Aluminum Pellets Research Articles

Fracturing With a High-Strength Proppant

Introduction The shortage of natural gas in the U.S. has caused an increasing number ofdeep well completions over the past several years--a trend that will likelycontinue. Many of these deeper wells will require hydraulic fracturingtreatments in order to produce at economic rates. To achieve successfulfracturing results, a material having properties superior to sand is needed toprop open the hydraulic fractures created at the high earth stresses present indeep wells. Silica sand, the commonly used propping material, tends to crush atclosure stresses encountered in deep formations, producing fine particles orfragments that can drastically reduce fluid conductivity of the proppedfracture. propped fracture. Efforts to develop a proppant capable of bearinghigh stresses without excessive crushing have produced such materials as glassbeads, steel shot, and aluminum pellets. Glass beads have been usedcommercially for over ten years, but there is evidence indicating that thestrength of the glass in multilayers is greatly decreased in the presence ofbrine. Metallic materials are presence of brine. Metallic materials arecomparatively expensive and corrode, so their use has been very limited. Otherresearch has looked at deformable materials, such as nut shells, that will notcrush and will prop open a fracture when a partial layer is present. The use ofdeformable propping materials in partial monolayer propping materials inpartial monolayer concentrations appears to have decreased in recent years. Exxon Production Research Company (EPR) has worked for several years todevelop improved, high-strength proppants. A wide variety of materials weretested in the laboratory under simulated reservoir conditions. One material, sintered bauxite particles, showed greatly improved properties particles, showed greatly improved properties over any material available in the past andit has been field tested to date in 12 wells--all deeper than 10,000 ft. This paper discusses laboratory studies of the new, high-strength bauxiteproppant, describes field applications of the proppant, and summarizes factorsaffecting gas well stimulation. The field results have shown that the benefitspredicted from laboratory studies can be realized. Widespread use of the newhigh-strength proppant is expected in the future.

Anodic Oxidation of Porous Aluminium Pellets

The anodization of porous aluminum pellets is accompanied by a change in the composition of the electrolyte within the pellet pores. This change can be accounted for by electrochemical transport of ions to the electrodes and the inability of the system to overcome the concentrating effects in the anolyte. It is shown that this effect can, depending on the composition of the bulk electrolyte, result in a strong acid environment or a weakly conducting electrolyte within the pellet. Either condition results in undesirable oxidizing characteristics; a strong acid will lead to the formation of a porous film which is poorly impregnated by the solid electrolyte, and the resistive electrolyte impedes the growth of oxide film. This work indicates that these extreme conditions may be avoided by the use of electrolytes containing salts of organic acids of moderate strength.

Debris clouds behind plates impacted by hypervelocity pellets

The effectiveness of two-plate meteoroid shields is determined by the character of the debris cloud ejected behind the front plate after a hypervelocity impact. The material velocities, distributions, and momentum intensities of these clouds have been determined experimentally for 6061-T6 aluminum, OFHC copper, and cadmium pellets impacting optimal thickness bumpers of the same materials at 7.0 km/sec. Debris dissection techniques, free suspended flyer plates, flash radiography, and high speed photography were used to make these measurements. The results were compared with numerical computations from a computer code that describes thin plate impacts as two-dimensional flow processes. Agreement was reasonably good with respect to debris trajectory, origin, and velocity comparisons (except for the Cd pellets), but predicted momentum profiles failed to agree with experiments near the cloud axes, and predicted cloud thicknesses were too great in all cases. On the whole, the discrepancies were considered to be sufficient to call into question any shield design based solely on the code predictions. Background T WO primary approaches are currently available for predicting the responses of spaced-plate shields to meteoroid impacts: 1) use of numerical analyses (computater codes that treat hypervelocity impacts as two-dimension al material-flow processes) and 2) extrapolation of the results of experimental impact data generated at lower velocities. Because the latter extrapolations require questionable assumptions regarding similarity of impact effects at different velocity regimes, and whereas the computer codes deal directly with the velocities of interest and are based on relatively plausible assumptions concerning materials response, the codes have been used widely in the design of meteoroid protection systems. In the present study, a typical code§ was used to predict general dynamic characteristics of clouds generated behind thin plates (bumpers) that were impacted by pellets traveling at velocities achievable with laboratory facilities.2 Particular impact situations were chosen to simulate the phenomena that are thought to be most important during actual encounters between meteoroids and spaced shields. These impact situations were then produced experimentally, the dynamic parameters were measured, and the results were compared with the code predictions. Results from this study are useful both for establishing the reliability of this code and other similar codes, and for guiding the development of more advanced versions with greater reliability.

Relation of Formation Rock Strength to Propping Agent Strength in Hydraulic Fracturing

Abstract The introduction of new fracture propping agents that are brittle but much stronger than sand created the problem of what loading strength is required for a propping agent to be effective in a given formation. It is shown that the load at which the propping agent crushes should exceed the load at which total embedment in the fracture faces is possible. Simple laboratory tests to determine loading strength of the propping agent and embedment in the fracture faces, and use of these data in selecting a propping agent for a given formation, are discussed. Introduction One of the most important factors in the design of hydraulic fracturing treatments is the selection of a propping agent that can effectively provide the fracture flow capacity needed for stimulation of a well. Sand, once generally accepted as being synonymous with propping agent in hydraulic fracturing, is now recognized as having limited effectiveness in many formations because of its low resistance to crushing. Sand particles are brittle and have relatively low strength. Because of this property, sand particles are crushed in rocks that offer high resistance to the penetration of fracture faces by the proppant particles when the fracture attempts to close under the action of the overburden load. For rocks that offer a high resistance to penetration, deformable particles are more effective propping agents than sand. However, for this same type of rock, a propping agent that does not deform, yet does not crush, is often more effective. Thus, a rigid propping agent with sufficient strength to prevent crushing is desirable. A method for determining the strength required for a rigid propping agent to function effectively in given formations is discussed. BEHAVIOR OF RIGID PROPPANTS AND FRACTURE FACES RELATED STUDIES An early qualitative description of the reaction of propping sand in fractures was given by Hassebroek et al. In discussing fracturing in deep wells, the authors mentioned that even though propping sand entered the fractures, a high flow capacity did not result due to crushing or embedding of the propping sand. Dehlinger et al. in discussing the reaction of propping sand surmised that, because of the hardness of sand particles, deformation occurred in the fracture faces contacting the propping sand. In later studies," methods of determining the embedment of propping sand in fracture faces of soft rock and the critical load at which propping sand is crushed by the fracture faces in hard rock were discussed. In working with deformable proppants, Kern et al. considered proppant articles to be deformed into cylindrical disks by action of the overburden and then pressed slightly into the fracture faces by further action of the overburden. Rixie et al. reported on embedment pressure and presented a method of selecting a propping agent for use in given formations. The propping agents included sand, walnut shells and aluminum pellets. All these studies have contributed materially to a better understanding of propping agent behavior; however, the strength of brittle proppants (sand, glass and ceramics) required to result in embedment rather than crushing has not been discussed. This topic will be covered in the ensuing discussion. PROPPANT PARTICLE CRUSHING-EMBEDMENT For this discussion, a rigid propping agent is considered to be one that is brittle and fails under tensile stress when loaded to a critical value. In an earlier study it was shown that the Hertzian loading theory could be applied to a spherical brittle propping agent if the propping agent and fracture faces behaved elastically. At the failure of the proppant, the ratio of the load to the square of the diameter of the particle should be constant for a given material combination, or: (1) A partial derivation of this equation from proppant and formation properties is included in the Appendix. Should a rigid particle not be crushed as a load is applied, it embeds in the fracture faces. A study of particle embedment in fracture surfaces has been published. The embedment can be described by an equation based on Meyer's metal penetration hardness relationships: (2) In Eq. 2, B and m are constants that are characteristic of the rock; the significance of the other terms is shown in Fig. 1. JPT

Initiation of Detonation by the Interaction of Shocks with Density Discontinuities

The basic processes in the shock initiation of inhomogeneous explosives have been investigated theoretically using the model of a cylinder of nitromethane containing a void or an aluminum pellet. The interaction of a shock with the density discontinuities, the resulting formation of a hot spot, and the buildup to propagating detonation were computed using two-dimensional numerical hydrodynamics of the ``PIC'' type with chemical reaction and accurate equations of state. The hot spots formed at aluminum pellets exhibit failure or propagation of detonation in approximately the same manner as the one-dimensional, hydrodynamic hot spots studied previously. The failure of hot spots formed at voids could be studied only in those cases in which the failure mechanism did not depend on details of the structure of the reaction zone, as this structure could not be reproduced in the calculation.

Stimulation of Deep Gas and Gas-Distillate Wells

Abstract This paper discusses recently developed gas and gas-distillate producing wells, deeper than 10,000 ft, in West Texas and Southeast New Mexico. High bottom-hole pressures and temperatures above 200F require modification of conventional completion and stimulation techniques. The problem of formation damage due to solid infiltration from drilling fluids and cement slurries is particularly severe. The use of high-density brines as completion fluids is described and recommended to minimize such formation damage. During completion, mud dispersal and removal acids are usually employed to clean up the critical area next to the wellbore. In case of severe permeability damage, it may be necessary to employ supplementary stimulation treatments using acids with retarded reaction rates. Pressure limitations usually require that such treatments be conducted through tubing. When treating acids can be pumped down the casing, utilization of large-volume, high-injection-rate treatments have resulted in increased benefits. Such treatments in the Azalea Devonian field have proven equivalent to fracturing treatments employing propping agents. Comparative lab tests of post-treatment fracture flow capacities indicate that propping sand may undergo crushing or embedment when subjected to high overburden pressures. Although the use of malleable propping agents such as walnut shells or aluminum pellets often results in considerable improvement in productive capacity following fracturing, even better results sometimes are obtained with acid. Nonuniform acid solubility of the fracture faces results in self-propping, thus providing highly permeable flow channels which are unblocked by propping material. High bottom-hole temperatures require the use of special inhibitors to avoid excessive corrosion of metal well equipment. In some cases, the problem of gyp deposition resulting from contact between spent acid and incompatible brine has been overcome by the use of suitable chelating chemicals. Case histories are included, illustrating treating procedures and results obtained under various circumstances. Correlation of reservoir conditions and treatment data have made possible the evaluation of various stimulation methods and selection of optimum treating techniques. Introduction Well stimulation has played an important part in the development and exploration of deep gas reservoirs in the West Texas-Southeast New Mexico area. Most of the recent activity has occurred in the Delaware basin, Sheffield channel, and in the Val Verde basin area. Two important West Texas discoveries, both near the eastern mouth of the Delaware basin in Pecos County, have triggered a new era of deep search throughout the region. Mobil Oil Co.'s No. 1 Kathleen Moore was completed in the Pennsylvanian at 15,041 to 15,047 ft for a calculated open flow of 102 MMcf/D for the discovery of the Rojo Caballos pool. Shut-in bottom- hole pressure was reported to be 12,590 psi. About 20 miles southwest of the Mobil well, another strike was made in The Atlantic Refining Co. No. 1 Kelly, to inaugurate the Hershey pool. This well became the deepest producer in Texas when it potentialed a combined flow of 52 MMcf/D from the Fusselman, Devonian and Montoya between 15,800 and 16,680 ft. Another significant gas discovery was the triplycompleted Shell Oil Co. and Humble Oil and Refining Co. No. 1 Blackstone-Slaughter in the Yucca Butte area, five miles southeast of Sheffield. This well had a calculated absolute open flow of 5.6 MMcf/D from the Pennsylvanian detrital at 8,190 to 8,310 ft, 12 MMcf/D from the Connell at 9,993 to 10,012 ft and 16.5 MMcf/D from the Ellenburger at 10,050 to 10,092 ft. Gas-distillate ratios were 67,000:1 for the Pennsylvanian, 16,500:1 for the Connell and 22,600:1 for the Ellenburger. Other important deep gas pools in the area under consideration include the Vinagerone, Brown-Bassett, Puckett, Emperor, Reeves, Remuda, Azalea, Henshaw, Lancaster Hill, Baggett Ranch, Kermit, Cobblestone, Joe T., Custer, Midland Farms, Jack Herbert, Vacuum, Stiles, Gladiola, Scharb, King, Lusk, Denton, Lea, Mescalero and Coyanosa. JPT P. 841^

Generation of High-Velocity Projectiles

A technique of controlling the shape of detonation wave fronts in high explosives by inert wave control inserts was applied to generate discrete ultrahigh-velocity pellets. Tests to determine the most suitable pellet shape as well as the optimum charge configuration are described, and velocities up to 7600 m/sec were realized for 0.95-g aluminum pellets. The mechanism whereby pellets are accelerated by ``shaped'' waves is discussed, and the conclusion is reached that a simple model based upon the transmission of shock from the detonation wave to the pellet is not applicable.

Ionization in the Trail of High-Velocity Pellets

Aluminum, magnesium, and lithium-magnesium pellets were accelerated to velocities as high as 4.5 km/sec by means of an explosive. The ionization in the trails of these pellets was determined by measuring the reflection of a microwave signal from the trail. It was found that the ion density in the trail is an increasing function of the velocity and for the velocity range between 1 and 4.5 km/sec lies between 1010 and 1015 electrons per cm of path. It was observed that aluminum pellets do not produce ionization at velocities below approximately 2.9 km/sec, while magnesium leaves an ionized trail at velocities down to approximately 1.6 km/sec and lithium-magnesium alloy down to approximately 1.3 km/sec.

The utilization of europium 152-154 in a cervical carcinoma applicator.

In previous communications (1, 2), a specially designed tripartite applicator has been described for treatment of carcinoma of the cervix utilizing cobalt 60. The advantages of this applicator are: (a) ease of insertion; (b) fixed geometric relationships to facilitate calculation of gamma-ray dosage to the pelvis; (c) carefully evaluated relative intensities of various capsular sources to permit an optimum dose pattern in the pelvis; (d) selective relative diminution of radiation directed to the bladder and rectum. The chief disadvantage is the half-life of cobalt 60, namely 5.3 years, necessitating relatively frequent decay corrections and rather long treatment times after about two years. With this disadvantage in mind, the applicator has been modified to utilize europium 152-154, which has a half-life of 12.4 years (3). Basic Physical Concepts: Unlike cobalt 60, which in its decay emits gamma rays of only two energies—1.17 and 1.33 MEV—europium 152 and 154, which are always admixed, emit a complex array of about eleven gamma-ray energies, ranging from 0.040 to 1.40 MEV, with an “average” emission not too dissimilar from that of cobalt 60, when relatively small amounts of filtration are applied. Europium 152 and 154 are derived by neutron capture and gamma emission, from stable europium 151 and 153, the latter having high neutron capture cross sections. The sources utilized in the above applicator required irradiation for two weeks in a reactor at a flux density of about 1013 neutrons/cm. Vsecond. Very little europium 154 will be produced in such a short neutron irradiation. The radioactive strengths of the sources were expressed as equivalent amounts of cobalt 60, by direct gamma-ray comparison at 1 meter with a Lauritzen electroscope. The actual strength of the source could not be predicted with greater accuracy than ± 15 per cent. It is not proportional to the mass of Eu2O3 in the capsule, due presumably to the shielding of the inner parts of a pellet and the high cross section for neutron absorption of the various isotopes and their daughters. Source Design and Molding: Since europium for irradiation in the pile is available only as Eu2 O3 powder, which has first to be pelleted and sealed hermetically, the individual sources are pellets of Eu203 powder, admixed with aluminum. Aluminum pellets of appropriate size are used as inert separators, and all are enclosed in thin-walled aluminum capsules.4 Each source capsule, designed to have an active length of 1 ern. (Fig. 1), consisted of seven pellets of 2.38 mm. diameter and 1.43 mm. length, within a cylindrical aluminum can of 3.97 mm. overall diameter and 13.0 mm. length. After loading, the end of the aluminum cylinder was sealed by spinning.

Time-Resolved Spectroscopy of Ultraspeed Pellet Luminosity

Improved optical instrumentation has resulted in high time-resolution spectrograms of the luminosity associated with ultraspeed aluminum pellets. These data indicate that in many cases the light is emitted in two phases: (1) the ballistic, or air shock, characterized by atomic metal lines and a strong continuum; (2) AlO bands that appear about 150 μsec after the metal is ablated from the pellet.

Phenomena Associated with the Flight of Ultra-Speed Pellets. Part III. General Features of Luminosity

Ultra-speed pellets of the lighter metals such as aluminum and magnesium generate intensely luminous trails when fired through air. A pronounced characteristic of the luminous trails is the intermittent manner in which the light is emitted. This effect has also been observed in meteors and in studies of conventional shaped charges. Photographs indicate that flashing is caused by yawing of the pellet. The brilliant flashes of light are associated with the ablation and subsequent burning of material from the pellet. There is evidence that the material is removed from the pellet in the form of small droplets. The brightness, luminous output, and temperature of the trail generated by an aluminum pellet have been measured. The brightness is approximately 25,000 lamberts, the luminous output is 30,000 lumen-seconds, and the color temperature is 2900°K.

Phenomena Associated with the Flight of Ultra-Speed Pellets. Part II. Spectral Character of Luminosity

The spectroscopic character of the luminous trails generated by ultra-speed pellets has been investigated. A total of seven spectrograms have been measured and reduced. Three of these were of 5.0 km/sec aluminum pellets; two were of 5.9 km/sec magnesium pellets; one was of a 6.0 km/sec magnesium-lithium-aluminum pellet; and one was of a titanium pellet whose velocity was estimated at about 4.5 km/sec. The pronounced features of the spectrograms are: (1) AlO bands in the aluminum spectra, (2) Mg lines and MgO bands at the magnesium spectra, (3) strong Li lines and a pronounced continuum in the magnesium-lithium-aluminum spectra, and (4) TiO bands in the titanium spectra. Other features of the spectra are: (1) prominent AlI lines at λλ3944 and 3961 and a relatively weak continuum in the aluminum spectra, (2) a stronger continuum in the magnesium spectra, and (3) relatively weak MgO bands in the Mg-Li spectra. The time resolved spectra show that the AlO persists in the excited state twice as long as the aluminum. The aluminum oxidizes almost completely leaving AlO in an excited state which continues to emit light after the aluminum is burned.

Discussion of “on the origin of the Carolina Bays”

John S. Rinehart (U. S. Naval Ordnance Test Station, Inyokern, China Lake, California)—Prediction of the shape of the crater that will be excavated by an impacting meteorite is a more complex problem than Schriever has indicated. The well‐established meteorite craters are too few in number to provide a sound basis for generalization, particularly in view of the fact that there are scant data regarding the masses, velocities, or angles of impact of the meteorites that formed the craters.During the last few years considerable data that bear on meteorite impacts have been acquired through studies of the impact of high‐velocity missiles [RINEHART, 1950], More recently, the craters produced in rocklike material by 8,000 to 15,000 ft/sec missiles have been studied [RINEHART and WHITE, 1952]. These studies have demonstrated conclusively that the diameter of the meteorite crater can be many times the diameter of the meteorite. A half‐inch diameter steel pellet that strikes a plaster of Paris target at 8,000 ft/sec produces a crater whose diameter is roughly four inches or eight times that of the pellet. The area of the mouth of the crater seems to depend primarily upon the kinetic energy of the missile. A 15,000 ft/sec, 0.6‐gm aluminum pellet and a 8,000 ft/sec, 2‐gm steel pellet, which are equivalent energy‐wise, make about the same size openings.

Shapes of Craters Formed in Plaster of Paris by Ultra-Speed Pellets

Observations have been made on the craters produced in plaster of Paris targets by steel pellets that weighed 2 g and impacted at a velocity of 2.5 km/sec and by aluminum pellets that weighed 23 g and impacted at a velocity of 4.7 km/sec. The angle of impact was varied from normal incidence to 75°. For angles of incidence between 0° and 45°, the mouth of the crater was substantially circular. At 60°, it had roughly the shape of an arrowhead. At 75° obliquity, the pellet ricocheted and produced an elliptical crater. The area of the mouth of the crater in every case was many times the area of the impacting particle. The craters were characterized by a large bowl-shaped excavation from 12 in. to 1 in. in depth with a shaft that extended a few inches into the plaster and whose area was approximately that of the pellet. The volumes of the holes have been measured and related to the impacting energy and momenta of the respective pellets.