bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Non-Darcy Flow in Propped Hydraulic Fractures
Authors: Martins J. P. , Milton-Tayler D. , Leung H. K.
Published: December 2007

Hydraulic fracturing is being applied to progressively higher permeability formations. In many cases, productivity improvements are controlled by the achievable fracture conductivities.

An analysis of the effects of non-Darcy flow in high rate oil and gas wells shows that in gas wells, fracture conductivities are dominated by non-Darcy effects and that effective conductivities are non-linearly dependent on proppant coverage.

Laboratory tests to investigate non-Darcy flow effects in proppant packs have been performed at rates much closer to field conditions than hitherto reported; both single and two-phase flows are considered.

Dry gas tests have demonstrated that there is a change in pressure loss behaviour and flow regime at high rates.

Three types of test involving gas and water flows have been performed. First the effects water-saturated gas flowing in a proppant pack at residual water saturation were compared with results on the same pack with dry gas. Two series of experiments were then performed to examine the effects of mobile water in the gas stream.

Pressure losses are shown to be very sensitive to the water rates, and the field implications are examined.

Finally field data from tests performed on high rate, hydraulically fractured, gas wells are examined. Perceived fracture conductivities are related to estimated proppant coverage, and it is shown that non-uniform vertical distributions of proppant may have a large impact on the overall fracture flow capacity.
Log Evaluation Of Deep Ellenburger Gas Zones
Authors: Neustaedter R.H.
Published: December 2007

Log evaluation of deep Ellenburger gas zones is complicated by the low porosities encountered, and by formation matrix and fluid effects on log responses. In these very low porosities even small inaccuracies in porosity determination produce proportionally large errors in reservoir evaluation.

Each of the logging devices commonly used for porosity measurement—sonic, density, and neutron—is affected by variations in formation lithology and fluid content. While the deep Ellenburger is primarily dolomite, variations in lithology produce inaccuracies in the porosities determined from any one log. Furthermore, gas saturation in the formation close to the borehole affects the neutron and density responses; the neutron gives values of porosity that are too low; the density, too high. While no gas effects have been observed on the sonic response this tool characteristically is pessimistic in zones of secondary porosity. Therefore, no single device reliably affords accurate porosity determination.

The most reliable values of porosity are obtained through a complex interpretation procedure using data from all three logs—sonic, density, and neutron. Computer processing makes this procedure feasible. This computer processing gives not only an improved value of porosity, but also the major lithologic components of the formations, and the gas and liquid saturations of the zones close to the borehole.

Resistivity logs are used in conjunction with the previously mentioned porosity logs. Resistivity values are expressed in terms of bulk volume of water, as in the MOP technique, for comparison with the porosity data.

The analog machine printout of the computed data simplifies the use of logs for formation evaluation and selection of intervals of completion.

INTRODUCTION

The deep Ellenburger gas play is characterized by extremes. The wells are extremely deep—and are correspondingly expensive to drill and complete.
Characterization and Cleanup of Chromium-Contaminated Soil for Compliance With CERCLA at the Naval Petroleum Reserve No. 1 (Elk Hills): A Case Study
Authors: Campbell R. E. , Akers R. T.
Published: December 2007

This is a case study of characterization and clean-up of chromium-contaminated soil at Elk Hills, carried out in compliance with the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA). Elk Hills is a Unit Operation between the U.S. Government and Chevron, USA and covers almost 48,000 acres. It has active production and drilling operations, and produces over 90,000 BOPD and over 360 MMCFD of natural gas. The authors are employees of the Unit Operator (UO), responsible for all aspects of CERCLA compliance at Elk Hills.

Chromium was used as an additive in drilling muds at Elk Hills from the 1950s through the early 1980s at which time its use was discontinued due to its classifications as hazardous waste. In accordance with CERCLA provisions for the identification and remediation of potential past hazardous waste disposal, an identification program was undertaken at NPR-1 in 1986. Through this process, 554 sites were designated at which chromium had been used or may have been used. All sites were inspected, and 62 were found to have some level of chromium contamination. To date, the sites have been remediated and are awaiting confirmation testing to satisfy the Lead Enforcement Agency (LEA) requirement of the cleanup to 1 ppm.
The Austin Chalk: Simulation of Horizontal Wells in a Heterogeneous Formation
Authors: Schnerk G. C. , Madeen C. N.
Published: December 2007

The Austin Chalk is a laterally partitioned reservoir. Horizontal wells penetrate additional partitions that are not produced from vertical wells. The horizontal well data presented in this paper shows that these horizontal wells have currently out produced vertical wells by a factor of five, and additional production is expected. Values consistent with pressure transient testing and core analysis are used to simulate vertical and horizontal wells, and to gain insight into the reservoir mechanisms. Rate derivative curves are used to better understand simulator results.
Modeling Fluid Flow Around Horizontal Wellbores
Authors: Norris S. O. , Piper L. D.
Published: December 2007

Modeling fluid flow around horizontal wellbores with conventional reservoir simulators is somewhat inefficient due to the fact that the radial flow patterns found in the vicinity of the wellbore must be simulated with rectangular coordinate grid-blocks. In this research, we present an efficient hybrid grid model for horizontal well simulation by incorporating radial gridblocks to simulate the radial fluid flow around the wellbore and introduce the concept of spherical gridblocks to model fluid flow around the end of the well. This configuration can dramatically reduce the number of grid-blocks (and therefore computer time) required to accurately simulate the physical model.

The spherical gridblocks consist of hemispheres, corresponding to each radii in the cylindrical coordinate system region, which are intersected by planes that allow coupling to the reservoir region gridblocks. Transmissibilities for the spherical gridblocks are calculated by use of the integrated finite difference method.

Two problems from the literature were chosen to demonstrate the effectiveness of the model. The first problem is a one-phase, constant rate pressure drawdown test for which an analytical solution is available. The second problem is a water cresting problem where the results for comparison were obtained from a commercial reservoir simulator using a grid that reportedly minimized numerical dispersion.
Measurement and Evaluation of Coal Sorption Isotherm Data
Authors: Mavor M. J. , Owen L. B. , Pratt T. J.
Published: December 2007

The proper measurement and interpretation of sorption isotherm data is of primary importance in understanding and predicting the gas production performance of a coalbed methane reservoir. These data are used to predict the release of gas from the reservoir as the pressure is reduced during production and the eventual gas recovery (reserves). A sorption isotherm is a laboratory measurement performed on a representative coal sample to determine the methane storage capacity as a function of pressure. The term "isotherm" results as the experiment is performed at a constant temperature which should be equal to that of the reservoir. This paper presents the use of the data, procedures for performing the measurements, a methodology for interpreting the experimental data for estimates of gas storage capacity and diffusion coefficients of the coal matrix, and isotherms obtained from a variety of coal samples.
Efficient Use of Domain Decomposition and Local Grid Refinement in Reservoir Simulation
Authors: Nacul E. C. , Lepretre C. , Pedrosa O. A. , Girard P. , Aziz K.
Published: December 2007

In order to get desired accuracy in reservoir simulation, one must refine the grid in certain regions, for example, the regions around wells. When this is done in conventional simulators, unnecessary refinement occurs in some regions. This problem is avoided by the use of "Local Grid Refinement" (LGR) techniques, but the resulting matrix is large and of irregular sparsity. In this paper we address several practical aspects of some methods of LGR, including the use of hybrid grid, and then present three highly efficient methods of solving resulting problems with some Domain Decomposition (DD) techniques. In the first method, a relaxation in the unknowns is performed. In the second one, we use overlapping boundaries between the subdomains. In the last one, a coarse grid solution is obtained first and it provides the boundary conditions for the fine grid solution. The LGR and DD methods developed in this work were implemented and tested in a three-dimensional, three-phase, black-oil model. The results are presented in this paper for three examples. It is also shown that the DD technique with overlapping boundaries is extremely efficient for solving problems containing one or more LGR regions. The method proposed in this paper can easily take advantage of parallel processors. Also, it is easy to implement the proposed techniques in existing simulators.

The LGR and DD techniques discussed in this paper improve the accuracy of reservoir simulation around wells and in other regions of high activity. Using these techniques, one not only obtains the correct well pressure, but also the correct saturation near the well. A consequence of this is that WOR and GOR are predicted accurately without well pseudofunctions.
Contractor's Role in Planning Economic Drilling Programs
Authors: Robinson Richard L.
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers Inc.

This paper reviews some of the pressing problems facing drilling contractors in West problems facing drilling contractors in West Texas. These problems are discussed with the idea of presenting solutions that are economically advantageous to the contractor, and that, in turn, would result in savings to the operator. These ideas largely concern operating procedures in which the contractor's ideas may procedures in which the contractor's ideas may vary somewhat from those of the operator. After there are several ways of doing a certain task, several of which could be equally correct. We believe that closer communication and understanding between contractor and operator could influence ways of accomplishing some operations more economically, the theory being that if an operator can do things to save the contractor money, it will, in the long run, save the operator money.

Introduction

Some phases in drilling a well that bear some review as to equipment requirements and operating procedure are blowout preventor and manifold requirements, deviation limits, and mud programs. Some other problems in which the operator should be sympathetic to the contractor include diminishing labor source, value of lost in-hole equipment while on day work, bid lists and procedures, and reduced volume of drilling.

The main reason for the present plight of the West Texas contractor is an over-supply of rigs, along with a continual decrease in drilling. During the period of the Snyder and Spraberry booms, many people were able to go into the drilling business because of the opposite situation—an under-supply of rigs. The contractor has been paying for the prosperous years since 1957. supply and demand are prosperous years since 1957. supply and demand are approaching a leveling-off point where prudent contractors can make a legitimate profit. Operators now are needed to help establish a sound drilling industry that can worry less about just simple survival and can spend some time, effort, and money in improving drilling techniques.

BLOWOUT PREVENTOR REQUIREMENTS

Vitally needed is for contractors and operators to get together on standardization of blowout preventor manifolds. Coral Drilling, Inc. has utilized approximately 20 different company "hook-ups". Fortunately, they never have lost control of a well kick. This would indicate that the majority, if not all, of their manifolds were suitable. Nevertheless, almost every time there is a change of operators, the manifold must be revamped. The cost of these changes varies, but in the long run it must be recovered from the operators.
Suffield Upper Mannville I Gas Storage Project
Authors: Eresman R. K. , Grant R. A. , Mungan N.
Published: December 2007

The conception, the design, the operation and the performance evaluation of a major gas storage project in Alberta, Canada are described. The observed pressure response during the injection/withdrawal cycles, coupled with new well and seismic data and with new geological and reservoir simulation studies, has given a more complete understanding of the reservoir and its behaviour. A study of the downhole temperature behaviour during injection and withdrawal has also been made. The project is performing successfully and meeting the originally anticipated economic benefits.
Performance of Secondary Gas Recovery Operations: North Alazan H-21 Reservoir
Authors: Cagle T. O.
Published: December 2007

From 1980 until 1989 the North Alazan H-21 reservoir was produced as a Secondary Gas Recovery (SGR) project. Much has been learned during the eight years of project operation. It has proven the technical feasibility of depressurizing watered-out gas reservoirs to reestablish gas productivity.

Computer reservoir simulation was used in the initial evaluation of the SGR project and in a recent reevaluation of the project. This latest reservoir simulation incorporates several refinements over the original H-21 reservoir simulation and has the benefit of history matching actual SGR performance. The computer simulation revealed several interesting results about past SGR operation. It was also used to predict future gas recovery from the project.
Performance Analysis in an Immature Waterflood: The Kuparuk River Field
Authors: Currier J. H. , Sindelar S. T.
Published: December 2007

Waterflood development on 160 acre well spacing has been staged over a period of several years in the Kuparuk River Field. The waterflood is implemented in two distinct reservoir sands which flood at significantly different rates due to differing reservoir permeabilities. This paper presents field data and analysis of waterflood performance in the Kuparuk River Field.

Analysis methods of decline curves, log WOR versus cumulative oil production, and the frontal advance X-plot technique are used and results compared. The importance of analyzing data by well and by zone in this dual-zone flood is demonstrated. The method of plotting log WOR versus cumulative oil recovery and the frontal advance X-plot technique result in very similar projections of ultimate recovery. Interpretation of the WOR versus cumulative oil plots are used to diagnose inadequate pattern performance. Waterflood performance trends indicate that decline curves are harmonic or hyperbolic, showing a decline exponent significantly higher than those suggested in industry literature.

Numerical simulations of C Sand waterflood patterns were performed to model layers of different permeability-thicknesses and match observed behavior. Resulting understanding of the C Sand reservoir description is discussed, as well as the implications to projecting waterflood recovery. This understanding is important to investment decisions in continuing field development, as well as to evaluating the potential of infill drilling and enhanced recovery methods.
Alternate Environmental Testing of Drilling Fluids: An International Perspective
Authors: Jones F. V. , Leuterman A. J. J.
Published: December 2007

Testing of drilling fluids and new additives before use offshore has become a common practice in the United States, Canada, and Europe. Standards for testing these systems vary depending on the concerns and perspective of each country. Testing within a country can also vary between regions. This complex set of testing procedures can complicate attempts to market new products. The high cost of testing products worldwide can limit the marketability of useful products and ultimately increase drilling costs.

Testing of drilling fluid systems onshore has taken on a different tack. Onshore disposal of the used mud system is the primary concern. Regulations regarding heavy metals, oil, and salt content in muds can restrict the method(s) of disposal. Because of these restrictions, most drilling operators are now requiring up front analysis of mud systems. This issue has become critical in the United States where each state has jurisdiction over disposal practices. Methods of disposal vary between states and even within states and regions depending on the state's environmental concerns.

Uniform methods of evaluation are being discussed by regulatory agencies now. In the United States, we are developing and reviewing the New Source Performance Standards which will provide a uniform method of evaluation. In Europe, the E&P Forum has developed product data flow charts to check drilling fluid systems and additives in the hopes of developing one standard to be used by all European agencies. In Canada, the regulatory agencies are also re-evaluating their methods of testing and trying to develop a uniform standard. Once these standards are in place, changing them or getting variances for new products will be difficult

This paper reviews the various test methods being used and offers a comparison. It is hopeful that this information can be used by the various regulating agencies as they develop and review their countries' standards.
Simulation Study of a Naturally Fractured, Oil-Wet, Water Drive Reservoir
Authors: Hamon G.
Published: December 2007

A reservoir simulation study of a highly fractured reservoir was carried out to gain insights into the field behaviour.

The field is subject to a natural water drive which provides full pressure maintenance. Water breakthrough occurred in the two producers after three years of production. Laboratory imbibition experiments indicated oil wettability. The reservoir is multi-layered and the ratio between horizontal and vertical fracture permeabilities deduced from pressure transients is very high.

Interesting features of the simulation include:

checks of the exchange term accuracy for an oil wettability case, matrix block height for water-oil gravity drainage is mainly determined by the distance between low permeability streaks rather than by vertical fracture spacing, watercut matching during periods following short term shutdowns of producers can be used to quantify the gravity drainage performance, a good history match even when large overall production rate changes occurred.

Conclusions drawn from this work include the following:

the matrix block height, imbibition capillary pressure, vertical and horizontal fracture permeabilities proved to be the critical parameters to the simulation, water-oil gravity drainage can be efficient in an oil-wet fractured reservoir if the matrix is not tight, phenomenological runs indicated significant watercut sensitivity to the oil production rate : for a given oil recovery, the larger the total production rate the higher the watercut, high initial production rates in oil-wet fractured reservoirs are not detrimental to the ultimate oil recovery, the timing of recompletions and the reduction of off-take rates is essential when large amounts of water produced by a fractured, layered, oil-wet reservoir cannot be disposed of.
A Breakthrough Time Correlation for Coning Toward Horizontal Wells
Authors: Ozkan E. , Raghavan R.
Published: December 2007

This paper presents an approximate analytical method to investigate the behavior of a water or a gas cone and to predict the breakthrough time. For long horizontal wells and large drainage radius, the method presented here requires only a numerical integration of simple trigonometric functions and is considerably simpler than the existing analytical methods. The results are also presented in the form of simplified correlations which can provide quick engineering estimates of the breakthrough time before detailed simulation studies. The method can be applied to both horizontal and vertical wells and permits us to compare horizontal and vertical well performances.
Extended Analysis of Live Reservoir Oils by Gas Chromatography
Authors: Burke N. E. , Chea C. K. , Hobbs R. D. , Tran H. T.
Published: December 2007

This paper describes the development and performance of a gas chromatographic method for determining the extended composition of live reservoir fluids including the permanent gases (N2, CO2,02, H2S) and the C1 through C15 hydrocarbons. The iso- and normal paraffins up through pentane are reported separately. Above pentane, the iso and normal paraffins are reported together. The heavy components of the oil are reported as a C16+ fraction. Information on the equipment used, the method development, calibration procedures, and calculations are provided. High pressure sampling valves are used for reproducible injection of pressurized samples up to 7000 psig [48366 kPa]. The technique determines the composition of the live oil in mole % and requires only a small oil sample. The procedure provides extended compositional data which can be input into reservoir and process design simulators. The method can also be used on stock tank oils, natural gases, liquefied petroleum gases, and other hydrocarbon fluids. Results from several oils are presented and compared with results from conventional gas chromatographic analyses and Podbielniak distillations.
Reduced Adsorption and Emulsion Tendencies in Sandstone Formation Through the Use of Ethoxylates
Authors: Paktinat J.
Published: December 2007

In recent years, nonionic surfactants have been very popular in application such as water flooding, fracturing and acidizing treatments. The most attractive features of this class of chemicals used in acidizing treatments, are their contribution to surface and interfacial tension reduction, water wetting, and low adsorption properties. Almost all surfactants, when applied at low concentrations in a system, alter the surface activities of the fluid by forming aggregates which lower free energy of the system, resulting in lower surface and interfacial tensions. However, many of these surfactants and chemicals adsorb to either the interface or to the solid media such as sandstone, reducing their effectiveness. This phenomenon may result in poor performance of these additives throughout the acidizing treatment and also, may promote emulsion tendencies which may lead to formation damage.

This paper presents results of laboratory studies of various nonionic surfactants and outlines the adsorption of these chemicals within the matrix of sandstone formations. Conditions affecting adsorption properties will also be discussed in this paper.
Prospects for Thermophilic Microorganisms in Microbial Enhanced Oil Recovery (MEOR)
Authors: Premuzic E. T. , Lin M.
Published: December 2007

Microbial activity in crude oils under reservoir and storage conditions has been known to exist for a long time. Such activity can cause deleterious effects in the quality and subsequent processing of crudes. In the past ten to fifteen years, however, a considerable research effort has shown that there are beneficial microbial systems which can be used in microbial enhanced oil recovery (MEOR), a promising process and the resulting biotechnology may be deliverable. In this laboratory, systematic studies are being conducted which deal with the effects of thermophilic, temperature adapted, acidophilic and chemotrophic microorganisms on the chemical and physical properties of selected types of crude oils over a wide range of temperatures, pressures and salt concentrations. Current studies indicate that during the biotreatment several properties of crude oils are affected. The oils are (1) emulsified, (2) acidified, (3) there is a qualitative and quantitative change in light and heavy fraction of crudes, (4) there are chemical changes in fractions containing sulfur compounds, (5) there is an apparent solubilization of trace metals and (6) the qualitative and quantitative chemical and physical changes appear to be microbial species dependent. In this paper, recent work with Boscan crude, a high sulfur, heavy crude oil from Venezuela will be discussed.
The Effect of Hydroxy Aluminum Disoaps on the Viscosity of Light Alkanes and Carbon Dioxide
Authors: Enick R. M.
Published: December 2007

Preliminary results have indicated that hydroxyaluminum disoaps, particularly hydroxyaluminum di(2-ethyl hexanoate) and hydroxyaluminum di (mixed iso-octanoate), can increase the viscosity of propane, pentane and hexane when present in dilute concentrations. These compounds are insoluble in dense carbon dioxide at 293K. Although it is unlikely that these compounds can dissolve in pure methane, they may serve as effective thickneners for hydrocarbon miscible gas mixtures since a large amount of the light alkanes which can be thickened by these compounds is used to enrich the gas.

These disoaps can form extremely high molecular weight, rodlike micelles in solution which increase solution viscosity by several orders of magnitude. These thickeners are water insoluble, and slightly soluble in a North Slope crude oil. Therefore, the partitioning of a small amount of the disoap into the crude oil should not result in a significant loss of mobility control.

Light alkane- and carbon dioxide-miscible cosolvents, such as carboxylic acids or alcohols, can be used in dilute concentration to increase the solubility of these compounds in light alkanes while greatly reducing the time required to achieve dissolution. Most cosolvents will decrease the solution viscosity, but increase the stability of the solution. The capability of various cosolvents to enhance the solubility of these thickeners in dense carbon dioxide is currently being evaluated.
Viscosity Behavior of Alkaline, Surfactant, Polyacrylamide Solutions Used for Enhanced Oil Recovery
Authors: Nasr-EI-Din H. A. , Hawkins B. F. , Green K. A.
Published: December 2007

An experimental study was conducted to examine the effects of various alkalis, surfactants and brines on the viscosity of dilute aqueous solutions of Alcoflood 1175L, a partially hydrolyzed polyacrylamide polymer, over a wide range of parameters.

In general, the viscosity-shear rate relationship exhibited a Newtonian behavior at low shear rates and a power-law behavior at high shear rates. Adding a non-ionic species (Triton X-100) had an insignificant effect on the viscosity-shear rate relationship. However, adding an ionic species, (sodium chloride, calcium chloride, or an anionic surfactant) reduced the hydrodynamic size of the polymer molecule (physical change), changing the viscosity-shear rate relationship. The viscosity-shear rate relationship was found to be a strong function of cation type only at salt concentrations less than 4 wt%. For a given polymer concentration, the power-law constants were found to be exponentially related.

The effect of alkalis on the viscosity of polymer solutions was complex as they affected the polymer chain both physically (charge shielding) and chemically (hydrolysis). For alkali/polymer solutions, the viscosity was found to be a function of alkali type, concentration and time after initial mixing. The effect of these parameters on the viscosity of alkali/polymer solutions diminished by adding NaCl. The addition of anionic surfactants at low concentrations slightly decreased alkali/polymer solutions viscosity. However, a significant viscosity enhancement for alkali/polymer solutions was observed at higher surfactant concentrations and over a narrow range of alkali concentrations.
A Case Study of High-Temperature Wells Fractured Using Multiple Fluids To Improve Conductivity and Well Performance
Authors: Wheaton W. E. , Lipari S. A. , Morris M. D. , Boney C. L. , Thomas R. L.
Published: December 2007

A study, directed at the improvement of hydraulic fracturing treatments performed in the Lobo Wilcox formation in south Texas, is presented. During the study, the performance of numerous gas wells fractured using a single-fluid (organometallic crosslinked) or a multiple-fluid (organometallic and borate crosslinked) technique was determined. During the multiple-fluid treatment (MFT) the organometallic-crosslinked fluid is pumped followed by a borate-crosslinked tail-in fluid.

The field study indicates Lobo Wilcox wells fractured using conventional high-temperature fracturing fluids (organometallic-crosslinked fluids) exhibit poor production in comparison to wells fractured using multiple fluids. Improved fracturing fluid recovery and improved well performance were observed in wells fractured with multiple fluids. The improved well performance is attributed to less conductivity impairment by the borate tail-in fracturing fluid. This technique can be used in any high-temperature well to "economically" improve fracture conductivity.
Control of Core Wettability With Crude Oil
Authors: Jia Duo , Buckley J. S. , Morrow N. R.
Published: December 2007

Consistent laboratory studies of the effect of wettability on fluid displacement in core flood experiments have long been hampered by the lack of cores with well defined, reproducible wetting states, other than strongly water or oil wet. There is ample evidence that wettability is an important factor in determining the outcome of core floods. Wetting can be altered using organic reactants, however the wetting state produced may not be representative of realistic wetting conditions. In this study, the control of wetting using crude oils at various aging conditions is explored.

Berea core plugs, saturated with brine, were flushed with crude oil and aged at a set temperature ranging from 22-90°C. Two crude oils were used, one from West Texas and the other from the North Sea. After aging, the crude oil was displaced by mineral oil and wettability was assessed using a variation of the Amott imbibition test. The procedure was developed for testing the effect of drilling mud filtrates on wettability for a range of wetting conditions.

Variables which affected the wettability index were often interdependent. They included the crude oil, the temperature at which the cores were aged with the oil, the initial water saturation, the aging time, and the volume of crude oil with which the core was flushed. Cores with wettability from strongly water-wet to neutrally wet could be produced by varying the conditions of crude oil exposure. Aging temperature and initial water saturation have predominant influence on the wettability induced by a given crude oil. However, all of the factors mentioned above must be considered in order to reproduce the state of wetting from one core plug to another. Stability of the altered wetting states was found to be reasonable for tests in which the cores were stored for two months in mineral oil.
A Model for Evaluating the Hidraulic Performance of Well Perforations
Authors: Shaw David C. , Dozzo Joseph A.
Published: December 2007

Perforation design is an important aspect of the completion of production and injection wells. Significant penalties can be incurred both through productivity loss or additional perforation costs if the design is not accurately optimized. These penalties are especially severe in the case of high-rate gas wells.

The Well Perforation Performance Model (PERF) was developed as a collaboration between SSI, London and BP Exploration, Aberdeen. It allows different perforating methods to be evaluated and compared to select the ideal gun and charge for a given perforation job.

A major technical feature of the program is the finite element simulator, which allows accurate modelling of complex geometries. It can analyze great detail on small computers.

The program allows the analysis to carried out in detail, using a state-of-the-art finite-element simulator, or more rapidly using a set of industry-standard nomographs. A database of gun and charge characteristics is provided, which records the results of API laboratory tests, so that typical perforating problems can easily be set up.

The results, in terms of a productivity index or flow efficiency, can be viewed graphically as a function of the main physical parameters, including: Shot Density, Perforation Length and Diameter, Phasing, Damage and Compaction, Gravel Packing.

Comparisons are provided against earlier published theoretical and experimental work, demonstrating improved accuracy and usability of the technology.
The Effect of Temperature and Interfacial Tension on Oil-Water Relative Permeabilities in Consolidated and Unconsolidated Porous Media
Authors: Okoye C. U. , Hayatdavoudi A. , Oungpasuk Piya , Wang Pin-Hu
Published: December 2007

Several displacement tests for primary and secondary oil recovery processes using conventional steam and caustic steamfloods (0.5% and 1.0% NaOH concentration by weight) were conducted to determine the oil-water relative permeabilities. The results of the test show that oil-water relative permeabilities are temperature and low tension sensitive. The tests for each oil recovery process were run at various temperatures ranging from 200°F to 400°F. Using the displacement data and oil-water physical properties, the relative permeability curves were constructed and the multiple regression analysis was employed to generate correlation equations. The relative permeability curves generated with the correlation equations fit fairly well the data points evaluated from experimental results.

The oil-water relative permeability curves shift toward higher water saturation with increase in temperature and/or decrease in interfacial tension. The oil relative permeability curve shifts for all test cases examined are substantial while the shifts of water relative permeability curves are relatively small for steamfloods and virtually coincident for caustic steamfloods. It was also observed, that for the same increase in temperature, the oil relative permeability curve shift is much larger tor caustic steamflooding processes than lor the conventional steamflooding. This observation clearly shows the effect of low tension systems on oil-water relative permeabilities.
PDC Bit Selection Method Through the Analysis of Past Bit Performances
Authors: Fernando Fontenelle Dumans Carlos , Edgar Maidla Eric
Published: December 2007

A method to evaluate the performance of PDC and tricone bits is presented based on their cost, on a foot basis, and the rock strength properties (shear stress for PDC bits and compressive stress for tricone bits). The results showed that much data is needed for PDC performance evaluation when compared to a similar procedure for tricone bits, mainly due to the better description of the tricone bit when using the currently proposed IADC classification system.
Front Tracking Applied to the Simulation of Water Flooding in a Braided River System
Authors: Sovold Knut , Rian Dag Terje , Sandvik Arnfinn
Published: December 2007

This paper describes the application of a front tracking simulator for studying flow in a 2D crosssection of a braided river systea. The internal sand body geometries were based on a braided river outcrop from the USA. Rock properties were derived from a North-Sea oil field.

Front tracking represents a direct, accurate and fast method to simulate oil and water flow in highly heterogeneous reservoirs. In the front tracking simulator the saturation solution is decoupled from the grid and its accuracy is to a large extent independent of grid block sizes and geometry. This makes the reservoir simulator well suited for modelling of complex geological architectures. The simulator has been compared with analytical methods and traditional finite difference simulators.

Results from a water-oil displaceaent process in a braided river systea are presented, showing fingering of the saturation fronts due to peraeability contrasts. For coarse grid systems, the front tracking simulator proved superior to the finite difference simulator with respect to the numerical solution.

An automstic grid fitting option that utilizes triangular grid cells enabled an easy and fast construction of the complex geological model.
Horizontal Well Performance Simulation
Authors: Prasad Raj K , Coble Larry E.
Published: December 2007

A single well, single phase, r-θ-z simulator was used to analyze a well test conducted in a horizontal well. Apart from the usual features of general numeric simulators, the simulator used for this work accounted for the effects of wellstorage, variable skin on different portions of the wellbore, turbulent flow, cross-flow between layers, hydraulic fractures with variable conductivity and partial penetration. Because of these features, the simulator is extremely versatile for well test analysis.

The horizontal well was modeled by using the horizontal portion of the well as an axis to set the radial grids which ensure radial flow around the wellbore. This near-wellbore radial flow condition cannot be modeled accurately during early test times with the Cartesian blocks used in most black oil simulators. In the r-θ-z simulator, top and bottom reservoir boundaries are defined using several r-θ blocks and eliminating grid blocks outside the boundaries as illustrated on Figure 1. Reservoir limits in the horizontal directions are defined by using several blocks along the well (z) axis and multiple radial blocks.

This r-θ-z simulator has been used to analyze buildup tests in horizontal wells where conventional analysis methods did not yield meaningful results because:

the early time data were influenced by the wellstorage and the top and bottom boundary effects and the so-called pseudoradial flow regime necessary for conventional analysis were absent due to insufficient test times.
Production Logging in Horizontal Wells: Applications and Experience to Date
Authors: Chauvel Yves Leon , Oosthoek Paul
Published: December 2007

Reservoir drainage by means of horizontal wells has become a new frontier in the oil industry, and all the divisions of this industry: drilling, cementing, logging, completion, stimulation and production are active in this endeavour, both at the research level and in the field. One of the most relevant reasons why horizontal wells are drilled and completed resides in the favourable productivity indices that are associated with horizontal well production.

In order to evaluate the flow mechanisms leading to these gains in productivity, production logging is becoming a common practice, in spite of some operational’ difficulties many of which have been overcome by means that we shall review. Production logs are used in horizontal wells to diagnose unwanted-fluid entries, to obtain flow profiles, to locate producing fractures or for transient testing.

In this paper we shall review the essential characteristics of production logging in horizontal wells. Some are due to the effect of the environment: flow regimes, well geometry. Some come from limitations of the current sensors, caused by the unorthodox position of the tool string as opposed to its traditional near-vertical position in standard wells. We shall also review the application of some measurements which have not been widely used, but which carry a high potential for diagnosis.

We shall give examples of data acquisition and interpretation, showing that satisfactory answers of often excellent quality can be obtained in many types of flow regime and completion configuration, in spite of the hostility of the environment.
Application on Horizontal - Test Methods
Authors: Donoso Jose Maria , Daniel Guillermo Alberto
Published: December 2007

The build-up performance for a vertical and two horizontal welltests in the same formation are investigated in this paper. Real time pressure and temperature acquisition were performed with a strain gauge and a downhole cable operated shut-in valve for all three tests. Unfortunately, the amount of time necessary for the horizontal test interpretation analysis to yield unique reservoir and well parameters is found to be insufficient.

Thus, external "information such as core analysis, deviation surveys and geological modeling is used in order to confirm all the available information. The proposed interpretation methodology is to match the actual data to an analytical solution of pressure and its derivative behavior. This is done by adequately combining this external knowledge of the well and reservoir with the calculated parameters from the well test analyses.

The values obtained in this way serve the purpose of checking this peripherical information against well testing interpretation and observe their combine results consistency.
New Slurry Mixer Improves Density Control in Cementing Operations
Authors: O'Neill Eamonn , Téllez Luis E.
Published: December 2007

Poor slurry density control in cementing operations leads to a failure to reproduce laboratory designs at the field level. Adverse consequences include poor bonding, incomplete fill-up, inefficiency of cementing additives, lower compressive strength, erroneous thickening time, and possible inability to control formation pressures.

In three locations worldwide, field testing of a new closed-loop control slurry mixer has demonstrated that density control can be achieved while mixing and pumping direct to the well. There is no need for batch-mixing facilities, because the entire slurry is pumped at the correct density.

The test installations, types of jobs and slurries pumped during the first 12 months, and the parameters recorded to measure the effectiveness of the mixer are discussed in this paper.

The results and conclusions demonstrate that the mixer can automatically control density during mixing within 0.1 lb/gal. Other results include improved field slurry rheology, capacity to mix conventionally problematic slurries, and shorter operational time.
Sucker Rod Centralizers for Directional Wells
Authors: Rivas O. , Newsky A. , Cedeno M. , Rivera P.
Published: December 2007

The industry trend towards directional and horizontal wells demands development and use of new equipment to solve the problems raised by the well deviation angle. Perhaps, the strongest limitation for the use of sucker rod pumping in directional and horizontal wells is the early failure of the tubing and sucker rod string. This is caused by the severe wearing of these components due to the continuos friction between them. The life of the subsurface pump life is strongly affected by stem misalignment All these problems are seriously increased if the well has been steam injected.

A Sucker rod centralizer, has been developed to reduce the wearing of the tubing, sucker rod string and subsurface pump. So far, centralizers have been installed in seven deviated wells in the Orinoco Belt Field. The use of these centralizers has resulted in a 300% increase of the active life of tubing, sucker rod string and subsurface pumps. These seven wells were steam injected and are producing under an emulsion scheme.
History Matching of Unsteady - State Corefloods for Determining Capillary Pressure and Relative Permeabilities
Authors: Grattoni Carlos Atilio , Bidner Mirtha Susana
Published: December 2007

A method for the simultaneous determination of capillary pressure and relative permeability curves of oil/water systems from coreflood experiments is presented. The Levenberg-Marquardt optimization technique is used to match results from a numerical simulator to laboratory coreflood data by applying a nonlinear least-squares procedure. The simulator is an IMPES finite-difference program which models the simultaneous one-dimensional flow of oil and water through a core. Exponentional functions are used to describe relative permeabilities and capillary pressure curves.

Results show that relative permeabilities can be in error when capillary pressure terms are neglected and that the adjustment of a variable which combines oil and total flow rate output data leads to better matches than the adjustment of cumulative oil recovery.
Well Testing Design Under Harsh Environment
Authors: Borges Fernando Assumpção , Felix Márcio , Bezerra Carvalho
Published: December 2007

The oil industry's search for new hydrocarbon accumulations has led to the drilling of ever deeper wells, normally under harsh conditions that involve high pressures, temperatures and mechanical strengths as well as sour gas production. In order to perform drill-stem tests (DSTs) safely, these constraints must be overcome.

PETROBRÁS, the Brazilian state owned oil company, has been drilling wells in ever deeper horizons, reaching up to 18,000 ft (5,500 m). During the last five years some important areas have been discovered, especially offshore, of which the Tubarão Field in Southern Brazil is one example. Based on well-testing experiences in the North Sea, as well as the company's own experience, PETROBRÁS has developed a new approach for testing deep wells: the use of a simple and reliable test-string assembly, achieved by reducing and replacing components, and the adoption of extremely rigorous safety standards and careful selection of materials suitable for use in the presence of hydrogen sulphide.

This paper presents a field-proven well-testing design, whose main concerns are offshore safety and environmental quality.
Special Operations Integrated System
Authors: Lopes D’Almeida Albino
Published: December 2007

ABSIBACT

A distributed processing system was designed to monitor and control special drilling operations. It is fed by five regional centers located across Brazil; all information is also available at the head offices in Rio de Janeiro, where data are grouped. This user-friendly system deals with technical, cost, equipment, and personnel data pertaining to fishing, core sampling, drill-stem testing, and cementing assembly operations.

It can generate consolidated reports containing statistical data as well as operation reports. The system monitors equipment service life and performs preventive maintenance tasks. Through the computer network, specific operations may be accessed and records transferred to accompany movement of personnel and tools.
Static Hydrocyclones: A Cost Effective Alternative for Produced Water Treatment
Authors: Choi Michael S.
Published: December 2007

Ever increasing water production and more stringent environmental standards have driven up the cost of produced water disposal. What was once a small consideration in the design of production facilities has become a high profile and costly component of offshore production projects. The large space and weight requirement for conventional produced water treatment (PWT) systems (skim tanks, CPI's and flotation cells) could have a large negative impact on the overall economics of a deep water development.

Recent advances in static hydrocyclone technology for PWT has added an attractive alternative to conventional systems. Within certain operating limits, hydrocyclones have proved to be effective in reducing oil-in-water content to environmentally acceptable levels. In contrast to a conventional PWT system, hydrocyclones provide offshore operators the benefits of light weight, compact size, easy and reliable operation, low maintenance, complete insensitivity to platform motions, low utility requirements and highly predictable capacity. In many cases, good performance is achieved without the use of chemicals. As water production increases, additional hydrocyclones can be added without extensive piping modifications or costly construction barge time. This unique feature allows operators the flexibility to phase in PWT capacity as it is needed. All this often adds up to lower costs for a non revenue producing function, and provides a cost effective alternative for meeting stringent corporate guidelines and environmental standards.