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By William Kobbé

I. INTRODUCTION THE word recovery as used in this paper is applied in its broader sense and not limited to wells producing from horizons of unconsolidated sands. Certain problems connected with the winning of petroleum from such horizons present themselves while drilling is in progress and should be considered before drilling is commenced wherever unconsolidated sands are expected. Maximum recovery depends not alone upon efficient pumping methods but also upon the selection of a proper drilling system and the completion of a well especially adapted to the extraction of these oil-bearing sands. II. DRILLING DETERMINING FACTORS IN SELECTION OF METHOD The selection of a drilling method for the development of a region in which the oil reservoir consists of unconsolidated sands is based on the following considerations: (1) Character of the formations overlying the reservoir; (2) thickness of the oil-bearing stratum or strata; (3) thickness and character of water or gas sands; (4) gas pressure to be encountered or expected; (5) total depth of well.

Jan 12, 1916

By Ralph Hayden

PAGE I. IntRoduction........239 II. Definition of Anaconda SLime....240 III. The Source of Slime......240 Remodeled Flow Sheet......240 Old Plow Sheet,.......242 IV. ConStitution of Slimes......243 Chemical........243 Physical.........243 V. The Slime Problem.......247 VI. THe Experimental Slime Plant....248 VII. Slime Thickeners. ETc .......249 Slime Ponds........249 Tanks.........249 Comparative Efficiency of Open and Baffle Tanks .260 Callow Tanks........252 Kuchs-Laist Centrifugal Separator....253 Garred Filter........256 Dorr Continuous Thickener.....256 VIII. Concentrators........257 Round Table........558 Peck Centrifugal Concentrator....259 Competitive Tests.......260 Twenty-Deck Round Table..... 260 Slime Feed Distributor......261 IX. ConcluSion.........262 I. Introduction. In the wet concentration of ores there is always a certain amount of very fine material with which to contend. and which invariably carries such quantities of value that the treatment of it is worth while. commercially. This fine material usually contains that portion of the ore which hinders the separation of the mineral values: namely. the colloidal material resulting from the decomposition of certain constituents of the ore. The object of this paper is to show what efforts have been made to solve the slime problem as it occurs in the concentrator of the Washoe

Jan 1, 1914

By J. Nutting, D. H. Kirkwood

The oxidation of lead sulfide in air between 200° and 350°C has been investigated by electron diffraction from thick sulfide films and from galena surfnces. It has been demonstrated that sulfate is the stable reaction product up to 570°C. Sulfate is HAGIHARA has investigated' single crystals of galena roasted in air by the reflection electron-diffraction technique, which owing to the very limited penetration of the beam into the crystal gives information of the nature of the surface only. He has shown that up to 280°C the first oxidation product is lead sulfate, followed by lead mono-oxysulfate (PbO . PbS04). At longer times and higher temperatures more complex patterns appeared which could not be analyzed. All of these patterns were of streaks or spots arising from crystals oriented on the galena surface, and it is probable that these crystals are lead compounds whose structures have not been determined, such as the other oxysulfates (2Pb0 • PbS04 and 4Pb0 . PbS04) or a number of oxides. Certain lead sulfide films, formed chemically, give ring patterns in transmission electron diffraction2 because they are polycrystalline, and should also give ring patterns of the products after oxidation. It was thought that a diffraction study would reveal the sequence of phases produced in the reactions at different temperatures, since X-ray powder patterns are available for many lead compounds. PREPARATION OF FILMS The films were prepared by passing H2S over a saturated solution of lead nitrate in water. Once a silvery film had formed on the solution surface, no further thickening was apparent. The films were transferred by a gauze to a bath of distilled water for washing and pieces of film were caught on small discs on which they were dried. The discs were formed initially on galena up to temperatures of 300°C, followed by oxide and oxysulfates in turn at longer times. The appearance of- these phases is believed to result from an inadequate rate of supply of sulfur to the top surface 01. the crystal. standard Siemens mounts, made of platinum alloy, and had seven 20-p apertures drilled through them. The parts of the film which had dried onto the disc surface were light blue in color, which is the interference color of a film about 600A in thickness. A strong pattern of lead sulfide was obtained in transmission electron diffraction through the apertures but slight broadening indicated a crystallite size of around 200A. Tilting a sulfide film in the beam produced arcing of the rings, increasing the intensities of the (Ill), (3111, and (222) rings and reducing (200) and (220). This arises from preferred orientation in the film, a [loo] direction of the crystallites being normal to the plane of the film. These specimens were oxidized in an oven maintained at the required temperature. The reported times include that taken to heat the film to the reaction temperature. STABLE PHASES FORMED IN OXIDATION The conditions in which various oxidation products of lead sulfide are stable have been considered by the authors in a previous paper.3 It was shown that in a normal atmosphere, taken as containing lo-' atm of SOs, lead sulfate would be stable up lo about 570°C. This was confirmed by oxidizing thin films of sulfide for several days, and the analysis of the transmission-diffraction pattern is given in Table 1. The fit with the patt$rn from X-rays is good, except for the missing 3.62A ring. Some disagreement in intensities of reflections given by X-rays and electrons is to be expected. Up to 570°C a spotty pattern of sulfate was still obtained, indicating grain growth, but above this temperature the film disintegrated. Probably this is associated with the decomposition to PbO . PbS04. It needs to be emphasized that the atmosphere

Jan 1, 1965

One of the most unusual assignments in the his¬tory of Loffland Bros. Co. is now in progress with the drilling of a 72-in. diam. shaft in Nevada for the United States Atomic Energy Commission. Projected depth being 3200 ft, by volume, this is the same as a 216,672-ft hole 83/4 in. in diam. Every aspect of the operation is king-sized. The 15,000-lb bit moves into position over the well on a specially-made railroad car riding on rails 14 ft apart. The single drill collar weighs 300,000 lb, is 60 in. in diam., and 43 ft long. The drill pipe is 133/s-in. 72-in. N-80 casing fabricated with special tool joints. The bit chews up 1.05 cu yd of rock for every ft of penetration (This is equal to the volume of 67.71 ft of 83/4-in. hole.

Jan 9, 1964

By R. J. Franklin, G. W. Beckman, D. Warren, E. Both, J. F. Libsch

BINARY and ternary alloys of iron, nickel and cobalt respond to annealing in a magnetic field by a characteristic change in the shape of their hysteresis 100p.l,2 An increase in retentivity and a decrease in coercive force produced by the magnetic treatment cause the hysteresis loop to approach the appearance of a rectangle. Materials with a rectangular hysteresis loop have made possible the contact-rectifier³ and have greatly improved the performance of pulse transformers4 and magnetic amplifiers." In the best material presently available for these applications, a 50 pct nickel-iron alloy," the desired characteristics are achieved by aligning the preferred crystallographic directions of magnetization along the rolling direction of the tape. The objective of the present study has been to produce rectangular hysteresis characteristics in materials with inherently high saturation. Iron-cobalt alloys, exhibiting saturation values up to 24,000 gausses' appeared to offer promise for the magnetic annealing technique, because they remain magnetic to very high temperatures,8 exhibit favorable magnetostriction properties: and show zero crystal energy at 42 pct cobalt.10 Among the ternary iron-cobalt-nickel alloys,7,11 response to heat treatment in a magnetic field is unfortunately limited to alloys having rather low saturation values.' It appeared interesting nevertheless, to study a series of compositions connecting the optimum composition (50/50) of the binary iron-cobalt system with the "Perminvar" composition (30 pct Fe, 25 pct Co, and 45 pct Ni). Very recently, R. Smoluchowski and R. W. Turner," have shown that under certain circumstances magnetic annealing can produce oriented recrystallization. A combination of this technique with the domain orientation utilized in the present study might well result in further improvements. The advantages of the powder metallurgy technique in preparing magnetic alloys for study have

Jan 1, 1951

By Dr. O’Neil Thomas J., Donald W. Gentry

"There are two characters to the value of mining properties-one mine may have a value, owing to its real intrinsic worth; an- other (having no intrinsic value) may have a value by being so situated as to harass the working of the really valuable mine-in mining camps one is looked upon as much of ligitimate enterprise as the other.'' -Victor Clement to Simeon Reed, Wardner, Jan. 11, 1890, Reed Mss. APPROACHES TO VALUATION Value and costs are two terms basic to financial analysis which cause, perhaps, the greatest amount of misunderstanding in mine valuation studies. When discussing the value of an asset or the costs of producing a product, it is absolutely essential that the speaker define the terms being used. There are many types of value and many categories of costs. Without specific accompanying definitions, value and cost data are not very meaningful. Value refers to a measure of the desirability of ownership of property. Some of the types of value which might be encountered in a mine valuation study are: 1) Market value 2) Full cash value 3) Salvage value 4) Replacement value 5) Capitalized value 6) Book value 7) Assessed value 8) Insured value Each of these has a specific meaning which can be applied to determine a monetary amount in a specific situation. The major item of interest here is the broader question of "what is the value of the mine?" or "what is the mine worth?" In this case, we are speaking of market value. Market value is the value (price) established in a public market by ex- changes between a willing buyer and a willing seller when neither is under duress to complete the transaction. Market value fluctuates with the degree of willingness of the buyer and seller and with the conditions of the sale. The use of the term market suggests the idea of barter. When numerous sales occur on a market, the

Jan 1, 1984

By C. A. Edwards

Jan 1, 1935

By C. A. Edwards

Jan 1, 1935

By Thomas Read

SUMMARY THE cost of labor turnover in industry is so large as to justify the adoption of almost any means to bring about its reduction. Intensive study has shown that faulty methods of hiring and discharging men is the most important factor in labor turnover. Complete control over hiring and discharging by the foreman is a relic of outgrown industrial conditions; centralized hiring permits this work to be put on a scientific basis and also does away with many serious evils that cannot otherwise be reached. Centralized hiring does not impair the authority of the foreman; he hires his men from the employment office and discharges them back to it, instead of from and to the street. The employment manager, being a direct representative of the employer, tends to restore the former relation of direct intercourse between employee and employer that was helpful in avoiding friction between them. Being a specialist, he is able to bring special knowledge and skill to bear upon the task of selling employment in his concern to desirable workmen; lie is also able to give the foreign workman the special attention he requires. Employment managers have been used for the past few years by a number of large organizations, a few of which are engaged in the mining and metallurgical industries. They have invariably reduced labor turnover, in some cases to as little as one-tenth of what it had been. So great a reduction is due in part to other changes made in the light of the data made available by scientific study of the labor problem. In my former paper on personnel work1 I advocated the more general use of the employment manager in mining and metallurgical enterprises as a means of reducing labor turnover. The form of organization recommended seems not be to understood by all, and I have requested the privilege of explaining it at greater length, since it is perhaps the most important factor of all in personnel work, and has a vital influence on the cost sheet of every industrial enterprise.

Jan 2, 1918

By R. T. Moolick, John E. Neill, O&apos

In selecting a particular stripping method the ultimate aim is the removal of material at the least possible cost. Accomplishment of this goal requires the careful consideration of many factors including geologic and topographic information, proximity of the stripping operation to waste disposal areas, possible problems of land reclamation, types of suitable equipment available, and auxiliary equipment requirements. 4.2-1. Selection of Stripping Methods. The size of an orebody and the distribution of values within that orebody normally will limit the variety of economical stripping methods which need to be considered. Much may depend upon the selectivity required in the mining due to the relationship between ore and overburden, as well as the character of the overburden itself. The following factors concerning the geologic nature and environment of an orebody, as well as the production requirements, must be determined before any selection of equipment is made: 1. The size of the orebody and distribution of the values within that orebody. Is the ore massive or scattered, bedded or disseminated, thick or thin? 2. The nature of the overburden to be removed. Is it a hard dense rock, bedded rock (thick or thin), friable material, earth, sand, elay, marsh, etc.? 3. The character and significance of geologic structures (fractures, faults, shear zones, etc.) associated with the ore occurrence. Are there water bearing formations with resulting water disposal problems? 4. In considering the nature of the overburden, including its alteration products, the physical or chemical conditions which, when combined with anticipated climatic conditions, may render certain equipment inoperable during unfavorable seasons.

Jan 1, 1968

By William Kelly, Frederick Laist

The slow, tedious and costly method of reducing copper matte to metallic copper in the reverberatory furnace, commonly known as the Welsh process, was displaced by the rapid and inexpensive converter process about fifty years ago. The art of refining copper was for many generations a carefully guarded secret among the Welsh furnacemen and was handed down among them from father to son. An attempt was made to apply it at Butte when the smelting of copper ore first started there but it proved too difficult and expensive under local conditions, and until the introduction of the converter process the entire output of copper was shipped to Swansea in the form of high-grade (60 per cent) matte. Before the construction of the Manhes converter, attempts had been made to reduce copper matte in the bessemer steel converter, but these failed, chiefly because the air was blown through the bottom of the vessel. The air holes became clogged with chilled copper as soon as the reduction started. Manhes partially overcame this difficulty by placing the tuyeres in the side of the vessel, some, distance above the bottom, thus allowing space beneath them for the copper to accumulate. Nevertheless the first attempts to operate such a converter at Butte were not successful, as no means had been provided for clearing away obstructions, which formed to some extent in front of the tuyeres. This difficulty was overcome by drilling holes in the outside wall of the air chamber directly opposite the holes in the shell and lining, so that these could be punched

Jan 1, 1934

By B. W. Gandrud

WET-PROCESS coal-washing tables as we know them today have been in use in this country for approximately 25 years. The literature records only a few table installations worthy of note prior to adoption of the present-day differential-motion table. According to Phillips,' six Campbell bumping tables were being operated by the St. Bernard Coal Co., Earlington, Ky., in 11893. As late as 1923, according to Richardson, 2 72 such tables were in operation in the Rosedale washery of the Cambria Steel Co., at Johnstown, Pa. Bumping tables probably were not used to any considerable extent except in the plant at Earlington, and at two or three plants in Pennsylvania, but they may be considered as forerunners of the present-day coal-washing table. The transition from bumping tables to the type of tables now in use signalized a revolutionary change in table design. The advantages of the new design over the old were so outstanding as to make its adoption inevitable. BUMPING TABLES Bumping tables, as the name implies, utilized a bumping action for conveying the refuse and discharging it over the refuse end. The tables were hung from rods attached to overhead supporting beams. A shaft and cam arrangement at one end of the table served as the actuating mechanism and imparted to the table an endwise, back-and-forth, swinging motion. A bumping block was fixed in the proper position at the shaft end, so that the table would strike against it at the end of each backward swing. The hanger rods or stirrups were so adjusted as to give the table a slight uphill slope toward the refuse end; that is, the end next to the driving mechanism. The feed box was near the upper end, of the table and designed to spread the mixture of coal and water over the width of the table. Wash water was added a short distance below the feed box with the table in motion and coal mixed with water being fed to it through the feed box, a certain amount of stratification took place, depositing heavy refuse at the bottom of the bed in contact with the surface of the table. Constant bumping and a certain amount of

Jan 1, 1943

By C. P. Miller

In order to determine the usefulness of geochemical and biogeochemical prospecting for nickel, ten localities representing several types of nickel occurrences were selected as sites from which to collect plant and soil samples. This report covers the investigations in two of the areas. After a brief geologic description of the areas, the author presents details of the experimental tests and resulting data. Conclusions drawn from the studies led to several general guides for further prospecting. In a study of the usefulness of geochemical and biogeochemical prospecting for nickel made about three years ago, approximately ten localities, representing several different types of nickel occurrences, were sampled and about 1500 samples of plant and soil were collected. This report will cover briefly the data and results for two areas, and a summary of guides for prospecting. DESCRIPTION OF AREAS SAMPLED One locality is the Red Flats nickel prospect in Curry County, Ore., about six miles southeast of Goldbeach, and the other is the Little Rocky Creek prospect in Stillwater County, southcentral Montana, just southeast of the Benbow chromite mine. The Oregon area is a lateritic-type nickel deposit formed on a nickel-rich serpentinite peridotite complex, similar to the Josephine intrusion in southwestern Oregon. The Montana area is a nickel prospect in norite, peridotite, and related rocks of the Stillwater igneous complex. The Stillwater complex is a series of layered basic and ultrabasic rocks, with a layer of norite-gabbro at the base and a series of peridotites and gabbros above. The nickel in the Oregon deposit occurs in both the peridotite and the overlying soil. A deep lateritic soil is developed locally on the peridotite and serpentinite and constitutes the ore. The average nickel content of the lateritic soil is less than 1 pct, whereas the nickel content of the weathered peridotite is about 1 to 1.5 pct. The nickel occurs as garnierite (Mg, Fe, Ni, Mn)3 (OH)4 (SiA1)2O5 in the soil and in the olivine and pyroxene in the peridotite where it probably substitutes for Fe2+ or Mg2+ in the silicate lattices. Nickel is found in three distinct ways in the Still-water rocks: 1) it is in the olivine and pyroxene minerals in norite, harzburgite, etc.; 2) it occurs as widely disseminated grains of pentlandite-pyr-rhotite, which tend to be concentrated in the lower norite band; and 3) it occurs as discrete bodies of pentlandite-pyrrhotite and chalcopyrite which are localized in the norite zone, close to the contact with the underlying rocks. The nickel content of the norite is probably less than 1 pct, and the nickel content of the pods and lenses within the norite is about 1 pct. PROSPECTING APPROACH Although the areas are different geologically, the approach in prospecting them is fundamentally the same. The procedure is twofold: 1) a rapid reconnaissance survey to outline an area of high nickel content, and 2) a more detailed survey to outline zones of possible ore grade within the area of high nickel. The possible ore at Red Flats is concentrated in the lateritic soil, whereas at Little Rocky Creek it is in the sulfide pods. Both types are surrounded by an area of relatively high nickel content. CHEMICAL ANALYSIS Chemical analyses of nickel were made by a di-methylglyoxime colorimetric test, similar to the standard test for nickel, utilizing concentrated sul-furic acid for extraction. The lower limit of detection for nickel in soil by the method used was about 10 ppm and for nickel in plants about 5 ppm. The relative deviation was about 25 pct. SOIL PROSPECTING General Statements: A summary of the approximate average parts per million of nickel in soil, as compiled from the literature and from my study, is given in Table I. Selected references are given at the end of the paper. Few of the investigators reported the type of extraction or analysis, so the data given may not be strictly comparable to mine, which were made with a sulfuric acid extraction. Any nickel concentration greater than these average values might be considered anomalous, although each area must be studied in relation to the surrounding rocks. Method of Soil Sampling: The soil samples were taken in a zone from 1 in. to 1 ft below the humus layer, and within a 15-ft radius around a station.

Jan 1, 1961

By V. F. Zackay, W. A. Goering

ALLOYS of iron and aluminum up to 35 wt pct aluminum are single-phase solid solutions, and are of potentially wide applicability.1-3 In spite of early and continued interest1-4 little progress has been made until recently in the preparation and evaluation of sound alloys containing more than 6 wt pct aluminum. Vacuum-melting techniques for the production of ductile Fe-A1 alloys have been described recently.1-7 A. procedure for air melting these alloys is presented here. Low-carbon iron is induction melted without a slag in a rammed magnesia crucible. At the beginning of melt-down, aluminum pig (99.95 pct Al), charged in a clay-graphite bottom-pouring crucible is placed in a pot furnace at 1800°F. The primary deoxidation of the molten iron after melt-down is effected by the addition of 0.1 pct aluminum and 0.5 pct manganese. (Hilty and Crafts" have reported a significant increase in the deoxidation efficiency of the aluminum and manganese combination over that of the aluminum alone.) A more drastic deoxidation designed to reduce the oxyen content to the lowest possible level is accomplished by plunging metallic calcium to the bottom of the melt. This is done by wiring small cubes of the metal to a steel rod. A circular shield larger than the diameter of the crucible opening is attached to the rod so that any spa'ttering of the molten metal will not endanger the operator. Since the temperature of the molten metal is above the boiling point of calcium, the bath is vigclrously purged by calcium vapor. It is believed that the calcium-vapor treatment permits a homogeneous distribution of calcium in the melt. Owing to the vigor of the reaction the temperature of the molten metal should be kept below 2900°F prior to the calcium addition. A total of 0.05 pct calcium is added in two stages in this manner. The second calcium deoxidation is made just before charging the molten aluminum into the iron, in order that an excess of calcium be present for the remainder of the melt. The aluminum, which has been removed from the holding furnace, is then hydrogen degassed by bubbling chlorine through a quartz tube immersed in the molten aluminum. The hydrogen-chlorine reaction is an exothermic one preventing the solidification of the aluminum during the 5-min chlorination. Approximately 0.1 pct calcium, based on the amount of aluminum, is then added to the aluminum. A further excess of calcium is introduced into the melt in this manner. The oxide dross is removed, fluorspar is added to the molten iron, and the molten aluminum is poured through the fluorspar slag. The fluorspar should be dried thoroughly prior to its use, as any water present will react with the aluminum. Aluminum oxide formed during the pouring operation reacts with the fluorspar slag to form gaseous aluminum fluoride and calcium oxide. A forced-draft ventilating system is required for this operation as aluminum fluoride is toxic. As soon as the molten aluminum has been added, vigorous manual stirring of the melt is required because the slag-aluminum oxide reaction is highly exothermic and tends to take place near the top of the melt. The combination of high temperature and the slagging action of the fluorspar quickly erodes the crucible at the slag line if the aluminum is not stirred uniformly into the melt. It has been found that at least 4 min of manual stirring combined with induction stirring are necessary to ensure homogeneity. The power is shut off 1 min prior to pouring to allow metal and slag to separate. As much slag as possible is removed from the melt, which is then poured directly into cast-iron molds. A mold wash of aluminum oxide is used to prevent ingot sticking. For slab ingots which are to be rolled into sheet, a carbon-tetrachloride vapor atmosphere or a chlorinated-pitch mold wash is desirable, as the aluminum oxide formed in the pouring operation is subsequently removed by the chlorine in the presence of carbon." As in vacuum melting, a pouring temperature of about 2900°F is recommended. Adequate hot-topping is important as iron-aluminum ingots are subject to very deep piping. Ingots are removed from the molds and buried in vermiculite, where they are allowed to cool slowly to room temperature. The ingots are radiographed,

Jan 1, 1959

By K. C. Hong, R. B. Jensen

The problem of determining the optimum set of steam volumes and cycle lengths for a single well undergoing multicycle steam stimulation in order to maximize the cumulative discounted net income has been formulated mathematically and programmed for a digital computer. The mathematical fonnulation of the problem and the method for its solution are discussed in this paper. The oil production performance during each stimulation cycle was simulated by either a constant percentage or a harmonic decline. Using simple analytical expressions for production performance, the cumulative discounted net income and cumulative time of operation were related to the pertinent process and cost parameters and two principal process control variables (cycle length and steam injection volume). The discrete maximum principles was used to transform the equations for cumulative time of operation and cumulative discounted net income into a set of simultaneous equations. The simultaneous equations then were solved by trial and error on a digital computer to determine the set of cycle lengths and stem injection volumes that gives maximum cumulative discounted net income over the project life. INTRODUCTION Steam stimulation is a process for improving the oil recovery rate from wells producing high-viscosity crudes. The process is applied on an individual well basis and is executed in a series of cycles, each consisting of three phases: steam injection, soaking (steam condensation), and production. Significant increases in production rate following the stimulation operation result from heating the reservoir around the wellbore. As heat is removed with produced fluids and dissipated into nonproductive formations, the production rate declines, usually to near the prestimulation value. Typical production responses are given in case histories reported by Owens and Suter,l and are depicted in Fig. 1. Duration of the production phase is equal to the time for the oil production rate to decline to some specified value and is called the cycle length. (Cycle length is defined as the producing portion of the cycle and does not include the downtime required for steam injection and soaking operations.) Termination of the production phase coincides with the start of steaming for the next cycle. The process is continued, cycle by cycle, until it becomes unprofitable. Models 2-4 have been developed to simulate behavior of a single well during one cycle of steam stimulation and have been used to investigate the effects of system and operating conditions on the production responses. However, these investigations have not shown how the models can be used to determine a most profitable set of operating conditions for a multicycle stimulation project. Perhaps these models are too complicated mathematically to be adapted readily to an optimization study. This paper presents a method for optimizing a multicycle steam stimulation project based on simple production performance models. First, the performance of a steam-stimulated well during each cycle was simulated by either a constant percentage or a harmonic decline model. Using these simple analytical expressions for production performance, the cumulative discounted net income (before tax) and cumulative time of operation for each cycle were related to the pertinent process and cost parameters and two process control variables—the cycle length and the steam injection volume. Finally, the profit function to be maximized was formed. The analogy between the above problem and problems of optimizing multistage decision processes that have been reported extensively in the chemical engineering literatures5-10 in recent years has led this investigation to the use of the discrete maximum principle.5-7 This principle was used to transform the equations for cumulative discounted net income and cumulative time of operation into a set of simultaneous equations characterizing the optimum operating conditions in terms of the two control variables. These equations

Jan 1, 1970

By K. E. Gray, M. S. Seth

Equations of elasticity for transversely isotropic, axisymmetric, homogeneous, porous media exhibiting pore fluid pressure were formulated. Using an analogy between thermal and porous body stresses, it was shown that the solution for a transversely isotropic porous body may be obtained by incorporating body forces and the stresses due to a boundary load into the corresponding solution for the thermal stress problem. Equations of elasticity ad the thermal analogy method were used to determine transient horizontal, tangential, and vertical stresses and radial displacement in a semi-infinite cylindrical region when either a constant pressure or a constant rate of flow is maintained at the wellbore. The vertical and tangential displacements are zero from the conditions of the problem. A numerical analysis was made of the solutions obtained by using a digital computer to determine the relative influence of each system variable. Considering rock as a porous body with internal fluid pressure generally gives results significantly different than considering the rock to be nonporous; the directional character of rocks leads to significant differences as compared to results based upon the common assumption of isotropy. Stress gradients are high near the wellbore but die out away from the well. Radial stresses are compressive or neutral, whereas tangential stresses are tensile, neutral or compressive, depending upon the boundary conditions and physical properties of the system Vertical stresses are compressive for an unbounded system. For constant wellbore injection rate, the vertical stress is proportional to the rate of fluid injection and decreases with time, whereas the radial and tangential stresses increase with time. At a given location, the radial displacement generally is very dependent upon time. INTRODUCTION A realistic appraisal of the state of stress in subsurface rock formations would be of considerable interest and use to the petroleum industry. For example, knowing the state of stress in proximity to a wellbore would be of fundamental importance in designing a fracturing operation or, more important, of clearly understanding the conditions necessary to produce rock failure of desired dimensions and geometry. Understanding conditions necessary for rock failure at the wellbore would also be of utility in a preventive sense. For example, borehole stability is an important consideration for many rock formations, and knowledge of the stress state at and near the wellbore under conditions of substantial pressure gradient due to fluid flow would be of great value. When fluid flows through a porous body which is initially at some uniform stress level, the following forces generate stresses at any point in the body. (1) Forces due to nonuniform pressure distribution. With increasing pressure the elements of a body are compressed. Such compression cannot proceed freely in a continuum when the pressure is not uniform throughout, and thus, stresses due to flow of fluid are set up. (2) Pore fluid pressure. This gives rise to normal stresses whose value at any point is the product of areal porosity and the fluid pressure. Although the fluid exerts uniform pressure, the stresses it creates in an anisotropic body may not be the same in all directions since the areal porosity in an anisotropic porous body is a direction-dependent quantity. This consideration leads to the concept of directional porosity. (3) Body Forces. The flow of the moving fluid imparts a force to the rock matrix, the magnitude of which depends upon the pressure

Jan 1, 1969

By D. L. Ritter, N. J. Grant, B. C. Giessen

The crystal structures of eight of the nine intermediate phases in the Nb-Rh system were investigated by X-ray techniques. The following structures occur: a,Nb3Rh (Cr3O type);o(ofe - cr type) (H.T. phase, structure unknown); Q2 (AuCU type); a, (orthorhombic, analogous to a,, (Ta-Rh)); a (AuCd type); a,, (monoclinic, related to samarium type); a-8 (VCo3 type); a, NbRh, (AuCu, type). Structural relationships between the six close-packed intermediate phases are discussed and a comparison with the Nb-Ir, Ta-Rh, and Ta-Ir systems is made. In the Nb-Rh phase diagram,' nine intermediate phases were encountered. In order to understand the phase sequence in the diagram and to be able to plot atomic volumes, several unknown crystal structures had to be worked out. These and the evi-

Jan 1, 1964

By Michael D. Martin

Pima Mining Co., managed and 50% owned by Cyprus Mines Corp., with Union Oil of California and Utah Construction and Mining Co. sharing equally in the remaining 50%, is a medium-sized open pit copper mine situated in the very active Twin Buttes mining district, 22 miles southwest of Tucson, Ariz. In 1965, a three-part paper described Pima's growth from 3,000 tpd (tons per day) in 1957 to 18,000 tpd nine years later. Within months of the completion of the last stage of this sixfold expansion, studies were being wound up on a further major expansion, this time to 30,000 tpd. This expansion is now a reality. Details of the enlargement of the crushing and concentrating plant have already been covered in a recent paper, and the present paper will cover pit engineering studies, equipment selection, and current operating practices. Key factors in top management's decision to go ahead with the latest expansion were: (1) a substantial increase in ore reserves coupled with an appreciable decrease in grade, (2) a generally favorable outlook for copper prices, and (3) better than expected performance by mine and mill equipment purchased for the expansion to 18,000 tpd. For the pit design studies, particular attention was paid to pit stability, a problem area at times in the past, and to the location and grades of the final ramp systems. In drawing up the long-term mining schedule, the attitude of the ore, with the higher grade material lying deeper, was a critical factor and considerable stockpiling of lower-grade material in the early years had to be accepted in order to keep the annual grades close to the average of the orebody. The expansion called for major purchases of mine equipment in order to gear up the mine for delivery of 30,000 tpd to the concentrator. In general, equipment chosen was of types already proven at Pima, al- though there were some exceptions to this practice. One of these excep-

Jan 1, 1969

By C. R. Sandberg, C. A. Connally, N. Stein

This paper describes the results of volumetric efficiency tests on oil well pumps handling gas oil mixtures. The work was performed in a large scale, above ground unit wherein test conditions could be accurately controlled and measured. The main variables studied were gas/oil ratio (including gas from solution and free gas mixed with oil), pump compression ratio, pump stroke length, pump speed, and clearance volume between the valves at their closest approach. Results are presented for two different pumps and for oils of two viscosities. Relatively small amounts of gas entering the pump resulted in large decreases in volumetric efficiency. Under conditions where the pump was operating at reduced efficiency because of the presence of gas, it was found that variation in the clearance volume between the standing and traveling valves had a considerable effect on pump efficiency level. This effect of the valve clearance volume was found to be significantly altered by the viscosity of the oil used in the tests. The effects on pump efficiency of the other variables studied were found to be relatively small over the range of conditions utilized. INTRODUCTION The production of oil by pumping is often hampered by low volumetric efficiency. A direct increase in lifting costs results from low volumetric efficiency. An indirect increase in lifting costs, probably greater than the direct increase, results from additional wear and tear on pumping equipment and from the down-time necessary for the repairs which can be traced to low-efficiency operation. Both increases in lifting costs tend to reduce economically recoverable oil. A number of different factors can contribute to low pump efficiency. A known basic cause of low efficiency is the presence of free gas in the pumped fluid. Pump volumetric efficiency is calculated only on the basis of liquid pumped and because any free gas pumped is discounted, this volume of free gas would represent a loss of pump efficiency. However, gas also causes a reduction in pump efficiency because it is a highly compressible fluid. It is known that pumps some- times "gas lock" because of excessive gas-to-liquid ratios in the pump barrel. Little is known of the role of gas compressibility in the intermediate case where the pump is operating at low efficiency. The opinion exists, however, that oil-well pumps tend to operate at higher efficiency with long stroke lengths at low speeds, but no quantitative studies of these pumping variables have been reported. It was believed that a much better understanding of the variables which control pump volumetric efficiency could be obtained and that possibly some suggestions as to the methods for increasing efficiency might be found from a study of the operation of pumps handling gas under closely controlled conditions. Previous investigators have studied the effects on pump efficiency of such factors as oil viscosity, oil temperature, slippage of oil. past pump plungers, pump submergence, valve size and spacing, pressure above pump plunger and fluid vapor pressure. However, none of these published investigations were conducted with pumps being subjected to large amounts of gas such as might be the case in a pumping well, nor did any of the investigations study the effect of variation in stroke length or pump speed. A large-scale teat unit was therefore constructed for studying the operation of pumps handling gas and for evaluating effects of such variables as pump stroke length and pump speed. PROCEDURE AND EQUIPMENT A schematic diagram of the pump testing equipment is given in Fig. 1. A 45-ft length of 6-in. casing is mounted vertically in a 65-ft tower. Sight ports are mounted in the casing at intervals near the location of the pump intake and the liquid level in the casing. These sight ports are fitted with Lucite windows sealed by neoprene "0" rings. The Lucite windows are machined to conform to the I.D. of the casing so that no obstruction to flow is present along the casing wall. The casing is fitted with a tubing head and 2-in. tubing is hung inside the casing. Pumps are seated in a shoe attached to the 2-in. tubing. A 1-in. polish rod is attacked directly to the pump without any intervening sucker rods. The top of the polish rod is attached to the weight carrier, which contains a number of weights to be used to force the polish rod in against tubing pressure on the down-stroke. This is necessary because a long string of sucker

Jan 1, 1953

By J. W. Hickman, E. A Gulbransen

The physical and chemical structure of the oxide films formed on metals and alloys is of interest in our understanding of their protective properties. According to Pilling and Bedworth,¹ if the specific volume of the oxide is equal to or greater than that of the metal, a compact or continuous structure results; if the volume of the oxide is less, a cellular or porous structure forms. With the cellular type of coating the surface layer of oxide offers no impedance to oxidation; at a given temperature the rate of oxidation is quite constant. On the other hand, the compact type of coating acts as an effective barrier to oxygen and the rate of oxidation will follow a parabolic law. The recent work of Gulbransen2 and of Leontis and Rhines3 on the oxidation of magnesium indicates that it is not necessary for the volume of the oxide to be greater than that of the metal in order that the oxidation may follow a parabolic rate law. One exception to the rule of Pilling and Bedworth¹ is noted by Scheil;4 namely, tungsten. At 500° and 700°C long-time oxidations indicate a linear rate law with time. However, Dunn's6 0xidation measurements from 700°to 1000°C indicate that a parabolic rate law is followed. The oxide is mainly yellow WO a with a thin layer of the blue oxide. Preliminary results on the oxidation of tungsten6 in the temperature range 400° to 500°C indicate that the oxidation does proceed according to a parabolic rate law. Irrespective of the actual rate law that tungsten may obey, it is of interest to compare the results obtained on the oxidation of tungsten in the thin film region with those found when the metal is scaling. A time-temperature study of the oxides formed on both molybdenum and tungsten may indicate whether there exist any peculiarities in the oxide structures of the thin film region compared with those of the scaling region of oxidation. In a recent paper the authors7 presented an investigation of the structures of the oxide films formed on the metals iron, cobalt, nickel, chromium and copper. The results of these studies are presented in graphical form as existence diagrams of the oxides on a time-temperature scale. The existence diagrams of the oxides occurring on some of the metals are simple and show few chemical transitions, but there are many cases in which the physical state of the oxide surface changes as a function of time and temperature, as evidenced by the appearance or disappearance of orientation effects and sharpness of patterns. In general an increase in temperature results in an increase in

Jan 1, 1947