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By Edward Steidle

THAT veterans are crowding the colleges is no longer news; 78 per cent of the 1916-47 enrollment in mineral industries curricula in the United States were veterans, but the rapid comeback from an estimated 1262 total mineral industries students in 1944-45 to 11,422 in 1946-47 is almost astonishing. The figure, which includes 1008 graduate students, is a substantial increase over the previous top record of 9619 in 1938-39. A small part of the increase is caused by the larger number of women entering the field, of whom there were c 9 in 1916-47. Petroleum leads the curricula with 34.5 % of the enrollment, metallurgy is second with 28%, and mining is third with 18%. Table 1. shows all curricula offered and those accredited by ECPD. Using the Mississippi River as a dividing line, 31 colleges in the East and 27 in the West offer curricula in the mineral industries.

Jan 1, 1948

By Basil B. Zavoico

ALTHOUGH the American petroleum industry was affected by the Second World War from its early beginning it was not until Dec. 7, 1941- that the industry was placed on full war footing. Even throughout most of 1942 the American overseas operations were limited and not until late in the year did expansion of military activities, more particularly the offensive in North Africa, affect the domestic supplies to such an extent that critical deficiencies developed locally in this country, particularly along the East Coast. The definite outlook for greatly expanded offensive operations by the United States on both Atlantic and Pacific fronts makes certain that during 1943 the domestic situation will. not be alleviated; rather it may become even more critical even though additional transportation facilities, now being built and planned. will be completed from the southwestern producing states to the East Coast.

Jan 1, 1943

By G. G. Biggar

A MATERIAL contribution to the success of our Armies in the field has been the portable pipe-line system. These are the words of Brigadier General R. F. Fowler, chief of the supply division of the War Department. The portable pipe line is one of the "secret weapons" the American forces employed in their swift advances through Tunisia, Sicily, and Italy. Constructed of a light steel so flexible it can be snaked around trees, it can be laid at a rate of ten to thirty miles daily right up to the fighting fronts. It has played a major role in supplying combat troops with products varying from petroleum to water.

Jan 1, 1943

By John M. Tinsley, Calvin D. Saunders, H. K. van Poollen

In the past few years much con-sideration has been given to the evaluation of the effect of hydraulic fracturing on the productivity of wells. Generally, these studies included the evaluation of fracturing materials, fracture extension and formation damage due to the use of various fracturing fluids. Only little consideration has been given to the characteristics, and in particular the flow capacity, of the fracture itself and its effect on well productivity. This paper presents the results of laboratory investigations pointed toward fie evaluation of the efficiency of various fracrures with special emphasis on the flow capacity of these fractures. Data presented in this paper are the results of both an electrical model study and physical testing. Under consideration are (I) effect of overflush, (2) premature production of well after treatment, (3) "tailing-in" with coarse sand near the end of the treatment, (4) effect of propping agent size and concentration, (5) reduction in effective frac-ture permeability caused by formation caused by formation fines, silt and clays, and (6) effect of various fluids on formation strength and competency. The results of this investigation indicate that the flow capacity of a fracture is affected by any or all of the various parameters mentioned above. The authors believe that a better understanding arid utilization of these factors should result in more efficient formation fracturing. INTRODUCTION Hydraulic fracturing has become almost a standard practice of many companies for stimulating production from old and new wells. Although most companies utilize this service, techniques of application vary widely between companies and areas. Probably too often when a well in an area responds favorably to a particular technique all future wells in the same area are treated in a similar manner. Possibly a modification of the technique would result in a further production increase. Variables, of which many are extremely difficult to evaluate from field results, hamper the selection of procedure changes. Attempts are being made by a number of organizations to analyze statistically treating techniques from production data. This is a very worthy and necessary approach but very possibly laboratory investigations may aid in evaluating some of the variables which tend to affect the results of a fracturing treatment. Some of the factors cannot be studied from practical field experience and only laboratory tests can show the possibilities which might exist. One of the factors which appears to be of major concern today is the flow capacity of the created fracture and how it can be changed. Papers on this general subject have been primarily concerned with the size of propping agent and the extent of fracture. Papers have also been written on the possible permeability damage to formations by fracturing fluids. In addition, it might be possible that another type of flow restriction is prevalent. This would be a restriction of flow through a sand-packed frac- ture caused by foreign materials integrating within the propping agent. This paper presents preliminary data obtained in an attempt to evaluate the effect of some factors affecting flow through sand-packed fractures. No attempt is being made to offer a fracturing technique adaptable to all areas and conditions, but to furnish data tending to show the possible effects which might be caused by variations in procedures and materials. PROPPING AGENT PERMEABLLITIES A hydraulically induced fracture containing sand as a propping agent may theoretically be classified as a packed-sand system. The flow of fluids through such packed systems has been the subject of much research. Although there have been numerous methods proposed for the evaluation of such systems, most writers agree on the general properties affecting their flow capacity or permeability. These properties include porosity, particle size, sphericity and the roughness of the particle. In some methods of evaluation . the particle size and sphericity terms are combined to produce an equation which is a function of the surface area of the particles. In this study the permeability of various fracturing sands was both measured and calculated. The apparatus for the permeability measurements consisted of a 52-in. Lucite tube with a 2.5-in. ID. A screen and drain plug were fitted in the bottom of this tube to retain and hold the sand in place while allowing fluid flow. Two pressure taps consisting of thin, highly perforated

By Frank V. Hicks

THE following paper-in no sense a technical paper-is a summary of a safety campaign instituted by a coal-mining company to improve an unfortunate safety record. The experience should be suggestive equally to coal and metal-mining companies. With few precedents to follow in the beginning, the course was charted by trial and error. The endeavor, often disheartening, finally resulted in the capture of the most coveted safety trophy in the mining industry, "The Sentinels of Safety," awarded by the Hercules Powder Co. of Wilmington, Del., through the U. S. Bureau of Mines. The period described covers the 10-year interval, 1924 to 1933, the year 1933 being that for which the award was made. The coal company considered has produced annually for a number of years an average of 2,750,000 tons of coal, employing at various times from 1.800 to 3000 men. Prior to 1924, the

Jan 1, 1935

By Jay A. Carpenter

WAR?S impact on Nevada mining and rnetallugrcal operations has brought about a rapid rise in the gross value of the ores mined and milled for the atratezic metals, and a sharp decrease in that for the precious metals. The State?s total production over the present war years will averaged out 10 per cent above the good record of $39,000,000 in 1937. However. this annual production is low in contract to that of nearly $47,000,000 in 1877 in the days of the great bonanza on the Comstock, and that of nearly $49,000.000 in 1918 during the last World War..

Jan 1, 1944

By W. F. Chiao

Ultrasonic attenuation, a, measurements in the frequency range of 5 to 55 mc per sec have been studied to determine their quantitative relationship with the following three variables of mixed microstructures in steels: 1) the volume percent, XF, of polygonal fer-rite in mixed structures of martensite and polygonal ferrite in Fe-Mo-B alloys: 2) volume percent, XA, of retained austenite plus martensite aggregates in high-carbon steel; and 3) substructural differences between 100 pct bainitic ferrite structures formed at various temperatures. The quantitative relationship obtained in the first two conditions by plotting a us the known structural parameters can be expressed, respectively, as: where al, a 2 and C1, Cz are constants. In the third condition the nature of the attenuation depends on the state of dislocations generated at the transformation temperatures and also on the alloy composition. From these measured results, the mechanism of ultrasonic attenuation caused by these mixed microstructures can also be studied. MUCH interest has recently been shown in the application of ultrasonic attenuation and wave velocity measurements to the study of the microstructural characteristics of steels. The general aims of most of the investigations in this field can be grouped into two categories: one is to study the mechanisms of ultrasonic losses caused by the characteristic phases in the microstructure of steel,''' and the other is to develop nondestructive test methods and applications for quality control.~' 4 Apparently no work has been done on the evaluation of ultrasonic attenuation meas -urements as a means of quantitative determination of a given phase in the microstructure of a steel. It is well-established that the decomposition of austenite results in four main microstructural constituents—polygonal ferrite, pearlite, bainite, and martensite—and that each phase has different mechanical properties. Thus, when a steel consists of mixed microstructures, the mechanical properties can often be related to a quantitative measure of the volume percent of each phase present. This study relates ultrasonic attenuation measurements to: 1) the volume percent of polygonal ferrite in mixtures of martensite and polygonal ferrite in Fe-Mo-B alloys; 2) the substructural differences between 100 pct bainitic ferrite structures formed at various temperatures; and 3) the vol- ume percent of austenite in austenite plus martensite aggregates in a high-carbon steel. The choice of the specimen materials was based on the laboratory stocks which were suitable to produce the required mixed microstructures for this study. EXPERIMENTAL PROCEDURES Materials and Heat Treatment. Polygonal Ferrite Plus Martensite Structures. This mixture of phases was produced in a vacuum-melted Fe-Mo-B alloy. The alloy was hammer-forged at 1900" ~ to a -f-in.-sq bar. By isothermally heat treating the alloy at 1300° F for various times and then water quenching, variations in the amount of polygonal (or proeutectoid) ferrite can be controlled in a microstructure in which the balance of the material is martensite. In the present work, four different times of isothermal transformation were adopted; after heat treatment, the four specimens were machined for ultrasonic measurements. The compositions, heat treatments, and dimensions of the four specimens are listed in Table I. 100 pct Bainite Structures Formed at Different Temperatures. It has been well-established by Irvine et al.= that the presence of molybdenum and boron in ferrous alloys can retard the formation of polygonal proeutectoid ferrite and expose the bainitic transformation bay, so that a more acicular or bainitic ferrite can be obtained over a wide range of cooling rates. Their investigation6 also showed that the mechanical properties of fully bainitic steels are usually closely dependent on the substructural characteristics of the steels. For studying the substructural characteristics in completely bainitic structures, six Fe-Ni-Mo alloys, of which five were free from carbon addition and one with 0.055 pct C addition, were selected so that a wide range of hardness values for 100 pct bainitic ferrite structures could be produced by normalizing at 1900" F followed by air cooling. The different bainitic transformation temperatures were recorded during air cooling. All of the alloys were vacuum-melted and then forged at 1900" F to square bars. Data on the six specimens of these structure series are summarized in Table 11. Austenite Plus Martensite Structures. The high-carbon steel used to study austenite plus martensite structures was vacuum-melted and then forged into Q-in.-sq bar. The series of mixed structures of austenite plus martensite was produced by quenching the specimens from the austenitizing temperature to room temperature and then refrigerating them at various temperatures within the range of martensite transformation to produce different amounts of retained austenite. Data on the four specimens of this series are listed in Table 111. Quantitative Analysis of the Microstructures. The microstructures containing martensite plus polygonal ferrite were analyzed by the point-counting technique.

Jan 1, 1969

By A. S. Nowick, C. Y. Li

It is deMonstrated that quenching from an elevated temperataupe accelerates the grain boundary relaxation in two solid solutions (aAg-Zn and a Cu-Al). This result is consistent with the proposal that, in solid solutions, grain boundary relaxation occurs by a mechanism of' self diffusion. Nevertheless, an alternative possibilitg, that quenching introduces vacancies into the boundary itself, must also be considered. THE phcnomenon of grain boundary relaxation has been well known for many years,1,2 yet the mechanism of this process is very poorly understood. One of the most interesting suggestions which relates to the mechanism of grain boundary relaxation was that of Ke,3 who claimed that the activation energy for grain boundary relaxation and for lattice self diffusion were essentially the same. The implication is therefore that the elementary step in the two processes is the same. This suggestion is particularly startling in view of the fact that activation energy for self diffusion along a grain boundary is very significantly lower than that for volume self-diffusion. Later evidence5-7 showed that there really are two grain boundary peaks, one which appears in high-purity metals, and the other (which develops at a higher temperature than the first) which appears in solid solutions beginning at solute concentrations in the range of 0.1 pct. Data for silver6 show that Kg's hypothesis is surely incorrect for the grain boundary peak in the high-purity metal, since it has an activation energy of only 22 kcal per mole, but that the hypothesis may still be correct for the grain boundary peak in various silver solid solutions, for which activation energies in the range 40 to 50 kcal per mole are observed. If the elementary step in the grain boundary relaxation process were the same as that for self-diffusion, it would be expected that the relaxation process could be hastened by quenching, 2.c. by introducing a non-equilibrium excess of lattice vacancies. Such a quenching effect has already been demonstrated in the case of another anelastic relaxation process, viz., the Zener relaxation effect. The Zener effect, which occurs in essentially all solid solutions, may be attributed to the reorientation of pairs of solute atoms in the presence of an applied shear stress,' and therefore must take place by means of a volume diffusion mechanism. The hastening of this process through quenching9 has been one way of demonstrating that atom movements in the lattice take place through a defect mechanism, presumably single vacancies. In order to see if the grain boundary relaxation is affected by quenching, it is particularly convenient to compare the grain boundary relaxation with the Zener effect, by choosing a specimen for which both relaxation effects appear. Specifically, a fine-grained sample of a solid solution shows in the curve of internal friction vs temperature, first a peak due to the Zener effect, then a second rise (and eventually a peak at substantially higher temperatures) due to the grain boundary relaxation. The same phenomena are also observable in static anelastic measurements, such as creep at very low stress levels. Thus, for the same fine-grained solid solution, the creepstrain, when plotted against log time, falls on a sigmodial curve with a sharp inflection point, due to the Zener effect, which is followed by a second rise and inflection resulting from the grain boundary relaxation. To look for a quenching effect, static measurements are preferable to the dynamic internal friction measurements, due to the fact that quenching effects tend to anneal out too rapidly at the temperatures at which the internal friction is measured.9 RESULTS AND DISCUSSION Creep experiments in torsion were carried out in an apparatus similar to that described by Ke1, whereby a wire is held under constant torque and its angular displacement is observed as a function of time. The alloy Ag-30 at. pct Znwas selected because of the large Zener relaxation that it displays. The two samples used were a "coarse grained" wire with a mean grain size about twice the diameter of the wire (diam = 0.032 in.), and a "fine-grained" wire which had several grains across the diameter. In Fig. 1 a comparison is made of the creep curves at 160°C of these two samples after they had been cooled slowly from 400°C. Curve A, which represents the coarsegrained sample, shows a unique relaxation process due to the Zener relaxation, with a relaxation time, T , in the vicinity of 100 sec. Curve B, which represents the behavior of the fine-grained sample, on the other hand, shows first the same relaxation process as that in A, followed by a turning up of the curve which corresponds to the onset of a second overlap-

Jan 1, 1962

By J. Chipman

There is no better way of paying tribute to the memory of a scientist than by developing and carrying forward those ideas which he has contributed to science and which are for us the very essence of his immortality. For a lecturer who has not had the great privilege of stdying under Professor Howe or 'ven of knowing him in person, these ideas must be transmitted through the printed word. It is our great good fortune that Professor Howe left to us a rich heritage of publication, not only in his classic monograph on the "Metallography of Steel and Cast Iron" but in a wealth of earlier hooks and papers in the transactions of this Institute arid of other scientific and engineering bodies. An outstanding characteristic of this published record is the great breadth of interest and of vision which it portrays. His was riot a narrow specialization in only the scientific aspects of ferrous metallographg. On the contra1y many of his important contributions had to do with a far broader field of metallurgicial endeavor. He insisted that his students be well grounded in 1 he fundamentals underlying the whole field and not led into the narrow groove of specific applications. Among his first major publications we find papers on copper smelting, extraction of nickel, the efficiency of fans and blowers, thermic curves of blast furnaces, the cost, of coke, and the manufacture of steel. These are the papers of a metalhurgical engineer and it was among engineers that Henry Marion Howe made his early and well-merited reputation. These early engineering contributions display very clearly the strongly sctientific inclination of their author. The classic work on "The Metallurgy of Steel" published in 1890 contains a thorough and critical discussion of all that was known at the time concerning the alloys of iron and of what we would now call the physical metallurgy of steel. In addition it describes steel-making processes in use and some that had become obsolete, and points out in critical fashion the reasons for success and failure. Steel mill design and layout were included as well as some pertinent discussion of refractories. The book is indeed an embodiment of one of Howe's outstanding characteristics—breadth. It is both the science and the engineering of steel production as known in that day. One of Howe's earliest technical papers was entitled "What is Steel?" That was nearly seventy-five years ago when many new processes and new kinds of steel were being developed. The time was ripe for such a question and the answers which Howe was able to give were helpful in understanding the phenomena of heat treatment. Twenty-five years ago Professor Sauveur repeated the question as the title of the first Henry Marion Howe Memorial Lecture. It seemed to him that this question, "What is Steel?," had served as Howe's motto throughout the remainder of his life. Today I shall present for your consideration a question of another sort: "What is Sletallurgy?" Perhaps it is not too much to hope that in the answer we may obtain a clearer and possibly broader view of the nature of our science and our profession. The time is ripe for giving careful consideration to what we mean by metallurgy. If our Metals Branch is to become in fact an American institute of Metallurgical Engineers, it is essential that we understand what is meant by metallurgical engineering. I am convinced that the best interests of the profession have not been served by a narrow interpretation of these terms. We must now place emphasis on the breadth of metallurgy as a science and as an engineering profession. With its usual brevity and wit. Webster's dictionary definesmetallurgy as "the science and art of extracting metals from their ores, refining them and preparing them for use." I shall riot assume that the words "science" and "art" and "metal" are so well understood as to require no defining but others among our contemporaries are better qualified than either your lecturer or the dictionary to present the broad meanings of these terms. When we say that metallurgy is among the oldest of the arts we are not classing it with painting or sculpture or music but rather with the making of tools or weapons or the building of bridges or chariots or cathedrals. In short we are saying that metallurgy is among the oldest of the engineering professions. The question " What is metallurg ? " has been one of rather more than ordinary concern to those of us who have the task of developing a curriculum for the education of students in this field. This development has been going on in a number of universities over a period of some years. but there seems to be as yet no unanimity as to what such a curriculum should contain. I believe there is fairly complete agreement that it must be founded upon sound

Jan 1, 1950

By C. E. Armantrout, J. A. Rowland, D. F. Walsh

THE close-packed-hexagonal structure of mag-J- nesium is converted to a ductile and malleable body-centered-cubic lattice by the addition of lithium in excess of 10 pct. Further, the density of magnesium or magnesium-base alloys is decreased by additions of lithium. The practical possibilities of such alloys as a basis for uniquely light, malleable, and ductile structural materials were pointed out by Dean in 1944' and by Hume-Rothery in 1945.2 It was apparent to these investigators, however, that more complex compositions would be required if strengths sufficient for structural applications were to be developed in these alloys. In a search for strengthening additions, various investigators w have examined a number of the ternary and more complex alloys containing magnesium and lithium. An investigation of the fundamental characteristics of these alloys was undertaken by the Bureau of Mines. The investigation was initiated with a study of the magnesium-rich corner of the equilibrium diagram for the ternary system, Mg-Li-Al. The following data from published investigations of Mg-Li-A1 alloys were available: 1—a description of isothermal sections at 20" and 400°C through the Mg-Li-A1 constitution diagram by F. I. Shamrai;' 2—a diagram by P. D. Frost et al." showing approximate phase relationships at 700°F for a number of the Mg-Li-A1 alloys; and 3—diagrams showing the constitution at 500" and 700°F for the Mg-Li-A1 alloy system published by A. Jones et al.' Where compositions and temperatures permit comparison, these diagrams show disagreement. The 700°F isotherms of Frost and Jones differ only in the placement of the phase boundaries. But Sham-rai's 400°C (752°F) isotherm shows a variation in phases as well as in phase boundaries. Although rigid comparison of these different isothermal sections might not be justifiable, it seems impossible to reconcile Shamrai's construction with the isotherms of Frost or Jones. The isothermal sections presented in this paper were prepared to determine compositions which might be suitable for age hardening and to develop the general slope and placement of the various phase boundaries in the magnesium-rich corner of the diagram. Sections at 375", 200°, and 100°C were selected for investigation. In constructing these sections, the solubility of aluminum in magnesium, as reported by W. L. Fink and L. A. Willey Vn 1948, was used at the binary Mg-A1 boundary and the solubility of lithium in magnesium was obtained from the equilibrium diagram for that system as reported by G. F. Sager and B. J. Nelson" in the same year. The solubility of magnesium in lithium was determined experimentally and conforms in general to data reported by P. Saldau and F. Shamrai." Parameters for AlLi and MgI7A1, were taken from American Society for Testing Materials X-ray diffraction data cards. Experimental Procedures Although the isothermal sections presented in this paper are not unusually complex, the experimental techniques involved in their construction are made extremely difficult by the relatively high vapor pressure of lithium and the great chemical activity of both magnesium and lithium. Because of these characteristics, which make precise control of the composition of equilibrium-treated filings practically impossible, the disappearing phase method was used in preference to the parametric method in conjunction with metallographic studies. The alloys used in this investigation were melted and cast in an atmosphere of helium using a tilting-type furnace which enclosed a steel crucible and mold in a single unit. Each portion of the charge (500 to 600 g) was cleaned carefully just before placing it in the crucible; and the charge, crucible, and entire melting apparatus were evacuated and then washed with grade A helium while preheating to approximately 100°C. The alloys were melted and chill cast in an atmosphere of helium. Alloys prepared in this way were relatively free from inclusions and a fluxing treatment was considered unnecessary. The cylindrical ingots obtained were scalped and then reduced 96 pct in area by direct extrusion, yielding % in. diam rod. Sections of the rod, approximately 3 in. long, were given equilibrium heat treatments and then sampled for metallographic examination, X-ray diffraction study, and chemical analysis. The surface of each equilibrium-treated rod was machined to a depth sufficient to insure removal of contaminated material before samples for chemical analysis or X-ray diffraction study were obtained, and all decisions on microstructure were based on the examination of the central portion of the metallographic specimen. All specimens homogenized at 375°C were analyzed after this equilibrium heat treatment. When the composition of an alloy placed it in a critical area of the 200" or 100°C isothermal section, a check chemical analysis was made on a sample taken from the alloy specimen as-heat-treated at the particular temperature. Standard chemical procedures of gravimetric analysis were used in the determination of magnesium and aluminum; lithium, potassium, and sodium were determined by flame photometer methods

Jan 1, 1956

By W. L. McMorris, A. H. Brisse

IN the last several years the coal industry has intensified its effort to solve the growing problem of cleaning and recovering fine mesh coals. On one hand these has been increasing civic pressure for cleaner streams, and on the other hand there has been increasing production of fine mesh coal, resulting directly from adoption of the modern mining methods so essential to the economy of the coal mining industry. Cleaning fine coal with the same precision possible with coarser coals is a difficult task, and for coals finer than 200 mesh it has been impractical. Furthermore, the inclusion of —200 mesh material in the final product markedly increases costs of de-watering and thermal drying, which are necessary steps if coal is to meet market requirements. Consequently these extreme fines have generally been wasted. As a result, problems have been created in many districts because there has not been enough area for adequate settling basins. Wasting of coal in the -200 mesh slimes may account for a loss in washer yield equivalent to 2.0 to 2.5 pct of the raw coal input. With rising mining costs the value of such a loss is constantly increasing and a need for a better solution to the fines problem becomes more pressing every day. From an operating viewpoint, also, continuous removal of extreme fines from the washing plant circuit permits good water clarification practice, improving significantly the overall cleaning efficiency. The obvious desirability of recovering a commercially acceptable coal from washery slimes prompted U. S. Steel Corp. to investigate the merits of the Convertol process developed in Germany." Although this process has been used commercially in Europe for some time, little if any consideration has been given to its possible adoption in the U. S. until very recently. Fundamentals of the Convertol Process: In the Convertol process, droplets of dispersed oil are brought into intimate contact with the solids suspended in the coal slurry to be treated. This contact causes oil to displace the water on the surface of the coal by preferential wetting, or phase inversion, after which the coal particles are allowed to agglomerate in a manner permitting their re- moval from the slurry by centrifugal filtration. The clay and other particles of mineral matter suspended in the slurry do not have the affinity for oil the coal particles have. Consequently the oil treatment is preferential to coal to the extent that more than 95 pct of the oil used reports with the clean coal recovered. Figs. 1 through 3 will clarify the steps involved in the process. Fig. 1 shows the suspended material in the slurry to be treated, which is a thickened product containing 40 to 45 pct solids. Oil is now injected into the slurry under vigorous agitation to produce good oil to coal contact conditions, which result in preferential oiling of the coal particles. These coal particles are then permitted to agglomerate by gentle stirring in a conditioner to form flocs, as shown in Fig. 2. At this point in the process the agglomerated oiled coal can be washed and partially dewatered on a vibrating screen, as shown in Fig. 3. Finally, the washed flocculate can be further dewatered in a high-speed screen basket centrifuge or in a solid bowl centrifuge. Commercial Application of the Convertol Process in Germany: The original Convertol process was developed by Bergwerksverband zur Verwertung von Schutzrechten der Kohlentechnik, G.m.b.H., a German research organization controlled by the Coal Operators Assn. of the Ruhr Valley. The process as reduced to commercial practice in Germany' is shown in Fig. 4. In this process a thickened slurry (40 to 45 pct solids) mixed with a predetermined percentage of oil is fed from a surge tank to the phase inversion mill. After the phase inversion step, the slurry is usually discharged directly to a highspeed screen centrifuge. From 3 to 10 pct oil is used, depending on type of oil, size consist of coal to be recovered, and operating temperature. The top size of fine coal cleaned in Germany by the Convertol process is limited by the size of the openings in the centrifuge screen basket. Any mineral matter coarser than the basket opening, which is generally 60 to 80 mesh, must remain with the oiled coal. If the coal fines have been effectively cleaned down to about 80 mesh, the cleaning performance of the process is practically unaffected by the presence of coarse coal particles. However, since recovery of coal much coarser than 80 mesh is mow economical by conventional methods, it normally becomes more costly to allow substantial percentages of this coarse coal in Convertol process feed. Where the general plant layout does not permit effective cleaning of coal sizes down to 80 mesh or lower. there is some justification for a coarser Con-

Jan 1, 1959

By R. V. Smith, E. J. Dewees, R. H. Williams

Before this paper was presented, the terms "f" and "v1/f in flow equations had been called "friction coefficient" and "friction factor," respectively. However, many authors have used the names for the terms interchangeably, with the result that considerable confusion has existed in the literature on flow of fluids. In an effort to establish a clear and concise terminology for these terms, the authors have designated f as "resistance coefficient" and dm as "transmission factor." Transmission factors for the flow strings of gas wells were determined by tests on wells in six fields of Oklahoma, Texas, and Louisiana. Data were collected on 14 gas wells while gas was flowing through 1 1/4, 2, 21/2, and 3-in. tubing and 51/2 and 7-in. casing. The transmission factors developed from these data were found to follow the resistance equation published by Nikuradse1 for turbulent flow in "rough" pipes with an average absolute roughness of 0.000,65 in. This average absolute roughness is believed to be representative generally of the flow strings of gas wells with the exception of those that have been exposed to corrosion or other conditions causing undue roughness. Also, use of an absolute roughness of 0.000,65 in. probably will result in transmission factors that are more representative of gas-well conditions than those in common use today, provided that the transmission factors are calculated by the methods outlined in this report. The authors believe that use of these transmission factors will permit calculation of more accurate subsurface pressures in gas wells than those in use today. Engineers use transmission factors in flow equations to compute subsurface pressures in flowing gas wells from measured wellhead pressures. These subsurface pressures are necessary for determining the productivity of gas wells from "back-pressure" tests. The methods of calculating pressures in flowing gas wells, as outlined by Rawlins and Schellhardt2 in Bureau of Mines Monograph 7, are based on the transmission factors in the well-known Weymouth formula" Natural gas engineers have realized that errors introduced by using transmission factors as given by the Weymouth formula are relatively unimportant in testing low-capacity gas wells; but they also know that such factors are important considerations in testing large-capacity wells. Accordingly, the research described in this report was undertaken to fulfill the need for more accurate means of calculating subsurface pressures in gas wells. This report is part of the Bureau's study of the flow of natural gas through pipe and commercial pipelines. Several of the conclusions regarding flow in the flow strings of gas wells were influenced by the results of the study of flow in horizontal pipelines. These instances are mentioned in the text of this report. METHODS OF COMPUTING TRANSMISSION FACTORS Methods and procedures for computing transmission factors for turbulent flow in circular pipes from test data taken on gas wells have been derived and explained in detail in a paper by Smith4. As these methods were used to calculate the transmission factors presented in this report, a summary is included. Starting with

Jan 1, 1955

By R. Adair, W. R. Hudspeth, W. T. McDaniel

D. C. Ralston (U. S. Bureau of Mines, Washington, D. C.)—Flake mica can be beneficiated by a wider variety of methods than almost any known mineral. However, most of these methods are not recorded. It is therefore a pleasure to find a written record of another application of a new method of beneficiation. The fact that the Humphries spiral gives a concentrate containing the mica flake mixed with the slime and small grit has forced a further separation by screening, in which the finest of the flake will pass through. Fine flake has its uses and if mixed with slimes or clay is recoverable reliably only by flotation. This loss must be charged against the spiral. On the other hand, the new muscovite mica paper recently brought out by General Electric Co., can be made only with grit free flake larger than 50 mesh. It is of interest to learn from the authors whether the washing of the flake on a 50 mesh screen can take the grit content below 1 pct, to meet this new demand. Must another degritting process be used on the flake, like electrostatic treatment of the dried material? H. D. Snedden (The Humphreys Investment Co., Denver)—When recovering mica in the spiral, gangue particles coarser than 16 mesh can be rejected more readily when operating at a high pulp density (35 pct solids) or a low volume rate (—15 gpm). A launder screen as used by Lehigh Coal Co. has proved very satisfactory to partially dewater the mica concentrate and to reject any gangue slimes it may contain. Under certain conditions mica cleaning in the spiral can be improved by reagentizing the spiral feed, the object being to insure wetting of the gangue minerals and to agglomerate or prevent wetting of the mica particles. R. B. Adair (authors' reply)—The grit content of the mica recovered on Humphreys Spirals varies with the fineness of the launder screen used to clean the mica product. Normal practice has been the use of 80 mesh screen, which will produce a mica product of acceptable grit content for most purposes. By using a 50 mesh screen, and increasing the screen area per ton of feed, it is felt by the authors that a mica of 99 pct plus purity could be obtained. This statement would hold only in the case of mica feed which was well de-laminated, and free from "clay balls," (semikaclinized feldspar), which tends to follow the mica through the process.

Jan 1, 1952

By Arnulf Muan, Klaus Schwerdtfeger, L. S. Darken

The equilibrium ratios CO/CO, of. a gas pharse coexislitrg with selected oxide phase assemblages of the system "FeO"-MnO-SiO2 and metallic iron have been determined at 1150°C. The data obtained are combined wilh the thermodynamic data on fayalite (Fe2SiOi) and "FeO"-MnO solid solutions to derive the actiuity-coiHpQsiUon relations for the various oxide components of the olivine (Fe2SiO4-,lIn2Si04) and pyroxenoid (standard free energies of formation of ferrosilile (FeSiO,), tephroite , and rhodonite from their oxides have been evaluated. In the Appendicc~s by Darken and Schivcerdtjeger the ideal solution law for solid deri oed. THE quaternary system Fe-Mn-Si-0 is of interest in many important phases of iron- and steelmaking. For instance, reduction in the blast furnace of ores containing Fe-Mn silicates, deoxidation of liquid steel with Mn-Si alloys, formation and subsequent alterations of oxide inclusions in steels, and the oxidation of manganese- and silicon-containing steels during processing are all governed largely by the thermodynamic relations existing in the system Fe-Mn-Si-O. Although the equilibria between liquid iron and Fe-Mn silicates have been studied in detail previously,' experimental data are lacking for equilibria among the solid phases. The present paper provides such data for a selected temperature, 1150°C. I) PREVIOUS WORK The general feature of subsolidus phase relations in the system iron oxide-manganese oxide-silica under strongly reducing conditions is known.' Fig. 1 represents an isothermal section at 1150°C. The phases present, in addition to silica, are three solid-solution series, viz.. the oxide solid-solution series "Fe0"-MnO (manganowiistite), the orthosilicate solid-solution series Fe2SiO4-Mn2SiO4 (olivine), and the metasilicate solid-solution series FeSi03-MnSi03 (pyroxenoid). The "FeO"-MnO solid solution is continuous between the two end members wustite and manganositeV3 as is the orthosilicate series between the two end members Fe2SiO4 and Mn2 SiO4. 4 The metasilicate solid solution, on the other hand, extends only part way from the MnSi0.l end member toward FeSiO because the latter end member is unstable relative to the phase assemblage fayalite + silica. The letters a through m in Fig. 1 identify end members of the individual solid phases dealt with [for instance, c designates fayalite (FeZSiO4) in equilibrium with wustite, e designates fayalite in equilibrium with silica, and so forth]. In addition to the phase relations there are some thermodynamic data available for the end members of the silicate solid solutions and for the "FeO" -MnO solid solution. The free energy of formation of fayalite (Fe2Si04) from its oxide components has been studied by several investigators. Unfortunately, the data obtained show considerable discrepancies. According to recent tabulations by Kelley, the change in standard free energy Affn for the reaction

Jan 1, 1967

By J. S. Billheimer, B. H. Sage, W. N. Lacey, C. G. Yundt

As a part of a general investigation of the separation of bitumen from hydrocarbon mixtures a study was made of a restricted quaternary system composed of methane, decane, tetralin, and bitumen. The work was limited to a pressure of 8000 psi, a temperature of 220 °F, and to a fixed relative proportion of decane, tetralin, and bitumen. The measurements permitted the determination of the distribution of these components in each of the fluid phases. It was not possible to distinguish a second liquid phase in the course of these measurements. Gas-liquid equilibrium "constants" of each of the components were found to vary markedly with the composition of the system while temperature and pressure remained fixed. INTRODUCTION The separation of bitumen frorn naturally occurring hydrocarbon mixtures has been of importance for a number of years in the production of petroleum, especially in the California area. The deposition of this material from crude oils was noted in earlier studies of the solubility of natural gas in crude oil.¹,²,3 Studies of the separation of bitumen from crude oils from the Greeley and Santa Fe Springs fields were carried out."." The behavior of these systems appeared complex and studies of two restricted ternary systems involving mixtures of n-pentane, tetralin, and bitumen,' and of decane, tetralin; and hitumen, confirmed this belief. Reviews of the literature pertaining to the separation of bitumen from naturally occuring and refined hydrocarbons are available." The important effect of methane in the separation of bitu- men from naturally occurring hydrocarbon mixtures was apparent from the earlier studies and for that reason it appeared desirable to investigate a restricted quarternary system involving mixtures of methane. decane, tetralin, and bitumen; data concerning the behavior of mixtures of decane. tetralin. and bitumen having already been obtained.V his study was restricted to a pressure of 8000 psi," a temperatue of 220° F, and fixed relative proportions of bitumen, decane. and tetralin. This composite constituent, hereinafter designated as the less volatile constituent, was made up of 0.0455 weight fraction bitumen. 0.0909 weight fraction decane, and 0.8636 weight fraction tetralin. The experimental method involved bringing together mixtures of methane and the less volatile constituent in varying proportions in a constant volume container at the pressure and temperature indicated above. The composition of each of the phases was determined and from this the extent of the separation of bitumen was established. MATERIALS The bitumen used in this investigation was obtained from the same stocks employed in earlier studies. The crude material from the North Coles Levee field was stored in the laboratory] in a closed drum for a period of five years. Several samples from this stock were subjected to refining operations which were described earlier,' and every effort was made to follow the same procedure in all cases. It was necessary to prepare supplies of bitumen for this investigation at two rather widely different times. These materials have been identified as samples 1 and 2. The composition of the crude bitumen after it was washed with n-pentane at room temperature

Jan 1, 1949

By Rex E. Cheek, Donald E. Menzie

The fluid mapper, a model relatively new to the petroleum industry, was used to study the effect of various mobility ratios on the areal sweepout efficiency for two typical spacing patterns. The experiments indicated the areal sweepout for the five-spot pattern varied from 51.8 per cent at a mobility ratio of 0.093 to 89.1 per cent for a ratio of 24.4. In the direct line-drive pattern, the areal sweepout varied from 58.7 per cent at a mobility ratio of 0.089 to 92.0 per cent at a ratio of 24.8. The fluid mapper may prove useful to determine quickly the effective areal sweepout for any well spacing. INTRODUCTION The effect of the mobility ratio on the areal sweepout efficiency during primary depletion of a water drive reservoir and during secondary recovery operations has recently become more widely recognized The mobility ratio, M, is defined as: _ kjp (displaced fluid) k/u (displacing fluid) where k = effective permeability u = viscosity When the displacing fluid is miscible with the displaced fluid, the permeabilities are equal and the mobility ratio may be expressed as a ratio of viscosities: u (displacing fluid) u (displaced fluid) The mathematical analysis for calculating the areal sweepout efficiency with mobility ratio other than unity is quite tedious.5,11 An experimental method by using a potentiometric model2 in a step-wise manner and in using an X-ray shadowgraph model3,12 with continuous fluid flow has been published. Several types of models have been used to study oil and gas reservoir performance. These models may be classified as physical, electrolytic, potentiometric, X-ray shadowgraph, and fluid mapper. The X-ray shadowgraph and fluid mapper are models relatively new to petroleum engineering and have not been used extensively for specific applications. The theory of the fluid mapper indicates it may be adapted to a study of areal sweepout efficiencies for various mobility ratios as well as other complex problems in petroleum engineering. The use of the model and results obtained when using displacing and displaced fluids of equal densities but different viscosities are discussed. FLUID MAPPER DEVELOPMENT H. S. Hele-ShawV eveloped a fluid mapper model based on the hydrodynamic theory. This theory is that in the steady flow of a viscous fluid between horizontal parallel plates spaced a very small distance apart, the effect of viscous shear is of such magnitude in the vertical plane that the motion in the horizontal plane is practically undisbrted streamline flow. Techniques developed by Hele-Shaw were not expanded and no additional developments in fluid mapper models were forthcoming until A. D. Moore, University of Michigan, published a series of papers starting in 1949, which describe the construction of a flexible and inexpensive model'h nd the fluid mapper technique for the solution of certain problems.' The essential components of the fluid mapper as developed by Moore are::.ln 1. A base slab. made of dental stone (calcium sulphate and water). which is shaped to represent the prototype. 2. Plate glass slightly larger than the slab and spaced

Jan 1, 1956

By W. N. Lacey, C. G. Yundt, B. H. Sage, J. S. Billheimer

As a part of a general investigation of the separation of bitumen from hydrocarbon mixtures a study was made of a restricted quaternary system composed of methane, decane, tetralin, and bitumen. The work was limited to a pressure of 8000 psi, a temperature of 220 °F, and to a fixed relative proportion of decane, tetralin, and bitumen. The measurements permitted the determination of the distribution of these components in each of the fluid phases. It was not possible to distinguish a second liquid phase in the course of these measurements. Gas-liquid equilibrium "constants" of each of the components were found to vary markedly with the composition of the system while temperature and pressure remained fixed. INTRODUCTION The separation of bitumen frorn naturally occurring hydrocarbon mixtures has been of importance for a number of years in the production of petroleum, especially in the California area. The deposition of this material from crude oils was noted in earlier studies of the solubility of natural gas in crude oil.¹,²,3 Studies of the separation of bitumen from crude oils from the Greeley and Santa Fe Springs fields were carried out."." The behavior of these systems appeared complex and studies of two restricted ternary systems involving mixtures of n-pentane, tetralin, and bitumen,' and of decane, tetralin; and hitumen, confirmed this belief. Reviews of the literature pertaining to the separation of bitumen from naturally occuring and refined hydrocarbons are available." The important effect of methane in the separation of bitu- men from naturally occurring hydrocarbon mixtures was apparent from the earlier studies and for that reason it appeared desirable to investigate a restricted quarternary system involving mixtures of methane. decane, tetralin, and bitumen; data concerning the behavior of mixtures of decane. tetralin. and bitumen having already been obtained.V his study was restricted to a pressure of 8000 psi," a temperatue of 220° F, and fixed relative proportions of bitumen, decane. and tetralin. This composite constituent, hereinafter designated as the less volatile constituent, was made up of 0.0455 weight fraction bitumen. 0.0909 weight fraction decane, and 0.8636 weight fraction tetralin. The experimental method involved bringing together mixtures of methane and the less volatile constituent in varying proportions in a constant volume container at the pressure and temperature indicated above. The composition of each of the phases was determined and from this the extent of the separation of bitumen was established. MATERIALS The bitumen used in this investigation was obtained from the same stocks employed in earlier studies. The crude material from the North Coles Levee field was stored in the laboratory] in a closed drum for a period of five years. Several samples from this stock were subjected to refining operations which were described earlier,' and every effort was made to follow the same procedure in all cases. It was necessary to prepare supplies of bitumen for this investigation at two rather widely different times. These materials have been identified as samples 1 and 2. The composition of the crude bitumen after it was washed with n-pentane at room temperature

Jan 1, 1949

By B. L. Averbach, Morris Cohen, L. L. Seigle

Free energies, enthalpies, and entropies of mixing of Ni-Au solid solutions containing 5 to 95 atomic pct Ni have been determined by the electromotive force method at 700° to 900°C. The thermodynamic activities exhibit large positive deviations from Raoult's law, and the entropies of mixing are almost twice those of ideal solutions. The enthalpies of mixing are positive (heat is absorbed) and are attributable to the lattice distortional energy resulting from the size difference between the nickel and gold atoms. This factor appears to be responsible for the miscibility gap at lower temperatures. IN the thermodynamic study of metallic solid solutions, most interest has been directed toward systems with negative deviation from Raoult's law, namely, those exhibiting superlattice or compound formation. The results of previous investigations are summarized in recent publications.'-' Relatively little experimental work has been carried out on solid solutions which manifest a positive deviation, possibly because the range of solubility in such cases is usually quite limited. Nevertheless, the relationship of the thermodynamic properties of these solutions to diffusion, nucleation, and precipitation in the solid state are of considerable importance. The binary Ni-Au alloys are particularly suited to an investigation of these relationships. Despite the presence of a miscibility gap at lower temperatures, Fig. 1, indicating a large positive deviation from Raoult's law, complete solid solubility is found above 840°C. Moreover, the difference in the atomic scattering powers of nickel and gold is sufficiently great to permit X-ray diffraction studies of atomic arrangements and pre-precipitation phenomena. Radioisotopes of both nickel and gold are available for diffusion work, and finally, a large difference in nobility between the two elements facilitates measurement of the thermodynamic properties. The present paper describes the experimental determination of the free energies, enthalpies, and entropies of mixing of solid Ni-Au alloys. Table I gives a list of the symbols used in the paper. Experimental Method The stability of nickel chloride relative to gold chloride" indicated that the galvanic cell method could be used for determining the thermodynamic properties of Ni-Au alloys. An electrolytic cell (Fig. 2) was constructed, similar to that of Weibke and Matthes,7 in which the electrodes were solid nickel and Ni-Au alloys, and the electrolyte was a fused mixture of alkali chlorides containing NiCl,. The cell electrodes were made from fine gold granules and carbonyl nickel shot melted together under argon, chill cast, swaged to 1/16 in. diam rod, and annealed for one week at 850°C. Commercial reagent and chemically pure grade salts, purified by dehydration, were used for the electrolyte. The cell, operating in an atmosphere of purified argon, was heated in a resistance-wound cylindrical furnace whose temperature was controlled to within ±0.5ºC. The potential developed between the pure nickel and the alloy electrodes, which is related to the thermodynamic properties of the alloys by standard equations to be presented later, was measured with a potentiometer and a mirror galvanometer sensitive to 10-7 v. Dehydration of the electrolyte was carried out in the assembled cell by evacuating at 100°C for about

Jan 1, 1953

By P. Hudock

Thin films of PbS and CdS have been deposited on insulutiug- sapphire substrates by euzploying a subliwzation technique rising near-equilibriurum conditions in ultrahigh vacuum. Oriented polycrystalline PbS and CdS films on sapphire have mobilities approachitzg values characteristic of bulk crystals. In the case of CdS, special purification procedures were crucial in obtaining high-mobility films. By performing the depositiotz of a compound within a small chamber heated to a UNiform temperature within a Vacuum systerrz, it is possible to approach equiilibrium cod-tions r.~litl~irs the chamber. In this way; the sublimation and condensation proceed under near equilibrium co?zditions, and it was found that the properties of dePosited corrzpounds were similar to those of the source material. Oriented PbS films on sapphire have a roor?l- temperature unobility of 700 sq cm per v sec and a T-5/2 temperature dependence characteristic of bulk crrystnls. CdS layers on sapphive Izazse a resistivity ~uhich is corrlpamble to the resistivity of the souvce crystals over a range of four ordem of rrlagnitude. Irz contrast, Ihe resistivity of CdS films prepared by conventional evaporation depends largely upon the substrate terrzperat~ire and postheating treatrrletlt, vather than upon the properties of' the solirce rrraterial. In the case oj the CdS films the achievment of high carrier mobility required the cargful exclusion of cont~~~~ii~unts from the films. The steps taken to accomplish this included presublimation of the source material, performance of the deposition at a backg-m~ozd pressure less than 10-8 Torr, and a solvent extraction with liquid cadminum, similar to that described by Aven and woodbury. The deposition of ,films under near-equilibrium conditions is being op-plied to other classes oj COmpounds. II should he of 1:allce ,tor llle deposition of nny matevial that decomposes in the vapor state. THIN films of PbS and CdS have been deposited on insulating sapphire substrates by employing a sublimation technique using near-equilibrium conditions in ultrahigh vacuum. Oriented polycrystalline PbS and CdS films on sapphire have Hall mobilities approaching values characteristic of bulk crystals. In the case of CdS, special purification procedures were crucial in obtaining high-mobility films. Depositions were performed in a small quartz sublimation cell shown in Fig. 1 that contained the compound and the single-crystal sapphire substrate. The substrates were etched in tapered solutions of hot phosphoric acid, rinsed in deionized water, dried, and transferred to the cell under dry nitrogen. Graphite crucibles and substrates were used in experiments where it was necessary to provide an inert test vehicle for the analytical determination of impurities in the source crystals and deposited films. The crucibles and substrates were machined out of spectrographic-grade graphite having less than 1 ppm of impurities. A quartz mask was sometimes used to define a pattern which could be used for Hall and resistivity measurements. Close spacing between the compound and substrate was maintained to insure better transport of each component from the source material.

Jan 1, 1968

By J. R. Elenbaas, J. A. Vary, D. L. Katz

The development of gas fields, oil fields and aquifers for storing natural gas is treated from two main vieu.-points: (I) the volumetric storage capacity for gas in a given situation and (2) the prediction of the number of wells required for the delivery of gas. Other experiences in the design and operation of storagc fields are incluclerl INTRODUC TION Storage of natural gas in underground reservoirs near the terminus of long distance pipelines has been the prime factor in opening the space heating market to the natural gas industry. Storagc has permitted a major. increase in both the load and the load factor of pipe-lines; some are now operating at steady load throughout the year. Thus, underground storage has been responsible for the rapid increase in demand for natural gas in recent years. Three types of reservoirs have been used for gas storage: natural gas reservoirs, oil reservoirs, and waterbearing sands or aquifers. This paper presents the factors to be considered when developing gas storage reservoirs of these three categories. There are two prime considerations tor any storage reservoir: (1) the volume of gas which a given reservoir will store advantageously and (2) the number 01 wells needed to provide the required peak deliverability. These two problems will be considered for the three types of reservoirs just noted STORAGE IN PARTIALLY DEPLETED GAS FIELDS Early storage operations consisted of replenishing the natural gas in a depleted gas field situated adjacent to the market. Today, newly discovered fields near the market may be considered for storage, and this discussion applies equally to both types of reservoirs. For reservoirs originally containing gas or oil, the question of the impermeability of the cap rock nor-mally does not arise. However, such fields are likely to have many wells drilled either to or through the reservoir under consideration. Positive assurance must be obtained that such wells are or can be made mechanically tight. Corroded casings may need to be lined or permanently plugged. Abandoned wells should bc reopened and properly cemented. The volumetric capacity for gas storage depends upon space available in the porous rock as well as pressure and temperature of the gas in the reservoir. The production-pressure decline data on partially depleted gas reservoirs without water drive permit calculation of the reservoir space for gas. Isopachous maps of sand volume and porosity data for the reservoir rock provide an alternate method of calculating the pore volume for water-drive reservoirs. The pressure range selected for the storage cycle depends upon ()) the safe upper limit of pressure. 2) the flow capacity of wells and (3) compression requirements when injecting gas into the reservoir or delivering to market. Normally, gas and oil fields have pressures at discovery in the range of 0.43 to 0.52 psi/ft of depth. Pressures of around 1.0 to 1.2 psi/ft of depth appear to lift the overburden1-3 and invite uncontrolled movement of fluids in the porous rock. Some top pressure is normally selected for a storage reservoir ranging from below discovery pressure for deeper reservoirs to 0.65 psi/ft of depth for shallower reservoirs. Pressures to 0.66 psi/ft have been experienced without difficulty. The lower pressure limit is set by water intrusion accompanying low pressures, reduced flow capacity for wells at lower pressures and compression requirements. Depletion-type gas reservoirs often encounter water problems in the later stages of gas production. Such water intrusion may be due to movement from the surrounding aquifer. Accordingly, displacement of this water back into the aquifer by gas pressure and subsequent surges of water corresponding to the gas storage pressure cycle must be considered. Storage fields often produce in four months a volume of gas equal to its initial content. Rapid decreases in reservoir pressure occur, such as 20 psi/day. Accordingly, closed-in pressure observation wells which reflect the pressure in the bulk of the reservoir are required for following the operation of the reservoir. It has been found that a plot of observation wellhead pressures against gas content, Fig. 1, is very useful in observing operation of the field, checking the inventory and predicting future behavior. The plot is based on a given quantity of base or cushion gas in place. The injection and withdrawal curves may spread depending upon the homogeneity of the reservoir rock. permeability of the rock, well spacing and flow rates.