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By W. F. Kieschnick, Eugene Harrison, W. J. McGuire

W. J. McGuire, et al, are to be commended for their undertaking of a mathematical solution of a very difficult problem. Unfortunately, however, a mathematical approach requires the application of several assumptions. These assumptions appear to be unrealistic and lead to answers which do not describe what actually happens when hydraulically fracturing oil and gas wells. Considering laboratory confirmation of breakdown phenomena, the authors appear to have tested their theories only on cement specimens and on samples of Austin limestone, much too small to provide any fracture system. This work resulted in the formation of vertical fractures. If the authors had tried similar experiments on thick walled cylinders made from almost any sandstone cores, they would have found that, using crude oil as the breakdown fluid, horizontal fractures would almost always occur, and at pressures much lower than any calculated. They would also find that by confining the fluid to within the bore (using oil base mud for example) on similar samples, the pressures required to burst the cylinders would be considerably higher and most of the fractures would be vertical. This breakdown pressure behavior has been duplicated in wells in Texas, Oklahoma, Kansas and in Wyoming. Considering field data the phenomena of different breakdown pressures for different breakdown techniques can be further illustrated. Most production and service personnel will agree that a breakdown can be more easily obtained if injection into a formation can be established prior to the occurrence of the breakdown. This is true whether the formation being treated is completed as open hole or as a perforated interval. This is clearly illustrated by a Lakota well in Wyoming, completed open hole at a total depth of 7,358 ft. An attempt to vertically fracture this well failed when a bottom hole pressure of 10,326 psi was insufficient to break down the formation. A non-penetrating type fluid (oil base mud) was in the well at the time the breakdown was tried." The oil base mud was then cleaned out of the well and replaced by a 30" API gravity crude oil. With this oil in the hole the formation breakdown was easily accomplished at a bottom hole pressure of 3,607 psi. This large difference in fracture pressures would be impossible according to the theories presented by McGuire, et al. The authors have used as an example the breakdown pressures experienced when acidizing Permian Basin wells. During acid treatments of limestone and dolomite the "breakdown" (drop-off in pressure) seldom occurs until some injection of acid has been accomplished. In these cases the breakdown is most likely to result from the chemical reaction of acid and rock in already existing vugs and fractures rather than from making a new fracture by hydraulic pressure. If this is true, then results in the Permian basin should not be used to validate the authors' calculations. *** AUTHORS' REPLY to ROSCOE C. CLARK and HENRY F. COFFER The purpose of our laboratory experiments in which thick-walled rock cylinders were hydraulically fractured was to determine the validity of the "thick pipe" formula for brittle materials, and not to predict nor demonstrate directly the orientation of field fractures. Our conclusions concerning field results resulted from calculations involving the "thick pipe" relationship as well as considerations of overburden stresses, rock strengths, and the geometry and dimensions of the field system. Clark suggests that had the models been more porous or contained weak bedding planes, horizontal fracturing would have occurred. This is undoubtedly true provided external stresses similar to those in the earth's crust are nor imposed. However, if we were going to design experiments to represent directly the field case we would impose the proper stresses on the models. It is generally recognized that the vertical compressive stress in the earth's crust arising from the weight of the overburden is approximately 1 psi/ft of depth. Then, as an example, even though a horizontal bedding plane has zero strength, the formation cannot be separated to form a horizontal fracture unless the hydraulic pressure exceeds the stress due to overburden. And in those cases in which the stress resisting vertical fracturing is significantly less than that resisting horizontal fracturing, vertical fractures should result, notwithstanding horizontal plane weaknesses. We agree that breakdown pressure will be less if the fracturing fluid penetrates the formation. In Appendix HI of our paper it is shown that leak-off reduces the pressure necessary to initiate either a horizontal or vertical fracture. It would be difficult to attempt to

Jan 1, 1955

By M. ROWE, H. E. Gilliland, L. BARNES

The authors of this paper are to be commended for a clear exposition of a timely subject. However, some important conclusions, in addition to those presented in the paper, can be drawn from the results of their elaborate and rather complete numerical computations. First of all, the major part of the calculations presented in the paper are for semi-infinite slabs of oil shale (the authors designate this as Model I) and a question must be posed — Are these elaborate computations needed to arrive at realistic estimates of the shale oil displaced. Consider the model of Lauwerier* that corresponds to the authors Model I if thermal conduction parallel to the fracture be neglected. If one also neglects the finite (but relatively small) heat capacity of the material in the fracture, it is easily shown from Lauwerier's solution that the cumulative oil production would be:

Jan 1, 1969

By F. F. Craig

The authors have done a commendable job in combining a number of recognized waterflood performance prediction methods into one composite method. The availability of a FORTRAN program for this composite method should encourage its widespread industry use. Pan American has had a computer program developed along similar lines for a number of years,' and it has received more use than any other reservoir prediction method. In three important stages of a pattern waterflood, the authors fail to consider fully the effects of water-oil mobility ratio on performance. This is discussed in the following paragraphs and modifications of the prediction method are suggested. During the early stages of a waterflood in a partially depleted formation, the injected water and its preceding oil bank move out radially from the injection wells. As pointed out in the author's paper the method of Yuster and Calhoun2 or predicting the water injection rate during this period assumes that the mobilities of the water and oil are equal. In his book, Muskat3 resents a modification of the Yuster-Calhoun approach that considers fully the influence of water-oil mobility ratio. In Muskat's method, the prediction of the injection rate-injected volume-time relationship is expressed in readily programmed dimension-less unts. At and following fillup the five-spot pattern consists of a water-invaded pattern with the remainder of the pattern containing only oil and connate water. In the paper, Eq. 18 is used to calculate the water injection rate at fillup. This equation considers that the entire pattern is invaded by water. To properly consider both the incomplete areal sweep of water and the water-oil mobility ratio, Eq. 18 should read:

Jan 1, 1969

By H. K. VAN POOLLEEN, W. Hurst, H. C. Bixel

In an earlier publication* I showed the development of the instantaneous point source solution for a well producing at a constant rate at the center of a system of two radial, adjoining sands of different permeabilities. I also showed how a wellbore radius could be incorporated if this were the development required. For the purpose of that paper and the point I wished to make, this solution served. It yielded a simplifying solution of sands in series identified by Eqs. VI-26 and VI-27. (These equations are reproduced in part by Bixel and van Poollen as their Eq. 3, Page 302.) I am well aware that the simplified solutions are approximations. The facts that these Ei-functions satisfy the diffusivity equation and meet the boundary conditions both at the well and at the interface between sands, and that the earliest time considerations yield zero pressure drop, are evidence that the solutions are good approximations. This was the purpose for these formulas, which I interpret that where the permeabilities are of finite order of magnitudes in the respective media, the relations give satisfactory answers. However, from the authors' point of view there are reservations, which leads me to consider their entire generalization as illustrated in their Figs. 1 through 14. What I understand from their storage capacity, relationship Fs, which is the ratio of the product of porosity and compressibility of Sand II to Sand I, that is employed here by the authors as a correlative means of identifying one figure from another, there is nothing in the exact mathematics that supports such a term as a means of correlation. This is taken out of context, unsustained that this applies. Here the mathematics are known, where the true correlation is the diffusivity term of one sand to another. This entails permeability that refers back again to the term M in their paper for the transmis-sibility of fluid from one sand to the other that should have also been a part of this storage capacity. In Figs. 8 through 14, which purported to show the simplified equation following this correlation, there are apparent discontinuities for M equal to or less than 0.1000 that differ from the trends for greater values of M. In this connection there is no reference radius given for this cumulative pressure drop in the paper that would permit me to make these calculations. However, what is clear for M equal to 0.1000 or less we are treated to almost a closed barrier at the interface; a condition entered by the writers without qualification. This across-the-board treatment of these simplified formulas, whatever the motive of the authors, enters into a range of permeabilities that even I as the contributor would have reservations that such could apply. Under comparable conditions I would be looking at a closed reservoir or some facsimile for such. The extent to which the approximation or the exact equations pertain is not evident in the generality offered by Bixel and van Poollen in their paper. Only when they or other writers show the comparison of the pressure distributions within the formations can one be able to judge the rational limits to subscribe to the simplified formulas.

Jan 1, 1969

By M. R. TECK, N. Rudd, L. K. Thomas, D. L. Katz

The authors are to be congratulated for presenting the first comprehensive paper on the theory and practice of threshold pressure determination in connection with underground gas storage. It is of particular value since most previous experimental work on this subject has been proprietary to the commercial laboratories engaged in such testing and to their clients. This dlscussion is presented in amplification of the subject paper, not in criticism, and is based upon our experience with approximately 5,000 threshold pressure determinations. Our comments are directed primarily to the experimental procedures as described by Thomas et al. It should be noted that, while clay mineral-rich lithologies are the most common caprock materials, the samples used (Table 1) include low permeability sandstones and carbonates, but do not include shales or other formations in which clav minerals exert a dominant effect. While our experience on samples analogous to those investigated by the authors generally confirms their findings, we have found that even more rigorous experimental conditions must be imposed where clay minerals are the controlling factor. These additional conditions result from the well-known molecular character of the clay minerals themselves in which water is interlaminated with, and bonded to, silicate sheets, thus becoming an essential component of the molecule. In many clay minerals the character of the intersheet bonding, and thus the dimension of the lattice, is strongly affected by variations in the identity and concentration of cations present in the intersilicate water. On a supermolecular scale, adsorbed water films on particle or "flakes" of shale provide much of the cohesive force necessary to maintain mechanical strength. The thickness of these films is variable and inversely proportional to intergranular pressure within the dimensional limits involved in caprock investigation. The thickness of the intersilicate water layers may also be subject to pressure under some conditions. These considerations are reflected in several necessary modifications of the experimental procedures described by the authors. Two of these are, in our judgment and experience, of such importance that they cast real doubt on the validity of data obtained on argillaceous materials without their application. The very careful resaturation procedures proposed by the authors should give good results in connection with the relatively "inert" lithologies used in their experiments. Our experience suggests, however, that they would create more problems than they would eliminate if applied to argillaceous materials. 1. Drying of the sample at the temperature and for the duration indicated by the authors not only will dessicate the sample with consequent shrinkage cracking, parting along bedding planes, and even total disassociation in the case of fissile shales, but it may also alter the character of the clay minerals themselves — in some cases irreversibly. 2. Prolonged evacuation to 2 microns Hg further dessicates the sample and is even more effective in reducing the intersilicate water content. 3. Resaturation with water differing in pH or chemical content from that existing originally in the sample also serves to alter the nature of the sample, particularly its structure and strength. 4. Our experience has been that, even with the thorough precautions proposed by the authors, complete resaturation of very fine grained materials is rarely obtained. Yet our experience confirms the

Jan 1, 1969

By D. N. Dietz

Jan 1, 1969

By G. L. Gates

The comments by George L. Gates are appropriate to the characteristics that we sought to feature in our study and they are appreciated by the authors. In our laboratory deposition tests the smoothness of the surface seemed to be more important than the type of surface. However, we also noted that even where very smooth glass, plastic or polished metal coupons were used, scale deposition still occurred though the rate varied. Much more information is needed, however, and new work to solve the mineral scale deposition problem by mechanical and chemical means is expected to continue.

By C. E. Murphey

C. E. Murphey, Jr., has presented a relevant, simplified comparison of drill string response when drilling with and without bumper subs. His point that drilling without bumper subs gives conditions further from resonance is valid. Thus, drilling from a floating vessel without bumper subs is undoubtedly feasible, especially when the heave motions of the drilling vessel are small. When these heave motions become large, an evaluation of the magnitude of the change of bit weight is a requirement for a realistic comparison between using and not using bumper subs. As Murphey states, this evaluation should include the effects of damping and presence of drill collars. The analysis would be similar to that presented in our Appendix, but is far beyond the scope of this Reply. ***

By J. Meintjest

As you pointed out, furnace power factor (and consequently transformer MVA rating) depends upon the inductive reactance, and so it is desirable to design for the lowest possible value of this parameter. The further introduction on the primary side of the transformer of capacitors, whether in shunt or in series, increases the network power factor but does not alter the furnace power factor; that is, the phase angle between electrode to- hearth voltage and current remains unchanged. Corrigenda The following amendments should be made to the article entitled 'Coal-preparation routes for maximum coal recovery', which was published in the August issue (vol. 80, no. 8) of this Journal:

Jan 1, 1980

By Derek Ellis

There are two environmental issues which have only recently begun to need planning in detail for marine mining. One is the environmental consequences of mine closure; the other is environmental terrorism. In principle it is not difficult to predict the pattern and rate of biodiversity recovery after mine closure on metalliferous depositional seabeds. 1-5 years to a self-sustaining community of organisms is a generalized guideline, depending on depth and particulate composition. The rate and pattern of biodiversity recovery on some metalliferous hard-rock habitats is far less predictable due to the patchiness and rareness of the habitat. Ecoterrorism at mines, whether on-land or marine, is now to be expected. A good example of resource industry ecoterrorism is the fire-bombing of logging and cement trucks in Oregon in 2001. But there have also been bombs at mine sites, as at Asbestos, Quebec. It is also possible to regard some resource-loss lawsuits as frivolous, hence forms of ecoharassment. Marine mining operations should take note of the development of environmental terrorism (and terrorism in general) and its various manifestations and impacts. Potentially these range from minor work stoppage inconveniences, to serious financial risk jeopardizing the economics of a mine, to jail for company executives, managers and environmental staff, and to harassment and killing of mine personnel.

Jan 1, 2005

By D. Van Orden, Y. Kamiya, R. Lee, E. Ilgren

Crocidolite is a well-known causative agent for mesothelioma. However, studies have shown that the pathogenicity of the fiber from different mines varies considerably and it has been postulated the parameter that appears most likely to account for this variation is fiber width although this has never been formally confirmed. To date, crocidolite appears to be the only asbestos mineral for which an epidemiological study comparing the risk of mesothelioma in a population exposed to ‘thin’ fibers with another exposed to ‘thick’ fibers of the same species may be carried out. Finnish anthophyllite, South African amosite, and African Transvaal crocidolite can also be classified as thick fibers, and there is a paucity of mesotheliomas in populations exposed to them compared to those exposed to thin Cape crocidolite. No thin occurrences of these minerals are known. Our previous study looked at crocidolite from several sources. The present study considers the amphibole anthophyllite found in many places in the world. This mineral, regardless of source, does not show the same variation in fiber width found with crocidolite from different areas. All anthophyllite fibers that have been mined may be classified as thick and populations exposed show very low levels of mesothelioma. We suggest the most likely explanation is related to the fiber width distribution and a concomitant reduction in the ‘Stanton fiber size’ fraction.

Jan 1, 2012

By Kennedy G. L

Experience is reporled in the operation of the pilot Lurgi carbonization plant at Morwell, afler it had been reconstructed to obtain better control of the heating of the briquettes in order to produce a strong char suitable for use as a metallurgical fuel. The theoretical Ideal Heating Cycle, which had been designed from earlier laboratory research, was closely approached in the carbonizer, and up to 97 per cent of the whole dried briquettes entering the carbonizer were recovered unbroken in the char.The strength of the char produced in the pilot plant was limited by the performance of the drier where the cracking and breakage of the briquettes was more severe. Theoretical studies have indicated that this limitation could be removed by using a hot briquette feed to the pilot plant. Experience indicates that with a hot briquette feed to the drier and with ideal heating in the carbonizer, hard char could be produced from Yallourn briquettes in continuous operation.The project has been terminated for economic reasons...

Jan 1, 1966

By Ash M

The world-class iron ore mines at Mt Whaleback, Torn Price and Paraburdoo located in the Hamersley Province of Western Australia must mine the Mt McRae Shale to obtain high grade ore from the Dales Gorge Member of the Brockman Iron Formation. The Mt McRae Shale contains a black pyritic shale lithology that reacts with ammonium nitrate-based explosives. This paper provides an overview of the problems associated with mining this reactive rock type as well as the development of a comprehensive procedure to safely and efficiently blast, excavate and dispose of this material. The strategy used to develop the procedure involved raising the awareness of relevant site personnel to the risks associated in mining the Black Pyritic Mt McRae Shale, obtaining the commitment of these personnel that a detailed procedure was required and that any procedure developed must be followed, otherwise the potential risks such as premature detonation were high. It was also necessary that an on-going training program be implemented so that all relevant new employees would be educated as to the reasons for adhering to the Black Pyritic Shale Procedure.

Jan 1, 1995

By M Ash, P Bellairs

The world class iron ore mines at Mt Whaleback, Tom Price and Paraburdoo located in the Hamersley Province of Western Australia must mine the Mt McRae Shale to obtain high grade ore from the Dales Gorge Member of the Brockman Iron Formation. The Mt McRae Shale contains a Black Pyritic Shale lithology that reacts with Ammonium Nitrate based explosives. This paper provides an overview of the problems associated with mining this reactive rock type as well as the development of a comprehensive procedure to safely and efficiently blast, excavate and dispose of this material.

Jan 1, 1995

By Peter Cain

Twenty years of research into the design of permanent gateroad support (packs) in coal mines have resulted in two methods of pack design based on engineering principles. The first, the detached block concept, is based on static loading of the support system by an hypothetical detached block. The second, the roof beam tilt concept, is based on the dynamic loading of the support system as the roof beam tilts over the roadway about a pivot point located in the rib-side. The roof beam tilt concept has been used on a number of occasions to design packs in a variety of conditions. However, recent work in the Sydney Coalfield of Cape Breton Island, Nova Scotia, has shown that design criteria based on the roof beam tilt concept in its present state of development are far from universal in application. After a review of published pack performance data, including detailed studies conducted in the UK, France and Canada, it was found that consideration of the mechanical properties of the roof beam produced a design criterion that fitted the available data. Modifications to the design process using the roof beam tilt concept are suggested for use in pack design. The work also revealed that current research in other aspects of coal mine ground control, particularly the areas of powered support design and subsidence prediction, may provide valuable information leading to major advances in this field. Such developments could also extend the application of the roof beam tilt concept to the design of pillar systems.

Jan 1, 1993

By H. F. Yancey

AT the annual meeting of this Institute held two years ago a new method, of estimating the grindability of coal was described, based on experimental work carried on by the Bureau of Mines at its Northwest Experiment Station. Since that time, several organizations concerned with the testing or utilization of coal as pulverized fuel have adopted and used the method in determining the grindability of several hundred samples of coal. In addition, a series of comparative tests of this method and three others has been carried out in five laboratories under the auspices of Committee D-5 of the American Society for Testing Materials. As a result the Committee has recommended that the Bureau of Mines method, designated as the "ball-mill method," and the Hardgrove method2, previously advanced, be accepted as tentative standards3. Since the ball-mill method was originally developed and published, an opportunity has been presented to apply it to a larger number of coals and to study intensively some of the principles upon which the method is based. This paper presents a resume of these further studies and includes a comparison with the Hardgrove-machine method. Trial runs were also made with another procedure recently proposed-the C.I.T. roll-test method4.

Jan 1, 1936

By K C. Corin, C T. O’Connor

In recent years it has been shown that the concept of using partial molar excess Gibbs energy (G̅ex) to explain the behaviour of collectors in the recovery of minerals can be usefully applied to explain flotation performance. Fundamentally this is because hydrophobicity of a mineral particle on which a collector is adsorbed may be strongly related to the fact that the alkyl chain associated with the collector behaves in the same way as any hydrocarbon would in an aqueous medium. This hydrocarbon-water system represents a classical non-ideal mixture, and such mixtures are quantified thermodynamically by determining the activity coefficient of the hydrocarbon moiety of the collector and hence its G̅ex in the mixture. It has been shown that G̅ex is a more rigorous indicator of the contributions of various alkyl groups of a collector than HLB (Corin and O’Connor, 2014) and was also able to explain aspects of froth behaviour (Harris and O’Connor, 2017) and hydrophobicity (O’Connor, 2021). The present paper is aimed at extending the above concepts in two different ways. Firstly, a study is undertaken of a range of results previously reported in which various reagents containing different alkyl groups were analysed in terms of their effect on contact angle and their performance as flotation reagents in terms of recovery. These results sustain the previous observations that there is a robust positive relationship between hydrophobicity as indicated by flotation recovery and contact angle and G̅ex of the alkyl group associated with the collector. Secondly, on the basis of the observation that increases in G̅ex are indicative of increases in the hydrophobicity of the mineral particle-collector aggregate, a study was undertaken to examine the effect of ions typical of electrolytes in water as well as the effect of the presence of alcohols and of pH on G̅ex of the collector alkyl group. In the former two instances the absence of any correlation between G̅ex and recoveries supported the proposition of the respective authors of these studies that the major effect of these electrolytes and added alcohols may be on particle–bubble attachment rather than on the hydrophobicity of the mineral/collector in the aqueous system. On the other hand, the effect of pH on G̅ex correlated reasonably well with changes reported in the literature on the effect of pH on recovery and contact angle.

Aug 24, 2022

By G. Vibert Douglas

Introduction A preliminary paper dealing with the subject of ore-shoots was presented to this Society at its Annual Meeting last year (1). The present paper records the attempts which have been made during the interval to further this study. In reporting this work, I wish to state that I do not consider the investigation complete; many more experiments will have to be carried out, and more field data will have to be recorded, before the geologist can say with confidence an ore-shoot should start at this point and pitch in that direction. The aim of these experiments is to find some criteria which will serve the mining engineer and mining geologist concerned with ore-shoots in hydrothermal veins.

Jan 1, 1935

By G. Vibert Douglas

IN a previous paper by Douglas and Gillies (1), a simple field test was given for gold. Later work by the present writers, and by others who have kindly written to us, shows that the test is not as satisfactory as it was hoped. In many cases, the gold mirror is completely obscured by a dense precipitate which, up to the present, it has been found impossible to remove. After many attempts, we have temporarily given up the iodine test and have been working on a simple pyridine reaction based on the work of Putnam, Roberts, and Selchow (2): The ore to be tested is ground to a fine flour. Place half a gram of this powdered ore (an amount that will cover a Canadian ten-cent piece, not heaped) in a six-inch test-tube and add 5 c.c. of aqua regia. The aqua regia. should be made up on each occasion, using four parts of hydrochloric acid and one part of nitric acid, both concentrated. Shake the solution in the test-tube for about one minute and allow to settle until dear. The rime to settle may be 30 to 60 minutes. When dear, a drop of the solution is with-drawn with a fine, dean eye-dropper or capillary tube and placed on à small glass plate. A slide such as is used for mounting rock sections is suitable. Now place an equal sized drop of pyridine solution on the plate beside that of the aqua regia solution to be tested. The pyridine solution, containing nine volumes of hydrogen bromide to one volume of pyridine, can be made up in advance and carried in a glass-stoppered bottle. Join the two drops with a glass thread or fine, dean stick, and allow the merged drops to stand undisturbed. I t is well to place the slide on a piece of white paper so that the presence of the crystals which may form can be easily seen. The time for their formation will vary with the amount of gold present, but the slide should be allowed to stand for at least 30 minutes before negative results are reported. A hand lens of at !east ten magnifications is essential. If gold is present, minute red crystals will form around the margin of the drops as these drops slowly evaporate.

Jan 1, 1938

By T. L. McCall

THE late Walter Herd1 in 1929 gave a full description of past and present conditions in No. 2 mine, Springhill, Nova Scotia, developed theories regarding the cause of these bumps and made certain suggestions regarding possible methods of future development. Recapitulating briefly from Mr. Herd's paper, the seam is bituminous coal, averages 9 ft. in thickness and has a well defined parting containing fusain about 14 in. from the roof. This roof coal is somewhat stronger than the rest of the seam and has a tendency to cling to the roof. The pitch of the seam where it is now being worked is about 20°. The first manifestations of bumps began when the room and pillar workings had reached a depth of cover of 1900 ft. and under continuously increasing depth of cover these bumps increased to such an extent, both in number and severity, that in the year 1924 it became apparent that some change in the system of extraction was necessary. After closely studying all the factors involved and benefiting largely by valuable out-side advice obtained by the Provincial Department of Mines of Nova Scotia,2 the system of working was changed from room and pillar to longwall retreating. Mr. Herd's paper described in detail three remarkable bumps in the year 1928 in April, July and October that affected the 5700-ft. and 5900-ft. East levels, the last bump being so severe both in intensity and in extent of damage done that this district was abandoned. The longwall workings to the west of the slope had been stopped in the year 1926 owing to an inbreak of water, coming from the flooded waste of No. 3 seam lying some 400 ft. vertically overhead. This inflow was not excessive, but a large quantity of water being impounded in the old workings it was considered advisable to take the prudent course and not incur the risk of possibly increasing the flow by further working. This district has remained idle ever since.

Jan 1, 1934