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By B. H. Caudle, L. H. Silberberg

Reservoir depletion by natural water drive is typified by the movement of water from an aquifer into the adjacent oil-bearing formation. Prior studies of this type 01 water movement have generally neglected the resistance to flow in the aquifer and its effect on the movement of water into the oil bearing zone. A method for designing and operating scaled models of such reservoir systems is presented. Experimental data on a model of an edge-water-drive reservoir are shown and discussed. INTRODUCTION Most petroleum reservoirs derive at least a part of their productive capacity from water influx. This water may be injected from the surface or it may come from an aquifer adjacent to the oil zone. In either case, the reservoir engineer must be able to estimate the advance of the water as a function of either the elapsed time or the fluid produced. This paper describes a type of fluid flow model which includes the effect of viscous and gravitational forces in the reservoir and the surrounding aquifer. Natural water influx can be divided into three general (but widely overlapping) categories according to the direction of flow in the aquifer. These are shown schematically in Fig. 1. Fig. l(a) illustrates an edge-water-drive mechanism. In this case, water advances updip along the stratum but the movement of water is essentially horizontal and very little of the oil is actually underlain by water. The bottom-water drive (Fig. l(b)) is characterized by a thick aquifer underlying the oil zone. The water movement is generally vertical in the aquifer. The third category is illustrated in l(c). Referred to as the "thin oil column", this type of oil accumulation consists of oil over water in a relatively thin stratum. Fluid movement is horizontal in both the oil and water zones, except close to the producing well. One characteristic which all three of these types have in common is that part of the water flow takes place in the water invaded region of the oil reservoir while the remainder of the water flow occurs in the aquifer. The resistance to the flow of water usually will not be the same in these two regions. This occurs because the porous rock normally contains only water in the aquifer, while the water-invaded region always contains microscopic globules of bypassed oil (residual oil) which interfere with the flow of water through the rock. The production history of any type of a water-drive system is a function of two phenomena — where the water goes, and how it displaces the oil in the area invaded by the water. It is usually impractical to study these two phenomena at the same time. In most cases one type of analysis is used to predict the gross movement of water in the reservoir, while a different type of analysis is employed to determine the amount of oil to be recovered from the gross volume contacted by the water. The portion of the oil reservoir which is invaded by water is mainly a function of the resistances to fluid flow in the several parts of the flow system. This gross water influx in the three types of natural water drive typically results in water cusping to the production wells either from the side or from below (water coning). In 1747, Muskat described a greatly simplified mathematical model for predicting the area invaded by water in a bottom-water-drive reservoir.1 This model used the Laplace equation and suitable boundary conditions to describe the isopotentials and streamlines in the flow system. The use of this model assumes that (1) the reservoir rock is homogeneous in nature, (2) the oil and water mobilities are equal, (3) there is no oil flowing in the water invaded region, and (4) external forces — such as gravity — do not affect the flow. This method has been used for both natural water drives and water injection projects. In this, as in most models, the method of images is used to reduce the size of the model necessary to describe the reservoir. The assumption of equal viscosities and permea-

Jan 1, 1966

Representatives from 100 countries will focus on aspects of energy, ocean mining, safety, and manpower training at Houston's Astrodomain.

Jan 4, 1978

With the inauguration of Petroleum Technology this year, and approval by the Board to add an Assistant Secretary to the New York staff to serve the Petroleum and Coal Divisions, the Petroleum Division looks forward to greater opportunities and responsibilities. An improved medium of publication offers further incentive to engineers and investigators in the oil industry to make contributions. The authorization by the Board of Directors of a new Assistant Secretary is an appreciation of the splendid contributions made to the industry by the open forum of the Petroleum Division. It is also a recognition of the possibilities of greater service to the membership along the lines established ten to fifteen years ago by DeGolyer, Fohs, Ambrose and Lovejoy, to mention a few leaders. It isexpected that the new officer will spend a substantial part of his time in the field, visiting the student sections, the respective Divisions, helping in the arrangement of papers and Section meetings and intensifying interest in the Institute. The Petroleum Division will hold three meetings this year. The Fall Meetings will be held on Oct. 6 and 7 in San Antonio and on Oct. 20 and 21 in Los Angeles. The programs for these meetings will deal chiefly with engineering research and production engineering problems. Papers on production statistics and general economics of the industry are reserved for the Annual Meeting in New York. The annual production symposium and statistics are accepted as standard for the industry. With continuously deeper penetration into the earth in search for and exploitation of petroleum, it is necessary to have a better understanding of reservoir conditions and to place more phases of the operation under engineering control. Among the subjects relating to reservoir conditions tha thave been proposed for the fall meeting programs are phase equilibria at high pressures, interfacial tension between oil and water, the flow of oil and water through sands, the chemistry of films and underground temperatures. Investigations relating to control of operations include methods of continuously logging while drilling both visually and electrically, methods of studying drilling samples, properties of drilling fluids, improved cementing practices for isolating thin sands under high-temperature conditions and gas conservation, particularly production from high-pressure reservoirs. Additional suggestions of general themes or individual subjects will be welcomed, since it is desirable to build a backlog of material for Petroleum Technology. 9

Jan 1, 1938

By Roger K. Clifford, Gary W. Hudiburgh

The amine flotation of feldspar from a magnetite concentrate produced at a domestic concentrator was investigated using zeta potential measurements, Hallimond tube flotation tests, and laboratory-scale flotation tests. The point of zero charge of six feldspars (microcline, orthoclase, albite, anorthite, anorthoclase, and oligoclase) range from pH 1.4 to 2.5. Hallimond tube flotation tests using amine flotation reagents were performed on these feldspars and on gangue material (quartz, albite, and microcline) from the magnetite concentrating plant. Laboratory-scale (623 g and 2500 g) flotation tests were performed on the magnetite concentrate to float the feldspar. The effects of three different collectors, two levels of collector concentration, three pH levels, starch, HF acid and regrind were investigated.

Jan 1, 1977

THE RELATION OF THE ENGINEER TO RECONSTRUCTION FIFTY-THIRD MEETING OF BOSTON SECTION The fifty-third meeting of the. Boston Section was held April 28. The speaker of the evening was the new president of the Institute, Mr. Howard V. Winchell, who spoke on "The Relation of the Engineer to Reconstruction." He told of the part engineers had played in the war and paid tribute to Herbert E. Hoover as an example of what engineers can do. He said that engineers are not taking enough interest in politics, although it is badly needed as shown by the evidences of Bolshevism even in America. Conditions have suddenly changed; whereas we formerly borrowed money we are now loaning widely to foreign countries and our investments, abroad have to be protected. A committee is badly needed to investigate and determine the actual conditions. The Government has already been invited to cooperate with the Institute along professional lines and this should lead to closer contact between our Society and the Government. Mr. Winchell then went on to describe some of the mining conditions in Russia. He brought out the point that the rich platinum deposits are exhausted and only the poorer sands remain. The largest copper properties average less than 2 per cent. copper and there are some 4,000,000 tons available in .the Caucasus region near Batum. There are approximately 100,000,000 tons of high-grade manganese ore scattered in small deposits in the eastern Ukraine. There are some copper mines in the East, butt they are almost exhausted. The Baku oil field is the second largest in the world and there is probably oil in Persia. There are also manganese in Siberia and coal veins of enormous thickness.

Jan 7, 1919

By Henry M. Howe

THE death of Sir Lowthian Bell removes almost the last of the group of heroic leaders who made their age and ours the Age of Steel-a group which his luster and the luster of his peers, Bessemer, Siemens and Tunner, made one of the most brilliant, perhaps even the most brilliant, in the annals of industry. Born on February 15th, 1816, in Newcastle-on-Tyne, he was the eldest son of Thomas Bell, an alderman of Newcastle, and of his wife Catherine Lowthian of Newbiggin, near Carlisle, in Cumberland, and was christened Isaac Lowthian, the name of his maternal grandfather. His father was born about 1788, and came in 1808 from Newbiggin to Newcastle, where he entered the office of the Cumbrian firm of Losh and Company, manufacturers of alkali and wrought-iron, at the Walker Iron and Alkali Works, at Walker, Dear Newcastle. Young Isaac Lowthian Bell was educated at Dr. Bruce's school in Newcastle, whence he went to Germany and Denmark, learning there German and Danish. On his return he studied at Edinburgh University, and then at the Sorboune in Paris. As a student he already showed the remarkable character and application which later gained him such distinction. After studying the manufacture of alkali near Marseilles, he returned, and when about twenty years old (A.D. 1836) was employed in his father's firm, then called Losh, Wilson, and Bell. After spending a year in their Newcastle offices, and after visiting the important iron-making districts of France, Germany, Poland, and Austria, he took charge of their rolling-mills at Walker, and profited so well by his opportunities, and especially by the teachings of his father and of Mr. John Vaughan (later one of the founders of the great firm of Bolckow, Vaughan & Co.), that he was made manager of the Walker works in or about

Sep 1, 1905

By Iley B. Browning, R. E. Strouder, Coleman D. Hunter, Ralph N. Thomas, George M. Straughan

Activity in the oil fields of the state was at a low ebb during the year because of the longest period of low prices that has yet prevailed, which has been detrimental to both the eastern and western sections of the state. Production for the state as a whole shows a drop of 209,192 bbl. during 1939, the total being 5,356,963 bbl. The loss is in the production of the western division, where a loss of approximately 300,000 bbl. more than offset a gain of approximately 100,000 bbl. in the eastern division. The loss in the western division can be attributed to decline in drilling activity due to the low prices prevailing, which were caused by flooding of the normal markcts with cheap Illinois crude. The gain in the eastern division is the result of repressuring operations begun in previous years and now showing results, and not to any renewed drilling activity. Gas development in western Kentucky during 1939 was of minor importance. In eastern Kentucky approximately 50 producing gas wells were drilled, which were sufficient for present market with excess reserves already developed. With the severe winter and additional industry load every gas well connected has been on line for the past three months. Although all demands are being met, development will be greatly increased during 1940 to meet depletion. From the geological point of view, the drilling activity in the western division developed additional information of benefit. Several wells on blocks of acreage assembled in previous years were drilled in the deeper parts of the Western Coal Basin—southern part of the Illinois Basin— giving for the first time accurate information about the Pennsylvanian and lower formations down to and through the Devonian.

Jan 1, 1940

By Iley B. Browning, George M. Straughan, Coleman D. Hunter, R. E. Strouder, Ralph N. Thomas

Activity in the oil fields of the state was at a low ebb during the year because of the longest period of low prices that has yet prevailed, which has been detrimental to both the eastern and western sections of the state. Production for the state as a whole shows a drop of 209,192 bbl. during 1939, the total being 5,356,963 bbl. The loss is in the production of the western division, where a loss of approximately 300,000 bbl. more than offset a gain of approximately 100,000 bbl. in the eastern division. The loss in the western division can be attributed to decline in drilling activity due to the low prices prevailing, which were caused by flooding of the normal markcts with cheap Illinois crude. The gain in the eastern division is the result of repressuring operations begun in previous years and now showing results, and not to any renewed drilling activity. Gas development in western Kentucky during 1939 was of minor importance. In eastern Kentucky approximately 50 producing gas wells were drilled, which were sufficient for present market with excess reserves already developed. With the severe winter and additional industry load every gas well connected has been on line for the past three months. Although all demands are being met, development will be greatly increased during 1940 to meet depletion. From the geological point of view, the drilling activity in the western division developed additional information of benefit. Several wells on blocks of acreage assembled in previous years were drilled in the deeper parts of the Western Coal Basin—southern part of the Illinois Basin— giving for the first time accurate information about the Pennsylvanian and lower formations down to and through the Devonian.

Jan 1, 1940

By James P. Kimball

AMONG the curious results of the recent advance of prices in the iron trade of the United States, one of them at least is to be regarded as of great importance. I allude to the utilization of mill cinder as a cheap and almost costless substitute for high-priced iron ores in many blast furnaces, situated within easy reach of such raw material. It has been, with but few exceptions, the practice in this country, based upon tradition rather than upon authority or European precedents, to waste this material on 'account of its high proportion of silicic and phosphoric acids, although known to contain more iron than most ores, and although also known to be sometimes applied to the blast furnace in greater or less quantities without serious detriment to the iron for specific purposes. While in use to a limited extent in the Hocking Valley and Hanging Rock iron regions of Ohio for several years, its use in Western Pennsylvania has only become general of late, under the exigencies of high prices and a short supply of ore. Especially has mill cinder largely entered into the stock of furnaces attached to rolling mills in and about Pittsburgh. Under such circumstances the cinder pig has been paddled on the premises, and the malleable iron produced has been unexpectedly good. Cautiously as at first mill cinder has been applied, it is evident that the temptation to use it freely is a strong one whenever the commercial rates for high-class ores are out of proportion to the general conditions of the iron trade, as sometimes happens in this country, especially as the free use of it is apparently justified by the quality of the iron produced from this cheap and abundant material. Indeed the consumption of cinder pig has., not been wholly confined to mills using up the production of furnaces belonging to the same plant. One furnace at least on the Ohio, at Covington, for several' months has been making foundry pig from "all cinder." The iron has gone into the general trade. It is probable that malleable iron of good quality can he made from the poorest cinder pig, but with what degree of economy will

Jan 1, 1881

By George Young

DURING the spring of 1910 I visited a number of open-pit brown-coal mines and underground workings in the vicinity of Halle, Halberstadt, Leipsic, Cologne and Bonn. The notes which I took and the observations which I made at the time have been condensed and make up the principal part of this paper. Certain supplementary information has been taken from several sources which are given in the paper. The mining of brown coal is one of the important industries of Germany. The coal varies in color from dark brown to almost black and is soft like loam. Pieces of wood and strips of bark and, even parts of tree trunks are frequently encountered in the excavation although the coal for the most part consists of a pulverulent, more or less matted mass of small particles of vegetal matter. It is a product between peat and lignitic coal. An analysis, taken from Coal Resources of the World shows the approximate composition of the material: Moisture, 53.73 per cent.; ash, 4.98; fixed carbon, 18.08; volatile carbon, 23.31 per cent. The principal characteristic is the amount of moisture. This seldom runs less than 48 per cent. The ash is usually low and ranges from 5 to 10 per cent. The sulphur content is usually less than 0.5 per cent. The heating effect of the fuel ranges from 2,000 to 2,500 calories.

Jan 2, 1916

By R. P. Smith

THE carbon content of iron-silicon and of iron-manganese alloys at fixed activities of carbon has been reported previously.' It seemed desirable to investigate a system which allows a more extended range of alloy composition within a single phase region. The iron-nickel system is ideal in this respect, in that all alloys from 100 pct Fe to 100 pct Ni are face centered cubic ("austenitic") at 1000 °C. The experimental procedure was similar to that previously described.1,2 The alloys, in the form of pieces about 2 by 2 by 0.2 cm thick, together with a similar specimen of pure iron, were equilibrated with each of a series carbon monoxide-carbon dioxide tnixtures of fixed composition, quenched in the carburizing gas in the top of the furnace and then analyzed for carbon. The carbon content of samples containing more than 0.3 wt pct C was determined by the usual combustion method; those with less carbon

Jan 1, 1961

By Theron Wasson

Michigan's production of 17,301,000 bbl. in 1945, which is in line with previous years, has been maintained by extensions to old fields like Deep River, Adams, Fork, and others. There were a number of new discoveries but, as in the past, these are not given very much importance because enough drilling has not been done to develop their potentialities; however, judging by the past, some of them will develop enough production so that 1946 -will probably be in line with other years. Activities in Michigan were confined to the Basin area of the lower Peninsula, which has been under development since 1925.

Jan 1, 1946

By R. W. Raymond

CLARENCE King born January 6,1842, at Newport, R. I. His ancestors on both sides mere New Englanders, of English blood, and among them not a few distinguished themselves in art, science, politics or commerce. His grandfather, Samuel Vernon King (partner in 1803 in the house of Talbot, O1yphant & King, later known as King $ Co.), was a pioneer in the China trade, and four of his sons succeeded him in the business. Three of the four died in the far East; and one of

Jan 1, 1903

By J. E. Johnson

(Cleveland Meeting, October, 11,1912.) THE subject of blast-furnace slag is one which has had much consideration, particularly from the scientific standpoint, and several years ago technical literature contained many learned discussions on the oxygen-ratio of the acids and the bases, all on the assumption that acids and bases must be present in a ratio depending on molecular weight and chemical valency. Much work has also been done, sometimes in conjunction with the former, on the total heat and the temperature of initial fusion or softening of various slags. A wider knowledge of the blast-furnace now enables us to say that for practical purposes this work has been of almost no value. It is now generally admitted that on the physical side the important point of a given slag is neither its total heat of fusion nor its softening-point, but its free-running temperature, since this is the critical temperature of the furnace. This temperature bears no definite relation to the softening-temperature, as determined by Seger cones, for instance, because some slags melt relatively like ice, with a very short viscous-range, while others melt relatively like tar, with a very long viscous-range. In one the difference between the softening- and the free-running temperature may be very small, as little as 100° F., while in another this difference may easily be 200° or 300°. The importance of this difference is so great in practice as to destroy completely the value of exhaustive investigations, even such as those of 0. Boudouard, published a few years ago.1 * Presented also at the Joint Meeting of the Institute with Section IIIa, Metallurgy and Mining, of the Eighth International Congress of Applied Chemistry, New York, September, 1912. 1 It may not be amiss at this point to call attention to the excellent suggestion of Woolsey McA. Johnson, made several years ago, for determining the temperature at which different slags have the same practical fusibility. This suggestion

Oct 1, 1912

By William P. Shinn

Jan 1, 1881

By P. H. Dudley

THE piping and segregation of ingots of steel is a comprehensive subject, and must be studied in reference to the different grades of soft, medium, and hard steel, rather than to discuss it in a general manner, as though applicable to all grades. Rail steel, however, will receive the most consideration in this paper, for the wheel-loads of the motive pourer and rolling stock have doubled from 1890 to 1910. Steel rails and tires which were efficient under the light loads, became less serviceable under the double wheel-loads, quadrupled tonnage, and higher speeds. Bessemer Steel. Bessemer steel of froth 0.10 to 0.15 per cent. of carbon, for splice-bars, spikes, and tie-plates, rises in setting, and is cast in bottle-mouthed molds, which must be capped to prevent an over-flow from the top. This grade of steel rises in the molds and makes a longer ingot than the volume of molten steel when first teemed. The ingots which are allowed to cool and then cut open, show, particularly in the upper part, large occluded blow-holes, and when they are Dot oxidized or do not contain foreign matter, weld more or less completely when the steel is rolled or forged above 1,100° C., and it :is in this way that the blow-holes are closed it the low-carbon steels.

Jan 4, 1913

By Truman H. Aldrich

The red, or fossiliferous, ore is found in the Clinton group of the Silurian formation. This group is from 100 to 500 ft. thick in Alabama, and its outcrops have been mapped by the State or the U. S. Geological Survey. In some places, it is entirely missing (doubtless islands in the Silurian Sea). In Etowah County, in part of Greasy Cove and vicinity, the upper seam is a coral reef impregnated with the red ore; in this same county, step faults bring up the ore in three or four practically parallel ridges. In Blount County and on Raccoon Mountain, the ore runs under the carboniferous rocks and outcrops in the valleys. When examining the logs of holes drilled for oil, wherever the drill has gone deep enough, the writer has found the Clinton group underlying the Warrior coal field. The following records of holes drilled primarily for oil, given in Bull. No. 22, Geological Survey of Alabama, show the presence of either ore or red rock, and suggest vast resources yet to be outlined and developed for ore in the future. The locations are given by number on the map. Hole No. 1 was drilled 6 miles southeast of Russellville, Franklin County, by the Woodward Oil & Gas Co. It passed through 160 ft. of the Clinton, but only a small show of red ore was found at 1280-1400 ft. A test well, No. 2, drilled near Atwood, Franklin County, in sectioil 26, township 8, range 14, penetrated the Clinton at 1608 ft. and found 38 ft. of limy red rock, also 8 ft. of some blood red ending at 1820 ft., making 46 ft. of red rock in all. It is reported that some good ore was cut through but this work was done by a churn drill. At least 400 ft. of the formation was classified as Clinton. Well NO. 3, called Frankford Well, was bored by S. A. Hobson and associates in the northwest quarter of section 7, township 6, range 12, Franklin County. At 927 ft., it is supposed to have entered the Clinton; the log is as follows: Ft. Sandy limestone with reddish, high ferruginous argillaceous inclusions 10 Same growing more ferruginous................................ 18 Hematitic limestone......................................... 30 Same with slightly less iron.................................... 23 81

Jan 1, 1925

By Joseph W. Leonard, T. S. Spicer

INTRODUCTION Reasons for Thermal Drying The continuing increase in the percentage of minus %-inch coal produced as a result of the increased use of mechanical mining methods has, over the years, tended to shift considerable portions of the work of producing saleable coal to the fine coal cleaning section of the preparation plant. Because a given weight of fine coal will contain substantially greater surface area than an equivalent weight of coarse coal, it follows that, when subjected to wet cleaning processes, the fines will absorb and retain consider- ably more moisture than coarser fractions. Increased moisture pickup in the finer sizes complicates fine coal cleaning since beneficiation may not be limited to the removal of ash and sulfur but often must be expanded to include the additional step of thermal drying to remove excessive moisture. Thus, water which provides the medium for cleaning fine coal is in itself detrimental and, like ash and sulfur, reduces coal quality. Removal of surface moisture by drying is done for one or more of the following 1 reasons: (1) To avoid freezing difficulties and to facilitate handling during shipment, storage and transfer to the points of use; (2) to maintain high pulverizer capacity; (3) to reduce heat loss due to evaporation of surface moisture from the coal in the burning process, thus increasing heating efficiency; (4) to improve the quality of coal used for special purposes, such as in the production of coke, briquettes, and chemicals; (5) to decrease transportation costs; and (6) to facilitate dry coal-cleaning processes. Because benefits to coal transportation and utilization are the most common reasons for thermal drying, the following sections will examine these areas in greater detail. Benefits to Transportation Initial benefits from drying are the reduction of shipping costs from the mine to the point of utilization since more coal can be concentrated into a given weight of product when worthless moisture is removed. Non- combustible~ such as water and mineral matter in railroad shipments of coal are billed the same as coal at $3.32 per ton, according to the recent average costs. Savings of 10 to 20 dollars from drying on the shipment cost of each 50 to 60 tons of coal contained in a typical railroad car is common. Savings on coal shipments from individual mines which result from coal drying can be expressed in terms of hundreds of thousands of dollars and more each year. For example, a reduction of shipping charges of only 5 percent on one million tons per year would mean a savings of 166,000

Jan 1, 1968

By J. E. Johnson

IT is the purpose of the present paper, while not excluding chemical considerations, to deal more extensively with some of the physical and mechanical aspects of the blast-furnace process, and to point out its dependence in these respects on well-known laws. The quantity and cost of ore and flux required to make a ton of iron being determined by circumstances over which the furnace-man, under given conditions as to quality and quantity of product, has commonly little control; the principal item of cost, apart from the saving of labor, which he can aspire to reduce, is that of fuel. To determine the limits of possibility in this direction is clearly the first step in d practical inquiry; and this step is represented herewith in Fig. 1, a diagram showing the total useful effect obtained from a pound of fuel under various conditions, and thus permitting direct comparison, under any given conditions, between actual results and the maximum possible results. The following statements will explain the basis upon which this diagram has been constructed. One pound of fuel, containing 90 per cent. of fixed carbon (which represents average conditions), is taken as the unit. The degree of oxidation of the carbon is measured by the ratio of the two oxides of carbon contained in the top-gases. It is necessary to remember that a considerable quantity of carbon is brought in as carbon dioxide by the flux, and to take account of it and of its condition. It is here considered that the carbon dioxide liberated by the limestone does not affect the analysis of the toll-gases, and that the ratio of CO to CO., will remain unchanged by the addition of limestone; enough CO, being reduced by the solution

Sep 1, 1905

By George J. Young

DURing the spring of 1910 1 visited a number of open-pit brown-coal mines and underground workings in the vicinity of Halle, Halberstadt, Leipsic, Cologne and Bonn. The notes which I took and the observations which I made at the time have been condensed and make up the principal part of this paper. Certain supplementary information has been taken from several sources which are given in the paper. The mining of brown coal is one of the important industries of Germany. The coal varies in color from dark brown to almost black and is soft like loam. Pieces of wood and strips of bark and even parts of tree trunks are frequently encountered in the excavation although the coal for the most part consists of a pulverulent, more or less matted mass of small particles of vegetal matter. It is a product between peat and lignitic coal. An analysis, taken from Coal Resources of the World shows the approximate composition of the material: Moisture, 53.73 per cent.; ash, 4.98; fixed carbon, 18.08; volatile carbon, 23.31 per cent. Thc principal characteristic is the amount of moisture. This seldom runs less than 48 per cent. The ash is usually low and ranges from 5 to 10 per cent. The sulphur content is usually less than 0.5 per cent. The heating effect of the fuel ranges from 2,000 to 2,500 calories. The commercial deposits are confined to the Tertiary period although

Jan 1, 1916