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By A. Habibi

The ventilation survey was conducted in an underground longwall trona mine. The mine is relatively shallow and categorized as a gassy mine. The ventilation system consists of nine shafts (three intakes and six exhausts). Three surface based axial fans ventilate the mine configured in a blowing arrangement. Following the ventilation survey airflow quantity, frictional pressure losses and air psychrometric characteristics have been quantified. An accurate resistance survey has been conducted to calculate the pressure drop with regard to moving cages and skips in the shafts. This paper discusses the benefits of utilizing high accuracy digital pressure transducers and psychrometers in a ?leapfrogging? survey to gather data needed to build the computer ventilation model. Two underground booster fans with VFD are currently idle but available at the mine. The ventilation model has been used to determine the optimal booster fan locations to decrease the overall operating cost by reducing the load carried by the main fans. A leakage study has been conducted to evaluate the effects on the system of additional pressure from a booster fan. The study finally prepares a future ventilation model for the next fifteen years of mine operation and investigates the effect of proposed scenarios.

Feb 27, 2013

By Juan L. Yarmuch, Gonzalo Sepulveda

Medium- and short-term mine planning holds immense significance in optimizing production and resource utilization. It serves as a vital link between the long-term strategic plans and the day-to-day operational activities of a mine. In this context, a mathematical formulation is proposed to incorporate mining width constraints into the production scheduling process, aiming to maximize the net present value (NPV) of the schedule while ensuring enough room for the operation of mining equipment.

Jul 1, 2024

By G. Kris Kapoor

Each new period of public concern, whether rooted in things political, social, economical, or technological, brings with it new words or phrases which highlight that new interest. With people's awareness of our rapid depletion of readily available energy sources and the enormous increase in energy .costs came the new, and now often heard, terms "energy intensive", "energy sensitive", and "energy conservation". Since its birth in 1926, Fuller Company had been directly associated and involved with energy intensive products and processes. We are located in the heart of the Cement Industry. Many of our products and processes are geared to the needs of the portland cement manufacturer, and a look at the inferno within an operating cement or lime kiln will certainly convince anyone that here is an energy intensive process. Fuller Company, then, has always been energy sensitive. Process kilns, hard rock crushers, tube and roller mills, fluid bed thermal reactors, pneumatic compressors and conveyors, material coolers - all are Fuller Company products utilizing or transferring large amounts of energy. Consequently, much of our success in the marketplace depends on how wisely we design and plan for efficient use of power and for conservation of each unit of heat available.

Jan 1, 1975

By Russell B. Cornell, William B. Plank

AT the close of the academic year 1940-'41 the largest number of students ever recorded received their first or bachelor degree in the mineral technology schools of the United States. The total of men thus prepared to enter their professional careers in the mineral industries was 1601, a number nearly 12 per cent larger than two years ago and nearly 75 per cent larger than four years ago. Notwithstanding this increase in the number of graduates and as had been predicted in the preliminary report in February, there was a slight decrease in the total student population of the schools in both the United States and Canada. During the college year 1940-'41, 9133 students were enrolled in the 54 schools of the United States and 764 in six of the seven schools of Canada.

Jan 1, 1941

By J Parmenter

Issues around water û its quality, use, availability and environmental value û can be a major point of tension between mineral projects and local communities. Failure to manage these issues appropriately can jeopardise the obtaining of regulatory approvals for new projects and place at risk the æsocial licence to operateÆ of existing operations. Conversely, there may also be significant opportunities for companies to engage constructively with communities over water issues and to make a positive contribution to the sustainable development of these communities. Using case studies, this paper will explore the various types of social risks and opportunities associated with water and mineral resource development and identify key learnings relating to the management of these issues.

Jan 1, 2006

By J. T. McCartney

In an effort to correlate the size of pyrite particles in coal and coal-particle association with the removal of pyrite before burning, the Bureau of Mines conducted a study of 61 coals presently being used for electric power production. The results were obtained by visual microscopic studies of polished briquets of minus l4-mesh samples. Mean pyrite particle sizes ranged from 20 to 400 microns and proportions of pyrite contained in coal particles to an extent greater than 50 percent by volume (estimated) ranged from 20 to 95 percent. These parameters were correlated with reductions in pyrite accomplished by float-sink tests at 1.60 sp gr on 14-mesh, 3/8-inch, and 1-1/2-inch samples. The correlation coefficients between pyrite removal and mean pyrite particle size were 0.89, 0.84, and 0.79, respectively, for these samples. Correlation coefficients between pyrite removal and coal-pyrite association parameter were 0.92, 0090, and 0.85, respectively. It is apparent that extent of pyrite removal can be fairly well predicted from microscopic analysis.

Jan 1, 1969

By R. V. Ramani

In this report, the application of the Open Pit Materials Handling Simulator (OPMHS) to a mine located in Ohio using a large stripping dragline, and truck and front-end loader (FEL) is described. The specific objective of the study is to demonstrate the application of the simulator to mine planning and coal production. On the basis of the simulations, it was concluded that the production from the haulback operation should be increased to accommodate improvements in both the stripping dragline's availability and mean cycle time. Several alternatives were studied for the best use of equipment if the present operating parameters could not be improved upon. No economic analysis of these proposals were made.

Jan 1, 1977

By Suzanne Young

The effect of LiF additions on liqt.1id1.:1s temperature and electrical conductivity over a wide range of cryolite bath ratios (1.0 to 1.5 weight ratio) was investigated. Results did not agree with multi-regression equations reported by Dewing and Choudhary over the entire region. New regression equations were developed. Reasons? are given for the differences. The models are used to discuss the economic implications of LiF additions to Hali cell electrolytes.

Jan 1, 1985

By R. W. METCALF, A. G. Charles, F. M. SHORE

To furnish the information frequently requested by producers and suppliers as to the fuel requirements of the Federal Government , the Bureau of Mines , with the cooperation of the consuming departments and establishments , has collected the data herein , showing the Government's fuel consumption during the fiscal year ended June 30 , 1930. The following tables show the quantities and kinds of fuels consumed by the Federal Government in each of its departments and their principal branches , in each State , and in Alaska , Hawaii , Panama Canal Zone , Porto Rico , and the Virgin Islands . The separate departments and establishments were asked to supply information for each Federal building or other plant and , as to vessel fuel , the amount loaded at each port of supply . Fuels consumed in internal combustion engines are not included . The report does not include fuels used by Post Offices of the fourth class , since their fuels are not purchased by the Federal Government but are covered by an allowance in each case for light and heat . In some cases the data supplied represent receipts , which are approximately equivalent to consumption . The present study is believed to be the first effort to bring together the data representing the Government's requirements for the various fuels which it consumes . Figures showing the coal consumed by the Federal Government were gathered for the year 1922. These data are shown in an article by O. P. Hood and R. H. Kudlich of the Bureau of Mines , contributed as a chapter to " Industrial Coal ; Purchase , Delivery and Storage , " published by the American Engineering Council . The figures of coal consumption presented herewith are approximately comparable with those published for 1922 , a relatively small difference being due to the fact that the 1922 figures include the Philippine Islands and all other territory in which any coal was consumed by the Government . At the present time , the only data on Government fuel consumption that are published regularly are those compiled by E. B. Swanson , chief economist of the petroleum economics division of the Bureau of Mines . These are published annually by the Bureau of Mines in " Sources and Distribution of Major Petroleum Products , Atlantic Coast States , " and by the bureau in cooperation with the American Petroleum Institute in the annual " National Survey of Fuel Oil Distribution . " It is believed that the data herewith will prove of interest and value to the fuel industries as well as to Government consumers and that it will also afford a basis for measuring future trends in the use of the various fuels by the Federal Government . Figures showing the quantities of the various kinds of fuels consumed by each of the executive departments and independent establishments , are given in Table 1. It should be noted that when one organization procures and delivers fuel to be consumed by other branches

Apr 1, 1932

By R. N. Roby

In the course of the Bureau of Mines investigations for suitable sources of high-aluminum clay for the production of alumina, the Whiteware clay deposit was examined in August 1942 by G.N. Bennett, mining engineer, Bureau of Mines, Montana District Office. This report presents the factual data obtained by the investigation, which also includes data on trenching and drilling, and the results of some refractory tests and chemical analyses of representative samples of the clay later taken from some of the best trench exposures and from adit dumps.

Jan 1, 1949

By P D. Franzmann, D J. Readett, J Peterse

A better connection between laboratory- and pilot-scale test results, and heap bioleaching performance can be achieved by generating reliable information on the fundamental microbial, chemical and physical processes that occur in heaps and incorporating this information into a comprehensive and robust model. More efficient heap bioleaching, particularly of chalcopyrite, has the potential to add value to the mining industry as well as deliver attractive environmental and social benefits to the communities within which those companies operate.The results of fundamental chemical and microbiological studies of the leaching mechanism, the temperature dependence of chalcopyrite bioleaching, and the optimisation of leaching conditions are described with examples from full-scale heaps. The development and application of a number of novel techniques and tools has assisted our understanding of heap subprocesses mineralogy, hydrology, chemistry and microbiology. The heap bioleaching model HeapSim, which embodies a large number of effects not previously accounted for in other models, continues to be refined and has been applied successfully to the study of several heap bioleach systems.

Jan 1, 2004

By Scott A. Walker, Roberto A. Lopez, Lori A. Simpson, David A. Shook

500 Folsom Street is part of the new Transbay neighborhood in San Francisco, which is being redeveloped after the 1989 Loma Prieta Earthquake damaged a freeway viaduct; removal of the viaduct created parcels of land available for development. The development consists of a 42-story residential tower with a six-level basement. The slender, core-only structure was designed using performance-based seismic design. Subsurface conditions include undocumented fill, Dune sand, marsh deposits, sand, and clay, all overlying sloping bedrock of the Franciscan Formation. The building is supported on a 10-foot-thick mat foundation approximately 62 to 72 feet below street grades; clay, sand, and bedrock are all present at mat subgrade. Under a portion of the mat, sand susceptible to liquefaction was present. The variable subgrade conditions and potential for ground failure, along with the depth of mat subgrade below street grade, created a challenge for the design and construction team to solve. The ground below mat subgrade needed to be improved to mitigate the liquefaction potential and provide more uniform support. The areal extent and depth of ground improvement necessary to support the mat with an acceptable amount of deformation was determined. Settlement was analyzed and subgrade moduli were provided for design of the mat, with multiple iterations performed to converge between the geotechnical and structural models. Based on the project schedule and logistics, it was beneficial to work from street grade to improve the ground. In order to target the depths below the mat and minimize wasted effort and materials within the depth of excavation, grids of jet grouting were determined to be the most economical ground improvement method; however, it was challenging to install the columns from 65 feet above the top of the target zone. During installation, QA/QC was performed to check that the jet-grouted columns were installed to the design depth and diameter and developed the design strength.

Jan 1, 2018

This paper reviews the gold mining history and recent exploration activities on a number of beaches in the Catlins area of coastal South Otago. Past mining history and recent sampling indicate the presence of economically significant concentrations of placer gold, as well as anomalous PGM, and various heavy mineral species. A local source for this placer mineralisation is considered a strong possibility, along with a contribution from the Waiau River catchment via longshore drift. Blacksand beds in Jurassic sandstones of the Southland Synclinorium may represent this local source of mineralisation on the modern beaches. The possibility of placer mineralisation extending onto the inner continental shelf is also considered. Further exploratory work is justified, both for in situ Jurassic blacksand deposits, and to delineate mineralisation in the modern beach and inner shelf environment.

Jan 1, 1992

By M. B. Kime

"A set of experimental batch leaching tests studied the effect of pH, time, temperature, and stirring speed on the relative Cu, Co, Ni, and Fe leaching yields of an oxidized copper-cobalt ore sample in an aqueous hydrochloric acid solution. The results were statistically analyzed and modelled using the structural equation modelling method. Models showed that Cu, Co, and Ni leaching yields were strong functions of the leaching time and leaching temperature, whereas the Fe leaching yield depended on the leaching temperature, stirring speed, and pH. Under optimum leaching conditions yields were 99.8% Cu, 82.4% Co, 91.3% Ni, and 30.6% Fe.RÉSUMÉ Une série d’essais expérimentaux de lixiviation en bâchée ont été menés pour étudier l’effet du pH, de la durée d’attaque, de la température et de la vitesse de brassage sur les rendements relatifs de lixiviation du cuivre (Cu), du cobalt (Co), du nickel (Ni) et du fer (Fe) d’un échantillon de minerai de cuivre-cobalt oxydé dans une solution aqueuse d’acide chlorhydrique. Les résultats ont été analysés et modélisés statistiquement à l’aide de la méthode de modélisation par équation structurelle (SEM, de l’anglais structural equation modelling). Les modèles ont montré que les rendements de lixiviation du Cu, du Co et du Ni dépendaient énormément de la durée d’attaque et de la température de la lixiviation ; le rendement de lixiviation du Fe, quant à lui, dépendait de la température de la lixiviation, de la vitesse de brassage et du pH. Dans des conditions optimales de lixiviation, les rendements étaient de 99,8 % pour le Cu, de 82,4 % pour le Co, de 91,3 % pour le Ni et de 30,6 % pour le Fe. INTRODUCTIONThe Katanga province in the Democratic Republic of Congo hosts the northwestern part of the Central African Copperbelt. This region abounds with large, rich deposits of sulfide and oxidized copper-cobalt ores. In general, the main valuable minerals present are malachite (CuCO3Cu(OH)2) and heterogenite (CoO(OH)). Common impurities found in heterogenite are Cu, Ni, Si, Al, Mn, and Fe. The substitution of Co by other cations (e.g., Cu, Ni, and Fe) has an influence on the crystallinity of heterogenite (Deliens, 1974). In general, well-crystallized varieties of heterogenite have lower impurity contents, whereas amorphous heterogenite types usually contain more impurities (Thys et al., 2009). Further, in heterogenite, Co can occur in the 2+ and 3+ oxidation states. The gangue generally consists of quartz (SiO2), talc (Mg3Si4O10(OH)2), kaolinite (SiO2·Al2O3·2H2O), limonite (Fe2O3·3H2O), and goethite (FeO(OH)). Oxidized copper-cobalt ores are often treated by hydrometallurgical methods, whereas sulfide ores are often treated by flotation or pyrometallurgy, depending on their grades. Hydrometallurgical methods typically entail selectively dissolving the metals of interest (Cu, Co, and Ni) in aqueous solutions (leaching), transferring the dissolved metals to an organic solution, and retransferring these to a second aqueous solution (solvent extraction). Copper and nickel are readily dissolved in an acidic aqueous media. In contrast, cobalt is difficult to dissolve, especially if it is present in the third oxidation state; however, this species becomes soluble after it is reduced to Co2+ (Mwema, Mpoyo, & Kafumbila, 2002; Kime & Makgoale, 2016)."

Jan 1, 2017

Sishen uses a state-of-the-art tracking system to track material from its position in blast blocks through various stockpiles and crushers. Qualities are blended directly to the crusher as opposed to blending from stockpiles. This poses an interesting challenge to the planning department to simulate these conditions. The software used in these simulations are Whittle 4X and Maximiser for long-term planning, Xpac for medium-term planning and Mine Works Planner for short-term planning. Geological models and mine design layouts utilise Surpac. Sishen introduced Xpac a number of years ago; the system has developed and changed over the years. With the Sishen Expansion Project (SEP), which aims to utilise low-grade material, major changes to the planning process have to occur. SEP requires that the mine have two different plants, which utilise two different ROM feeds and have different beneficiation curves. Xpac is used to produce a rolling 18-month plan, which is as close to actual operations as possible. In order to do this, the simulations have to take into account the plants beneficiation curves, stockpile movements, hauling distance and equipment needs. On top of this, the schedule has to continually consider specifications for Fe and the contaminants. Plant yields also have to be kept within a certain bandwidth. Xpac is used to simulate the above parameters, as well as generate the raw data required to produce a mine budget. The paper will also show how the 18-month planning process and subsequent planning processes are measured and aligned. Xpac has proved to be an excellent tool to achieve these goals.

Jan 1, 2005

By W. A. Turcotte, A. D. Paananen

Introduction The large reserve of fine grained oxidized iron-formation at the Tilden mine has been the object of research and development efforts to concentrate the iron oxides as far back as 1949. Due to the nonmagnetic nature of the ore and the fine grinding required to liberate the iron oxide minerals, this crude ore was not amenable to concentration by conventional methods. The iron oxides of the Tilden, ore body have a grain size of less than 25 microns and recovery of the finer, well-liberated iron oxides is essential. Conventional methods of desliming employing cyclones or thickeners were not feasible because of the excessive loss of iron oxides in the finer fractions. Development of selective flocculation-desliming was a key to commercialization of the process. Operations started in late 1974 with Algoma Steel Corp. Ltd., J & L Steel Corp., The Steel Company of Canada Ltd., Wheeling-Pittsburgh Steel Corp., Sharon Steel Corp., and The Cleveland-Cliffs Iron Co. as participants. Cleveland-Cliffs operates and manages the operation. Development of the Tilden Flowsheet The geology and ore reserves of the Tilden mine have been detailed in a paper by Villar and Dawe (1975). A joint program was undertaken in 1961 with the US Bureau of Mines in Minneapolis using the flowsheet developed by the Bureau employing the selective flocculation-desliming and calcium activated anionic silica flotation method (Frommer, et al, 1966; Frommer, 1964; Frommer, Wasson, and Veith, 1973). During this time, parallel testing at Cleveland-Cliffs Research Laboratory and Pilot Plant centered on the same type of desliming but was followed by the cationic flotation of silica with amine collectors (Columbo and Jacobs. 1976). The cationic silica flotation system was eventually chosen for its overall efficiency and simplicity. Regardless of the flotation method chosen, the technique of selective flocculation-desliming prior to flotation is the key to the success of the process. The flowsheet is described in detail by Villar and Dawe (1975). [Figure 1] shows a simplified one-line flowsheet of the Tilden concentrator. A total tailings thickener has been added to the original flowsheet and was placed in operation in 1978. The total-tailings thickener overflow reports to the reuse water pond and the underflow is pumped approximately 8 km (5 miles) to a storage basin. A flowsheet of the reuse water system is shown in [Fig. 2]. Selective Flocculation-Desliming Data have been published on the mechanisms and factors affecting selective flocculation in iron oxide-silica systems. The intent of this paper is not to discuss the theoretical aspects of selective flocculation, but rather to present experience gained from the commercial Tilden operation and from bench and pilot plant testing of fine-grained oxidized iron ores. From the bench and pilot plant testing prior to plant startup, certain reagent combinations and rates for the commercial Tilden plant were established. In the experience gained from three years of plant operation at Tilden, some of these reagent dosage rates have required significant adjustments due to changes in reuse water quality and to meet the requirements of varying ore types. Reuse Water The process water quality is a major concern at the Tilden mine and is constantly being monitored for selected chemical and physical characteristics. This monitoring has continued on a regular basis in order to gain a more thorough understanding of the interactions taking place in a dynamic water system and particularly as water quality is influenced by seasonal variations. Control of the reuse water chemistry is essential to the Tilden process both in the selective flocculation-desliming and flotation stages of concentration. With roughly 75% of the reuse water used in grinding-desliming operations, it is readily apparent that the biggest "reagent" in the selective flocculation-desliming process is water. Not enough can be said about the close control that must be exercised on the overall reuse water system. Control of the chemical treatment of the feed to the total tailings thickener is of utmost importance in order to produce a reuse water for the concentrator that is compatible with all stages of the concentrating process. There are many analyses made which aid in judging the quality of the water. Some of these are shown in [Table 1]. Five are particularly important and are monitored daily so that reagent adjustments can be made as required: suspended solids, calcium hardness, pH, dissolved silica concentration and temperature.

Jan 1, 1981

By A. S. Macfarlane

Over the last few years, and especially the last few months, issues relating to Corporate Governance in industry in general, and the Minerals industry in particular, have become increasingly topical, as a result of a number of scandals and failures. The development of International and National Codes for the reporting of Mineral Resources and Reserves began some years ago, and has been followed by more stringent Listing Rules for the Securities Exchanges, as well as more standardised formats and protocols for financial reporting of assets and activities. More recently, some countries have adopted Codes for the Valuation of Mineral Properties, which have focussed on standardisation of valuation approaches to be adopted, and the qualifications of people deemed competent to sign off such valuations. This process has not been without criticism, the main criticism being the proliferation of local standards and regulations, which are often difficult to apply and regulate, or which are too prescriptive for multinational mining companies to deal with. In South Africa, these concerns have been recognised, while at the same time a need has been identified to establish a Code which could be applied to South Africa, and the African continent as a whole. Such a development would necessitate that the Code satisfies the needs of the continent, but in a global context. This global context has already been set by the activities of the International Organisation of Securities Commissions, the International Valuations Standards Committee and the International Accounting Standards Board. This paper explains the progress and process that has been established in South Africa for this purpose, and highlights the key issues which are open to public debate, so that the process is inclusive and transparent, whilst at the same time it is consistent with international time frames, and provides a deliverable product that meets the desired objectives.

Jan 1, 2004

By F. Block, K. Kohli

Outcrop barrier pillars serve to keep mine personnel and the public safe from sudden uncontrolled flows of water accumulated in active and abandoned underground mine workings. When an outcrop barrier fails, the result is an outbreak of water to the surface and is termed as blowout. Mine blowouts are associated with above-drainage mines and can occur through the coal outcrop and sealed portals. A blowout is often catastrophic, a threat to the people on the surface living or working in the path of a potentially large flood. In addition, blowouts can destroy homes, cause landslides and severe erosion and release pollution and acid mine drainage. This paper provides guidance on the planning, design, evaluation and inspection of barriers to address the problem of mine blowouts associated with above-drainage coal mines.

Jan 1, 2007

By C. D. Haynes, S. C. Gambrell

The practice of roof bolting in WORLD-WIDE mining activities is very well-known, having been used extensively for over 50 years. The theory of roof bolting, however, is extremely complicated, and only recently have investigators attempted to explain the theory. Various means of stress analysis have been utilized in rock mechanics, most of which reduce rock to an isotropic, homogeneous medium that can be easily analyzed. One of the indirect research methods is the photo-elastic technique, the theory of which is widely known and needs no elaboration. This technique has been used extensively to examine the state of stress around underground openings of various shapes in certain types of strata, and under various loading configurations.'-" In-Situ Mine Roof Trusses The photoelastic technique was employed here to evaluate the state of stress above a mine opening where support is provided by the in-situ mine roof truss. This support configuration, shown in Fig. 1, has gained popularity in recent years, particularly in mines with bad roof conditions." To the authors' knowledge, no scientific determination has been made of the advantages roof trusses may offer over conventional bolting configurations comparable to roof trusses. Ordinary mine roofs usually sag or bulge downward soon after mining. Normally, after some movement the roof begins to stabilize, but the face of this bulging mine rock is usually in tension and will almost always fail unless supported. Because rock fails easily in tension, it is desirable to "preload" the roof, that is, to impress a compressive force on the mine roof to prevent bulging and subsequent tensile failure. Ordinary rock bolting installations, particularly if the bolting is perpendicular to the mine roof plane, do not produce a preloading effect. Although bolting installations squeeze the strata together and produce a beam effect desirable for support, they do not have the advantage of actual uplift. They pull down at the anchorage point with a force equal to the bolt tension which sometimes causes a separation in the plane of the anchorage detrimental to roof strength. In-situ mine roof trusses require the installation of steel tension rods in the roof of the mine much the same as conventional roof bolts, except that the rods are arranged to produce a stress pattern above the upper surface of the opening similar to that of a prestressed beam. The roof rock acts to transmit the compression force. The simplest form of truss consists of two steel rods anchored to the back of holes drilled at an angle of approximately 45 over the mine pillars. These rods are collared near the middle of the room, and the lower ends of the rods are connected by tie rods and turn-buckles. Used in this manner, a small-diameter steel rod can provide essentially the same support as a wide-flange steel beam. By tightening the turnbuckles, an uplift on the roof can be produced. Objective of the Investigation The objective of this investigation was to determine qualitatively the state of stress that exists above a mine roof after the installation of the in-situ mine roof truss vs. that of two angle roof bolts, hereafter referred to as "roof bolts," drilled and placed in the same configuration, that is, 45" above each pillar and connected together in the middle of the room by a bearing member such as a steel beam. Each state of stress was to be identified, insofar as possible, as compression or tension above the mine opening. Model Construction A photoelastic model of a mine opening was coil-structed from -in. thick PLM-4B birefringent plastic and was machined to specification shown in Fig. 2. The dimensions of the opening were chosen to simulate a width-to-depth ratio of 3 to 1. Two % -in. holes were drilled at 45" angles, as shown, to provide for the loading devices. After construction, the model was annealed at 240°F to remove stresses produced during machining.

Jan 1, 1971

By K. Leutwyler

The key to realistic casing stress analysis in thermal recovery installations is accurate knowledge of the temperatures involved. Much information leading to prediction of heat losses from tubing string to wellbore has been published. This .same information permits calculation of casing temperature under certain conditions. This paper reviews the basis for most of the published work, the line source solution to the diflusivity equation and examines some of its application criteria in the light of unsteady-state conditions. An alternate finite differences method is presented for correlation, and experimental data pertaining to the heat transfer mechanism in the annulus is reported. In the light of the information presented in the paper, it appears that the assumption of a line source for the tubing-wellbore system is valid even for reasonably short periods of heat flow, .such as "steam soak" operations. The empirically modified equation presented earlier matches computer derived results of the finite differences approach lor periods as short as 50 hours. Previously predicted cas ing temperatures and the associated stress levels are thus verified based on these correlative computations and the reported experimental information. Fall out from the computer output resulting in some studies of the influence of insulating cement properties on casing temperature, and experimentally studied effects of nitrogen placed in the annulus at various pressures., are described. INTRODUCTION Generally speaking, predictions of average casing temperatures have been based on an idealized model involving a centralized tubing string at uniform constant temperature radiating energy towards the casing under steady-state conditions.'. ' Heat is transferred away from the casing to the formation by unsteady-state conduction across thermal barriers consisting of cement and the mud sheath. Heat balances written on the casing permit prediction of instantaneous casing temperatures. During early periods of injection, casing temperature varies appreciably as a function of time; however, for long injection times this variation decays as heat flow from the wellbore to the formation stabilizes, and it becomes virtually negligible as conditions surrounding the wellbore become quasi-steady-state (Fig. 1). Carslaw and Jaeger -escribe a solution to the diffusivity equation for a line source (Fig. 2). A constant supply of heat is introduced into the medium from the line placed into the origin of the x-y coordinate system and parallel to the z-axis. Heat spreads outward in the infinite cylindrical solid and the temperature increase on a line going through point (x, y) parallel to the z-axis at a distance r can be predicted by: The following criterion must be considered: the Carslaw and Jaeger equation is obtained on the basis of a large

Jan 1, 1967