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By Ira B. Joralemon

Neighboring mines, like men who live in the same environment, often assume similar characteristics. In the Bridge River area of the Lillooet district in central British Columbia there is a remarkable exception to this rule. The Pioneer mine has a simple fissure over 3000 ft. long, with no faults of more than a few feet and with only minor variations in width; the Bralorne mine, 2½ miles away at the other end of the same intrusion, has developed one of the most intricate vein and fault systems in the West. Hinged faults displace the main vein for hundreds of feet, and sometimes become valuable veins themselves. The width of ore varies in a few yards from 2 to 60 ft. Changes in grade of ore are just as abrupt. The rocks that follow the veins or are cut by them often grade into one another or into the ore with no definite contacts. Although the complexity of the structure has left many problems unsolved, the development has indicated a fascinating geological pattern. The Bralorne is in the eastern portion of the Coast Range, 55 miles by spectacular mountain road from the Pacific Great Eastern Railway station of Bridge River. The adit tunnel runs easterly from Cadwallader Creek, a tributary of Bridge River that flows into the Fraser River. Steep mountains rise from 3300 ft. elevation above sea level at the creek to peaks and ridges at 8000 to 9000 ft. altitude. The lower slopes are heavily wooded while above 5000 ft. bare rocks, glaciers and snow-fields extend far above timber line. See Fig. 1. Story of the Bralorne The Lorne claim, staked in 1897, was one of the earliest lode locations in the Bridge River district. At that time it was 70 miles by steep and treacherous trail from the railway. For the next 15 years Arthur Noel, Will Haylmore and other local prospectors mined the small, irregular, oxidized quartz veins to a maximum depth of 200 ft., and treated the ore in arrastres and later a five-stamp mill. The total production to 1912 was only $55,000. Noel and associates later formed the Lorne Amalgamated Mines Co., which they worked in a desultory way until 1925. Increasing sulfide and arsenide content in the veins

Jan 1, 1935

By G. M. T. Marshall

Plans to bring the Geco Mines property in Manitouwadge, Ont., into production began in 1954. At that time over 12 million tons of copper-zinc ore were indicated in a zone 2700 ft long. A concentrating plant was built to handle 3300 tpd of ore and a production shaft was sunk about 1500 ft. MINE LAYOUT Vertical attitude, width, rake, and competent country rock of a 4-million ton orebody west of the main diabase dike suggested a system of blasthole stopes, undercut with scram drifts connected by a transfer raise system to a crusher on the 1250-ft level and this system was employed. A 42-in. conveyor on this level transfers the ore about 1200 ft to a loading pocket at the No. 1 shaft. The system has a number of advantages: 1) Cost of tramming is eliminated. 2) Rate of extraction from any stope is controlled only by the scraping capacity of the scram. 3) Rate of extraction from the stoping area can be very rapid. Fast extraction makes it possible to cut mining costs for the following reasons: The number of stopes actively producing is kept to an economical minimum; the operating area is concentrated-manpower can be used more effectively; and active life of the stoping block is short, making ground support problems simpler and less costly.

Jan 8, 1959

By Frederick Laist

While remodeling No. 1 section of the concentrator at the Washoe Reduction Works of the Anaconda Copper Mining Co. during the summer of 1912, for the purpose of ascertaining what additional metal recoveries could be made by improvements in concentration practice which had been developed by the staff of the Boston & Montana Reduction Department, at Great Falls, it was deemed advisable to carry on some experiments on the treatment of the regular mill tailings by roasting and leaching, to see whether the losses of metal values might not be still further decreased. In the course of these experiments about 5,000 tons of tailings were roasted, and of the resulting calcine about 200 tons were leached. The results were so satisfactory that it was decided to continue the work on a larger scale, particularly as regards the leaching end of the process, and construction work on an 80-ton roasting and leaching plant was accordingly commenced during the latter part of February, 1913, and is being pushed as rapidly as possible. 80-Ton Leaching Plant. This plant will consist of one 20-ft. roasting furnace of the Mac-Dougall type, specially adapted to the work of roasting for leaching; two leaching tanks, 32 ft. in diameter by 12 ft. deep, together with the necessary solution tanks, air lifts, precipitating launders, etc. It has been decided to precipitate the copper from solution on scrap iron, so as not to hamper the roasting and leaching departments by any weakness that might develop in the precipitating department. It is, however, the intention to experiment with a number of different methods of precipitation; for example, by electrolysis and by hydrogen sulphide. The acid required for the operation of this plant will be purchased, ad the quantity required is not sufficient to justify the installation of an acid plant. An acid plant will, however, be established in con-

Jan 1, 1914

By C. O. Brawner

FACTORS THAT INFLUENCE STABILITY AND STABILIZATION METHOD The most effective stabilization method and design can only be developed if the cause(s) and mechanics of the slide are known. Therefore, it is important that the stability be evaluated by an engineer who has had extensive rock stability experience. The most important factors that influence stability are structural geology, ground water, blasting and the mining method or methods. Structural Geology - The majority of failures in rock slopes occur along discontinuities in the rock (joints, bedding planes, shear or fault zones, etc.). Therefore, on all surface mining projects, the development and maintenance of a comprehensive structural geologic mapping program should be a first priority program that is considered a part of the operations function. This program should include mapping all major features - faults, shear zones and through going joints. All structural features which could influence stability should be mapped and presented in a structural domain format for the entire mine (Canmet, 1977). Where planes, wedges or blocks will be undercut by the mining excavation, shear strength and strain to failure tests should be performed on the joints, fault gouge and gouge-rock contact surfaces. These tests must be performed on the samples in the direction of potential slide movement and must determine the range of peak and residual shear strength values. A preliminary assessment of friction angle can be obtained from measurements of failed surfaces in the field (Figure 1) or from core sliding tests (Barton, 1981). An assessment must be made of the past geologic history of

Jan 1, 1983

By O. W. Ellis

RECENTLY there has been a considerable revival of interest in the effects of the various elements commonly added to brass for the purpose of increasing its strength. For many years the work of Guillet2? alone gave reliable information in this regard. Even today his determination's of the coefficients of equivalence of the various elements relative to zinc in brass are those universally employed in industry. This is so because these coefficients have stood the test of time-their substantial correctness has been proved in almost universal practice. It is not our intention to discuss here these coefficients or their use. Rather do we wish to emphasize the need for further systematic studies of the mechanical properties of the ternary systems of copper, zinc, and other individual elements. Since Guillet published the results of his first investigations Millington,16 Smalley33 and Thibaud45 have added somewhat to our information. In general they have confirmed the findings of Guillet, which may be stated in the following rather general terms: 1. The addition of aluminum to the 70:30 and 60:40 brasses progressively increases their hardness and strength and reduces their ductility and resistance to shock. 2. The addition of small amounts of iron to a 60:40 brass improves its strength without affecting its ductility. 3. The addition of small amounts of manganese to a 60:40 brass causes a progressive increase in its strength and reduction in its ductility. A considerable amount of information has been amassed in regard to the effect of nickel on brass (9, 22, 41) which it is unnecessary to refer to here, in view of the scope of this paper.

Jan 1, 1929

The industrial might of the Bowen Basin is primarily the result of Utah Development Co.'s work- which has opened up the Blackwater, Goonyella, Peak Downs, and Saraji mines; built the Hay Point port; and is now developing the Norwich Park mine.

Jan 1, 1977

By Richard V. Hughes, Rudolf J. Pfister

The necessity for getting more water into sands of low permeability in any secondary-recovery water-flood operation in order to recover all the available oil always has been a major problem. In the early days of water-flooding the addition of soda ash and caustic soda to fresh input waters was recommended and tried without success in the Bradford field. The most frequent difficulty was sand plugging. The use of natural and artificial brines often has been suggested for water-flooding, in the belief that laboratory observations of decreasing fresh-water throughput rates in measuring water permeabilities of consolidated sand cores might be partially explained by swelling of clays. A review of available literature bearing on the subject and related laboratory experiments are presented herein, offering an explanation for failure in use of soda ash and caustic soda waters and supporting the recent concept that every water used for input purposes in the secondary recovery of oil should possess such physical and chemical characteristics as to keep the clay content of the producing sands in a permanently flocculated condition. Produced brines meet this requirement. Their use is recommended as a means of increasing intake rates of tight sands and oil recoveries, as a solution to brine-disposal problems, and as a means of conserving a natural resource. Introduction There is a general belief among those engaged in the secondary recovery of oil by water-flooding that one of the most important requirements for the success of any such project is an adequate supply of good, fresh water. Fresh waters have the advantages of being more easily stabilized than salt waters and of being usable about the lease for all purposes. The use of brines for water-flooding never has been given much consideration in the Pennsylvania Grade area. The use of brines in Mid-Continent operations has been considered largely as a substitute for fresh waters, which were economically unobtainable for many operations. Estimated recoveries for some water-drive fields indicate that less of the original oil in place will be left upon abandonment than with the above-average practices used in Pennsylvania Grade water-flood operations. Lower residual oil saturations than 25 pct of the pore space following the water-flooding of Third Bradford sand cores in the laboratory are unusual. In comparison, water-flushed sands surrounding any virgin oil pool are found to be practically devoid of oil. Such lower natural residual oil saturations may be the result of a time factor much longer than economic under artificial water-flood operations, but neither the producer of primary oil nor the producer of oil by secondary recovery can obtain maximum recoveries unless full advantage is taken of all natural forces and

Jan 1, 1947

By Richard V. Hughes, Rudolf J. Pfister

The necessity for getting more water into sands of low permeability in any secondary-recovery water-flood operation in order to recover all the available oil always has been a major problem. In the early days of water-flooding the addition of soda ash and caustic soda to fresh input waters was recommended and tried without success in the Bradford field. The most frequent difficulty was sand plugging. The use of natural and artificial brines often has been suggested for water-flooding, in the belief that laboratory observations of decreasing fresh-water throughput rates in measuring water permeabilities of consolidated sand cores might be partially explained by swelling of clays. A review of available literature bearing on the subject and related laboratory experiments are presented herein, offering an explanation for failure in use of soda ash and caustic soda waters and supporting the recent concept that every water used for input purposes in the secondary recovery of oil should possess such physical and chemical characteristics as to keep the clay content of the producing sands in a permanently flocculated condition. Produced brines meet this requirement. Their use is recommended as a means of increasing intake rates of tight sands and oil recoveries, as a solution to brine-disposal problems, and as a means of conserving a natural resource. Introduction There is a general belief among those engaged in the secondary recovery of oil by water-flooding that one of the most important requirements for the success of any such project is an adequate supply of good, fresh water. Fresh waters have the advantages of being more easily stabilized than salt waters and of being usable about the lease for all purposes. The use of brines for water-flooding never has been given much consideration in the Pennsylvania Grade area. The use of brines in Mid-Continent operations has been considered largely as a substitute for fresh waters, which were economically unobtainable for many operations. Estimated recoveries for some water-drive fields indicate that less of the original oil in place will be left upon abandonment than with the above-average practices used in Pennsylvania Grade water-flood operations. Lower residual oil saturations than 25 pct of the pore space following the water-flooding of Third Bradford sand cores in the laboratory are unusual. In comparison, water-flushed sands surrounding any virgin oil pool are found to be practically devoid of oil. Such lower natural residual oil saturations may be the result of a time factor much longer than economic under artificial water-flood operations, but neither the producer of primary oil nor the producer of oil by secondary recovery can obtain maximum recoveries unless full advantage is taken of all natural forces and

Jan 1, 1947

By William Waters Van Ness

The Pierrefitte mines, situated in the South of France, in the district of the Hautes-Pyrenees, owe their name to the fact that the first mining operations of any extent, and of comparatively reccnt date, were carried out in the neighborhood of the village of Pierrefitte, which is a branch terminus of the Midi railway. The Pierrefitte mines, however, embrace a wide extent of country and several different concessions, on most of which comparatively little exploration-work has been done. The portion of the property presently to be described is a zone running roughly E—W., over a distance of about 5 miles from the valley of Cauterets to the valley of Estaing, the ridge dividing these valleys being a spur of the main chain of the Pyrenees, and running more or less at right angles to it. According to local tradition, which various indications tend to confirm, these mines are of ancient date, the first workings being attributed to the Romans, who are supposcd to have sought not only the lead but also the silver which is contained in the ore. Old slags have been found in the neighborhood which might well have been produced from the cupellation of lead-ores. These old workings, while of considerable extent at times, do not seem to have extended beyond a depth of 100 ft., even this depth being somewhat exceptional. The old notarial records of the district show that mines were known to exist, and that they were even worked, in the sixteenth century, but since the mines were abandoned (by the Romans or others) considerably prior to this period, very little

Jan 1, 1909

By K. A. Johnson, F. H. Ellinger, C. C. Land

The Pu-La alloy systenz has been studied by thertnal, tnzcrographic, and X-ray diffraction methods. It is churacterized by a liquid miscibility gap, a maximum solubility of about 20 ut. pct PM in y lanthunum and 19 at. pct PI* in 0 lanthanum, very little soluibility of lanthanum in the plulonium allotropes, and the absence of intermediate phases. THE existence of immiscible liquids in the Pu-La system has been reported by Schonfeld.1 A tentative phase diagram based on the results of thermal-analysis experiments has been constructed by Poole et a1 2 This diagram shows a liquid immiscibility loop with a monotectic at 77 at. pct La and 846°C. 7 lanthanum is shown to dissolve 20 at. pct Pu and to decompose by an inverse peritectic reaction (y La = L , + p La) at about 82 at, pct La and 833°C. The ß lanthanum solvus was not determined, but the thermal work indicated a maximum solubility of 16 at. pct Pu in ß lanthanum. The present investigation has defined the solubility limits of plutonium in y lanthanum and 0 lanthanum, and, with the exception of minor discrepancies, has verified the results of Poole et al. 1) EXPERIMENTAL The electrolytic plutonium melting stocks were better than 99.9 wt pct pure, the main impurities being 90 ppm Fe and 50 ppm W. The lanthanum melting stocks, supplied by Research Chemicals and the Cerium Metals Corp., were about 99 wt pct pure, the main impurity detected by our spectrochemical analysis being 2000 ppm Fe. The components for each alloy button (-5 g) were weighed on an analytical balance and were melted together in a conventional arc furnace. If no significant weight loss occurred during melting, the as-weighed

Jan 1, 1968

Jan 10, 1951

By Anson Hayes

THE quality of sheet and strip products made of rimming steel is closely related to the structure and chemistry of the ingots. The varia-tion in composition throughout the ingot, as affected by segregation, is of great importance, as are also the form and distribution of the voids that result from the gases evolved. It is because of this importance that the considerable literature in this field has accumulated. No attempt is made in the present paper to compile a bibliography of the excellent work that has already been done, as this has been adequately covered in the many excellent reports on the heterogeneity of steel ingots prepared by a joint committee and published by the British Iron and Steel Institute.1 From time to time, in any field of investigation new tools and new technique are developed, which make further progress possible. In the field with which this paper is concerned, this is true. The development of the vacuum-fusion method as a means of following oxygen segregation, and a technique for obtaining the volume and composition of the gases evolved during solidification, have opened the way to obtaining data by means of which some considerable progress has been realized in developing more of the detailed mechanisms of solidification and segregation in rimming-steel ingots.

Jan 1, 1938

By W. E. Remmers

The fact that gray iron increases in volume, cracks and distorts upon repeated heating and cooling is rather conlmon knowledge. In ingot molds, Diesel engine pistons, carburizing boxes, continuous furnace parts, grate bars, stoker parts, and all castings that are subjected repeatedly to high and low temperatures, the phenomenon of growth presents a vital problem. Ingot molds distort and produce cracks which result in seams or laps and later appear as defects in the finished product. The heads of Diesel pistons frequently fail by cracking in a stellar shape. This is attributed usually to the result of permanent growth. Distortion and change of dimension of furnace parts frequently renders them entirely unusable. In chain grate stokers, mechanical difficulties frequently are caused by the growth of the links. In proper operation these links should never attain a temperature sufficiently high to start growth; nevertheless, some have grown in. on an 8-in. length when improperly operated. Even though the phenomenon is generally known there still exists a deficiency in the explanation of the mechanism of this growth. The field of investigators of this subject has a decided variation in opinion concerning the causes. The problem is of sufficient importance therefore to warrant further consideration. Review of Published Work Since the published work, particularly the European, contains much detail, only the outstanding results and conclusions of the investigators will be reviewed. The pioneering investigations of Outerbridge in 1904 and 1905 brought forth the conclusion that growth was not a function of chemical or crystallographic changes but was a result of the formation of fine hair cracks. These cracks are supposedly due to a nonuniformity of thermal expansion and contraction which ruptures the structure of the material. More recently Benedicks and Lofquist presented a purely mechanical theory, which is similar to that of Outerbridge. These investigators believe the temperature gradient from the outside to the center of the cast piece causes a contraction of the outer layers on passing

Jan 1, 1931

By E. G. Leonardon, C. Schlumberger, M. Schlumberger

The object of this paper is to describe the adaptation of electrical resistivity measurements to the particular case of exploration in which the surface is an expanse of water (river, lake, sea). Water in itself does not constitute an obstacle to electrical exploration. It is merely an overburden, which is fluid instead of being solid, and as a consequence the routine of the measurements has to be modified. Also, in many instances, the liquid under consideration is highly conductive (salt water). This introduces an additional difficulty into exploration work, and has to be overcome by the geophysicist. We do not propose to discuss here the basic principles of electrical resistivity measurements, which have been dealt with in various previous papers,' but will simply recall the two fundamental techniques which govern its field application: 1. Horizontal exploration, or method of the resistivity map, in which a series of electrical measurements are carried out at various stations, keeping the same electrode spacing. Thus, a horizontal layer of the subsoil, of a practically constant thickness, is explored. 2. Vertical exploration, or "vertical sounding"2 method, in which a seriesr of measurements is made with increasing electrode spacings at one or several stations. In this way, the apparent resistivity is determined at a given station for various increasing thicknesses of the ground.

Jan 1, 1934

By Frank H. Riddle, Wilfrid R. Foster

GENERAL treatment of the various minerals of importance in refractories appears in the chapter entitled "Refractories" elsewhere in this volume. The present chapter is restricted to a discussion of minerals of the sillimanite group and brings up to date the excellent information contributed by Prof. Paul F. Kerr to the first edition (1937). Since the appearance of that edition, the status of the group has changed some- what. Kyanite remains the preferred source material for mullite refractories but total consumption of kyanite has increased considerably.85 The exigencies of World War II forced an increased dependence on domestic sources and led to an intensification of the search for higher-grade deposits of kyanite and allied minerals. The first discovery of massive kyanite similar to that of India has been reported from Georgia.37 British East Africa has joined India as a substantial supplier of our imported kyanite, but that from India continues to hold preference.85 During World War II, prices of both domestic and foreign grades reached peaks unparalleled since the earliest years of the use of kyanite and as yet have shown no tendency to return to prewar levels. Topaz, by virtue of the deposit outlined in South Carolina, merits inclusion in the group.20,36,95 Large andalusite deposits, which threaten to rival our one large domestic occurrence, have been found in Russia.69,88 Sillimanite has not yet attained an important position among these useful minerals because of the lack of accessible deposits of high-quality material in adequate supply.37,50,58 Tests by the Bureau of Mines have indicated the possibilities of economically beneficiating low-grade sillimanite and kyanite.105.106,140 Government, university, and industrial

Jan 1, 1949

By Leo J. Vogel, E. D. Hummer

INTRODUCTION by E. D. HUMMER An efficient refuse-disposal system is a necessary part of the modem cleaning plant. The large-scale refuse system and disposal area, engineered for the lifetime of the plant, has become more important due to the greater tonnages of refuse produced from increased quantities of mechanically mined and prepared coal. Laws and increased government regulations have affected the design and operation of disposal systems. THE EFFECT OF MINE AND PLANT OPERATION Refuse disposal starts at the mining face. The mining system, the type of roof support, the machinery used, and the degree of discipline at the face contributes to the amount and type of refuse that must be removed through the disposal system. Economies gained through modification of the mining system or mining machinery may be partially offset by increased dilution of the mined coal with impurities from associated rock formations. In some cases the change in the mining system and equipment has reduced the dilution. In all cases the ratio of impurities that must be removed from the raw-coal feed to the plant not only affects the maintenance and operating costs of the plant, but greatly affects the design of the refuse disposal system. The design of a mine and plant should include the location and the estimated capacity of the disposal areas for the life of the property or plant. Complete evaluation of the disposal system and an estimate of its annual cost of operation over the life of the property or plant should be incorporated in the plant and mine evaluation. Plant design should be as simple as possible, consistent with the efficient production of clean coal. Material transfer points, crushing, screening and pumping operations should be kept to a minimum to reduce degradation and the subsequent increased difficulty and cost of refuse removal. The maintenance of good process control by operating management will result in a minimum of misplaced material in both refuse and clean coal. Reduction of misplaced float material in the plant refuse is an important factor in preventing combustion in the refuse storage pile. THE REFUSE DISPOSAL AREA Combustion in refuse piles occurs when air enters the pile in sufficient quantity to support oxidation. At certain rates of air in-filtration, the heat produced by the oxidation process is not dissipated and temperature rises.

Jan 1, 1968

By G. M. Webster, G. E. Dawsongrove

The use of percussion-type side-wall cores as an aid in detection and evaluation of hydrocarbon shows and in examination of rock properties has become increasingly popular in recent years. Sidewall coring has an advantage over normal bottom-hole coring methods in that the zones may be surveyed with the electric log prior to selection of sample depths. This allows an efficient sampling of all zones of interest, a procedure not possible with bottom-hole coring techniques unless the costly procedure of continuous coring is utilized. Percussion sidewall coring presently provides the most rapid and lowest cost method of obtaining sidewall cores. It has been recognized for some time that certain discrepancies exist between core analysis data obtained from percussion cores and data obtained from other types of core Samples. This paper presents existing field and laboratory data that were available to the authors. Several examples of comparative core analysis data obtained from various fields are presented along with photomicrographs of thin sections of conventional and percussion cores. The results of this investigation are presented to throw more light on the possible disturbed condition of percussion sidewall cores. SAMPLE DISTURBANCE AND FRACTURING The principal cause of discrepancy between conventional core analysis data and percussion sidewall core analysis data is believed to be the shattering and re-adjustment of the grains due to the large impact shearing forces produced by mechanics of percussion coring. Figs. 1 through 5 are photomicrographs of thin section slides of formation samples obtained by means of diamond cores, conventional cores, and percussion sidewall cores. Figs. 1 and 2 show samples of the

By AIME AIME

THE report of the united. States Steel Corporation for the' year 1928 gives the, following ,figures of raw materials and' finished products . Raw materials, tons :

Jan 1, 1929

By T. D. Lynch, N. B. Pilling

The development of a proper treatment for shells in conncction with war contracts has brought to our attention the fact that the temperature of the liquid bath in which steel is quenched has a decided influence on the speed of cooling in the case of some liquids and very little in the case of others. Widely different physical results have been obtained by the use of water spray, water immersion, and oil immersion and further experiment has shown that the quenching effect of water used as a spray or an immersion varies greatly with the temperature of the water. The present experiments were undertaken with the idea of obtaining information of a quantitative nature regarding the quenching properties of a number of liquids used commercially in hardening steel. The general features of such cooling media are common knowledge and in the literature may be found records of numerous attempts to evaluate the cooling power of a liquid when used as a quenching bath. Much, if not most, of the data given on this subject is in the form of a simple statement of the time required for a certain heated mass to cool between two arbitrary temperatures when immersed in the liquid, quite regardless of the path of the temperature change. Our own purpose has been somewhat different. We have attempted to isolate that property of these liquids having to do with their ability to absorb heat rapidly, as distinct from the behavior of a considerable mass when exposed to different thermal environments. More specifically, from the data obtained through autographically recorded cooling curves of a small standard mass quenched under various conditions, we have tried to analyze the mechanism of heat absorption by the several liquids, measure the changes in its rate as a function of the temperature of the surface of transference, and ascertain the influence of the temperature of the liquid itself upon both. Without attempting an exhaustive citation of the literature, mention may be made of some of the more important contributions, notably the pioneer work of Le Chatelier,' followed by the extensive investigations

Jan 1, 1920

By W. G. Bearden, P. P. Scott, G. C. Howard

This paper concerns the rupture or breakdown of rock formations as related to drilling, completing, and stimulating production of wells, and comprises data compiled from a study of literature and records of treatment of oil and gas wells. and from tests conducted in bores drilled into rock cores and outcrops of rock. Results of the investigation indicate that the internal pressure to rupture cylinders of rock and to breakdown rock formations surrounding a bore in the earth is dependent upon the extent of intrusion of fluids. the position of bedding planes. the ratio of internal to external diameter, the tensile strength of rock, and magnitude of confining pressure, and is independent of the size of bore, degree of fluid saturation. and temperature of rock within practical limits. It is concluded that the mathematical relationship of pressure in bores and stresses in the surrounding rock must not be limited by the simplifying assumptions of homogeneity. isotropy, and impermeability; that the incidence of lost circulation of drilling fluids to induced fractures may be reduced by preventing intrusion of fluids into the small intrinsic fractures along weak bedding planes; and that the magnitude of the breakdown pressure of wells to be treated may be lowered by removal of mud cake. INTRODUCTION The purpose of this paper is to present and discuss the results of tests which may serve to broaden the understanding of the phenomena of rupture or breakdown of rock and thus contribute to the improvement of the techniques for drilling and completing wells. including such operations as preventing lost circulation, stimulating production, and placing cement. Since the early recognition of the possibility of rupturing rock adjacent to a well by fluid pressure, the distribution and magnitude of stresses around a well and the internal pressure to cause failure have been expressed mathematically by application of the principles defining the elastic and inelastic behavior of thick-walled cylinders of a homogeneous. isotropic, impermeable material. In either the elastic or plastic state, if the conditions of homogeneity. isotropy, and impermeability were the normal characteristics of rock. there would be no reason to question the validity of the above principles when applied to rock. However. since most rock formations are characteristically permeable to some degree, contain bedding planes and small intrinsic fractures. and are heterogeneous, rendering invalid the assumptions of homogeneity, isotropy, and impermeability, the application of the thick-walled cylinder theories to the behavior of rock formations penetrated by a bore appears illogical. Also the failure to consider the effect of the properties of the drilling fluids, which certainly intrude in various degrees into most rock formations. is further cause for questioning the application of these principles. Even in the case of cylinders of hardened chrome-nickel steel, which would he considered relatively homogeneous isotropic. and impermeable, as compared to rock, it has been observed that the internal pressure capable of being withstood by the cylinders varied with the sizes of molecules comprising the rupturing fluid used. Because of these apparent weaknesses in the theories of the behavior of thick-walled cylinders when applied to bores in rock, and the importance of knowing the true behavior of rock under the influence of fluid pressure when planning drilling and completing procedures for wells, tests were undertaken to determine by observation the actual rupturing pressure of cylinders of rock and the effects of such variables as environmental conditions and characteristics of rock formations, fluid properties, and bore dimensions. It was intended that by these tests the validity of the thick-walled cylinder theories when applied to rock would be determined and, if found invalid, mathematical expressions would be derived for predicting stress and rupturing pressure of rock formations under various conditions. Since the derivation of mathematical expressions has been only partially completed, all of the results of the latter phase are not included in this paper. PROCEDURE The investigation was initialed with a study of the theories pertaining to the rupturing of thick-walled cylinders of homogeneous. isotropic, impermeable material and a study of the

Jan 1, 1953