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By Richard L. Ash, J. H. Kelley, W. H. McCracken, William Bellano, J. D. Morgan, D. R. Mitchell

Rubber-tired shuttle cars are finding increased use as gathering units in under-ground mines. As the name implies, they shuttle back and forth between the loading machine and the section transportation system. In many mines their use has in-creased the efficiency of the loading and gathering operations, resulting in increased output per man employed and decreased costs per ton. A car motivated by cable reel is shown in Fig I, and a car with battery power in Fig 2. A brief chronological account of the development of rubber-tired haulage equip-ment follows: 1936. J. H. Fletcher1 installed his first unit for the Blue Bird Coal Co., Carrier Mills, Illinois. This unit consisted of a battery-powered industrial tractor and a trailer with drop-bottom doors. The coal was transported for short distances to a hopper for discharge into mine cars. 1938. A battery-powered self-contained shut-tle car with rubber-tired wheels was built by the Joy Manufacturing Co. Two units were installed for the Katherine Coal Co., Lumberport, West Virginia. The shuttle car consisted of a materials-receiving body with a conveyor in the bottom to move the coal forward during loading and to unload the coal at the discharge station. 1938. A cable-powered shuttle car with four-wheel drive and four-wheel steer was developed by A. L. Lee. Special wheels mounted on king pins on the car permitted all four wheels to be steered. The cable reel was driven by a torque motor to give the cable proper tension during the payout and uniform tension when rewound on the reel. 1940. A Joy shuttle car equipped with trolley poles and a cable reel was developed to operate on a double trolley-wire system.2 This unit was installed at a potash mine of the International Minerals and Chemicals Corporation at Carlsbad, New Mexico. It is believed to have been the first installation of its kind, and the first of shuttle cars for handling material other than coal. 1941. Truck haulage3 was introduced in the Tri State District by the Eagle-Picher Mining and Smelting Company. Storage battery electric trucks were rebuilt to handle a bottom-dump trailer. 1941—Joy shuttle cars were installed in a mine of the United States Gypsum Company, Oakfield, New York. 1943—Joy shuttle cars were installed in several bauxite mines.4,5 1945—Joy shuttle cars installed in a lime-stone mine. Because of the nature of bituminous coal beds trackless equipment has had its greatest application in bituminous coal mining. Usually a shuttle car is filled by a continuous type of loader. In Fig 3 is shown a continuous machine loading coal into a battery-powered shuttle car, 48-in. coal. However, intermittent types of load-

Jan 1, 1949

By W. A. Koehler, M. E. Hinkle

THE oxidation of pyrites and marcasite in coal-mine strata to produce discolored acid mine drainage has long been explained by chemical reactions occurring in three stages: 1. The iron sulphide minerals are oxidized by air in the presence of water to produce a nearly colorless solution of ferrous (iron) sulphate and some sulphuric acid. 2, The ferrous sulphate and part of the sulphuric acid combine with additional oxygen to form ferric (iron) sulphate. 3. The ferric sulphate hydrolyzes to form a reddish-brown precipitate and additional sulphuric acid. Nevertheless, chemical data alone are not sufficient to explain all observed facts. The first stage seems to proceed more slowly in the chemical laboratory than in nature. The second and third stages normally occur to a marked extent within a few days with raw mine water. However, the visible discoloration that characterizes these latter stages will not develop for months if the mine water is sterilized. By means of bacteriological techniques, two organisms have been isolated from acid coal-mine drainage. These are believed to have a part in promoting the chemical reactions summarized above. One organism is considered to be Thio-6aciZZus thiooxidans, which is known to be able to convert elementary sulphur or sodium thiosulphate to sulphuric acid. Its relation to the formation of acid mine drainage has not Yet been established. Apparently it does not Promote the oxidation of ferrous iron compounds in mine drainage to the ferric state. The second organism has not been identified by name but is described as " Gram negative, non-spore-forming rods approximately 0.4 micron wide by 0.8 to 1.0 micron long." A pure culture of this when added to sterile mine water will cause the latter to become amber and develop the typical rusty precipitate. However, it has not been found to convert sulphur compounds to sulphuric acid. Further research is planned to determine whether or not these microorganisms play a significant part in the first stage of oxidation whereby pyrites and marcasite minerals go into solution. Some of the conditions found in abandoned sections of coal mines, such as a reduced Percentage of Oxygen and increased percentage of carboll 'dioxide in the air, as well as the existing temperature and acidity ranges, will be tolerated by and may even be favorable to these organisms. Acid Coal Mine Drainage Acid coal mine drainage has been the concern of coal mine operators, industrialists, sportsmen and public officials for many years. The amount of acid flowing into our streams in the coal-producing areas varies considerably from mine to mine and from

Jan 1, 1949

By A. T. Beckwith

This paper concerns measurements of low-velocity air currents and investigations on mine ventilation by means of chemical smoke. The chemical smoke used is produced without flame and at ordinary mine temperatures, and therefore presents no ignition hazard in gaseous mines. Mining men who have worked in open-light mines are familiar with the use of tobacco smoke in determining the direction of air travel and approximately measuring low-velocity air currents. The use of chemical smoke is merely a refinement on the use of tobacco smoke and the flameless low-temperature source of chemical smoke has the additional advantage that it can be used in gaseous mines. Ventilation smoke apparatus, Fig I, is a simple device for producing dense white smoke. The apparatus as shown consists of a rubber aspirator bulb which is used to force air through a glass "smoke tube" containing a chemical substance that produces a dense white smoke on contact with air. The apparatus was developed by engineers of the U. S. Bureau of Mines.' It is inexpensive, weighs less than 3 oz, is easily carried in a pocket, and requires no skill to operate. Smoke apparatus is invaluable in practical mine ventilation work for: (I) measuring low-velocity air currents, (2) detecting air leakage, (3) observing airflow characteristics. This paper is written to show the merits of the apparatus, and is based upon findings through its extensive use, during the past six years, in mines operated by the Lehigh Navigation Coal Co. Inc. The Apparatus Certain chemicals, such as stannic chloride (SnCl4) and pyrosulphuric acid (H2S2O7) produce "white smoke" when exposed to air. Stannic chloride gives off vapors which on contact with moist air cause the formation of solid hydrates, of which SnCl4.5H20 is the most important. Pyrosulphuric acid decomposes when exposed to air with the evolution of sulphur trioxide (SO3) fumes, which become white upon contacting moisture in the air. A chemical, such as one of the above, is the active substance in a smoke tube. The glass tubes are hermetically sealed during manufacture, and are made ready for use by merely breaking off the tips at the conveniently located file cuts. When the smoke tube is connected to the aspirator, depressing the aspirator bulb forces air into contact with the chemical, and smoke discharges from the open end of the tube. A white solid (a hydrate if stannic chloride is used, or sulphur trioxide if pyrosulphuric acid is used) may occasionally form a cake in the outlet opening of a smoke tube. A small wire such as an ordinary paper clip can be conveniently employed to dislodge the cake should it seal the tube. When the assembled apparatus is not

Jan 1, 1949

By John E. Conley

The slate industry of the United States has shown a marked decline in value of products made annually since the peak year 1925, although there has been moderate improvement over the lean years 1932 to 1934. In 1940, the value of all slate products sold was approximately 5¾ million dollars for a total output of 473,450 short tons. The quantity sold was a little less and the value a great deal lower than the annual averages for the past two decades. Enormous quantities of waste materials result from the quarrying, splitting and milling of slate. Obviously, utilization of such waste material is desirable, not only from the viewpoint of economical operation but also for the purpose of conserving natural resources. One possible use is to produce expanded or puffed lightweight aggregate for use in concretes. Such concretes are strong enough for specific uses, and the advantage of lightness could be obtained in such structures as the walls and roofs of buildings, suspension-bridge roadways and various other applications where weight is a factor. Conceivably, these uses could consume an appreciable annual tonnage. Use of Waste Slates for Making Aggregates The lightweight-aggregate industry has been discussed elsewhere4,5 and need not be covered in detail in this paper. The materials commonly utilized are naturally occurring aggregates such as volcanic cinder, tuff and pumice; by-product materials, such as ordinary cinders and air-cooled slags; and the specially manufactured products, including Haydite, Pottsco, Gravelite, Cel-seal, Superock and Waylite. Slates, however, have not been given the consideration they merit, especially in the United States. In the British Isles, some work has been done3 on certain Welsh slates by the Building Research Station to stimulate the use of these wastes. Requirements for Raw Materials As pointed out by Hughes,4 the lightweight-aggregate industry is segregated in regions adjacent to large cities in order to localize the market and avoid the necessity of long freight haulage. Waste slate from the deposits of eastern Pennsylvania, northern Maryland, and Virginia would meet the basic requirement of ally low-priced structural raw material. One apparent advantage is attained when slate waste, normally discarded, is utilized in the manufacture of a by-product. Mining or quarrying costs usually have been assessed against the main product. Some additional grinding might be desirable, but this operation would be relatively cheap, as most slates grind easily. It is believed that virtually all slates, when properly heated, will expand to some degree. However, types that will expand from 3 to 7 times their original volume are preferred. Fig, I illustratcs the expansion of a Pennsylvania slate. The cube originally

Jan 1, 1942

By John E. Conley

The slate industry of the United States has shown a marked decline in value of products made annually since the peak year 1925, although there has been moderate improvement over the lean years 1932 to 1934. In 1940, the value of all slate products sold was approximately 5¾ million dollars for a total output of 473,450 short tons. The quantity sold was a little less and the value a great deal lower than the annual averages for the past two decades. Enormous quantities of waste materials result from the quarrying, splitting and milling of slate. Obviously, utilization of such waste material is desirable, not only from the viewpoint of economical operation but also for the purpose of conserving natural resources. One possible use is to produce expanded or puffed lightweight aggregate for use in concretes. Such concretes are strong enough for specific uses, and the advantage of lightness could be obtained in such structures as the walls and roofs of buildings, suspension-bridge roadways and various other applications where weight is a factor. Conceivably, these uses could consume an appreciable annual tonnage. Use of Waste Slates for Making Aggregates The lightweight-aggregate industry has been discussed elsewhere4,5 and need not be covered in detail in this paper. The materials commonly utilized are naturally occurring aggregates such as volcanic cinder, tuff and pumice; by-product materials, such as ordinary cinders and air-cooled slags; and the specially manufactured products, including Haydite, Pottsco, Gravelite, Cel-seal, Superock and Waylite. Slates, however, have not been given the consideration they merit, especially in the United States. In the British Isles, some work has been done3 on certain Welsh slates by the Building Research Station to stimulate the use of these wastes. Requirements for Raw Materials As pointed out by Hughes,4 the lightweight-aggregate industry is segregated in regions adjacent to large cities in order to localize the market and avoid the necessity of long freight haulage. Waste slate from the deposits of eastern Pennsylvania, northern Maryland, and Virginia would meet the basic requirement of ally low-priced structural raw material. One apparent advantage is attained when slate waste, normally discarded, is utilized in the manufacture of a by-product. Mining or quarrying costs usually have been assessed against the main product. Some additional grinding might be desirable, but this operation would be relatively cheap, as most slates grind easily. It is believed that virtually all slates, when properly heated, will expand to some degree. However, types that will expand from 3 to 7 times their original volume are preferred. Fig, I illustratcs the expansion of a Pennsylvania slate. The cube originally

Jan 1, 1942

By R. K. Hopkins

For a great many years fusion welding has been used in and around petroleum refineries, but it is only within six or seven years that the more important pressure vessels have been constructed by this process, because before that time the properties of fusion welds would not withstand such rigorous service. Since the adoption of fusion welding for the construction of this equipment, the refiner has required pressure vessels suitable for operation over a very wide range of conditions. On the one hand, vessels must operate at extremely high temperatures, in the range of 950" to 1000° F., and on the other vessels must be suitable for operation at sub-zero temperatures down as low as —75" F. Also, vessels are required suitable for operation at pressures upwards of 1000 lb. per sq. in., and as low as a 29-in. vacuum. In addition, vessels are required to withstand the attack of very corrosive mediums. It has been a rather difficult task for the fabricator to meet all of these requirements, but as a result of the extensive research carried on by steel manufacturers and several fabricators of class I vessels, practically all of these demands have been met. In order to meet the refiners' requirements for this wide range of conditions, the fabricator has worked closely with the metallurgist. This has enabled him to choose the proper base metal for each service condition, but it has been the fabricator's problem to develop a welding rod and welding technique, as well as a heat-treatment, that would produce in the welded vessel characteristics in and around the weld comparable to those in the base metal. Where corrosion is not a serious problem, and where the operating temperatures are not too high, ordinary carbon steel has served very well. But, when corrosion is serious, and/or when the temperatures are either very high or very low, it is necessary to use some form of alloy steel to give satisfactory service. A great deal of credit is due to the members of the Boiler Code Committee and also to the members of the Joint A.P.I.-A.S.M.E. Committee, who have formulated codes that insure the safety of the

Jan 1, 1935

By R. K. Hopkins

For a great many years fusion welding has been used in and around petroleum refineries, but it is only within six or seven years that the more important pressure vessels have been constructed by this process, because before that time the properties of fusion welds would not withstand such rigorous service. Since the adoption of fusion welding for the construction of this equipment, the refiner has required pressure vessels suitable for operation over a very wide range of conditions. On the one hand, vessels must operate at extremely high temperatures, in the range of 950" to 1000° F., and on the other vessels must be suitable for operation at sub-zero temperatures down as low as —75" F. Also, vessels are required suitable for operation at pressures upwards of 1000 lb. per sq. in., and as low as a 29-in. vacuum. In addition, vessels are required to withstand the attack of very corrosive mediums. It has been a rather difficult task for the fabricator to meet all of these requirements, but as a result of the extensive research carried on by steel manufacturers and several fabricators of class I vessels, practically all of these demands have been met. In order to meet the refiners' requirements for this wide range of conditions, the fabricator has worked closely with the metallurgist. This has enabled him to choose the proper base metal for each service condition, but it has been the fabricator's problem to develop a welding rod and welding technique, as well as a heat-treatment, that would produce in the welded vessel characteristics in and around the weld comparable to those in the base metal. Where corrosion is not a serious problem, and where the operating temperatures are not too high, ordinary carbon steel has served very well. But, when corrosion is serious, and/or when the temperatures are either very high or very low, it is necessary to use some form of alloy steel to give satisfactory service. A great deal of credit is due to the members of the Boiler Code Committee and also to the members of the Joint A.P.I.-A.S.M.E. Committee, who have formulated codes that insure the safety of the

Jan 1, 1935

By G. E. Archie

Data given in this paper indicate that certain relations exist between different characteristics of sandstone. These relations are not rigid, for all sandstones are more or less heterogeneous. Not every increment of a given horizon follows exactly the relationship; however, studying a reservoir as a whole from a large number of samples, definite trends are found to exist. Apparently nature's processes of sedimentation and diagenesis are such as to give some degree of uniformity. Average relationships are valuable because electrical measurements in a borehole comprise a considerable volume of rock near the hole. Also, it is desirable that a given producing reservoir be studied as a unit. In a permeable reservoir whose pores are filled with a saline solution, it was found that the total porosity and the type of sandstone influence the relationship between its electrical resistivity and the RO and the resistivity of the brine R,. The relation can be expressed by the following empirical equation, Ro = R10O— [i] where 0 is the porosity expressed as a fraction and the numerical value of the exponent lies between 1.8 to 2.0 for consolidated sandstones, and is about 1.3 for clean, unconsolidated packs. This equation indicates that an appropriate electrical log can be used to estimate the porosity of a saline water-bearing reservoir when Rw and the type of rock are known. The fraction R0rw, is called the "formation resistivity factor." It reflects the effect of the nonconducting rock structure on the resistivity of the salt water that fills the tortuous paths through which the electricity must pass. The formation resistivity factor F is found to be related to permeability k. In this case the type of rock plays an important role, as shown by the relation F = ak-b [2] where the values of a and b must be determined experimentally for each horizon. Therefore Eq. I rather than Eq. 2 is used when it is desired to determine the value of F, because small changes in rock structure particularly in the pore size are not critical. Another useful relation, R = R0S- [3] where R = resistivity of rock when partially saturated with brine and partly with oil or gas, S = fraction of the pore space filled with brine, and n equals approximately 2 for both unconsolidated and consolidated sandstone, shows that the connate water of an oil or gas reservoir can be estimated in situ from a resistivity log. Equation 3 shows that in order to estimate the water content of a reservoir a knowledge of R and Ro is essential. The first value can be obtained from the electrical log when all factors influencing the resistivity curve can be properly taken into account. The latter may be obtained when a log is available on the same horizon where it is entirely water-bearing and has

Jan 1, 1946

By G. E. Archie

Data given in this paper indicate that certain relations exist between different characteristics of sandstone. These relations are not rigid, for all sandstones are more or less heterogeneous. Not every increment of a given horizon follows exactly the relationship; however, studying a reservoir as a whole from a large number of samples, definite trends are found to exist. Apparently nature's processes of sedimentation and diagenesis are such as to give some degree of uniformity. Average relationships are valuable because electrical measurements in a borehole comprise a considerable volume of rock near the hole. Also, it is desirable that a given producing reservoir be studied as a unit. In a permeable reservoir whose pores are filled with a saline solution, it was found that the total porosity and the type of sandstone influence the relationship between its electrical resistivity and the RO and the resistivity of the brine R,. The relation can be expressed by the following empirical equation, Ro = R10O— [i] where 0 is the porosity expressed as a fraction and the numerical value of the exponent lies between 1.8 to 2.0 for consolidated sandstones, and is about 1.3 for clean, unconsolidated packs. This equation indicates that an appropriate electrical log can be used to estimate the porosity of a saline water-bearing reservoir when Rw and the type of rock are known. The fraction R0rw, is called the "formation resistivity factor." It reflects the effect of the nonconducting rock structure on the resistivity of the salt water that fills the tortuous paths through which the electricity must pass. The formation resistivity factor F is found to be related to permeability k. In this case the type of rock plays an important role, as shown by the relation F = ak-b [2] where the values of a and b must be determined experimentally for each horizon. Therefore Eq. I rather than Eq. 2 is used when it is desired to determine the value of F, because small changes in rock structure particularly in the pore size are not critical. Another useful relation, R = R0S- [3] where R = resistivity of rock when partially saturated with brine and partly with oil or gas, S = fraction of the pore space filled with brine, and n equals approximately 2 for both unconsolidated and consolidated sandstone, shows that the connate water of an oil or gas reservoir can be estimated in situ from a resistivity log. Equation 3 shows that in order to estimate the water content of a reservoir a knowledge of R and Ro is essential. The first value can be obtained from the electrical log when all factors influencing the resistivity curve can be properly taken into account. The latter may be obtained when a log is available on the same horizon where it is entirely water-bearing and has

Jan 1, 1946

By William M. Newton, John E. Sherborne

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By John E. Sherborne, William M. Newton

The value of the electric log as a means of interpreting underground structures has been increasingly demonstrated by its almost universal present-day use. It becomes important, therefore, to be able to evaluate the factors that affect the values obtained. By far the greatest number of electric logs are measured today in boreholes filled with rotary mud, the properties of which may exert an important influence on the electric log. In an effort to establish what the order of magnitude of such effects might be, a series of investigations was made in the laboratory and the field. Apparatus suitable for either field or laboratory use was designed and a procedure established for determining the factors that affect the resistivity of drilling muds over a wide variation in mud condition. Five muds representative of the types of clay-base muds employed in California were tested and the following observations were made: 1. The effect of raising the temperature from 8o° to i8o°F. is to decrease the resistivit~ of the mud or filtrate approximately 50 per cent. 2. The resistivity of the mud in most cases closely approximates that of its filtrate. 3. The change in the resistivities of muds caused by the addition of chemical is not the same function of the amount of chemical added for each mud. 4. The effect produced by increased sodium chloride content is to reduce markedly the resistivity of the mud and its filtrate. 5. Weighting materials, such as baroid and limestone, tend to increase the resistivity of drilling mud. 6. Cement and counteracting reagents reduce mud resistivity. The results of the investigation indicate that the mud resistivity is materially affected by the addition of electrolytes whether these are added for the purpose of conditioning the mud or enter the mud when salt beds or highly saline structures are penetrated. It should be observed, however, that the magnitude of the effect produced upon the electric log by changes in mud resistivity is also dependent upon the relative salinity of the water en. countered in the formation being logged. The laboratory data are supplemented by field data, which indicate that both the self-potential and resistivity curves are influenced by mud resistivity.

Jan 1, 1946

By W. M. Rust, W. D. Mounce

The almost universal acceptance of electrical logging by the petroleum industry calls for a critical examination of the physical bases of the common methods. This is particularly needed for the natural potential log. The conventional explanations are based on the phenomena of electrofiltration and electro-osmosis. However, experimental data show that they fail to give a basis that is quantitatively sound. Moreover, they lead to interpretations of details of electrical logs that are erroneous. It was found experimenlally that when a plug of shale is placed in a chain of dissimilar electrolytes, a current flow results. Experiments on oil-well cores and fluids similar to those existing in wells show that potentials are set up which are in reasonable agreement with those encountered in electrical logging. Doubtless other sources of potential are important but this explanation not only accounts for much of the potential but also clarifies some fairly familiar examples of misinterpretations. Introduction The extraordinary value of electrical well logging as a tool for petroleum engineers and geologists is now so universally recognized that it is not necessary to point out the ways in which it can be useful. It is sufficient to mention only the saving that has resulted from the elimination of much coring that would have been necessary under former practices and the considerable additions to reserves resulting from the discovery of sands missed in coring. Paradoxically, the very remarkable success that has resulted from the application of electrical logging to correlation and completion problems has cost some of its most consistent users dearly.' The fact that some operators have placed unwarranted faith in erroneous interpretatioils of electrical logs does not reduce the value of the logs. It should, however, make one pause long enough to ask why experienced users should be misled. The answer to this question is not hard to find. In nearly every case, the fault has been oversimplification. This is illustrated very aptly by the familiar interpretation and theory of the natural potential log. Recording and Interpreting Logs The natural potential log is extremely simple to record precisely enough for all present-day uses. One needs only an electrode, a cable to lower the electrode through the drilling mud, a recording meter and a surface ground connection. The electrode can be elaborate but need not be. A simple brass rod 2 in. in diameter and 2 or 3 in. long is quite satisfactory. The cable need not be particularly well insulated, nor need it have a very low resist-

Jan 1, 1946

By W. M. Rust, W. D. Mounce

The almost universal acceptance of electrical logging by the petroleum industry calls for a critical examination of the physical bases of the common methods. This is particularly needed for the natural potential log. The conventional explanations are based on the phenomena of electrofiltration and electro-osmosis. However, experimental data show that they fail to give a basis that is quantitatively sound. Moreover, they lead to interpretations of details of electrical logs that are erroneous. It was found experimenlally that when a plug of shale is placed in a chain of dissimilar electrolytes, a current flow results. Experiments on oil-well cores and fluids similar to those existing in wells show that potentials are set up which are in reasonable agreement with those encountered in electrical logging. Doubtless other sources of potential are important but this explanation not only accounts for much of the potential but also clarifies some fairly familiar examples of misinterpretations. Introduction The extraordinary value of electrical well logging as a tool for petroleum engineers and geologists is now so universally recognized that it is not necessary to point out the ways in which it can be useful. It is sufficient to mention only the saving that has resulted from the elimination of much coring that would have been necessary under former practices and the considerable additions to reserves resulting from the discovery of sands missed in coring. Paradoxically, the very remarkable success that has resulted from the application of electrical logging to correlation and completion problems has cost some of its most consistent users dearly.' The fact that some operators have placed unwarranted faith in erroneous interpretatioils of electrical logs does not reduce the value of the logs. It should, however, make one pause long enough to ask why experienced users should be misled. The answer to this question is not hard to find. In nearly every case, the fault has been oversimplification. This is illustrated very aptly by the familiar interpretation and theory of the natural potential log. Recording and Interpreting Logs The natural potential log is extremely simple to record precisely enough for all present-day uses. One needs only an electrode, a cable to lower the electrode through the drilling mud, a recording meter and a surface ground connection. The electrode can be elaborate but need not be. A simple brass rod 2 in. in diameter and 2 or 3 in. long is quite satisfactory. The cable need not be particularly well insulated, nor need it have a very low resist-

Jan 1, 1946

By Warren J. Jackson, John L. P. Campbell

Automatic recording of the radioactivity of the earth's formations provides a log of relative intensities that, if properly interpreted, can be applied to oil-field engineering. Production, engineering, and geological departments regard the radioactivity log as a forward step in the securing of more conclusive information for successful well completions. Explanations of the technique, together with some of the problems to which radioactivity logging have been applied, are presented in this paper. Introduction Those responsible for the completion of new oil and gas wells, or with planning workover operations on old wells, have followed closely the development of radioactivity well logging because they are interested in reducing the number of unknowns that usually are present in such work. Many operators have made use of the log, or are acquainted with at least one of the applications, but it is unlikely that any one operator is familiar with all of the many applications that are possible. The purpose of this paper is to present a representative example of each of the many applications, wherever the information has been released by an operator, and to illustrate by hypothetical examples other applications, releases for which have not been given. In this way, it is hoped that a better understanding of the scope of this new engineering tool may be obtained. Athough the literature contains many references that describe in detail the theory, development, and application of radioactivity well logging, a brief discussion of the technique may be helpful to those who are investigating the subject for the first time, All rocks contain radioactive material in varying concentrations. In general, shales contain relatively more radioactive material than sandstones or limestones. These radioactive materials disintegrate with time into other materials of lower atomic weight, and in that process of disintegration the rocks are emitting many rays, the most penetrating of which is the gamma ray. The intensity of emission of the gamma ray is proportional to the quantities of radioactive materials present. A higher rate of emission would be observed, therefore, opposite a shale than opposite a sandstone or limestone. Since measurable intensities of gamma rays are capable of penetrating as many as five concentric strings of casing, and as the gamma-ray intensity is relative to the formations, the measurements of variations in gamma-ray intensities offer a means of identifying cased-off formations in their proper stratigraphic sequence. TEe Gamma-ray Curve The measurement of gamma-ray intensi ties is accomplished by means of an ioniza-tion chamber that consists of a heavy cylinder, about 3 ft. long, that contains two insulated electrodes and is Med with an inert gas under high pressure. Under normal conditions no current will flow through the gas when an electrical potential is set up between the electrodes, but when

Jan 1, 1946

By John L. P. Campbell, Warren J. Jackson

Automatic recording of the radioactivity of the earth's formations provides a log of relative intensities that, if properly interpreted, can be applied to oil-field engineering. Production, engineering, and geological departments regard the radioactivity log as a forward step in the securing of more conclusive information for successful well completions. Explanations of the technique, together with some of the problems to which radioactivity logging have been applied, are presented in this paper. Introduction Those responsible for the completion of new oil and gas wells, or with planning workover operations on old wells, have followed closely the development of radioactivity well logging because they are interested in reducing the number of unknowns that usually are present in such work. Many operators have made use of the log, or are acquainted with at least one of the applications, but it is unlikely that any one operator is familiar with all of the many applications that are possible. The purpose of this paper is to present a representative example of each of the many applications, wherever the information has been released by an operator, and to illustrate by hypothetical examples other applications, releases for which have not been given. In this way, it is hoped that a better understanding of the scope of this new engineering tool may be obtained. Athough the literature contains many references that describe in detail the theory, development, and application of radioactivity well logging, a brief discussion of the technique may be helpful to those who are investigating the subject for the first time, All rocks contain radioactive material in varying concentrations. In general, shales contain relatively more radioactive material than sandstones or limestones. These radioactive materials disintegrate with time into other materials of lower atomic weight, and in that process of disintegration the rocks are emitting many rays, the most penetrating of which is the gamma ray. The intensity of emission of the gamma ray is proportional to the quantities of radioactive materials present. A higher rate of emission would be observed, therefore, opposite a shale than opposite a sandstone or limestone. Since measurable intensities of gamma rays are capable of penetrating as many as five concentric strings of casing, and as the gamma-ray intensity is relative to the formations, the measurements of variations in gamma-ray intensities offer a means of identifying cased-off formations in their proper stratigraphic sequence. TEe Gamma-ray Curve The measurement of gamma-ray intensi ties is accomplished by means of an ioniza-tion chamber that consists of a heavy cylinder, about 3 ft. long, that contains two insulated electrodes and is Med with an inert gas under high pressure. Under normal conditions no current will flow through the gas when an electrical potential is set up between the electrodes, but when

Jan 1, 1946

By H. G. Doll

'This paper discusses a method and apparatus for determining the dip of formations traversed by a drill hole, by means of electrical measurements in the hole. The process consists in recording the Spontaneous Potentials present along three oriented generatrices in the hole. By comparison of the three curves thus obtained, after application of a correction factor to compensate for any deviations of the hole, the dip angle and the dip direction are determined. Excellent accuracy is obtained for dip angles over 10°. Because the method is simp1e and the apparatus rugged, the measurements are rapid and reliable; consequently, they can be made at all the levels that are of interest at any time after the well has been drilled. Mechanical cores are not needed to evaluate the dips. A convenient, time-saving procedure is to perform the dipmeter survey at the time the electrical log is taken, using for both operations the same cable and truck. Actual examples of results obtained in wells of the Gulf Coast area are given. Introduction The problem of determining the angle and direction of the dip of the strata traversed by a drill hole has practical interest, and sometimes vital importance, which need not be emphasized to the oil industry. The need for that type of information has existed ever since wells have been drilled. Certainly it has not subsided, in spite of the numerous inventions and improvements made in other fields of the art of drill-hole exploration. The few examples given in this paper are but illustrative of this fact. In the past, methods have been devised, and used, to solve this problem, but generally they have met with limited success, possibly because they failed more or less to answer the requirements of a modern age for fast yet accurate measurements. If accurate, the results were obtained at the cost of very tedious and lengthy operations. The new S. P.* dipmeter service offered to the oil industry is the result of exhaustive and in this particular field. In 1032 a dipmeter and electromagnetic teleclinom-eter service was made available. The apparatus employed then was of a rather delicate and costly construction, and the measurements had to be made with precautions sometimes difficult to secure on the rig. Although the information given by the electromagnetic dipmeter was limited to the direction of the dip, very interesting results were obtained in California, Trinidad, Venezuela, Rumania and, most notably, in the Netherlands East Indies.+ Apparatus The S. P. dipmeter surveys present none of the drawbacks mentioned above. The apparatus is rugged and free from constructional complications, therefore well adapted to field use. This, combined with the new, basically simple approach to the problem, explains the rapidity of execution of the measurements. The results are remarkably accurate and they are complete, giving the

Jan 1, 1946

By H. G. Doll

'This paper discusses a method and apparatus for determining the dip of formations traversed by a drill hole, by means of electrical measurements in the hole. The process consists in recording the Spontaneous Potentials present along three oriented generatrices in the hole. By comparison of the three curves thus obtained, after application of a correction factor to compensate for any deviations of the hole, the dip angle and the dip direction are determined. Excellent accuracy is obtained for dip angles over 10°. Because the method is simp1e and the apparatus rugged, the measurements are rapid and reliable; consequently, they can be made at all the levels that are of interest at any time after the well has been drilled. Mechanical cores are not needed to evaluate the dips. A convenient, time-saving procedure is to perform the dipmeter survey at the time the electrical log is taken, using for both operations the same cable and truck. Actual examples of results obtained in wells of the Gulf Coast area are given. Introduction The problem of determining the angle and direction of the dip of the strata traversed by a drill hole has practical interest, and sometimes vital importance, which need not be emphasized to the oil industry. The need for that type of information has existed ever since wells have been drilled. Certainly it has not subsided, in spite of the numerous inventions and improvements made in other fields of the art of drill-hole exploration. The few examples given in this paper are but illustrative of this fact. In the past, methods have been devised, and used, to solve this problem, but generally they have met with limited success, possibly because they failed more or less to answer the requirements of a modern age for fast yet accurate measurements. If accurate, the results were obtained at the cost of very tedious and lengthy operations. The new S. P.* dipmeter service offered to the oil industry is the result of exhaustive and in this particular field. In 1032 a dipmeter and electromagnetic teleclinom-eter service was made available. The apparatus employed then was of a rather delicate and costly construction, and the measurements had to be made with precautions sometimes difficult to secure on the rig. Although the information given by the electromagnetic dipmeter was limited to the direction of the dip, very interesting results were obtained in California, Trinidad, Venezuela, Rumania and, most notably, in the Netherlands East Indies.+ Apparatus The S. P. dipmeter surveys present none of the drawbacks mentioned above. The apparatus is rugged and free from constructional complications, therefore well adapted to field use. This, combined with the new, basically simple approach to the problem, explains the rapidity of execution of the measurements. The results are remarkably accurate and they are complete, giving the

Jan 1, 1946

By Richard H. Zinszer

Application Of electric logs has been used in correlation of subsurface structure to determine the size and shape of the oil reservoir. Such a knowledge is hardly complete until saturation and productivity are determined for the various horizons. It is difficult to use electric logs successfully for this purpose because of the many factors that influence the curves. In this work an effort was made to establish an empirical correlation between formation resistivity for a series of electric-log curves and water saturation and oil productivity of sand. Electric logs were obtained by recording with 10 different electrode spacings through the same interval of a well. In the analysis of these curves all factors except two, a dependent and independent variable, were held constant. The interval studied had been cored and a large number of samples were analyzed in the core laboratory in order to compare the values of permeability and saturation with the measured values of formation resistivity. Results of this analysis indicate: (I) the depth to which mud filtrate enters a sand body, (2) a correlation between permeability and sand resistivity for shallow penetration depths, and (3) that the water saturation for an oil sand can be determined from the measured sand resistivity after making suitable corrections for sand thickness. The procedure in the last method depends on a correction for thickness factor and a theoretical curve. The accuracy of the theoretical curve is now being tested in the laboratory Introduction In an effort to place the analysis of electric logs on a quantitative basis, there is need for a better understanding of the many factors that influence an electric-log curve. These factors may be large differences in sand thickness, permeability of the sand, salinity of the interstitial water, mud resistivity, formation temperature, and other sources. A number of examples were presented by Archie,' which treat the effect of sand thickness on measured resistivity. He compared the true resistivity of a sand with the observed resistivity for sands 8 it., 16 ft., and 24 ft. thick, and found the observed resistivity of the 8-ft. sand to be approximately

Jan 1, 1946

By Richard H. Zinszer

Application Of electric logs has been used in correlation of subsurface structure to determine the size and shape of the oil reservoir. Such a knowledge is hardly complete until saturation and productivity are determined for the various horizons. It is difficult to use electric logs successfully for this purpose because of the many factors that influence the curves. In this work an effort was made to establish an empirical correlation between formation resistivity for a series of electric-log curves and water saturation and oil productivity of sand. Electric logs were obtained by recording with 10 different electrode spacings through the same interval of a well. In the analysis of these curves all factors except two, a dependent and independent variable, were held constant. The interval studied had been cored and a large number of samples were analyzed in the core laboratory in order to compare the values of permeability and saturation with the measured values of formation resistivity. Results of this analysis indicate: (I) the depth to which mud filtrate enters a sand body, (2) a correlation between permeability and sand resistivity for shallow penetration depths, and (3) that the water saturation for an oil sand can be determined from the measured sand resistivity after making suitable corrections for sand thickness. The procedure in the last method depends on a correction for thickness factor and a theoretical curve. The accuracy of the theoretical curve is now being tested in the laboratory Introduction In an effort to place the analysis of electric logs on a quantitative basis, there is need for a better understanding of the many factors that influence an electric-log curve. These factors may be large differences in sand thickness, permeability of the sand, salinity of the interstitial water, mud resistivity, formation temperature, and other sources. A number of examples were presented by Archie,' which treat the effect of sand thickness on measured resistivity. He compared the true resistivity of a sand with the observed resistivity for sands 8 it., 16 ft., and 24 ft. thick, and found the observed resistivity of the 8-ft. sand to be approximately

Jan 1, 1946

By C. S. Corbett

EARLY in the development of every oil field, the operators of relatively large tracts of land must decide upon a spacing plan for the wells to be drilled upon their respective tracts. Usually it is desirable to have a system of regular spacing laid out over the entire tract, making such adjustments as may be necessary near land boundaries. Unless the dip of the producing formation is very steep, the equilateral triangular arrangement is the one most generally preferred, for the very good reason that it gives the maximum amount of drainage area for the wells up to the limit at which mutual drainage interference begins. Assuming that the equilateral triangular pattern is to be used, there still remains to he decided the matter of distance between wells. Many variable factors enter into the problem of proper spacing, some of which are physical and some economic. It is not the purpose of this paper to discuss these factors, as that has been done in several comprehensive articles during the past few years. In the end the decision must be based upon an estimate of the relative importance of various factors which apply to the field in question and to economic conditions in the oil industry at the time the development is getting under way. Even if the best possible spacing distance should be chosen when the problem arises, changing economic conditions and variation in physical conditions in different parts of the field may cause the original choice to become more or less unsatisfactory. Obviously, it is advantageous, once a spacing plan has been adopted, to avoid alteration of it as the field becomes better known or as conditions in the industry change, and yet be able to vary somewhat, the acreage per well in extending the area of development. Or, it may be desired to provide for an ultimate spacing considerably closer than conditions seem to warrant early in the development of the field. With these contingencies in mind, it is of interest to examine the possibilities which the equilateral triangular system affords. Orientation of Coordinate System In this system the well locations may be considered as the inersectionst of three sets of coordinate lines, the lines of each set intersecting those of the other two sets at 60. For convenience in placing such a system

Jan 1, 1930