Search Documents

By William Johnson

IT is now recognized that several important types of reactions in metallic systems proceed by the formation of nuclei and the growth of these nuclei. The process, of freezing is a simple example of this, as Tammann pointed out years ago.1Tammann held that the rate of freezing is determined by a rate of nucleation, expressed as the number of nuclei formed per unit volume of unfrozen liquid per second, and a rate of growth of these nuclei, expressed as the linear rate of radial growth in units of length per second. For isothermal freezing the conception is simple; for ordinary freezing, extending over a range of temperature, it is not as simple, for the values of the two constants must change with change in temperature. There is ample evidence that the postulated mechanism is correct even though a quantitative derivation of the rate of isothermal or of ordinary freezing in terms of the two constants has been lacking. In recent years other reactions have been found to proceed in a similar fashion. It has been well established, particularly by Bain,2-8 that the formation of pearlite from the eutectoid decomposition of the solid solu-tion austenite proceeds in such a way, and Polanyi and Schmid, Tammann and Crone, Parnop and Sachs, and others'-1 have shown that the process of recrystallization proceeds in a similar way. Isothermal reaction rates have been determined for eutectoid decom-position by a number of investigators. Bain's2-8 work on the formation of pearlite from austenite is especially valuable in this respect-the type of isothermal reaction curve obtained, as illustrated in Fig. 13, showed an initial slow rate, accelerating to an intermediate maximum rate which then decelerated to the completion of the reaction; similar curves have been obtained by Wever and his collaborators.' Other eutectoid decompositions show similar behavior: for example, the decomposition of the beta eutectoid in the copper-aluminum system, studied by Smith

Jan 1, 1939

By Arthur F. Daily

8.5-1. Bucket Line Dredge. INTRODUCTION. The modern bucket-line dredge for mining placer deposits is a combined floating excavating machine and a gravity concentration system. Material is excavated at the forward end by the buckets, elevated, washed and screened, concentrated for recovery of valuable mineral, and discharged off the stern as coarse and small fractions. The end product is a concentrate consisting either of the valuable mineral(s) and associated heavy minerals, which are taken to a treatment plant on shore; or in the case of gold, a clean amalgam ready for retorting. The bucket-line dredge may be adapted for purposes other than mining for valuable mineral by installing, in lieu of a concentrating system, machinery for pumping all of the solids ashore in a pulp, or for producing washed gravel in selected size fractions of which all or a selected fraction is pumped to disposal areas on shore or into side barges. The two principal types of bucket-line dredges designed for mining are: 1) those having an inclined belt conveyor stacker to discharge the coarse fraction of washed tailing well astern of the hull, and sluices to discharge the sand fraction (Fig. 8.5-1), and 2) those having only sluices for discharge of all tailing astern. Use of the latter type has been confined, with few exceptions, to mining cassiterite-bearing deposits in Malaysia and at sea off Indonesia. Small dredges having only flumes for washing and concentrating all material dug by the buckets have been used for mining shallow stream valley deposits. GENERAL ARRANGEMENT. The general arrangement of a modern bucket-line dredge for mining tin, with a primary concentrating plant on board, is shown in Fig. 8.5-2. The hull and superstructure of most dredges are fabricated of structural steel; wood also has been used for both small and large dredges with complete satisfaction. All-riveted or partially welded unit hulls have been widely used and are desirable for exceptionally severe service. The hull

Jan 1, 1968

By Luis N. Henriquez

One form of encouragement for the small copper mining sector in Chile has been the construction and management of custom mill facilities to process the ore. The paper describes an economic analysis framework for the evaluation of government custom milling opportunities. Feasible mill locations and capacities within a region are selected and the infrastructure and milling costs associated with each combination of location and capacity are assessed. For each combination, the economics of developing and operating known copper deposits in the region is evaluated, and an optimum cut-off grade and mine capacity is selected for the deposits which justify development. Since the total ore supply from mines in the region may exceed a particular custom mill capacity, mine development is scheduled to optimize the economics of the mill facility. Finally, the best custom mill location and capacity is selected on the basis of overall costs and benefits. A copper mining region in northern Chile is used to illustrate the application of the model. A mobile mill approach is examined and compared with the fixed location mill alternatives. Results are analyzed as a function of copper price.

Jan 1, 1977

By Walter P. Jenkey

[ ] I. THE REDUCING ACTION OF CARBON AND OF HYDROCARBONS. Carbon has long been recognized as one of the most powerful reducing agents in the deposition of ores. Investigations, made by myself, of the zinc- and lead-deposits in Southwest Missouri, in the region centering about Joplin, where the formation of the metallic sulphides has been due to the action of bitumen, carbonaceous shales and bituminous coal, Lace afforded abundant evidence that the solid oxygenated hydrocarbons, particularly, when in fine powder and in suspension in the waters circulating through the ore-bodies, are the most energetic and powerful reducing agents known. Bitumen, liberated by the decomposition of the ore-bearing limestone, is found in the Joplin mines in all degrees of fluidity and hardness, dependent on the amount of oxidation it has undergone. From semi-fluid maltha it grades into partly oxidized mineral-pitch, which, by further oxidation, changes to hard asphalt, finally breaking up, from continued absorption of oxygen, into a fine powder resembling in appearance powdered coal. In this condition oxidized bitumen, from its light gravity, is transported readily in suspension in the underground circulating-waters. Bituminous coal and black carbonaceous clays and shales occur as surface formations, often in intimate association with

Jan 1, 1913

By William Johnson

IT is now recognized that several important types of reactions in metallic systems proceed by the formation of nuclei and the growth of these nuclei. The process of freezing is a simple example of this, as Tammann pointed out years ago.1 Tammann held that ' the rate, of freezing is determined by a rate of nucleation, expressed as the number of nuclei formed per unit volume of unfrozen liquid per second, and a rate of growth of these nuclei, expressed as the linear rate of radial growth in units of length per second. For isothermal freezing the conception is simple; for ordinary freezing, extending over a range of temperature, it is not as simple, for the values of the two constants must change with change in temperature. There is ample evidence that the postulated mechanism is correct even though a quantitative derivation of the rate of isothermal or of ordinary freezing in terms of the two constants has been lacking. In recent years other reactions have been found to proceed in a similar fashion. It has been well established, particularly by Bain,2-8 that. the formation of pearlite from the eutectoid decomposition of the solid solu-tion austenite proceeds in such a way, and Polanyi and Schmid, Tammann and Crone, Karnop and Sachs, and others9-11 have shown that the process of recrystallization proceeds in a similar way. Isothermal reaction rates have been determined for eutectoid decom-position by a number of investigators. Bain's2-8 work on the formation of pearlite from austenite is especially valuable in this respect-the type of isothermal reaction curve obtained, as illustrated in Fig. 13, showed an initial slow rate, accelerating to an intermediate maximum rate which then decelerated to the completion of the reaction; similar curves have been obtained by Wever and his collaborators.12 Other eutectoid decompositions show similar behavior: for example, the decomposition of the beta eutectoid in the copper-aluminum system, studied by Smith

Jan 1, 1939

By A. W. Jenike

A theory of gravity flow of bulk solids like ores, concentrates, coal is outlined and an example of design for unobstructed flow is given. Mass-flow and plug-flow patterns are defined and related to the geometry of the bin. The effect of these patterns on segregation, first in-first out flow, and caking is described. This paper is a report on the results from the AIME sponsored project "Flow of Bulk Solids" which was carried out under the author's direction at the Utah Engineering Experiment Station, University of Utah, during the period 1956-1962. The theory has been applied to the design of numerous industrial storage plants. A QUANTITATIVE METHOD OF DESIGN FOR FLOW There is hardly an industry which does not store and handle solid materials in bulk form. When the volume of the solids is large, gravity is invariably relied upon to cause the solids to flow out of storage, through channels and chemical reactors. Such materials as ore, coal, cement, flour, plastics, clay, soil, to which a general term of bulk solids is applied, flow by gravity or are expected to flow by gravity in thousands of installations and by billions of tons annually. The chemical and process industry depends on gravity flow of solids in process and out of storage. Mining relies on gravity flow in block-caving, in ore passes, as well as in storage and loading bins. Agriculture uses gravity flow in elevators, in feed plants, and in farm silos. In practice, satisfactory gravity flow is seldom attained. Such problems as doming, piping (rat-holing), lack of live capacity, segregation, deterioration in storage, harass industry. In spite of the universality of these problems, until recently, there has been no theory of solids flow, no method of predicting how a solid would behave, and how the channel, bin, or hopper should be designed. In the late nineteen forties and early fifties, the theory of plasticity came of age and simultaneously the computer became widely available. These two factors permitted the development of a theory of flow of bulk solids. The work was conducted during the years 1953-1961. In conjunction with the development of the theory a method to measure the flowability of solids was also developed1-7 and the theory was ap-plied to the design of ore pockets, storage plants,16 chemical reactors and adsorption columns. A comprehensive report of this work is given in a previous work." THEORY OF FLOW The most important question which a theory of flow has to answer is: what conditions need to be satisfied for a given solid to flow uniformly and without obstructions through a channel? First of all, the following observations are made:

Jan 1, 1967

By R. T. DeHoff

In any structural transfortnation which is driven by surface tension, the geometric variable of fimdamental importance is the local value of the mean surface curvatuve. Acting through the suvface free energy, this quantity determines the magtnitude of both the pressure and the chemical potential that develops in the neighborhood of an arbitrarily curved surface. A metallographic method which would permit the quaniitatiue estinzation of this propevty is of fundarnerztal irztevest to studies of such processes. In the present paper, it is shoun that the average value of the mean surface curvature in a structuve can be estimated from two simple counting measuretnents made upon a vepresentative metallograpIzic section. No simplifyirlg geonzetric assurmptions are necessary to this deviuation. It is further shoum that the result may be applied to parts of interfaces, e.g., interparticle welds in sintering, or the edge of growing platelets in a phase transformation, without loss of validity. In virtually every metallurgical process in which an interface is important, the local value of the mean surface curvature is the key structural property. This is true because the mean curvature determines the chemical potential of material adjacent to the surface, as well as the state of stress of that material. The theoretical description of such broadly different processes as sintering,1,2 grain growth,3 particle redistrib~tion4,5 and growth of Widmanstatten platelets8 all have as a central geometric variable the "local value of the mean surface curvature". The tools of quantitative metallography currently available permit the statistically precise estimation of the total or extensive geometric properties of a structure: the volume fraction of any distinguishable part:-' the total extent of any observable interface,10,11 and the total length of some three-dimensional lineal feature:' and, if some simplifying assumptions about particle shape are allowed, the total number of particles.'2"3 The size of particles in a structure, specified by a distribution or a mean value, can only be estimated if the particles are all the same shape, and if this shape is relatively simple.14-16 The relationships involved in converting measurements made upon a metallographic section to properties of the three dimensional structure of which the section is a sample are now well-established, and their utility amply demonstrated. In the present paper, another fundamental relationship is added to the tools of quantitative metallography. This relationship is fundamental in the sense that its validity depends only upon the observation of an appropriately representative sample of the structure, and not upon the geometric nature of the structure itself. It involves a new sampling procedure, devised by Rhines, called the "area tangent count". It will first be shown that the "area tangent count" is simply related to the average value of the curvature of particle outline in the two-dimensional section upon which the count is performed. The average curvature of such a section will then be shown to be proportional to the average value of the Mean surface curVature of the structure of which the section is a sample. The final result of the development is thus a relationship which permits the evaluation of the average value of the mean surface curvature from relatively simple counting measurements made upon a representative metallographic section. The result is quite independent of the geometric or even topological nature of the interface being studied. QUANTITATNE EVALUATION OF AVERAGE CURVATURE IN TWO DIMENSIONS The Area Tangent Count. Consider a two-dimen-sional structure composed of two different kinds of distinguishable areas (phases), Fig. l(a). If the system is composed of more than two "phases", it is possible to focus attention upon one phase, and consider the remaining structure as the other phase. The reference phase is separated from the rest of the structure by a set of linear boundaries, of arbitrary shapes and sizes. These boundaries may be totally smooth and continuous, or piecewise smooth and continuous. An element of such a boundary, dA, is shown in Fig. l(b). One may define the "angle subtended" by this arbitrarily curved element of arc, dO, as the angle between the normals erected at its ends, Fig. l(c). Now consider the following experiment. Let a line be swept across this two-dimensional structure, and let the number of tangents that this line forms with elements of arc in the structure be counted. This procedure constitutes the Rhines Area Tangent Count. Suppose that this experiment were repeated a large number of times, with the direction of traverse of the sweeping lines distributed uniformly over the semicircle of orientation.' Those test lines which ap- proach from orientations which lie in the range O to O + dO form a tangent with dA; those outside this range do not, see Fig. l(c). Since the lines are presumed to be uniformly distributed in direction of traverse, the fraction of test lines which form a tangent with dA is the fraction of the circumference of a semicircle which is contained in the orientation range, dO; i.e., vdO/nr or dB/n. If the number of test lines is N, the number forming tangents with dA is N(d0/n). Since each test line sweeps the entire area of the sample, the total area traversed by all N test lines is NL2. The number of tangents formed with dA, per unit area of structure sampled, is therefore

Jan 1, 1968

By C. Schlumberger

SINCE the, beginning of the year 1928 the senior authors and their associates have applied a series of procedures which makes possible the detailed study in situ of the formations traversed by a drill hole before the casing has been landed. They have given the name "electrical coring" to the ensemble of these processes, which now replace in a large measure the mechanical coring performed by the drillers, and permit the gathering of bottom-hole data hitherto unobtainable. Three years have elapsed since the technique and interpretation of these measurements emerged from the experimental stage and entered the field of industrial application on a large scale. The total length of drill holes so far surveyed by the authors and their associates, all over the world, amounts to several millions of feet. Practical and strongly built equipment has been evolved, which permits the examination in a short time of an open hole several thousand feet long. No comprehensive paper has yet been published discussing the essential principles of the processes applied and bringing into evidence their economic interest. This is the object of the present paper.1 Numerous examples of field work performed under varied geological conditions are given, constituting a concrete illustration of the services rendered by the new methods.

Jan 1, 1932

By R. L. Loofbourow, Roger V. Pierce

THE degree to which our mineral requirements are being met by mining leaner, more complex or more remote deposits is indicated by developments during 1953. Heavy capital investment, skilled technical advice, planning, and able execution are requirements for the typical venture. Producers, faced with rising costs and with softer prices, are seeking improved mining and recovery. Developments in production of iron ore are typical of the course being followed in metal and nonmetal mining. Iron ore development in the U. S. is concentrated on the spectacular work with Lake Superior taconite, while in Canada new production is expected from Labrador and output from Steep Rock, Algoma, and Newfoundland is being increased. Shipment of iron will soon be made from Venezuela.

Jan 2, 1954

By Albert H. Fay, William B. Plank

In practically all rock-excavation problem there is need for a careful study of the rock structure, its fault, cleavage or bedding planes, and even the texture of the rock itself. These studies should form the bases upon which an excavation method is selected and they should be carefully considered in predicting the amount and extent of the excavation. The need for such studies was forcibly illustrated in the problems involved in a cut made in 1929, along and underneath a 200-ft. high rock projection for a State highway near the City of Easton, Pennsylvania. The rock mass was badly faulted and also contained a number of cleavage planes at approximately right angles to the fault planes. Much of this structure was visible and could have been studied and analyzed before the work was begun. The State had rigid specifications as to finished grade and slope of cut, which apparently were made without reference to the geologic structure. The contractor complied with the specifications, under the close inspection of the State engineers. A tunnel blast was placed in the base of the cliff, with the result that 65 per cent more rock was broken than was intended by the specifications. About four years after the blast, the writers of this paper studied the circumstances surrounding the operation, to determine the cause of this excess excavation. Scope of Work The section of the roadway involved was about 200 ft. long and on a 6' curve. It was necessary to relocate points on the curve, from which all faults and cleavage planes were located and measured by the use of transit and clinometer. A plan (Fig. 1) showing the blasting tunnel, the roadway, and traces of the faults and cleavage planes on the level of the roadway, was prepared; also 13 cross-sections at varying intervals, showing the original face of the hill and the face after the blast. The original and final profiles of the rock face, taken from the plans of the State engineers, are shown in Figs. 2, 3 and 4.

Jan 1, 1937

By J. Kittl, D. Arias

THE decomposition on cooling of the high-temperature ß bcc phases in copper- or silver-based binary systems usually takes place by a martensitic. massive, bainitic, or pearlitic reaction depending upon the particular conditions of each system. The AgAl system is one of these systems in which a massive or a martensitic transformation can occur upon cooling from the 3 phase field. Recently Hawbolt and Brown1 observed both massive and martensitic transformation products in a 22.7 at. pct A1 alloy. In the present work the massive and the martensitic transformations were investigated in a number of alloys for the composition range between 23.2 and 27.9 at. pct Al. The alloys were prepared using high-purity silver, 99.999 pct, supplied by ASARCO and aluminum, 99.999 pct, supplied by ALCOA. The metals were melted using a graphite or a sintered alumina crucible which was sealed in quartz tubes under an argon atmosphere. The alloys Were remelted to reduce segregation and homogenized in the 13 phase field for 24 hr. The weight of the alloys after homo-genization compared with the initial weight indicating the alloy composition to be within k0.1 pct of the in- tended composition. Chemical analysis of several samples confirmed the estimated alloy composition. All metallographic observations were performed on samples electropolished with ac current using a 10 pct solution of KCN and a stainless-steel electrode. The samples were cut into -1-mm-thick slices, polished, heat-treated in the ß phase field, and quenched in air, ice water, or iced brine. Some heat treatments consisted of a 2-min anneal carried out in air to allow maximum quenching speeds. Other samples were heat-treated in a vacuum of 10"4 torr and quenched using a helium blast in a quenching apparatus described elsewhere.&apos; In both cases, no appreciable losses of silver or aluminum were noted at the sample surface by sectioning and electropolishing. Table I summarizes the microstructure resulting from the various quenching treatments. The composition of the alloys investigated is also indicated on the equilibrium diagram in Fig. 1. The <, hcp phase, typical of a massive ß — cm, transformation, was observed in all alloys. A minimum temperature of 450°C was estimated for this transformation based on preliminary cooling experiments. the results being included in Fig. 1. In these

Jan 1, 1970

By C. E. Mills

Studies of ground movement and subsidence resulting from mining operations cover a broad field. It is also a very important consideration and one that eventually affects nearly every mining operation of any extent. The damage to surface buildings, removal of mine surface plants and replacements of main hoisting shafts must reach an astounding expenditure were these cost figures available over a period of years. Were the subject one of mathematical formula and dependent only on the angle of draw of the walls or country rocks, the problem would be relatively simple. Consideration must be given to depth and extent of workings; structural conditions of the orebodies and enclosing country rock; physical properties of these same rocks, including schistosity, bedding, jointing, slips, dikes, faults, and other structural weaknesses. The method of mining, extent of openings, supporting pillars, and amount of moisture or water underground are other pertinent factors. With such a large number of variable factors, it is apparent that the subject of subsidence is one that must be based largely on experience and results at other mines where conditions are somewhat comparable. In presenting this paper, it is the intent to describe the progressive results of past ground movements at the United Verde, to bring out physical conditions largely responsible for this movement, but to refrain from theorizing on the ultimate extent of subsidence resulting from future mining operations. Geology and Structure1 The ore deposits of the United Verde are of the massive sulfide, schist-replacement type. A structural anticline formed by the intrusion of diorite between bedding planes of steeply dipping and severely folded greenstones and porphyry localized the deposit of sulfide. The mineralized zone is of great horizontal extent varying from 200,000 to 400,-000 sq. ft., and extends from the surface to the lowest levels at a steep dip of from 50° to 75. The irregular interfingering of the sulfide with

Jan 1, 1934

By Frank Doxey

AT Dominion Steel & Coal Corp. it has long been recognized that continued mechanization of mine operations is necessary in the Pictou, Cumberland, and Sidney coal fields of Nova Scotia. The varied physical conditions in these fields call for special consideration of individual cases before planning is finalized. Because standard equipment cannot be procured which would operate successfully, many experiments have been necessary over the years to keep pace with the progress made in other countries. There are two mines, producing 2000 tpd, located in the Pictou coal field. The field is badly distorted and crossed by many faults. Seams are highly inclined and irregular and vary in thickness from 5 to 40 ft. Entries are difficult to maintain because of squeezing of the coal. ribs and movement of the roof and pavement. Output from the three operating mines in the Cumberland field is 3000 tpd. The field is highly inclined, inclination varying from 12° to 32°. Overlying beds consist of shales and massive sandstone lenses of extreme toughness and are responsible for bumps when the stresses are relieved by extraction. At greatest depth these are among the deepest coal workings in the world. Depth of cover ranges from 2300 to 4000 ft. This prohibits room-and-pillar working and necessitates longwall operation. Working of contiguous seams concurrently to maintain output increases the already difficult conditions. The Sydney field, with a frontage of about 30 miles, is the most important of the Nova Scotia coal fields. With the exception of one small area it is now wholly submarine. Output is approximately 21,000 tpd. Seams are 21/2 to 8 ft thick, and cover in the areas varies from 600 to 2300 ft, with an average of 1500 ft from sea bottom to the top of the seam. The seams dip in a seaward direction, pitches ranging from 6" to 4.0". The shoreline is the last place of entry to the seams and distance from the bank to the working faces is generally over 3½ miles, in some cases as much as 6½ miles. Ventilation is a problem and requires the construction of large permanent airways. Getting and Loading Coal: In 1925, in view of heavy pressures exerted by thickness of cover overlying the seams, roadways and pillars of the room-and-pillar system being worked began to break up and coal was lost. It was decided that a change in the method of extraction in areas with heavy cover was necessary, and experiments were made with many short walls and longwalls varying between 90 and 250 ft. Trial and error proved that the best operating length was between 400 and 500 ft, delivering all coal to the dip, with roadways to the face following a level course. The change-over was gradual, and the technique of roof control developed with the system, so that falls to the face are now very infrequent. An advantage of longwall mining is that it yields 95 pct extraction, especially important in coal seams of high quality or in seams where faults or disturbances restrict the workable areas. This percentage of extraction is based on the fact that the longwall advancing system takes development faces where pitch permits instead of driving headings and leaving roadway pillars. This system yields high tonnage during development and limits loss in extraction to duff left during operations. Accompanying disadvantages, on the other hand, are the heavy construction cost of main roadways and the necessity of driving all new flank face roadways through the gob. If the main roadways are driven through the solid, and large enough pillars are left on each side for protection against flank face weights, then the width of solid coal is approximately 1700 ft. This represents 10.6 pct of the coal available, or 89.4 pct extraction of the whole. These pillars, however, are of such size that they provide a useful pillar drawing area as a final operation of the mine. It may be that although the seam cannot be generally mined by the room-and-pillar method, it can be adapted to

Jan 1, 1955

By Robin P. Gardner

A radioisotope tracer method combined with a suitable back-calculation method is proposed and evaluated for the determination of model simulation parameters in open-circuit continuous ball mills. The method essentially consists of using impulse and/or step injections of short-lived radioisotopes of the naturally occurring trace elements manganese and sodium. It is evaluated here on the basis of the minimum standard deviations of the product weight-size distributions. These minimum standard deviations are taken as those predicted by a Poisson distribution of the number of particles present in size fractions of the samples taken for analysis. Previously developed tanks-in-series lumped parameter models are used in the evaluation. The results indicate that the method is very promising.

Jan 1, 1976

By H. R. Hanley

THE characteristics of alloyed anodes and their influence on the products of electrolysis and power consumption have been noted previously in the literature.1 This paper presents data in continuation of the subject given in an earlier paper by the authors.2 As noted in the authors&apos; previous paper, the objectives of this work are the reduction in the cell voltage and the purity of the cathode product resulting from the use of alloyed lead anodes. The fundamental facts developed in the previous paper were: (1) that the presence of a small amount of calcium lowers the anode potential approximately 50 per cent. below that of pure lead; and (2) that thallium when present to the extent of 4 per cent. rendered the anode practically stable, thereby lowering the contamination of the cathode by lead to a very insignificant amount. The specific features determined in this recent work are as follows: 1. The lowest limit of calcium in the lead which will still give maximum lowering of the anode potential. 2. The characteristics of the thallium-calcium-lead anode. 3. The characteristics of the silver-calcium-lead anode. 4. The characteristics of the thallium-silver-calcium-lead anode. It was determined that 0.1 per cent. calcium in the anode was sufficient to lower the anode potential approximately 50 per cent. Table 1 shows the characteristics of alloyed anodes tested. The anode composed of 0.1 per cent. calcium, 4 per cent. thallium, and 95.9 per cent.

Jan 1, 1931

Jan 1, 1923

By W. H. Patnode

The effect of suspended solids on the resistivity of slurries is discussed and the relationship between drilling mud resistivity and mud filtrate investigated. It is concluded that it is erroneous to substitute mud resistivity for mud filtrate resistivity in electric log calculations. A recommendation is made that both the bud resistivity and the mud filtrate resistivity be determined when electric logs are run. INTRODUCTION The electric log is influenced not only by the resistvity of the drilling mud in the borehole at the time of logging but also by the resistivity of the drilling mud filtrate. Sherborne and Newtoni investigated the relationship of mud resistivity to mud filtrate resistivity and concluded that, "The resistivity of the mud in most cases closely approximates that of its filtrate," and "In fact, with the exception of Aquagel and its filtrate, the figures for any particular mud and filtrate are almost identical." Present practice is to determine only the drilling mud resistivity and apply this same value to calculations involving the mud filtrate. The purpose of this study is to reexamine the factors governing the relationship between mud resistivity and mud filtrate resistivity. EFFECT OF BOREHO1.E FLUID ON THE ELECTRIC LOG Resistivity Log The resistivity log may be modified by the resistivity of the borehole fluid in two different ways: (1) The apparent resistivity of a for-formation may be different from the true resistivity of the formation because of the flow of some current through the drilling mud in the borehole. Therefore the resistivity of the mud is an important factor. (2) The apparent resistivity may differ from the true resistivity, if a formation is invaded by mud filtrate, because of displacement by the mud filtrate of some of the interstitial fluid in the formation. In this case the resistivity of the mud filtrate rather than the resistivity of the mud is the important factor. Self Potential Log The self potential arises, in part, from electrochemical effects resulting from the interaction of connate waters in porous formations and the fluid in the borehole. Expressed in simple form, E = Klog-p where E is the electrochemical self potential, K is a derived constant, pl is the resistivity of the borehole fluid, and p2 the resistivity of the water in the formation. A theory of the electrochemical component of the self potential in boreholes has been recently set forth by Wyllie.3 In the above equation resistivities have been substituted for activities of the ions in the fluids.&apos; It is therefore apparent that the resistivity of the mud filtrate is more nearly representative of the activities of the ions than is the resistivity of the mud. However, it is possible that in some instances the ionic activities of cations from certain clays may contribute to the total cationic activity of the drilling fluid to such an extent that the mud resistivity is more nearly representative of the activities than the filtrate resistivity. This is particularly the case when the resistivity of the mud is less than the resistivity of the mud filtrate. In addition the apparent self potential may be influenced by the resistivity of the drilling mud because of current flow through the borehole. RESISTIVITY OF SLURRIES Aqueous drilling muds are slurries containing fine-grained solid particles. The solid constituents consist mainly of added clays and weighting materials in addition to solids contributed by the drilled formations. The filtrate is primarily water in which quantities of salts or other chemicals are dissolved. The resistivity of the fiiltrate is a function of the type and quantity of dissolved material whereas the resistivity of the mud is a function of the combined resistivities of the filtrate and the resistivities of the suspended solids. Experiments have been carried out to determine the relationship between the resistivity of solutions and the quantity and type of solid matter insus-pension. Solid materials of high resistivity, as well as solid materials of relatively low resistivity, have been used. The data obtained make possible the evaluation of the probable effect of suspended solids on the resistivity of drilling mud. Procedure Resistivities were determined by means of a conventional conductivity cell with platinized-platinum electrodes. Total resistance between the electrodes was measured by Kohlrausch&apos;s alternating current bridge method using a General Radio Company Type 650-A impedance bridge with telephone. The cell was standardized with potassium chloride solutions of known normalities in order to calibrate the cell so that measured resistances of slurries could be converted to resistivities. Resistivities were determined for mixtures of potassium chloride solution and solid materials by placing a measured quantity of solution in the cell and adding weighed quantities of solid materials in small increments to the solution. The net change in resistance on addition of solid materials was measured. Even distribution of the solid particles was maintained within the cell by a motor-driven glass propeller before measurements were made. Slurries Containing High-Resistivity Solids Powdered silica sand having a maximum diameter of about 60 microns and precipitated chalk of commercial grade were used to make the slurries whose resistivities were measured. Both of these substances have high resistivities, are virtually insoluble, and effectively do not carry current in a slurry. The resistivities of slurries composed of potassium chloride solution and these two solid materials are given in Table 1. The ratio of the resistivity of the solution to the resistivity of the slurries was computed and was found to follow the relationship established by Archie

Jan 1, 1949

By W. H. Patnode

The effect of suspended solids on the resistivity of slurries is discussed and the relationship between drilling mud resistivity and mud filtrate investigated. It is concluded that it is erroneous to substitute mud resistivity for mud filtrate resistivity in electric log calculations. A recommendation is made that both the bud resistivity and the mud filtrate resistivity be determined when electric logs are run. INTRODUCTION The electric log is influenced not only by the resistvity of the drilling mud in the borehole at the time of logging but also by the resistivity of the drilling mud filtrate. Sherborne and Newtoni investigated the relationship of mud resistivity to mud filtrate resistivity and concluded that, "The resistivity of the mud in most cases closely approximates that of its filtrate," and "In fact, with the exception of Aquagel and its filtrate, the figures for any particular mud and filtrate are almost identical." Present practice is to determine only the drilling mud resistivity and apply this same value to calculations involving the mud filtrate. The purpose of this study is to reexamine the factors governing the relationship between mud resistivity and mud filtrate resistivity. EFFECT OF BOREHO1.E FLUID ON THE ELECTRIC LOG Resistivity Log The resistivity log may be modified by the resistivity of the borehole fluid in two different ways: (1) The apparent resistivity of a for-formation may be different from the true resistivity of the formation because of the flow of some current through the drilling mud in the borehole. Therefore the resistivity of the mud is an important factor. (2) The apparent resistivity may differ from the true resistivity, if a formation is invaded by mud filtrate, because of displacement by the mud filtrate of some of the interstitial fluid in the formation. In this case the resistivity of the mud filtrate rather than the resistivity of the mud is the important factor. Self Potential Log The self potential arises, in part, from electrochemical effects resulting from the interaction of connate waters in porous formations and the fluid in the borehole. Expressed in simple form, E = Klog-p where E is the electrochemical self potential, K is a derived constant, pl is the resistivity of the borehole fluid, and p2 the resistivity of the water in the formation. A theory of the electrochemical component of the self potential in boreholes has been recently set forth by Wyllie.3 In the above equation resistivities have been substituted for activities of the ions in the fluids.&apos; It is therefore apparent that the resistivity of the mud filtrate is more nearly representative of the activities of the ions than is the resistivity of the mud. However, it is possible that in some instances the ionic activities of cations from certain clays may contribute to the total cationic activity of the drilling fluid to such an extent that the mud resistivity is more nearly representative of the activities than the filtrate resistivity. This is particularly the case when the resistivity of the mud is less than the resistivity of the mud filtrate. In addition the apparent self potential may be influenced by the resistivity of the drilling mud because of current flow through the borehole. RESISTIVITY OF SLURRIES Aqueous drilling muds are slurries containing fine-grained solid particles. The solid constituents consist mainly of added clays and weighting materials in addition to solids contributed by the drilled formations. The filtrate is primarily water in which quantities of salts or other chemicals are dissolved. The resistivity of the fiiltrate is a function of the type and quantity of dissolved material whereas the resistivity of the mud is a function of the combined resistivities of the filtrate and the resistivities of the suspended solids. Experiments have been carried out to determine the relationship between the resistivity of solutions and the quantity and type of solid matter insus-pension. Solid materials of high resistivity, as well as solid materials of relatively low resistivity, have been used. The data obtained make possible the evaluation of the probable effect of suspended solids on the resistivity of drilling mud. Procedure Resistivities were determined by means of a conventional conductivity cell with platinized-platinum electrodes. Total resistance between the electrodes was measured by Kohlrausch&apos;s alternating current bridge method using a General Radio Company Type 650-A impedance bridge with telephone. The cell was standardized with potassium chloride solutions of known normalities in order to calibrate the cell so that measured resistances of slurries could be converted to resistivities. Resistivities were determined for mixtures of potassium chloride solution and solid materials by placing a measured quantity of solution in the cell and adding weighed quantities of solid materials in small increments to the solution. The net change in resistance on addition of solid materials was measured. Even distribution of the solid particles was maintained within the cell by a motor-driven glass propeller before measurements were made. Slurries Containing High-Resistivity Solids Powdered silica sand having a maximum diameter of about 60 microns and precipitated chalk of commercial grade were used to make the slurries whose resistivities were measured. Both of these substances have high resistivities, are virtually insoluble, and effectively do not carry current in a slurry. The resistivities of slurries composed of potassium chloride solution and these two solid materials are given in Table 1. The ratio of the resistivity of the solution to the resistivity of the slurries was computed and was found to follow the relationship established by Archie

Jan 1, 1949

By Nelson Severinghaus

Consolidated Quarries Corp. must conduct operations for an average sales price of $1.25 per ton, about the same price at which stone was sold 25 years ago when the dollar was worth twice what it is now. To maintain success in a competitive business, the company must solve the usual production problems, which will be discussed here in the order they occur in the flowsheet. Most crushed stone quarries must first remove soil and decomposed rock. Although seasons of lower sales sometimes release regular quarry excavating and haulage equipment for this purpose, overburden is often too extensive for this method to be used. In such cases, special equipment must be assigned or the job may be contracted. As many earthmoving contractors have heavy duty specialized equipment well suited to overburden removal, they should be seriously considered before the job is undertaken. Pockets of clay beneath peaks of hard stone sometimes defy mechanized removal. Pick and shovel laborers at this point might be supplanted by more ingenious use of pumps and water or some other mechanical means. Where overburden is extremely heavy or difficult to remove, underground mining must be considered.

Mar 1, 1956