based on initial testing may be in error due to liquid saturation increases around the wellbore created by invasion of drilling and/or workover fluids. Flow coefficient C and exponent n of the backpressure test equation may change after a well has been placed on production. This change will depend on the degree and nature of saturation, and on properties of the reservoir being investigated. This article discusses examples of field test data obtained during the producing life of many Gulf Coast area gas wells. The data indicate a shifting of the backpressure curve, and show that deliverability may significantly improve after a well has been placed on production. This improvement is due mainly to an increase in the relative permeability to gas. Also discussed are time requirements for cleaning up a gas completion.

Introduction

Accurately predicting gas well deliverability is a common problem in the natural gas industry. These predictions are essential to any attempt at optimum operation of a gas-producing complex. The large investments required for additional deliverability demand that both current and future capabilities be known as accurately as possible for each well in a gas sales system so that a minimum of standby or backup deliverability is required. Future deliverability predictions become especially important since in many cases major additions of deliverability require at least 1 year of lead time for installing the required field equipment.

A large amount of data obtained during the past 10 years indicates that deliverability characteristics of a gas well may improve from an initial value after the well is placed on production. The noted improvements have been great enough to merit a thorough analysis of these data. This article presents results of this investigation in hopes that the conclusions will help provide the industry better answers to two basic questions concerning gas well test data:

- How reliable is initial backpressure test data for predicting future deliverability?

- Recognizing that liquid saturation increases around the wellbore caused by drilling and/or workover fluids will adversely affect backpressure test data, how long must a well be cleaned before this area of increased saturation is removed or reduced to a point where reasonably accurate test data can be obtained?
Application of Material and Energy Balances to Geothermal Steam Production
Authors: Whiting Robert L. , Ramey Henry J.
Published: December 2007

The material-energy balance developed in this study has been used successfully to match performance and to forecast production for the Wairakei geothermal field of New Zealand. The equations should be applicable to other geothermal fluid reservoirs, provided the assumptions used are realistic.

Introduction

The basic study from which this paper was prepared was started as the result of the growing need throughout the world for increasing quantities of energy in all forms. Quite obviously, natural forms of energy that are readily available at low development cost are those in greatest demand. The underdeveloped countries - and particularly those having little or no petroleum resources - are the countries in which the most interest is being shown in the newer energy sources. One of the least expensive energy sources is natural geothermal steam. Although this form of energy has been recognized for centuries, it has been only during the past 20 years that serious efforts have been made to harness it. Natural geothermal steam energy in Italy, New Zealand, Mexico, Japan, and California is now being produced through wells to drive turbines and generate electricity. Further, active exploration for natural geothermal steam is being conducted in Hawaii, Fiji, Taiwan, Chile, Russia, Greece, and Katanga.

It is surprising to find that most geothermal steam exploration is in the "steam seep" stage. That is, surface studies are made and exploratory wells are drilled in the general area of steam seeps. However, in the larger geothermal steam areas, there have been efforts to apply the most modern geological and reservoir engineering principles in order to define the reservoir parameters, particularly those relating to estimates of reserves and future productivity. This paper is concerned with the development of appropriate equations and techniques to facilitate these estimates.

Production of natural steam or hot water presents problems different from those experienced in the production of oil and gas. For example, steam or hot water systems may be essentially single-component systems, while hydrocarbon systems are most frequently multicomponent fluid systems. Heat effects are much larger for water than for hydrocarbon systems; and the natural steam production may or may not be isothermal, while production of petroleum reservoirs is considered normally to be isothermal. Petroleum reservoir engineering principles may be applied to natural steam or hot water reservoirs if the inherent differences in the systems are considered. The basic considerations involved in geothermal steam reservoir engineering are: thermodynamics, physical and thermal properties of water, materials and energy balances, fluid influx, and performance matching and predicting.

Thermodynamics

Fig. 1 is a pressure-temperature diagram for the liquid-vapor region for pure water, showing the critical point and five other points representing possible initial conditions for a geothermal steam reservoir.

JPT

P. 893ˆ
Measurements and Theoretical Models on Rig Suspension and the Effect on Drillstring Vibrations
Authors: Aarrestad T.V. , Kyllingstad A.
Published: December 2007

The top suspension system comprises the kelly, the swivel the drilling hook, the travelling block, the drill lines and the derrick. This paper includes measured high-rate data of accelerations and forces and a discussion on simple and more complex models for the top suspension system. The simple model of lumped mass and spring is shown to be insufficient for describing the boundary conditions for longitudinal drillstring vibrations. The two models for explaining the observed dynamics included in this paper are i) resonant derrick vibrations and ii) non-linear coupling to transversal drill lines vibrations.

Introduction.

Drillstring vibrations have been discussed in many publications during the last decades. There are several reasons for studying such vibrations, fatigue problems, improving rate of penetration, directional control and data transmission can be mentioned as examples. Drillstring vibrations do mainly occur due to bit-formation infractions or drillstring-borehole interactions.

In the present work a discussion on the boundary conditions for longitudinal vibrations are given. With a few exceptions publications on drillstring vibrations do not seem to be very much concerned about boundary conditions. An early paper on longitudinal and angular vibrations modelled the downhole boundary condition as a sinusoidal excitation of the displacement with a constant amplitude and the top boundary condition as a spring from the elasticity of the cables and a lumped mass of the travelling equipment. For most situations these two boundary conditions are relevant to get an overall idea of the problem. This paper has also contributed considerably in the understanding of drillstring vibrations and several later publications have used the same type of boundary conditions when modelling longitudinal drillstring vibrations.

In a recent paper a thorough discussion on some phenomena concerning the boundary condition at the bit was given. The authors conclude that a non-linear coupling between longitudinal and torsional vibrations may exist at the bit. In this paper a discussion of the boundary condition at the rig-floor for longitudinal vibrations is given. It is shown that real drillstring vibration data cannot be explained by the commonly used boundary condition. Two different possible explanations to the phenomena seen are discussed, i) the effect of internal rig vibrations and ii) a coupling between longitudinal drillstring vibrations and transversal vibrations in the drill lines.

The theory presented will be supported by measurements from Ullrigg. Ullrigg is a full-scale research drilling rig with dimensions similar to the rigs on off-shore installations.

P. 331^
Maximum Entropy Inversion of Induction-Log Data
Authors: Freedman Robert , Minerbo Gerald N.
Published: December 2007

This paper describes the development and application of some new algorithms based on the maximum entropy method (MEM) for inverting (i.e., deconvolving) induction-log data. The MEM has earned a reputation in many physical science fields as a technique that provides robust and accurate reconstructions of instrumentally blurred data. Dyos recently applied a MEM algorithm to the inversion of synthetic deep-induction-log data. This paper develops some new MEM algorithms that are applied to inversion of model data and to field data from the PhasorSM induction tool. The new algorithms overcome some of the limitations of previous inversion methods and inverse-deconvolution-filter techniques.

This paper examines two different MEM algorithms. The first algorithm is based on a functional used to study MEM inversions of synthetic data with a Doll approximation forward model. A second, more efficient MEM algorithm, based on a new Lagrangian functional, is used with an exact forward model to study the inversion of a field log and some model formations. Use of an exact forward model is essential in obtaining accurate and high-resolution MEM inversions in the presence of skin and shoulder effects. The MEM inversions of model data and field logs exhibit vertical resolution, accuracy, and stability that exceed those obtainable with state-of-the-art linear inverse filters.

An example of the MEM inversion of a field log in a formation with numerous high-contrast thin beds is discussed and compared with the spherically focused log (SFLSM) and the deep enhanced-resolution Phasor- (IDERSM-) processed log. The MEM inversion exhibits resolution comparable to that of the SFL. It is shown that, as a byproduct, the MEM provides synthetic logs that serve as a self-consistency check on both the quality of entered data and the validity of the Rt profile obtained from inversion.
Automatic Facility Safe Chart Generation Through the Use of a Computer-Aided Drafting System
Authors: Persky S. W. , Sargent G. L.
Published: December 2007

This paper describes the development, use, and purpose of a computer program designed to create safety analysis function evaluation (SAFE) charts. The SAFE chart generation program is designed to work in conjunction with advanced computer-aided drafting design (CADD)1, 2 software. This paper also describes many common problems that occur during manual creation of SAFE charts and explains how the program can reduce or, in some cases, eliminate these problems.
Field Evaluation of Acid-Fracturing Treatments Using Geometry Simulation, Buildup, and Production Data
Authors: Elbel J. L.
Published: December 2007

This paper presents evaluations of acid-fracturing treatments. When fracture penetration and conductivity obtained from the analysis of both pressure-buildup and production data agree, then the combinations of fluid loss and retardation factor, which are required for geometry simulation to agree with the penetration, are determined. These parameters and other engineering assumptions can be used in the design of future treatments.
The Nuclear Energy Impact on the Pacific Coast
Authors: Worthington J.D.
Published: December 2007

Nuclear energy as a generating source for electric power has become a commercial reality. Nuclear plants already in operation on the Pacific Slope have proven that nuclear energy is more economical than gas to generate machines. A history of the electric utility and the future plans for the use of gas and nuclear power as generating sources is presented.

Introduction

Commercial nuclear electric power is changing and challenging not only the electric industry, but also the associated industries that provide fossil fuels for the conventional thermal electric plants. The impact of nuclear power upon the uses of gas for electric power generation cannot be grasped without a clear understanding of the past. What has happened, and what is happening to challenge and change the electric industry in general, and where does its bright and promising new child, nuclear power, fit?

First, it must be recognized that one of the primary jobs in any business is to plan for the future. In the case of an electric utility, not only must it plan, but it must also convert those plans into action well in advance of the day a customer turns on another light or starts another motor. Seldom can the utility wait to commit itself to a new source of generation as late as 4 years in advance. It must make the commitment 5 or 6 years before the need for the energy has developed. Consequently, electric utilities are presently concerned with what kind of generations will be added to serve its customers 5 or 6 years from now. The gas industry is equally concerned with the electric utility's selection because that selection shapes future markets for gas.

The nuclear power industry, as much as any business in existence today, reflects the accelerating change in our world. In the early days, the nuclear power industry concentrated on research and the acquiring of experience with a new power source. Commercial feasibility seemed somewhat remote. Then, almost overnight, nuclear power became a full-fledged commercial reality. The process was dramatic and rapid - so much so that probably neither the gas nor electric industry has really been able to assess the impending impact of nuclear power upon the use of gas fuel in electric plants.

Today, with new electric power sources being planned, virtually all utilities are weighing carefully the merits of nuclear power. Many companies are choosing this new source of power. Many more might be doing so if it were not for the uncertainties of the long lead times currently caused by manufacturing and regulatory backlogs. The industry is pressing to remove these uncertainties so that every utility can make its selections with known and reasonable lead times.

It is really not possible to obtain a precise measure of the future impact of nuclear power because the electric utilities are not committed beyond 5 or 6 years. However, with a few assumptions, the signs for the future become fairly clear.
Artificial Lift With Coiled Tubing for Flow Testing the Monterey Formation, Offshore California
Authors: Peavy M. A. , Fahel R. A.
Published: December 2007

This paper provides a technical comparison of jet-pump and nitrogen lift during the drillstem tests (DST's) of a low-gravity, high-viscosity crude on a semisubmersible drilling vessel. Eight DST testing sequences are presented to demonstrate that jet-pump-lift operations are better suited than nitrogen-lift techniques for obtaining reservoir data during Monterey DST's.
Methodology for the Specification of Solvent Blends for Miscible Enriched-Gas Drives
Authors: Sibbald L. R. , Novosad Zdenka , Costain T. G.
Published: December 2007

Many Alberta EOR projects rely on injection of enriched natural gas to displace oil left by primary or secondary operations. An important practical design requirement in such projects is to specify the solvent—a blend of an expensive C2+ enriching stream (which varies in composition) and dry gas—to minimize the cost of the displacing fluid. This paper outlines the derivation with a new methodology of a C2+/dry-gas blending correlation for a large Alberta miscible flood. The blending correlation used data from rising-bubble apparatus (RBA) experiments, which allowed fast, precise determinations of solvent/oil miscibility. Before undertaking the derivation, the RBA test was shown to give the same results as the standard slim-tube experiment for the system studied. This correspondence was anticipated from previously developed theoretical concepts about the relevant mechanism of miscibility development. Proper description of the mechanism is crucial for correct interpretation of miscibility experiments. Equation of state (EOS) multiple-contact flash calculations and EOS-based compositional simulation of the displacement process were used to analyze miscibility development for this system. This conceptual understanding formed the basis for the use of the recently developed RBA technique to generate data for the blending correlation.
Treatment of Individual Wells and Grids in Reservoir Modeling
Authors: Van Poollen H.K. , Breitenbach E.A. , Thurnau D.H.
Published: December 2007

Reservoir modeling, mathematical modeling, or simulation of a petroleum or natural gas reservoir enables the engineer to examine and evaluate the physical a-nd economic consequences of various physical a-nd economic consequences of various alternative production policies.

Approximations are inherent in all workable, economical simulators. This paper describes three workable, useful approximations. (1)a method to compare observed field pressures with those calculated by a numerical simulator, (2) a method to reduce three-dimensional problems to two space dimensions with pseudo-third-dimensional features, and (3) a method to calculate the productivity index (PI) and the water-oil ratio (WOR) in a partially penetrating well partially penetrating well

These methods, although admittedly approximations, are workable and have been found to be very useful. Their general utility will, however, depend upon the extent to which any underlying assumptions used in their formulation apply to a particular problem. particular problem

Introduction

The objectives, applications and mathematical background of reservoir modeling have been described in other works.

Ideally networks should be as shown in Fig. 1. Here, the grids are smaller near the wellbore than farther away. However, the number of grid points becomes large, even in a two-dimensional grid. Also, the small block sizes force one to use very small time steps, which can increase the computer time to the point of rendering the study economically unfeasible. Fig. 1 shows an example where the wells are located on a regular pattern. If that pattern becomes irregular enough, all cells pattern becomes irregular enough, all cells eventually will have to be small.

In order to proceed with a study, modelers are forced to use linger grid sizes, as shown in Fig. 2.

We realize that, by using large grid sizes, the fundamental flow equations are not truly represented. The network approaches a set of interconnected material balances with flow terms as a function of pressures and saturations. This paper describes the present method of handling wellbores in models with grid sizes many times the wellbore diameters. A method to compare pressures observed in the field with those calculated in the model is presented.

A method also is given to reduce three- dimensional problems to two-dimensional grids.

SPEJ

P. 341
Workstations for the Wellsite: An Integrated Information Management System
Authors: Morley A. R.
Published: December 2007

This paper describes an innovative management system designed to assist drilling, engineering, and geological decision makers. The problem of providing powerful and flexible applications without creating complexity has been solved by an intuitive graphical user interface. Through the adoption of industry standards, an open system was designed to facilitate information input and output. Careful attention to emerging computer standards has resulted in a system that is portable across a wide range of current hardware from multiple vendors and that will be easily movable to new hardware platforms as they become available.
Case Study of an Executive Information System
Authors: Belcher L. W. , Hall D. L.
Published: December 2007

The value of information systems is best proved with the implementation of an executive information system (EIS). An EIS brings strategic information on activities of various operating units into a single, easy-to-use system for the executive. A properly functioning EIS will enhance the activities being monitored and the data generated by those activities.

The corporate EIS has been highly successful at some companies but not so successful at others. This paper describes a very successful EIS, exemplified by its implementation and active use outside the corporate headquarters and beyond the executive suites. This paper describes the use of this EIS and suggests critical success factors in its implementation.
Interactive 2D Basin Modeling on Workstations
Authors: Fjeldskaar W. , Mykkeltveit J. , Johansen H. , Langfeldt J. M. , Christie O. H. J. , Tyvand P. , Skurve O. , Bjørkum P. A.
Published: December 2007

Basin modeling, the modeling of physical and chemical processes that cause oil and gas generation in sedimentary basins, is a valuable tool in the search for new reservoirs. It traditionally has been run on minicomputers or mainframes because of the demand for high processing power. With the increasing processing capability of today’s PC’s and workstations, the road is open for moving basin modeling to where it belongs, to the geologist doing the basin modeling.

The 2D basin-modeling system presented here has emphasized standardized software, with UNIX as its operating system and X-Windows for interactive graphics. Thus, the basin modeling software fits into the open environment with systems ranging from PC’s to mainframes, thus making basin-modeling tools available to the geologist.

The system is modular; i.e., each geological process is represented as an independent module. The user has full control over the modeling process, can modify parameters, and can monitor the results between each step of the modeling process.

A geohistory module reconstructs the sedimentary basin through time, taking into account the progressive sediment compaction. The fault blocks can be moved by a fault-balance module to balance the profile. The subsidence resulting from sediment weight is computed by the isostatic module, which, together with a tectonic module, provides an estimate of the paleo heat flow in the basin. The paleo heat flow is an important input parameter for the thermal module, which computes the basin’s thermal history. The kinetic module is used to compute the timing and amount of petroleum generation.
CT Determination of Heterogeneities and Miscible Displacement Characteristics
Authors: Wlthjack E. M. , Graham S. K. , Yang C-T.
Published: December 2007

This paper presents a computer tomography (CT) method for determining small-scale permeabilities in rock cores. Correlation of small-scale permeability and porosity demonstrates a CT capability for core characterization. CT-monitored miscible corefloods investigate the influence of heterogeneities and the mobility ratios on sweepout.
Unit Mobility Ratio Displacement Front Passing a Circular Permeability Discontinuity
Authors: Parsons R.W.
Published: December 2007

When a displacement front encounters an isolated permeability heterogeneity, it will be perturbed permeability heterogeneity, it will be perturbed The details of this perturbation will depend on the heterogeneity size and shape, the permeability contrast, and the mobility ratio.

This paper deals with the displacement front behavior for one, simple, mathematically tractable model: a circular permeability discontinuity and unit mobility ratio. The progress of an initially planar front is shown or four permeability planar front is shown or four permeability contrasts: k2/k1 = 0, 1, 2,... The front distortion is more pronounced than streamline and isopotential distortion and it approaches a constant shape downstream from the discontinuity.

Introduction

The impact of reservoir heterogeneities on oil displacing processes depends upon the variation of the heterogeneous property (frequency distribution), its disposition (spatial distribution), and the inherent stability of the displacement mechanism. The interplay of these factors plus the impracticability, if not impossibility, of describing a natural rock system in any detail makes exact displacement front movements difficult to determine.

It is useful, however, to be able to qualitatively visualize what heterogeneities will do to a displacement front. In this respect certain simple models that can be treated analytically are of value. The following analysis will show the displacement front behavior for one such model.

MODEL DESCRIPTION

The flow field two-dimensional and infinite in extent. The fluid flow is single phase, steady state and unidirectional at x, y - +/- 00, or before insertion of the discontinuity. A circular permeability discontinuity is placed at the origin. permeability discontinuity is placed at the origin. Porosity and thickness are the same within and exterior to the Porosity and thickness are the same within and exterior to the heterogeneity. This is exactly the same model that was used by Greenkorn et al. to check analytically streamlines as determined by Hele-Shaw flow models and finite difference computer techniques.

FRONT POSITION CALCULATIONS

The results of displacement front calculations are presented in Figs. 1 through 4 for four different permeability contrasts: k2/ki = 0, 1/2, 2. m. The permeability contrasts: k2/ki = 0, 1/2, 2. m. The times corresponding to the front locations are the same for the 0 and oo cases, and for the 1/2 and 2 cases.

The determination of front positions at various times is based on known analytical expressions for velocity potentials (phi) and stream functions (psi).

SPEJ

P. 347
A New Model for a Fractured Well in a Radial, Composite Reservoir
Authors: Chu Wei-Chun , Shank G. Deane
Published: December 2007

A flow problem was identified by using a pressure-derivative technique to analyze several hundred pressure-falloff tests from the Big Hom basin. To handle the problem, a new analytic model was developed to allow direct analysis of fractured wells with either finite conductivity or uniform flux in a radial, composite reservoir. In this paper, we demonstrate that this simple model further explains the buildup-pressure behavior of a fractured well producing below dewpoint pressure in a gas-condensate reservoir.
An Application of the Product-Solution Principle for Instantaneous Source and Green's Functions
Authors: Chen H. Y. , Poston S. W. , Raghavan Rajagopal
Published: December 2007

Basic building blocks to apply the product-solution method in the Laplace domain are derived. Example applications illustrate the utility of these building blocks. These solutions should be useful in applying computer algebra to develop pressure distribution in reservoirs.
Analysis of Bimetallic Pipe for Sour Service
Authors: Kane Russell D. , Wilhelm S. Mark , Yoshida Toshio , Matsui Shigetomo , Iwase Toshinori
Published: December 2007

This paper presents the results of laboratory investigations conducted to better our definition of the serviceability of bimetallic pipe manufactured by the thermohydraulic (tight-fit) method for Mobile Bay service. Both Alloy 625/API X-65 and Alloy 825/API X-65 tight-fit pipe (TFP) were evaluated under conditions of (1) standard corrosion test environments to evaluate the metallurgical conditions of the corrosion-resistant-alloy (CRA) liner tubes, (2) long-term, full-scale TFP exposure under a simulated Mobile Bay production environment containing high levels of H2S and CO2, and (3) hydrogen-permeation experiments designed to examine potential effects of CRA liner collapse from hydrogen produced by corrosion on the ID and/or cathodic protection on the OD. Results indicate that bimetallic TFP exhibited an acceptable metallurgical condition of the CRA liner materials. Under the simulated Mobile Bay production environment, TFP exhibited good resistance to general corrosion, stress-corrosion cracking (SCC), and liner collapse. Hydrogen-permeation tests indicate that very conservative estimates of service-life liner collapse from interfacial hydrogen pressure range from 150 to more than 800 years, depending on conditions. For all practical purposes, liner collapse from hydrogen is not a limiting factor for TFP flowline applications.
Automated Rock Characterization With SEM/lmage-Analysis Techniques
Authors: Clelland W. D. , Fens T. W.
Published: December 2007

This paper describes the use of a scanning electron microscope (SEM)/X-ray/image-analysis system to perform automatic petrographic analyses of sandstone samples. The methods developed involve the combined use of backscattered-electron (BSE) imaging and X-ray analysis with image-analysis procedures to quantify the mineralogy, grain texture, and pore structure of polished rock samples. The procedures are fully automated and, once set up, can be run without operator involvement (e.g., overnight). A wealth of quantitative data can be obtained with this single approach, providing useful information for many fields of petroleum engineering (diagenetic studies, prediction of physical properties, etc.). These methods should help replace, at least partially, the tedious and time-consuming manual petrographic methods currently used.
Viscosity, Density, and Composition Measurements of CO2/West Texas Oil Systems
Authors: Lansangan R. M. , Smith J. L.
Published: December 2007

Shear viscosity coefficients, volumetric properties, and equilibrium-phase compositions for CO2/West Texas oil mixtures are presented. Effects of solution gas, nitrogen in the CO2 stream, and viscosity dependence on phase density and CO2 concentration also are examined. The work shows that measured CO2-rich phase viscosities increased as solution gas in the oil increased. Nitrogen in the CO2 stream results in lower CO2-rich phase viscosities and densities compared with those from an identical run with pure CO2 solvent. CO2/crude-oil viscosity measurements reveal viscosity and density behavior patterns that are unique to these systems. Undersaturated CO2/crude-oil mixtures show an abnormal viscosity dependence on density. The viscosities show a monotonic decrease, while the densities increase with continued dilution of the oil with CO2. The equilibrium vapor (dense fluid) and liquid phases, however, exhibit normal viscosity/density behavior. Data are compared with a popular reservoir-fluid-viscosity correlation commonly used to estimate CO2/crade-oil viscosities in reservoir simulation studies. We show that the correlation cannot predict CO2/crude-oil-system viscosities accurately.
Compatibility of Hydrosoluble Polymers With Corrodible Materials
Authors: Audibert Annie , Lecourtier Jacqueline
Published: December 2007

Application of water-soluble polymers in the oil industry (e.g., fluid-loss reducer, polymer flooding, and water-based drilling muds) requires hydrosoluble polymers to be compatible with corrodible materials. The behavior of polyacrylamides and xanthans in the presence of various materials used for oil production (steel, stainless steel, carbon steel, and Inconel™) has been studied vs. different water salinities, oxygen contents, and temperatures. The influence of such commonly used additives as oxygen scavengers and sequestrants on corrosion and polymer stability has also been investigated. For both types of polymers, as corrosion occurs under anaerobic conditions, strong interactions between polymer chains and divalent cations (Fe2+ or Ni2+) are observed. Such interactions also depend on polymer quality. In the presence of oxygen, corrosion induces a molecular-weight degradation of the polymer followed by a gelation process for xanthan. Some additives may accelerate the transformation of Fe2+ to Fe3+, thus inducing polymer degradation, but this reaction depends on the nature of the chelating agent. These results provide guidelines for the implementation of polymers in oil production, including the selection of materials, water treatment, or mud formulation.
Interpretation of Laboratory Gasfloods With Multidimensional Compositional Modeling
Authors: Mohanty K. K. , Johnson S. W.
Published: December 2007

Corefloods were conducted and simulated to evaluate oil recovery from field cores by injection of hydrocarbon solvents. Heterogeneity and fingering were evaluated separately by conducting computed-tomography (CT) -aided single-phase stable and unstable floods. In the absence of bypassing, oil displacement by an equimolar mixture of C2, propane, and butane (C234) is first-contact miscible and C2 (C2) flood is multicontact miscible. In corefloods, heterogeneity and fingering cause oil bypassing. Bypassed oil remains miscible with injectant C234 but becomes immiscible with injectant C2. Two heaviest pseudocomponents drop out in the bypassed region to form a residual oil saturation (ROS) of ≈ 25%.
Use of a Massively Parallel SIMD Computer for Reservoir Simulation
Authors: Rutledge J. M. , Jones D. R. , Chen W. H. , Chung E. Y.
Published: December 2007

Massively parallel single-instruction, multiple-data (SIMD) computers have shown much promise in solving numerically intensive problems ranging from molecular modeling to computational fluid dynamics. Much of the research on the use of parallel computing for reservoir simulation, however, has been limited to coarse-grain, shared-memory computers or medium-grain hypercubes. We report here on research performed on a massively parallel SIMD computer with 65, 536 processors.

This work addresses issues in machine architecture, programming environment, and formulation of a reservoir simulator on SIMD computers. Toward this end, a three-phase, 3D, implicit-pressure, explicit-saturation (IMPES) compositional simulator was developed in FORTRAN 90. Problems associated with reservoir simulation on SIMD computers (such as an appropriate data structure for the SIMD architecture, treatment of multiple fluid phases, data communication, and the matrix solution) are addressed in this paper. In addition, table lookup poses a unique problem for SIMD computers because storage of large tables on each processor is impractical, as is the use of the front-end computer to perform this function. The problem is overcome through a novel use of local memory access.

We found that massively parallel computers can be used to run very large reservoir models and that the cost of data transfer between processors need not be prohibitive. Reservoir models with two hydrocarbon components and up to 2, 097, 152 gridblocks were run successfully with this simulator. Computational speeds on the order of 1 GFLOP's (1 giga floating point operations) were achieved for the generation of the Jacobian matrix and the matrix solution with 65, 536 processors.
Production Decline Curves for Low-Pressure Gas Reservoirs Undergoing Simultaneous Water Production
Authors: Mohaghegh Shahab , Bilgesu H. I. , Ertekin Turgay
Published: December 2007

A family of production decline curves for low-pressure gas reservoirs are presented for radial flow geometry with closed outer boundary and with a centrally located well. The proposed production decline curves are applicable to conventional gas reservoirs that produce gas and water simultaneously. The proposed decline curves exhibit unique characteristics for a variety of reservoir and fluid properties and pressure, specifications at the well. The performance of the proposed decline curves were investigated against two different numerical simulators, and they were found to be capable of predicting the production of conventional gas reservoirs under two-phase flow conditions with good accuracy.

The decline curves presented in this paper have the potential of providing a practical tool by which production performance of gas reservoirs under two-phase flow conditions can be predicted for pragmatic purposes without using sophisticated numerical models.
A Convective-Heat Transfer Model for Underground Combustion
Authors: Kuo C.H.
Published: December 2007

In the underground combustion process, part of the heat generated at the combustion front is carried downstream by convection. Temperature distribution in the combustion process can be obtained by including a delta function for heat generation at the combustion surface. This is similar to the hot-fluid injection model of Lauwerier. The dimensionless temperature in the reservoir, phi T1(x, t), and the overburden, phi T2(x, y, t), are as follows:

..........................................(1)

..........................................(2)

The ratio R of the heat-front velocity, u, h, to the combustion front velocity, uc, is one of the most important factors governing the temperature distribution in the pay zone. For cases of ub less than uc, no heat is carried ahead of the combustion front and the temperature at the combustion front remains constant for all times. The fraction of the heat stored between the heat front and the combustion front decreases as the time increases. This is because more of the heat is consumed in heating the formation behind the heat front and in heating the cap and bass rock.

A more advantageous condition obtains for uh is greater than uc. For this case, the formation ahead of the combustion front is preheated and the amount of heat in this region increases with time. Therefore, due to heat generation and preheating, the total temperature rise at the combustion front also increases with time. Eq. 1 also shows that the temperature at the combustion front is higher at a given time for a thinner reservoir. This seemingly paradoxical result takes place because the amount paradoxical result takes place because the amount of heat recovered from the overburden and subrock upstream of the combustion front is almost independent of the pay zone thickness. On the other hand, this heat is distributed in the pay zone, which has a heat content directly proportional to the formation thickness b. For thin reservoirs, therefore, the temperature rise in the pay zone due to heat recuperation is higher than that in thick reservoirs. For very thick pay zones (h-oo) there would be no heat recuperation, and consequently the combustion- front temperatures would be lowest.

For many cases encountered, uh is smaller than uc. Convective-heat transport. ahead of the combustion front can be achieved by increasing uh to obtain the condition uh, >uc. The wet and partially quenched combustion processes have a similar objective. The temperature at the combustion front, however, decreases as the uh/uc ratio increases. If this temperature should fall below the ignition point, the fire would die out. Consequently, at any point, the fire would die out. Consequently, at any time there exists a maximum ratio of uh/uc for which the formation ahead of the combustion front can be heated to increase oil mobility while combustion is maintained.

For the case where the heat front moves faster than the combustion front (uh is greater than uc), the downstream heat efficiency E can be derived by applying the integration method given in Ref. 3.

P. 323
Evaluation of Residual Oil Saturation After Waterflood in a Carbonate Reservoir
Authors: Verma Mahendra K. , Boucherit Michel , Bouvier Lucienne
Published: December 2007

Four different approaches, including special core analysis (SCAL), log-inject-log, thermal-decay-time (TDT) logs, and material balance, were used to narrow the range of residual oil saturation (ROS) after waterflood, Sorw, in a carbonate reservoir in Qatar to between 23% and 27%. An equation was developed that relates Sorw with connate-water saturation, Swi, and porosity.
An Investigation of the Flow Regime for Hele-Shaw Flow
Authors: Smith R.C. , Greenkorn R.A.
Published: December 2007

Hele-Shaw cells are used to model creeping flow through porous media (where Darcy's law is valid). The effects of inertia on flow about obstructions in a Hele-Shaw cell can be calculated by a perturbation method if one can determine a solution to Laplace's equation.

Results of a computer solution for flow about circular, square and elliptical obstructions are presented These results show that for a modified presented These results show that for a modified Reynolds number of less than 1, the inertia terms are small; and for values of less than 3, the average streamline predicts the ideal flow. Therefore, the analogy might be used for studying flow in porous media up to a modified Reynolds number of at least 3.

Introduction

The nature of fluid flow in porous media is of interest in the fields of soil mechanics, ground water flow, petroleum production, filtration and flow, in packed beds. Because it is very difficult to study the phenomenological behavior of flow in porous media, homologs and analogs are used to study flow characteristics. A Hele-Shaw model, made of two closely spaced plates - usually glass - is often used as an analogy to two-dimensional flow in porous media. Hele-Shaw showed experimentally that the streamline configuration for creeping flow around an obstacle located between two closely spaced parallel plates is the same as for two-dimensional parallel plates is the same as for two-dimensional ideal flow about the same obstacle. Stokes verified these observations mathematically. The usual equation of motion for flow in porous media is Darcy's law. The form of the mathematical statement of Darcy's law is identical, within a multiplicative constant, to the expression for the average velocity over the place gap in the plane of a Hele-Shaw model. These models may be used to describe flow in both homogeneous and heterogeneous porous media.
Inflow Performance of Horizontal Wells
Authors: Goode P. A. , Kuchuk F. J.
Published: December 2007

This paper presents formulas for evaluating the inflow performance of a horizontal well in a rectangular drainage region bounded above and below. The upper boundary may be either sealed to flow (no flow) or at constant pressure (e.g., gas cap). The well can be placed anywhere within the drainage volume and be of any length. The inflow-performance formulas for horizontal wells presented in the literature make certain limiting assumptions about the well relative to the size of the drainage region, the formation thickness, and the well location. In addition, simplified formulas are derived that are applicable over a wide range of practical interest for a variety of reservoir geometries.
Long-Term Gas Deliverability of a Dewatered Coalbed
Authors: Seidle J.P.
Published: December 2007

Gas and water production from a coal deposit can be divided into three distinct stages. In the first, gas and water production rates are almost constant. The second stage, beginning production rates are almost constant. The second stage, beginning once pseudosteady state is reached, is characterized by a "negative decline" in gas production rate and a declining water rate. The third stage begins when the peak gas rate is reached. This final stage spans most of the economic life of a coal well and is characterized by a gentle decline in gas rate and negligible water production. Gas production in this stage is described by two production. Gas production in this stage is described by two equations. The first is a gas-deliverability equation using the real-gas pseudo pressure developed by Al-Hussainy et al. This equation is applied to published data from a well in the Deerlick Creek field in the Warrior basin of Alabama. The second is a mass-balance equation combining elements from conventional and shale gas reservoirs. The two equations can be coupled to predict gas rates and recoveries of dewatered coal wells. Published simulation results from the Warrior basin Brookwood field and a San Juan basin coal well are compared. The deliverability equation also is used to construct gas-deliverability curves for a typical Brookwood coal well. The method presented here is applicable to coal wells completed in dry coalbeds.

Introduction

An important characteristic of a gas well is its deliverability over the course of reservoir depletion. A considerable body of literature describes conventional gas-well behavior mathematically. Theoretical aspects of wells completed in conventional dry gas reservoirs have been discussed thoroughly. Gas flow in porous media can be described by three methods: pressure, pressure-squared, and the real-gas pseudo pressure of Al-Hussainy et al. and Al-Hussainy and Ramey. While the last method is more cumbersome to use than the first two, it is more rigorous and is the only reliable method when large drawdowns exist. This paper shows that the traditional real-gas pseudo pressure can be extended to describe gas deliverability of a dewatered coal well.

Coal deposits are naturally fractured gas reservoirs. Initially, the natural fractures, or cleats, of the coal typically are water saturated and the coal matrix adsorbs most, if not all, of the gas. Coal gas is mostly methane with minor amounts of CO2, nitrogen, and heavier hydrocarbons, similar to dry natural gas from conventional reservoirs.

Wells completed in coal deposits progress through three distinct stages, as Fig. 1 illustrates. In the first stage, gas and water production rates are almost constant. The second stage is characterized by a negative decline in gas production rate and a declining water rate. Once the peak gas rate is attained, the third stage of production begins where the gas production rate shows a gentle decline and water production is often negligible. This final stage spans most of the economic life of a coal well.
New Single-Well Test for Determining Vertical Permeability
Authors: Burns William A.
Published: December 2007

A short-term vertical interference test between isolated sets of perforations in the same well can be used to determine the vertical perforations in the same well can be used to determine the vertical and horizontal permeabilities of each tested interval as well as to determine the effectiveness of tight streaks as barriers to vertical flow.

Introduction

Vertical flow is an important mechanism in many petroleum reservoirs. Yet no adequate method has petroleum reservoirs. Yet no adequate method has heretofore been proposed for determining the in-situ vertical permeability in a reasonable length of time. Core measurements of vertical permeability do not necessarily represent effective in-situ values. Cores may be representative of only localized pockets of high or low permeability, and total reliance on cores night cause one to overlook the presence of vertical fractures altogether. Conventional single-well tests, interference tests, and pulse tests commonly are used to determine horizontal transmissibility, k(h)h/mu, but generally are not designed to measure vertical transmissibility or other groups containing vertical permeability, k(v). permeability, k(v). A new well test described here provides a measure of in-situ vertical permeability as well as the previously measurable horizontal permeability. This previously measurable horizontal permeability. This "vertical test" determines the vertical diffusivity, k(v)/phi c mu, and horizontal transmissibility, k(h)d(1)/mu (where d(1) is the length of injection or production perforations). The test is basically a production perforations). The test is basically a short-term interference or pulse test normally lasting less than a day. Conventional down-hole equipment is used between two isolated sets of perforations in the same well, as shown in Fig. 1. A "layer-cake" description of a reservoir can be obtained by running two or more vertical tests in the same well, each over different vertical intervals. Each test can be analyzed for the effective vertical and horizontal properties of the interval tested. In addition, a vertical well test can determine the effectiveness of a shale barrier or tight zone by testing across it. Field use to date of vertical testing has confirmed its utility in reservoir description.

Mathematical Basis

Interpretation of vertical tests for k(v) and k(h) is based on comparison of measured pressure response with computer-generated response. Pressure behavior during a vertical test in a homogeneous, anisotropic, infinite-acting reservoir (infinite in radial extent and bounded in both directions vertically) is given by the diffusion equation for slightly compressible fluids with negligible gravity effects.,.........(1)

with the boundary and initial conditions

= 0, ..........(2)

lim,.....(3)

lim,

,....(4)

,........................(5)

,........................(6)

JPT

P. 743