bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Pressure Analysis of Horizontal Wells in Anisotropic Naturally Fractured Reservoirs
Authors: Agullera Roberto , Ng Michael C.
Published: December 2007

Analytical solutions are presented for pressure-drawdown and -buildup analyses of horizontal wells in anisotropic reser voirs with tectonic, regional, or contractional natural fractures. (The reservoirs might be limited by parallel sealed boundaries.) These solutions have led to the identification of various flow periods, including radial in a vertical plane, transitional as a result of flow from the matrix into the fractures, linear when the transient pressure reaches the upper and lower boundaries of the reservoir, pseudoradial toward the wellbore in a horizontal plane, and linear when the transient reaches the outer parallel boundaries. Recognition of these flow periods leads to the calculation of pi or p*; permeabilities in the x, y, and z directions; storativity ratio, ω; average distance be tween natural fractures; fracture porosity; and fracture aperture, skin, and pseudoskin caused by vertical and horizontal partial penetra tion. Calculations are illustrated with an example.
Travis Peak Core Permeability and Porosity Relationships at Reservoir Stress
Authors: Luffel D. L. , Howard W. E. , Hunt E. R.
Published: December 2007

Relationships of permeability to porosity are shown from analyses of more than 2, 100 core plugs from nine wells in the Travis Peak, a low-permeability, tight-gas sandstone formation in northeast Texas. Effects of reservoir vs. ambient stress are shown for permeability, porosity, and the Klinkenberg factor. The relationship of brine permeability to gas permeability is also shown.
Geometric Concerns for Accurate Measurement of Capillary Pressure Relationships With Centrifuge Methods
Authors: Christiansen Richard L.
Published: December 2007

Accuracy of capillary pressure relationships obtained from centrifuge experiments is widely recognized to depend on the quality of raw data, the homogeneity of the rock sample, and the methods used for data reduction. However, the systematic error caused by the radial nature of centrifugal fields is not widely recognized. This paper shows that this radial error can be greater than errors caused by poor data-reduction methods. The radial error can be estimated from the geometry of centrifuge rotors and rock sample dimensions. Careful experimental technique can minimize radial error. Furthermore, data-reduction methods can eliminate radial error by properly accounting for the radial nature of centrifugal fields.
Surveying Techniques With a Solid-State Magnetic Multishot Device
Authors: Thorogood John L. , Knott David R.
Published: December 2007

An electronic magnetic multishot instrument was introduced in 1985 to overcome accuracy and reliability limitations associated with conventional photomechanical multishot systems. This paper describes the survey system and the instrument's performance capabilities. Our aim is to develop a tool-performance model for general application to the management of surveying operations. Accuracy is considered in two parts: sensor errors are considered in detail, and external effects on accuracy—e.g., axial misalignment, bottom-hole-assembly (BHA) deflection, geomagnetic influences, and drillstring-induced interference—are analyzed and quantified. We found that geomagnetic influences and drillstring-induced interference dominate the ultimate performance of all magnetic tools, particularly this electronic multishot instrument. This paper also describes "in-hole referencing, " a method of eliminating these errors that involves surveying the first part of an openhole section with a high-accuracy gyroscope and aligning data derived from subsequent magnetic surveys with it. Using this method, we can achieve gyroscope-survey levels of accuracy with magnetic instruments in highly deviated and extended-reach wells without incurring the costs and penalties of running wireline surveys.
Pressure-Transient Analysis for a Slanted Well in a Reservoir With Vertical Pressure Support
Authors: Abbaszadeh Maghsood , Hegeman Peter S.
Published: December 2007

Analytical solutions are presented for the pressure response of a slanted limited-entry well in an infinite reservoir subject to pressure support from a gas cap, bottomwater drive, or a combination of both. The well's inclination angle ranges from 0 to 90°, covering vertical and horizontal wells as limiting cases. An interpretation method based on nonlinear regression provides a useful analysis procedure for well tests from such reservoirs. The pressure support from the gas cap or bottomwater often masks the late-time reservoir features, making conventional semilog analysis difficult. Field tests are interpreted to illustrate the applicability and limitations of the regression method.
The Underwater Production System
Authors: O'Brien E. J. , Hetiand Torger
Published: December 2007

The underwater production system (UPS) is a subsea hydrocarbon production system developed jointly by Statoil and Mobil Exploration Norway Inc. through a project team based in Trondheim, Norway. This paper describes the system and the key development activities that led to the project goal of a fully developed system design.
Formation Damage Caused by Cement Filtrates in Sandstone Cores
Authors: Yang X. M. , Sharma Mukul M.
Published: December 2007

A series of core damage experiments was conducted with filtrates containing various cement additives, such as dispersants and fluid-loss additives. Results clearly show that the extent and location of the permeability impairment varies, depending on the relative rate of particle precipitation and the residence time in the core. Results of the core-flow experiments are interpreted in conjunction with particle-size distribution and concentration results obtained in batch experiments. Variations in the average particle size and the number concentration of particles with time in various compositions of cement filtrates are reported. These prove to be useful indicators of the extent and location of the damage observed in the cores.
A User's Approach to Qualification of Dynamic Seals for Sour-Gas Environments
Authors: Abrams Philip I. , Kennelley Kevin J. , Johnson Dale V.
Published: December 2007

The selection and performance of dynamic-seal materials for use in aggressive, subsurface, sour-gas environments have often been unsuccessful and resulted in costly field failures. Seal performance is adversely affected by H2S, CO2, high temperature, corrosion inhibitors, and dynamic movement. Standard laboratory test methods to evaluate elastomeric materials for subsurface sealing applications have not allowed reliable prediction of seal behavior in actual field service. This paper presents a new and unique test apparatus that can be used to evaluate dynamic-seal materials and to qualify entire seal-stack configurations for subsurface sour-gas environments.
Field Detection and Implications of Mercury in Natural Gas
Authors: Bingham Mark D.
Published: December 2007

This paper details the operating implications of handling and processing natural gas containing mercury, methods for detecting mercury, suggested sampling procedures, and related field experiences.
The Dynamic Two-Fluid Model OLGA: Theory and Application
Authors: Bendlksen Kjell H. , Malnes Dag , Moe Randl , Nuland Sven
Published: December 2007

Dynamic two-fluid models have found a wide range of application in the simulation of two-phase-flow systems, particularly for the analysis of steam/water flow in the core of a nuclear reactor. Until quite recently, however, very few attempts have been made to use such models in the simulation of two-phase oil and gas flow in pipelines. This paper presents a dynamic two-fluid model, OLGA, in detail, stressing the basic equations and the two-fluid models applied. Predictions of steady-state pressure drop, liquid holdup, and flow-regime transitions are compared with data from the SINTEF Two-Phase Flow Laboratory and from the literature. Comparisons with evaluated field data are also presented.
Guidelines for Ultrasonic Cement-Sheath Evaluation
Authors: Goodwin K. J.
Published: December 2007

The primary objective of cement-sheath evaluation devices is to define the presence of set cement in the annulus, regardless of its density, compressive strength, or quality. Accepting the premise that any set cement in the annulus with a compressive strength greater than 0 psi cannot be replaced by squeeze cementing emphasizes the necessity of recognizing ultralow-compressive-strength cement (< 100 psi) from cement-sheath evaluation devices. Typically, most bond logging instruments cannot define satisfactorily the presence of these generally low-density, low-compressive-strength cements (such as foamed cement, cements filled with sponge-like microspheres, cements containing hydrogen for control of annular influx, or any cement contaminated with gas percolation). The ultrasonic cement evaluation instruments can define these gas contaminated, unset, or low-quality cements, provided the computing parameters are set and the tools calibrated correctly. This paper provides the mechanisms and data required to calibrate the ultrasonic cement evaluation devices correctly and the correct computing parameters for cement-sheath evaluation. Correct interpretation of the cement quality and quantity in the annulus permits the formulation of intelligent annular squeeze decisions.
Oil-Based Drilling Mud as a Gas-Hydrates Inhibitor
Authors: Grigg R. B. , Lynes G. L.
Published: December 2007

Gas-hydrates formation must be considered when petroleum reservoirs are developed in arctic regions and deepwater environments. This paper demonstrates that gas hydrates can form in oil-based muds, but that two major components—oil and dissolved solids in the aqueous phase—significantly inhibit this formation. This work identifies two major components in oil-based drilling mud that affect gas-hydrates formation. The temperature and extent of gas-hydrates formation both can be inhibited significantly, but not necessarily prevented, in oil-based drilling muds. A system that contained 20-vol% water and had an oil-continuous phase inhibited gas-hydrates formation 5 to 10°F. Dissolved solids in a 19.22-wt% calcium chloride (CaCl2) brine inhibited gas-hydrates formation 20 to 25°F and significantly reduced the extent of formation. Gas-hydrates formation in an oil-based drilling mud, prepared with 20- vol%, 19.22-wt% brine, was inhibited more than 30°F over the pressure range studied, 500 to 4, 500 psig. In most cases, oil-based mud can be prepared with sufficient concentrations of dissolved solids to prevent gas-hydrates formation under downhole conditions. Mud samples should be tested to determine the temperature of gas-hydrates formation before field use.
Permeability Transects of Eolian Sands and Their Use in Generating Random Permeability Fields
Authors: Goggln D. J. , Chandler M. A. , Kocurek Gary , Lake Larry W.
Published: December 2007

This paper reports on observations derived from more than 10, 000 permeability measurements taken from eolian sands and their use in generating permeability fields for reservoir simulation input. Results show that classification and statistical measures of variability and spatial correlation (but not mean permeability) are portable between the outcrop and the subsurface.
Outcrop/Subsurface Comparisons of Heterogeneity in the San Andres Formation
Authors: Kittridge Mark G. , Lake Larry W. , Lucia F. Jerry , Fogg Graham E.
Published: December 2007

An integrated outcrop and subsurface study of permeability variations in the San Andres formation demonstrates the extreme heterogeneity present in this economically important carbonate horizon. Permeability measurements were made with a field permeameter and were compared to subsurface core data. Geostatistical techniques were used to predict variability and scales of spatial correlation. Measured permeability showed substantial variability within units arranged in three correlation scales. Outcrop permeability data exhibited no marked permeability anisotropy in predicted spatial correlation length. Several scales of spatial variability have been observed in an outcrop section, with subsurface results in agreement.
Pore-Space Statistics and Capillary Pressure Curves From Volume-Controlled Porosimetry
Authors: Toledo Pedro G. , Scriven L. E. , Davis H. Ted
Published: December 2007

Far more information about pore spaces of reservoir rock samples can be obtained from volume-controlled mercury porosimetry than from conventional pressure-controlled mercury porosimetry. Yuan and Swanson demonstrated this in landmark experiments with their apparatus for pore examination (APEX). With a mechanism-based, computer-facilitated model of pore-level displacement, we discover how much useful information about a porous medium can be extracted from volume-controlled mercury porosimetry. APEX mercury injection is quasistatic; so is our simulation. Displacements under this condition consist of smooth, reversible changes punctuated by jumps in capillary pressure, Pc, the sequence of which follows from the structure of the porous medium and the saturation history. Thus, careful examination of Pc fluctuations provides detailed information about pore-size distributions. The results account quantitatively for the APEX mercury Pc curves precisely measured by Yuan and Swanson. In our work, sample size—an aspect not reported previously—is a main factor in APEX response. Using Monte Carlo simulation, we find the optimum-sized specimen for examining a pore space with particular properties and investigate withdrawal experiments, withdrawal after partial reinjection, and full scanning loops.
Experimental Measurement of the Persistence of Permeability Reduction in Porous Media Treated With Xanthan/Cr(III) Gel Systems
Authors: Eggert R. W. , Willhite G. P. , Green D. W.
Published: December 2007

A series of long-term experiments was conducted to determine the persistence of flow resistance in unconsolidated sandpacks treated with xanthan/Cr(m) gels. Gels were prepared with 2, 000 ppm xanthan and Cr(m) concentrations from 25 to 200 ppm. These systems exhibit various degrees of swelling or syneresis. The experiments were conducted by first allowing a gel to set up in a sandpack and then continuously flushing the sandpack with brine for up to 4 months at a constant pressure drop of 13.3 psi/ft. Flow rate was monitored to calculate permeability changes with time. Flow experiments indicated that the measurement of swelling and syneresis in bulk-gel tests is not a good predictor of gel response in unconsolidated sandpacks. Excellent permeability reduction was obtained in sandpacks when gels that exhibited 35% to 60% reduction in volume in bulk tests owing to syneresis were used. Gels were most effective at retaining flow resistance in the range of 35 to 75 ppm Cr(m), where the sandpacks regained < 0.1 % of their original 4, 000 md permeability during the experiments. These observations were supported by experimens in which the pH of the injected brine was varied between 3.0 and 6.5. The swelling tests on the bulk gel indicated that permeability would decrease as pH increased and would increase as pH decreased. This occurred; however, the magnitude of the permeability change was less than inferred from bulk-gel measurements. Other experiments indicated that residual oil does not affect permeability modification in sandpacks. The amount of Cr(m) removed from the sandpack during brine flushing ranged from 38% for the 25-ppm-Cr(III) gel to 70% for the 200-ppm-Cr(III) gel. In all systems, effluent Cr(III) concentration declined exponentially as flushing continued, suggesting that the Cr(III) recovered never reacted with the polymer.
Pseudocomponent Selection for Compositional Simulation
Authors: Newley T. M. J. , Merrill R. C.
Published: December 2007

This paper describes a scheme for combining the components in a multicomponent equation of state (EOS) into fewer components for compositional studies. The method is based on minimizing the difference between the Κ values of the original components and the Κ value of the pseudocomponent to which they are assigned. New rules to determine pseudocomponent properties are presented. The rules, based on K-value weighting, ensure that information about both coexisting phases is used in the derivation of pseudocritical temperatures and pressures. Results for the lumped models developed by this method are compared with the original multicomponent models. The method is shown to work for a variety of gas-condensate, miscibility, and gas-injection problems.
Water Tracing Enhances Miscible Pilot
Authors: Wood Kelvin N. , Li Francis S. , Heacock Dennis W.
Published: December 2007

Radioisotope water tracers were used extensively during a produced-water preflush of the Redwater field hydrocarbon miscible pilot. The results from tracer injections in two zones in the original oil column of the reservoir provide convincing evidence of a preferred flow direction toward the southwest. In addition, they confirm the existence of communication across the shoal margin between foreslope and back reef facies and provide insight into the different flow characteristics inherent to the back reef and shoal margin. Excellent results were obtained with tritiated water (HTO) and cesium (Cs) tracers; cobalt (Co) tracer performance was poor, most likely because the formation retained the tracer. Summaries and discussions of these results, including an assessment of their effects on the pilot, are presented. The paper examines key factors that contribute to a successful tracing program and describes a wire-line tracer injection tool designed specifically for the project. No attempt is made to assess overall pilot performance because this work preceded the miscible flood.
The Use of the Effective-Medium Theory and a 3D Network Model To Predict Matrix Damage in Sandstone Formations
Authors: Khatlb Z. I. , Vitthal Sanjan
Published: December 2007

The size-matching technique and the effective-medium theory (EMT) were used to develop a model to predict the in-depth plugging of a formation core as a function of the solids particle size in the injection water. The pore-size distributions were determined with capillary pressure data [measured by the apparatus for pore examination (APEX)] rather than with the conventional capillary pressure curve. The morphology of the pore space was represented by a random 3D disordered network of pore bodies interconnected by pore throats. The absolute air permeability of the network was calculated with the EMT. The calculated permeabilities for Berea and Bentheim sandstones were compared with those calculated by the traditional bundle-of-capillary-tubes model and laboratory-measured values. A simple method is also presented that relates the ratio of plugged to unplugged pore throats to the loss in permeability for a given matching pore/particle-size criterion. With the three particle/pore-plugging criteria, the reduction in permeability caused by matrix plugging was closely predicted as a function of the median diameter of the injected solids for a given concentration.
Thermal Effects on Single-Well Chemical-Tracer Tests for Measuring Residual Oil Saturation
Authors: Park Y. J. , Deans H. A. , Tezduyar T. E.
Published: December 2007

The single-well chemical-tracer (SWCT) test for measuring residual oil saturation, Sσr, often involves injecting cool fluid containing a reactive tracer into a warm formation. The Sor estimation with this method depends on the separation between reactant and product tracers. Because the reaction rate is temperature-dependent, accounting for the thermal effects may be necessary to obtain reliable results.

Two simulator models are normally used to interpret SWCT tests. The ideal model is used for relatively homogeneous sandstone formations. The pore-diffusion model is used for heterogeneous carbonate formations. Both models have now been solved with appropriate heat-balance equations. These nonisothermal models have been used to reinterpret several previously reported field tests. For the worst case, the estimated Sor value from the nonisothermal model is 5% PV higher than that from the isothermal model.

Inequality conditions have been developed that divide the parameter space of SWCT tests into two regions, depending on the location of the temperature front relative to the tracer bank during the reaction period. In the "safe" region, the estimated Sor values from isothermal and nonisothermal models are essentially equal. The inequality conditions have been extended to include the effects of over-and underburden layers and intervening shales in layered systems.
Foam Flow Through an Oil-Wet Porous Medium: A Laboratory Study
Authors: Sanchez J. M. , Hazlett R. D.
Published: December 2007

A laboratory study of the steady generation and flow of gas and surfactant solution through an oil-wet porous medium indicates that foam is formed and is effective in reducing gas permeability. A comparison of the flow characteristics of foam in oil-wet and water-wet media showed that at similar surfactant concentrations gas permeability reduction in both systems is approximately equal. The ability to form stable foam in situ in an oil-wet porous medium appears to result from the alteration of the initially hydrophobic surface to hydrophilic by two mechanisms: surface tension reduction and surfactant adsorption. Wettability alteration of the hydrophobic surface is evidenced by a dramatic shift in liquid relative permeability when surfactant is present in the aqueous phase. The liquid relative permeability curve of the oil-wet porous medium, in the presence of surfactant, essentially matched that of the water-wet porous medium. Such shifts in liquid relative permeability have not been observed for foam flow in strongly water-wet porous media. No alteration in either liquid or gas relative permeability occurred with added surfactant when a residual mineral oil was present in the oil-wet system. Transient measurements, however, indicated the formation of foam in the water-wet system when residual oil was present.
Sampling Gas-Condensate Wells
Authors: McCain W. D. , Alexander R. A.
Published: December 2007

The industry has a procedure for stabilizing and sampling retrograde-gas (gas-condensate) wells; however, no investigation of the quality of the samples resulting from this procedure has been published. During sampling, bottomhole flowing pressure (BHFP) typically is less than the dewpoint pressure of the original reservoir gas. This causes condensate liquid to build up in the reservoir around the wellbore. This paper presents the results of a study of the sampling procedure and of the buildup and stability of the condensate ring around the wellbore. A procedure designed to give the best chance of obtaining a representative sample is presented.
Reservoir Simulation on a Hypercube
Authors: Wheeler John A. , Smith Richard A.
Published: December 2007

The rapid evolution of parallel computers with distributed memory promises to reduce computer hardware costs by an order of magnitude. To examine the extent to which this promise can be realized in practice, we coded and tested a 3D parallel implicit reservoir simulator for an Intel iPSC/2™ hypercube with 16 vector processors. The simulator is based on an oil/water model and does not account for a gas phase. Test results were favorable. A correlation of computation efficiency with problem size and the number of processors demonstrates that up to 96% of the available CPU time on the hypercube can be used. Such high efficiencies were achieved by developing special algorithms well suited for multiple processors and distributed memory.
Ekofisk Nitrogen Injection
Authors: Thomas L. K. , Dixon T. N. , Pierson R. G. , Hermansen Hroar
Published: December 2007

This paper summarizes a study performed to evaluate nitrogen injection in Ekofisk and includes a geological description, measurement of physical properties, model development, mechanistic studies, and cross-sectional nitrogen-injection simulations.
Factors Contributing to Cement Sheath Deposition in Casing Under Highly Deviated Well Conditions
Authors: Sabins F. L. , Smith R. C. , Broussard M. D. , Talbot K. J. , Olaussen S. R.
Published: December 2007

Deposition of a cement sheath inside 9⅝-in. intermediate casings cemented in highly deviated North Sea wells often required reaming before drilling operations could be resumed. Attempts to remove or prevent solids deposition by means of additional wiper plugs, flushes, or flow-rate variation were ineffective and led to a laboratory investigation of the factors contributing to the cement sheath formation in highly deviated wells. The laboratory study was conducted in a large-scale cement-displacement test facility previously used in similar investigations to simulate field conditions in scale-model proportions with actual field operation pumping equipment, materials, and techniques. This paper describes the identification of cement sheath deposition through case histories, test facilities, conditions, and results and indicates a satisfactory resolution for this problem.
Foamed-Cement Characterization Under Downhole Conditions and Its Impact on Job Design
Authors: de Rozières Jean , Ferrière Rèmi
Published: December 2007

The engineering properties of foamed-cement slurries were studied in detail with an original methodology based on new equipment. With this laboratory equipment, foamed cement can be mixed and characterized at pressures and temperatures representative of field conditions and at densities as low as 400 kg/m3. The pressure and shear field under which a foam is generated are found to have a strong effect on bubble-size distribution (BSD), permeability, and to a lesser extent, compressive strength. Data on thickening time, fluid loss, and the effect of temperature on foam properties are also presented.

A better understanding of foamed-cement properties allows optimization of job design so that prescribed pressure and density profiles in the column are achieved both during circulation and after placement. Critical design parameters are identified and their relative influence is shown through a case study.
Quality of Bentonite and Its Effect on Cement-Slurry Performance
Authors: Grant W. Hal , Rutledge John M. , Gardner Craig A.
Published: December 2007

This paper shows the results of a 2-year study on the quality of cement-grade bentonite now available commercially. A comparison of laboratory-designed slurries with field-blend samples shows drastic alteration of cement-slurry performance from poor blending procedures and/or poor-quality bentonite, which could cause catastrophic consequences.

Evidence from microscopic examination, chemical-quality procedures, and cement-slurry performance data shows a failure rate approaching 50% among more than 150 samples tested from field stocks. Laboratory data on cement-slurry performance with bentonite that passed and failed the current API specification test are presented.
Case History: Ice Island Drilling Application and Well Considerations in Alaskan Beaufort Sea
Authors: Angell V. W. , Graham H. J. , Post G. J.
Published: December 2007

During Winter 1988-89 Chevron U.S.A. Inc. and Mobil Oil Production Co. constructed an ice island with seawater spray to drill the Karluk prospect. A land-drilling program was modified to drill the exploration well to 11, 190 ft total depth (TD). The project was completed in the allotted time and within its budget, despite one of the most volatile winters on record.
Development of Lightweight Steel Drillpipe With a 165-ksi Yield Strength
Authors: Tsukano Yasushl , Ueno Masakatsu
Published: December 2007

This paper describes the development of a lightweight steel drillpipe with a 165-ksi [1137-MPa] yield strength. The drill-pipe was developed according to three design objectives and verified by full-size and material-evaluation tests. The lightweight steel drillpipe has two advantages over standard API G-105 pipe with the same pipe-body OD—it weighs 25% less and has a 20% lower hydraulic loss (loss of fluid pressure)—but maintains a performance level comparable with that of G-105 pipe.
The Traveling-Cylinder Diagram: A Practical Tool for Collision Avoidance
Authors: Thorogood J. L. , Sawaryn S. J.
Published: December 2007

The "traveling-cylinder" diagram aids collision risk assessment during planning and collision avoidance during direc tional drilling at multiwell locations. Survey results can be plotted directly on the diagram, enabling an immediate visual risk assess ment. This paper describes the conceptual basis of the diagram, how the diagram is used during planning and drilling, and how the information on the diagram can be interpreted.
Radioactive Steam Tracer Comparison Between Krypton-85, Xenon-133, NaI-131 (Methyl Alcohol Based), and NaI-131 (Water Based)
Authors: Crowe Thomas L.
Published: December 2007

Radioactive steam tracer surveys are run routinely in steam injection wells to check for tubing holes, packer leaks, open perforations, and steam migration behind casing. A field study comparing krypton-85, xenon-133, NaI-131 (methyl alcohol based), and NaI-131 (water based) was conducted to determine which radioactive tracers are the most accurate for these surveys. Testing showed that all tracers are accurate except NaI-131 (water based).
A New System for Controlling the Crosslinking Rate of Borate Fracturing Fluids
Authors: Cawiezel K. E. , Elbel J. L.
Published: December 2007

This paper describes a delayed-crosslink activator system for borate fracturing fluids that allows crosslinking rates to be controlled to give low friction pressure in the wellbore. Data from laboratory development, full-scale friction tests, and fracturing treatments are included to illustrate the fluid properties and the ability to couple fluid performance with treatment design. Field case histories include friction-pressure data, which profile the changes that occur as the fluid is crosslinking at different stages in the tubing. Results indicate that different crosslinking rates can be recognized by their "friction-pressure signature" and that the crosslinking rate can be altered easily during a treatment to minimize total treating pressure. This technique, with its resulting friction pressure profile, has proved to be an extremely useful tool for field optimization of crosslink times.
Reactivity of San Andres Dolomite
Authors: Anderson Mary S.
Published: December 2007

The San Andres formation is routinely stimulated with acid. Although numerous acidizing simulators are available to aid in treatment optimization, existing reactivity data were generated with quarried rock rather than formation samples. This paper presents reactivity data for five San Andres dolomite samples. These data can be used in most fracture-acidizing-design simulators to allow more accurate simulation of the acidizing process.
The Ford Geraldine Unit CO2 Flood— Update 1990
Authors: Pittaway K. R. , Rosato R. J.
Published: December 2007

This paper updates the operating history of the tertiary CO2 flood in the Ramsey (Delaware sand) formation of the Ford Geraldine Unit (FGU). The discussion focuses on injection and production history, operational considerations, data collection and monitoring techniques, and plans for the flood.
Three-Phase Gas/Oil/Brine Relative Permeabilities Measured Under CO2 Flooding Conditions
Authors: Dria D. E. , Pope G. A. , Sepehrnoori Kamy
Published: December 2007

Steady-state three-phase gas/oil/brine relative permeabilities were measured in a carbonate core under CO2 flooding conditions. Results show that the relative permeability of each phase depends only on the saturation of that phase instead of on two saturations, as many previous studies have concluded. All previously reported gas/oil/brine relative permeability studies have been conducted with low-pressure N2 gas or air. In this work, CO2 gas, oil, and brine were injected into a carbonate core at 71°C and 9.65 MPa so that the phase behavior and flow would be similar to reservoir conditions. Results show that significant differences exist between the three-phase gas/oil/brine relative permeabilities measured when the gas is CO2 and those measured when the gas was N2.
Mobilization of Waterflood Residual Oil by Gas Injection for Water-Wet Conditions
Authors: Oren P. E. , Billiotte Joël , Pinczewski W. V.
Published: December 2007

Mechanisms by which waterflood residual oil is mobilized and recovered during tertiary gasflooding at quasistatic rates and strongly water-wet conditions were investigated with 2D glass micromodels. Two three-phase oil/water/gas systems were used in the displacement experiments. One system had a positive spreading coefficient, the other a negative coefficient. Results for the two systems were compared to determine the differences in displacement mechanisms and oil recovery efficiency. Displacement in both systems proceeds by a double-drainage mechanism where a gas/oil displacement is always associated with an oil/water displacement. The oil/water displacement leads to coalescence and reconnection of oil blobs. Oil recovery was significantly higher for the positive spreading system. The higher displacement efficiency resulted from flow through thin but continuous oil films that always separated the oil and water phases in the positive spreading system. The absence of oil films and the possibility of direct gas/water displacements reduced oil recovery for the negative spreading system.
Phase Behavior, Fluid Properties, and Displacement Characteristics of Permian Basin Reservoir Fluid/CO2 Systems
Authors: Creek J. L. , Sheffield J. M.
Published: December 2007

The formation of a CO2-rich second "liquid" phase in mixtures of CO2 and Permian Basin reservoir fluids now is well-established. This paper presents our experimental measurements of fluid properties in this liquid/liquid/vapor (L1/L2/V) region and their effects on the displacement of Permian Basin crude oil samples with CO2. We first present detailed measurements of phase volumes, viscosities, densities, and interfacial tensions (IFT's) for a Permian Basin/CO2 reservoir fluid system. We describe how these properties change as the L1/L2/V region is traversed. The extent to which the Peng-Robinson equation of state (EOS) is capable of modeling these properties also is discussed. We have observed that the unusual behavior in slim-tube displacement tests at Permian Basin reservoir conditions correlates with the formation and properties of these phases. Conventional criteria defining minimum miscibility pressure (MMP)—e.g., recovery at 1.2 PV injected—are unsatisfactory for these systems. We propose criteria based on maximum ultimate recovery and secondary observations that are more satisfactory.
A Semianalytical Thermal Model for Linear Steamdrive
Authors: Gajdica Ronald J. , Brigham William E. , Aziz Khalid
Published: December 2007

A semianalytical model was developed for 1D linear and 2D cross-sectional systems. New methods are introduced to determine the shape of the steam front and the sweep efficiency of the water front. The model was much faster than a thermal simulator but produced accurate matches of thermal simulator results.
Surfactant Flood Process Design for Loudon
Authors: Maerker J. M. , Gale W. W.
Published: December 2007

Laboratory steps required to design a successful surfactant flooding process for the high–salinity Loudon field are described. These steps involved (1) phase-behavior tests to identify two synthetic surfactant components; (2) Berea coreflood tests to establish the desirability of incorporating polymer in the microemulsion and to optimize blend ratio, microemulsion salinity, drive–water salinity, and bank size; and (3) Loudon rock corefloods to provide a final check in reservoir core material. The process recovered significant quantities of residual oil in two 1–acre pilot tests without the use of a cosurfactant, a cosolvent alcohol, or a low-salinity preflush.
Use of Mixed Surfactants To Generate Foams for Mobility Control in Chemical Flooding
Authors: Llave Feliciano M. , Olsen David K.
Published: December 2007

The application of mixed surfactant foams as an alternative method for mobility control behind a low-concentration chemical flood was evaluated in laboratory experiments. Results indicated that use of alternating slug cycles of gas and selected mixed surfactants resulted in significantly higher differential pressures, Δp, compared with use of only the individual surfactant components, even at low surfactant concentrations. Foams generated with these systems were more stable, even in the presence of oil. The synergistic effect of enhancing foam-generation behavior and stability of these types of systems can improve propagation of a mobility-control front through porous media.
Effect of Polymers on the Imbibition Process: A Laboratory Study
Authors: Ghedan Shawket G. , Poettmann Fred H.
Published: December 2007

Polymer flooding of fractured reservoirs is common. In water-wet fractured reservoirs, the primary recovery mechanism may be imbibition. This paper presents results of an experimental study investigating the effect of polymers on the imbibition process. Two sets of experiments, static and dynamic, were performed. The static experiments showed that the amounts of oil ultimately recovered by water and polymer-solution imbibition are practically equal. The rate of oil recovery by the polymer solutions, however, is always less than the rate with water. The dynamic experiments consisted of flooding oil-saturated fractured cores through the fractures. The oil-recovery behavior in these experiments depended not only on the rate of injected fluid imbibition from the fracture into the matrix blocks, but also on the operating injection rate and the efficiency of the injected fluid in displacing the oil in the fracture.
An Application of Geostatistics and Fractal Geometry for Reservoir Characterization
Authors: Aasum Yngve , Kelkar Mohan G. , Gupta Surendra P.
Published: December 2007

This study presents an application of geostatistics and fractal geometry concepts for 2D characterization of rock properties (k and ϕ) in a dolomitic, layered-cake reservoir. The results indicate that lack of closely spaced data yield effectively random distributions of properties. Further, incorporation of geology reduces uncertainties in fractal interpolation of wellbore properties.
Effects of CO2 Solubility in Brine on the Compositional Simulation Of Co2 Floods
Authors: Enick R. M. , Klara S. M.
Published: December 2007

A compositional simulator was modified to account for the effects of brine on CO2 solubility and aqueous-phase density and viscosity. Simulations of oil displacements using continuous injection of CO2, CO2 slugs, and CO2 water-alternating-gas (WAG) injection were conducted to determine the effects of brine on the performance of CO2 EOR processes.
Borehole-Stability Analysis for the Design of the First Horizontal Well Drilled in the U.K. Southern V Fields
Authors: Fuh G. F. , Dew E. G. , Ramsey C. A. , Collins Keith
Published: December 2007

This paper presents the method and results of a borehole-stability analysis conducted on the first horizontal well successfully drilled in the North Valiant field in the Southern North Sea. Previous drilling data obtained from the same area were analyzed by numerical simulations of potential mechanical behavior of the wellbore. The magnitude of the in-situ horizontal stresses was determined by the analysis of fracture-stimulation data from wells in the fields. The directions of the stresses were derived from anelastic-strain-relaxation (ASR) measurements of fresh cores. Effects of hole azimuth on wellbore stability were evaluated. The analysis resulted in a design of optimum mud weights for maintaining borehole stability during drilling. This paper also discusses field results and well completions.
Dynamic and Static Filtrate-Loss Techniques for Monitoring Filter-Cake Quality Improves Drilling-Fluid Performance
Authors: Chesser B. G. , Clark D. E. , Wise W. V.
Published: December 2007

This paper describes properties that are desirable in a water-based filter cake and test methods that can be used to measure these properties. One method uses a dynamic filtrate-loss apparatus that stirs the fluid mechanically during filtration. Test results show that the initial dynamic filter-cake formation is very important in controlling all future filtration properties and cake quality. The various factors affecting filter-cake quality and how they can be controlled to give better field performance are discussed.
Real-Time Pore-Pressure Evaluation From MWD/LWD Measurements and Drilling-Derived Formation Strength
Authors: Rasmus J. C. , Stephens D. M. R. Gray
Published: December 2007

Traditional pore-pressure interpretations in tertiary undercompacted shales have been based on empirical relationships between a particular measurement (such as resistivity) and pore pressure in pounds per gallon. It is well-known, however, that the measurements are responding to the "excess" porosity in the shale rather than to the pore pressure directly. A new technique is illustrated in which all available measurements are first characterized in terms of this excess porosity and lithology with measurement-response equations. This allows a mathematical minimization technique to solve simultaneously the various measurement-response equations for this porosity and lithology on a foot-by-foot basis. A conventional compaction porosity/effective-stress model is then used to determine the additional pore pressure caused by this excess porosity. The result is a single pore-pressure estimate that is independent of the number of measurements and that has an accuracy that improves with the total number of measurements used in the interpretation. The interpretation can be performed at the wellsite in real time by use of rate of penetration (ROP), measurement while drilling (MWD), and logging while drilling (LWD) measurements or after drilling by use of these measurements in conjunction with wireline measurements.
Cement Sheath Stress Failure
Authors: Goodwin K. J. , Crook R. J.
Published: December 2007

Observation of the sudden appearance of annular pressure in wells exposed to high temperature changes or excessive internal casing pressure prompted a laboratory investigation to simulate conditions under which cement sheath failure could occur and thereby define the causes, characteristics, and limits of the problem. Cement sheath failure is manifested by interzonal problem. Cement sheath failure is manifested by interzonal annular-fluid movement and abnormally high annular pressure at some point behind the casing up to and at the surface. Cement sheath point behind the casing up to and at the surface. Cement sheath failure can be observed in any producing area where excessive flowing temperatures exist at the surface or where excessive internal casing test pressures are used. The detrimental effects of cement sheath failure are numerous and may include lost revenue from lost production, potentially hazardous rig operations (especially when annular isolation loss creates shallow-water sands supercharged with gas), and potentially hazardous producing operations. Exposure of steel casing to excessive temperature increases or internal test pressures causes diametrical and circumferential casing expansion. This circumferential force creates a shearing force at the cement/casing interface, causing failure at the cement/casing interface or radial fracturing of the cement sheath from the inner casing surface to the outer casing (or borehole) surface.
Closed-Loop Operation With Alternative Dewatering Technology
Authors: Halliday W. S. , Bray R. P. , Youens J. W.
Published: December 2007

The introduction of dewatering devices for closed-loop drilling-fluid circulating systems and reserve pits is derived from technology that has been used in the industrial- and sanitary-waste treatment industries for years. This paper describes an overview of the need for closed-loop systems and provides the optimum design layout, including the fit of a dewatering device, for a drilling location. The introduction of a nonconventional dewatering device, called a screw press/thickener, is reviewed. A case history describing use of this technology in a southern Louisiana inland-marsh-area well is analyzed for the technical and economic viability of operating in a closed-loop mode. Results from this effort include a viable alternative to hauling off waste fluids from drilling sites and the realization that use of this technology can be justified economically.
An Experimental Study of Miscible Displacements in Heterogeneous Carbonate Cores Using X-Ray CT
Authors: Hicks Paul J. , Narayanan K. Ram , Deans Harry A.
Published: December 2007

A series of flow visualization experiments have been conducted with X-ray computerized tomography (CT) on 10.16-cm-diameter carbonate core samples to study local displacement mechanisms on a 1-mm scale. Liquid-phase miscible displacement experiments were performed with and without a residual phase. Simulations have been performed with a linear, 3D cell model that includes capacitance effects.
Microscopic Imaging of Porous Media With X-Ray Computer Tomography
Authors: Jasti Jay K. , Jesion Gerald , Feldkamp Lee
Published: December 2007

This paper presents a new method for imaging the 3D microstructure of porous media. The method is based on high-resolution X-ray computer tomography (CT) where a cone-shaped, diverging X-ray beam is used to generate 2D transmission images. Unlike traditional X-ray CT, a 3D reconstruction array is created directly instead of creating a series of 2D slices. This allows direct measurement of 3D geometric and topologic properties of porous media on a microscale. Our results also demonstrate the effectiveness of the high-resolution system for imaging the distribution of two fluid phases in the void space. The imaging system overcomes the limitations of current methods and has enormous potential for quantifying the microstructure of chaotic porous media.
Impact of Miscible Flooding on Wettability, Relative Permeability, and Oil Recovery
Authors: Rao Dandina N. , Girard Marcel , Sayegh Selim G.
Published: December 2007

The fluid-flow effects in miscible gas processes were studied in several series of corefloods involving water-wet, intermediate-wet, and oil-wet reservoir systems. Three more series of floods were conducted in Berea cores for the same three crude oils used in the previous set. Each of the coreflood series involved three cycles of water and miscible gasfloods, with each cycle consisting of the steps necessary to cover the range of saturations from connate water to miscible flood residual oil saturation (ROS). The results from these flow tests revealed that the oil/water relative permeabilities, saturations, and oil recoveries can be significantly different from cycle to cycle, indicating alterations in the in-situ wettability caused by miscible flooding. These wettability alterations had a significant positive effect on the miscible flood oil recoveries in the case of intermediate-wet and oil-wet reservoirs, while their influence in a strongly water-wet reservoir was negligible. In some cases, a mixed-wettability condition developed as a result of miscible flooding, resulting in higher subsequent waterflood oil recoveries. The water/oil relative permeability ratios have been used to identify the development of mixed-wettability in cores.
Theory and Implementation of a Borehole Caliper Measurement Made While Drilling
Authors: Paske W. C. , Rao M. V. , Twist J. R. , Mack S. G. , Spross R. L.
Published: December 2007

Like comparable wireline measurements, measurement-while-drilling (MWD) formation-evaluation tools are dependent on the borehole condition. Because of this dependency, the borehole size must be known for appropriate borehole corrections to be made to porosity measurements. This paper describes caliper measurements that can compute the effective diameter of a uniform or nonuniform borehole with nonmechanical means. The basis for the caliper measurement is a gamma/gamma density sensor that uses asymmetric detector placement to define the borehole size. The derivation of the caliper is presented with field log comparisons.