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By Joseph E. Chilton, Robert J. Timko, Charles D. Taylor

No regular monitoring of methane is required in areas of gassy coal mines outby the mining face. Methane ignitions that have occurred in mine outby areas indicate the need to provide better protection to workers. Handheld methane monitors are now used by some miners to make periodic measurements of methane at the working face. The IYONI II gas detector which is incorporated into a miner’s cap lamp and worn on a miner’s helmet can continuously provide an alarm signal whenever methane levels exceed a set level. Tests were conducted to evaluate the performance characteristics of this methane detector by measuring response times with methane gas supplied through a calibration fixture or adaptor. Other response time tests were performed with the detector in an environmental test box. Performance was also evaluated in a full scale test gallery where face methane emission and underground ventilation were simulated. Procedures for calibration by response time measurement of the IYONI II detector have been developed. In limited testing, the IYONI II detector was found to reliably detect the presence of 1 percent by volume methane.

By C. P. Lazzara, R. A. Franks, G. F. Friel, J. C. Edwards, J. J. Opferman

A fire detection research program conducted at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research Laboratory (PRL) recently demonstrated the advantage of multiple fire sensors for early fire detec¬tion and nuisance alarm discrimination in underground coal mines. As an example, research has shown that an appropriate combination of smoke, CO, and metal oxide semiconductor (MOS) sensors has the capa¬bility to detect a smoldering conveyor belt fire which produces low visibility due to smoke, but CO concentrations too low for an early fire alarm. Such a sensor combina¬tion has the additional advantage of being able to distinguish a nuisance alarm event such as those produced by diesel engines or acetylene torches from mine fire products¬-of-combustion (POC) produced by a real tire. Research has also shown that the problem of hydrogen (H2) gas cross-interference with chemical CO sensors at battery-charging operations in diesel-emissions backgrounds can be resolved with a smoke sensor and a MOS sensor sensitive to NOx associated with diesel emissions. Other underground conditions, such as rock dust, exacerbate the problems with sensors. NIOSH has developed a neural network that takes many of these variables into account as it assesses real-time sensor data to discriminate nuisance alarms.

By D. A. Flanagan, B. L. Landrum, P. B. Crawford, B. C. Norwood

Herern is described a heat conduction model which has been developed to predict the pressure distribution within a reservoir being subjected to rrnsteady-state depletion. Although potentiometric models have been widely used to study reservoir pressure distribution, their application is limited to the study of steady-state cases. Electrical analyzers may be used to study unsteady-state phenomena, but their application and simulation have certain limitations. Much of the now accepted theory of unsteady-state fluid flow in porous media has evolved from previous heat conduction knowledge. An analogy between the flow of fluid in an unsymmetrical reservoir and con-duct ion of heat in a similarly shaped unsymmetrical metal plate is made to show adaptability of the hear conduction principle to transient reservoir cases. A description of the model and necessary instrumenrarion is included. Data show influence of well location on pressure distribution during unsteady-state deple[ion. Application of results is made to a hypothetical reservoir and to a reservoir located in an irregular aquifer. INTRODUCTION Development of methods for predicting behavior of petroleum reservoirs has resulted partially from adaptation of electrical and thermal flow concepts to the flow of fluids through porous media. Extensive investigation of electrical and thermal flow problems has resulted in mathematical solutions applicable to many reservoir problems. The relative ease of measuring electrical flow has brought wide acceptance of the use of the potentiometric model to study certain field problems. Potentiometric models are restricted to the study of steady-state conditions because of the instantaneous response of electrical flow to changes in the applied potential. The electrical reservoir analyzer has been one of our most useful instruments for studying certain phases of unsteady-state behavior1. Other than approximation techniques, no method exists for determining pressure distribution in an irregular reservoir during primary depletion. Heat flow, like fluid flow, is inherently transient. The model described here was developed to use this transient nature of heat flow, measurable in the laboratory, to simulate transient flow of fluids in the porous medium of the reservoir above the bubble point. A metal plate shaped like the reservoir to be studied was heated by a "well" source. Temperature increase in the plate is analogous to pressure decline in the field if the field is being depleted, or pressure increase if fluid is being injected. This study is intended to determine the feasibility of using the transient nature of the heat flow to study the transient behavior of fluid flow. It is hoped that this new technique will aid in the understanding of one of the more complex phases of reservoir engineering. THE FLUID FLOW-HEAT CONDUCTION ANALOGY The similarity of the equations which describe the flow of fluids through a porous medium and the conduction of heat through a solid is well known2. Rate of flow of fluids is given by Darcy's law3. while the rate of flow of heat is given by Fourier', (I,, - KA 4T........(2) Combining Eq. 1 with the equation of continuity for a compressible liquid", i.e.,results in Expressing y in terms of the compressibility, i.e., pr = peey ,..........(5) and by expanding the exponential and neglecting higher orders of cp one can obtain

By Glenn Stevens

After 40 years of operation with the original design, Pan Pacific Copper determined it was necessary to rebuild the Saganoseki Flash Smelting Furnace to continue safe operation. The original design employed a rigid steel frame, which, through hearth growth, led to severe distortion of the frame. Contributing to the continued growth of the hearth were thermal cycles that occurred during the government mandated annual shutdowns. Hatch designed a unique sprung bound, pivoting binding frame to maximize crucible size within the existing furnace footprint, while integrating the PPC designed cooling jackets. The bound system maintains tight brick joints, while the new conductive hearth design with integrated bottom cooling produces a protective freeze layer to accommodate higher furnace throughput. Minimization of furnace downtime for the rebuild was achieved through effective construction planning, highly trained contractors, and through an efficient start-up and ramp-up to full production.

By R. Cameron

The growing use and acceptance of electric vehicles (EV), as evidenced by the record sales of over 750 thousand vehicles in 2016 and a current global EV stock of 2 million vehicles, is putting pressure on sourcing raw materials such as cobalt, and to a lesser extent, nickel. Global supply is poorly diversified, with 50– 60% of global cobalt production sourced solely from the Democratic Republic of Congo (DRC). One potential source for cobalt and nickel are low-grade nickeliferous pyrrhotite tailings, of which 50–100 million tonnes are present in the Sudbury area alone. This paper presents the extraction of cobalt and nickel from this material using a combination of flotation and bioleaching technologies. The findings of a high-level techno-economic analysis of the proposed processing flowsheet are presented.

By J. C. Edwards, C. C. Hwang

In ventilated tunnel fires, smoke and hot combustion products may form a layer near the ceiling and flow in the direction opposite to the ventilation stream. The existence of this reverse stratified flow has an important bearing on fire fighting and evacuation of underground mine roadways, tunnels and building corridors. In the present study, conducted by the National Institute for Occupational Safety and Health, a CFD program (fire dynamics simulator) based on large eddy simulations (LES) is used to model floor-level fires in a ventilated tunnel. Specifically, the critical ventilation velocity that is just sufficient to prevent the formation of a reverse stratified layer is simulated for two tunnels of different size. The computer code is verified by checking the computed velocity profile against experimental measurements. The CFD results show the leveling-off of the critical ventilation velocity as the heat release rate surpasses a certain value. At this critical ventilation, the ceiling temperature above the fire reaches a maximum for both tunnels. The velocity leveling-off can be explained from this observation. An extended correlation of Newman (Combust. Flame 57 (1984) 33) is applied to the temperature profiles obtained by CFD. At the critical ventilation, temperature stratification exists downstream from the fire. The computed critical ventilation velocity shows fair agreement with available experimental data taken from both horizontal and inclined fire tunnels. The CFD simulations indicate that the Froude modeling is an approximation for tunnel fires. The Froude-scaling law does not apply to two geometrically similar fire tunnels. The CFD results are compared with two simple theories of critical ventilation by Kennedy et al. (ASHRAE Trans. Res. 102(2) (1996) 40) and Kunsch

By Keith A. Heasley, John L. Ellenberger, Paul W. Jeran

In this paper, a state-of-the-art, three-dimensional, full waveform, microseismic system was used to analyze the rock failure around a deep (> 750 m (2500 ft) of cover) bump-prone longwall panel. The microseismic system consisted of both underground and surface geophones coupled through radio telemetry and a fiber-optic network to produce pseudo real-time detection and location of seismic events surrounding the coal seam. This was the first microseismic installation of this scope at a U.S. coal mine, and the system was intended to help determine the exact strata mechanics associated with the redistribution of stress and the associated gob formation at one of the U.S.’s deepest longwall mines. Overall, 5,000 calibrated seismic events were recorded during the mining of one panel, including a Richter magnitude 4.2 event which occurred inside of the array. Analysis of these events provides a number of notable insights into the rock mass behavior. For instance, the longwall panel was widened during the retreat process, and the mining-induced seismicity shows a distinctly different behavior between the start of the panel, the mining of the narrow part of the panel and the mining of the wider part of the panel. Also, in itself, the acquisition of the ML 4.2 event was a major milestone in geomechanical and bump research. This is the first time that such an event has been recorded with this detail and accuracy at a bump-prone coal mine in the U.S. The analysis of this single event has set distinct new limits on the relationship between mining seismicity and coal bumps.

By S. C. Miller, R. D. Carter, H. G. Riley

A merhod based on theoretical considerations is presented for estimating srabilized performance of gas wells from data obtained from short-term flow tests. Calculated results are presented for II gas wells evaluated with four-to five-hour flow tests. For seven wells on which comparison war available, satisfactory agreement between measured and calculated performance was obfained. Although the final results are favorable, diflerences in flow capacity k,h obtained from flow tests conducted at different rates were observed. This inconsistency did not seriously affect the calculated results in the test wells. INTRODUCTION In order to negotiate the sale of gas from newly drilled gas wells and to plan otherwise for the orderly exploitation of gas reserves, it is necessary to predict the long-term withdrawal rates physically possible for each well. Since low permeability gas wells do not stabilize except after a lengthy period of flow, the operator is unable, without wasting large amounts of gas, to measure directly the stabilized performance prior to contracting for sale of the gas and connecting the well to a pipeline. This problem is not new, but is one which has recently received considerable attention because of the rising importance of natural gas in the economy and new emphasis on the development of gas reserves. Thus, a method is needed for estimating stabilized performance from information obtained from short-flow tests in which stabilized flow is not attained. Such short tests would be suitable for wells not connected to a pipeline since the tests require only small amounts of time, labor and production of gas. Other requirements of such a method are short calculation time and use of a model of the gas well and its reservoir drainage area which is as consistent as possible with present theoretical, experimental and field knowledge. The method presented herein was developed in an effort to meet these requirements. It has been named the "two-Row method". In addition to the section on the evelopment and description of the method, a description of field application of the method and a discussion of well test results are in- cluded. Finally, there is a section on an additional consideration prompted by some of the test results. The Appendix contains certain details of the derivation of the two-flow method and a sample calculation for Test Well 1. MATHEMATICAL DEVELOPMENT AND DESCRIPTION OF THE METHOD The method is based upon the following assumptions: (1) The system can be described as a finite cylindrical gas reservoir produced by a single cylindrical well located at the center of the reservoir. Flow is strictly radial. (2) Flow obeys Darcy's law except very near the well where a quadratic flow law is assumed. (3) The system is also characterized by a laminar flow skin factor. The use of a quadratic or turbulent flow term is more fully justified in Refs. 1 and 2. When such a system is opened at the wellbore to constant rate flow from an initial condition of uniform pressure distribution, the radius or drainage quickly passes through the non-Darcy flow and "skin effect" region imrnediately surrounding the well. After the drainage radius or "transient" has passed beyond this region and before it reaches the external boundary, drawdown can be expressed by'." After the drainage radius reaches the external boundary, stabilized flow exists and drawdown is given by'," Eqs. 1 and 2 form the basis for the method. The validity of these equations will now be examined in the light of some well test data previously available. It has been found by actual measurements on gas wells that the relationship between drawdown and flow rate, that is the performance curve, is closely approximated by' Eq. 3 is a straight line on log-log graph paper. Eq. 2 and, for any lixed value of time, Eq. 1 plot as a curve which is slightly concave upward on log-log graph

By N. T. Lowe, R. E. Miller

When two pieces of heavy equipment interact, jolting and jarring can occur. During haulage truck loading for example, there is a chance that the operator of one or both pieces of the equipment will experience jolting and jarring. Additionally, a jolt can occur when an off highway equipment operator drives over a road defect or inadvertently strikes a berm. Aside from the operators, there is seldom anyone else that witnesses the interaction and can accurately describe the extent of the jolting. This makes it difficult for health and safety managers to address jolting and jarring. The devices and software described in this paper constitute a method for installing “black boxes” called Shox Boxes onboard equipment that already have a GPS system onboard. The resulting configuration provides an objective assessment of jolting and a chance to determine the root causes of it. The Shox Box system reviews data in real time, onboard the vehicles, 24 hrs a day, and sends pertinent information via radio to a central database. The data generated shows whether jolts are above or below a supervisor defined target value for the equipment and the tasks being performed. This allows health and safety personnel to demonstrate safe operation of heavy equipment and recommend proactive actions to maintain jolting within a reasonable range.

By K. L. Young

The general energy equation, including change in kinetic energy, was solved by numerical integration and used to evaluate simplifying assumptions and application practices over a wide range of conditions. When extreme conditions were encountered, sizable errors were caused by large integration intervals, application of Simpson's rule and neglecting change in kinetic energy. A maximum error of only 1.31 percent was caused by assuming temperature and compressibility constants at their average value. It was discovered that a discontinuity can develop in the integral for the injection case. This discontinuity indicates a point of zero pressure change and is an inflection point in the pressure traverse. INTRODUCTION When a pressure in a gas well is to be calculated, one of the first decisions is to select a method of calculation. In many instances, this selection becomes a problem because the literature, at best, provides an evaluation of any method for only a limited range of conditions. Once a method has been selected, a question often arises as to the size of the calculation interval which should be used. The question regarding calculation interval arises because an analytic solution is not obtainable and approximate solutions must be used. This paper presents an evaluation of major assumptions and application practices of probably the two most widely used methods for calculating steady-state single-phase gas well pressures. The two methods are Cullender and Smith1-" (numerical integration), and average temperature and com-pressibility. The Cullender-Smith method assumes that change in kinetic energy is negligible and is normally applied in two steps with a Simpson's rule correcton. The average temperature and compressibility method, in addition to neglecting kinetic energy change, asumes that temperature and compressibility are constant at their average values. This method is normally applied for wellhead shut-in pressures of less than 2,000 psi, and in one step. Computer programs were written to compute bottom-hole pressure with and without the assumptions, using various approaches. Values of input parameters investigated are shown in Table 1. Flow rate was limited to a maximum of 5,000 and 10,000 Mcf/D for tubing sizes of 1.610 and 1.995 in. ID, respectively. Flow rate was also limited to 10,000 Mcf/D for a tubing size of 2.441 in. ID when wellhead flowing pressure was 100 psia. These limitations were imposed on flow rate so as not to exceed sonic velocity. The z factor routine available necessitated limiting bottom-hole temperature to 240F and wellhead pressure to 3,000 psia. Pressures were compared on the basis of percent deviation from the trapezoidal integration of Eq. l or 2 at 100-ft intervals. A preliminary investigation indicated that a 1,000-ft interval solution would differ from a 50-ft interval solution by less than 0.25 percent; therefore, the 100-ft interval was chosen for a base. For the purpose of comparison, deviations less than 1 percent were considered insignificant. where 111.1 qeC2/d p = kinetic energy term. Eqs. 1 and 2 can be evaluated numerically at specific depths using the trapezoidal rule as shown by Cullender and Smith. If change in kinetic energy is neglected and temperature and compressibility are assumed constant at their average values, Eq. 1 can be integrated to give the average temperature and compressibility equation,

By T. Sterry Hunt

THERE are about sixty bodies which chemists call elements ; the simplest forms of matter which they have been able to extract from the rocky crust of our earth, its waters, and its atmosphere. These substances are distributed in very unequal quantities, and in very different manners. As regards the frequency of these elements in nature, neglecting for the present those which constitute air and water, and confining ourselves to the solid matters of the earth's crust, there are a few which are exceedingly abundant, making up nine-tenths, if not ninety-five hundredths, of the rocks so far as known to us. The elements of which silica, alumina, lime, magnesia, potash, and soda are oxides, are very common, and occur almost everywhere. There are others which are much rarer, being found in comparatively small quantities. Many of these rarer elements are, however, of great importance in the economy of nature. Such are the common metals and other substances used in the arts, which occur in nature in quantities relatively very minute, but which have been collected by various agencies, and thus made available for the wants of man. It is chiefly of the well-known metals, iron, copper, silver, and gold, that I propose to speak to-night ; but there are two other elements not classed among the metals, which I shall notice for the reason that their history is extremely important, and will, moreover, enable , us to comprehend more clearly some points in that of the metals themselves. I speak of phosphorus and iodine. You all know the essential part which the former of these, com-

A. H. Mokken: I am pleased to have been given this opportunity to make a contribution to Dr Muller's paper tonight. The reason for this is that, at one stage in our careers, we were associates in the same undertaking. Dr Muller, then fresh from University, with a degree in pure science, had just stepped onto the first rung of the ladder, which, it was then thought, would lead him to a career in gold extractive metallurgy. However, endowed with an enquiring mind and conscious of a lack of fundamental training in general metallurgy and engineering, he felt a need for further academic study. To meet this need and, more importantly, to meet the necessary finances, he found his opportunity in steel. Armed with a bursary, he bade farewell to gold and proceeded overseas, to the University of Sheffield, to train as a steel metallurgist. The outcome of these academic efforts, which were followed by assignments in the steel industry and a further period at Sheffield, is the man we have listened to tonight-a highly qualified metallurgist who has displayed a sound knowledge of his subject. In choosing Sheffield, Dr Muller became associated with a steelmaking centre of world renown, a centre usually credited with the first systematic production of alloy steels, as far back as the 18th century. Since that time, great advances have been made in the production of alloy steels and this is especially so in the last decade or two, when major developments in civil, mechanical, electrical, aeronautical and nuclear engineering have been made possible by the development of steels with improved properties. In spite of spectacular advances in the technology of non-ferrous alloys, plastics and other materials of construction, steel has maintained its role as a pre-eminent material for engineering use. With the gradual accumulation of data on the properties of steels, and the use of thin film electron microscopy, to study the behaviour and characteristics of such phenomena as dislocations in metals and other microstructural features, the physical metallurgist appears to be approaching the stage of an exact understanding of such phenomena as strength, ductility and brittleness-a knowledge which could lead to close control of such properties and, therefore, to the attainment of the highest goals. An interesting example, illustrating the use of fundamental principles, based on physico-metallurgical research, is the development of the maraging steels developed by Bieber at the International Nickel Company. These steels have met the extreme technological requirements of the space age by providing the material for the cases of large rockets in which qualities, such as high tensile strength, toughness, workability and weldability are most important. Attractive as they might appear to be in considerations of savings of weight, cost of erection, transport of materials and foundations, the use of high strength steels has been accompanied by special problems such as brittle fracture, hydrogen embrittlement, notch-toughness and fatigue. It has been found that high strength steels, which performed acceptably in conventional tension tests, were found to undergo failure, in a brittle manner, in service. Hydrogen embrittlement has caused spectacular failures at a fraction of the normal ultimate tensile strength, and a lack of correlation between fatigue and tensile strengths has diminished the advantages to be obtained from the use of high strength steel in some applications. A new approach to the selection of materials for engineering design has resulted from a consideration of these phenomena in which strength, as such, is no longer as significant as it was previously. Parallel with the development of high strength steel has been the need for suitable techniques for joining component parts and here welding has played an

By Larry G. Stolarczyk

An underground medium frequency radio communications system has been developed and demonstrated in both coal and metal/non metal mines. The principal advantage of the system are its low cost, ease of installation and the ability to provide radio communications to any vehicle or roving miner in the underground mine. The system provides high quality radio coverage in work areas and along manways with existing "wireplant" conductors. The conductors include AC power cable, telephone cable, metal water and high pressure air pipes, etc. The measured communications range from the base station to mobile transceiver exceeded 12,500 ft without the use of repeaters. A cost/benefit analysis shows that the initial cost of the equipment can be returned 2-6 times in the first year. The mine productivity increases by approx. 13 percent.

By K. L. Cashdollar

A project to evaluate the South African bagged stone dust explosion barrier was successfully completed at the National Institute for Occupational Safety and Health (MOSH), Pittsburgh Research Laboratory's (PRL), Lake Lynn Experimental Mine (LLEM) during the period November 1999 through May 2000. The tests were conducted in a three- entry section of the LLEM. Two types of explosions were used to evaluate the distributed and concentrated bagged barrier performance in a multi-entry mine section. The fuel zone of the first explosion type was only in the center B-drift. In the second explosion type, coal and stone dust mixtures were place in all three drifts. A total of six explosions, including two baseline and four barrier evaluation explosions, were conducted. Of the four barrier explosions, the distributed and concentrated barriers were each evaluated against the two explosion types. For these explosion tests, the distributed barrier extended from about 74 to 170 m and the concentrated barrier from about 74 to 104 m in B-drift. The distributed barrier successfully stopped flame propagation in both types of explosion tests. The flame extended further for the explosion tests where the dust was loaded in all three entries compared with dust loaded only in the center entry% but in both cases the flame was stopped within the barrier zone. The concentrated barrier was also successful in stopping flame propagation m both explosion tests. From the full-scale experimental mine test results, it can be concluded that both bagged barrier designs were effective in stopping coal dust explosions in the multiple entries of the LLEM.

By Richard J. Mainiero, Sapko, Marcia L. Harris

Since 1988, there have been thirteen documented incidents in the United States and Canada in which carbon monoxide (CO) is suspected to have migrated through near surface strata into structures or other enclosed spaces as a result of nearby trench blasting or surface mine blasting. From these incidents, there are thirty suspected or medically verified CO poisonings and one fatality associated with these incidents. To better understand the variables contributing to this hazard, the National Institute for Occupational Safety and Health (NIOSH) carried out a small-scale field study to identify key factors that may contribute to the migration of CO through the ground. NIOSH conducted single-hole heavily confined experimental test shots to measure the radial pressure pulse as it propagated through surrounding monitoring holes to determine if a relationship existed between the pressure pulse and resulting CO measurements afterwards. NIOSH also monitored blasts at an airport construction site. Following the detonations, the concentrations of CO, nitric oxide (NO), and nitrogen dioxide (NO2) were monitored for several days in the surrounding satellite holes. The peak CO measurements relative to distances from the shots were compared. Pressure histories and peak particle velocities (PPV) were measured at monitoring boreholes. It was found that the differential pressures recorded within the boreholes give some indication as to the likelihood of CO appearing, whereas the PPV measurements do not seem to be as good an indicator for potential CO migration. In this limited study, changes in barometric pressure had very little influence on removing the trapped detonation products, whereas applying a vacuum to the monitoring holes was effective in reducing the entrapped CO concentration.

By R. L. Perrine

A stability theory is developed for miscible liquid-liquid displacement within a porous medium. In the usual case considered, a high-density high-viscosity "oil" is displaced downdip by a low-density low-viscosity "solvent'! Perturbation methods are used to find the conditions under which the spreading mechanism changes from the stable dispersion process to unstable viscous fingering. We find that instability is conditional, that there is a dependence on the shape of a disturbance leading to a"diameter" effect and that very difficult experimental scaling problems may result. A useful consequence is the definition of a minimum "slug size" for stable miscible displacement. This should make possible optimum use of the solvent process for oil recovery. The results may apply to many situations in which one fluid displaces another of somewhat different fluid properties within a porous medium. INTRODUCTION The process of miscible liquid-liquid displacement looked very favorable when it first received serious consideration as a means to increase petroleum recovery. Some early laboratory results were interpreted to mean that only a small "slug" of solvent was needed, perhaps 2 to 3 per cent of a hydrocarbon pore volume. This "slug" could recover the oil in an entire reservoir provided the fluids remained miscible.1,2 Only a slow growth of the "mixing zone", or gradual transition from oil to solvent, should occur. This would follow naturally from mixing by a dispersion mechanism such as that described by Scheidegger.3 And, indeed, laboratory cores have shown this kind of behavior provided solvent viscosity was at least as great as that of the oi1.2,4-6 The same kind of behavior has also been observed with solvent viscosity lower than that of the oil after the distance traversed became large. Not all laboratory results have been this favorable, however.7-9 Mixing zone growth may become proportional to the distance traveled rather than the square root of this quantity. Such behavior accompanies high rates in short systems of large diameter, provided the viscosity ratio is adverse. If this more rapid spreading were to persist in a reservoir, the solvent requirement for miscible "slug" displacement could exceed 30 per cent of a pore volume. There is considerable economic importance in the difference between 3 and 30 per cent solvent. A 1ogical conclusion is that two different kinds of flow behavior are possible, with each kind leading to a different result. One kind gives efficient displacement, the other does not. In the efficient case, the solvent bank spreads out only by the mechanism we have termed dispersion. Under these conditions, displacement is as near piston-like as possible. In the second kind of flow, found only with adverse viscosity ratios, viscous fingering occurs. That is, permeability variations cause a small finger of low-viscosity solvent-rich fluid to move ahead of its average position within the mixing zone. This creates a path of low resistance to flow, and an even greater amount of solvent-rich fluid follows. Thus, the process is autocatalytic. Once started, the fingering mechanism rapidly becomes dominant. The question to be answered is this. Under what conditions will each of these two different kinds of flow occur? In particular, what conditions denote the transition from dispersion to viscous fingering as the solvent spreading mechanism? The answer may tell us whether or not the desirable, near piston-like miscible displacement process is practical. An answer to this problem can be obtained from theory by the use of perturbation methods. The procedure is as follows. We first formulate a mathematical representation of the system. Then a small disturbance (or perturbation) in solvent concentration profile is introduced and observed to see what happens. Unstable flow is indicated when a small disturbance will grow larger. This will lead to eventual viscous fingering. If on the other hand the disturbance dies out, the displacement is stable. In this latter case, with dispersion as the spreading mechanism, near piston-like displacement is possible. Thus, this paper presents the development of a stability theory for miscible liquid-liquid displace-

By L. A. Rapoport, W. J. Leas, C. W. Carpenter

A program of scaled flow model experiments has been undertaken to study the performance of five-spot water floods. The modeling procedures are discussed and the construction and operation of the flow models are described. The tests were specifically designed to investigate the effects of injection rate and of oil-to-water viscosity ratio on oil recovery. The areal sweep of five-spot water floods was also studied, and direct comparisons between five-spot and linear flooding behavior have been established to permir better utilizatfon of core analysis results for purposes of field waterflood evaluations. INTRODUCTION For a long time reservoir engineering procedures have been confined to the consideration of idealized, one-dimensional or linear systems.11* However, direct application of the linear waterflood mechanism to the evaluation of actual field performance is justifiable only for the purposes of rough approximation. To obtain a realistic analysis of field behavior, it is necessary to account for reservoir geometry and well distribution, and to take into consideration the configuration of the flow of fluids between injection and producing wells. In the past it has been attempted to account for the complex nature of the fluid movement in the reservoir by associating each well pattern with a certain "sweep-efficiency constant", e.g., a sweep efficiency of 72 per cent for the conventional five-spot pattern.' More recently, methods of waterflood evaluation have been improved by the introduction of variable sweep-efficiency factors, defining the areal coverage as a function of cumulative water injection and viscosity or "mobility" ' ratio.""' These variable sweep-efficiency factors, derived from miscible fluid displacement experiments, require the assumption of piston-like displacement of oil by water. This implies that only one fluid, either oil or water, is moving at any one point of the reservoir ht any moment. Such an assumption, however, is incompatible with the bulk of the experimental evidence and also theoretical considerations which indicate that usually in the area invaded by water, both oil and water are flowing in varying proportions, in accordance with the relative permeability characteristics of the porous medium. Another recent approach toward the evaluation of five-spot flooding behavior involves correlations of the areal sweep efficiency (observed in immiscible fluid experiments) with a "mobility ratio," based on the consideration of the "average" relative permeability to the displacing fluid. Combination of these correlations with a modification of the Buckley-Leverett frontal-drive equation leads to a computational procedure for predicting the recovery performance of areal water floods. While of considerable interest, this approach has no complete theoretical justification and, therefore, does not entirely clarify the features of five-spot water floods. Rigorous, theoretical treatment of waterflood behavior in two- or three-dimensional systems as encountered in the reservoir, including proper consideration of relative permeability and capillary-pressure functions, is as yet beyond the scope of analytical or computational methods. The, behavior of such water floods can, however, be studied by means of scaled flow model ekperiments, which is the approach followed in these investigations. The flow model experiments described in this paper simulate a uniform, horizontal formation of constant thickness with fully penetrating wells. The system under consideration is entirely liquid saturated and not influenced by compressibility effects, which is representative of the situation achieved after gas fill-up under practical conditions. Gravity segregation effects are assumed to be negligible, which implies a relatively thin reservoir formation and/or low vertical permeability. THEORETICAL CONSIDERATIONS For a flow system of uniform thickness with no appreciable effects of gravity segregation, the analysis of water-oil displacement can be confined to a two-dimensional treatment based on the consideration of a "slice" of unit thickness. Referring to previously established derivations," the displacement of oil by water in such a system can be described by the following, dimen-sionless equations:

By John Henry Harden

This shaft, located in the northern anthracite coal-field about 2300 feet southwest from the court-house at Wilkes-Barre, in the County of Luzerne, Pa., is the property of the Lehigh & WilkesBarre Coal Company. The sinking and cribbing to the solid rock (see isometrical view on Plate IX) was conducted by Mr. W. W. Kenrick. Dimensions of the earthwork to the foundation of the cribbing, 51' 2" long, 17' 4" wide, 31' deep. Total amount of excavation in cubic yards, 998.5. Dimensions within the permanent cribbing, 45' 4" long, 11' 16" wide, 31' deep, divided into six parts by buttons 8" x 12", each division, 7' x 11' 6". Permanent cribbing 12" x 12"; temporary cribbing 8" x 10" ; backing, 3" thick ; clay puddle to exclude surface water, 12" thick; conductors, 8" x 5"; lining, 1" thick from top to bottom of the shaft. In the latter part of the year 1871, Mr. H. Murray & Son contracted with the company for the continuation of the work at the rate of four hundred dollars per yard in depth, to a point 100 feet below the Hillman seam of coal; for the succeeding 100 feet the price to be increased twenty-five dollars per yard, and so on until the bottom rock of the Baltimore seam of coal was found. The size of the shaft within the cribbing timbers is 45 feet 4 inches by 11 feet 6 inches, having six divisions of equal dimensions, 7 feet by 11 feet 6 inches, giving room for what is known as the "standard diamond " car, whose capacity when level full is 100 cubic feet, but when loaded by the miner 4 inches above the top contains 112 cubic feet." Two divisions of this shaft are intended for hoisting coal from the Hillman seam, two from the Baltimore seam, one for ventilation, and one for pumps. The works were planned for two pairs of direct-acting, high-pressure engines, twenty-four boilers, and for an estimated output of 2500 tons of coal per day from the two seams.

By C. K. C. K. Gupta

The rare earths in elemental form are required for a variety of scientific and technological purposes. They are not easily obtained in this form, due to the great chemical stability of the rare-earth compounds and the strong tendency of elemental metals to react with everything they come in to contact with, especially at high temperatures. Beginning in the 1950s, when sufficient quantities of separated rare earths became available, as the result of intense research and development, three processing routes were developed to accomplish the preparation of all 16 naturally occurring rare-earth elements. They are chemical reduction of the halide intermediates, the oxides and electrochemical reduction of chlorides and oxide-fluoride mixtures. Not all the processes are effective with all the rare earths. In spite of the celebrated similarity of trivalent rare earths, the physical properties of individual rare-earth elements are sufficiently different that a variety of techniques are required for their preparation. The development of reduction processes for the rare-earth metals are covered in this paper, with focus on the oxide reduction routes. The strong reliance of effective reduction processes on the fundamental science of reduction reactions is highlighted.