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By H. A. Wheeler

The great depths attained by some of the older mines, and the milch greater depth at which they will have to he worked in the not distant future, strongly emphasize the imperfect and inadequate character of our present hoisting-practice. The depth of 3000 feet having been exceeded at several places, and 4000 feet almost reached

Jan 1, 1891

By J. H. Johnson, H. J. Schock

The cases of no auxiliary ventilation and ventilation with tubing were mathematically modeled, using a turbulent dispersion model. The Scooptram® used to load is modeled as a variable-speed, variable-strength source of pollutants moving in and out of the dead-ended drift. Model predictions are compared to experimental measurements. A parametric analysis was performed to determine If a relationship existed between C02 and NO levels. It was concluded from this analysis that when modeling a load-haul-dump cycle, it is necessary to use a model that can predict changes in source strength as well as source location. Carbon dioxide was used as a tracer to calibrate the model since, knowing the fuel flow rate, it is possible to calculate C02 production. The model was then verified after this calibration process using additional experimental results. With the calibrated model, it is possible to predict pollutant concentrations at any location in the heading using an engine map and the previously calculated flow field.

Jan 1, 1984

By Harry R. Cedergren

Properly designed drainage systems can be of great benefit to many kinds of Civil Engineering works, including embankments, and often are the most economical way to protect such works from the damaging effects of water. To function properly, drains must be able to remove water without also removing soil or becoming clogged with soil or erodible rocks. The first criterion to be used in designing drainage systems, called the filter criterion, can prevent all such problems (erosion and clogging) when properly fulfilled in design and construction. The second requirement of drains is that they must be capable of removing all of the incoming water without the build-up of large amounts of head that can damage the protected works. To insure this kind of perfomance, the discharge capabilities of drains should always be verified by appropriate hydraulic and seepage calculations. This paper describes these two basic drain design criteria and also gives examples of application of seepage principles to the evaluation of the potential benefits of drains and to the design of drains for mine waste embankments.

Jan 1, 1985

By Raymond Wilson

GRINDING costs are an important item in cement manufacture, and the cost of power is one of the large items in grinding costs. Even where power is of secondary importance, cost items dependent on mill capacity are influenced by the efficiency with which the mill uses power. Tube mills typify the grinding mills most generally used in cement plants, though other types are in use. Tube mills have been widely criticized as being extremely inefficient, and this feeling regarding them has led to many attempts to design more efficient grinding equipment. Other types may be an improvement over tube mills, but the improvement has certainly not been revolutionary, at least as applied to clinker grinding. The very fact that there is doubt regarding the relative efficacy of various types of mills is an indication that an adequate basis for an analysis of performance is lacking. The development of methods of analyzing mill performance has been hampered by the lack of a suitable method for measuring the work actu-ally done in pulverizing. There has been no acceptable standard to which mill performance might be compared. As a consequence, it was not known whether the margin of possible improvement in pulverizing operations was large or small. Even direct comparison of different types of mills was seldom possible because most plants had only one type of mill for each type of service. Comparisons between plants were difficult because of differences in the grinding characteristics of various clinkers. Some recent developments complete a chain of circumstances that place the cement, industry in a particularly fortunate position for the study of its clinker-pulverizing operations. Modern investigators of grinding phenomena have generally agreed that the best measure of mill performance is the production of new surface. For most materials this measure of performance is largely theoretical and has a rather remote connection with the practical aims of the grinding operation. In clinker grinding, on the other hand, surface area is intimately connected with the properties conferred on the cement by grinding. Moreover, the determination of surface area is rapidly coming into routine use as a test

Jan 1, 1937

By Alexander Anderson

In many oil fields a great variation in the production of adjoining wells has long been observed, and a certain proportion of dry holes, situated between prolific producers, has been regarded as normal without thorough investigation as to cause. Similarly, an occasional prolific producer has been found in a part of a field where all other holes have proven disappointing. Adjoining wells which showed an unreasonable difference in production have been surveyed, and the bottom of the poorest producer has been found to have lost sufficient vertical depth, through its drift, to diminish seriously its penetration in the oil zone. Again, the bottom of the good producer has been found to he more favorably situated by its migration up structure. Surveying of wells in California fields has shown many instances where the dry hole has drifted far off the structure to such a degree that no amount of deepening could ever convert it into an oil well. In other cases, edge wells have been found to drift into the field. At this time, in California, the surveying of oil wells is beginning to he accepted as a routine part of operating procedure. Some operators are surveying all of their new wells and, in some of the recently discovered fields, this practice is providing invaluable assistance in methodical development. The information that has been obtained from the surveying of many wells has convinced most operators that it pays to give careful attention to the drilling of wells. Chews are now usually cautioned to avoid reckless competition with each other. Whereas, formerly, certain companies demanded a large footage from their drillers, they now issue orders that a very moderate speed in drilling shall he maintained and that every care be taken to avoid practices likely to cause excessive deviation of the hole frorn vertical. As a result of these new instructions to drilling crews, a distinct decline in the average drift of the wells drilled by these operators has taken place and fewer dry holes are being drilled from good locations. To the petroleum engineer and the geologist, oil-well surveys provide the necessary data required for the construction of the correct cross-

Jan 1, 1929

By G. B. Walker

THE sink-float methods designated by heavy-media separation processes were pioneered by C. Erb Weunsch for the treatment of base metal ores as an improvement over jigs. The work of Weunsch was further developed by Victor Rakowsky and The American Zinc, Lead and Smelting Co. Early in the development of the processes, the inherent unsuitability of galena as the solid constituent of the medium was recognized and ferrous media amenable to magnetic recovery and control were developed. The high efficiency and low cost of magnetic recovery and cleaning of ferrous media regardless of particle size, slime contamination, or surfacial oxidation had led to the adoption of ferrous media by all of the sink-float plants operating under the heavy-media separation processes patents controlled by American Zinc, Lead and Smelting Co. Approximately 2,000,000 tons of base metal and nonmetallic minerals are treated each month by these methods.

Jan 1, 1949

By George J. Young

The nature of slimes handled in the treatment of gold- and silver-ores has been discussed in technical literature to a considerable extent. The subject of slime-filtration from the practical worker's stand-point has also received much comment, arid scattered through the literature of the subject are descriptions of many slime-filtration installations. Articles of this nature serve a valuable purpose and assist materially in the design of new and the improvement of old plants. The subject of the physics of slime-filtration has been touched upon to only a slight extent. The underlying principles are worthy of niore intensive study and experimeritation than they have received, and the main purpose of this paper is to present the results of such study and experimental work as will serve to make clear in part at least many of the principles which control the filtration of slime. Nature of Slime. Much has been written concerning an accurate definition of the term "slime," but no comprehensive definition seems to be gcnerally accepted. The reason for this is clear. A slime consists of at least three different substances, each, when separated, possessing distinctly different physical and to a certain extent chemical properties. These substances are extremely fine sand, a colloidal material which may bc and generally is in a coagulated condition, and a colloidal material which is in a non-coagulated condition. Suspending a slime in a relatively large volume of water by shaking and allowing sedimentation to take place, results in the fine sand settling out with comparative rapidity, followed by the coagulated material, which settles niuch more slowly and finally a certain portion remains

Jan 1, 1912

By John R. Edwards

Introductory.—There are many interesting and important events connected with the petroleum problem. The remarkable men who conceived 'the thought of transporting petroleum by pipe line, conserving the byproducts of the commodity, and conducting extended investigation and research whereby the flash point of the oil was raised, its cost reduced and its supply assured, are deserving of the gratitude of this nation. It was primarily the success attained by Captain Lucas, after his comprehensive search for oil in Texas and Louisiana, that was the impelling cause which prompted the Navy Department to conduct the extensive series of liquid fuel-oil tests that were made from 1901 to 1903. The sensational discovery of oil at Spindle top made a deep impression upon Rear Admiral George W. Melville, then Engineer-in-Chief of the Navy, and the discovery of the vast oil field in Texas convinced him that, within a generation, if not within a decade, crude petroleum was going to play a very important part in warfare, and that the commodity might possibly develop into a necessary munition of war. The United States' Commanding Position as a Petroleum Producer.— In the study of the various problems relating to the world's production of crude petroleum, the position of the United States is one of commanding importance, whether viewed from the industrial or the military aspect. The present yield of this country is practically double that of the rest of the world, and, in view of the productive and prospective fields possessed by various countries, together with the comprehensive and exhaustive search that has been made throughout the world for petroleum, it is extremely probable that this lead will be maintained for the next decade. As regards the character of the crude-oil yield of different countries, America possesses the greater part of the supply that contains a paraffine base, and therefore a considerable portion at least of the American product produces the best illuminant. Of all the crude-oil distillates, kerosene is in many respects thc most important, and the Appalachian product for this purpose is favored, particularly in the Far East, above that of any other petroleum yield of the world.

Jan 1, 1915

By J. D. Forrester

SINCE the introduction of the first percussion rock drill in about 1850, drilling equipment has undergone a progressive evolution so that a wide range of special classes of machines now are marketed by several manufacturers. Essentially all of the drilling machines presently employed for blasthole drilling are of the hammer-drill type. They are classified as hand-held hammers (jackhammers, sinkers, etc.), drifters (light or heavy), and stopers and are of many sizes; varying in weight and rotative and blowing power. Most makes of drill machines fundamentally are the same in principle of operation as they are designed to strike a blow on the end of a drill rod in the manner of early-day hand drilling. However, beyond this common characteristic, the similarity among different makes ceases. In choosing between similar machines of one make or another, it is important to remember that rock drill manufacturers have not attempted to standardize drill parts, the result being that a mine operator must approach, because of replacement parts, standardization by limiting the makes of machines used. The present-day selection of any particular drilling machine is dependent fundamentally on its inherent ability to make a hole, or series of holes, as speedily and as cheaply as is possible. Two categories of controlling elements become apparent in any analysis devoted to making the choice of a drill, namely: 1-Conditions under which the equipment is to be used, such as mining method practiced, type of labor available, character of rock material. 2-Physical characteristics or features of the given drilling machine. Regardless of the controls of class 1, above, the elements of this category are fixed by several factors. All of them are interrelated and, though some often are more important in one case than in another, an unfavorable variation of any-others being essentially equal-is sufficient to discredit the optimum applicability of the particular drill machine. The relative factors in the selection of a machine are as follows: First cost-This is not generally an important item on a comparative basis as the marketing of drill machines is highly competitive and most makes are priced closely.

Jan 1, 1952

By G. L. Oldright

Nearly all of the present schemes for treating complex (i. e. lead-silver-zinc-copper) ores are based on the idea that lead holds, and will hold for some time, the strongest economic place from the viewpoint of supply and demand of all the non-ferrous metals. Copper, it is thought, will come back to its own when European affairs are stabilized, although at that time competition from Chile, Peru, and Katanga, in particular, will be more severe than in pre-war days. The future for silver and for zinc is uncertain. New uses are developing for zinc, and the market has remained better than many expected, but the stabilization of world markets will bring in foreign competition instead of relief. The cost of producing zinc from simple zinc ores, by the retort process, will, from the nature of the labor required and the increasing cost of fuel, increase steadily. As a result, the small producers of purely zinc ores around Joplin are shutting down their mines, even with a good market price for zinc; on the other hand, the producer of lead from complex ores, in the Rocky Mountain states, is confident of a profit from the sale of his lead, and is seeking means to make the zinc in his ore pay some part of the cost of treatment. However, the tonnage costs for mining and ore dressing are much higher in the Rocky Mountain states, as may be seen by comparing tax-return statements from the various states. Even before the recent drop in the price of silver, many mines were operating on a very slender margin of profit; labor and supplies cost more. Mining at greater depth has shown most orebodies to grow increasingly more complex, so that improvements in mining and ore-dressing practice have not been sufficient to compensate for the additional expense involved in beneficiating these ores. The smelters have bad to meet the same general economic situation, so they can only give

Jan 1, 1924

By B. D. Thomas

GRAVITY concentration is a general term designating processes for separating and sorting granular material by means of forces that depend on the density, size and shape of the particles. When these forces are applied to the particles the latter are caused to move, those of a given density along one path and those of a different density along another, until ultimately they are sufficiently separated to be removed from the operation of the process. The forces producing this separation are in general complex and, unfortunately, no completely rigorous analysis of them has as yet been devised. The science of the hydrodynamics of viscous fluids deals with the little that is known about the problem. Every observer of nature is familiar with the fact that an object moving in a fluid encounters a force of resistance. We have only to walk against a brisk wind or stir a cup of coffee, or observe the slow fall of a grain of sand in water, to experience directly the fact that such forces exist. The exchange of force between an object and a fluid in which it is moving operates on the fluid as well as on the object. Thus a sailboat may be set in motion by the force exerted by the wind on the sail; but the sail also deflects the wind-furthermore, the water in which the boat floats is set in motion by the force exerted by the boat as it cleaves through the water. The wind is thus enabled to do work on the water through the intermediary of the boat. In general, an object moving through a fluid encounters a force that opposes the motion and also acts to change the motion of the fluid. In gravity concentration we are dealing with this force of resistance acting on the granular particles that are to be separated. Furthermore, the motion induced in the fluid by a particle will in turn affect the motion

Jan 1, 1943

By R. S. Dean

THE numerous theories of hardening which have been advanced in recent years are all satisfactory in accounting for some of the phenomena observed in hardening metals, but none so far presented account for all of the facts observed. Some years ago one of the authors, R. S. Dean,1 presented a theory to account for some of the properties accompanying work hardening. The present paper develops this theory further in the light of recent experimental, work and extends it to other forms of hardening. Many of the ideas included have come from the writings and personally communicated thoughts of others. We have attempted to give proper credit in every case, but it is possible that we have not always done so. As an historical basis it is desirable here to review very briefly the hardening theories which have been current. The first comprehensive theory of work-hardening phenomena was due to Sir George Beilby.2 He contributed the idea that with cold work part of the structure of the metal was rendered amorphous and that it was to this amorphous material that the cold-worked metal owed its difference in properties. According to Beilby's theory this amorphous material was a super-cooled liquid and, therefore, had the characteristics of a vitreous material. That such a theory is not capable of explaining the property changes in metals has been repeatedly pointed out. This theory also allowed a slip to take place only once on a given plane, which, as has been pointed out by Jeffries and Archer,3 is not consistent with the observed length of an individual slip and the amount of elongation which can be obtained by wire drawing. The modifications, which have been proposed to this hypothesis to make it coincide with the experimental facts, have to a considerable extent robbed the theory of its clean-cut characteristics. The commonest of these modifications replaces the amorphous phase with an

Jan 1, 1927

By David R. Mitchell, R. B. Hewes

MANY processes for cleaning coal that are in use depend primarily on physical properties of coal and refuse other than specific gravity and surface conditions relating to froth flotation. These properties are shape, coefficient of sliding friction, resilience, friability, magnetic susceptibility, and electrical conductivity. In many of these processes specific gravity does have some effect and many separators are designed to utilize more than one of the physical properties cited. Although the processes described herein do not have a widespread application, yet for specific coals and specific conditions, they are economically important. A problem confronting many coal-mining districts is the marketing of the slacks or screenings and dust passing the final sizing screens. Processes in commercial use installed primarily to increase the form value, and hence the market value, of these slacks and dusts include briquetting, packaging, and low-temperature carbonization. MECHANICAL PICKERS Machines utilizing shape, frictional resistance, and differences in resilience of coal and impurities are usually called mechanical pickers. They require a closely sized feed, therefore their use is confined to the pea, nut, and egg sizes. Various types of these devices are described by Berrisford, 1, 2 Taggart,3 and Peele.4 Shape In general, coal differs in shape from its accompanying dirt throughout the range of commercial sizes. Coal, breaking into roughly cubical particles, contains a greater number of axes that are approximately the same length than does the dirt. The latter, consisting of pieces of slate and shale and lenses of pyrite, is flatter in nature. Further, flat coal often has a dirty, slaty appearance, even though of high quality. Mechanical pickers known as flat pickers, or "flatters," are widely used in the Pennsylvania anthracite region to remove flat coal .from the final clean coal. This practice greatly improves the appearance of the final market product. Flat pickers for removing impurities or flat coal ("flats") are usually installed on shaker screens, shaking conveyors, and chutes. In Fig. 1 three

Jan 1, 1950

By L. D. Anderson

WHEN, after years of troublous experiences in roasting sulfide ores with heavy dust and fume losses resulting from the equipment and methods first available, there appeared on the scene of metallurgy that revolutionary process known as sintering, it was felt that at last there had been found the ideal method for preparing sulfide ores for blastfurnace reduction. Not only were the sulfides roasted but also the fine oxidized ores were bound together with them in strong porous cellular masses which were in the best possible condition for reduction. With the experiences gained in the manipulation of the Huntington-Heberlein, Carmichael-Bradford, and Dwight & Lloyd processes there developed a refinement of detail which brought the whole plan of roasting by sintering to a high plane of perfection. But that metallurgy is never stationary is revealed by the fact that changes in milling practice, particularly the development of flotation, have introduced a new set of problems in sintering itself. Inasmuch as it is felt that these problems have not yet been solved in an entirely satisfactory manner this paper is written to record the present practice of the Salt Lake Valley smelters with the hope that there will be brought forth such discussios as may perhaps lead to still better practice. By far the greater proportion of the sulfides smelted today are flotation concentrates. Usually they are high grade, sometimes as high as 70 per cent. and more in lead. They are extremely fine, many mills grinding the ore so that from 60 to 80 per cent. will pass through screens of 200 mesh. The physical condition in which many of these concentrates reach the smelters is disconcerting to the metallurgists. Some are of about the consistency of putty. Others are of a sticky, slimy nature. Others again, dried to the limit, are veritable powders. Remembering that the down-draft sintering charge for the best results must be porous enough to let air be drawn through it reasonably well, must be thoroughly mixed, and must have some coarse material in it to segregate out and form a layer on the grates, it will be understood that the advent of this extremely fine material has made necessary still further elaboration in the equipment and processes of preparing sulfides for the blast furnaces,

Jan 1, 1929

By F. A. Forward, A. H. Ross, J. Halpern

IN treating carnotite ores by carbonate leaching it is often necessary to subject the ore to a prior roast. Among the advantages that may result from roasting are: 1) improvement in settling and filtering characteristics of the ore; 2) destruction of carbonaceous impurities that would otherwise contaminate the leach solution and consume carbonate reagent; and 3) substantial increase in extraction of vanadium, which is usually low when the un-roasted ore is leached. Recovery of vanadium may be an important factor in processing carnotite ores, and the fact that vanadium is usually recovered in good yield by acid leaching has often been an economic advantage over results obtained with carbonate leaching. It has been found that response of an ore to carbonate leaching, following roasting, depends primarily on its composition and on the conditions of the prior roast treatment, particularly with regard to the roasting temperature, the atmosphere maintained above the charge during roasting and cooling, and the presence of certain reagents. These factors, especially the last, virtually determine the extractions of uranium and vanadium attainable by carbonate leaching, as well as the reagent consumption on leaching, whereas adjustment of the leaching conditions has only a limited influence. These variables were examined systematically to elucidate roasting and carbonate leaching of carnotite ores and to establish a treatment yielding high recoveries of both uranium and vanadium. Tests were conducted on samples of four different Colorado Plateau ores, described in Table I. Roasting Procedure: The roasting tests were conducted in an electrically heated furnace in which the temperature was controlled to +15oC. The ore (usually a 500-g charge) was ground to —100 mesh, mixed with the desired reagent, and spread in a silica tray to a bed depth of about 1/2 in. During the roast the charge was rabbled at intervals of 15 min. To provide free access of air the furnace was usually ventilated; however, in a few experiments a controlled atmosphere such as carbon dioxide or hydrogen was maintained above the charge. Leaching Procedure: The pulp, generally comprising 500 g of ore and a 2000-cc solution containing 80 g per liter of Na2CO3 and 20 g per liter of NaHCO3, was agitated in an autoclave at 120°C, under 30 psi O2. Samples were withdrawn periodically, and the solution and ore residue were analyzed. Under the conditions employed, maximum attainable extractions were generally achieved in 4

Jan 1, 1958

By Donald Barton

Geophysical methods of prospecting taken as a whole do not seem to offer much promise to a young man planning to enter them in the future. They have come to stay, to be sure, and they will continue in at least moderate use for a long time. Domestic use of those methods presumably is at a maximum at the present time. Geophysical pros-pecting is expensive; the effects of the law of diminishing returns in efficiency in finding prospects can already, be recognized. Small oil companies, independent oil operators, and royalty buyers have been doing much geophysical work. But in face of the increasing costs of discovery of prospects and in face of the probably decreasing favorability of the prospects discovered, I expect to see a sharp drop in their use of geo-physics within the next 10 years. The major oil companies and the larger small oil companies will continue to use geophysics indefinitely, but it seems doubtful whether the very extensive domestic campaigns of a few companies will be maintained for many years, certainly not for 10 years. The use of the geophysical methods in foreign countries has not yet reached its peak, and probaby will continue to increase for several years. That peak level of activity will probably be held for 10 years, although the site of maximum activity will shift from country to country; by the end of 25 years from now, I should expect the foreign use of the methods to have leveled off to one-fourth to one-half the peak level. Foreign service in geophysics does not seem to offer an attractive career, except for men of exceptional disposition. Young men just out of college, who are willing and who can afford to spend three or four years having a fling at adventure before settling down, will find it attractive, but when their tour of foreign service is over, they probably will have harder work finding a job than when they were seniors, and their foreign experience will count for little, except for further foreign service. A few men, mainly the higher men, will have headquarters at civilized or semi-civilized cities and towns or at permanent oil-company towns, and can

Jan 1, 1938

By Thos. W. Gibson

The object of taxation is the raising of a revenue. Unless a tax accomplishes this, it is a failure. The right to take for public purposes a part of the moneys obtained from the carrying on of private enterprises is an attribute possessed only by a lawful government, and may indeed be called the supreme attribute of government. In free, democratic communities this power must of necessity rest upon the consent of the governed. Power implies obligation, hence it is obviously the duty of a government, in framing a system of taxation, to provide one which, while effective in producing a revenue, is also just and impartial. • It will be conceded that mines and mining property ought to bear a fair share of the public expenditure. The question is, upon what basis taxation should proceed. Two separate taxing principles are usually contended for: Taxation should be proportionate to the benefits received by the person or property taxed; taxation should be based on ability to pay. A third is sometimes added, taxation should have reference to the extent and value of the natural resources enjoyed. As applied to mining taxation, it is pointed out by those who support the fist mentioned basis that, mines being usually situated in rocky and hence sparsely peopled regions, mining companies are frequently obliged to construct roads, railways, telegraph and telephone lines, schools, water and sewerage systems, and many other amenities and conveniencea of civilization the cost of which in regions better suited for agriculture, and consequently more thickly populated, has either been defrayed locally, or can be spread over a sufficiently large taxable group of people to materially lighten the financial burden on the mine. The mining company, it is argued, having made these outlays, should receive credit for them and be relieved of taxation to a corresponding extent. There may be some force in this contention, but the situation is capable of relief without attempting to place taxation upon so unworkable a basis as the value of benefits received. Who is to be the judge of these benefits, and how are they to be valued? The very existence of a mining company and its ability to carry on business in peace and security depeind on the prevalence of law and order, which is a result of good government. The state provides protection against violence, and courts of law for

Jan 1, 1920

By C. Willard Hayes

Introduction.—The recent developments in the metallurgy of aluminum and its consequent rapidly growing use in the arts are at present attracting considerable attention to its ores. The success of the Hall electrolytic process, by which the metal is obtained directly from the oxide, has removed bauxite from the position of a rather uninteresting mineral to that of an important ore. Its production on a commercial scale is so recent, particularly in this country, that little attention has yet been paid to its mode of occurrence and origin.. Any investigation, therefore, which throws light upon these points should be of interest to mining engineers- at the present time, especially if the conclusions afford a basis for estimating the probable extent and value of deposits already known and a mane of directing search for others. Two localities in the United States have so far yielded bauxite in commercial quantities. These are in Arkansas and in the Coosa valley of Georgia and Alabama. According to descriptions of the Arkansas deposits by Branner, they bear little resemblance to those in the Southern Appalachians and their geological relations appear to be entirely different. Only the latter deposits are considered in the following paper. These have been briefly described by McCalley† and Spencer.† They were visited by the writer during the past summer and somewhat carefully examined, in connection with the study of the areal geology of the region. Location of the Deposits.—The ore is found irregularly distributed within. a narrow belt of country extending from' Adairsville, Ga.,

Jan 1, 1895

By Edward Martinez

The reactions occurring in the copper segregation process were studied by heating mixtures of chryso-colla, salt, and a reducing agent. The techniques used in this investigation were differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). The initial chloridizing of the oxide copper occurs below 500°C and cupric chloride may be the compound formed. Volatilization and reduction of the copper chloride take place above 550°C, although these reactions do occur to some extent below 550°C. A difference in the distribution of the metallic copper in the reducing agent was found when sodium chloride was used compared to magnesium or calcium chloride. Segregation was obtained with mixtures of cupric oxide, salt, and charcoal with no quartz or silicate present. Preliminary tests indicate that segregation may occur even in the absence of water vapor. The DTA and TGA techniques were found to be of great value in studying these reactions. The copper segregation process is a method for treating oxide copper ores. The ore is heated, most commonly in a kiln, with a reducing agent and a halide salt, generally sodium chloride, to approximately 700°-750°C and held for 30 to 60 min. The addition of the salt results in the migration and reduction of the oxide copper to metallic copper on the surface of the reducing agent rather than in the original mineral structure. The metallic copper can then be recovered by a subsequent leaching or flotation step.1-4 Experimental work in 1923 on oxide copper ores from the Sagasca mines in Chile led to the discovery of the reduction process. It was found that during the reduction of the copper mineral with coal, at about 700°C, the copper migrated to the surface of the coal instead of remaining disseminated in the ore. The unusual behavior of the copper, which caused it to migrate from the ore particles to the coal, was traced to the presence of a small quantity of sodium chloride occurring in the ore. Further experiments with oxide copper ores proved that the presence of a halide, either occurring naturally or admixed with the ore, caused the copper to migrate from the ore particles and to segregate in the charge. The ratio of salt to reducing agent may vary somewhat, but in general 0.5% to 1.5% sodium chloride and 0.5% to 1.0% coal or coke have been mixed with the ore. Less than stoichiometric amounts of salt are required to convert all the oxide copper to a chloride, so that a cycle of reactions appears to be occurring. Several investigations reported in the literature have proposed reactions to explain the mechanism of the process.5-10 There appears to be general agreement that water is necessary for the reactions to occur; that once the sodium chloride reacts with silica or silicates in the ore, the hydrochloric acid formed will convert the cupric oxide in the mineral structure to cuprous chloride. However, there appears to be a conflict of opinion on the reactions involved in the reduction of the cuprous chloride to metallic copper on the surface of the carbon. Rey has indicated that salt, water vapor, and

Jan 1, 1968

By H. A. Wahl

This paper presents methods of designing hydraulic fracture treatments in formations saturated with slightly compressible liquids. Howard and Fast describe the fluid-loss control resulting from the viscosity and compressibility effects of the reservoir fluid in terms of a fracturing fluid coefficient. However, for horizontal fractures, this coefficient is applicable to infinitely thick reservoirs. These methods of evaluating fluid loss from horizontal fractures during treatment differ from previous methods in that: (I) formation thickness is incorporated in the velocity function describing the rate of fluid loss to the formation; and (2) for a given thickness the relative position of the fracture to the horizontal boundaries of the reservoir or any interrnediate permeability barrier is incorporated in the design procedure. This theory is applied to several actual and hypothetical field cases. The results of these calculations demonstrate that the eflect of formation thickness on fluid loss from horizontal fractures may result in fractures several times larger than predicted by other methods. INTRODUCTION Hydraulic fracturing has been the dominating well-stimulation technique during the last decade. From the time it was commercially available, fracturing has had a very favorable success ratio compared to other stimulation methods. However, numerous wells that were successfully stimulated remained economic failures. Only in the last few years has the oil industry recognized the importance of designing treatments for each well which will yield the maximum profit. This implies that for a given set of treatment conditions the size and general physical characteristics of the fracture can be determined. One of the outstanding contributions in the field of fracture design was presented by Howard and Fast.' In their paper, three flow mechanisms that control fluid loss from the fracture to the formation are defined: (1) viscosity effects of the fracturing fluid, (2) viscosity and compressibility effects of the reservoir fluid, and (3) wall-building effects of a treated fracturing fluid. The rate of fluid loss to the formation adjacent to a fracture is shown to be a function of time. For each flow mechanism the velocity function v(t) is expressed as a constant or fracturing fluid coefficient divided by the square root of time. This form of v(t) can be used in the Carter equation, as developed in the Howard and Fasc paper, to estimate the areal extent of fractures. This equation may be written as In the following sections the effect of formation thickness on fluid loss from horizontal fractures is evaluated when the controlling flow mechanism is the viscosity and compressibility of the reservoir fluids. The major assumptions inherent in the Carter equation are brought out in subsequent mathematical developments. THE EFFECT OF RESERVOIR FLUIDS ON FRACTURE EXTENSION When a fracture treatment is performed using a fracturing fluid identical to the reservoir fluid, the only flow mechanism controlling fluid loss is the viscosity and compressibility effects of the reservoir fluids. In developing a fracturing fluid coefficient for this mechanism, Howard and Fast considered a segment of the formation bounded by a unit area on the fracture face and extending to infinity in the direction of leak-off as shown in Fig. 1(a). The direction of leak-off z is normal to the fracture face. The equation governing the linear isothermal flow of fluid into this segment is where a = Eq. 2 is a form of the diffusivity equation. It is derived from the equation of continuity, Darcy's law and Eq. 3