GB497329A - Single cable electrical well-logging - Google Patents

Abstract

497,329. Prospecting for minerals &c. STANDARD OIL DEVELOPMENT CO. June 14, 1937, No. 16429. Convention date, June 25, 1936. [Class 37] Apparatus for deter. mining the electrical characteristics of earth strata traversed by a borehole, comprises means for lowering at least one of a pair of electrodes which are fed by alternating - current, the impedance of the circuit and the natural earth potential existing between the electrodes being measured independently and substantially simultaneously. One electrode may be suspended in the borehole by a single cable conductor and the other electrode located at surface level, or both electrodes of the cable can be spaced within the borehole. The generator 33 supplies electrodes 6, 12 and the impedance is measured on instrument 34, a high resistance instrument 32 for measuring the natural earth potentials being also connected to the electrodes but electrically separated from the supply circuit by a filter 31. If the velocity of the electrode or electrodes down the well is high, the indications of natural earth potentials correspond to a generated alternating-current, and the frequency of the impedance measuring circuit is made several times higher than this, the device 31 then being substituted by a high-pass filter. The measurements may also be made by alternately switching over the instruments that respond to each component. U.S.A. Specification 2,037,306 is referred to.