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By James D. Sisler

Among the various studies made by the Coal Fact Finding Commission, appointed by President Warren G. Harding in 1922 to investigate all phases of the coal-mining industry in the United States and to report to Congress, was one concerning the amount and nature of losses in mining bituminous coal in the eastern part of the United States. This study was carried on under the direction of the U. S. Bureau of Mines. The writer was appointed field engineer to investigate the problem in Ohio, Pennsylvania and West Virginia. Some 400 mines were studied in these three states and conclusions were drawn from many sources of data. The summary report written by George S. Rice and J. W. Paul states that "the field reports indicate that the recovery in Ohio will remain about as at present, except in the Belmont district; whereas in Pennsylvania it will gradually improve, and in West Virginia it will improve rapidly." Since 1922, the writer has been interested in gathering material to substantiate or contradict these prophecies. Nature of Coal Losses There are six general causes of losses of coal in mining: (1) coal left on the roof and bottom; (2) coal lost in room, entry and panel pillars; (3) coal lost in oil-well or gas-well pillars; (4) coal lost under buildings, railroads and boundaries; (5) coal lost in handling and prepayation, underground and surface; (6) coal lost by rolls, thin or dirty areas and under streams. Local economic aspects that dominate the type of mining conditions determine to some extent whether certain losses are avoidable or unavoidable. In general, however, unavoidable losses include coal lost in the protection of buildings, streams, railroads, restricted properties and around oil and gas wells. Barrier pillars and other safety pillars are unavoidable losses as long as their size does not exceed the minimum for adequate safety. Natural physical conditions beyond human control, such as rock faults, clay veins, partings and binders, bad top and bottom, rolls and horsebacks, cause unavoidable losses. Unavoidable losses

Jan 1, 1931

By John P. Harmon

This paper was written with two objects in view: (1) To describe in detail what has been done toward the ventilation of the main unit of the Portovelo mines and the results; (2) to give information that may be useful to anyone who may have to make a preliminary mine ventilation survey, with recommendations for the improvement of the existing system and finally the maintenance of the improved system. General Description The mining operations of the South American Development Co. at Portovelo, Province of El oro, Ecuador, are described here only briefly, as a full discussion does not fall within the scope of this paper. The orebodies are of the steeply dipping, gold quartz vein type, averaging about 2.0 meters wide. As shown in Fig. 1, the ore chutes are relatively far apart, making considerable development work necessary before connecting raises can be driven between the levels. Faulting' on a large scale and a parallel vein system have made long dead-end drifts and many crosscuts necessary in the exploration of veins. The ventilation of these dead ends is described under Auxiliary Ventilation. The method of mining2 is the filled rill stope method, similar to the method that is largely employed at the Butte mines. The main shaft of the mine is in the Amarillo Valley, on either side of which mountains rise abruptly to a height of several hundred feet above the collar of the shaft. Entrance is made to the mine: (1) Through the American shaft, which extends vertically from the surface to a depth of 1100 ft., of which only the first 700 ft. are in active use at the present time; (2) levels are driven from the American shaft at intervals of 30 m. (100 ft.), of which only the third, fifth and seventh levels need be considered in the ventilation problem; (3) adits at intervals of 30 m. (100 ft.), with a few exceptions, above the collar of the American shaft.

Jan 1, 1931

By Alexander L. Holley

THE Pernot system of rotating and withdrawing the hearth of a Siemens regenerative gas furnace for the production of Martin or open-hearth steel, is, perhaps, the most conspicuous of the several improvements which have lately been made in the steel manufacture. These several improvements in the open-hearth plant are not combined in any existing works, but most of them will be combined in not less than three works now erecting in the United States; and it seems probable that their joint result will not only reduce the cost of products of ordinary grades to Bessemer rates, but that it will produce new and better grades of products. The open-hearth steel furnace and its operation are so generally understood that but a few words of general description are necessary. The ordinary furnace is not unlike the common reverberatory puddling furnace, except that an intense, uniform, and controllable temperature is maintained by the Siemens gas regenerative system. The materials. employed are various : melted or unmelted pig with ore, and with or without scrap; pig iron purified from silicon and phosphorus, with or without scrap; pig iron and scrap, melted together in a cupola, or charged hot or cold, together or separately, into the steel furnace; a pig-iron bath, and hot or cold steel or iron scrap, direct sponge or Catalan or puddled blooms charged into the bath. The operation is, to a greater or less extent, according to the nature of the materials used, a desiliconization and decarburization of the pig or other crude iron, and its dilution by already purified materials. Manganese is employed at the end of the operation to remove oxide of iron and silica, a regulated amount of manganese remaining in the product. Figs. 2 and 3, Plate IV, represent the hearth and roof of the Pernot furnace; Fig. 1 shows, in cross section, the general arrangeent of open-hearth plant with Pernot furnaces, as generally designed by the author, and now building at two works. The engrav-

Jan 1, 1879

By Robert Archer

Two new alloys of the "strong alloy" class having improved fabricating qualities are described; also methods of producing alloys of the duralumin type with greater strength and hardness than previously obtained, are given. IT is about fifteen years since the development in Germany, largely by Alfred Wilm, of the aluminum alloy called duralumin. In this alloy, combining as it does the tensile strength of mild steel with the lightness and corrosion resistance of aluminum, a distinctly new material was presented to the engineering world. Despite the evident usefulness of this material, however, its commercial development has been slow, due in part to the difficulties involved in its fabrication. In view of the potentially great utility of strong aluminum alloys, it seemed desirable to find means of producing such alloys with better fabricating properties, and work was undertaken with this object in the laboratories of the Aluminum Company of America several years ago. This work has resulted in the production of two new types of aluminum alloy of the "strong alloy" class, having distinctly improved fabricating qualities. The knowledge gained has also made it possible to produce alloys of the duralumin type with greater strength and hardness than previously obtained. There have thus been made available some new engineering materials which it is the object of this paper to describe. These alloys, including duralumin, are fundamentally wrought alloys. Castings of the same compositions, heat-treated in the same manner give inferior physical properties, particularly as to ductility. The statements made subsequently concerning properties and heat treatment apply to material that has received sufficient working to thoroughly break down the cast structure. The material referred to has; in general, undergone a reduction in section of at least 80 per cent. by mechanical working. It may be mentioned in passing that other compositions have been found that are suitable for the production of the maximum physical properties in heat-treated castings.

Jan 2, 1925

By Vsevolod Krivobok

IT is generally recognized that "low temperatures" have a definite effect on the properties of metals and alloys. Furthermore, it is also generally understood that the effect is decidedly adverse. The possibility that the same low-temperature treatment might be employed for the purpose of improving certain properties of the .alloys has received less attention until recently, and the experimental and theoretical knowledge consequently is meager. The effect of low temperatures may be studied in two ways: by studying such properties as tensile strength, hardness, impact resistance, etc., at low temperature, and by studying the properties of alloys at room temperature after these alloys have been subjected to a low-temperature treatment. Even in the latter case, certain properties will differ materially from the same properties obtained on identical material but without cold treatment. In other words, subjecting alloys to cold treatment results in an irreversible change in mechanical properties. Changes of this character are usually indications of the appearance of a new phase or phases, and would be likely to occur in alloys which, either by virtue of their composition or by heat treatment, are retained at room temperature in a metastable condition. Consequently, studies of the effect of low temperatures logically should be conducted from the physicochemical point of view, since the results of such studies not only would furnish metallurgists with interesting theoretical data but would clearly indicate the classes of alloys that would hold promise of improvement, and, possibly, of new applications. As the present investigation deals with chromium and chromium-nickel alloys of iron of the stainless variety, it has been thought desirable to present the data concerning low-temperature properties of these alloys, available from the most recent and most comprehensive work of H: S. Russell.' A summary, of these data is given in Table 1. The data are confined to a limited number of alloys of the type dealt with in the present

Jan 1, 1931

By Maxwell Gensamer, Vsevolod N. Krivobok

It is generally recognized that "low temperatures" have a definite effect on the properties of metals and alloys. Furthermore, it is also generally understood that the effect is decidedly adverse. The possibility that the same low-temperature treatment might be employed for the purpose of improving certain properties of the alloys has received less attention until recently, and the experimental and theoretical knowledge consequently is meager. The effect of low temperatures may be studied in two ways: by studying such properties as tensile strength, hardpess, impact resistance, etc., at low temperature, and by studying the properties of alloys at room temperature after these alloys have been subjected to a low-temperature treatment. Even in the latter case, certain properties will differ materially from the same properties obtained on identical material but without cold treatment. In other words, subjecting alloys to cold treatment results in an irreversible change in mechanical properties. Changes of this character are usually indications of the appearance of a new phase or phases, and would be likely to occur in alloys which, either by virtue of their composition or by heat treatment, are retained at room temperature in a metastable condition. Consequently, studies of the effect of low temperatures logically should be conducted from the physicochemical point of view, since the results of such studies not only would furnish metallurgists with interesting theoretical data but would clearly indicate the classes of alloys that would hold promise of improvement, and, possibly, of new applications. As the present investmigation deals with chromium and chromium-nickel alloys of iron of the stainless variety, it has been thought desirable to present the data concerning low-temperature properties of these alloys, available from the most recent and most comprehensive work of H. S. Russell.l A summary of these data is given in Table 1. The data are confined to a limited number of alloys of the type dealt with in the present

Jan 1, 1931

By Hisaaki Takada, Atsushi Yoshida, Kazuo Satoh, Norikazu Nanko, Naoshichi Higashi

Kamioka Mine of Mitsui Mining & Smelting Co., Ltd. is the largest lead-zinc mine in Japan and is composed of two mines, Tochibora Mine and Mozumi Mine, which have daily production rates of 5,200 metric tons and 1,800 metric tons of crude ore respectively. In the mines, there are many massive pyro-metasomatic deposits which have been derived from the replacement of limestone. The deposits are composed of skarn minerals which mainly contain hedenberite. The country rock is generally hard and fine-grained gneiss. These deposits have been mined by means of the sublevel stoping method, induced block caving method and sublevel caving method at Tochibora Mine and mainly by the cut and fill method at Mozumi Mine. Since the 19601s, the trackless mining system has been introduced successfully into both mines, and is still promoted to be applied over wider areas. The underground hauling system is simplified remark- ably and much improved by adopting trackless ramps to the existing vertical and horizontal underground framework. Moreover, through the combination of the trackless mining system with the mining methods stated above, a notable increase in efficiency has been achieved. This is due to the high performance of the introduced machinery, reductions in man power of miscellaneous jobs, and also has enabled a highly efficient performance through its mobility. In addition, as it becomes possible to realize a flexible development to meet the irregularly shaped deposits and also becomes much easier to recover the remaining pillars by secondary mining, the extraction rate of ore has been improved considerably. With the introduction of the trackless mining system, the development method has been changed, thus former hand-hold leg-drills are now mostly re- placed by jumbo-type drills. Repair shops for Load-Haul-Dump machines also have been provided with an established service system. Reinforcement and rearrangement of the ventilation system has been carried out.

Jan 1, 1977

By Alfred W. Gauger, George A. Burrell

The senior author of this paper, while in Colorado on other official business, made a trip to the Cripple Creek gold-mining district to get more data than are at present available regarding the composition of the gas that issues from the rock into the mines of the district. This was done at the suggestion of George S. Rice, Chief Mining Engineer of the Bureau of Mines. There are -many questions of interest and importance in connection with the ventilation of the mines in the Cripple Creek district, such as the menace to life and mining of a suffocating gas entering the mines from the rock, the danger due to powder smoke (from blasting operations), and danger of continued inhalation of rock dust by the miners. This report confines itself to the first problem, the gas from the rock, and principally to one phase of this question, the composition of the gas and its effects on men and lights. A more thorough study of this and other ventilation problems is planned. That the rock gas is a real menace is shown by the fact that miners (variously estimated from 25 to 50 by different persons interviewed) have been killed by it in the 25 years that mining has been vigorously carried on at Cripple Creek. Many men have had narrow escapes from death, some of them having been incapacitated for days. In addition, much loss of time results because at certain periods of the year or on certain days it is impossible to enter some workings. At a few mines, fans force air into the workings, thus supplementing the natural ventilation and much improving conditions, but the improvement is not entirely adequate at all times. Origin of the Gas Lindgren and Ransome1 think that the gas found in the rocks of the Cripple Creek mining district represents the last exhalations of the ex-

Jan 1, 1917

By Charles E. Reed

With the increasing importance of clay in drilling operations which demand more precise and exacting control over its behavior, there has come the realization that most of our present methods of control over many of its important properties still represent more of an art than a science. Such a situation with respect to a material of such industrial significance is unfortunate, and naturally many investigations have been conducted to improve our knowledge. In general, these investigations have revealed the complex nature of clay behavior and while sometimes they may not have seemed to contribute directly to a solution of the field operator's problems they have been of inestimable importance in bringing to light the broad fundamental scientific principles upon which must be based any effective working theory correlating the known facts of clay behavior and predicting profitable new lines of attack for its improvement. Major Facts Concerning Behavior of Clays In the study of clays, as in that of most other colloidal materials, it has been impossible to make progress by the study of isolated facts. On the other hand, analysis of large groups of facts, many of which seem at first completely unrelated, can lead to a deeper insight into the structure of clays and the mechanism of their behavior. It will be well to list the major facts on which the analysis here presented is based, starting with those that have emerged repeatedly from past investigations and which thereby constitute an impregnable foundation upon which must rest any comprehensive theory of clay behavior: 1. Clays consist of hydrated aluminosilicates of extremely fine and variable particle size. 2. Suspended in water, clays exhibit variable degrees of swelling, depending upon their origin and upon the chemical and colloidal nature of any other substances present. The magnitude of the swelling is a direct indication of the extent to which the clay has become dispersed.

Jan 1, 1938

William Kent, New York, N. Y.:—The Institute may congratulate itself on the opportunity of reading the splendid address of President Brunton. It is an admirable summary of the progress that has been made in the mining and metallurgical arts in recent years. The paper rightly gives the chief credit for this progress to the aid which has been rendered to these arts by the advances in mechanics, chemistry, and electricity. It is notable that most of the headings in Mr. Brunton's address refer to the work of the mechanical engineer, the electrical engineer, and the chemist, rather than to that of the specialist in mining-operations. It seems that the most successful mining engineer of the present day is the one who makes the most intelligent application of the inventions and designs of engineers and others who are not directly engaged in mining. A tabulation of the headings of the address, grouped as below, shows this most clearly. Work of the Mechanical Engineer—Rock-drills, hoisting-machinery, tramming, pumping, ventilation, dredging, Sampling, concentration, briquetting, fume-recovery. Work of the Electrical Engineer—Electric machinery for hoisting, pumping, tramming, lighting and signaling, electric transmission, electric smelting. Work of the Chemist and Metallurgist—Explosives, chlorina-tion, cyanidation, roasting, lead-smelting, and copper-smelting. Work of the Geologist—Economic geology. Work of the Mining Engineer—Mine-mapping, surface-mining, timbering, tunneling; and planning and supervision of the work in general. The mining engineer of the present day, who is in responsible charge of a large plant, finds his chief work not in doing those things he was trained to do as a specialist, but in making use of the knowledge of geologists, chemists, and electrical and

Jan 1, 1910

By E. Gybbon Spilsbury

In the course of the persistent and rapid advance of our country towards the goal she has set for herself, of commercial and manufacturing supremacy, there stand out certain periods or cycles of prosperity or depression, succeeding one another with a comparative regularity as to their ultimate trend, but of varying lengths and intensities. I might compare this course to that of a railroad between two points at different levels, with intervening mountain ranges and valleys, the up-grades climbing towards the final upper terminal of prosperity, while the down-grades retard the ascent, and tend to return to the valleys below. Just at the present time we are evidently at the bottom of one of these valleys, and, before starting to climb the next divide, it may be prudent for us to look into the condition of our rolling-stock, and especially into that of our brakes, and see what the experience of our downward journey has taught us, and whether we are properly equipped for the new upward advance which now lies before us. Probably no previous period of the same duration has produced in all branches of mining and metallurgy improvements SO many and so various as have the last ten or twelve years. Not that they have brought forth any such startling and revo-

Jan 1, 1898

By Augustus Locke

WHY should I, a geologist, be coming before you to talk about finding ore? Certainly, the great discoveries of the past have not been made by geologists, but by men of very different tastes and training. If, in the year 1800, the course of ore discovery could have been foreseen, there would have been no reason to put it into the hands of geologists or other men of technical preparation. It was not geologists but explorers, Indian fighters, prospectors, manual laborers, and hardy financiers, who initiated the American mining industry. Then why this association of geological technique with ore finding? Why this feeling that the way to find ore is to apply to the problem what we call geo- logical principles? Well, to put it broadly, the old method has run out on us. It no longer works. Or, to put it another way, the cost of finding ore by the old method has mounted so high that one old district after another has become, practically speaking, dead, and various other old districts that are still going apparently at full strength are actually beginning to limp, and, with the cost of discovery mounting yearly, to fear, more than they will acknowledge, that the end is approaching.

Jan 1, 1926

By John B. Campbell, George G. Binder, Loren H. Jenks

Conventional methods of producing crude oil generally leave in the depleted reservoir 1 to 3 bbl of oil for every barrel brought to the surface. This paper describes a field test which explores the possibility of using gas-driven liquid propane to improve oil recovery efficiency. Laboratory theoretical and experimental studies leading to the field test indicated that low residual oil values could be obtained using limited amounts of propane driven by gas. The field test involved (I) repressuring the reservoir to the vapor pressure of liquid propane, (2) injecting the liquid propane, and (3) injecting dry natural gas to drive the propane and oil to the producing wells. Considerable preliminary work, including new drilling, work-overs, and a pressure survey was necessary. During the test, oil production rates have averaged about nine times the final primary rates. The field average GOR is still below the pre-test value. Oil recovery to date is 112,000 STB. About one-third of the 143,-000 bbl of propane injected has been produced to date. Results of the C-2 block test are encouraging and larger, more definitive field projects ore indicated. INTRODUCTION The cost of finding new crude oil reservoirs continues to increase. Today the oil industry is drilling more and deeper wells and making fewer big discoveries. Nevertheless, the demand for oil and oil products increases each year. It is natural that oil companies, faced with this situation, concentrate on recovering more of the oil existing in our known crude oil reservoirs. There is room for much improvement. For every barrel of oil brought to the surface by present day methods of producing crude oil, generally 1 to 3 bbl are left behind in the depleted reservoirs. The "unrecoverable" oil in petroleum reservoirs is largely "trapped" by capillarity. Since flushing with a solvent is exceedingly effective in combatting oil loss due to capillarity, much effort in this direction has been made in recent years1,2,3,4,5. Liquefied petroleum gas (LPG) has been suggested as a relatively inexpensive. abundant, easily recoverable solvent for crude. Some operators have observed striking responses in oil recovery at production wells offsetting input wells in LPG storage reservoirs6,7,8. In spite of the low unit cost of LPG, however, it is uneconomic in general to inject a volume of LPG into a reservoir to remove a like volume of oil. A modification of solvent flushing in which a limited quantity of liquid propane is gas driven through a reservoir appears capable of recovering much more than 1 bbl of oil per barrel of propane injected. Also, most of the propane injected should be recoverable for sale or re-use. Since such a process could well have widespread and profitable application, The Carter Oil Co. is making an extensive evaluation of the technique's possibilities. Laboratory development of the gas-driven propane recovery technique was sufficiently encouraging to justify testing in the field. Since 1952, the Production and Research Departments of The Carter Oil Co. have cooperated in a field test in the C-2 Block leases of the

Jan 1, 1958

By Michael Bradbury

INTRODUCTION A major change in financing exports in recent years has been the decreased importance of subsidized export credits, following the commitment of the OECD countries to eliminate the subsidy element. Subsidized export credit rates are now often more expensive than market rates as the financing for exporters has decreased in volume and importance. The forfait market, in recognition of this decreasing importance, provides a rapidly expanding source of nonrecource finance for exporters. The following is a step by step guide to what it is, how it works, its benefits and problems. WHAT IS FORFAITING? Forfaiting is not new. It has been used in Europe for about 25 years to provide export finance for both capital goods and commodities without recourse to the exporter. Although long the preserve of exporters in Germany, and more lately Italy, forfaiting is now used increasingly by exporters in Great Britain, the United States, Canada and Scandinavia. It is a fairly simple operation with easy straight-forward documentation. The transaction involves the purchase by the forfaiting bank of a bill of exchange or a series of bills without recourse to the exporter. These bills will have been drawn by the exporter, accepted by the importer, and will usually bear the unconditional guarantee of the importer's bank. They are normally drawn payable at intervals during the credit period agreed between importer and exporter and are purchased at a discount by the forfaiter. The exporter thus obtains his cash payment and the importer receives his credit period. The forfaiter collects the amount of the bills as they mature directly from the importer. Credit periods vary, depending upon the type of goods and the country and commercial risk of the importer. The period is generally between one and five years with six monthly maturities. The usual forfait currencies are US dollars. Deutschmarks and Swiss francs and others, such as sterling, French francs, and the Scandinavian currencies are being used more frequently. CHOOSING FORFAITING Most types of financing require the continued involvement of the exporter in the financial side of the transaction during the credit period. Forfaiting has certain comparative advantages. In particular, it is possible to forfait 100 percent of the risk without recourse to the exporter, unlike government sponsored export finance schemes, where some retention of the risk by the exporter is required. In addition, exports from country sources do not present problems and forfaiting can also cover trade within the EEC. Other benefits for the exporter are: (a) The exporter's balance sheet is improved; debts are turned into cash thus improving the liquidity of the company and enhancing its cash flow. And there are no contingent liabilities for bills of exchange. (b) If the sales contract is in a foreign currency forfaiting removes the risk to the exporter of adverse movements in foreign exchange during the credit period. (c) Fluctuations in interest rates during the credit period can be ignored since in forfaiting the transaction is usually done on fixed interest rate terms on a discount basis. (d) The political and transfer risks are taken by the forfaiter. (e) The commercial risk is taken by the forfaiter. (f) The costs of administration and collection etc. during the credit period are removed.

Jan 1, 1985

By AIME AIME

HEREWITH is presented a preliminary report of a special committee, consisting of Erle V. Daveler, Paul D. Merica, and C. H. Mathewson (chairman), dealing with sundry matters of which many are of vital interest to all members of the American Institute of Mining and Metallurgical Engineers. As the report states, the initial purpose of the investigation was to determine ways and means to stimulate "the welfare and growth" of the Institute of Metals and Iron and Steel Divisions. However, it soon became apparent to the committee that most of the problems and possible correctives were of no less vital concern 1o members of the other Divisions and to the "unattached" group of members. Consequently, the Committee has authorized publication of the report and invites written comment from any member on the specific recommendations or on any other phase of the broad subject.

Jan 1, 1943

By ROBERT E. CROCKETT

MAGNETITE mining and milling in New York, New Jersey and Pennsylvania continued to remain comparatively inactive during 1933, owing to the low rate of output of the steel industry and also to unrestricted importation of foreign ores. However, some improvement over conditions existing in 1932 was noticeable, particularly in New Jersey, where one plant, that of the Washington mine of the Alan Wood Mining Co., at Oxford, went on full production in August. At Lyon Mountain, N. Y., the Chateaugay Ore and Iron Co. resumed mining and milling operations in October, on a reduced scale, principally to provide employment during the winter months. The Chateaugay company produces a special low-phosphorus pig iron. During the year they obtained a contract to supply their product for use in the manufacture of the suspension cables of the New. Golden Gate Bridge.

Jan 1, 1934

By AIME AIME

AN entirely new type of classifier is being put on the market by The Dorr Co., following three years of development and the experimental use of thirty machines of the improvement design in various parts of the world. It is known as the Multizone classifier. Compared with the older type the lower or overflow end has been decked over and is surmounted by one or more circular overflow columns. Feed is introduced near the middle of the machine and passes downward and under a vertical baffle, then along the underside of the deck to the base of the overflow columns. Under the baffle there is a restricted turbulent zone of high pulp velocity which holds the fine and critical size particles in suspension, preventing

Jan 1, 1937

By C. C. Miller, A. B. Dyes

The cost of finding and developing new reserves is continually rising. We must meet these rising costs with more economical operations. This can he accomplished if we revise our ideas of proper well spacing and well allowable to consider the concept of optimum well spacing. According to this concept, the optimum spacing is the one which leads to the maximum present worth for a reservoir when ail factors affecting total cost and total revenue are considered and when the wells are produced in the most eficient manner. Application of this principle efficiently utilizes available well potential and properly considers the recovery eficiency in addition to fixing the spacing on the basis of the amount and value of the oil to he recovered. This Study presents an analysis of one producing zone containing low gravity crude to illustrate the effect of these factors on the present worth and on the optimum economic spacing under two production drives—-evolved gas and water drive. The maximum present worth occurs when the optimum number of wells for open-flow operation is employed. Frequently, this optimum development cal1s for very wide spacing and the ideal field rates are not unreasonable. Under other circumstance. where proration is necessary, an optimum combination of well spacing and well allowable exists which permits production at relatively high rates. The optimum well density in a field depends on the recovery efficiency and the valule of the oil. In solution gas-driven reservoirs this optimum spacing for operation at high producing rates can vary from extremely wide spacing to handle viscous low gravity oil in thin formations to relatively close spacing in thick sands where good recoveries are expected. Because of the better recovery from water-driven fields, the optimum spacing in these fields is closer than in solution gas-driven fields. Also, the water encroachment pattern is dependent upon the well spacing, and an adequate numher of wells is needed to assure a good sweep eficiency. The economic optimum well density in a water-driven field is high enough for this purpose. INTRODUCTION From year to year domestic oil becomes more difficult to find. The fields we do locate are frequently smaller and deeper than older fields and the costs for men, material and equipment are continually rising. To replenish our reserves we must continue to search for and develop new fields, but experience has shown we cannot expect prices to rise in proportion to costs. Consequently, we must meet increasing costs by more economical operations. A vigorous effort is being made within the industry to improve exploration methods, to cope with the problems of deeper drilling, and to obtain a secondary yield from older fields. Many significant contributions have resulted from these efforts. The economic operation of new fields can be further improved by developing these fields on optimum spacing and producing the wells at higher rates. This would avoid the drilling of unnecessary wells and provide additional capital for seeking new oil. While the benefits of these practices are obvious, the problem of defining the optimum development of a field for natural depletion can become very complex. A study of the effect of well spacing and several reservoir variables on economic worth of a specific field is reported here to illustrate the problem and to show the magnitude of the benefits to be realized. This study is necessarily limited to the field conditions selected and is not intended as a general solution of the well spacing problem. It does, however, indicate factors to be considered, the trends to be expected, and the direction in which we should proceed in developing new fields. NO consideration is given to land and legal considerations which might arise. METHOD OF ANALYSIS The optimum method of developing and producing a field is to use the combination of spacing and prora-tion which gives the maximum return. In addition, we do not want to lose recovery. These considerations of maximum return and maximum recovery present no serious conflict. The value of each method of operation is conveniently expressed in terms of its present worth. According to the present worth method of evaluation,' an acceptable annual percentage return is assigned to the operation, and all incomes, capital costs, and expenses are discounted at this rate to the start of the operation. This net value is the present worth. If we apply the same discount rate to several alternate methods of operation, the one yielding the greatest present worth is the best method. If we express net income in terms of price per barrel of oil produced, drilling and equipment costs on a well basis, and expenses as cost per well year, this evalu-

By Oliver Bowles

DISCUSSIONS of trade and commerce are generally more comprehensive today than in the past; the problems are approached with a vision unrestricted by national boundaries, and broad enough to comprise the entire world. The extent to which the limited viewpoint that has characterized past ages is yielding to an economy of world-wide scope is exemplified by the Atlantic Charter which blazes a trail in the direction of trade principles that aim to preserve the interest of each individual country in the commonwealth of nations. Its fourth article promulgated the principle that all nations should have access on equal terms to the trade and to the raw materials of the world which may be needed for their economic prosperity. Future developments in reciprocal international trade may have some effect upon the flow of nonmetallic minerals but such effects are not likely to be great because tariffs and trade policies have not affected that flow profoundly in the past. Nevertheless conditions may change and new problems may arise demanding important decisions. Sudden changes are not to be expected, but rather an orderly evolution in which national interests will merit due consideration in establishing broader policies.

Jan 1, 1945

By G. Stuart Jenkins

CONDITIONS at the properties of the Consolidated Coal Co. had reached a point where improvements were almost impractical. The mines, sunk years ago, had shafts and entries so small as to preclude the use of large mine cars. A radical change was necessary in the type of mining and also in the type of mine to accommodate such haulage units. After due consideration, the company decided to enter the field of trackless mining, utilizing belt conveyors and chain-flight conveyors, the belt conveyors to take the long haul, and the chain-flight conveyors to be used for gathering. It was decided not to sink a shaft, but to drive a slope on an inclination of 17 1/2°, which the company believes to be about the limit on which coal can be carried on a belt without rolling back unduly.

Jan 1, 1939