bluuebunny/crossref_metadata_2025 huggingface dataset:
TrkB Agonists Ameliorate Obesity and Associated Metabolic Conditions in Mice
Authors: Tsao David , Thomsen Heather Koenig , Chou Joyce , Stratton Jennifer , Hagen Michael , Loo Carole , Garcia Carlos , Sloane David L. , Rosenthal Arnon , Lin John C.
Published: December 2007

Mutations in the tyrosine kinase receptor trkB or in one of its natural ligands, brain-derived neurotrophic factor (BDNF), lead to severe hyperphagia and obesity in rodents and/or humans. Here, we show that peripheral administration of neurotrophin-4 (NT4), the second natural ligand for trkB, suppresses appetite and body weight in a dose-dependent manner in several murine models of obesity. NT4 treatment increased lipolysis, reduced body fat content and leptin, and elicited long-lasting amelioration of hypertriglyceridemia and hyperglycemia. After treatment termination, body weight gradually recovered to control levels in obese mice with functional leptin receptor. A single intrahypothalamic application of minute amounts of NT4 or an agonist trkB antibody also reduced food intake and body weight in mice. Taken together with the genetic evidence, our findings support the concept that trkB signaling, which originates in the hypothalamus, directly modulates appetite, metabolism, and taste preference downstream of the leptin and melanocortin 4 receptor. The trkB agonists mediate anorexic and weight-reducing effects independent of stress induction, visceral discomfort, or pain sensitization and thus emerge as a potential therapeutic for metabolic disorders.
The Area Analysis of Resources
Authors: Webster Barbara , Stewart John
Published: December 2007

There has been increasing interest in this country in variations in expenditures between different local authorities among political scientists, social administrators, economists, and others, as there has been elsewhere. All these and other studies are distinguished by their concentration upon variations in expenditure between local authorities. The local authority has been treated as the basic unit. There has been no parallel development in studies of the degree of variation of expenditure within the area of the local authority.

Some of the factors considered as determinants of variations in expenditure in the inter-authority studies will also vary within the area of the local authority. Social conditions, for example, may differ markedly over an urban area. The question therefore arises as to whether any variation in expenditure by the local authority is, or should be, related to such social differentiation. An intra-authority analysis of resources is supported by research aimed simply at describing or explaining social patterns within cities. Work has been undertaken to identify areas of social malaise or areas of multiple deprivation within urban areas. A comparison of the areal distribution of resources with that of social malaise or deprivation may provide guidance for future allocation decisions.
Using the Computer to Estimate Entitlement: A Feasibility Study
Authors: Adler Michael , Feu David du
Published: December 2007

As reported elsewhere we have developed a computer program which, on the basis of information about a family’s financial and household circumstances derived from a single application form, assesses that family’s entitlement to virtually all the statutory and discretionary means-tested benefits available in the County of Midlothian. The program lists the name and calculates the amount of each benefit to which the family is entitled and states where and how the benefit can be claimed. It has obvious implications for such problems as low take-up, the development of advice and information services, the relations between authorities and departments which dispense benefits and, in the longer term, for a more profound reform of our system of income maintenance. In this research note, we describe in some detail the small feasibility study carried out during July 1973 in Midlothian. As we did not possess the resources for a comprehensive, larger-scale evaluation of the program, the feasibility study was restricted to exploring the potential of a number of different methods of distributing the application forms and discovering the kind of practical problems likely to arise during implementation. Even with these limited objectives, the study had to be on a small scale.
Integral equations for an inverse boundary value problem for the two-dimensional Stokes equations
Authors: Alves C. J. S. , Kress R. , Silvestre A. L.
Published: December 2007

The problem to determine the location and shape of a perfect conductor within a conducting homogeneous host medium from measured current and voltages on the accessible exterior boundary of the host medium can be modelled by an inverse Dirichlet boundary value problem for the Laplace equation. For this, recently Kress and Rundell suggested a novel inverse algorithm based on nonlinear integral equations arising from the reciprocity gap principle. The present paper extends this approach to the problem to recover the location and shape of a rigid body immersed in a fluid from the measured velocity and traction at the exterior boundary of the fluid, that is, to an inverse boundary value problem for the Stokes equation. The mathematical foundation of this extension is provided and numerical examples illustrate the feasibility of the method.
Institutional Repositories in the Context of Digital Preservation
Authors: Wheatley Paul
Published: December 2007

This report will focus on the requirements, functions and use of digital preservation in an institutional repository context. It will also provide an overview of existing institutional repository software as well as details of working systems and their core aims and purpose. Software that could be installed and used to perform the role of an institutional repository will be covered by this report.
Book Reviews
Authors: Modenos Lisa
Published: December 2007

Echoes from the Dead Zone: Across the Cyprus Divide. Yiannis Papadakis. I.B Tauris & Co. Ltd. 2005. 224 pages. ISBN: 185043428X.
Book Reviews
Authors: Judd Maya
Published: December 2007

Barren States: The Population “Implosion” in Europe. Carrie B. Douglass (ed.). Berg: Oxford, New York. 2005. 270 pages. ISBN: 9781845200480 (cloth) and 9781845200490 (paper).
Book Reviews
Authors: Selby Jennifer
Published: December 2007

Why the French Don't like Headscarves: Islam, the State, and Public Space. John Bowen. Princeton and Oxford: Princeton University Press. 2007. 328 pages. ISBN‐10 0691125066.
Book Reviews
Authors: Unger Susanne B.
Published: December 2007

Europeanisation, National Identities and Migration: Changes in Boundary Constructions between Western and Eastern Europe. Edited by Willfried Spohn and Anna Trainadfyllidou. Routledge Advances in Sociology, London and New York. 2002. 304 pages. ISBN 978‐0415296670.
Book Reviews
Authors: Burland Daniel
Published: December 2007

Ethnic Conflict and Terrorism: The Origins and Dynamics of Civil War. Joseph L. Soeters. Routledge. 2005. 124 pages + notes + bibiliography. index. ISBN 0415365880.
Sport, Landscape, and the National Identity: Representations of an Idealized Vision of Nationhood in Slovenian Skiing Telecasts
Authors: Kotnik Vlado
Published: December 2007

The paper explores the role of the televised landscape in presenting alpine skiing as a Slovenian national pastime as well as being distinctive TV sport. Alpine skiing is one of those sports where the Slovenian nation‐imagining has been exercised extensively throughout the last decades. In Slovenia, alpine skiing with its related natural scenery, sporting events and national heroes, is one of the main sports arenas in which the recent Slovenian emancipatory nationalism has been significantly negotiated. After Slovenia's political secession from Yugoslavia, with the so called “ten‐day‐independence‐war” in 1991, the new nation‐state also needed a new national landscape. Many tourist resorts, natural monuments and sights and places perceived as well‐known Slovenian identification symbols since the 19th century, were noticeably revitalized through live sporting and cultural TV broadcasts. Our findings show the ways in which skiing and its natural setting have been utilized by Slovenian National Television to establish and reproduce an idealized vision of nationhood and national identity in past decades, but particularly in recent winter seasons.
A Psychometric Analysis of the Epworth Sleepiness Scale
Authors: Heaton Karen , Anderson Debra
Published: December 2007

Psychometric performance of the Epworth Sleepiness Scale (ESS) has not been evaluated in groups of workers. This study evaluated its use in a sample of 843 long-haul truckers. Interitem correlations and Cronbach’s alpha were conducted. Correlation of the ESS with the sleep problems subscale of the Trucker Strain Monitor (TSM) was performed. Dimensionality was evaluated using factor analysis. Cronbach’s alpha (.79) was strong. Interitem correlations were significant. A weak but significant correlation between the ESS and TSM sleep problems subscale (r = .18, p = < .001) was shown. Factor analysis yielded two factors that explained 56.2% of scale variance. The ESS performed well in the current sample. It is an inexpensive, time/cost-effective instrument. It should be considered for use in studies of workers in naturalistic settings.
Development and Psychometric Evaluation of the Self-Efficacy for Appropriate Medication Use Scale (SEAMS) in Low-Literacy Patients With Chronic Disease
Authors: Risser Jessica , Jacobson Terry A. , Kripalani Sunil
Published: December 2007

Medication nonadherence remains a significant obstacle to achieving improved health outcomes in patients with chronic disease. Self-efficacy, the confidence in one’s ability to perform a given task such as taking one’s medications, is an important determinant of medication adherence, indicating the need for reliable and valid tools for measuring this construct. This study sought to develop a self-efficacy scale for medication adherence in chronic disease management that can be used in patients with a broad range of literacy skills. The Self-efficacy for Appropriate Medication Use (SEAMS) was developed by a multidisciplinary team with expertise in medication adherence and health literacy. Its psychometric properties were evaluated among 436 patients with coronary heart disease and other comorbid conditions. Reliability was evaluated by measuring internal consistency and test-retest reliability. Principal component factor analysis was performed to evaluate the validity of the SEAMS. Reliability and validity analyses were also performed separately among patients with low and higher literacy levels. The final 13-item scale had good internal consistency reliability (Cronbach’s α = 0.89). A two-factor solution was found, explaining 52.3% of the scale’s variance. The scale performed similarly across literacy levels. The SEAMS is a reliable and valid instrument that may provide a valuable assessment of medication self-efficacy in chronic disease management, and appears appropriate for use in patients with low literacy skills.
Comparing the Rotary With Potential Drilling Methods
Authors: Simon R.
Published: December 2007

Most new methods of oil well drilling achieve increased rates of penetration essentially by increasing the mechanical power input to the rock over the maximum practical power level obtainable by conventional rotary drilling. However, whether this would decrease the drilling cost per foot of hole depends upon other factors as well, such as the cost of operation per unit time, well depth and the distribution of rocks of various drillabilities at the well site.

Introduction

Rotary drilling, introduced about 1900, is today the most widely used method of drilling oil wells in this country. The past 50 years have seen great strides in improved equipment and techniques for rotary drilling. However, the limitations of rotary drilling have long been recognized and there have been many attempts to develop new drilling methods to supplement or to supplant rotary drilling. The potentialities of some of these new drilling methods for decreasing the cost of drilling oil wells are discussed herein.

Drilling Rate and Mechanical Power

One significant result of a study of the fundamentals of rock drilling made at Battelle is that the fracture of brittle rock from the bottom of a hole by repetitive, indexed mechanical loading involves the expenditure of a certain amount of mechanical energy per unit volume of rock fractured out. Therefore, the rate of penetration of any mechanical drilling machine would be essentially directly proportional to the mechanical power developed in the rock per unit area of hole and inversely proportional to the drilling strength, which is the energy required to fracture off a unit volume of rock.

Limitations of Rotary Drilling

The mechanical power output to the rock for conventional rotary drilling is proportional to the torque required to turn the bit at the bottom of the hole and to the rate of rotation of the bit. The torque reaction to rotation associated with a given amount of static weight loading on the bit is less for the rocks of greater drilling strength. Since less mechanical power is developed in rocks of greater strength, the rate of penetration decreases more rapidly than in inverse proportion to the drilling strength. There is, consequently, a wide range in the drilling rates obtained by rotary drilling, perhaps about 50 to 1 from the weakest to the strongest rock of interest in oil well drilling.
Early Performance Review of a Successful Pressure Maintenance Project in a Deep Louisiana Reservoir
Authors: Greenwalt Don R.
Published: December 2007

The Broussard oil sand unit, operated by Tidewater Oil Co, is located in the Erath field, Vermilion Parish, La. The unit was formed as a reservoir-wide pressure maintenance project utilizing salt water injection below 12,500 ft. Formation of a reservoir-wide unit was accomplished and pressure maintenance operations were initiated in April, 1961. Actual performance of the project during the more than three years of operation has been very close to predicted performance. Reservoir productive capacity is in excess of the unit allowable of 1,764 BOPD. Performance of the project to date indicates that ultimate recovery from the reservoir will reach or exceed the predicted value of 7.4 million STB oil.

Introduction

The Broussard oil sand unit is located in the Erath field of Vermilion Parish, La. (Fig. 1). The Broussard sand was proven productive with the completion of the Tidewater Oil Co. H. H. Broussard Well No. 1 (B-4) in Jan., 1957. Development of the reservoir was completed in 1959, with 13 oil completions producing 1,538 B/D from an average depth of 12,440 ft sub-sea. In addition to the 13 producing wells, four dry holes were drilled before the reservoir limits were completely defined. Pressure-production performance of the reservoir indicated the reservoir energy mechanism is solution-gas drive with a weak water drive. Reservoir engineering studies indicated that the natural reservoir energy would recover only 31 per cent of the estimated 12.8 million STB oil initially in place. Secondary recovery feasibility studies indicated that pressure maintenance by water injection could greatly increase the ultimate recovery from the reservoir. The reservoir was unitized on a 100 per cent acre-foot basis, effective April 1, 1961. On that date, Tidewater Oil Co. became operator of the first reservoir-wide unit to be formed under Louisiana Department of Conservation Act 441, Act 441 provides for forced pooling of a reservoir to prevent mineral waste if 75 per cent of both the royalty interest owners and the working interest owners approve the unitization.

Sixteen days after unitization was effective, pressure maintenance operations were initiated by down-dip water injection in one well. Additional development has expanded the injection pattern to five wells, all of which are injecting water below a depth of 12,500 ft sub-sea. The pressure maintenance project has been in operation for over three years. During this time over 1.9 million bbl of oil have been produced and 3.1 million bbl of water have been injected. This paper is a review of the operation of the project during the three years since unitization with a comparison of predicted pressure maintenance performance vs the actual performance.

Geological and Reservoir Data

The Broussard oil sand unit is one of Louisiana's and the petroleum industry's deepest water injection projects in an oil reservoir. The reservoir is located on a monocline from a depth range of 12,200 to 12,600 ft sub-sea (Fig. 2).

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The Effect of Temperature on Gelation Time for Polyacrylamide/Chromium (III) Systems
Authors: Jordan Deborah S. , Green Don W. , Terry Ronald E. , Willhite G. Paul
Published: December 2007

Gelled polymers are being applied to modify the movement of injected fluids in the vicinity of injection and production wells in secondary and enhanced oil-recovery projects. One approach to gelation is to form a bulk gel in situ by injecting a slug of a Polyacrylamide polymer solution containing chromium(VI) followed by a polymer slug containing a reducing agent such as sodium bisulfite. Upon mixing, CR(VI) is reduced to Cr(III), and in the subsequent reaction a gel is formed. The gelation time controls the volume of fluid that can be injected in the treatment and thus is an important variable in the process. Gelation time is known to be a function of the concentration of the reactants (chromium ion, reducing agent, and polymer) as well as the polymer type, and some data relating these variables to gelation time have been reported. Another variable affecting the reaction rate is temperature, but no data relating gelation time and temperature have been published.

The purposes of the work described in this paper were to obtain experimental data on the effect of temperature on gelation time for typical polyacrylamide/Cr(III) gel systems over the range of temperatures commonly encountered in reservoirs and to develop a method of correlating the data. Gelation times were measured for five different polymers, including polymers with various degrees of hydrolysis and polymers with nonionic, anionic, and cationic character. The temperature range was 25 to 80°C. Polymer, metal ion, and redox system concentrations and salinity also were varied. It was determined that, for a given polymer-reducing agent system at a specified concentration, the gelation time decreases as temperature is increased. The data were correlated in a manner analogous to the Arrhenius method of correlating chemical reaction rate data. That is, plots of the logarithm of gelation time vs. the reciprocal of the absolute reaction temperature were linear over the temperature range studied. By use of a simple nth-order reaction rate model, the slope of the Arrhenius-type plot was related to activation energy. These activation energies were found to vary only slightly for the polymer systems and concentrations investigated.

The results have direct application in the design of gel treatments for injection or production wells. The correlation method provides a way of predicting the effect of temperature on the time required for a given system to gel. It is recognized that in field applications factors beyond the scope of data taken in this paper may affect the gelation process.
Changes in Earth Stresses Around a Wellbore Caused by Radially Symmetrical Pressure and Temperature Gradients
Authors: Perkins T. K. , Gonzalez J. A.
Published: December 2007

Pressure and temperature gradients are created around wellbores during waterflooding or when fluids are injected in connection with any other secondary or tertiary recovery process. These gradients result in changes in earth stresses, which in turn cause hydraulic fracturing pressures to change.

In this paper, analytical solutions have been used to determine the stresses resulting from radially symmetrical temperature and pressure changes around a wellbore. These stresses are required to predict the change in fracture extension pressure that is caused by the injection process. Exact, closed-form solutions are given for the stresses. These have been evaluated with a computer, and more convenient empirical formulas have been fitted to the calculated results. Solutions for discrete cylindrical or disk-shaped regions of changed temperature and pressure are shown. Also, the solutions can be adapted to annular elements of finite thickness that are convenient for incorporation to an r-z-type computer program. Such a program could then be used to compute the stresses resulting from temperature and pressure fields that vary gradually in the radial direction.

This paper gives examples to illustrate the effect of injecting a large volume of liquid that is cooler than the insitu reservoir, as is common when waterflooding. The cooling can have a large effect on lateral earth stresses, and for some conditions vertical hydraulic fracturing pressures can be significantly reduced.
Pembina Pilot Water Flood Proving Successful
Authors: Justen John J. , Hoenmans Paul J.
Published: December 2007

Introduction

The Pembina field, located in the Province of Alberta in Western Canada as shown above, is the largest oil field in Canada and one of the largest in the North American continent. The productive area, as defined by the Alberta Oil and Gas Conservation Board, is approximately 300,000 acres. Over 2,000 wells have been drilled. The original oil in place is estimated to be 4 billion STB. Although less than five years old, the pool to date has produced nearly 100 million bbl of oil. The current production rate is 100,000 B/D. The graphic reservoir history is presented in Fig. 1.

The reservoir is a stratigraphic trap producing from the Cardium formation. Neither bottom water nor free gas has been found. This sandstone has an average net thickness of 19.0 ft, an average porosity of 14.2 per cent and an average interstitial water saturation of 10.5 per cent. The average permeability varies from 34 md in the main part of the pool to 9 md in the western part. Nearly every well has been fractured to obtain production in commercial quantities.

The crude oil was initially undersaturated with a major portion having a solubility in the order of 500 scf/bbl and a bubble point in the order of 1,700 psig. The average gravity is 37.1°API.

Increasing gas-oil ratios, decreasing productivities, and rapid pressure decline have established the producing mechanism to be the expansion of the undersaturated crude oil followed by solution gas drive. The natural depletion recovery has been estimated at 12.5 per cent.

Pressure maintenance studies of various areas in Pembina have indicated that the recovery can be increased 2½ times by water flooding. Beginning in 1956, waterflooding operations were commenced by several operators. Most of these operations were pilots. One such operation was commenced by Mobil Oil in Canada, Ltd. which has more than 50,000 acres and over 550 wells.
Real Gas Pseudopressures For CO2 Reservoirs
Authors: Tiab Djebbar
Published: December 2007

This paper presents a new method for correlating real gas pseudopressure values of gas reservoirs containing large amounts of CO2. Special attention is devoted to gas reservoirs in Colorado, New Mexico, and Utah. These reservoirs have 95 to 100% CO2 concentrations. The effects of CO2 on the skin factor also are analyzed.

The main results of this study are that (1) the effects of CO2 on the conventional pressure analysis techniques are severe at higher mole fractions and at pseudoreduced pressures greater than one, (2) if real gas pseudopressure data are not properly corrected, the reservoir permeability calculated from pressure buildup and drawdown tests will be considerably less than the actual value, and (3) the proposed technique is simple, quick, and accurate enough to calculate pseudopressure values. This method is also useful in gas reservoirs with 0 to 100% CO2 concentrations.

CO2 affects the skin zone both physically and chemically, in most cases favorably. The total skin factor is slightly dependent on time for very short transient flows. However, it ultimately will become constant as the CO2 gas sweeps the entire skin zone.
Pressure Transient Analysis of Two-Phase Flow Problems
Authors: Chu Wei-Chun , Reynolds A. C. , Raghavan Rajagopal
Published: December 2007

This paper considers the analysis of pressure drawdown and buildup data for two-phase flow problems. Of primary concern is the analysis of data influenced by saturation gradients that exist within the reservoir. Wellbore storage effects are assumed to be negligible. The pressure data considered are obtained from a two-dimensional (2D) numerical coning model for an oil/water system. We consider constant-rate production followed by a buildup period and assume that the top, bottom, and outer boundaries of the reservoir are sealed.

First, we consider the case where the producing interval is equal to the total formation thickness. Second, we discuss the effect of partial penetration.

In both cases, we show that average pressure can be estimated by the Matthews-Brons-Hazebroek method and consider the computation of the skin factor. We also show that a reservoir limit test can estimate reservoir PV only if the total mobility adjacent to the wellbore does not vary with time.
Recovery of Bitumen From Tar Sand Deposits With the Radio Frequency Process
Authors: Sresty Guggilam C. , Dev Harsh , Snow Richard H. , Bridges Jack E.
Published: December 2007

The IIT Research Institute (IITRI) radio frequency (RF) process for tar sands consists of two steps: (1) the deposit is volumetrically heated with RF energy to lower the viscosity of the bitumen, and (2) the bitumen is produced by one of several petroleum recovery methods. The RF heating step is accomplished by inserting tubular electrodes into boreholes and by energizing them with an RF power source. The electrode pattern is designed so that the deposit between the electrodes is uniformly heated with a minimum energy loss. The operating frequency is selected on the basis of the electromagnetic characteristics of the deposit. The recovery techniques that we investigated include replacing the heated bitumen with sodium silicate solutions, by gravity drainage, and by autogenously developed steam and hydrocarbon gases.

Two small-scale field experiments were conducted in the Asphalt Ridge tar sand deposit near Vernal, UT. About 25 m3 [33 cu yd] of the deposit was heated with RF energy, and about 35% of the total in-place bitumen was recovered during the 3-week test period.
In-Situ Leaching of South Texas Uranium Ores—Part 1: Laboratory Studies of Ore Composition and Leaching Performance
Authors: Paul J. M. , Tsui T. F. , Edwards J. T. , Holmes B. G. , Venuto P. B.
Published: December 2007

This paper presents data on mineralogy and laboratory chemical-leaching tests for ore samples from several areas of the south Texas tertiary Catahoula formation. Optical microscope, electron microprobe, spectroscopic, X-ray diffraction (XRD), and various chemical analyses were performed. Batch screening tests gave qualitative estimates of leach rate and potential recovery. Packed column tests using hydrogen peroxide or pressurized oxygen gave more quantitative recovery estimates. The frequently friable sandstones contained highly variable amounts of quartz, feldspar, calcite, and clay, and in some cases, zeolite or mica. Clays were mainly mixed layer illite/smectite type. High cation exchange capacities (CEC's) correlated with clay (and zeolite) content, while high reducing capacities were often associated with pyrite level. Coffinite, in various environments, was the main uranium mineral. With batch tests using pseudo-first-order rate constants, ore leach rates were generally characterized as "fast" on a scale of fast, intermediate, and slow. However, there was variability in leach rates, both in samples from different areas and in samples taken at different depths in the same well. Fast rates and recoveries greater than 80% were observed in most column pack tests, but there was variation with leachate composition and sample source. The chemistry and kinetics of leaching are also discussed.
Carbon Dioxide Flooding Evaluation of High-Pour-Point, Paraffinic Red Wash Reservoir Oil
Authors: Frimodig James P. , Reese Norman A. , Williams Craig A.
Published: December 2007

Engineering methods are being developed to evaluate reservoir fluid systems for suitability to CO2 flooding. This paper presents our evaluation procedure as applied to laboratory data for a high-pour-point [95°F (35°C)] oil from the Red Wash field in Utah. The data were obtained from phase behavior and slim tube experiments.

The results of this work indicate that high pressures are required for a miscible displacement of the highly paraf-finic, high-pour-point Red Wash oil. The minimum miscibility pressure (MMP) was found to be 4,650 psia (32 060 kPa), increasing only 5% to 4,900 psia (33 784 kPa) when the injected CO2 contains a 10 mol% nitrogen contaminant. These pressures are not currently economically obtainable in the Red Wash field.
The Relationship Between Rate of Return, Payout and Ultimate Return in Oil and Gas Properties
Authors: Phillips Charles E.
Published: December 2007

Rate of return is being recognized more widely as a measure of the attractiveness or profitability of investments in oil and gas properties. "Rate of return" is that interest rate which results in the discounted present worth of future net income being equal to the initial investment in the property. It is usually calculated by means of trial-and-error. In this paper a factor, called "composite decline-discount factor," is introduced which eliminates trial-and-error for properties having constant percentage decline. Formulas have been derived and charts plotted showing the relationships between rate of return, payout, ultimate return, market value expressed as a fraction of discounted present worth, and "average annual rate of return". Rate of return on equity capital in oil payment transactions is also investigated.

Introduction

The evaluation of a proposed drilling prospect or purchase of a producing property does not end with a report giving its cost and estimated net income by years. Management must have some criterion or yardstick for judging the attractiveness or profitability of the project.

Probably the most common criteria are payout and ratio of ultimate return to investment. Their disadvantage is that they represent two independent yardsticks and do not give a single, unique answer to the question, "How attractive is this project?" For example, which is more desirable, a property having a three-year payout and an ultimate return-investment ratio of 2 to 1, or one having a five-year payout and an ultimate return-investment ratio of 3.5 to 1?

To answer this type of question, various methods for measuring the earning power of invested capital have been applied to oil and gas properties. One of particular merit is the rate of return method, also called the internal rate of return method, the discounted cash flow method, or the investor's method. Rate of return is that interest rate which results in the discounted present worth of future net income being equal to the initial investment in the property.
Internal Flows in Geothermal Wells: Their Identification and Effect on the Wellbore Temperature and Pressure Profiles
Authors: Grant Malcom A. , Bixley Paul F. , Donaldson Ian G.
Published: December 2007

Geothermal wells exhibit a variety of internal flow effects caused by the flow of water, steam, or both between distinct permeable zones tapped by the well. These internal flow effects are described and it is shown how they may be recognized from downhole pressure and temperature profiles.

Pressure transients measured at depths other than that of the well's primary permeable zone can be corrupted by such flows. The effects of such flows on injection and discharge transients are discussed.
Relationship Between Horizontal Stress and Depth in Sedimentary Basins
Authors: Breckels I.M. , van Eekelen H.A.M.
Published: December 2007

Previous work on establishing a relationship between in-situ stress and depth is reviewed. On the basis of data from literature, supplemented by available field data, equations are proposed to describe the trend of horizontal stress with depth for normally pressured formations in the U.S. gulf coast region. A separate correlation between horizontal stress and pore pressure allows this trend to be extended to formations containing abnormal pore pressures.

Having achieved a good correlation for data from this well-documented region, we repeat the process for other parts of the world, using data from hydraulic fracture treatments and formation integrity (leakoff) tests. Similar relationships between horizontal stress and depth are found to hold for normally pressured areas that are geologically and tectonically similar to the U.S. gulf coast. Coupled with regional correlations between horizontal stress and pore pressure, these relationships enable horizontal stress levels to be estimated for a given depth, provided the pore pressure also is known.

Introduction

The instantaneous shut-in pressure (ISIP) recorded during or after a fracturing job or during a minifracture test provides a good approximation to the minimum principal in-situ total stress components sHmin. The vertical total stress or overburden stress sV (normally the maximum principal in-situ stress) can be derived by integration of the formation density, compensated (FDC) log. In tectonically inactive areas, the intermediate principal stress, sHmax, can be assumed approximately equal to the minimum principal stress: sHminsHmaxsHmin, the value of sHmax in principle can be derived from the formation breakdown pressure pb as measured at the start of a fracturing job. For a fully plastering fluid, for instance, pb 3sHmin-sHmax-Pc where Pc is the pore pressure.

In practice, however, sHmax cannot be determined accurately because the breakdown value will be influenced by hole geometry, hole integrity, mud-cake properties, and the extent to which the fluid penetrates into and pressurizes the pore space around the borehole. Also, hydraulic fracturing data are often lacking in many areas of the world. The only remaining way, then, to obtain information relation to in-situ stresses is to analyze the results of formation integrity tests (leakoff tests and casing-seat tests). In these tests, the pressure at which the formation starts taking fluid may range from sHmin to 2sHmin-Pc. Therefore, it is the lower end of the range of values from formation-integrity tests that is of interest for in-situ stress determination.

Review of Previous Work

The majority of hydraulic fracturing/formation-integrity test data quoted in literature are from the U.S. gulf coast and Santa Barbara Channel (CA). From these data, a number of authors have derived fracture gradient correlations to be used in planning drilling programs.
Sulfonate Retention and Residual Oil Saturation
Authors: Presley C. Travis
Published: December 2007

This paper describes an empirical relationship between sulfonate retention and final residual oil saturation achieved by a micellar/polymer oil-recovery process. Using this relationship and certain assumptions, one can derive expressions for predicting oil recovery performance in coreflood experiments. The equations contain two experimental constants: (1) sulfonate retention and (2) a factor related to the oil-recovery efficiency of the sulfonate slug in cores, specific to both the slug and core material. This same relationship applies to both linear and radial cores.

The equations derived predict nonlinear scaling effects. These effects have been demonstrated in laboratory corefloods.
Laboratory Experiments in Fracture Propagation
Authors: Medlin W. L. , Massé L.
Published: December 2007

This paper describes fracturing experiments in dry blocks of various rock materials. The results have application to evaluation of hydraulic fracturing theories. The block dimensions were 3 in.×4 in.×12 in. [7.6 cm × 10.2 cm × 30.5 cm] with metal plates epoxied to the 3-in. × 12-in. [7.6-cm×30.5-cm] faces. Remaining faces were coated with soft epoxy to provide an impermeable jacket. The blocks were loaded in a pressure cell with an upper movable piston bearing on the 3-in.×4-in. [7.6-cm× 10.2-cm] faces. A servocontrolled press applied constant stress to these faces higher than a lateral confining stress applied by oil pressure. Fractures were initiated by injection of various fluids into a small notch located on a center plane parallel to the 4-in. × 12-in. [10.2-cm ×30.5-cm] faces. Fracture growth along the same plane was assured by the stress conditions. Use of these experiments to test theories of fracture propagation required measurement of three variables, fracture width bi, and propagation pressure pi at the notch entrance, and fracture length, L. bi was determined by a capacitance method, and pi, was measured directly by a pressure transducer. L was measured by two methods—either ultrasonic signals or pressure pulses generated in miniature cavities. The ultrasonic method confirmed the existence of a Barenblatt liquid-free crack ahead of the liquid front whose relative length decreased with confining stress. The metal plates bonded to the 3-in.×4-in. [7.6-cm× 10.2-cm] faces prevented slip at the top and bottom of the fracture, giving a three-dimensional (3D) crack of constant height. However, the bi, pi, and L data followed trends predicted by two-dimensional (2D) (plane strain) elastic theory reasonably well. Fracture closure measurements after shut-in showed an initial period of leakoff-controlled closure and a final period of creep-controlled closure. A pi, slope change at the transition is identified with the instantaneous shut-in pressure (ISIP) in field records and is higher than the true confining stress.
A Thermoelectric Device for Measuring Thermal Conductivity of Rock
Authors: Khan A.M. , Fatt Irving
Published: December 2007

A new type of steady-state thermal conductivity apparatus is presented and described. Results of measurements on Berea sandstone, Solehofen limestone, Banders sandstone and Bakelite are presented. The measurements were made in a two-hour period at temperatures up to 80C and axial stress to 125 bars. Results show that the thermoelectric beat pump and thermistor-controlled electric heater can be used in a steady-state apparatus for measuring thermal conductivity of rock. Steady-state is reached within two hours. With Urethane foam insulation, not more than 3 per cent of heat is lost by radial flow. The apparatus can be used as a comparator or for absolute thermal conductivity determinations.

Introduction

Calculations of heat flow through the earth, both for scientific purposes and engineering design, require thermal-conductivity data on rock. However, the high variability of rock often makes handbook thermal-conductivity data of little value. For engineering purposes in particular, it is desirable to have measured data on samples of the rock mass under study. Laboratory methods for measuring thermal conductivity of rock use either time-dependent or steady - state temperatures. The time-dependent (transient) techniques give thermal diffusivity from which thermal conductivity can be calculated if the specific heat and density of the sample is known. Most transient techniques require lengthy and involved sample preparation. Also, the accuracy tends to be low. Steady-state techniques are more exact and are the most commonly used. The steady-state methods, however, also have their difficulties. A long time is often required to reach steady state, troubles have been encountered in establishing good thermal contact between the heating and cooling elements and the rock sample, and unaccounted-for heat losses are difficult to prevent. In this paper we present a description of a new type of steady-state thermal conductivity apparatus. With it, measurements have been made in two hours at temperatures up to 80C and axial stress to 125 bars. Sample preparation is simple and no thermal conductivity standard is needed.

APPARATUS

Our steady-state apparatus is an improvement over the conduction pile used by Zierfuss and van der Vliet and Somerton. A linear heat flux is established through a conduction pile consisting of the rock sample and a standard material of known thermal conductivity in series.

SPEJ

P. 113ˆ
Experience With Piston and Piston-Rod Seals for High-Pressure Reciprocating Compressors Injecting Natural Gas on North Sea Production Platforms
Authors: Wilson R.S.
Published: December 2007

The need to restrict flaring of associated natural gas has emphasized the importance of reliability of high-pressure reinjection compressors installed on certain North Sea platforms. This paper reviews the contribution made by the development of piston and rod seals used on injection compressors, with reference to three important fields: Beryl, Statfjord, and Thistle.

Early North Sea Reinjection Experience

During 1977 the first associated natural gas was reinjected in the U.K. oil sector. This operation is performed by two-stage reciprocating compressors. Early experience with these compressors revealed that the piston and rod seals. which are subjected to pressures approaching 400 bar [40 MPa], were a major source of machine failures. These failures consisted of severe scuffing and wear between the bronze sealing elements (piston and packing rings) and the countersurface (liners and piston rods), causing erratic seal life, sometimes of only a few hours' duration, together with badly damaged liners and piston rods. The typical condition of used bronze piston rings is illustrated in Fig. 1, and the operating lives achieved with bronze seals are summarized in Table 1. The most serious consequence of this unreliability was its effect on continuity of oil production, and an immediate development program to eliminate such failures was begun by the platform operator in collaboration with the appointed seal manufacturer. Details of this development are presented, including an analysis of the causes of seal failures and measures taken to remedy them, with particular attention to seal material and design and to lubrication requirements. Field experience gained in the application of the modified seals is summarized in three case histories. details of which arc given in Tables 2 through 4, with comparative results listed in Table 5.

Selection of Seal Material

At the outset of this development program, a change to nonmetallic seal materials for both the piston rings and the rod packings was considered on the basis of a proprietary grade of filled polytetrafluoroethylene (PTFE), which had already been used successfully for packings and piston rings in various lubricated compressor installations, includingethylene primary compression to 350 bar [35 MPa],ammonia synthesis gas compression to 350 bar [35 MPa], andhydrogen compression in refinery service to 200 bar [20 MPa].

JPT

P. 2294^
Modeling Infinite-Conductivity Vertical Fractures With Source and Sink Terms
Authors: Nghiem Long X.
Published: December 2007

This paper describes a method for handling infinite-conductivity vertical fractures in reservoir simulation by using source and sink terms. It begins with a review of the concept of source/sink in reservoir simulation, and uses that concept to develop a method for computing the flow into or out of the fracture by assuming elliptical flow and by using the pressures of the blocks surrounding those containing the fracture. The assumption that the flow into the fracture is everywhere perpendicular to the fracture plane (i.e., linear flow) and the effect of the skin factor are also investigated.

Test runs showed excellent agreement between computed results and those obtained by analytical and variational methods for single-phase systems. The formulation was extended to multiphase systems, and simulation of a waterflood yielded physically reasonable results.
A Practical Method for Modeling Fluid and Heat Flow in Fractured Porous Media
Authors: Pruess Karsten , Narasimhan T. N.
Published: December 2007

A multiple interacting continua (MINC) method is presented, which is applicable for numerical simulation of heat and multiphase fluid flow in multidimensional, fractured porous media. This method is a generalization of the double-porosity concept. The partitioning of the flow domain into computational volume elements is based on. the criterion of approximate thermodynamic equilibrium at all times within each element. The thermodynamic conditions in the rock matrix are assumed to be controlled primarily by the distance from the fractures, which leads to the use of nested gridblocks. The MINC concept is implemented through the integral finite difference (IFD) method. No analytical approximations are made for the coupling between the fracture and matrix continua. Instead, the transient flow of fluid and heat between matrix and fractures is treated by a numerical method. The geometric parameters needed in a simulation are preprocessed from a specification of fracture spacings and apertures and the geometry of the matrix blocks.

The numerical implementation of the MINC method is verified by comparison with the analytical solution of Warren and Root. Illustrative applications are given for several geothermal reservoir engineering problems.
Interpretation of Well-Block Pressures in Numerical Reservoir Simulation With Nonsquare Grid Blocks and Anisotropic Permeability
Authors: Peaceman Donald W.
Published: December 2007

Previous work on the interpretation of well-block pressure (WBP) for a single isolated well is extended to the case of nonsquare grid blocks (∆x ≠ ∆y). Numerical solutions for the single-phase five-spot problem, involving various grid sizes, show that the effective well-block radius (where the actual flowing pressure equals the numerically calculated WBP) is given by ro=0.14 (Δx2+Δy2)½.

This relationship is verified by a mathematical derivation for a single well in an infinite grid. The exact value of the constant is shown to be eγ/4, where γ is Euler's constant.

Finally, the analysis is extended to include anisotropic permeability, and an expression for the effective well-block radius in terms of Δx, Δy, kx, and ky is derived.
Kinematics of the Cone Bit
Authors: Ma D. K. , Yang S. L.
Published: December 2007

The bits' and bit cones' angular velocities are variable with time. All published papers on cone bit kinematics, however, are based on the supposition that the motions of cones are uniform. This supposition, therefore, has been the main obstacle to determining the objective law of the working cone bit.

The apparatus, methods, and tests results for measuring the bit and cone instantaneous angular velocities are described. A new theoretical analysis of cone bit motion is proposed and some interesting new conclusions are obtained that will help designers and users of cone bits.
Numerical Simulation of Coning Behavior of a Single Well in a Naturally Fractured Reservoir
Authors: Huan-zhang Chen
Published: December 2007

The history matching and predicting of an actual well in a reservoir with double porosity is performed with a new coning simulation model that gives satisfactory results. A discussion of the parameters used for matching provides some insight into the structure and parameters of the reservoir. Other points discussed include (1) bottom-water rising characteristics, (2) a comparison between the dual porosity and the single porosity (assuming that the mass transfer between the fracture and matrix is equal to zero), and (3) the imbibition characteristics of matrix.