bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion Attendant Sodium/ Hydrogen Ion Exchange in Reservoir Sands
Authors: Jensen J. A. , Gillis J. V. , Radke C. J.
Published: December 2007

Chromatographic lag observed upon injection of dilute alkali into reservoir sands is now well explained in terms of sodium/hydrogen ion exchange. However, the spread of the eluting hydroxide is more extreme than that associated with axial dispersion. We postulate an additional mass-transfer resistance caused by molecular diffusion in a microporous clay fraction. A quantitative model for this diffusion resistance is presented that compares favorably with experimental hydroxide histories from a water-saturated Berea sandstone. Both thin-section and scanning electron microscope (SEM) examination of the Berea rock confirm the presence of microporous regions of clay fines.
Laboratory Studies of Microscopic Dispersion Phenomena
Authors: Blackwell R.J.
Published: December 2007

This paper presents the results of a laboratory investigation of the process by which one fluid is displaced from a porous medium by a second fluid which is miscible with the first. The study included investigations of the microscopic mixing processes and of the gross displacement behavior. The results of this study are useful in scaling small bench-scale models or reactors to represent larger systems such as oil reservoirs or large, fixed bed reactors.

Mixing in both the direction of flow and perpendicular to the direction of flow was measured in sand-packed columns. Dispersion coefficients were calculated from data obtained over a range of rates for various fluid pairs and sand-grain sizes. The data are presented by plotting the ratios of the dispersion coefficients divided by the molecular diffusivity vs a dimensionless parameter relating the forward transport by convection to lateral transport by diffusion. It was found that both longitudinal and lateral mixing are governed by molecular diffusion at low rates and by convection at high rates. At high rates, however, the lateral dispersion coefficients are about 1/24th those in the longitudinal direction. The ratio of lateral to longitudinal dispersion coefficients is compared with that predicted by various mathematical models of the pore system in a packed bed.

The use of dispersion coefficients in scaling laboratory models to represent solvent floods in oil reservoirs is discussed briefly.

Introduction

The physical processes involved in the displacement of one fluid from a porous medium by a second fluid which is miscible with the first are fundamentally important in many diverse fields. For example, chemical engineers have been particularly concerned with the relationship of such fundamental aspects of displacement processes as the distribution of heat and mass, and the effect of fluid mixing on reactor efficiency. The specific problem of fluid mixing in fixed bed reactors has been investigated by Bernard and Wilhelm and others. Because high reactor efficiencies often require turbulent motion of the fluids within the individual flow channels of the porous medium, the emphasis in most of these studies has centered on fluid mixing in the turbulent or almost turbulent flow regimes. The mixing between miscible fluids in the laminar flow regime at very low Reynold's numbers is of particular interest in the field of and in recovery of oil.
Stresses Caused by Bit Loading at the Center of the Hole
Authors: Cheatham J.B. , Wilhoit J.C.
Published: December 2007

Although an oil well is a long cylindrical hole with an irregular bottom, it appears likely that the nature of the stress concentration at the bottom of the hole can be ascertained from an analysis of the stresses around a short cylindrical cavity with rounded corners and smooth bottom. Such a cavity is studied primarily because it leads more readily to a solution to the problem by the use of stress functions in this paper the stress distribution around a short cylindrical cavity subjected to bit loading, overburden and drilling fluid pressures is determined by means of an analytical solution which approximately satisfies the boundary conditions of the problem. From this solution the stresses at the corner of the hole are calculated to be about 35 per cent lower than comparable results obtained by photoelastic and relaxation analyses. This difference is apparently due to the large radius of curvature at the corner of the cavity in the present analysis. Since good agreement is obtained between the results of this analysis and the stresses calculated for a similar loading on a semi-infinite elastic solid, it is concluded that the bit action in the region near the center of the hole is not appreciably affected by the presence of the sides of the hole.

Introduction

Much has been written concerning drilling "under down-hole conditions" and pertaining to the stress distribution in the rock at the bottom of an oil well. For example, it is known that identical rocks can be drilled more rapidly at the surface than under subsurface conditions of pressure and stress. Information on the behavior of rocks under loading can be obtained from triaxial test data. From such tests it is found that rocks exhibit brittle failure when the confining pressure and pore pressure are equal, but the mode of failure may change to ductile as the difference between the confining pressure and the pore pressure is increased. Brittle failure implies that there is very little permanent deformation before fracture, whereas ductile failure indicates that permanent deformation takes place before fracture. Some rocks are ductile at differential pressures of 5,000 psi, but other rocks are brittle even at differential pressures of more than 50,000 psi.
Corrosion and Cracking of Steel in Production of Gas With Liquid H2S and Brine
Authors: Mlyssaka Aklhiro , Denpo Kozo , Ogawa Hiroyuki
Published: December 2007

Laboratory autoclave tests were carried out to investigate the corrosion and cracking behaviors of steels in brine- saturated liquid HjS. Traditional low-alloy steels and 13% Cr steel underwent severe corrosion and sulfide stress cracking (SSC). On the basis of the test results, anti-SSC steel and high-chromium and -molybdenum stainless steel were selected as candidate materials for the environments. The corrosion mechanism of steel in the solution was attributed to the promotion of cathodic reaction of H2S reduction resulting from the catalytic effect of water in liquid H2S.
Corrosion Reduction in Production Tubing With the Aid of a Phase-Equillbrium Model
Authors: Reinhardt J. R. , Powell T. S.
Published: December 2007

A model is described that predicts where the corrosion of production tubing caused by condensed water in gascondensate wells is most likely to occur. The prediction is made by combining flash equations and thermodynamic equilibrium principles within a computer algorithm for use with a personal computer.
An Approximate Method for Determining Areal Sweep Efficiency and Flow Capacity in Formations with Anisotropic Permeability
Authors: Mortada M. , Nabor G.W.
Published: December 2007

The effects of anisotropic or directional permeability on the areal sweep efficiency and the flow capacity are examined. The paper points out the importance of taking directional permeability into consideration in planning a flood. It analyzes the two-dimensional flow pattern associated with the skewed line drive for a unit mobility ratio. The direct and staggered line drives are treated as special cases of the skewed line drive. Analytical expressions are developed for the areal sweep efficiency at breakthrough and the flow capacity. They are related to the spacing between like wells, the distance between a row of injectors and the nearest row of producers, and the degree of skewness of the line drive. The latter quantity is defined such that it is equal to zero for the direct line drive and equals one-half for the staggered line drive. The a real sweep efficiency and the flow capacity depend also on the orientation of the flood pattern with respect to the principal axis of anisotropy. The paper provides a simple method for determining the a real sweep efficiency and the flow capacity for a formation in which the permeability in the bedding plane is anisotropic.

Introduction

Directional or anisotropic permeability is manifested by the ability of the formation to conduct fluids more readily along certain preferred directions. This situation occurs in many producing formations and is usually attributed to depositional features in which the sand grains are oriented in a preferred direction. In some cases it results from the formation of a major and a minor fracture system. Directional permeability should be taken into account in many phases of the production and exploration activities. Recognizing its existence in the formation of interest and planning accordingly can lead to increased recovery and substantial savings. For instance, the areal sweep efficiency in a water flood depends to a great extent on the orientation of the flood pattern with respect to the principal axis of permeability. Anisotropic permeability is specified by the directions of its three principal axes and the permeability along each axis. The principal axes of permeability are mutually perpendicular. This paper deals with the areal sweep efficiency at breakthrough and the flow capacity for formations with anisotropic permeability. The flood pattern considered consists of alternate rows of injecting and producing wells. The rows of wells are parallel and form a developed, skewed line drive which is illustrated in Fig. 1. The staggered and direct line drives are treated as special cases of the skewed line drive.
The Response of the Electromagnetic Propagation Tool to Bed Boundaries
Authors: Anderson Barbara I. , Safinya Kambiz Ali , Habashy Tarek M. , Davidson Andrew , Gilmore Rowan
Published: December 2007

Because of its high vertical resolution, the electromagnetic propagation tool (EPTSM) has proved to be valuable in thin bed analysis, in addition to its primary use in determining water-filled porosity. Using computer models corroborated by experimenta data, we analyze the response of the EPT to bed boundaries, showing that thin beds just under 2 in. [5.08 cm] can be resolved, and the response to even thinner beds may be predicted.
Well-Test Analysis for Solution-Gas-Drive Reservoirs: Part 2—Buildup Analysis
Authors: Serra Kelsen V. , Peres Alvaro M. M. , Reynolds Albert C.
Published: December 2007

This work presents new analysis methods for pressure-buildup data from a well completed in a solution-gas-drive reservoir. New procedures for estimating effective phase permeabilities as functions of pressure and saturation are presented.
Modeling of Acid Fracturing
Authors: Lo K. K. , Dean R. H.
Published: December 2007

The paper presents a theoretical framework for modeling acid fracturing stimulations. Starting from the fundamental equations of fluid mechanics, fracture mechanics, convection, and diffusion, the paper outlines the steps necessary to derive simplified equations for an acid fracturing model. Unlike some existing models, the coupled problem of fracture geometry, acid transport, and diffusion is solved simultaneously in this paper. Although an infinite reaction rate is assumed in the solution of the problem, an empirical correlation is used to account partially for finite reaction rates. Errors in the governing equations of some of the existing models are identified. To assess the accuracy of the approximations used in the present model, exact solutions are used for comparison. Predictions from the present model are compared with a model in the literature, and the results are found to be in reasonable agreement. As in all existing acid fracturing models, not all the phenomena of the acid fracturing process have been incorporated into the present model. Nevertheless, the present model is improved over existing models because it is derived from fundamental equations and thus forms a basis from which further improvements can be made.
Lagrangian Formulation for Penny-Shaped and Perkins-Kern Geometry Models
Authors: Lee W. S.
Published: December 2007

Basic theories for vertical penny-shaped and Perkins-Kern (PK) geometry models have been developed with a Lagrangian formulation combined with a virtual-work analysis. The Lagrangian formulation yields a pair of nonlinear equations in Rf or Lf and bf, the fracture radius or length and half-width. By introduction of a virtual-work analysis, a simple equation is obtained that can be solved numerically. This equation is written in a form that can be used to determine fracture geometry when the fluid-loss coefficient of the fracturing fluid is known. Also, this equation, coupled with a material-balance equation after shut-in, can be used to analyze pressure-decline data after shut-in to determine the effective fluid-loss coefficient and fracture geometry.

Geometry prediction of the new theory agrees well with other methods for the same models. A unique advantage of this approach, however, is that the geometry estimated from prefracturing design is consistent with the geometry determined from the pressure-decline analysis. Thus, it allows the engineers in the field to predict precisely the amount of fracturing fluid required for a designed fracture radius or length in a full-scale treatment from information gained in a minifracture treatment.
The EMSU Waterflood Project: A Case History of Infill Drilling, Completions, and Workovers
Authors: Mitchell R. K. , Salvo G. S.
Published: December 2007

The Eunice Monument South Unit (EMSU) waterflood project is a large-scale (354 wells) example of implementing a waterflood in a highly depleted reservoir. Because of the maturity of this field (>50 years), several problems were encountered, such as drilling depleted intervals, corroded wellbores, and stimulating depleted and scaled-off formations. This paper discusses procedures to deal with these problems. Other topics discussed include infill drilling techniques, drilling and completion of high-volume water-supply wells, use of air/mist in drilling and deepenings, and water/CO2 injection equipment. By using existing techniques and implementing new ideas, we continually cut costs throughout the life of the project. Operations were improved through continuity, implementation and analysis of new techniques, and good communications. All improvements are documented with field results and show how continual monitoring and adjustments in operations can lead to an operationally efficient, cost-effective project.
Case History of an Ultradeep Disposal Well in Western Colorado
Authors: Flak Larry H. , Brown John J.
Published: December 2007

Between Dec. 1986 and Dec. 1988, the U.S. Bureau of Reclamation drilled, tested, and completed the world's deepest disposal well. The well will be used to dispose of brine that currently seeps into the Dolores River. This natural brine spring is the largest point source of salt contamination in the Colorado River system.
Measurement of Molecular Weight Distribution of Polyacrylamides in Core Effluents
Authors: He Qingong , Young Teng-Shau , Willhite G. Paul , Green Don W.
Published: December 2007

A procedure to measure the molecular-weight (MW) and size distributions of polymers in core effluents by size-exclusion chromatography (SEC) and low-angle laser-light scattering (LALLS) was used to analyze Berea core effluent samples containing either a hydrolyzed or unhydrolyzed Polyacrylamide (PAAM). The average MW's of the PAAM's were measured with a precision better than ±5% at a 95% confidence level. For both PAAM's, the polymer in an early effluent sample after breakthrough had a narrower MW distribution and fewer low-MW molecules than the injected polymer. This led to a higher weight-averaged MW, Mw, for the early effluent than for the injected polymer. The effluent Mw decreased with increasing PV of polymer solution injected and approached the injected polymer's Mw after a large throughput. The results of the MW distribution measurements, which suggested a relatively large inaccessible PV for larger polymer molecules, are discussed in terms of steric-exclusion effects and dependence of retention rate on polymer size.
Use off Entrainers in Improving Mobility Control of Supercritical CO2
Authors: Llave Fellciano M. , Chung Frank T-H. , Burchfield Thomas E.
Published: December 2007

The use of entrainers (cosolvents) to improve CO2 mobility control for EOR was investigated. The cosolvent serves as a miscible additive that modifies the phase behavior of supercritical solvents and enhances the solubility of crude oil components in the CO2-rich phase. The presence of the cosolvent increases the viscosity and density of the gas phase. The improvement in supercritical extraction power and enhancement of bulk fluid properties result in improved mobility ratios.
Tertiary Application of a Hydrocarbon Miscible Flood: Rainbow Keg River "B" Pool
Authors: Nagel Raymond G. , Hunter Brian E. , Peggs Jonathan K. , Fong David K. , Mazzocchi Enrico
Published: December 2007

The Rainbow Keg River "B" pool EOR scheme calls for placement of a 12% (net after recycle) -original-HCPV miscible bank in the crestal region of the pool. This bank will be chased vertically downward with more than 1 PV of dry gas. The injected solvent and chase gas will push the oil/water contact (OWC) downward as the previously injected water is produced. A tertiary oil bank will be formed in the region previously occupied by the water. This paper reports tertiary flood performance, results of the 1987 reservoir simulation study, and the operational strategy and problems encountered in monitoring the flood. The well-completion technique implemented to operate the flood is described, and the scheme economics is reviewed. Performance of the tertiary flood to date is encouraging.
Interpretation of Temperature Observations From a Cyclic-Steam/ In-Situ-Combustion Project
Authors: Nzekwu Ben I. , Hallam Richard J. , Williams G. J. J.
Published: December 2007

Data collected at 10 temperature observation wells were analyzed to evaluate the implementation of a combined process of cyclic steam stimulation followed by pressure-up/blowdown combustion for the in-situ recovery of bitumen. The temperature profiles at four observation wells, along the northeast/southwest fracture plane (on-trend direction), confirmed the height and orientation of the vertical fractures during cyclic steam stimulation. Six off-trend wells indicated that the heat transfer away from the fracture plane was predominantly conductive, with varying amounts of convective flow. During the in-situ combustion phase, frontal temperatures > 2, 200°F [1200°C] were detected. Data also indicated that the vertical location of the combustion front can be controlled by either gravity or mobility effects. The off-trend heating was improved as a result of higher convective heat fluxes.
Mathematical Modeling of High-pH Chemical Flooding
Authors: Bhuyan Debojit , Lake Larry W. , Pope Gary A.
Published: December 2007

This paper describes a generalized compositional reservoir simulator for high-pH chemical flooding processes. This simulator combines the reaction chemistry associated with these processes with the extensive physical- and flow-property modeling schemes of an existing micellar/polymer flood simulator, UTCHEM. Application of the model is illustrated for cases from a simple alkaline preflush to surfactant-enhanced alkaline-polymer flooding.
Carbon Isotope Analysis: A New Tool for Monitoring and Interpreting the In-Situ Combustion Process
Authors: Hallam Richard J. , Moore R. Gordon , Krouse H. R. , Bennion Douglas W.
Published: December 2007

This paper investigates the use of carbon isotope analysis for monitoring and interpreting responses from the in-situ combustion process. The major finding was that the type of reaction occurring at the combustion front can be distinguished by carbon isotope analyses. These reactions include the classic burning profile at the leading edge; super-wet or low-temperature combustion; a wide combustion zone with a secondary front, which is indicative of oxygen channeling; and carbonate decomposition in carbonate core material. This tool is valuable because, at times, making these interpretations without temperature data or from gas analyses alone is not possible. The study also demonstrated the feasibility of using carbon isotope data to track communication among injection and production wells.
Constant-Internal-Phase Design Improves Stimulation Results
Authors: Harris Phillip C. , Klebenow Donald E. , Kundert D. Pat
Published: December 2007

For several years, foam fracturing has been an excellent technique for stimulating low-pressure reservoirs. Conventional foam treatments, however, have been inconsistent in placing high sand concentrations and often reached a pressure limitation, which prematurely terminated the treatment.

A new design approach to foam fracturing, the constant-internal-phase technique, has overcome previous sand limitations and has allowed treatments to be pumped with less severe pressure fluctuations. This approach treats all internal phases (gas, liquid, or solid) the same and recognizes the similarities in behavior among foams, emulsions, and slurries. A fluid's bulk viscosity increases as the total internal-phase fraction increases, particularly at high internal-phase ratios. The constant-internal-phase approach has produced more predictable wellhead treating pressures (WHTP's), used less hydraulic horsepower, and virtually eliminated premature job termination owing to pressure limitations.
Gravel Packing for the Duri Steamflood
Authors: Shryock Steven G. , Ahmad Syafriwal , Meloy James M. , Kent John W.
Published: December 2007

The multibillion-barrel Duri field is being developed for steamflooding. The completion designs have evolved over 20 years of huff 'n' puff steaming and pilot steamflooding. A reduced-density slurry-packing method is being applied in single- and dual-zone, openhole gravel packs (OHGP's) and cased-hole gravel packs (CHGP's) to complete shallow, underpressured formation sands. Continuing problems include lost circulation, loss of pack upon steaming, and lower-than-expected productivity. Recent improvements have been made in well preparation, fluid cleanliness, liner design, and gravel-placement techniques. When lost circulation or unstable hole conditions are encountered, foam has been used for drilling, underreaming, and gravel packing. This case history demonstrates the importance of well-completion details in obtaining sand control with high productivity for a large steamflood.
Real-Gas Effects in the Expansibility Factor for Subsonic Differential-Pressure Flowmeters at High Pressure
Authors: Finjord Jan
Published: December 2007

Real-gas corrections in the expansibility factor are expressed by an equation of state (EOS). A virial EOS is introduced, with low-order virial coefficients calculated from a cubic EOS. The approach is composition-independent. EOS-dependent cancellations between real-gas effects are revealed. The current Intl. Organization for Standardization (ISO) standard is not always reliable for high-accuracy orifice measurements of gases with arbitrary composition.
Inhibition of Barium Sulfate Deposition by Polycarboxylates of Various Molecular Structures
Authors: van dor Leeden M. C. , van Rosmalen G. M.
Published: December 2007

To establish a relationship between the molecular structure of polycarboxylates and their growth-retarding influence on barium sulfate, seeded-suspension-growth experiments were performed at various inhibitor concentrations and pH values. Two types of polycarboxylates with a molecular structure based on either polyacrylic or maleic acid were studied. The molecular structures of these compounds were varied by partial substitution with monomers containing hydroxyl, amide, and sulfonic acid, as well as hydrophobic groups. Hydrophobic groups are detrimental to good inhibitor performance, whereas the introduction of OH, NH2, or SO3H groups presents opportunities to enhance the inhibitor effectiveness. The sequence in performance of the compounds on barium sulfate was compared with the sequence formerly obtained for calcium sulfate dihydrate.
A Straight-Line Approach To Determine the Distance to Barriers
Authors: Duong Anh N.
Published: December 2007

The pressure response for a well located near a linear impermeable barrier is differentiated and rearranged so that a linear relation between the two variables of the pressure-derivative group and 1/t is obtained. A plot of log|2.303p′t/m − 1| vs. 1/í yields a straight line with a fixed intercept and a slope proportional to the square of the distance to the barrier (or boundary). The straight-line approach is also extended to apply to two perpendicular no-flow barriers and to buildup test data. The advantage of the approach presented here is that pressure data can be analyzed to determine the distance to barriers even if the late-time semilog straight line whose slope is twice or four times the slope of the first semilog straight line is not reached. A field example is included for illustration.
Tight Carbonate Intervals: Vertical Permeability and Threshold Pressure Estimation Models
Authors: Mitrl K. T. , Abed A. -F. A. -R.
Published: December 2007

This paper presents a synergetic study of dense stylolitic intervals within Lower Cretaceous heterogeneous (multilayer) carbonate reservoirs. A new method for characterizing vertical permeability of the dense limestone intervals is developed on the basis of a semiempirical lumped-parameter model. Empirical extension of the method yielded estimates of threshold pressures. The adopted reservoir-description approach provides a purely explicit and interconsistent framework that is especially useful as basic input for detailed full-field simulation-study applications. The concept of excess interfacial tension (IFT) is introduced, and a generalized relationship is proposed for the equivalency of capillary pressure measurements with different fluid pairs by use of a correction term to the classic ratio of IFT's that becomes significant in very-low-permeability media.
The Zakum Telesystem: An Application of Large-Scale SCADA Systems to a Major Offshore Oil Field
Authors: Kahoul Jamel M.
Published: December 2007

Various types of supervisory-control and data-acquisition (SCADA) systems are in use in oil fields around the world, assisting field personnel in maintaining safe and profitable operations. The Upper Zakum field, one of the largest offshore fields, requires a far more extensive SCADA system with higher levels of distribution than generally needed. This paper outlines the environment and extent of the field, emphasizing the need for unmanned operation and the evolution of the Zakum telesystem to meet the special requirements. Specification and predesign phases are shown to be vitally important parts of the project, in both assessing the telesystem's final extent and predicting what the field operators need to control the field. The telesystem implementation is described in detail, including system architecture, operator facilities, hardware and software considerations, and various interfaces with other systems. The problems encountered during the project and their solutions are discussed, and conclusions are drawn for future projects. The need for the highest available level of technology and the likely consequences of compromising this need because of cost considerations are also discussed. Finally, recommendations are proposed for future selection of large-scale SCADA systems.
Well-Test Analysis Following a Closed-Fracture Acidizing Treatment
Authors: Soliman Mohamed Y. , Hunt James L. , Daneshi Tahereh
Published: December 2007

A new model representing fluid flow in a reservoir treated with closed-fracture acidizing (CFA) is presented. The model is characterized by a low-conductivity fracture (representing the closed fracture) and highly conductive wormholes (owing to acid flow). Application of the model to pressure-transient data analysis following a CFA treatment is presented through a field example.
Procedures and Practices of Dual-Completion Design in Abu Dhabi
Authors: Gabert Robert F. , Ghneim George J.
Published: December 2007

The first generation of dual completions run by Abu Dhabi Marine Operating Co. (ADMA-OPCO) had a 7-in. liner and 9⅝-in. casing/tubing annulus as an independent string. Modifications were introduced later to protect the casing and the liner top and to optimize tubing sizes to suit reservoir monitoring and production/injection requirements. This optimization was accomplished with full dual tubing strings ("tubular-flow" completions) or a combination of dual tubing strings and 7-in. liner/tubing annulus ("modified-tubular-flow" completions). This paper discusses equipment selection and solutions to operational problems. The modified-tubular-flow completions were easier to run and to recover than the tubular-flow completions.
Quantitative Determination of the Mechanical Properties of Shales
Authors: Steiger Ronald P. , Leung Peter K.
Published: December 2007

Shales make up more than 75% of drilled formations and cause at least 90% of wellbore-stability problems. Physical measurements of shale properties are required to develop realistic constitutive relationships and to understand and define shale strength and behavior under downhole conditions. Quantitative shale-strength data are needed to improve wellbore-stability model predictions. This paper describes a research test program to determine the mechanical properties of different classes of shales and to build a database on their characteristics and mechanical behavior. Shale samples from undisturbed block samples were prepared under controlled conditions. Mechanical test techniques were developed to measure effective-stress/strain properties accurately for shales. The tests require a heavy-duty, triaxial test load frame and other specially designed equipment to obtain precise pore pressure measurements. During the tests, pore pressure, stresses, and strains were monitored accurately by an automatic data-acquisition system. The test techniques described can be used to test shales with different characteristics: soft, hard, brittle, plastic, etc. On the basis of results of several shale tests, high-quality, effective-stress/strain data and failure criteria (shale strength relationships) can be obtained routinely.
Attenuation of Casing Cemented With Conventional and Expanding Cements Across Heavy-Oil and Sandstone Formations
Authors: Beirute R. M. , Wilson M. A. , Sabins F. L.
Published: December 2007

Studies were conducted with a large-scale displacement model containing manmade tar and competent (hard) manmade sandstone formations. This paper investigates the cement placement process and the acoustic response with standard logging tools. This investigation revealed that the formations behind the cement make a significant contribution to the pipe-attenuation rate. The large-scale acoustic experiments indicate that lower pipe-attenuation-rate levels are measured when tar formations are cemented. This occurs even with the same type of cement and the same annular clearances. The tests suggest that low-attenuation-rate levels also may be measured across other low-restraint formations.
A Model for Predicting the Density of Oil-Based Muds at High Pressures and Temperatures
Authors: Peters Ekwere J. , Chenevert Martin E. , Zhang Chunhal
Published: December 2007

A compositional material-balance model was used to predict the densities of diesel- and mineral-oil-based muds at elevated pressures and temperatures. We measured the densities of diesel oil, two mineral oils, and calcium chloride solutions from 78 to 350°F and from 0 to 15, 000 psig. The measured densities were used in an existing compositional material-balance model to predict the densities of 11- and 17-lbm/gal oil-based muds. We also measured the densities of these muds at elevated pressures and temperatures and compared them with the predicted values. The results show excellent agreement between measured and predicted densities. The experimental density data were used to predict downhole densities and static wellbore pressures for the oil-based muds. Results show that the mineral-oil muds are not only more compressible than the diesel-oil muds, but also more susceptible to thermal expansion. Therefore, all the oil-based muds tend to give essentially the same static-wellbore-pressure profile.
Re-Evaluation of the Misoible WAG Flood in the Caroline Field, Alberta
Authors: Birarda Gary S. , Dilger Chris W. , Mcintosh Ian
Published: December 2007

Premature water breakthrough led to reassessment of a miscible water-alternating-gas (WAG) injection scheme. The reassessment involved detailed geological modeling and a reservoir simulation study. A matching of the complex reservoir history was achieved, and the economic benefits of the scheme were reaffirmed.
The Effects of Steam on the Combustion of Oil on Sand
Authors: Urban David L. , Udell Kent S.
Published: December 2007

A simultaneous differential thermal analysis (DTA)/evolved gas analysis (EGA) system was developed to study in-situ oil-oxidation reactions. The oxidation of crude oil deposited on sand was studied, including catalysis by dissolved ionic compounds and reservoir sand materials and changes in the reaction mechanism caused by the presence of steam. The influence of steam was the most significant of these factors. In the presence of steam, the low-temperature-oxidation (LTO) exothermicity is similar to the dry case, but the oxygen consumption is dramatically reduced and, unlike the dry case, all consumed oxygen appears in the effluent carbon oxides. Participation of water and its radicals in the reaction mechanism is probably responsible for this change. These reactions should have a major influence on wet in-situ combustion.
Light Oil Recovery From Cyclic CO2 Injection: Influence of Low Pressures, Impure CO2, and Reservoir Gas
Authors: Monger T. G. , Ramos J. C. , Thomas Jacob
Published: December 2007

This paper is a laboratory and field investigation of the CO2 huff ‘n’ puff process for the enhanced recovery of light crude oil. Cyclic CO2 displacement results with live and dead oils in watered-out Berea cores are presented. Sixty-five single-well cyclic CO2 field tests conducted in a pressure-depleted reservoir are evaluated.
Toward a Unified Theory of Well Testing for Nonlinear-Radial-Flow Problems With Application to Interference Tests
Authors: Peres Alvaro M. M. , Serra Kelsen V. , Reynolds Albert C.
Published: December 2007

This work presents an analytical solution for the pseudopressure function that represents the reservoir and wellbore responses resulting from production at a constant oil rate in a solution-gas-drive reservoir. The solution can also be reduced to obtain the analytical solution for the corresponding single-phase-flow problem. The general analytical solution suggests a new definition for the dimensionless flow rate. The analytical solution is used to construct new type curves for analysis of interference tests conducted under multiphase-flow conditions. It is shown that if we ignore multiphase-flow effects and analyze interference data with the line-source-solution type curve, then the estimates of the permeability and porosity-compressibility product obtained may be in error by 20 to 40%.
Nomograms for Analysis of Pressure-Buildup Data Influenced By Heterogeneity
Authors: McKinley Richard M. , Streltsova Tatiana D.
Published: December 2007

This paper presents nomograms that assist in the correct identification of the middle time region (MTR) straight line on a semilog or Horner plot of buildup data from a heterogeneous reservoir. These nomograms also provide a realistic assessment of the types of heterogeneity that affect the buildup data. The nomograms are a quantitative extension of the widely used derivative-analysis method. The heterogeneities considered cover lateral discontinuities in reservoir transmissibility, naturally fractured, and vertically stratified and lenticular formations.
Comparison of an Expert System to Human Experts in Well-Log Analysis and Interpretation
Authors: Einstein Elizabeth E. , Edwards Ken W.
Published: December 2007

Comparisons of results produced by an expert system to those produced by log-analysis experts are discussed using case histories from a variety of wells from several countries. The results, in general, exceeded initial expectations, with the expert system showing surprisingly "intelligent" behavior in some circumstances and actually highlighting mistakes made by the human experts. In other examples, the expert system fails to emulate the human expert closely. Failures are shown to result from the application of knowledge gathered from outside the realm of log analysis or from a lack of information entered into the expert system.
Injection-Well Testing in a Light-Oil Steamflood, Buena Vista Hills Field, California
Authors: Zlegler Victor M.
Published: December 2007

Pressure-falloff and step-rate injectivity tests were performed during a light-oil steamflood at the Buena Vista Hills field, CA. Data obtained from these tests allowed determination of steam-zone properties and formation fracture pressure at an injection well. Information obtained from an offset temperature-observation well and from a heat balance corroborated the pressure-analysis results and allowed estimation of steam-zone thickness. An effective method for monitoring steamfloods, pressure-transient testing of steam-injection wells may be used with other surveillance techniques to improve reservoir management.
An Improved Regression Algorithm for Automated Well-Test Analysis
Authors: Nanba Takao , Horne Roland N.
Published: December 2007

Automated well-test analysis is a familiar technique, but the procedure still depends on the speed and robustness of the regression algorithms used. We examine a modification of the Cholesky factorization (CF) method for the solution of nonlinear-parameter-estimation problems and show that this modification is a very beneficial adaptation of the Gauss-Newton method. The new algorithm, the modified Gauss-Cholesky (MGC) method, is more robust under unfavorable conditions than two of the most reliable existing algorithms [the Gauss-Marquardt (GM) and the Newton-Barua (NB) methods]. This robustness seems to depend on the algorithm's ability to control the rapid change of ill-defined parameters and not on computational singularity or higher-order representation.
Wettability Alteration Caused by Oil-Based Muds and Mud Components
Authors: Yan J-N. , Menezes J. L. , Sharma Mukul M.
Published: December 2007

Wettability alteration caused by oil-based muds and mud filtrates is of great concern in coring operations. This paper shows that mud filtrates from whole muds can change the wettability of water-wet cores significantly. Individual components primarily responsible for this wettability alteration are identified.
Dual Concentric Gas-Lift Completion Design for the Thistle Field
Authors: Moore P. C. , Adair Paul
Published: December 2007

A unique dual concentric gas-lift completion was installed in two wells in the Thistle field during 1987. This paper outlines the completion concept and design, including vertical-lift performance and tubing movement/stress analysis. Results of field performance after 1 year of production history are presented and compared with predicted values.
Ion Exchange and Dissolution/ Precipitation Modeling: Application to the Injection of Aqueous Fluids Into a Reservoir Sandstone
Authors: Bazln Brigltte , Labrld Jean
Published: December 2007

Ion exchange and dissolution/precipitation processes are of considerable concern when aqueous fluids are injected into reservoir sandstones, as in waterflooding or alkaline flooding or in well treatments. This paper describes a flow model that takes into account several ion exchange equilibria and the precipitation/dissolution of carbonates and hydroxides. Its validity is tested through simulations of laboratory experiments dealing with brine and alkali injection. Some insights into the effects of ion exchange and precipitation on flow properties are given.
A Study of the Morphologies and Inversions of Model Oilfield Dispersions
Authors: Smith Duane H. , Lim Kyung-Hee
Published: December 2007

Using the surfactant/oil/water system C4H9OC2H4OH/n-C10H22/brine (0.01-M NaCl) and electrical-conductivity measurements, we determined the emulsion morphologies and the phase volume fractions at which inversion occurred at temperatures below the lower critical endpoint temperature and above the upper critical endpoint temperature. In both cases, inversion occurred at 45±5 vol% internal phase when that phase was the water-rich phase and at 60±5 vol% internal phase when that phase was the oil-rich phase. These results contradict the correlation between phase behavior and emulsion morphology that has been almost universally reported in the oil-recovery literature, but are in much better agreement with models for emulsion inversion that are based on packing arguments.
The Effect of Flow Rate on the In-Situ Gelation of a Chrome/Redox/Polyacrylamide System
Authors: Marty Luc , Oreen D. W. , Wlllhlte Q. Paul
Published: December 2007

This paper presents experimental data on the gelation of a polyacrylamide/thiourea/Cr(VI) gel system in unconsolidated sandpacks at flow rates typical of those encountered beyond the immediate vicinity of a wellbore. At these low rates, in-situ gelation during flow was characterized by an abrupt increase in flow resistance that occurred over a short distance at a specific location along the sandpack. The location of this region was a function of flow rate, and its distance from the inlet increased as flow rate increased. Filtration of gel aggregates appears to be the mechanism causing this behavior.
Oilfield Applications of Colloidal Silica Gel
Authors: Jurinak J. J. , Summers L. E.
Published: December 2007

A practical reservoir fluid-flow control system based on colloidal silica gel was developed. Colloidal silica gel is an environmentally benign system that provides easy surface handling, reliable gel-time control at temperatures up to 250°F, and high in-situ performance. Extensive laboratory testing was completed and is discussed elsewhere. Colloidal silica gel has been used in 11 well work-overs for water-injection-profile modification (four wells), water-production control (three wells), and remedial casing repair (four wells). Only one of the four injection-well treatments was a clear-cut technical success, with failure typically caused by pressure parting the gel plug after the well treatment. Two of the three water-production-control jobs were technical and economic successes. Temporary success was achieved in three of the four casing-repair treatments.
Electrical Conductivities in Oil-Bearing Shaly Sands
Authors: Waxman M.H. , Smits L.J.M.
Published: December 2007

A simple physical model was used to develop an equation that relates the electrical conductivity of a water-saturated shaly sand to the water conductivity and the cation- exchange capacity per unit pore volume of the rock. This equation fits both the experimental data of Hill and Milburn and data obtained recently on selected shaly sands with a wide range of cation-exchange capacities.

This model was extended to cases where both oil and water are present in the shaly sand. This results in an additional expression, relating the resistivity ratio to water saturation, water conductivity and cation-exchange capacity per unit pore volume. The effect of shale content on the resistivity index- water saturation function is demonstrated by several numerical examples.

INTRODUCTION

A principal aim of well logging is to provide quantitative information concerning porosity and oil saturation of the permeable formations penetrated by the borehole.

For clean sands, the relationships between measured physical quantities and porosity or saturation are well known. However, the presence of clay minerals greatly complicates log interpretation, particularly the electrical resistivity and SP logs, and considerably affects evaluation of hydrocarbon-bearing formations. The conductance and electrochemical behavior of shaly sands and their relation to log interpretation have been studied by many workers. Wyllie and Lynch reviewed this work in some detail.

Virtually all laboratory measurements of electrical resistivity and electrochemical potential of shaly sands published to date are the work of Hill and Milburn.
Case History of Drillstem Failures Offshore West Africa
Authors: Sweet R. G.
Published: December 2007

A high incidence of drillstem (or drillstring) failures was experienced by Conoco Inc. during drilling of exploration wells offshore West Africa. A data base of failure information was used to identify quickly where the majority of the problems occurred. Almost all failures were related to fatigue and corrosion. A study resulted in several recommendations that included improved practices in drillstem selection, quality assurance, and corrosion control. After the recommendations were implemented, a significant reduction in failures was recorded. This increased operating efficiency, reduced drilling costs, and improved safety.
A New General Pressure-Analysis Procedure for Slug Tests
Authors: Peres Alvaro M. M. , Onur Mustafa , Reynolds Albert C.
Published: December 2007

A new analysis procedure for determining formation flow capacity and skin factor from slug-test data is presented. The procedure arises from exact deconvolution equations that convert measured slug-test pressure data into equivalent pressure and pressure-derivative responses that would be obtained if the well were produced at a constant surface flow rate. The converted data then can be analyzed by use of existing wellbore-storage and skin type curves for the particular reservoir or well model represented by the field data. For cases where the slug test is short, we show that flow rate convolution can be incorporated to improve analysis reliability. The analysis procedures do not require direct knowledge of the sandface flow rate.
Experiences With Pumping Well Testing
Authors: Kabir C. S.
Published: December 2007

This paper presents our recent experiences with pumping well testing using the acoustic method. Three areas of testing are examined: computation of changing liquid density throughout the liquid column at every timestep, interpretation of the test with simultaneous downhole pressure and flow-rate data, and static and dynamic responses of the acoustic device. An algorithm is developed to incorporate the gas/oil mass transfer effect (solubility) so that accurate gas velocity and, in turn, improved liquid density in the annu-lus can be computed. The effect of gas solubility is to reduce gas volume and hence the total bottomhole flow rate (BHF) without affecting bottomhole pressure (BHP) significantly. Transient interpretation improves when the gas solubility is taken into account.

This study reviews some commonly used wellbore two-phase correlations. The Godbey-Dimon model is modified to simulate the moving liquid column during a buildup test. Field examples are used to examine both the static (accuracy) and dynamic (resolution) responses of the acoustic device. The literature suggests that the acoustic method can faithfully reproduce the absolute static gauge BHP. This study shows that the results from dynamic (buildup) tests compare very favorably with those from downhole measurements.
An Analytical Model for History Matching Naturally Fractured Reservoir Production Data
Authors: Watson A. Ted , Gatens J. Michael , Lee W. John , Rahim Zillur
Published: December 2007

This paper presents a method for analyzing production data from naturally fractured gas reservoirs. A normalized time is used to modify analytical solutions to model gas flow in finite, dual-porosity reservoirs. Procedures for validating the dual-porosity reservoir model, determining the suitability of simpler reservoir models, and determining the best parameter estimates are illustrated with field data from naturally fractured reservoirs.