Based on the data reported in this paper, it is evident that the zinc salts of acrylic acid and methacrylic acid are effective coagents for the peroxide curing of EPDM and NBR. They appear to be unique among coagents in their ability to maintain high elongation while increasing the hardness and tensile properties of these elastomers. Zinc diacrylate was found to be the most effective in providing high hardness and high tensile properties. Zinc dimethacrylate gave a slightly better balance of properties by providing the highest elongation for a given hardness or modulus value.
A new dual-spacing neutron tool developed for porosity determination and gas detection in open or cased boreholes is combinable with various other logging tools. Simultaneous recording saves rig time, and an overlay log presentation facilitates wellsite interpretation. presentation facilitates wellsite interpretation. Introduction A two-detector neutron tool has been developed to determine porosity in open and cased boreholes. The response of the tool is determined by the rate at which the thermal neutron population decreases with distance from the source. This rate of decrease is principally determined by the porosity of the formation. The quantity measured is the ratio of counting rate from the near-spaced detector to that from the far-spaced detector. The surface control panel converts this ratio to a porosity index, which is then displayed on a linear scale. Individual counting rates, count-rate ratio, and porosity index may also be recorded on magnetic tape for subsequent machine computation. The dual-spacing measurement provides compensation for the effects of hole conditions - salinity, temperature, mud type, and mud cake. The residual effects are generally small. The log has therefore been named the compensated neutron log (CNL*). The porosity uncertainty caused by statistical variations is diminished through the use of a high-yield chemical neutron source. A unique feature of the tool is that it may be run in combination with other logging tools such as the formation density, thermal decay time. sonic, and induction-spherically focused logs. Such combinations make possible overlay presentations for wellsite interpretation, and offer the advantages of reduced rig time and positive depth matching. Dual-Spacing Neutron Detection Principle Principle Fast neutrons from a point source radiate into an infinite homogeneous medium and are slowed down by repeated collisions until they are in thermal equilibrium with the atoms of the medium. The thermal neutrons continue to diffuse, but, on the average, suffer no further energy loss. Eventually they experience absorbing collisions (capture collisions) and disappear from the system. In the process of slowing down, the neutron "cloud" spreads out spatially. The width of this spatial distribution is frequently characterized by a single property, called the slowing-down length. This is a measure of the size of the cloud of neutrons of a particular energy. It is proportional to the mean particular energy. It is proportional to the mean distance that neutrons travel from the source in slowing down to that energy. An alternative theoretical model emphasizes the so-called group-diffusion theory. In this case, one treats all the neutrons in the medium (usually down to some preassigned energy) as if they had the average energy of the group. This approach, also, leads to the definition of a characteristic parameter, the diffusion length, which is a measure of the width of the spatial distribution of the neutrons in the group. P. 1073
A sidewall epithermal neutron tool has been developed to substantially reduce environmental effects that have previously complicated neutron log interpretation. Designed for operation in uncased wells, the device provides increased accuracy in both liquid-filled and empty holes. A brief discussion of neutron moderation, diffusion and capture shows that logs using epithermal neutron detection depend on a smaller number of formation-characterizing parameters than those using thermal neutron or capture gamma ray detection. Thus, they come closer to providing an unambiguous determination of hydrogen content. In this new device a directionally sensitive epithermal neutron detection system has been incorporated in a sidewall source-detector skid to minimize borehole effects. The effects of variations in borehole size and shape, mud type, temperature and salinity are greatly reduced. Small residual borehole effects are then computationally accounted for in the surface control panel to provide a borehole-corrected neutron log. The log presents a direct recording of neutron-derived porosity on a linear scale. With corrections for bore hole effects already applied, this direct recording of porosity simplifies log interpretation. Furthermore, comparison with a linear porosity presentation of a formation density log permits sandstones, limestones and dolomites to be readily identified. Thus, in complex or variable lithology, porosity is determined with greater accuracy and reliability that heretofore. Laboratory data and field results demonstrate the improvements in neutron logging afforded by this new sidewall epithermal neutron logging device. Introduction The new Sidewall Neutron Porosity (SNP) logging system, designed for use in uncased wells, provides reliability and accuracy never before achieved with neutron logs. The effects of variations in borehole diameter and shape, fluid salinity, mud weight and temperature parameters that have long complicated neutron log interpretationare suppressed or corrected for by this sidewall epithermal neutron detection system. Furthermore, to simplify interpretation the SNP log presents a direct recording of Computed porosity on a linear scale. The performance improvements achieved by this new system arise primarily from the combination of two important design features. First, though not unique to this new tool, an epithermal neutron detection system is used, Epithermal neutron detection substantially reduces the perturbing influences of the thermal neutron absorption properties of rock matrices and water salinity. Second, the neutron detection system is mounted in a directionally sensitive sidewall skid to greatly minimize borehole effects. The purpose of this paper is to explain briefly the advantages offered by the detection of epithermal neutrons, to describe the SNP equipment and the log, to present calibration and correction data and to give examples of interpretation methods made especially convenient by this new system. ADVANTAGES OF EPITHERMAL NEUTRON DETECTION Epithermal neutron detection, of all the neutron methods in current commercial use, provides the simplest determination of formation hydrogen content. Advantages of epithermal neutron detectors, as compared with thermal neutron and gamma ray detectors, are probably best explained by a brief review of the life of a source-emitted neutron. A fast neutron from the source will eventually be captured by the nucleus of an atom. However, before capture is likely to occur, the fast neutron (energy of 100,000 electron volts (ev) or more) will be slowed down until it is in thermal equilibrium with its surroundings. The neutron is then considered to be a "thermal" neutron (average energy of 0.025 ev at 25C). The overwhelming majority of the slowing down thus occurs in reaching epithermal energies (energies just above thermal 0.5 to several ev). After reaching thermal energy, the neutron will "diffuse" through the formation with, on the average, no further energy change until capture. Upon the capture of the thermal neutron, relatively high energy gamma rays are usually emitted. Hydrogen plays a very important role in the process of slowing down fast neutrons. On the other hand, the absorption effects of water salinity and low concentrations of other strong thermal neutron absorbers relatively unimportant in the moderation process are very important in thermal diffusion, capture and the production of gamma rays. Thus, by detecting only epithermal neutrons with the SNP, spurious effects due to these thermal neutron absorbers are greatly minimized as compared to the effects on tools using thermal neutron or gamma ray detectors. The epithermal neutron detection system affords another important advantage. JPT P. 1351ˆ
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