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By F. A. Guo

Ultrafine-grained surface layers were obtained by surface mechanical attrition treatment (SMAT) in copper and titanium samples. The thermal properties of the deformed layers were characterized using a scanning thermal microscopy (SThM) that allows thermal conductivity to be mapped down to the submicrometer scale. A theoretical approach, based on this investigation, was used to calculate the heat flow from the probe tip to the sample and then estimate the thermal conductivities at different scanning positions. Experimental results and theoretical calculation demonstrate that SThM can be used as a powerful tool for the thermal property and microstructural analysis of ultrafine-grained microstructures.

Jan 1, 2006

By M. Ye. Melnikov

The report is about oceanic ferromanganese crusts ? covers of iron and manganese hydroxides developed over an opened rock of seamounts and rises. Ore bed parameters of crusts are understandable as their thickness and content of main economic components ? manganese, cobalt and nickel. All known results of research activity on ferromanganese manganese crusts point to that crust are characterized by notable variability of thicknesses and composition. It is possible to separate few levels of variability. The most evident is the first level of parameters variability, which is manifested in various regions of the Ocean, and connected first of all, with an age of submarine mountains, a host objects for a crusts. It was proved by many authors, that most powerful crusts are connected with submarine mountains of Cretaceous age. [1]. Crust thickness at the Magellan Seamounts reaches, for example 12-15 cm, sometimes exceeds 20-22 cm. Thicknesses of Hawaii Archipelago or Tuamotu crusts in 3-4 times less. Biostratigraphy studies of crustal sections at the Magellan Seamounts already show, that its main part started to form in the Late Paleocene. Four layers with well expressed features in structure and composition of a layer are separated in the section. From foot to top: Late Paleocene ? Early Eocene layer I-1, Middle-Late-Eocene layer I-2, Miocene layer II and Pliocene ? Quaternary layer III. Relics of more ancient Campanian ? Maastrichtian ore layer [2, 4] were discovered. It is evident for example, that Oligocene mountains could not be a host for two lower layers in the crust section.

Jan 1, 2010

By M. Ye. Melnikov

The report is about oceanic ferromanganese crusts ? covers of iron and manganese hydroxides developed over an opened rock of seamounts and rises. Ore bed parameters of crusts are understandable as their thickness and content of main economic components ? manganese, cobalt and nickel. All known results of research activity on ferromanganese manganese crusts point to that crust are characterized by notable variability of thicknesses and composition. It is possible to separate few levels of variability. The most evident is the first level of parameters variability, which is manifested in various regions of the Ocean, and connected first of all, with an age of submarine mountains, a host objects for a crusts. It was proved by many authors, that most powerful crusts are connected with submarine mountains of Cretaceous age. [1]. Crust thickness at the Magellan Seamounts reaches, for example 12-15 cm, sometimes exceeds 20-22 cm. Thicknesses of Hawaii Archipelago or Tuamotu crusts in 3-4 times less. Biostratigraphy studies of crustal sections at the Magellan Seamounts already show, that its main part started to form in the Late Paleocene. Four layers with well expressed features in structure and composition of a layer are separated in the section. From foot to top: Late Paleocene ? Early Eocene layer I-1, Middle-Late-Eocene layer I-2, Miocene layer II and Pliocene ? Quaternary layer III. Relics of more ancient Campanian ? Maastrichtian ore layer [2, 4] were discovered. It is evident for example, that Oligocene mountains could not be a host for two lower layers in the crust section.

Jan 1, 2010

By W Assibey-Bonsu

The paper provides a brief review of the multivariate uniform conditioning and the localised multivariate uniform conditioning techniques and presents a case study based on a porphyry copper gold deposit in Peru. Two other important scenarios have been investigated and will be particularly emphasised: The recovered selective mining unit (SMU)s depend on a combination of copper and gold content, which can be expressed by means of ænet smelter returnsÆ (NSR). Two approaches are compared. Firstly, the application of a composite cut-off on NSR on the joint distribution of each grade and the application of uniform conditioning to three variables is investigated, ie for the first approach NSR is used as the main variable. The second approach considers copper as the main variable. In the case of multiple domains the procedure used to apply the technique to process mixed panels is clarified and recommendations are made.

Sep 26, 2011

By James Boyd

REACTIVE metals are not only those sufficiently radioactive to be used as fuels, such as uranium and thorium, but all metals that will find application in power reactors. It is required of such metals that they be relatively inert or chemically unreactive, dimensionally stable at high temperatures and pressures, and either very absorbent of radioactivity or transparent to it. To gain the right perspective concerning these metals it is necessary at this point to explode some erroneous concepts propounded so often they have become accepted as fact. The first of these is that the great industrial nations, especially the U. S., have reached their pre-eminent position chiefly because they possess abundant mineral resources. Some U. S. mineral economists, echoed by the politicians, have taken this position so often that many of their theories and policies are based on the presence of developed mineral resources as a sine qua non to the country's greatness. Actually the reverse is true- under a social and political system granting free rein to the initiative and creativeness of its people, many hidden mineral resources that otherwise would have lain fallow have been developed into productive enterprises to the benefit of the national industrial economy. Again, once the proper incentive was furnished, other countries have also been able to establish valuable mineral enterprises in recent years; resources long dormant for lack of a proper economic environment suddenly have become valuable and productive. It is possible to name immediately several nations where such domestic economic developments have had favorable repercussions within the last decade. The absence of productive mines in any country is no indication that workable deposits do not exist within its territory.

Jan 11, 1957

By Walton J. Greer, System By John E. Owen

The guard electrode system measures the resistivity of formations by employing a thin disk of current which is caused to flow perpendicular to the bore hole. The control of this current disk is obtained in a brute force manner through the use of relatively long equipotential electrodes above and below the measuring electrode. The log obtained from the system is free of "lag," "plateau," "shadow," "reflection" and other distortions evident on conventional logs. The proportionate contributions of the hole size and invaded zone resistivity to the apparent resistivity reading are reduced when the mud and filtrate resistivities are lower. Thus, the guard system favors the use of conductive muds. The mathematical development of the theory is given in an appendix. Equations are derived to evaluate the effects of mud resistivity, hole size, invaded zone resistivity and depth, and the true formation resistivity. Sample logs from several provinces are reproduced and compared with conventional electric logs to illsutrate the much greater detailed lithology that can be presented by the guard electrode system. INTRODUCTION With increased ability of those in the petroleum industry to analyze formation characteristics from electrical resistivity data, there has become apparent the need for more precise measures of that parameter. The measurement of the resistivity of a homogeneous and isotropic material can be made simply when the body of the material is infinite in all dimensions and the measuring electrodes can be placed within the body. In such a case, the current leaving an electrode follows a spherical distribution and the mathematical expression for the potential level at any distance from that electrode can readily be derived.'.' If it is considered that the active electrodes are within a bore hole filled with mud of a resistivity different from that of the formation. the current does not flow in a spherical pattern near the current source or sink, and the calculations of potential levels become more difficult. The additional consideration of a section of formation invaded by mud filtrates, and thus having resistivity different from either that of the mud, the adjacent formations or of the undisturbed formation, makes the mathematical problem extremely complex. Should the vertical dimensions of the formations be considered as finite. the problem becomes so complex as to preclude reasonable solution. Yet, even these considerations have not described adequately the conditions encountered in a large proportion of the wells to be studied. In efforts to evaluate the effects of the various conditions. combinations of twn, three. and four electrode logging con- figurations of the conventional types have been used. The resulting logs have left much to be desired in some provinces. It has become apparent that the use of such configurations will not result in adequate measurements being made, particularly in cases where the formation is composed of thin sections. If all the current of a resistivity measuring circuit is made to flow through the formation opposite the exploring electrode, many of the shortcomings of the conventional measuring system are eliminated. In the guard electrode method of electrical well logging to be discussed in this paper, the current is so controlled by causing it to flow in a thin disk normal to the axis of the logging tool. EARLY HISTORY The guard electrode method of electrical well logging in its early years was a joint development by the Geophysical Research Corp. and the Amerada Petroleum Corp. The method was first experimentally investigated by means of model studies. The results of these studies indicated that current focusing systems properly applied to electrical well logging

Jan 1, 1951

By System By John E. Owen, Walton J. Greer

The guard electrode system measures the resistivity of formations by employing a thin disk of current which is caused to flow perpendicular to the bore hole. The control of this current disk is obtained in a brute force manner through the use of relatively long equipotential electrodes above and below the measuring electrode. The log obtained from the system is free of "lag," "plateau," "shadow," "reflection" and other distortions evident on conventional logs. The proportionate contributions of the hole size and invaded zone resistivity to the apparent resistivity reading are reduced when the mud and filtrate resistivities are lower. Thus, the guard system favors the use of conductive muds. The mathematical development of the theory is given in an appendix. Equations are derived to evaluate the effects of mud resistivity, hole size, invaded zone resistivity and depth, and the true formation resistivity. Sample logs from several provinces are reproduced and compared with conventional electric logs to illsutrate the much greater detailed lithology that can be presented by the guard electrode system. INTRODUCTION With increased ability of those in the petroleum industry to analyze formation characteristics from electrical resistivity data, there has become apparent the need for more precise measures of that parameter. The measurement of the resistivity of a homogeneous and isotropic material can be made simply when the body of the material is infinite in all dimensions and the measuring electrodes can be placed within the body. In such a case, the current leaving an electrode follows a spherical distribution and the mathematical expression for the potential level at any distance from that electrode can readily be derived.'.' If it is considered that the active electrodes are within a bore hole filled with mud of a resistivity different from that of the formation. the current does not flow in a spherical pattern near the current source or sink, and the calculations of potential levels become more difficult. The additional consideration of a section of formation invaded by mud filtrates, and thus having resistivity different from either that of the mud, the adjacent formations or of the undisturbed formation, makes the mathematical problem extremely complex. Should the vertical dimensions of the formations be considered as finite. the problem becomes so complex as to preclude reasonable solution. Yet, even these considerations have not described adequately the conditions encountered in a large proportion of the wells to be studied. In efforts to evaluate the effects of the various conditions. combinations of twn, three. and four electrode logging con- figurations of the conventional types have been used. The resulting logs have left much to be desired in some provinces. It has become apparent that the use of such configurations will not result in adequate measurements being made, particularly in cases where the formation is composed of thin sections. If all the current of a resistivity measuring circuit is made to flow through the formation opposite the exploring electrode, many of the shortcomings of the conventional measuring system are eliminated. In the guard electrode method of electrical well logging to be discussed in this paper, the current is so controlled by causing it to flow in a thin disk normal to the axis of the logging tool. EARLY HISTORY The guard electrode method of electrical well logging in its early years was a joint development by the Geophysical Research Corp. and the Amerada Petroleum Corp. The method was first experimentally investigated by means of model studies. The results of these studies indicated that current focusing systems properly applied to electrical well logging

Jan 1, 1951

By H. G. Doll

As a continuation of the earlier paper on the general subject of the SP log, a more complete analysis of certain features of the SP log in shaly sands is given. The pseudo-static SP in front of shaly sands is compared, on a theoretical basis, to the static SP in front of clean sands, as a function of the respective amount of shale and sand in the formation, and of the relative resistivities of the shale, of the uncontaminated part of the sand. and of the invaded zone of the sand. As a conclusion, the advantage of using reasonably conduc. tive mud in this case is shown. The discussion is illustrated by field examples. INTRODUCTION The discussion reported in the present paper is based on a theoretical analysis, and not on experiment. The field examples, joined to the text. are shown only as qualitative illustrations of the essential results of this analysis. Although the hypotheses made in the theoretical developments may perhaps be somewhat improved, it seems, nevertheless, that the results obtained account reasonably well for the actual phenomena, and give a fair approximation of their order of magnitude. The paper contains a mathematical analysis of a tri-dimen-sional distribution of potentials and current lines. due to spontaneous electromotive forces arising at the contact of shales and free electrolytes. as a function of the geometry and of the respective resistivities of the different media involved. It is assumed, although this hypothesis is not proven, that the emf's remain the same even if the shale occurs in very thin layers or in dispersed particles. It has already been pointed out 1,2,3 that, all other conditions being the same, the deflection of the SP log in front of a shaly sand is smaller than opposite a clean sand. When the thickness and the conductivity of a clean sand are large enough. the deflection of the SP log reaches a limiting value which is equal to the "static SP" of the clean sand. It is generally convenient to take the static SP of shale as the reference value or "base line." As a consequence, and for the sake of abbreviation, the expression. "static SP of a clean sand," is often used to designate the difference between the static SP of that sand and that of the shales, which difference is a measure of the total electromotive forces involved in the chain mud sand-shale. A similar limiting value is; also observed for the SP deflec-lion opposite a thick shaly sand, but it is smaller. just as if the total electromotive force involved were smaller in that case. This limiting value has been called the "Pseudo-Static SP" of the shaly sand. The static SP of a clean sand depends on the salinity of its connate water with respect to that of the mud, and, to a certain extent. on the differential pressure which controls the electro-filtration potentials, but it does not depend on the resistivity of the sand. On the contrary. the pseudo-static SP of a shaly sand depends not only on the salinity of its connate water and on the differential pressure, but also on the percentage of shale and on the resistivities of the shale, of the uncontaminated part of the sand, and of the zone invaded by the mud filtrate. If the three resistivities above were equal, the pseudo-static SP would be proportional to the percentage of sand in the shaly sand, and its departure from the static SP of a clean sand having the same connate water would simply be proportional to the percentage of shale. In that case, the pseudo-static SP of a shaly sand containing 10 per cent of shale would he 10 per cent less than the static SP of a clean sand. When. however. the sand is. on the average. substantially more resistive than the shale. the percentage of departure of the pseudo-static SP from the static SP of a clean sand is much larger than the percentage of shale. For that reason, the peaks of the SP log opposite shaly sands are systematically of smaller amplitude when the sands are oil-bearing than when they are water-bearing, all other conditions being the same. This feature is observed even when the sand beds are thick. and even when they do not contain a large percentage of shale. All this has already been described in all earlier publication", but mostly in a qualitative way. The present paper will analyze in more detail the action of the local SP currents which are generated inside of the shaly sands, and which are responsible for the abnormally low value of the pseudo-static SP. The quantitative computations have been extended to the general case of thin interbedded layers of sand and shale, where the resistivities of the shale and sand streaks do not have the same value: they are summarized in charts giving values of the pseudo-static SP of a shaly sand as a function of the different parameters involved. DEFINITIONS The static SP of a clean sand has been defined as the potential that would exist in the mud opposite that sand, were the SP current prevented from flowing. Such an ideal condition is represented on Fig. I-A. By analogy, the pseudo-static SP of a shaly sand can be defined as the potential that would exist in the hole, if the circuit shaly sand — surrounding shales — mud column were interrupted by the insulating plugs placed at the boundaries

Jan 1, 1950

By R. H. Winn

A method for the selection of the most suitable corrosion inhibitor for a particular system is given. The method involves the evaluation of surface passivity by means of copper ion displacement after the metal surface has been subjected to the corrosive atmosphere. The application of the method to the selection of suitable inhibitors for use in producing wells is described. Correlation with recognized laboratory tests has beet1 found to be good within the limitations of the test. The use of the test to evaluate inhibitor persistencc is described. INTRODUCTION Corrosion as it is associated with the industry shows wide variations in its qualitative as well as its quantitative aspects. This complicates the work of the corrosion engineer. In the past few years the efforts of the corrosion engineer have been further taxed by the large numbers of products being marketed as corrosion inhibitors by various manufacturers. These products are submitted to him together with a limited amount of data to support their use as inhibitors. The data are usually authentic and reliable yet all too often when these products are applied to an actual corrosive system the results are disappointing due to the ineffectiveness of the inhibitor and the corrosive system. The corrosion engineer must select a comparatively limited number of inhibitors for field trial from the large number available. The selection is usually made on the basis of a standardized laboratory test such as that adopted by the National Association of Corrosion Engineers or by field experience in an area; however, testing of this type is discouraging on large numbers of compounds, particularly in view of the specificity of environment. It has been an object of this work to devise a method which will allow the corrosion engineer to select the best inhibitor for a specific environment under field conditions. The test would of necessity be rapid and inexpensive. It would preferably eliminate the need for expensive and delicate instruments. STATEMENT OF THEORY The test as developed makes use of the fact that metal ions will be displaced from solution by metals having a more positive electrode potential. Thus, if an active iron surface is exposed to a solution of a copper salt, free copper will plate spontaneously on the iron surface as it is displaced from the salt solution by iron ions. If the iron surface is passified, as by coating with an insulating-type organic corrosion inhibitor, it is no longer capable of displacing the copper ions due to its own limited ionization. The result will be a change in the amount of copper plated upon exposure to a neutral copper salt solution. In practice it has been found possible to measure the magnitude of the alteration of the cell potential by determining the copper deposited on a standard iron surface under controlled conditions. This means that, as the film builds up, the resulting shift in the electrode potential tends to cause the iron surface to act more like a noble metal, resulting in a reduction in the cell potential to a point that copper will no longer plate spontaneously. Obviously, the salts of other metals such as silver, gold or platinum might be used for this operation; however, copper was selected because of the color difference of the plate, the comparatively low cost of copper salts and the ease of evaluation of the plated copper. Furthermore, its high cell potential provides a substantial driving energy. The determination of the copper is readily done colorimetrically by dissolving it in 5 per cent ammonium hydroxide solution containing 2 per cent potassium per-sulfate. The blue color of the copper ammonic complex ion so developed may be compared with standards prepared by dissolving known quantities of copper powder in the same reagent. In routine screening it is seldom desirable to determine the amount of copper plated. It is usually more important to determine the concentration of inhibitor required to prevent the plating of copper.

By P. Majani, F. P. Kokesh, M. Grosmangin

Determination of the quality of cementation of casing in oil wells in the past has involved inflow and circulation tests to insure that the producing zones were adequately sealed off from the adjacent zones. Existing logging methods, such as temperature and radioactivity surveys, may detect the presence of cement behind the casing. However, the qualities of the cement (i.e., its hardness and particularly its bond to the casing) are not indicated. The new logging method described in this paper operates on the principle that the attenuation of a sonic pulse transmitted by a casing is greatly increased when that casing is bonded to an outer annulus of hard material (such as set cement) which has an appreciably smaller sonic-wave velocity than that of the casing. The down-hole tool contains a source of recurrent sound pulses which are detected by a receiver spaced a few feet from the source The amplitude of the detected casing-borne pulse is measured, and the resulting signal is transmitted to the surface where it is recorded vs depth. Since amplitude is a function of attenuation, the log is readily interpreted. Laboratory studies have shown straightforward relationship between attenuation and such variables as source-detector spacing and per cent of circumference bonded. It is shown that cement not set or not bonded to the casing has compara- tively little attenuating effect. Field examples show not only the cement top, but also the variation in cementation quality below the top. Further, the increase of bonding with time and after squeeze cementation is depicted. The detection of poor cement jobs is confirmed by production tests and by formation-test results. It is anticipated that the method will have wide application in evaluating cementation quality prior to formation testing in completions and recompletions. The analysis it affords may aid in further improving cementation techniques. INTRODUCTION The main purpose of oilwell cementing is to isolate a production zone from other undesirable zones. To investigate whether this purpose has been accomplished, several logging methods have been used such as temperature logs, radioactive tracer logs, etc. While these logs all respond to the presence of cement behind the casing, they do not indicate the degree of bonding of the cement to the casing. Early in the application of sonic logging, it was noticed that considerable attenuation of sound signals takes place in cemented pipe and is often made evident on the standard Sonic log by cycle skipping.' The development of a circuit capable of continuously recording the amplitude of the casing-borne sound signal has made possible an extensive series of laboratory and field tests, which gave the following results. The amplitude of a sound signal after it has traveled in a firmly cemented pipe is only a small fraction of that recorded by the same device in free pipe. This provides a wide spectrum of energy levels; for given local conditions, empirical values of the amplitude can be correlated with the quality of cementation. Interpretations made in this manner generally have been confirmed by production tests, circulation tests and squeeze cementation. The purposes of this paper are to give a general description of the new logging method and to present some laboratory and field results. CYCLE SKIPPING Early attempts to study the quality of the cement behind the casing were performed with a standard Sonic log, which measures the transit time At, and were based on the well known phenomenon of cycle skipping.' Cycle skipping normally is interpreted as being a manifestation of weak signals at the receivers. The log of Fig. 1 was run with the recording instrumentation adjusted to enhance cycle skipping. A mirror-image presentation was used for better visual interpretation. The transit time of sound in steel is about 58 microseconds/ft (corresponding to a velocity of 17,000 ft/ sec), and the portions of the log where this value is recorded are interpreted as zones with no cement bond. Where cycle skipping produces a higher value of At, weak signals (or a high rate of attenuation) are indicated, and a good cement bond may be present. The occurrence of cycle skipping, however, depends too much on instrument adjustment to give a uni-

By S. E. Szasz, E. J. Moore, B. F. Whitney

An accurate value of formation water resistivity R, is essential in calculating formation porosity and fluid saturation from electrical well logs. In the cases where R, has not been measured directly, it must be obtained from other data, e.g., the SP curve. This paper deals with another approach: how to calculate R, from the chemical analysis of the formation water. INTRODUCTION It is known that the resistivity of aqueous solutions of pure salts depends on their concentration and on the temperature; the concentrations are given in MPL (mg of solute per liter of solution), or sometimes in ppm (mg of solute per kg of solution): MPL = ppm X specific gravity. Values for different pure salts are available in the literature, but not for solutions of mixtures which are of practical interest. The major component of the dissolved material in almost all formation waters being sodium chloride, it is customary to express the resistivity of formation waters in terms of equivalent sodium chloride concentration, i.e., the concentration of a solution of pure NaCl which has the same resistivity at a given temperature as that of the formation water under consideration. Thus, the problem of calculating R, from the chemical anaylsis can also be stated as how to convert the other constituents of the solute into equivalent NaCl concentration. Salts dissolved in water are at least partly dissociated into ions, and do not conserve their identity. If known amounts of several salts are dissolved in water, the solution does not necessarily contain the same salts in the original proportion, but perhaps some other combination of the ions, along with free ions in solution. This is why the chemical analysis of formation waters is often given in terms of ions, as if all dissolved salts were completely dissociated. Our problem then boils down to how to convert the concentrations of the various ions to equivalent concentrations of Na' and C1-. Dunlap and Hawthorne' have proposed to convert the concentration of all other ions to equivalent Na' and C1-concentrations by means of constant multipliers; e.g., 0.95 for Ca"; 2.0 for Mg"; 0.27 for HCO 3-; 0.5 for SO, -, etc. Their factors were based on measurements made at 68F on 26 formation water samples from the Texas Gulf Coast, ranging in concentration from 1,500 to 75,000 ppm. The Dunlap method is widely used in electric log interpretation, and is often extrapolated beyond its original concentration range. A comparison of R, values calculated by this method and values actually measured on formation water samples has shown large discrepancies, especially at higher concentrations. Therefore, two new methods were developed at Sinclair Oil Corp.'s Tulsa Research Center to calculate equivalent sodium chloride concentration from the chemical analysis of formation water samples. FUNDAMENTAL CONSIDERATIONS The resistivity of a solution, or its reciprocal the conductivity, at a given temperature is determined by the charge, concentration and mobility of the ions actually present. Monovalent ions such as Na' or C1- always carry the same charge. Compounds of polyvalent ions, however. may show incomplete dissociation, e.g., NaSO; + Na' instead of SO,-- + 2Na'. This happens especially in more concentrated solutions. Only very dilute solutions are completely dissociated, as assumed in the chemical analysis report. At higher concentration, the degree of dissociation depends not only on the nature and concentration of the particular salt under consideration but also on the nature and concentrations of the other solutes. Mobility of the ions depends on the viscosity of the solution. It also depends on the degree of hydration of the ions, which in turn is a function of the nature and the charge of the ions and also of the amount of free water available per ion, i.e., the total ionic concentration. The net effect is that the conductivity increases slower than proportional to the concentration, even if a solution contains only one salt such as NaC1, and is different for different salts (Fig. 1). Conductivity can even decline with a further increase in concentration, e.g., if additional salt is little dissociated but ties up some of the free water and/or causes an increase in viscosity. In solutions containing more than one salt, the contribution of one salt to the total conductivity depends not only on the fractional concentration of this same salt, but also on the concentration of all other solutes. A perfect method would give the conductivity or resistivity of a solution as a function of the concentrations of all solutes present. This is so complicated as to be impractical, and a simpler method must be found which is of acceptable accuracy. The Dunlap method, on the other hand. is too simple because it askmes that at any concentration the contrih-

Jan 1, 1967

By J. D. Milburn, H. J. Hill

In quantitative interpretation of electrical logs the presence of clay minerals introduces an additional variable which further complicates an already complex problern. Although recognizing the difficulties introduced as a result of the heterogeneity of natural sediments and despite the present incomplete state of knowledge regarding electrochemical behavior of shales, dissemirzated clay minerals and concentrated electrolytes, it was felt that useful empirical correlations might be obtained from experimental investigation. Six typical sandstone formations, having a wide variety of petrophysical properties, were selected for the study. Approximately 45 samples from each formation were selected to satisfactorily represent the range of pore size distribution within the particular formation, As a matter of general interest, four limestone formations were also included in the investigation. Previously proposed equations relating to resistivity, SP and interrelationship of the two phenomena have, where possible, been tested with data obtained in this investigation. These equations do not satisfactorily describe experimental behavior of samples through all degrees of shaliness or throughout the range of brine solution resistivities normally encountered in logging practice. An empirical equation has been developed which quantitatively relates formation resistivity factor to satirrnting solution resistivity, porosity, and "effective clay content." This relation is indicated to be uniformly applicable to clean or shaly reservoir rocks. It is shown that both the SP and resistivity phenomena of shaly samples are related to the sample cation exchange capacity per unit pore volume. The independent chemical determination of this parameter is thus a means of determining the "effective clay content" of samples. Some implications regarding theory and electric log interpretation of shaly sands are discussed. INTRODUCTION The use of electrical resistivity logs as a means for estimating formation porosity is based upon the original work of Archie1. It was shown by empirical methods that the resistivity of a rock, when 100 per cent saturated with brine solution, could be related to rock porosity through the equation, F = Ro/ RW = f-m.......(1) where F, the formation resistivity factor, is defined as the ratio of the resistivity of the 100 per cent water saturated rock, Ro, to the saturating solution resistivity, Rw; f is the ratio of pore volume to bulk volume; and m is the slope of the average line when the data are plotted on log-log paper. This relation was established for relatively shale-free formations containing water having high salt concentrations, and under these conditions F may be considered constant for a given rock sample. Applications of Eq. 1 to interpretation of logs of shale-free formations has been quite successful when satisfactory formation water resistivity data could be obtained. The most readily available means of estimating formation water resistivity is the self-potential log. Conventional methods of SP log interpretation involve correct.

Jan 1, 1957

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

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

By R. H. Winn

In this paper a heterogeneous carbonate reservoir is considered as a succession of layers of formations of radically different porosities, permeabilities, water saturations, and rock matrix types; i.e., the heterogeneity is vertical rather than radial to the wellbore. Presumably each layer is more or less homogeneous. To determine the "net oil in place" in this reservoir it is desirable to know the porosity and water saturation of each layer. In addition, the section must be subdivided into that which will produce oil, that which will produce water, and that which will produce little or nothing. In numerous wells drilled in these reservoirs radioactivity surveys, guard electrode surveys, and caliper surveys have been made. These logs have been compared with core analysis data, when available, and the analysis of the surveys compared with production data. This study, still in progress, is intended to provide improved analytical techniques if such are possible. This paper is a progress report on the work. DETERMINATION OF POROSITY The neutron-gamma log has long been recognized as a measure of hydrogen concentration.1,2,3 In reservoirs that are free of clay, shale, or other hydrogen containing matrices, it has been accepted as a measure of porosity.4,5 Empirical methods to relate relative neu-tron-gamma intensity to porosity are often employed." To provide a more precise determination of porosity from the neutron-gamma log each instrument is calibrated immediately prior to each survey by a method which refers all tools to a hydrogenous cylinder. To insure stability a calibration check is made after each survey. These calibration records are printed as an integral part of the log that is recorded in standard counts per second. A detailed description of the calibration procedure is available in the literature.' The procedure employed insures that each Survey is numerically reproducible within the limits of statistical variation. To relate the standard neutron counts per second to porosity and hole size, records were made in test wells constructed of blocks of limestone. The porosities of the blocks were accurately measured and the blocks completely saturated with fresh water. Fig. 1 presents some of the results obtained in these test wells.' The lines shown in Fig. 1 were obtained by deriving an empirical equation relating the 11 points shown so that the relationship may be projected to larger and smaller hole sizes. A detailed description of the tool is available in the literature.' Field tests indicate that the tool is adjacent to the wall of the hole most of the time when the surveys are made in uncased holes drilled with saline muds. In this circumstance porosity may be calculated from Fig. 1 if the hole size is known. When fresh muds that form thick mud cakes are employed, the centralizing effect of the mud cake must be considered and the porosity determination is less reliable. In cased holes the combined effect of variations in hole diameter and the unknown eccentricity of the casing in the hole may make porosity determinations extremely unreliable. In any event, an accurate knowledge of hole size is essen-

Jan 1, 1958

By R. P. Alger, M. P. Tixier, D. R. Tanguy

In the combination induction-electrical log used at present in the field, the induction logging tool is appropriate for the investigation of moderately invaded formations. A new induction sonde with a radius and investigation about twice as large has been developed recently for the case of deep invasion. It has very nearly the same vertical resolution as the present sonde so that thin beds are defined as accurately as before. The characteristics of the new tool are described, the corresponding interpretation charts are given and field examples are discussed. The design of the sonic logging tool has been modified to improve the calibration and the reliability. The fact that porosity can be accurately recorded by means of the sonic log has prompted new interpretation procedures for saturation estimation, wherein the data concerning the various permeable beds in a given well are correlated. One approach consists of plotting transit time vs true resistivity, with an appropriate scale. With this approach, saturations can be estimated conveniently even in cases where formation water resistivity is not well known. In another approach, a comparison is made of the values of the formation waters computed from the re- sistivity and sonic logs. Using the concept of continuity, this procedure makes possible a quick determination of zones of saturation in shaly sands and/or in case of appreciable variations of formation salinities with depth. It has been found that the comparison of porosity from the sonic log with the apparent porosity computed from a short-investigation resistivity log may reveal, in many cases, the presence of residual oil and thus detect potentially productive formations; this procedure is valuable when the true formation resistivity and the resistivity of the formation water are in doubt. INTRODUCTION During the past year, the efficiency of log interpretation has been vastly improved. The improvements have largely resulted from the introduction of a deep-investigation induction device and from the application of new interpretation techniques that utilize sonic vs resistivity readings. Since the new interpretation techniques depend, in part, upon good values of true formation resistivity, the new induction log will be discussed under Part I. The sonic interpretation techniques will be studied under Part 11. Early in 1959, the 6FF40 induction equipment was introduced in the field. This device was designed for a better approach to true formation resistivities in deeply invaded zones. The greatly improved radial investigation of the 6FF40 equipment has been achieved without sacrificing vertical resolution. The first combination induction-electrical log, the 5FF40, was introduced as a standard tool in 1956 for the logging of wells drilled with fresh muds. The tool has received wide industry acceptance in the United States. 'The 5FF40 induction log has a radial investigation sufficient to overcome average depths of mud filtrate invasion. At 5d invasion, for example, the 5FF40 induction log will read about 1.4 R. in a water sand where R., = 10R,. At 10d invasion, such induction log would read 2.45 R. in the same water sand. In either case, the effects of invasion would not be sufficiently great to cause a water sand to be mistaken for a shale-free oil- or gas-producing zone. Some formations, however, invade deeply — in excess of 10d. Such water zones could be mistaken for oil-or gas-saturated sands unless the porosity balance' can clearly make the distinction. It is for these deeply invaded formations that the 6FF40 was developed. CHARACTERISTICS OF THE 6FF40 Radial Investigation Characteristics To describe the comparative responses of the 5FF40

By R. J. S. Brown, B. W. Ganison

A new logging method has been developed, based on measurement of the nuclear magnetism of formation fluids. The nuclear magnetism log (NML) is the only log that responds solely to formation fluids. It operates equally well in both oil-base and water-base muds and in empty holes, and can be used in all kinds of formations except strongly magnetic ones. Two separate NML measurements can be made, one of which provides a continuous formation fluid curve. This fluid curve is called the free fluid log (FFL) and is believed to indicate a minimum effective porosity in most formations. The FFL not only delineates fluid-containing zones, but provides an excellent correlation curve that can be obtained under conditions where conventional correlation logs are ineffective. Preliminary tests indicate that the second kind of NML measurement may help distinguish oil and water zones and provide information concerning permeability and wettability. (The FFL itself appears to provide some information on permeability.) The second kind of NML measurement requires stopping the logging tool for a short time opposite a zone of interest and taking more extensive NML data that can be displayed as nuclear magnetic relaxation curves. In some instances, oil and water saturations for the region immediately adjacent to the borehole can be read from these relaxation curves. INTRODUCTION In 1946, Bloch, Hansen and Packard and Purcell, Torrey and Pound3 independently announced the successful demonstration of the phenomenon of nuclear magnetic resonance. During the past 13 years, there have been many applications of nuclear magnetic resonance, including applications to the study of chemical structure and to the measurement of magnetic field strengths. Preliminary experiments on the feasibility of using nuclear magnetism measurements in well logging were made independently by California Research Corp. and Varian Assoc., the Varian work being sponsored by the Byron Jackson Tools, Inc. Since then a cooperative research program on nuclear magnetism logging has been carried out by the Byron Jackson Div. and Research Center of Borg-Warner Corp., and California Research Corp., subsidiary of Standard Oil Co. of California. The use of nuclear magnetism in well logging is of special interest because it offers a way of making direct measurements on the hydrogen in the formation fluids and not on the rock matrix. Within the past 1 1/2 years, successful measurements have been made with a research model logging tool in wells in California, Tex as, Utah, Louisiana and Wyoming. NUCLEAR MAGNETISM SIGNALS Polarization, Relaxation and Precession Many atomic nuclei possess magnetic moments and spins; that is, they are similar in some respects to bar-magnet and gyroscope combinations. Molecules and their nuclei are subject to thermal motion, which has a scrambling effect, tending to leave as many nuclear spins oriented in any one direction as in any other. However, if a magnetic field is applied, the magnetic nuclei tend to align in the direction of the field. The scrambling and aligning forces compete with each other, with the result that a few more spins are oriented parallel to the field than in other directions. This gives a net magnetization, or polarization, which is directly proportional to the strength of the applied magnetic field (aligning influence) and inversely proportional to the absolute temperature (scrambling influence). When the magnetic field in, or temperature of, a liquid sample containing protons is changed, the new equilibrium value of proton polarization is not established immediately but requires an amount of time which depends on the nature of the hydrogen-containing materials. The process of approaching the equilibrium value of polarization is called relaxation.'.' Polarization is a vector quantity, and the components parallel to and perpendicular to the magnetic field must be considered separately. Relaxation of the component parallel to the field is called "thermal relaxation", or "longitudinal relaxation", and the corresponding time for this component of non-equilibrium polarization to decay by a factor of e (natural log base) is denoted T. The relaxation of the perpendicular component is called "transverse relaxation", and the corresponding relaxation time is denoted T,. The potential energy of a magnet in a uniform field depends on the angle the magnet makes with the field; therefore, a change of the component of net polarization parallel to the magnetic field involves an exchange of energy between the spin system and the thermal motion of the molecules, leading to the term thermal relaxation for the relaxation of this component. Suppose we subject a sample to a strong magnetic field at right angles to the earth's field for a time greater than TI. A polarization, thus, is established at right an-

By R. L. Caldwell, E. E. Glenn, L. J. Norton, A. J. D. Straus, S. V. Holcomb, J. Zemanek

A new and unique logging tool, called the Borehole Televiewer (BHTV), has been developed to inspect boreholes and to evaluate formations. Even though geologists and engineers have had only about 3 years' experience with the BHTV, the thinking of many of them has been radically influenced by the fascinating and revealing "log-picture" recorded with the tool. The BHTV fills a need for a logging tool that can produce a direct and descriptive record of the physical properties of the borehole environment. Although primarily developed to evaluate fractured reservoirs, the BHTV has been used successfully to solve a variety of problems related to formation evaluation and borehole inspection. Geologists and petroleum engineers have been confounded for many years by the problems of locating and evaluating fractures. Interpretation of the usual resistivity, acoustic or radioactivity logs, as well as the analysis of cores, for evaluation of fractured reservoirs is extremely difficult and often not definitive. This is understandable since analysis of cores from fractured formations has reported variously: (a) low porosity, (b) no effective permeability, (c) lack of any matrix oil saturation and (d) oil stains on fracture planes as the only indications of potential production.14 In recent years acoustic amplitude logs have been introduced and used with varying degrees of success to locate fractures.8'9'11"13 Conventional amplitude logs at best give only qualitative answers where quantitative ones are desired. The logs reveal nothing of the orientation of the fractures. In addition to these logs, various types of cameras, television, and rubber impression packers have been used for borehole inspection. (See Appendix.) The BHTV logging tool supplies both the quantitative and the orientation answers about fractures. The borehole can be filled with any homogeneous, gas-free liquid such as fresh water, saturated brine, crude oil or drilling muds. This tool takes an "acoustic picture" of the borehole wall. The resulting log is a representation of the borehole wall as if it were split vertically and laid flat. The log is oriented with respect to magnetic north. Any physical changes in the borehole wall are seen as changes in picture intensity. In this way, fractures, deformation or pits are reflected on the log. Tool Description The fundamental parts of the BHTV are shown in Fig. 1. A piezoelectric transducer probes the borehole wall with bursts of acoustic energy. A flux-gate magnetometer senses the earth's magnetic field and provides the means for determining the orientation of the log. A motor rotates the transducer and mag-

Jan 1, 1970

By M. L. Millican

The objective of this study has been to develop a method of log interpretation in the Delaware sand whereby the effects of the shale contained within the sand can be recognized and accounted for in a quantitative solution for porosity and water saturation. Both theoretical and empirical considerations are discussed. A simplified interpretation chart is presented which provides a means of amending the conventional porosity resolution of the Sonic log to compensate for the presence of shale. The amount of shale within the sand and its degree of lamination may be inferred from a calibrated gamma ray log. The resulting porosity value may then be used in conjunction with a knowledge of the formation resistivity to determine water saturation. Of added interest, particularly in the Delaware sand, is an approximation of permeability which may be derived empirically from the simplified chart. The discussion is illustrated by field examples. INTRODUCTION The performance of the Sonic log in defining the porosity fraction in clean, consolidated formations is well known, particularly in sandstones that are well compacted and free of shale. An approach to Sonic log porosity determination in shaly sands has been recently developed.' This method involves correcting the Sonic log readings by means of an a factor, where a is the ratio of the pseudo-static SP to, the static SP, and is a function of the amount of shale present. This method is dependent upon a contrast between the salinities of the drilling fluid and the connate water in the formation, inasmuch as this contrast produces the SP effect. In wells drilled with salt mud, the contrast, and with it the means of obtaining the a correction, disappear. In the Delaware basin, the large majority of rotary wells drilled to the uppermost sands of the Bell Canyon group employ salt mud as the drilling fluid. These sands have been the objective of most of the drilling exploration in the basin to date. A comparison of porosity values in these sands, as determined by core analysis, to Sonic log readings has indicated that a correction for the shaliness of the sand is needed. In the absence of an SP curve to determine the correction factor, the porosity resolution of the Sonic log in these sands has been questionable.

A combination of the needs of business, employee desires and safety and health considerations is stimulating increasing attention to the time spent by people at work and the timing of that work. Particularly we are seeing: - innovative work schedules for 24-hour mining businesses; and - response from industry to accommodate the needs, even the desires, of employees in return for systems which are more productive and more capital efficient. There appears to be an evolutionary trend for business management to become more sophisticated and responsive to the need for achieving close to best cost work schedules to sustain continuous improvement. The underlying motivating forces driving this trend for improved techniques in organising attendance at, and time spent at work, is the seemingly inseparable combination of technological advance and ever-increasing accumulation of capital. The mining industry has not remained untouched by this thrust for ever-increasing need for best use of labour, to adopt advances in technology and to provide attractive opportunities for putting accumulated capital to work. An essential component of this on-going thrust is a substantial effort by the mining industry to improve the performance of labour by providing most-productive work schedules.

Jan 1, 1996

By S. R. Noble, F. R. Harris, E. T. C. Spooner

"The Logtung deposit discovered in 1976, is an example of large tonnage (162 million tonnes), low grade (0.13% WO3 and 0.052% MoS;) W(scheelite)-Mo mineralization related to multiple felsic intrusions. Because mineralization is predominantly fracture-controlled (> 95 %) rather than disseminated, Log tung is not a skarn deposit. Metamorphism of the Logtung country rocks (interbedded calcareous shale and graphitic quartizite) to a series of competent reaction skarns (quartz-diopside-garnet calc-silicate, biotite quartzite and wollastonite-vesuvianite calc-silicate) clearly precedes W-Mo mineralization. Hence mineralization was related to permeability created by hydraulic fracturing and not replacement processes.Logtung shows a theme of several phases of mineralization (4) related to multiple intrusions (>2) which is similar to that of the Climax and Urad-Henderson Mo systems. The earliest quartzmolybdoscheelite vein system, which consists of a typical ""porphyrystyle"" crackle-breccia of thin (0.5 mm to 4 mm) quartz-garnetdiopside- molybdoscheelite veins, is related to a high Si02 (approx. 76%), seriate-porphyritic monzogranite stock (approx. 2 km by 0.5 to 1 km) of Cretaceous age (118 ±2 Ma [2u]; Stewart, 1983). Later quartz-pyrite scheelite (fluorite-KINa-feldspars-molybdenite) veins, with prominent green, hornblende-bearing alteration selvages, and quartz-molybdenite (-pyrite-jluorite-scheelite) veins are related to a quartz-feldspar-spessartine-rich garnet porphyritic felsic dike complex approximately 500 m across. Both intrusive phases have anomalously high Wand Mo concentrations of about 100 ppm and 50 ppm respectively, which Stewart (1983) attributes to a primary enrichment. The final stage of mineralization consists of a prominent 4.5 km by 1 km zone of 1 em to 1 m wide polymetallic sheeted veins centred on the felsic dike complex. The system is zoned from quartz scheelite-molybdenite-pyrite-blue-green beryl-jluoritebismuthinite veins in the core to Pb-Zn-Ag veins with abundant arsenopyrite and minor Sn (approx. 0.1%) in the northeast. The focus of recurrent intrusive and hydrothermal activity was located above a flank or nose of the monzogranite stock.The distribution of WO3 and MoS2 grades within the approximately 750 m (across) by 300m (evaluation depth) mineralized zone is a result of the variable superimposition of the four separate vein systems each with different W:Mo ratios. Well-defined Wand Mo ore, shells such as those at Climax, Henderson and Mt. Emmons did not develop at Logtung. The upper surface of the mineralized zone, as shown by the 0.03% MoS2 contour defines an elongate dome with an apical region approximately coincident with the felsic dike complex. Hydrothermal alteration occurs as well-defined vein selvages, and not as pervasive zones.The Logtung deposit shows many similarities to porphyry Mo deposits in the western Cordillera and may be identified as a porphyry W(scheelite)-Mo deposit, with a W:·Mo ratio of 3.3:1. The principal reasons are: (1) mineralization is spatially associated with porphyritic granitic intrusions and (2) much of the scheelite and molybdenite occurs in typical ""porphyry-style"" vein stockworks"

Jan 1, 1995