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By J. S. Osoba, J. W. Graham, P. H. Monaghan

Of the many factors which affect the productivity of hydraudically fractured wells, the wettability of the propping sand has received little attention in the pas/. This paper shows that the wettability of the propping sand is an important factor which shorcltl not he overlooked. An analysis of relative permeability data shows that fractures packed with water-wet sand should be more permeable to oil than are fracturer packed with oil-wet sand. Laboratory results verify this conclusion. Cnlculations show that higher permeability to oil in the fracture should provide higher well productivity. A method is presented which ensures that the propping sand in an induced fracture is water-we1 even though oil is used as the fracturing fluid. The rnethod has been used in more than 150 field jobs: the field resrrlts are discussed briefly. The fluidized nature of water-wet sand in oil has giver1 unexpected benefits. This characteristic of water-wet sand and how it has been used advantageously in field operations are discussed. INTRODUCTION Hydraulic fracturing of subsurface strata to increase the productivity of oil and gas wells has been practiced for about 10 years. Today, fracturing is used more often than any other method of well stimulation. Basically, the process consists of breaking down (fracturing) a subsurface formation with pressure applied by means of a carrier fluid, usually oil or water, and propping the induced fractures apart by means of an agent, usually sand. suspended in the carrier fluid. Currently about 68 per cent of all fracturing is done with a simple mixture of refined oil or lease crude oil and sand'. The research of other investigators has suggested that dry sand is rendered oil-wet when it is contracted with certain types of crude or refined oils.' Hence, it may be expected that some fracturing operations employing an oil as the carrier for sand leave fractures packed with oil-wet sand. Conversely, those operations which employ water as the carrier for the sand probably leave the fractures packed with water-wet sand. Since the permeability of a sand-packed fracture to a mixture of oil and water is dependent upon the wettability of the fracturing (frac) sand, research was undertaken to determine to what extent the wettability condition (water-wet or oil-wet) controls fracture permeability which, in turn, affects well productivity. Additional research was directed toward the development of a method for obtaining the desired fracture wettability. In this report both theoretical and experimental evidence is presented to show the desirability of employing water-wet sand in fracturing operations. A method to obtain water-wet sand is discussed, and field results are reviewed briefly. DEPENDENCE OF WELL PRODUCTIVITY ON FRACTURE WETTABILITY To determine the dependence of well productivity on the wettability of the frac sand, it is necessary to know, first, the effect of fracture wettability on fracture permeability and, second, the effect of fracture permeability on well productivity. The relationship of these variables is considered separately in the order indicated. Effect of Wettability on Permeability Fig. 1 shows relative permeability relations for 20-30 mesh Ottawa sand. Inspection of these curves reveals that the relative permeability to oil when a small amount of water accompanies the flow is considerably higher when water rather than oil is the wetting phase. For

By K. L. Gabby

Selective removal of mercury from cyanide leaching solutions while retaining silver has been a long-standing problem, due to the chemical similarity of mercury and silver. In order to be practical, a mercury removal process needs to be both highly selective and use inexpensive materials. This paper reports the use of zinc sulfide (ZnS) as a precipitant for mercury. The mercury cyanide complex (Hg(CN)4 2-) undergoes a replacement reaction with the zinc sulfide, forming insoluble HgS, while the silver cyanide complex (Ag(CN)2 -) remains in solution. Under appropriate conditions, the separation of mercury from silver is nearly quantitative, with close to 100% removal of mercury, while nearly none of the silver is precipitated.

By T. K. Perkins, L. R. Kern

A study of fluid mechanics, rupture of brittle materials and the theory of elastic deformation of rocks shows that, for a given formation, crack width is essentially controlled by fluid pressure drop in the fracture. Operating conditions which cause high pressure drop along the crack (such as high injection rate and viscous fluids) will result in relatively wide cracks. Conversely, operating conditions which cause low pressure drop (low injection rates and thin fluids) will result in relatively narrow cracks. Charts and equations have been derived which permit the estimation of fracture widths for a variety of flow conditions and for both horizontal and vertical fractures. INTRODUCTION There has been considerable speculation concerning the geometry of hydraulically created fractures in the earth's crust. One of the questions of practical importance is the width of fractures under dynamic conditions, i.e., while the fracture is being created and extended. Such width information could be used, for instance, to help estimate the area of a fracture generated under various conditions. Also, there has been a recent trend toward the use of large propping partiles.13, 15 Therefore is is desirable to know what factors can be varied in order to assure entry of the large particles into the fracture. There has been some work on fracture widths reported in the literature. In particular, there have been several Russian publications dealing with this sub-jeCt.1.31,3 These papers have dealt principally with the elastic theory and the application of this theory to hydraulic fractures. These studies have not led to an engineering method for estimating fracture widths under dynamic conditions. A recent paper3 has reviewed and summarized the Russian concepts. An earlier paper- from our laboratories also discussed the application of the elastic theory to hydraulic fractures. This first approach, based largely on photoelastic studies, has proved to be too simplified to accurately describe the fracturing process. However, these early thoughts have served as a guide during the development of more exact concepts. We would like to present in this paper our current concepts regarding fracture widths and some estimates of hydraulic fracture widths for several conditions. We believe that it is now possible to predict with fair accuracy the factors influencing fracture widths. Furthermore, the method of prediction has been reduced to a simple and convenient graphical or numerical calculation. CRACKS IN A BRITTLE, ELASTIC MATERIAL Many investigators2, 4, 30 have shown that competent rocks behave elastically over some range of stresses. Of course, if the tensile stress imposed upon a rock exceeds some limiting value, then the rock will fail in tension. In similar manner, there are some limiting shear stresses that can be imposed upon rocks. Hubbert and Willis11 have discussed the shear conditions which will lead to failure. Under moderate stress conditions (such as those likely to be encountered when hydraulically fracturing) and when stresses are rapidly applied, relatively, most rocks will fail in a brittle manner. Hence, for this discussion of hydraulic fractures in the earth's crust, we assume the rocks behave as brittle, elastic materials. Let us develop the discussion in the following way. (The following thoughts are applicable only to brittle materials.) 1. First we consider a brittle, elastic system. An energy balance will show the minimum pressure necessary to fracture rock, and from this pressure we calculate the minimum crack width resulting from extension of a hydraulic fracture. 2. Then we will show that, under ordinary fracturing conditions, fracture widths are appreciably greater than the minimum widths of extending fractures. In fact, we will find that crack width is controlled by fluid pressure drop in the fracture. 3. We will discuss pressure drops in fractures and resulting crack widths for various operating conditions and both vertical and horizontal fractures. 4. Finally, we will discuss the significance of these concepts, their relationship to fracturing pressures, etc. First, consider minimum fracture extension pressures. We can shed some light on this question by considering the theory proposed by Griffith7, 8 Yo explain the rupture of brittle, elastic materials. Griffith recognized that solid materials exhibit a surface energy8 (similar to surface tension in a liquid). The fundamental concept of the Griffith theory is that, when cracks spread without the application of external work (in the interior of an elastic medium which is stressed

By Deventer Johanna van

Ore bodies around the world are declining in grade, whilst increasing in complexity. The level of impurities relative to the valuable metal is steadily increasing, posing new challenges to existing operations. Ion exchange is widely used in the hydrometallurgical industry for both primary recovery of metals and the removal of impurities. The superior selectivity of ion exchange resins makes them exceptionally suitable for the removal of target impurities to very low levels, thereby saving operating costs, increasing the value of the final product and significantly improving revenue. The ion exchange process in these applications is very simple, using standard ion exchange equipment and acid regeneration. The process can be fully automated, requiring minimal operator interference and supervision Examples of impurities that are successfully removed via ion exchange include iron, antimony and bismuth from copper electrolyte. In the copper electrolysis process, antimony, bismuth and arsenic tend to form slimes which are dispersed in the electrolyte. These slimes contaminate the cathode and/or decrease the quality of the copper deposition. A special chelating resin was developed to remove antimony and bismuth, while at the same time ensuring minimal chloride leakage to the sulphate matrix. The work is described in more detail in this paper. Ion exchange is also used to remove copper, zinc and nickel from cobalt electrolyte. This paper addresses a few of these examples in more detail.

By J. W. Walker, G. J. Heuer, E. W. Hough

An improved apparatus is described for the deterrni-nation of interfacial tension* by the pendant drop method in the pressure range from 15 to 15000 psi and the temperature range from 100º td 280°F. The chief characteristics of this apparatus are reliability and ease of operation. Temperature control was accomplished by means of an electrically heated jacket which could he completely removed while cleaning the apptrratus. The cell was designed so that the camera could he placed about I in, from the window without overheating the carnera lens. Separate "0" rings employed to seal each window and corresponding window backup plate gave very reliable window operation at 10,000 psi. An extra pistorr-cylinder combination was added so that a high compression ratio could he attained when gas was employed as one phase in the pendant drop cell. Other essential parts of the system were similar to an apparatus already described.' The interfacial tension for carbon dioxide and water varies from about 69 dynes/cm at 15 psi to about 19 dynes/cm at 1,250 psi for 100°F. For pressure.r between t,500 and 3,500 psi, the interfacial tension is between 32 and 24 dynes/cm at this temperature. The interfacial tension at 280°F varies from about 50 dynes/cm at 200 psi to about 17 dynes /cm at 10,000 psi. The maximum surface excess for carbon dioxide, assuming the surface excess of water to be zero, occurs at about 1,500 psi jor the 100°F isotherni and Itas a value of about -79 X 1014 mol/sq cm. At 160°F this maximum IS shifted to about 2,000 psi and has a value of about 10 X 1014 111ol/.sq cm. Other maxima, us well as several minima, are present at these and other temperatures. Judging from the data on the solubility of water in carbon dioxide at elevtrted pressures2,3, it appears that the principal maxinza natned are in regions of increasing solubility of the water in the carbon dioxide rich phase. INTRODUCTION AND APPARATUS A pendant drop interfacial tension apparatus which would accommodate an opaque liquid in a gas phase was constructed several ycars ago' for industrial purposes. This apparatus was used as a starting point for the present development. The objective of the present development was to enhance reliability and convenience of operation. Other articles'" have described pendant drop apparatus which could not accommodate a gaseous phase adjacent to the windows. A schematic diagram of the apparatus is shown in Fig. 1. The water used followed the path; A, intro-

By Jeremy Butkovich

Dynamic soil-structure interaction (DSSI) analyses are becoming more common in bridge designs, especially in seismically active areas. Because of its proximity to two active fault zones, the Evergreen Point west approach bridge replacement will be base isolated, and will be designed using DSSI. The project team completed two independent bridge designs to satisfy peer review requirements. The designs required substantial characterization of the soil dynamic behavior using both laboratory and in-situ testing. The analyses made use of earthquake time histories spectrally matched to conditional mean spectra. This led to reduced, and more realistic seismic demands on the structure, compared to conventional uniform hazard spectrum matching. The bridge analyses suggest that the preliminary bridge design is relatively conservative. This will allow the design team to potentially reduce shaft/column diameters and reinforcement. The design team estimates that the dynamic analysis design could represent a net savings of around $60 to $90 million compared to a conventional design.

By Stephen C. Tadolini, Thomas M. Barczak, Peter (Yunqing) Zhang

A cooperative study was conducted with Emerald Coal Resources, L.P., an affiliate of Foundation Coal Corporation, and the National Institute for Occupational Safety and Health (NIOSH) to evaluate the effectiveness of (partially) pre-driven longwall recovery rooms supported with pumpable roof supports. This paper evaluates the load transfer mechanics associated with the advancement of the longwall face into the pre-driven recovery room and the widening of the room to recover the longwall shields. The results show that the yielding of the panel fender produced uncontrollable convergence that caused yielding of the shields and stiff pumpable roof supports when the face was approximately 10 ft from the recovery room. The shields continued to yield until the face advanced into the recovery room. Convergence in the pre-driven recovery room typically reached 6-8 in once the pumpable supports yielded and shed load through a declining residual load capacity prior to being cut out by the longwall shearer. Roof deformations occurred beyond the 32-ft horizon with total deformation ranging from 2 to 4 in, indicating that standing support was necessary to help control the span as the longwall face advanced into the pre-driven recovery room. Stability improved as the pumpable supports were cut out, thereby reducing the span between the shields and the outby pillars. In the end, the shields were successfully recovered under stable ground conditions. However, a disconcerting discovery was the load shedding of the outby pillars as the recovery room was mined into. It is postulated that this may be due to the progression of the rear “abutment” moving toward the recovery room as the panel fender and standing support in the recovery room yield and shed load. This behavior was not expected with a relatively narrow room that is fully supported with standing support. If this mechanism is indeed occurring, the width of the room and performance of the standing support becomes even more critical. Premature failure of the support can lead to excessive convergence on the shield line that cannot be controlled even with modern shields, resulting in roof instabilities that can lead to catastrophic results.

When most people think of coal mining, they envision men in soot-covered clothes and hard hats digging at deposits in deep underground caverns. These mental images commonly include coal cars rumbling on rails as they emerge from the earth, filled to the brim with rocky ore. The world of modern, longwall coal mining is a far different place. Yes, it?s underground, the miners still wear hard hats and the environment is filled with soot. However, today?s mining operations are carefully monitored and the entire process is highly automated. Five kilometers (3 miles) underground, a sophisticated, high-powered mining machine moves steadily through a 2-m (6-ft) high tunnel at an average speed of 3.2 km/h (2 mph), carving out coal, then conveying it to a crusher and carrying it to the surface. Instead of digging out the ore, a longwall mining system slices it from the exposed tunnel face, using giant rotating shears. The shorn coal tumbles onto a conveyer below the shears and is conveyed to the stageloader, where it is crushed and dumped onto the main conveyer belt that eventually hauls it out of the mine. Integral to the longwall shear and conveyor is a moving metal roof that protects it from the thousand plus feet of ground above. The ceiling panels automatically advance above the shears, powered by hydraulic roof supports that stand on the other side of the tunnel, moving in a slow, sideways lock-step with the shears. This complex and massive machine makes longwall mining the most ef?cient and productive method for excavating coal. In fact, it produces 2.7 kt to 22.6 kt (3,000 to 25,000 st) of ore per shift, versus 544 to 907 st (600 to 1,000 st) for the conventional room-and-pillar mining. Using that method, miners develop one section of a mine at a time after carving out load-bearing columns of coal to support the roof above their heads. Longwall mining also is considered safer than the room-and-pillar method, largely because the process is mostly automated, requiring fewer workers. Still, longwall mining has its drawbacks: The equipment is expensive and the mining conditions are harsh. An entire longwall system can cost between $50 million and $100 million, while the electrical controls used to operate it can cost an additional $1 million to $2 million. These investments grind away all day, every day, in hot tunnels filled with coal dust.

By V. C. Robinson

INTRODUCTION Most presidential addresses are in the nature of a review of some specific topic and this will be no different. In thinking about the subjects which might be suitable for this address I decided that as next month will see my retirement from the gold mining industry I might review the four decades since I started in the industry in 1929. These four decades have been more than usually in',~resting and exciting. They have covered a period when the price of gold increased from the old figure of 84/- an ounce to the price of $35 an ounce today, taking in on the way at least two periods of premium sales from which the producer benefitted. The industry in these four decades has survived the most totally destructive war in history and has seen fundamental changes in the political, economic and governmental life of South Africa. There have been great technological changes and improvements, some of which I shall refer to later, and in addition there have been profound changes in the relations between employer and employee in the industry which have affected not only the economy of the industry but the traditional thinking of both management and labour. I believe that the address presented to this Institute on the occasion of its 75th Anniversary by Mr Goode covered more than adequately the history of the Institute and the part it has played in the mining industry of South Africa. It would be merely repetitive, therefore, to discuss the affairs of the Institute of Mining and Metallurgy. Having said this, however, it is also necessary to point out that the history of the Institute is, and always will be, an important record of the history of mining in South Africa. There are many facets, however, on which we ought to look back and to re-examine. One of the most rewarding, but at the same time one of the dullest, places to look for historical facts is in the annual reports of the Chamber of Mines. I suppose that some of the dullest of these have been the reports for which paragraphs have been prepared by me personally. The notes which follow do not claim to be anything like a full record of this exciting period. RISE AND FALL OF THE GOLD MINING INDUSTRY In talking about the mining industry of South Africa it is inevitable that one talks, particularly in the historical sense, about the gold mining industry - an industry of fundamental importance which has made South Africa what it is and which has been dying since the early part of this century. In Table I is shown the progress of the gold mining industry measured by its output of ounces of fine gold from the beginning of operations until the end of 1969, and if you are interested in the productivity of the men who work this industry the table, composed entirely from figures set out in the Chamber's annual reports, also shows the production of gold expressed as fine ounces per European and fine ounces per Bantu worker over a long period. If you are still minded to think of this industry as dying then the last column in the table shows how uranium has played such a vital part in the prosperity of the country.

By Kenneth N. Han

The effect of anions such as sulfate, chloride and nitrate on the solubility of rare earth element (REE)-bearing phosphates and fluoro-carbonates was examined using relevant thermodynamic data. The study found that these anions have significant influences on the overall dissolution of REEs from various sources in the aqueous media.

The phenomena of nature cannot present themselves to any thinking wild without claiming from it some solution. The earth, as it has often been observed, is laid out like a well ordered cabinet, presenting to us, in measure, some means of judging how the laws of nature and the essential properties of matter have worked out all we see before us. "That there have been depositions of strata gradually laid down aud stocked with the remains of the living objects, vegetable and animal, that flourished when they were being imposed, is an universally acknowledged fact. It speaks of a constantly maintained series of operations whereby the globe has been brought to its present condition, and which are ever advancing it to stages that are still before it. That immeasurable ages have been consumed in effecting these developments is also conceded. We witness the very graduated rate of the existing advances and can see that the past action must have been conducted in the same slow deliberate manner. There are many questions, however, upon which inquirers are not agreed, hence they are still within the domains of fair discussion.What has led to those great climatic changes whereby the same portions of the earth have had at various times climates that were glacial, temperate, and tropical? What causes the constant contortions and dislocations of strata and the upheaval and depression of land levels, and that there is a tendency to alternation in the parallel areas undergoing opposite kinds of movement as if the sinking of one area balanced the rIsing of another? What is the reason that the centres of volcanic action are continually shifting, and that the line of greatest activity is always upon the rising areas? That portions of the earth have been subjected to intense alid long continued volcanic action, and again to long periods of repose, and that the periods of activity and repose are·recurrent at long intervals of time? What the mountain chains of the world are in broadly parallel bands? What has caused the stratified rocks to be tilted from their original?

By Atsushi Shibayama

The aim of this research was to develop a copper recovery process from mine tailings (0.34%Cu) using flotation followed by high-pressure oxidative leaching (HPOL) and solvent extraction. The results of HPOL using the concentrate of mine tailings obtained by flotation under the optimal conditions of the previous study shown that an efficient copper dissolution of 94.4% was achieved in an H2O media, while the copper concentration of PLS reached to be 2.9 g/L. The solvent extraction of PLS obtained from the optimal HPOL showed that 91.3% copper was recovered in stripped solution under the determined optimum conditions, in which the copper concentration achieved to be 44.8 g/L. Finally, a proposed copper recovery process from the concentrate of mine tailings was developed by combination of HPOL and solvent extraction, while a total copper recovery of 86% was achieved.

By K. Adham

For use in many existing and emerging applications, the purification of natural graphite is required to achieve +99.9% carbon content with minimum metallic impurities. Currently, the hydrofluoric acid process is used, which carries certain environmental and workplace health and safety impacts. While thermal purification of graphite at temperatures over 2500 °C is a known alternative, such high-temperature furnaces are expensive to build and operate. Using chlorine at lower temperatures to purify graphite is also known and patented, but is currently limited to treating solid synthetic graphite shapes in small-scale batch furnaces. Chlorine treatment of natural flake graphite resources can be used commercially, if certain drawbacks are addressed through process improvements that can be helped with the use of fluidized bed reactor technology.

By Todd M. Ruff

The lack of visibility near earthmoving equipment resulted in six fatalities in U.S. surface mining operations during 2003. These accidents were the result of either a piece of equipment striking another vehicle or worker, or the equipment traveling over the edge of an embankment. Figure 1 is an example of a recent accident that resulted in serious injuries to one worker and fatal injuries to two others when a van parked in front of a haul truck. Two fatalities occurred in separate incidents when front-end loaders struck workers. Another two workers were killed when their equipment backed over the edge of a highwall or dump point [1]. There is clearly a need to provide better information to equipment operators regarding their surroundings. [ ] Researchers at the National Institute for Occupational Safety and Health (NIOSH), Spokane Research Laboratory, are working to reduce these accidents by developing systems that sense obstacles and changes in terrain near the equipment and provide this information to the operator. Many off-the-shelf proximity warning systems that were developed for automobiles, light trucks, and recreational vehicles were evaluated on off-highway dump trucks [2]. Many limitations were found with existing systems, including frequent false alarms, limited detection range, a lack of specific information on an obstacle (e.g., location, identity), difficulties in finding suitable mounting locations, and an inability to withstand the environment. These limitations have necessitated the development of new systems designed specifically for large, off-highway, earthmoving equipment. New off-the-shelf systems available for mining equipment include radar and tag-based detection systems. Prototype systems now being developed include a proximity warning system based on the Global Positioning System (GPS) and a computer-assisted stereovision system. Development of these new systems was accomplished by working with manufacturers to modify existing systems to meet the needs of surface mining and through cooperative research with organizations to develop completely new solutions. A typical proximity warning system consists of a sensor or antenna mounted on the equipment that detects the presence of obstacles and an alarm interface in the cab of the equipment. Some systems, as described in more detail below, also require that other vehicles and personnel on the ground be outfitted with electronic tags that transmit an “I’m here” signal back to the system (e.g., radio signal detection systems or GPS). Many types of proximity warning systems are on the market, but they are not all discussed in this paper. APPROACH In past work, engineers at NIOSH evaluated several off-the-shelf proximity warning technologies in order to verify their effectiveness on off-highway dump trucks [2]. Dump trucks were chosen because of the number and severity of accidents involving this type of equipment and because extensive blind areas around these trucks are typical. This experience allowed engineers to limit the number of systems chosen for long-term tests at mine sites to those systems showing

By Edmund C. Pechin

The Lucy furnace, owned by Messrs. Carnegie, Kloman & Co., and located on the Alleghany River, on the outskirts of Pittsburgh, is a splendid modern furnace, 75 feet high, and 20 feet bosh. She had been working well on low grade ores of about 50 per cent., producing daily 68 to 75 tons. There was on stock 500 tons of Republic ore, one of the purest and best of the Lake Superior ores, averaging over 68 per cent. of iron, which had been procured for the purpose of making a trial for Bessemer iron. This was charged by itself, and Mr. Skelding, the founder, reports that he did not succeed in getting a single cast when it came down, before the furnace chilled from the hearth to the top of the boshes, some 25 feet. Every effort was made to save her, without avail, and the disagree-

By W. Hurst, R. E. Leeser, W. C. Goodson

Three aspects of gas deliverability are presented in this paper. The first treats with the gas deliverability or availability of a normal depletion-type dry gas field. Such encompasses not only the period of stabilized constant rate, but more so, the "tailings" when a fixed abandonment pressure is reached and the rate by necessity must decline. A comprehensive work plot is offered, developed from mathematics herein included, that removes the triai-and-errnr computations that attended such undertakings in the past. The second part treats with the discount factor of the open flow potential constant from what is observed initially in testing a gas well to what is evidenced when stabilization is reached. This prevails in tight formations, such as the Kansas Hugoton field which is offered as the example. The means of establishing this factor are pressure build-up curves which, as sustained by analytical deductions, reproduce this entire period of transient flow under conditions of a constant rate influx. Finally, what is offered in this paper is the deliverability performance of an exceedingly rich gas condensate field producing from a tight formation. The example shown is the Knox Bromide field in Oklahoma, producing from the Bromide formations. The results are ominous, showing early reduction in permeability to gas pow, due to the retrograde condensate forming in the pore space, with the attending early logging-up of these wells. The analytics of lowered permeability are incorporated in the gas deliverability formula along with the PVT data that gives the increased condensate liquid saturation as the gas flows to the well bore. This paper would not be complete without a critique oflered at the end. With the many gas wells now in production and those that have completed their life, there has been no factual information collected by any source as to what constitutes that permeability range where a gas well would be unimpaired in its gas deliverability by the presence of rich condensate content, and the lowered range where such would be harmful. This question confronts all producers. INTRODUCTION Various aspects of gas deliverability are presented in this paper that includes depletion-type reservoirs, deteriora- tion factor of the gas deliverability constant, and the performance of a rich gas condensate reservoir producing from a tight sand. With respect to the presentation of gas deliverability and its tailings for depletion-type gas reservoirs, one notes that this is essentially the information offered by every gas transmission company and producer appearing before the Federal Power Commission for Letters of Conveyance in the dedication of reserves. In the ordinary procedure, as many engage upon this study, trial-and-error calculations are included, particularly as apply to the tailings. For many years one of the writers has employed mathematical analyses to perform this step and avoid the complexities so associated. In the preparation of this paper these analyses have been amplified to include any slope n for the open flow potential relationship for which the tailings can be determined from Fig. 1. With reference to the deterioration or discount factor of the open flow potential constant as such occurs in the gas deliverability formula, this for the most part has been an unexplored subject. Although the issue first appeared in the Kansas Hugoton field, where such was surmised but only recently resolved, this situation of a deterioration of the gas deliverability constant can occur wherever dry gas production from a tight sand is encountered. The first concerted attacks upon this problem were the presentations of Hurst' and Goodson' before the Kansas Corporation Commission to show that transient fluid flow and unsteady-state flow formulas prevailed. This was amplified later before the Federal Power Commission3 to show that this deterioration factor could be identified from pressure build-up curves. This has been reported by McMahon.4 Its importance to the industry merits the review of these essential features in completing the program on the aspects of gas deliverability. Finally, as illustrated here, for a low permeability formation such as the Knox Bromide field where the gas is rich, representing some 165 bbl of condensate per MMcf of effluent gas, the gas deliverability can be of limited extent in the life of the field, leaving substantial amounts of condensate and gas unrecovered. In cases such as this, gas cycling is mandatory. This is particularly revealed by the fluid mechanics introduced here, employing factual field as well as laboratory data, to show this-restriction upon gas deliverability. PRESSURE DEPLETION What will now be offered is the study of gas deliver-

By C. van der Poel

When oil is displaced from a horizontal formation by another fluid of lower density, the latter tends to override the former in the shape of a tongue owing to gravity segregation. This gravity tongue has an adverse influence on the oil recovery. If the fluids are miscible, diffusion (mixing) takes place at the interfacial boundary of the gravity tongue. This mixing should have a favorable effect on oil recovery. The report describes a laboratory study of the magnitude of the mixing zone under various conditions, so as to assess the effect of diffusion on oil recovery both in laboratory experiments and under actual field conditions. The technique used enables visual observation and measurement of the size of the mixing zone in transparent glass-powder packs. The results show that in experiments in small models and cores the width of the mixing zone may well be of the same order of magnitude as the height of the model. In such cases oil recovery is favorably affected by mixing. It can further be concluded that, under conditions prevailing in the field, mixing of the injected fluid with reservoir oil is equal to that caused by molecular diffusion alone, eddy-mixing not taking place to any appreciable extent. A simple calculation, then, shows that molecular diffusion is too small for a beneficial effect to be expected from the injection of miscible fluids in horizontal or nearly horizontal reservoirs unless pay zones are thin. INTRODUCTION This paper gives results of experiments made on the mixing which occurs when a miscible displacement is carried out in a horizontal reservoir. This mixing takes place at the interfacial boundary of the gravity tongue formed when the lighter injected fluid overrides the oil present in the reservoir. The object of the experiments was to simulate the field case where, for example, propane with a viscosity of 0.075 cp under reservoir conditions displaces an oil of viscosity 0.6 cp. In the experiments the lighter fluid had a viscosity of about 1 cp and the heavier one a viscosity of about 8 cp, so as to obtain the same viscosity ratio. In order to enable the results to be compared with those published in the literature, a set of experiments with viscosity ratio equal to one was also performed. EXPERIMENTAL TECHNIQUE The technique developed for the purpose enables the width of the mixing zone to be studied as a function of time and place. A glass-powder pack is saturated with a water-glycerine mixture of suitable viscosity, which represents the reservoir fluid. The pack is then rendered transparent by dissolving sufficient ammonium thiocyanate in the mixture to obtain a solution with a refractive index matching that of the glass powder. Alkaline water to which phenol-phthalein has been added is used as the lighter and less-viscous displacing fluid. In those places where mixing or diffusion of the two liquids occurs, the slightly acidic ammonium-thiocyanate solution neutralizes the alkali in the water, and the glass pack shows up white against the red-colored invading water. If a black cloth is hung over the back of the apparatus, the transparent part of the glass pack appears black. In this way the position of the two phases and the transition zone between them is clearly visible, as shown in Fig. 1 (where the red-colored invading water is the grey-shaded zone lying uppermost). In all experiments the amount of alkali in the water was chosen such that the upper contour corresponded to a concentration of 5 per cent of the dense liquid. The lower contour is determined by the size of the glass grains and the thickness of the pack and, consequently, varies from experiment to experiment. Corresponding concentrations of the dense liquid range from about 97 per cent for packs of small grain size (permeability = 1 darcy) to about 95 per cent for those with large grains

By Shubin Wang

Copper(II) and nickel(II) are often recovered from ammoniacal alkaline solutions by solvent extraction using hydroxyoxime extractants: both copper(II) and nickel(II) are extracted from ammoniacal alkaline solutions and, from the loaded organic phase, nickel(II) is selectively stripped with a dilute acid followed by copper(II) stripping with an acid of higher concentration. Since a small portion of ammonia is co-extracted with copper and nickel, the extracted ammonia should be scrubbed using a dilute acid before metal stripping. In the present study, a mechanistic model has been developed in order to support design and control of this process. The equilibrium distribution ratios of copper(II), nickel(II), and ammonia at 298 K using LIX® 84-I (active component, 2-hydroxy-5-nonylacetophenone oxime) as the extractant are successfully correlated by considering the relevant equilibria. Based on these results, quantitative prediction of equilibrium distribution ratios in the process has been made possible, and suitable conditions for the efficient separation of copper(II) and nickel(II) are discussed.

By A. A. El-Midany, R. M. Farag, A. M. Salem, S. E. El-Mofty

Bentonite represents one of the main players in the stability of the drilling mud. Its particle size and particle size distribution affect the physical properties of the drilling mud especially the rheological properties. Therefore, a specific particle size distribution was recommended by American Petroleum Institute (API) for use in drilling mud. To clarify the effect of individual size and size distribution, in this study, the bentonite sample was classified into different size fractions. Each size fraction was tested separately in terms of controlling properties such as filtration loss, plastic viscosity, gel strength, cake thickness, and packing density. The effect of each size fraction on the rheological properties of the suspension was correlated to the behavior of the whole particle size distribution in the bentonite sample. The results indicate that the coarser the particles, the higher the rheological properties; in this case, the API mixture is the highest. The filtration loss and cake thickness for the API mixture are lower than that of the individual size fractions due to its wider size distribution due to the filling of voids between larger particles with smaller ones, which lead to bed compaction and consequently lower fluid loss and cake thickness.

By F. Ikumapayi

Hydrogen peroxide production was measured during the grinding of a complex sulfide ore, and its oxidizing effect on solid surfaces was investigated using Fourier transform infrared spectroscopy (FTIR) with diffuse reflectance attachment measurement. In turn, an attempt was made to correlate the formation of hydrogen peroxide, surface oxidation and sphalerite flotation. Additionally, in order to predict and minimize detrimental production problems due to the recycling of process water in sulfide ore processing, the effects of major components of calcium and sulfate species present in recycled process water and the effect of temperature on sphalerite flotation were investigated through bench-scale flotation tests using complex sulfide ores. The significance of process water species in flotation was studied using tap water, process water and simulated water containing calcium and sulfate ions. Formation of hydrogen peroxide was revealed during the grinding of the complex sulfide ore, and its formation was counteracted by diethylenetriamine (DETA). The FTIR spectrum of the pulp solid fraction showed varying degrees of oxidized surface species, which are related to the concentration of H2O2 analyzed in pulp liquid. Bench-scale flotation using two different complex sulfide ores showed that sphalerite recovery is better in process water than in tap water. Flotation results also indicated a varied recovery of sphalerite at different temperatures in either tap water or process water.