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By J. Suarez

The innovation initiatives for world-class mines today and in the future focus on automation and robotics in equipment and machinery. These innovations have benefited from the development of advanced tools in global positioning, the Internet, the capabilities of data storage, transmission and handling, and intelligent systems. Forward-thinking companies have been investing in automated trains and trucks, selfdrilling rigs, intelligent flotation systems, etc. Considering that the emphasis has been mostly laid on improving the performance and reliability of the equipment and machinery, it is not surprising that the visibility was geared toward mechanical, electrical, process, and metallurgical engineering. One of the critical disciplines, mining engineering, has had less shine from the spotlight of automation and robotics. Mining engineering is concerned with the design, the operation, the management, and the reclamation of mines and mining facilities. In essence, it does benefit from the advantages of automation and robotics in equipment and machinery. However, being ?left out? in the innovation process may impede the core capabilities of this engineering discipline, which would create a two-tier knowledge and technology system in mines. For example, shovels in an open pit may be equipped with technology that can send real-time data of actual payload, number of buckets, mechanical status, etc. But, are mining engineers aware of the possibility to incorporate the data into their planning tools in order to have updated forecasts and accurate information? And if they are, are they equipped with the tools to reap the rewards of those technologies? And if so, is the personnel trained to use the tools efficiently? This paper is a contribution to the discussion on the technological advances in mining engineering. For the authors, the roadmap to the future requires a smart integration of technological advances in hardware and software so that mining engineers are not only aware of the possibilities, but also trained and capable of using the available tools. Essentially, this paper believes that automation and robotics in equipment alone will be undervalued and underutilized if the owners and drivers of the mining systems (i.e. the mining engineers) do not possess the tools and training to integrate the technological advances into the functions of mining engineering. The intent of the paper is to analyze the available technologies for the core mining engineering functions of design, planning, scheduling and optimization. The analysis will lead to discussions and suggested solutions on integrative technology solutions that would create optimum value for the mining processes and equipment technologies.

Aug 1, 2013

By F. J. Macias, A. Bruland, F. E. Dahl

"Tunnelling by use of Tunnel Boring Machine (TBM) is gaining a greater presence as a suitable excavation method. Disc cutter consumption has a strong influence on performance and cost when using TBMs and the influence becomes even more relevant in hard rock. Furthermore, good predictions of TBM performance and cost facilitate the control of risk as well as avoiding delays and budget overruns. Since abrasive wear is the most common process affecting cutter consumption, good laboratory assessments are needed. A new abrasivity test method called Rolling Indentation Abrasion Test was developed. The goal of the new test design and procedure is to reproduce wear behaviour on hard rock tunnel boring in a more realistic way than traditionally used methods by introducing wear by rolling contact on intact rock samples. INTRODUCTIONHigh investments are involved in the tunnelling industry, especially in Tunnel Boring Machines (TBMs) projects. Performance predictions and cost estimations are crucial for planning and risk management of TBM projects. Cutter consumption has a large influence in terms of time and cost, and an even greater effect in case of hard rock projects. Many factors are influencing the amount of cutters consumed in hard rock TBMs. Normal TBM operation results mainly in abrasive wear on the cutters and appropriate methods for abrasivity assessment are needed. Rock abrasiveness cannot be considered as an intrinsic property and the complete tribological system should be considered in addition to the geological properties of the rock.In the present paper, a new test method for abrasivity assessment in tunnel boring called Rolling Indentation Abrasion Test (RIAT) is presented. The traditionally used test methods for determination of rock abrasiveness uses sliding or impact contact in order to cause wear while the RIAT introduces rolling contact on intact rock samples. The ambition of the new test device is to have a reliable method to evaluate the cutter wear in hard rock tunnel boring by reproducing wear behaviour on rolling disc cutters in a more realistic way. It has been established by many authors that the abrasion of a cutter ring is proportional to its rolling distance (Rostami, 1997; Bruland, 1998). In the present work, the weight loss of a mini-cutter ring is measured subsequent to testing in order to evaluate wear in the rolling process and could hence be related to cutter ring wear. Indentation of the tools in the intact rock sample is considered as an indication of the surface hardness of the rock or the resistance to indentation by rolling."

Jan 1, 2015

By D. L. Katz, M. J. Rzasa

The derivations of three methods of computing the static pressure gradients in natural gas wells have been presented to show the assumptions made. Charts were developed from which the pressure gradients may be read when the well-head pressure, the well fluid gravity, depth, and the average well temperature are given. A chart for estimating the well fluid gravity from the condensate content and separator gas gravity is included. The effect of the increased average well temperature after flow on the calculation of the static pressure gradient is discussed. Introduction Reservoir pressures have been calculated from well-head pressures for gas wells for many years. As the pressure measurements become more accurate, the need for a reliable calculation of the static pressure gradient often arises. This paper will develop the several methods for computing the pressure gradient in gas wells and make a comparison between them. The method of calculating static pressure gradients in common use is Eq. I (ref. I) or its counterpart which includes a factor for the deviation of the gas from the ideal gas law. P2 - P1 = P1(e0.0000347GX _ I) Eq. [I] in which P1 = pressure at well head, lb. per sq. in. abs. PP = pressure at bottom of well, Ib. per sq. in. abs. G = gas gravity X = depth of well, ft. An alternate method is to compute the average density of the gas in the well and multiply by the well depth in a manner similar to that used for liquid gradients. Derivation of Formulas A static pressure gradient is a special case of the general fluid-flow equation. Consider a pound of fluid flowing in a vertical column from point I to point 2, Fig. I. By an energy balance for fluid flowing from I to 2: U1 + P1V1 + u12/2g + X1 + q = U2 + P2V2+ u22/2g+X2 +W [2] in which U = internal energy, ft-lb. per lb. P = pressure, lb. per sq. ft. V = volume, cu. ft. per lb. u = average linear velocity, ft. per sec. X = height above datum, fl. q = heat absorbed by fluid, ft-Ib. pcr lb. W = work done by system, ft-lb. per lb. An energy balance on the fluid itself gives: U = ?TdS - ?PdV + etc. [3] in which T = temperature, deg- R- S = entropy, ft-lb. per deg. R. per lb.

Jan 1, 1945

By L. J. Cabri

Although no complete mineralogical balances have been published, the background knowledge and proven, highly sensitive analytical techniques to produce them already exist. For PGE-Cu-Ni sulphide ores a combination of ore microscopy, image analysis and electron microprobe analysis with proton microprobe analysis of sulphides for Pd, Rh and Ru and ion microprobe analysis for Pt, Ir and Rh (in some minerals) should provide the necessary data when combined with reliable assays. Other sulphide ores, such as the Cu-Ni-(PGE) ores of Sudbury, Ontario, require a similar approach except that the ion microprobe would be more suitable for the analysis of Pd, Pt and Rh because of its greater sensitivity. Oxide-silicate ores may be harder to deal with quantitatively, although the potential to confirm the presence of trace PGE within silicates and oxides may be greater than in PGE sulphide and Cu-Ni-(PGE) sulphide ores. However, solid solution of PGE in oxides and silicates still requires thorough documentation and evaluation in terms of their significance for the overall metallurgical balance

Apr 1, 1994

Late in 1974 at a meeting with the Cedar Coal Company in Chelyan, West Virginia, a very definite requirement for an automatic heat sensing fire suppression system for the type coal augers used in their mine was revealed. Several fires had been experienced, and while equipment loss was a consideration, operator safety was also a concern. As of that date no one had developed an automatic system specifically for fire suppression on coal augers. II. EQUIPMENT DEVELOPMENT As a result of the above meeting, an unsolicited proposal was made to the Bureau on March 1, 1975, and a contract was issued to provide the following services: A. Determine and define fire hazard problem on Compton Coal Auger. B. Modify or otherwise mike a Lease "AFEX" system suitable for protecting the fire hazard area developed in paragraph "A". C. Make installation of "AFEX" system. D. Monitor installation for reliability for a period of 90 days after installation. C. ConJurt a simulated fire test to determine effectiveness on system.

Jan 1, 1975

By Neil Schofield

"The estimation of recoverable ore reserves for feasibility in precious metal deposits such as Pine Creek must account not only f or the extreme variability of the ore grade but also for the complexity of the geology. Compatible models f or both must be adopted. Further, very selective mining demands reserve estimates be based on small selection units whose individual grades cannot be estimated reliably from the exploration drilling data.Multigaussian kriging is one method based on a multivariate normal model for estimating recoverable reserves under such conditions. In this paper, a non-mathematical description of the multigaussian model is presented together with its application to the Pine Creek Gold Deposit. The results, when compared to the first year of production, are encouraging for the model but not without surprises.Together, Part 1 and Part 2 of this study combine a detailed and geologically conditioned variogram analysis with an appropriate estimation method for a highly variable low-grade gold deposit. This and other studies of gold deposits familiar to the author show convincingly both that while the appropriate geostatistical skills and techniques are necessary to tackle the question of reserves, equally important but often discounted is the need for an appropriate and compatible geological model. IntroductionThe Pine Creek gold mineralization is associated with saddle reefs, and quartz and quartz- sulphide veining within the Enterprise Anti cline. The anticlinal structure is complex and, prior to mining, the mineralization was considered to be mainly strata controlled. Grades vary up to 160 grams in l .5rn core samples with coefficients of variation in excess of three.The estimation of the recoverable reserves for such a depo sit must account for both the geological complexity and the extreme variability of the gold grade.Part 1 of this work presented the geological model for the deposit and summary statistics 0 f the gold data. A detailed structural and variogram analysis considered both gold grades and the normal score (or gaussian transform) of these gold grades for different composite sizes."

Jan 1, 1988

By David R. Hanson

Seismic tomographic imaging, based on the same principles as a medical CAT Scan (Computer-Aided-Tomography). has been used for many years in the oil industry for large-scale subsurface stratigraphic characterization. and has most recently been applied to various structure- and stress-related problems in the coal industry. New developments in signal processing have greatly enhanced the speed, resolution, and range of applications of topographic imaging in underground settings, and recent innovations in data acquisition hardware have further increased data reliability and repeatability. Whereas past structure mapping applications relied on Seismic velocity and/or attenuation tomopraphy within an enclosed seismic source gram receiver array, recent developments in "True Reflective Tomography- (TRT TM) have expanded the application of this technology considerably. For example, in-seam TRT TM seismic reflection tray now he used to image structure, and/or old workings from one general location in the mine face areas of mains and panel developments) well ahead of planned developments largely eliminating the need to probe-hole drill on regular intervals. This new reflective technology bas also been combined with traditional cross-hole seismic tomography-providing a comprehensive, powerful tool for velocity attenuation. and reflective imagine utilizing the same source/receiver array data sets (borehole-to-borehole. borehole-to-entry and entry-to-entry). These new developments in data acquisition and image processing have greatly expanded the variety of applications for tomographic site characterization allowing the mine operator considerable flexibility to cost-effectively characterize previously inaccessible areas of the property. This paper presents examples of 2-D and 3-D .seismic topographic imaging applied to (1) the location of old works in Appalachian room-and-pillar operations and (2) the identification of anomalous zones ahead of mining/tunneling developments these applications demonstrate the state-of-the-art in seismic ground imaging using velocity, attenuation. aril reflection techniques land combinations thereon, and further illustrate the flexibility of data acquisition from a variety of tinning arid tunneling settings. Recent examples are presented from projects in the United States and Europe.

Jan 1, 2000

By Cyril Wells

THE diffusion of carbon in gamma iron plays an essential role in many metallurgical processes. In carburizing, in graphitizing, in homogenizing, in the formation of pearlite from austenite, and in other processes, migra-tion of carbon in gamma iron occurs.1,2 A full understanding of the rate at which these processes occur obviously requires a knowledge of the rate of diffusion of carbon. In carburizing, for example, the depth of carbon pentration is determined by the carbon concentration in solid solution at the surface, and by the rate of diffusion inward of the carbon. Until reliable data on the rates of diffusion of carbon are available it is unlikely that a full quantitative description of this process will be obtained. In the formation of pearlite from austenite, the segregation of carbon and alpha iron from the austenite obviously requires the diffusion of carbon; the rate at which pearlite nodules grow is evidently controlled at least in part by the rate of diffusion of carbon; it is unlikely that we shall understand the factors that determine the rate of growth unless data on rates of diffusion of carbon, and the variation of these with com-position, grain size, and temperature are available. Accordingly it was decided: (1) to determine, more accurately than hitherto, the diffusion coefficients of carbon in austenite over a wide temperature and a wide concentration range, (2) to study the influence of grain size and impurities on this diffusion coefficient, and (3) to study the effect of manganese and nickel on the rate of diffusion of carbon in the austenite of manganese and nickel steels, respectively; the influence of carbon on the rate of diffusion of manganese and of nickel will be made the subject of later papers. The rate of diffusion of carbon in gamma iron has been studied by Runge3 by Tammann and Schönert4, by Bramley and co-authors,5-14 and

Jan 1, 1940

By R. A. Morse, W. O. Keller

The properties of limestone reservoir rocks such as the distribution and degree of continuity of the pore systems, and the relative volumes and permeabilities of the systems making up the complex cause large variations between performance of individual limestone reservoirs and their susceptibility to secondary recovery methods. The effects of these factors on the mechanism of fluid flow cannot be adequately evaluated with presently developed concepts, laboratory data, and geological information. The observance and interpretation of the performance of individual limestone reservoirs provides, at present, the most adequate approach for evaluating the integrated effects upon performance of the many. now immeasurable variations in the properties of limestone reservoirs. INTRODUCTION The development and application of techniques for increasing the efficiency of oil recovery from natural reservoirs is a problem of primary importance to the industry. During the past several years, a great deal of effort has been expended by the technical personnel of the industry toward the improvement of present known methods of oil recovery. and evaluating the factors which control the susceptibility of particular reservoir types to economic application of secondary recovery methods. Providing adequate and accurate laboratory data on the properties of the reservoir rock and its contained fluids. together with good production statistics, are available, methods have been evolved for estimating with reasonable accuracy the performance of an oil reservoir under either continued natural depletion or conditions imposed by introducing additional displacing fluid into the reservoir from an extraneous source through the injection of gas and/or water. The susceptibility of limestone reservoirs to secondary recovery by gas injection is very much dependent upon gas-oil relative permeability relationships for the reservoir in question. In a rock formation in which the porosity is of the intergranular type such as is found in sand stones and some non-fractured dolomites, a representative sample of the pore structure can be obtained in a small core plug. In this type of reservoir, it has been shown that relative permeability data obtained from laboratory experiments can be Properly applied to evaluate the flow relationships actually observed during the depletion of a reservoir. In addition, a good idea of the fraction of the reservoir which will be swept by the injected gas may be obtained from the spacing pattern used and the permeability profile of cored wells. From these data, it has been demonstrated that reliable estimates of performance and recoveries under gas injection operations can be made for reservoirs in which the Porosity is of the intergranular type. Limestone reservoirs on the other hand often present much more complex problems. One reason that the performance of limestone reservoirs is so variable is that there may be, in reality. two or more pore systems, the integrated performance of which will depend upon the physical properties of each system and their inter-relationship. For instance, in a limestone reservoir, the main pore structure, as far as void spaces for storage of hydrocarbons is concerned, may be represented by the intergranular openings of the rock. Usually in limes and dolomites, the intergranular pore openings are very small and the matrix permeabilities extremely low. Often, as in the case of Many dolomite and oolitic lime reservoirs, this is the only pore system, and performance is observed to be very similar to that of a sand stone of similar permeability. However, in the great majority of' the limestone reservoirs, there is present, in addition to the intergranular pore system, a complementary system of openings caused by fracturing or solution.',' The openings in the latter system are usually many times more permeable than the intergranular pore system due to their much larger size, and may contribute almost all the fluid carrying capacity of the formation, even though their volume may be a very small part of the total pore space in the reservoir. Obviously, the performance of such a complex under either primary or secondary control will deend upon the distribution and degree of continuity of both systems, the relative volumes and permeabilities of the

Jan 1, 1949

By Wilbur I. Duvall

INTRODUCTION This chapter outlines some general principles and procedures that a rock mechanics engineer can use to arrive at a logical design for the size, shape, and spacings of underground openings in various types of com¬petent rock formations. Rock formations can be clas¬sified into six major categories which are useful for design purposes, provided the necessary input data are available regarding the geology of the site, the physical properties of the rock, the in-situ stress field in the rock, and the general geometry of the underground openings. The US Bureau of Mines (USBM) developed a rock classification system based upon these concepts and found it to be useful for design purposes (Obert, et al., 1960; Obert and Duvall, 1967). This classification sys¬tem is given in Table 1; however, an extra column has been added to the original classification to indicate the appropriate design techniques for each rock class. In this classification system, two main classes of rock are considered: competent rock and incompetent rock. Competent Rock Competent rock is any rock which, because of its mechanical and geological characteristics, is capable of sustaining underground openings without the aid of any structural support except that provided by unmined rock in the form of pillars and side walls, etc. Roof bolts and small random props which support only local loose rock are not considered structural supports. Competent rock is further subdivided into three ad¬ditional categories-massive, laminated, and jointed¬ which are defined as follows: Massive Rock: Massive rock is a rock formation where the spacing between mechanical defects such as joints, partings, or faults is equal to or greater than the critical dimensions of openings, or where the strength of the bond across these mechanical defects is com¬parable to the rock strength. Laminated Rock: Laminated rock is a rock forma¬tion divided by approximately parallel planes of weak¬ness into lamina whose thicknesses are small compared to critical dimensions of openings and where the bond between the lamina is weak compared to the rock strength. Elastic Rock-This is rock whose physical proper¬ties will permit the use of elastic theory to predict strains and displacements from applied stresses. Inelastic Rock-This is rock whose physical proper¬ties are such that strains and displacements are a strong function of time as well as applied stress. Incompetent Rock Incompetent rock is any rock which, because of its mechanical and geologic characteristics, is not capable of sustaining underground openings without the aid of additional structural support in the form of linings, steel sets, or systems of props. This classification system for rock depends not only on the mechanical and geologic characteristics of the rock but on the size of openings and their depth be¬low the surface. For example, many competent rocks at shallow depths for small stress fields could become inelastic rock at greater depths and larger stress fields, or competent massive rock for small openings could be¬come laminated or jointed rock for larger openings. Thus, to classify rock for design purposes requires a knowledge of the geologic properties of the rock mass, the physical properties of the rock, the general size of the openings to be mined, and the average range of the in-situ stress field to be encountered. To design underground openings and structures in rock, it is necessary to use criteria of failure for rock under various stress conditions, and to use safety factors to allow for differences between laboratory and in-situ strength properties of rock and to account for errors in¬troduced by the various assumptions made in the design process. Criteria of failure based on maximum stresses have been found to give reliable results in practice. Thus, it is assumed that rock will fail in tension when the tensile stress exceeds the tensile strength of the rock as determined by a standard modulus of rupture test on samples of rock core. If the tensile stresses in rock are small, then it is assumed that the rock will fail at a value of compressive stress equal to the compressive strength of the rock as determined by standard uniaxial compres¬sive strength tests on samples of rock core. These fail¬ure criteria, when used with appropriate safety factors, can be expressed as:

Jan 1, 1982

By E. S. Anolick, Joseph Singer

The magnetic after-effect, in the form of time decay of permeability (l/µ), has been used to obtain independent data on the solubility of' carbon in pure iron. The results differ slightly from the solubilities obtained through internal -friction experiments. The mechanism of the time decay being the magnetic analogue of internal friction, it appears necessary to explain the observed discrepancies, and some suggestions are made. THE purpose of this work was to establish the reliability of the time decay of permeability as a measure of dissolved interstitial in the body-centered-cubic lattice, and further, to establish techniques suitable for such measurements with samples of a form convenient for various other measurements. This particular sample form was the "epstein" strip, i.e., 25 cm by 3 cm by 0.035 cms. While the general conclusions are not limited by this geometry, there are two aspects of the samples that may be relevant: a) texture, and b) grain size, which ranged generally from 1 to 10 mm. Effects due to these two possible parameters were thought to be small and were not investigated. Calibrating the time decay technique and the other experimental procedures by measuring the solubility of carbon in pure iron suggested itself because of the accumulation of data on this subject through the related technique of the internal friction'; The essentials of this report have been published in a somewhat condensed form.5 Since then some additional data have been taken. It is the purpose of this paper to add these data and to provide more complete description of the experimental techniques than was possible then. The time decay of permeability is a form of the magnetic after-effect.6,7 Permeability is measured immediately after demagnetization (µº) and also long after (µ8). The time decay, ?(l/µ), is the difference 1/µ8 - 1/µ0 and has been considered to be proportional to the concentration of a dissolved interstitial6,8,9,12 The relaxation time! 7, is characteristic of a particular diffusion, and affects the permeability as follows: where he being the activation energy for diffusion of the interstitial. Reference is made to the works of snoek6 and Neel7 for a complete discussion. A brief exposition of the principal ideas may be in order here, as follows. On the basis of the simplest model, resistance against domain wall motion increases with time after demagnetization due to the diffusion of interstitials to preferred sites created by the magnetostrictive tetragonolization under the strong magnetic field. Thus permeability, measured with a small field after the abrupt removal of the large field, will continuously fall with the process of diffusion of the interstitials, and the total "time decay" (or "time decrease") should be proportional to the amount of interstitial in solid solution. In the present report, use is made only of the total time decay rather than of the nature of the progress of the decay; the only problem involved in this approach is the need for assurance that only one interstitial is contributing to the effect as used. It is felt that the special use made here of the total time decay warrants the conclusions. Other work has been going on elsewhere on the detailed study of the nature of the time decay.8'9 EXPERIMENTAL A) Materials—12-lb ingots were made in a vacuum furnace from high-purity iron and by a series of hot and warm reductions were brought down to 14-mil strip. This was cut into 25-cm epsteins. The pure iron was decarburized at 750 °C by hydrogen. The time decay measurement for the decarburized iron (see below) indicated a satisfactorily low starting level of interstitials. Grain growth to grain sizes of 1 to 10 mm was produced in the pure iron by a 700" anneal in hydrogen after a critical reduction of about 7 pct as suggested by previous trials. No measurement of texture in the pure iron was made. The grain size was taken to be large enough to be beyond any sharply critical size regarding solubility. B) Infusion of Carbon—Since the permeability measurement required about two dozen epsteins, a special method of carbon infusion had to be developed to ensure homogeneity of infused carbon. This was accomplished by setting the samples edgewise in a

Jan 1, 1961

By Richard G. Warren, Michael M. Minor, Gayle J. Thomas

INTRODUCTION Los Alamos Scientific Laboratory (LASL) initiated its effort in the Hydrogeochemical and Stream Sediment Reconnaissance (HSSR), a part of the Department of Energy (DOE) National Uranium Resource Evaluation (NURE) program, in late 1975. Since that time, LASL has completed sampling of the Rocky Mountain states of New Mexico, Colorado, Wyoming, and Montana at a density of about one water or waterborne sediment sample per 10 km2 and has sampled about 85% of Alaska at a density of at least one per 25 km2. Analytical results for these samples are reported by National Topographic Map Series (NTMS) quadrangle. All collection and analytical procedures have been standardized from the outset (Sharp, 1977; Sharp and Aamodt, 1978). Until early 1979, only uranium results were reported for these samples; thereafter, results include analyses for at least 42 additional elements in the sediment samples. Each LASL HSSR report also includes a discussion of the relationship of these analytical data to known or possible uranium resources; more recently, these data have been re- examined for their relationship to resources for other metals (Beyth et al., 1980; 1980a). Analytical results for LASL HSSR sediment samples are both comprehensive, including 43 elements, and precise, allowing close inter-comparison of data between quadrangles. A recent HSSR study shows that elemental concentrations in sediment samples from the Dixon Entrance quadrangle in Alaska are insensitive to the choice of sieve size fraction and do not vary significantly between stream locations a few meters apart, except for extremely high elemental concentrations (Warren, et al., 1980). Elements that are particularly reproducible include thorium, hafnium, and the .ram earth elements. Fortunately, sensitivities for these elements, which are often associated with uranium, are excellent by the nondestructive analytical technique of neutron activation analysis that LASL employs. Wet chemical techniques may not always give reliable results for these elements in sediment samples due to the difficulty of dissolving the resistate mineral phases that normally contain these elements. LASL has recently open-filed results for a large number of NTK3 quadrangles; to date analyses have been reported for about 605 of the quadrangles within the states of the Rocky Mountain region. As a result, uranium analyses am now complete for all sediment samples collected from the state of Wyoming. We have chosen to sumnarize the analytical results for Wyoming and portions of adjoining states hereafter termed "the ~ Wyoming regionn (Fig. 1 ) ; nearly 24 000 uranium analyses and nearly 17 000 analyses for 42 additional elements are available for sediment samples collected from this area. The DOE open-file report numbers are shown in Fig. 1 for reports open filed before September 1, 1980. The Wyoming region provides an ideal area for an examination of regional geochemical patterns ex- hibited by sediment samples. It is endowed with a variety of exposed geologic units and with widely distributed uranium districts associated with host units of several ages. However, discussion will focus on rock units of Eocene and Precambrian ages because they are widely exposed and host the majority of the uranium resources within the region (Fig. 2). Miocene units are also widespread and host mineralization in the Brown's Park Formation (Fig. 2). Epigenetic uranium mineralization occurs in sand- stones of lower Eocene age such as the Wasatch, Battle Springs, and Wind River Formations whereas vein type mineralization occurs in Precambrian crystalline rocks. Precambrian rocks within the region consist of a variety of granitic and meta- morphic rocks with l .4-2.8 billion year ages, except within the Uinta Arch, where they consist of a sequence of very low grade metamorphosed or unmetamorphosed 1.0 billion year old sedimentary rocks. Precambrian rocks have served as sources for much of the clastic material comprising the lower Eocene units, and may also have provided the source for the uranium in mineralized Eocene or Miocene sandstones (Stuckless, 1979). The remainder of this paper describes the relationship of elemental concentrations in HSSR sediment samples to exposures of Eocene and Precambrian rocks. The results are used primarily to determine where these Precambrian rocks might provide the most suitable uranium source areas and to infer the direction of transport toward adjacent depositional basins during the Eocene.

Jan 1, 1980

By R. J. Wagner, G. H. Gronhovd, A. J. Wittmier

The paper describes the results of a series of full-scale boiler tests run to determine the ash fouling characteristics of a North Dakota lignite as a function of sodium content of the coal. Four levels of sodium were investigated and rate of fouling was determined both by boiler performance and by specially constructed probe equipment. Discussed is information on chemical and physical properties of the ash deposits. The vast lignite deposits in North Dakota are becoming increasingly important as a source of low-cost fuel for power generation. A new 200-megawatt lignite-burning plant located near Stanton, N.D., was placed in operation early in 1966. Another 172-mega-watt unit in the same area is scheduled for operation late in 1966, and plans have recently been announced for a 212-megawatt unit to be in operation by 1970. If these plants show good performance, western North Dakota could become a major power production center for a large geographic area in the upper midwest. One of the problems associated with the use of lignite in power boilers is its tendency to form troublesome ash deposits on boiler tube surfaces. This problem varies considerably from one lignite-fired boiler to another and is dependent upon such factors as source of lignite, boiler design, load factor, tube metal temperatures, and soot-blowing practices. This report presents data on sodium content* variation in a North Dakota mine, describes the results of a series of tests performed to determine the relationship between ash fouling tendencies and the sodium content, and tells how the mining company and electric utility have coordinated their operations to reduce the ash fouling problem. GENERAL BACKGROUND Until recent years it was generally assumed that North Dakota lignite from a given mine had qualities peculiar to that mine, but that within the mine, the lignite was quite uniform. In 1959, the Otter Tail Power Co. installed a 53.5-megawatt lignite-burning unit at its Hoot Lake plant, Fergus Falls, Minn. Shortly after the unit was put into operation, it was noted that at certain times under high load conditions, ash fouling problems were quite severe, but not consistent or predictable. Each time fouling occurred in the unit the position of the loading shovel at the mine was noted. Within two years it became apparent that there were certain areas in the Knife River Coal Mining Co. mine at Beulah, N.D., where the lignite apparently had a high fouling tendency for the Hoot Lake unit. Results from analyses of the coal did not show large differences in moisture percentage, ash percentage, heating value, or ash fusion temperature between the highly troublesome and less troublesome coals. After three years of operation, the troublesome areas had been quite well defined and the mining company started a procedure of bypassing these areas when load conditions at the plant were high and then returning to the troublesome areas to load the lignite during the summer months when peak loads were lower. It was noted that the lignite from the areas which caused severe fouling under high load conditions produced much less fouling at the lower summer loads. However, bypassing certain areas in the strip pit caused the mining company to disrupt their continuous loading schedule, which in turn upset their continuous stripping schedule and made for less efficient mining operation. Meanwhile, at the Hoot Lake plant, the number of soot blowers on No. 2 boiler had been increased from 30 to 55, and a very rigorous blowing schedule had been adopted resulting in soot blowers operating at least some part of 21 hrs per day. Fouling problems continued, with a resulting reduction in plant economy and reliability. During this period the Federal Bureau of Mines Coal Research Laboratory at Grand Forks, N.D., had initiated various research programs relating to the study of lignite ash and ash fouling problems. One project was a survey in which full seam samples were obtained from various locations in all the major

Jan 1, 1968

By Robin O. Williams

The increase in internal energy as the result of deformation has been measured for lead, aluminum, silver, nickel, iron, and zirconium by using rapid, adiabatic compression. The stored energy increase is roughly Proportional to the strain; the propor-tionality constant increases rapidly with increasing melting point. The fraction of the mechanical energy which is stored increases more slowly, since the strength of the metals also increases with melting point. The values of the stored energy are considered accurate to about 10 pet. The present values appear about 50 pet larger than the more reliable published results where comparisons are possible. It is possible that this difference is due to the high strain rate used in this investigation. Immediately after deformation all these metals release energy at a rate roughly proportional to (time)-'. This release is considered to be associated with dislocation motion but in aluminum (and copper) some additional process seems to be present. This release can represent 20 pet or more of the stored energy. WHEN pure metals are plastically deformed, most of the mechanical energy is converted into heat. The energy remaining within the metal is significant in that it is the energy of the disorder produced and thus detailed knowledge of this energy is a powerful tool in understanding the nature of deformational disorder. While much effort has been expended on this problem, the amount of information available is limited. The situation as of 1958 has been carefully reviewed by Titchener and ever.' The present results have been obtained by a new experimental approach to this problem. The method necessitates high-strain rates which make comparisons with published results less certain, but a high-strain rate is an advantage in that the energy release immediately after deformation can be followed. EXPERIMENTAL PROCEDURE In the experimental method used, the internal (stored) energy is given as the difference between the mechanical work used in deforming the sample and the heat which is released (the first law of thermodynamics). The work is supplied by two identical hammers swinging freely from a fixed height, the available energy being the product of the mass, the gravitational constant, and the distance through which the center of gravity moves. The initial temperature rise of the sample represents the heat produced by the deformation. The sample temperature is determined by a small thermocouple embedded in and supporting the sample. This process can be repeated over and over to produce increased strains. Most samples are run through about five cycles to a total strain of around 0.7. Further details are covered elsewhere. The determination of the heat is dependent upon the sample weight, its specific heat, the rise in temperature, and any gains or losses to the surroundings. One is dependent on published results for specific heals (the values were taken from a collection).3 The values must be accurate to about 0.1 pet in order that they not affect the results. The best values thus do not contribute to the uncertainty, but this is probably not always the case. The accuracy of the temperature rise is limited primarily by knowledge of the thermocouple characteristics over short temperature intervals, but careful calibration eliminates this as an important factor. One can calculate readily the heat flow between the sample and hammers if the time of contact and the sample temperature are known and if there were no oil at the interface. Assuming the maximum temperature difference, upper values for this interchange have been calculated (the time of contact is determined from the decrease in sample length) and it may or may not be significant. However, no correction is colnsidered necessary because of the presence of a thin oil film which has a thermal conductivity much less than the metals. Except for the possible uncertainty in specific heat, the heat is considered to be adequately known. The mechitnical losses which are recognized as important are: 1) friction between the sample and the hammer:;, 2) the kinetic energy in the hammer suspension system which may not be entirely usable, 3) the rebound energy of the hammers, and 4) the vibration of the hammer heads. All these have been covered in detail elsewhere2 and only the more significant points are made here. The friction turns out to be small except for soft materials (lead)

Jan 1, 1962

By R. C. Davis, R. F. Berry, G. W. White, B. T. O’Connell, L. A. Stacha

The formation density logging tool provides a radioactivity measurement that yields formation densities in situ. The relationship between bulk density and porosity is well understood. With knowledge of grain and fluid densities, porosity may be computed from the indicated formation bulk densities in shale-free formations. The porosities thus determined may be used with a resistivity log for water-saturation determinations. One technique utilizes a density vs resistivity plut. A plot of density vs Sonic-log transit time is used for porosity determinations in shaly sands. This method is particularly suited to wells drilled with oil-base or salt muds. In shale-free formations, comparisons of density values nnd neutron-log readings are used to identify lithologr and, thus, to select appropriate values of grain density for porosity computations. Through the use of Formation Density, Sonic and neutron logs, the interpretation problems caused by complex matrix lithologies are simplified. Other applications of the Formation Density log are found in the identification of minerals in evaporite deposits and in yield determinations of "oil shales". INTRODUCTION Widespread field application has demonstrated that the measurement of formation density is a useful and revealing technique for well logging. Responding to the bulk density variations of the formation, the Formation Density log affords valuable data on the porosity, lithology and fluid content of the formations. Although not without its own limitations, the Formation Density tool may provide effective interpretation under conditions that hamper or preclude the use of other porosity devices. When used in conjunction with other devices, such as the Sonic or neutron, complex matrix conditions may be better understood, defined and evaluated. A previous paper' described the valuable contribution of the Formation Density tool in the logging of empty, or gas-filled, holes. The purpose of the present paper is to describe applications of the device in liquid-filled holes. THE FORMATION DENSITY TOOL The Formation Density tool was devised to measure the bulk densities of formations in situ. Actually, the device responds to electron density, but in the overwhelming majority of cases of interest, the electron density is very closely proportional to the bulk density. In other cases appropriate corrections can be made if necessary. Comparisons of log-derived densities with true densities for the more common matrix minerals are shown in Table 1. The tool consists of a gamma-ray source and detector mounted in a skid which, during the logging operation, is in contact with the borehole wall (see Ref. 1 for schematic). Gamma rays are emitted by the source and diffused through the formation. The number of diffused gamma rays reaching the detector at a fixed spacing from the source are counted. An increase in counting rate by the detector indicates a decrease in bulk density in front of the skid. Conversely, a decreased counting rate signifies an increase in bulk density. A measurement of hole diameter, between the face of the skid and that of the eccentering arm, is recorded simultaneously with the measurement of diffused gamma rays. Since the tool is a wall-contact device, the size of the borehole has little influence, provided good contact is maintained with the wall of the hole. Only in extremely large or small boreholes does the actual diameter become significant. However, for most accurate measurements the borehole size should be taken into account. Fig. 1 presents the departure curves for the conversion of counting rate to bulk density for liquid-filled holes of various sizes. It is of utmost importance that the skid maintain good contact with the wall of the hole. If, due to roughness or caving, there is mud between the skid and the formation, the tool will include in its response the relatively low-density mud, and the apparent density reading will be too low. Normally, permeable beds do not cave appreciably, so that reliable readings are usually available for zones of interest. Nevertheless, the caliper reading over the zone of interest should be examined for any wall roughness. When mud cake exists between the skid and the formation, the Formation Density log sees it as part of the formation. When thick mud cakes exist, a correction is required. For best results in wells having thick mud cakes,

By A. V. Bradshaw, R. I. L. Guthrie

The behavior of large bubbles in the size range 4 to 25 cm3, rising through molten silver, has been studied. It was found that rising velocities were equivalent to those in aqueous systems of low viscosity. Mass transfer coefficients for oxygen bubbles dissolving in silver were found to be 0.036 ± 0.007 cm sec-1, being close to those predicted for transfer through the front surface of the spherical cap bubble only. It is suggested that the surface active nature of oxygen in silver could account for the relatively low coefficients obtained. MANY metallurgical processes involve interactions between gas bubbles and liquids. Examples include the removal of carbon monoxide in Open Hearth Steelmak-ing, the removal of sulfur by blowing air through copper matte during converting, and the removal of hydrogen from steel during vacuum degassing or inert gas flushing. The steps involved in such refining processes include; transport of the dissolved species to the bubble interface, adsorption and chemical reaction of the species at the interface, desorption of product molecules from the interface, and transport of product gas into the bulk gas phase of the bubble. It has been concluded1 that all the interfacial steps involved proceed so rapidly at steelmaking temperatures that transport of the solutes, present in the metal, become the important rate controlling factors provided nucleation phenomena are not restrictive. The O-Ag system was chosen for the investigation into gas bubble-molten metal interactions due to the relatively high solubility of oxygen that enables rates of oxygen transfer to be measured from changes in bubble volume. Other advantages of this system include the absence of a stable oxide phase at an oxygen pressure of 1 atm and the relatively low melting point of the metal which permits the use of a metallic container, providing that it is resistant to oxidation. In those metallurgical processes where bubbles have an important influence, bubble volumes are usually greater than 5 cm3. For this reason the present study relates specifically to single large bubbles of oxygen rising in silver. These bubbles adopt the characteristic spherical cap shape similar to that shown in Fig. 1 for a 30 cc bubble rising in water. After an initial investigation to determine the velocities of inert (nitrogen) bubbles rising in molten silver, experiments were carried out with oxygen and the rates of mass transfer between the oxygen bubbles and the silver were measured. EXPERIMENTAL Apparatus. The apparatus, Fig. 2, for containing molten silver, was constructed from "Nimonic 75" Alloy (75 pet Ni, 20 pet Cr, 5 pet Fe, Mn) and provided for the release of single bubbles from an hemispherical cup, situated at the bottom of the column. The cup was turned by translating the rotation of the drive shaft through 90 deg. This was accomplished by the use of a bevelled gear system, and a smooth drive was provided by the lubricating action of the silver on the gears. Since reliable high temperature seals at 1000°C were found to be impracticable, the filling and drive shaft tubes were extended outside the 3.5 kw resistance wire tube furnace, where connections were made using easily accessible O-ring seals. The apparatus remained gas tight to the atmosphere at pressure differentials far in excess of those used. The filling tube was connected via a small bore tube to the differential pressure transducer. Gas could be bubbled into the inverted cup from two i-in. tubes which passed down the inside of the column to preheat the gas. The temperature of the silver was maintained at 1020°C during all experiments. Measurement of Bubble Volume. In order to calculate mass transfer rates, it was necessary to obtain a continuous record of the bubble's volume during its passage through the column of molten silver. The method adopted for measuring the bubble volume involved closing off the top gas space to the atmosphere prior to each experiment, and recording the variation in gage pressure of this space during the formation and rise of the bubble. Since any change in bubble volume results in an equal change in top space volume, Boyles Gas Law may be applied (for isothermal con-

Jan 1, 1970

By Jozef S. Stachulak

Inco Limited operates 11 underground mines in the Sudbury District. The mines are located on the rim of the Sudbury Basin, an oval with the axis in the range of 27 and 60 km. The ore dips to at least 3000 m below surface. The ores are mined primarily for nickel and copper. Total ore production from underground is in excess of 55,000 tons per day. Over 40 surface fans have been installed since the late 1960's. All of the fans are adjustable pitch, axial flow units. A major factor influencing ventilation design in the last 30 years has been the introduction of diesel equipment underground. Volumes per fan have ranged from 60 to 330 (cubic metres per second), with motors from 100 to 2500 hp. Fans of the axial flow type have been in common use for main fan installations at Canadian mines for many years. The standard arrangement has been to mount these fans horizontally, i.e. with the fan shaft and the long axis of the housing horizontal. This is a natural arrangement for an underground fan, but for a surface installation, a vertically mounted fan has definite advantages. The surface area taken up by a typical vertical fan installation is generally about one quarter of that with a horizontal fan of the same capacity. (1) This is not a problem with isolated fans and flat surface outcrop sites, but where the installation is to be near existing buildings, or where there are poor surface soil conditions, space and cost considerations greatly favour vertical fans. MAIN FANS INSTALLED There are 43 main surface fans in operation at 11 mines. Twenty-seven of these fans are supply units, and 75% of them are vertical installation. The remaining 16 units are main surface exhaust fans, with predominantly horizontal installation. Within the last five years, some 20 main booster fans have been installed underground at several mines. Axial flow fans, with adjustable pitch blades, are used for both surface and underground installations. Exhaust fans are equipped with stainless steel or cast aluminum blades. Main underground fans are arranged horizontally and the majority of them have a floating shaft between the fan shaft and the motor. (2) The size of the fans in service varies from 1.8 m to 5 m in diameter, with the majority ranging from 1.8 to 2.5 m. The pressure produced by these fans varies from 0.25 kPa to 2.0 kPa. At Inco Limited, two main fans in parallel are preferred, rather than a single fan, so that if one fan fails, the remaining fan can still supply up to 70% of normal air quantities, while the damaged fan is repaired. This requires closure doors on each of the fans so the fan can be isolated in case of failure. It is more expensive than a single fan, but results in less production interruptions. The fan installations are well away from sharp inlet and outlet bends. FAN DESIGN INTEGRITY Both the mine operator and the fan manufacturer must understand that the main fan is critical to the mine operation, and that everything technically possible must be done in design and manufacture to ensure the highest degree of reliability. Some of the design parameters and criteria, based on Inco experience, are outlined and discussed below. RESONANT FREQUENCIES AND HOUSING MODEL ANALYSIS Any fan assembly will have many different resonant frequencies. It is a challenge to the designer to arrive at a design in which forcing frequencies do not coincide with any of these resonant frequencies to produce unacceptable vibration levels in operation. Finite element analysis is a useful tool that can be used to identify the most critical of these, so that housing and blade stiffness can be adjusted to change any resonances that might be close to forcing frequencies. Shaft critical speeds should be at least 25% above the fan operating speed, and there should be sufficient separation between other resonant and forcing frequencies to avoid excitation that might result in high vibration levels. QUALITY ASSURANCE Radiographic Blade Examination Mine fan blades are normally cast in small lots. To ensure that the castings are sound, a full radiographic examination is recommended in the highly stressed lower 1/3 of the blade.

Jan 1, 1995

By A. Kenneth Schellinger

THE terms surface tension .and surface energy are well known when applied to liquids and are generally described by referring to the excess energy of the air: liquid interface as a result of unsaturated molecular forces surrounding the surface molecules of the liquid due to the presence of the air phase on one side. Such unbalanced forces produce the familiar water droplet of spherical form and are generally summed up as a surface tension measured in dynes per centimeter which can be shown mathematically to be equal numerically to a corresponding surface energy expressed in ergs per square centimeter. A specific surface energy, however, is best thought of as the energy necessary to produce one unit of new surface on a substance. Hence, in producing a bubble in a flotation cell the impeller must supply surface energy corresponding to the air: liquid interfacial area on the interior of the bubble. Inasmuch as it is relatively easy to extend or contract the surface of a liquid, there are a number of successful methods for liquid surface tension, or energy, measurement based upon surface deformation. This happy state of affairs does not, however, extend to solids, which are considered to possess surface energies for the same reasons as do liquids, i.e. because of unsaturated ionic bonds at the solid gas interface. As in the case of the flotation cell producing surface on liquids as new bubbles, it takes energy to produce new surface on solids as new particles. As every mill man knows, this surface is produced on mineral solids in a grinding mill by the action of a tumbling mass of iron balls. But here so much energy usually is wasted by the inefficient action of these balls that a large amount of heat is generated, and the surface energy production may be easily confused with the energy necessary to produce this ineffective heat. The tumbling balls and fracturing minerals ultimately take their energy from a rather large electric motor. It has been variously estimated that from 10 to 20 pct" only of this energy from the motor does not appear as heat and may be presumed to appear as surface energy on the minerals present.. Such a production of new surface on the mineral phases is accompanied, of course, by a size reduction that is inevitable as more and more mineral interior molecules become surface molecules by the fracture exposure. This size reduction of mineral particles, although the most obvious feature and perhaps the sole object of the milling operation, is from this energy viewpoint the outward manifestation of the production of surface energy only. Measurement of the characteristic surface energies of pure minerals and their various mixtures in ores would be a step towards understanding of the energetics of the commercial grinding operation. In addition, the characteristic surface energy of a mineral is probably a physical property specific for that mineral, and therefore, from a scientific standpoint, should be measured. It is interesting to note that, in contrast to the large body of work on the surface tensions of liquid systems and biological systems, the field of solid surface energies has been neglected. Prior to. 1920 it is difficult to find more than one or two references to work on solid surface energies in Chemical Abstracts. Since 1920 such references number somewhat less than 100, while those on liquid systems are numbered in the thousands. Much of this apparent neglect of the field of solid surface energies (the term is intended to be somewhat inclusive at this point and refers both to the solid: gas, and the solid: liquid interface) is because of the lack of a reliable method of measurement rather than any lack of scientific curiosity. It was, and still is, difficult to produce new surface on a solid without the simultaneous production of interior changes in the same solid which may consume part of the energy used. The extension in the surface area can be measured, but the interior crystal-

Jan 1, 1952

By M. J. Marcinkowski, E. N. Hopkins

An investigation has been made of the ß(fcc) — a(hexagonal) transformation which occurs in lanthanum using both electrical resistivity and transmission electron microscopy techniques. It has been shown that the ß phase can be retained below the transformation temperature by rapid quenching but that the sample immediately begins to transform to the a phase. The transformation is observed to nucleate in the vicinity of inclusions. Based on the above observations, a detailed model of the transformation has been advanced which involves the nucleation of an extrinsic stacking fault bounded by a pair of Shockley partial dislocations in the vicinity of some heterogeneity, i.e., an inclusion. The stress field of the resultant dislocation pair acts to nucleate extrinsic faults in adjacent planes and leads quite naturally to the B-a conversion with a minimum of strain energy induced in the crystal. LANTHANUM possesses an fcc structure ß) (8) upon cooling transforms to a hexagonal modification (a) in much the same way as cobalt. The one exception, however, is that the stacking sequence of the closest packed planes in a La is ABAC ABAC, and so forth,1 whereas in cobalt it is ABAB, and so forth, i.e., hep. Mainly on the basis of transmission electron microscopy techniques, there seems to be little doubt that the 0 — a transformation in cobalt involves a dislocation mechanism2 although its exact nature still remains obscure. Although the ß - a transformation in lanthanum is somewhat more complex than that occurring in cobalt, it was thought that its very uniqueness would be helpful in understanding fcc — hexagonal transformations in general. Such a general understanding of these transformations is important since they represent what are perhaps the simplest of the martensitic class of transformations. The experimental techniques used were those of electrical resistivity and transmission electron microscopy. EXPERIMENTAL PROCEDURE The lanthanum used in this investigation was prepared by the calcium reduction of lanthanum fluoride in a tantalum crucible under an argon atmosphere as described by Spedding et al. The residual calcium was removed by vacuum remelting in a tantalum container. Portions of the metal were then analyzed by emission spectroscopy as well as vacuum fusion. The amounts of the various impurities that were found are listed in Table I. A portion of the lanthanum ingot was swaged at room temperature into 0.030-in.-diam rod for the resistivity samples while the remainder was rolled into 0.010-in.-thick sheet for the transmission electron microscopy phase of this investigation. In order to eliminate the plastic deformation induced in the samples during fabrication, they were sealed in evacuated tantalum lined quartz capsules and annealed for 1 hr at 700° C. Specimen resistances were measured using the conventional "four-wire" technique described by MacDonald, 4 employing a type K-3 Universal Potentiometer and a standard 0.001-ohm resistor, both manufactured by Leeds and Northrup Co. By taking into account all of the possible errors in the apparatus, it was felt that the absolute resistivities of the approximately 0.87-in.-long specimens measured are reliable to 3 pct. Resistances from room temperature to 700°C were measured using a vacuum furnace. In order to avoid sample contamination by the thermocouple, chromel-alumel leads were spot-welded into a tantalum shield which in turn was welded to the lanthanum specimen. Resistances below room temperature were obtained by transferring the sample to a helium gas-filled quench tube and slowly dripping liquid nitrogen into a surrounding dewar flask. A steady reduction of temperature to about —190°C was completed in about 23 hr, and the resistances were measured at various temperature intervals. As will be shown shortly, rapid quenching from above about 350°C was sufficient to suppress the B -a transformation initially but subsequent annealing at lower temperatures leads to a partial ß --a conversion. To investigate this aspect of the transformation, the samples were suspended in the hot zone of a helium-filled furnace from which they could be rapidly dropped into the quench tube mentioned previously which was now

Jan 1, 1969

By R. A. Morse, W. O. Keller

The properties of limestone reservoir rocks such as the distribution and degree of continuity of the pore systems, and the relative volumes and permeabilities of the systems making up the complex cause large variations between performance of individual limestone reservoirs and their susceptibility to secondary recovery methods. The effects of these factors on the mechanism of fluid flow cannot be adequately evaluated with presently developed concepts, laboratory data, and geological information. The observance and interpretation of the performance of individual limestone reservoirs provides, at present, the most adequate approach for evaluating the integrated effects upon performance of the many. now immeasurable variations in the properties of limestone reservoirs. INTRODUCTION The development and application of techniques for increasing the efficiency of oil recovery from natural reservoirs is a problem of primary importance to the industry. During the past several years, a great deal of effort has been expended by the technical personnel of the industry toward the improvement of present known methods of oil recovery. and evaluating the factors which control the susceptibility of particular reservoir types to economic application of secondary recovery methods. Providing adequate and accurate laboratory data on the properties of the reservoir rock and its contained fluids. together with good production statistics, are available, methods have been evolved for estimating with reasonable accuracy the performance of an oil reservoir under either continued natural depletion or conditions imposed by introducing additional displacing fluid into the reservoir from an extraneous source through the injection of gas and/or water. The susceptibility of limestone reservoirs to secondary recovery by gas injection is very much dependent upon gas-oil relative permeability relationships for the reservoir in question. In a rock formation in which the porosity is of the intergranular type such as is found in sand stones and some non-fractured dolomites, a representative sample of the pore structure can be obtained in a small core plug. In this type of reservoir, it has been shown that relative permeability data obtained from laboratory experiments can be Properly applied to evaluate the flow relationships actually observed during the depletion of a reservoir. In addition, a good idea of the fraction of the reservoir which will be swept by the injected gas may be obtained from the spacing pattern used and the permeability profile of cored wells. From these data, it has been demonstrated that reliable estimates of performance and recoveries under gas injection operations can be made for reservoirs in which the Porosity is of the intergranular type. Limestone reservoirs on the other hand often present much more complex problems. One reason that the performance of limestone reservoirs is so variable is that there may be, in reality. two or more pore systems, the integrated performance of which will depend upon the physical properties of each system and their inter-relationship. For instance, in a limestone reservoir, the main pore structure, as far as void spaces for storage of hydrocarbons is concerned, may be represented by the intergranular openings of the rock. Usually in limes and dolomites, the intergranular pore openings are very small and the matrix permeabilities extremely low. Often, as in the case of Many dolomite and oolitic lime reservoirs, this is the only pore system, and performance is observed to be very similar to that of a sand stone of similar permeability. However, in the great majority of' the limestone reservoirs, there is present, in addition to the intergranular pore system, a complementary system of openings caused by fracturing or solution.',' The openings in the latter system are usually many times more permeable than the intergranular pore system due to their much larger size, and may contribute almost all the fluid carrying capacity of the formation, even though their volume may be a very small part of the total pore space in the reservoir. Obviously, the performance of such a complex under either primary or secondary control will deend upon the distribution and degree of continuity of both systems, the relative volumes and permeabilities of the

Jan 1, 1949