Method and Apparatus for Determining Acoustic Permeability Logs in Bore-Holes

摘要

1,176,350. Geophysical prospecting. INSTITUT FRANCAIS DU PETROLE DES CARBURANTS ET LUBRIFIANTS. 30 June, 1967 [1 July, 1966], No. 30366/67. Heading H4D. The permeability of a geological formation, i.e. the facility of the passage of fluids therethrough, is determined by taking the received signal in an acoustic well-logging device as it passes through the formation and plotting either the ratio of the values, for two of three consecutive half-cycles of the signal, of a parameter related to the peak amplitudes of the selected two half-cycles or the ratio of the values, for the half-cycle of maximum amplitude and an adjacent half-cycle, of a like parameter. In one apparatus the output of receiver R in the logging sonde, previously tested in an artificial standard bore-hole containing glass balls for distinguishing the unwanted "fore-runner" from a wanted received train such as D 12 , is fed via a threshold device 12 so as to eliminate background noise (and may be set after a trial run in the actual bore-hole through the geological formation of interest) to a switch 14 which is closed by half-cycle A 1 . Detection of the maximum amplitude h 2 of a successive halfcycle is effected by a coincidence circuit 15 and a circuit consisting of a differentiator 17, a multivibrator 19 and a further differentiator 21. Circuit 15 passes only the signal applied to its terminal 24 during a brief period corresponding to a pulse having the same polarity, e.g. 25; the output signals are directed to measuring means 25a, 26 which store amplitudes h 1 , h 2 which are applied to a divider 27 whose output is recorded in synchronism with the movement of the logging sonde through the bore-hole. In the embodiment the sonde starts from the bottom. In a modification the ratio h 3 /h 1 is recorded, Fig. 11 (not shown). The parameter proportional to peak amplitude of a half-cycle may be the slope of the tangent at the initial zero-crossing thereof: a signal D 35 is in this case obtained by differentiation of signal D 12 . Two emission frequencies, for measurements corresponding to different penetrations of the formation, may be employed: two transmitters and two receivers are utilized, Fig. 12 (not shown), the signals from the receivers being displayed on a cathode-ray tube which is photographed.