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Wire-line well-logging refers to the measurement of some physical characteristics of the underground formations traversed by a borehole. The corresponding equipment involves a bottom-hole sensing device which generates signals that are directly a function of the measured parameters, an insulated electric cable whereby these signals are transmitted to the surface, and an apparatus for the continuous recording of the measurements.
The parameters commonly recorded in oil wells are the following:
(1) Electrical resistivities, which can be obtained with the greatest accuracy and detail by means of induction log, laterolog, microlog and microlaterolog, depending on the cases. From the knowledge of electrical resistivity an estimation of porosity can be made.
(2) Spontaneous potentials, for the definition of permeable formations, and the estimation of interstitial water salinity.
(3) Natural radioactivity.
(4) Density (by gamma ray scattering).
(5) Porosity by means of neutron logging.
(6) Compressed sound wave velocity, either by steps over large intervals (several hundred feet), or continuously over short intervals (1-3 feet).
(8) Formation dips.
Other operations can be performed by means of equipment attached to the electrical cable: for example, sampling of formation and of the impregnating fluids from the wall of the hole. It seems offhand that all these operations could usefully be performed in the Mohole, at the level of the sedimentary rocks. In the igneous rocks and in the mantle, some of them could be omitted, because of unfavorable conditions. However, the recording of natural radioactivity, density, porosity, and some velocity would be highly desirable. It is also possible that the electric cable will be used to transmit the signal of other non-standard bottom-hole devices, which may be especially developed for the Mohole, such as a gravity meter, or an NMR magnetometer.
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