IE39998B1 - Method and apparatus for investigating earth formations - Google Patents

Abstract

1484200 Well logging SCHLUMBERGER Ltd 22 Aug 1974 [23 Aug 1973(2)] 36878/74 Heading G1N Micro-wave well-logging apparatus has a transmitter and two receiving antennas spaced along the log-tool whereby the dielectric constant of the earth formations can be determined from measurements of the phase difference and attenuation between the two received signals. The antennas may be cavity-backed-slots Figs. 6, 7 (not shown). In a basic arrangement Fig. 1, the transmitting antenna T is fed by oscillator 45, and the received signals from R1, R2 are heterodyned by beat oscillator 49 which is connected in a phaselocked-loop 50, 51 with the transmitter 45. The phase difference of the "intermediate" frequency signals is determined by phase detector 53, and the attenuation is determined by amplitude comparator 54. A more sophisticated PULSED SYSTEM is shown in Fig. 9, with two transmitting antennas T 1 ', T 2 ' alternately energized through switch 247 driven by a squarewave M from generator 260. In this system the received intermediatefrequency signals are fed to detectors 271, 272, which produce spiked pulses III, IV Fig.11, every time the signals I, II cross zero, in a positive direction, as shown. The phase displacement of the spikes is measured by a sub-system 270. The spikes are fed to gates 273..276 operated in synchronism with the antenna switch by pulses M, M from 260. These gates determine the duration of setting and resetting flip-flop 277 whose output pluses V, Fig. 11, are integrated at 278. Similarly a subsystem 280 is M, M switched to differential amplifier 289 to measure the average attenuation. From the dielectric constant information about the porosity, saturation or lithology of the strata may be estimated. [GB1484200A]