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By Xiaoming Huaa

The effect of the anodic polarization on the composition and morphology of the surface layer formed on chalcopyrite during ammonia–ammonium chloride leaching was investigated. The anodic polarization on the chalcopyrite electrode was used for oxidation and dissolution of chalcopyrite, and the resulting oxidized layers were characterized by XPS, SEM and optical microscopy. The results show that oxide layers exist on the chalcopyrite surface with or without any anodic polarization in the leaching solution at ambient atmosphere. However, the composition and morphology of the layers are strongly depended on the extent of polarization. The distribution of FeOOH and Fe2O3 within the oxidized layer was inhomogeneous for the sample at the open circuit potential (OCP). The composition and morphology of the oxidized layers which were formed at anodic potentials lower than 0.3 V versus SCE were similar to those of the chalcopyrite at the OCP. At anodic potentials above 0.4 V, the oxidized layers contained many cracks, and they were fragile and exfoliated. Furthermore, the sulfide had been oxidized to sulfur species with higher oxidation states. The oxidation of the chalcopyrite seemed to undergo a cyclically oxidative process that suggested growth and spallation of oxidation layers on chalcopyrite in a layer-by-layer sequence.

By Baptiste Laubie

Agromining is a phytotechnology aiming at producing commercial metal compounds from low-grade ores thanks to hyperaccumulating plants. The fern Dichranopteris dichotoma is a rare earth element (REE) hyperaccumulator, which naturally grows on former mine tailings in China. It accumulates up to 0.35% of REEs in its aerial parts. Different hydrometallurgical processes are currently developed to recover these elements directly from the biomass or from ashes after combustion. The process presented here consists of a direct extraction by EDTA solution, followed by precipitation with acid oxalic. Optimal precipitation pH and influence of organic matter are determined by modelling and by experimental studies. The final solid contains 4.3% of REEs, with calcium as the main cationic impurity (0.45% of the precipitate). The recovery yield is similar for major REEs and is around 70%. After optimization, upscaling of the process will allow the agromining development to recover REEs from secondary resources with more environmentally friendly techniques.

By S. B. Bealko

Mining haul trucks comprise the majority of the equipment used in underground limestone mining operations and are known to emit high levels of noise. A previous study conducted by the National Institute for Occupational Safety and Health (NIOSH) indicates that 70-90 percent of all miners have a noise-induced hearing loss (NIHL) great enough to be classified as a hearing disability by retirement age. These results demonstrate the public health need to protect the hearing of workers in the mining industry, including haul truck drivers. Cab enclosures present an opportunity to isolate the haul truck operator from both truck and other noise in the mining environment. A total of twenty-five haul truck cabs were studied which were divided into three style (treatment) categories determined by soundproofing features and technology for noise reduction: old-, new-, and retrofitted-style. This study examines the contribution of cab acoustics, operator performance, and maintenance to noise reduction for each cab style. Dosimeters were used to measure 8-hr time weighted average sound pressure levels (TWA8 SPLs) inside and outside the cabs to determine if different acoustical treatments affect cab attenuation. Adherence to the Mine Safety and Health Administration (MSHA) Permissible Exposure Limit (PEL) of 90 dB TWA8 (with a 90 dB threshold) was used as the main indicator of overall noise reduction achieved. Dosimetery results indicate only 2% of the samples exceeded the PEL, but samples could still be reduced much further. Descriptive and comparative statistics indicate that noise levels inside the new-style cabs are significantly lower than the other two cab styles. Also, data suggest that there is no difference in noise exposures when comparing the old-style to retrofitted cab styles. Operator influence (opening doors and windows) was a significant factor for increasing noise exposure. This paper demonstrates that properly designed cabs can achieve major noise reductions, but noise levels could still be reduced much further below the MSHA PEL. New-style cabs, equipped with modern noise-reduction treatments, exhibit much lower noise exposures than the other two cabs styles, and the effectiveness of the current noise-reduction treatments for retrofitted cabs is questionable. Haul truck driver observations indicate that improved noise exposure reduction training is needed. Finally, specific targets for future noise reduction research are suggested that will further contribute to the prevention of hearing loss for haul truck operators.

By J. Torma-Krajewski, C. Hipes

Although many mining companies apply ergonomic principles, it is usually done either informally and/or reactively. An example of an informal approach is replacing worn equipment (such as seats) with models that have ergonomic features. Another example is modifying a task to eliminate safety hazards. Such approaches reduce risk-factor exposures that can lead to musculoskeletal disorders (MSDs). A reactive approach is followed when modifying a task/ equipment after an MSD occurs. However, neither of these approaches involves a systematic method of proactively applying ergonomic principles to actually prevent injuries or illnesses. This paper discusses how Vulcan Materials Company applied ergonomic principles and implemented interventions to reduce risk-factor exposures.

By W. M. Courtis

This district commences near Pigeon River, the northeastern boundary between Minnesota and Province of Ontario, and extends entirely around the north shore of Lake Superior, terminating for the present at the Bruce Mines on Lake Huron. The discoveries of mineral-bearing veins have been confined for the most part to the lake shore, or to the country opened up by the Dawson Red River road. As yet the country back from the lake has been but little explored, on account of its roughness, being intersected by steep, rocky trap bluffs, 1000 or more feet high, and alternating white cedar and tamarack swamps. The forests are exceedingly difficult for prospectors. In many places Titanic piles of rocks, protected by chevaux-de-frise of dead cedars, with their hooked, tough, sharp branches, and a covering of spongy moss, sometimes several feet thick, successively guard against the discovery of hidden treasure. The Hudson's Bay Company for nearly a century have maintained trading-posts at Fort William and other points, which probably opened the way to the first discoveries that were made at Prince's Bay, near the western limit of the district. At this point a large vein was worked by Colonel Prince, the owner, as early as 1846. The richest part of the vein seems to have been on Spar Island, but work was stopped on account of excess of water. Sir William Logan states that a mass of ore weighing several hundred pounds and carrying 3 per cent. of silver was taken out. On the mainland small quantities of native and sulphide of silver were found, together with iron and copper pyrites, zinc blende, and galena, in a large spar vein. On the main shore a drift 165 feet long and 90 feet in depth

By W. A. Heitbrink, M. Schmitz, J. A. Organiscak, A. B. Cecala, E. Ahrenholtz

Operator cabs on a front-end loader and a rotary rock drill were retrofitted with ceiling mounted heating1AC units and air filtration systems. Subsequently surface coal mine field studies were conducted to evaluate the respirable dust protection these retrofitted cab systems offer to the equipment operator. A significant 10: 1 respirable dust protection factor (ratio of outside to inside cab dust levels) was measured for the front-end loader cab with positive pressurization of the cab interior. Whereas an insignificant 3: 1 respirable dust protection factor was measured for the drill cab without positive pressurization of the cab interior. These results indicate that achieving positive interior cab pressurization with retrofitted cab filtration systems is a key element to their dust control effectiveness.

By Deborah Shields

Aggregate is an essential input to every economy, so governments need to ensure a sustainable supply of these resources through planning. There is also a need to shift from a linear economy to a more circular one, in which wastes are recycled rather than landfilled, so as to increase eco-efficiency. The purpose of the Sustainable Aggregates Planning in South East Europe (SNAP-SEE, SEE/D/0167/2.4/X) project is to develop a Toolbox for Aggregates Planning to assist governments and stakeholders in national, regional, primary and secondary, aggregates planning in southeast European countries. The Toolbox comprises documents on stakeholder consultation, data and analysis methodologies, a vision of best practices in aggregates planning and how to build an aggregates plan. The Toolbox will also support ongoing efforts to enhance minerals policy in the European Union (EU) as called for by the European Innovation Partnership on Raw Materials. Industrialized and developing nations see long-term and continued economic growth as essential to the well-being

By R. E. Cook

This work presents the development and application of equations of the form developed by Martin1 to describe gravity segregation performance during natural depletion. One-dimensional depletion analyses are applied to several hypothetical reservoirs. Considerable attention is given to the changes in saturation distribution in the dip direction resulting from depletion at various rates. Vertical gas saturation distribution within a sand having vertical permeability is studied to illustrate conditions which provide For low gus-oil ratio production from wells selectively completed away from sand tops, as observed from well performance. Results of performance calculations are shown graphically and illustrate the rate sensitivity of the gravity segregation mechanism and the influence of reservoir geometry and withdrawal distribution. It is shown that for sufficiently high depletion rates gas saturation distribution in the dip direction is characterized by the formation of two discontinuities, or saturation "fronts"; the updip front being the gas-oil contact of the secondary gas cap and the downdip front occurring at a position dependent upon the reservoir depletion rate, withdrawal distribution and reservoir geometry. The gas saturation in the region between fronts is shown to continually increase with time, while that downdip from the lower front remains very low and relatively stable. The effect of increased depletion rate is to reduce the region of stable gas saturation and thus enlarge the portion of the reservoir producing with continually increasing gas saturation. Special attention is given to the performance of reservoirs having sufficient vertical permeability to permit liberated gas to segregate vertically within the sand section before proceeding in the updip direction. It is shown that reservoirs of this type are far less sensitive to depletion rate due to the mechanical control of producing gas-oil ratios afforded by selective well completions away from sand tops. It is shown that gravity segregation performance is adversely af- fected by decreasing reservoir cross-section area in the updip direction. It is also shown that down-dip withdrawal concentrations can restrict gas segregation rates in the dip direction. INTRODUCTION The natural depletion performance of several large producing reservoirs in Western Venezuela has unmistakably shown the significant role that gravity forces play in governing the gas-oil ratio behavior of individual wells and the over - all pressure-production performance of the reservoirs. Analysis and prediction of the natural depletion performance of these reservoirs is of great importance in determining the economics of pressure maintenance operations. In 1957, a method for the analysis of pressure maintenance performance was presented by Martin1 which, in the original and more general form of the equations involved, provides a physically sound basis for the analysis of one-dimensional gravity segregation performance during natural depletion. The work reported herein is an application and extension of Martin's outstanding developments to a series of hypothetical reservoirs in an attempt to explain the general behavior of the gravity segregation mechanism and the influence of such parameters as depletion rate, reservoir geometry and withdrawal distribution. The study considers two types of flow: "distributed flow", where vertical permeability in the reservoir is zero and fluids flow only in the dip direction while uniformly distributed over the sand thickness; and "segregated flow", where vertical permeability is sufficient to permit gas to segregate against the sand top before proceeding updip. This latter type of flow has been recognized as an important mechanism active in the massive sand reservoirs of Western Venezuela. ANALYSIS OF ONE-DIMENSIONAL DISTRIBUTED FLOW SYSTEMS For an inclined reservoir having zero vertical permeability, the velocities of oil and gas flow at any point in the reservoir can be derived from Darcy's equations as

The Institute was founded in 1894 as the Chemical and Metallurgical Society of South Africa. In 1904 it was reconstituted as the Chemical Metallurgical and Mining Society of South Africa and in 1956 it became the South African Institute of Mining and Metallurgy. The objects of the Institute are to advance the science and practice of mining and metallurgy, to afford opportunities for the interchange and recording of knowledge of mining and metallurgy and to ensure high standards of professional conduct and competence. Membership benefits include monthly issues of the Journal of the Institute, monthly General Meetings at which papers are read, symposia, excursions to mining and industrial concerns and the use of club facilities at Kelvin House. Technical journals received on an exchange basis are available to members at the Johannesburg Public Library. The current membership of the Institute is over 1,600. Membership applications are accepted from suitably qualified persons and the requirements for entrance to the various grades of membership are summarised below. Fellows shall not be less than 30 years of age, shall be university graduates in pure or applied science or shall produce evidence to the satisfaction of the Council that they have successfully completed a co-ordinated course of study in pure or applied science of at least three years' duration at an approved university or institution deemed by the Council to be of equivalent status. Members shall have been employed in senior technical positions in important mining or metallurgical undertakings for at least five years or they shall have practised as mining or metallurgical consultants for at least five years. They shall be practising their profession at the time of application. Entrance fee RI0.00, Annual subscription RI7.00. Letters of designation: F.S.A.I.M.M. Members shall be not less than 25 years of age and shall be university graduates in pure or applied science, or shall have successfully completed co-ordinated courses of study in pure or applied science of at least three years' duration. They shall have been engaged in work of an approved technical character in the mining or metallurgical industries, of which not less than two years shall have been in positions of responsibility. A candidate shall be practising his profession at the time of his application. Entrance fee R8.00, Annual subscription RI5.00. Letters of designation: M.S.A.I.M.M. Associates shall be not less than twenty-five years of age, and shall have been engaged in positions of responsibility in, or associated with, the mining or metallurgical industries for periods of not less than three years. If, however, the candidate for admission to the higher grade of Associate, is at the time of his application, already a Student, he need satisfy the Council only that he is, at the time of his application, engaged in a position of responsibility in or associated with the mining or metallurgical industries. In all cases the applicants shall satisfy the Council that they are fit and proper persons to become Associates. Entrance fee R8.00, Annual subscription RI5.00. Graduates shall be not less than 21 years of age and shall be university graduates in pure or applied science, or have completed co-ordinated courses of study in pure or applied science of at least three years' duration at an approved university or institution. They shall not remain Graduate members after attaining the age of 30 years without the permission of Council. Entrance fee R2.00, Annual subscription R10.00. Students shall be persons not less than 18 years of age who are being educated or trained in a manner approved by the Council, to occupy a technical position in or associated with the mining or metallurgical industries and who, furthermore, shall not have attained the qualification required for a higher grade of membership. They may remain Students until they have obtained the necessary qualifications for transfer to a higher grade of membership, but not after the end of the Institute's financial year in which they attain the age of 28 (twenty-eight) years. They shall then transfer to a higher grade to retain membership of the Institute. The Council may relax the provisions of this clause in such cases as it considers appropriate. Entrance fee nil; Annual subscription R3.00. Other. The Council has the power to elect to the grade of Fellow or Member, candidates who may not fulfil all the requirements for entrance to these grades but whose status, professional achievements and practical experience in mining or metallurgy justify such election. Applications. Requests for membership application forms should be addressed on the attached form to the Secretary, South African Institute of Mining and Metallurgy, P.O. Box 61019, Marshalltown, Transvaal.

A Special General Meeting, followed by the February General Meeting of the Institute, was held in Kelvin House, Johannesburg, on 18th February, 1970, at 4.30 p.m. Mr J. K. E. Douglas (President) was in the Chair. There were also present 24 Members: Messrs A. R. C. Fowler, R. C. J. Goode, Prof D. D. Howat, Messrs D. G. Maxwell, J. A. Nixon, P. W. J. van Rensburg (Council Members), C. A. Border, J. C. Fritz, E. K. Gibson, P. L. Grimbeek, S. D. Hill, D. A. Immelman, P. J. Uoyd, M. Mrost, C. S. Macphail, D. G. Malan, W. D. Ortlepp, R. S. Pearson, A. J. H. Pole, Dr W. S. Rapson, L. W. P. van den Bosch, R. A. von Maltitz and Dr A. Whillier. Eight Associate Members: Dr M. I. Brittan, Messrs J. Brett, I. E. Clarke, C. L. de Jongh, W. B. Evans, D. Loubser, R. C. More O'Ferrall and G. R. Still. One Graduate: Mr T. J. Kotze. One Student: Mr J. A. Cruise. Nine Visitors: including Dr N. G. W. Cook, Messrs M. D. Labuschagne, A. Nicoll, S. Sadowski, Dr A. M. Starfield and Dr H. Wagner. Secretary: Mr D. C. Visser. Total present: 45. SPECIAL GENERAL MEETING The President: "You will have received notices of the Special General Meeting and I declare it duly constituted. In keeping with the trend of overseas and local institutes, your Council recommends that we should change our membership classification as indicated in the notes of the meeting. The new grades are proposed to replace those presently in the Constitution and By-Laws. In terms of Clause 4.8 of the Constitution a special general meeting must be held for the purpose of considering and, if approved, adopting with or without amendments, the revision of the undermentioned clauses of the Constitution, which Council now recommends should read as follows. Clause 2.2 'Corporate Members shall comprise the grades of Honorary Life Fellow, Fellow and Member', these being the equivalent of Honorary Life Member, Member and Associate Member. Clause 2.6. 'Non-Corporate Member shall comprise the grade of Honorary Fellow, Graduate, Associate and Student.' Are there any questions in regard to this proposal? If not would someone propose that these clauses be amended and adopted?" Proposer: Mr A. J. Nixon. Seconder: Prof D. D. Howat. The motion was then adopted. The President: "It is recommended that Clause 2.15 should read, 'A Corporate of the Member of the Institute shall be entitled to use the following authorised letters designating the grade of Membership in Honorary Life Fellow and Fellow, F.S.A.I.M.M. and Member, M.S.A.I.M.M.' Previously we used the letters M.S.A.Inst.M.M. and your Council considered that we should adopt the simpler lettering. Could I ask someone to propose that this amendment be adopted?" Proposer: Mr R. C. J. Goode.

By F. Brons, V. E. Marting

In the past, other authors.1, 2 have studied the influence of a skin effect on the productivity of a well. This skin effect, expressed by the skin factor S, is considered to be caused by a thin layer of impaired permeability immediately around the wellbore and extending vertically over the whole productive interval penetrated by the well. The skin factor S is defined as follows. Based on this, the impairment in productivity caused by a skin can be expressed by the fractional loss in productivity I, which is the loss in productivity divided by the total unimpaired productivity. For compressible flow in a stabilized well which drains a circular area of radius re, 1 is given by The present paper deals with a different kind of productivity impairment. Consider a well in which part of the productive formation is blocked off completely, either by incomplete penetration or by exclusion of parts of the productive zone by blank casing. In Fig. 1 (A, B and C), three examples are shown. Fig. 1(A) shows the situation where a well only partially penetrates the formation. This often is done to combat the actual or imagined danger of bottom-water coning. Fig. 1(B) shows a well producing from only the central portion of a productive interval. This type of completion is sometimes used where both water and gas coning are a problem. Although the case of a well producing through perforated casing cannot be treated in a manner similar to the previous two cases (where radial flow in the horizontal plane is assumed), Fig. 1(C) shows several intervals open to production and qualitatively describes this case (as will be discussed later). To study the loss in productivity in all these cases, two parameters are introduced which fully determine the impairment. The first is the penetration ratio "b," i.e., the total interval open to fluid entry divided by the total thickness of the productive zone. The second is the ratio hlrw. In this ratio, rw is the wellbore radius. The definition of h is more cumbersome. In Fig. 1(A), h is the thickness of the total productive interval. The streamline configuration for this case of partial penetration is basic to the other two cases considered (Views B and C of Fig. 1). It will be obvious from Fig. i (A) that the flow lines in the uppermost portion of the formation will be essentially horizontal, while those in the lower portion will curve upward toward the well. In Fig. 1(B), with only the middle portion of the zone open to production, the streamline configuration. of the upper half will be an exact mirror image of that in the lower half of the zone. Hence, for the case illustrated in Fig. 1(B), h is defined as one-half the total sand thickness. It follows, then, that in Fig. 1(C) h is one-half the distance between corresponding points in adjacent intervals. (In gun-perforated casing, h would be one-half the distance between perforations.) In a paper by Nisle4 and a paper given by the present authors5, the mathematical theory was developed for the cases under consideration. In the present publication, the emphasis is put on the results of these studies; consequently, the equations derived in Refs. 4 and 5 will be omitted, for the most part. The pressure drop p in a well producing from only a portion of the total formation thickness can, in analogy with Eq. 1, be expressed by Numerical solution of Eq. 5 by use of the IBM 650 leads to the following important conclusions. First, during a short period after starting production (usually on the order of a few minutes), the function p(b) is given by

By Charles P. Williams

The lead-bearing area of Missouri has been subdivided, geographically, into the Southeastern, the Central, and the Southwestern

By Steven J. Page, John A. Organiscak

Prolonged exposure to airborne respirable coal mine dust is responsible for coal workers' pneumoconi¬osis (CWP): Furthermore, miners who show evidence of higher radiographic categories of simple CWP are at increased risk of developing progressive massive fibro¬sis (PMF). As of 1990, there were nearly 130,000 coal miners in the United States. "' This excludes mines that produce less than 10,000 tons annually and the anthracite coal mines. Estimates indicate that at age 58, an average of 7/1000 U.S. workers and 89/1000 U.K workers will have developed PMF(2-1) Health research studies have iden¬tified that the risk of developing and the severity of CWP arc directly related to (1) the amount of respirable dust exposure and (2) the coal rank.,'- The rank of coal is its stage of formation in the series peat, lignite, sub-bituminous, bituminous, and anthra¬cite (in order of increasing rank). The rank of coal can also be represented by the com¬mercially important characteristics specified by its proximate analysis: fixed carbon, vol¬atile matter, mineral matter, and moisture content.

By Steve Kral

The third edition of the Underground Construction Association of SME?s (UCA) Cut-ting Edge series of conferences focused on a challenge every underground construction and tunneling project faces: controlling ground water. The conference, held in New York City in November, is a partnership between the UCA and The North American Tunneling Journal. It featured more than 20 technical presentations by professionals from around the world. Each described specific challenges unique to their projects and the solutions employed. More than 175 professionals attended the two-day conference that included an exhibition featuring 17 companies. In addition to the technical program, the Cutting Edge conference featured a site visit to the $10.4 billion East Side Access Project. Sponsors of the meeting included Soil Freeze, Traylor Bros., Kiewit, Skanska, Moretrench, Aecom and The Robbins Co.

By J. O. Scott

Transient pressure behavior of wells intersected by a single vertical fracture has been examined by means of a heat pow analogy. Results are correlated in terms of dimensionless pressure change and dimensionless transient time. The resulting curves are found to lie between the dimensionless curves for a cylindrical well and a line source when effective well radius is expressed as one-fourth of the total fracture length. Results are also shown for various degrees of afterflow. Use of the curves provides a means of determining reservoir permeability, wellbore radius, and thereby fracture length, even when the final slope of the transient curve is not obtained. Superposition of curves may be used to confirm existence of vertical fractures in the reservoir adjacent to the well or to indicate a damaged zone on the fracture face. INTRODUCTION Hydraulic fracturing has become a standard well completion practice for the purpose of increasing flow. Results are normally gauged in terms of some sort of "stabilized" flow rate established before and after the treatment. This procedure may be misleading because pressures in or around the well do not become "stabilized" during the test period. Transient pressure tests on fractured wells can overcome the objections to stabilized flow tests by indicating when a stable pressure gradient is reached. In addition, the transient pressure tests can be used to determine formation flow capacity and effective wellbore radius. The effective wellbore radius may be used as a measure of the success of the fracturing operation. The slope and position of the transient pressure-log time curve may be used to determine the flow capacity and wellbore size after sufficient lapse of time so that the pressure gradient in the vicinity of the fractures becomes constant. However, in tight reservoirs or in short tests this condition may not be reached. Presence of the fractures in tight reservoirs may cause a constantly increasing slope to the transient pressure curve. If this slope is picked too soon, formation flow capacity will appear high and the fracture size will appear too small. This paper is intended to clarify the early transient behavior of vertically fractured wells. It shows how formation flow capacity and wellbore size can be determined even though the maximum slope of the transient pressure curve is not obtained during the test. Development of the techniques of transient pressure analysis for wells has been summarized by Perrine.' He reviews the various definitions of wellbore effects such as skin effect, productivity ratio, damage factor and condition ratio. In the present paper, use of these terms is avoided by defining an effective wellbore size. For the fractured well this effective wellbore size is larger than the actual wellbore. Assumptions made are constant flow rate at the well, constant fluid compressibility, constant fluid mobility and uniform porosity and formation thickness. From the basic differential equations of flow, two different solutions may be obtained. The first, the line source solution, is commonly used in transient pressure analysis.' It expresses the change in pressure at any radius due to withdrawal or injection of fluid at the line source from an infinite reservoir at uniform initial pressure. This equation, in oil field units: is

By A. K. Csazar, L. W. Holm

This paper describes our investigation of a post-water-flood, oil recovery process which consists of injecting a slug of propane followed by water. Also described are the results obtained by applying a modification of the process in which gas was injected ahead of the water. Under the conditions of the latter experiments, misci-bility was not achieved between the propane and gas. Preliminary experiments or) uniform, watered-out sandstone cores showed that an oil bank could be formed and produced by applying this recovery process. However, since reservoirs are not uniform in structure, the process also was applied to porous media containing irregular porosity and to stratified sand systems. As a supplenzerrt to the experinlental work, a mathernatical procedure was developed for calculating the performance of the recovery process in a bounded, layered, porous system with crossflow between layers. As a specific example, the method was applied to predict the perforrnance of the recovery process in a 6-ft long, two-layer, stratified, unconsolidated sand model for comparison with experinlental data. The calculations were programed for the ZBM 704 computer. The equations and calcula-tional procedure presented can be extended to systems containing any number of randomly distributed permeability variations or any number of parallel layers. INTRODUCTION The problem of recovering the oil that remains in a reservoir which has been waterflooded is receiving considerable attention now as an increasing number of water floods reach an economic limit. A large number of the waterflood projects are in shallow reservoirs which are at pressures below 1,000 psi. It has been demonstrated in the laboratory that post-waterflood oil can be recover-ered by miscible displacement, but the LPG-gas, miscible flood and the enriched gas drive cannot be applied effectively at pressures below 1,000 psi. Only a few reports have appeared in the literature2-4 on low pressure, partially miscible recovery methods. However, it is possible to use LPG in a partially miscible displacement process in a reservoir where pressures of 200 to 1,000 psi can be achieved. Under these Pressures and at normal reservoir temperatures, propane is miscible with the oil; but, of course, gas or water used to drive the propane slug would not be miscible with the propane. Because of the lack of complete miscibility, it has generally been concluded that excessive amounts of propane would be required to recover oil and that such a recovery method would not be economical; however, we have found that under conditions present in certain reservoirs, an imrniscible recovery process can be applied effectively. The oil saturation in reservoirs at the economic limit of waterflood projects is usually in the range of 20 to 35 per cent of the pore space." A certain portion of this oil is left trapped by water in various size pores of the rock, but a good part of this so-called "residual" oil can be present in the less permeable lenses or layers of the reservoir rock which were by-passed to some degree by the water. The oil in these permeability traps can be produced only if favorable pressure gradients are formed in the reservoirs between adjacent zones of high and low permeabilities. A low viscosity liquid, miscible with the oil in place, which is driven by water through a stratified or heterogeneous porous system can aid in the development of these favorable pressure gradients. The oil that is released thereby from the permeability traps can be recovered by the subsequent water flood. Studies were made to determine how much oil could be recovered from homogeneous and stratified cores and models, which had been water flooded, by injecting a slug of propane and driving it with water. The effect of injecting a slug of gas ahead of the water was also determined. Most of the work described herein was done with the propane-water combination; unless otherwise specified, no gas was injected. The principal objectives of the investigation were to determine (1) if an oil bank could be formed and (2) what ratio of oil recovered to propane injected would be obtained. A further objective was to develop a method for calculating fluid-flow performance in stratified systems which would account for fluid transfer between zones in hydrodynamic communication but of different permeabilities. THEORETICAL ANALYSIS In a theoretical study of the recovery process, analytical expressions were derived to calculate the pressure distribution, the fluid flux in longitudinal (parallel to layers) and transversal (across the layers) directions, and the fluid distribution at any point in the system. The equations were developed for a two-layer porous system in which it was assumed that the fluids in the system were incompressible and that capillary and gravity effects were

By H. D. Hodges, J. K. Godbey

In order to better understand the fracturing process, bottom-hole pressures were measured during a number of typical fracturing operations. A recently developed system was used that allows simultaneous surface recording of both the bottom-hole and wellhead pressures on the same chart. The results from six fracruring treatments are summarized on the basis of the pressure data obtained. Al-though no complete analysis is attempted, the value of accurate pressure measurements is emphasized. Important characteristics of the bottom-hole pressure record do not appear at the wellhead because of the damping effect of the fluid-filled column. In four of the six treatments described, the formations apparently fractured during the initial surge of pressure with only crude oil in the well. The properties of the fluids used during the treatments are given and the fluid friction losses are obtained directly from the pressure records. This technique is also shown to be adequate for determining when various fluids, used during the process, enter the formation. INTRODUCTION Hydraulic fracturing for the purpose of increasing well productivity is now accepted in many areas as a regular completion and workover practice. Numerous articles have appeared in the literature discussing the various techniques and theories of hydraulic fracturing'. In general, three basic types of formation fractures are recognized today. These are the horizontal fracture, the vertical fracture, and fractures along natural planes of weakness in the formation'. Any one or all three of these fracture types may be present in a fracturing operation. However, with only the wellhead pressure record as a guide, it is difficult at best to determine if the formation actually fractured, and is almost impossible to determine the type of fracture induced. These difficulties arise in part because the wellhead pressure record, especially when fracturing through tubing, does not accurately reflect the pressure variations occurring at the formation. Several factors contribute to this effect and preclude the possibility of using the wellhead pressure as a basis for accurately calculating the bottom-hole pressure. These factors are: 1. The compressibilities of the fluids which damp the pressure variations. 2. The changes in the densities of the fluids or apparent densities of the sand-laden fluids. 3. The flowing friction of the various fluids and mixtures, which is dependent on the flow rates and the condition of the tubing, casing, or wellbore. 4. The non-Newtonian characteristics of a sand-oil mixture and its dependence upon the fluid properties, the concentration of sand, and the mesh size used. 5. The unknown and variable temperatures throughout the fluid column. Because of these reasons it was determined that in order to obtain a more accurate knowledge of the nature of fracturing, the bottom-hole pressure must be measured along with the pressure at the surface during a fracturing treatment. Even with accurate pressure data, a reliable estimate of the nature of fracturing is still dependent upon knowledge of the tectonic conditions. However, the hydraulic pressure on the formation is basic to any approach to a complete analysis. In order to accomplish this objective a system was developed to record the wellhead and bottom-hole pressures simultaneously at the surface. By recording both pressures on a dual pen strip-chart recorder, it was possible to greatly expand the time scale so that rapid pressure variations would be faithfully recorded. By such simultaneous recording, time discrepancies inherent in separate records are eliminated, thus overcoming one of the most difficult problems associated with bottom-hole recording systems. This paper illustrates the results obtained by using this system during six typical fracturing operations. All of these tests were taken in wells that were treated through tubing. By a direct comparison of the wellhead and bottom-hole pressures, the importance of obtaining complete pressure information during a fracturing treatment is emphasized. THE INSTRUMENTATION AND PROCEDURES The bottom-hole pressure measuring instrument consisted of a pressure-sensing element, a telemetering section, and a lead-filled weight or sinker bar. The pressure-sensing element used was an isoelastic Amerada pressure-gauge element. By using an isoelastic element, no temperature compensation was necessary in the tests described, since the temperature was believed to be well below the maximum temperature limit of 270°F. The rotary output shaft of this helical Bourdon tube element was coupled to a precision miniature potentiometer. The rotation of the pressure-gauge shaft thus changed the resistance presented by the potentiometer

By Edward Peters

Scandium (Sc) has unique properties and is one of the more valuable elements in the periodic table. Scandium can be used in solid oxide fuel cells and to produce high strength aluminium alloys of value, for example, in the aerospace industry. Scandium is often grouped together with the rare earth elements (REE). Amongst others, scandium can be found in bauxite residues, so called red mud. It is possible to extract and enrich scandium from red mud by leaching and solvent extraction. Scandium can then be recovered from the pregnant strip liquor by crystallization. The strip liquor will however still contain certain impurity elements. In the present work, a method for obtaining a pure scandium solid phase by direct crystallization from the strip liquor is evaluated. It was found that Fe and Ti co-precipitate with Sc under the conditions employed.

By Gordon R. Sima, John L. Bennett, Roger L. King

Electric shocks are a serious problem in the mining environment. Because of extremely wide ranging use of electrically powered equipment in the mining industry, the hazard to personnel due to electrical shock and related injuries are not restricted to any single area but cover the entire spectrum of mining activity. Electrical accidents, resulting in personal injury, due to im- proper or complete lack of grounding of electrically operated mining machines, form a significant percentage of the overall electrical accident picture. The object of this paper is to describe methods of detection of unsafe electrical conditions with respect to the grounding of electrically operated mining equipment. It also includes a discussion of prototype instruments which effectively monitor the condition of the grounding safety devices currently in use on mining equipment and warn of dangerous conditions as soon as they appear. The paper is based on work accomplished under USBM Contract Number 50357115. The contract was initiated under the Pittsburgh Mining and Safety Research Center Program. It was administered under the technical direction of PM and SRC with Mr. Roger L. King as the Technical Project Officer. Mr. Daniel B. Dawkins was the Contract Administrator for the Bureau of Mines.