Patent GB-968843-A (GB)
Abstract: 968,843. Seismic surveying. SCHLUMBERGER WELL SURVEYING CORPORATION. Sept. 21, 1960 [Sept. 21, 1959], No. 32474/60. Heading H4D. In an acoustic-velocity well logging apparatus comprising, in the bore hole, an acoustic energy transmitter and at least one acoustic energy receiver and, at the surface, a recorder providing indications as a function of depth of the travel times of each of a succession of acoustic waves between the transmitter and receiver, or between two spaced receivers, the transmitter is actuated from the surface to emit acoustic pulses at regular intervals at successive depths and the output of the transmitter and the receiver(s) are converted to sharp electrical pulses by means of down-hole circuits to provide at the surface precise indications of the instants of transmission and reception for actuation of the recorder. The equipment in the bore hole comprises a cartridge 10 containing the transmitter T and receivers R1, R2, R3 (see also Fig. 2) together with an assembly 10 housing the other equipment shown in Fig. 2. The surface equipment is shown in Fig. 3. In operation (switch 14, Fig. 3, in log position) a switch 11, controlled by the cable circle 9 which carries the logging apparatus and also controls the movement of the record medium in recorder 12, operates via multivibrators 13 ... 17 to produce a fixed number of master pulses per foot of travel of the apparatus in the bore. These pulses which are sent down the bore hole on conductor 18, control the acoustic transmitter T (Fig. 2) via multivibrator 19 and pulser 20. The output of 19 also controls a multivibrator 22 operating a channel switch 25 (see also Fig. 4) which alternately directs the output of receiver R1 and of either R2 or R3 (depending on switch 62 controlled by span control 61, Fig. 3) through a gain controlled amplifier and thence via an anti-noise gate 27 (controlled by multivibrator 26 and the 120 Ás delayed output of 19) to a multivibrator 31, the output pulses of which define the interval #t (see Fig. 4) corresponding to the transmission time for acoustic waves between the two receivers considered. After amplification in 32 these pulses are sent to the surface via conductor 33 and there, after amplification in 39 (Fig. 3) are utilized via multivibrator 41, anti-noise gate 38, multivibrator 42 and time-to-amplitude converter 43 (detailed in Fig. 8, not shown) to produce a signal, for operating the record marking element, of amplitude proportional to the interval At, i.e. proportioned to the reciprocal of the velocity of the wave travel. For measuring the total travel time of acoustic waves over an extended distance in the bore, each output pulse from multivibrator 42 opens a gate 48 which connects a crystal oscillator 49 with a series of " flipflop " counting circuits 50, 51, the output of the last stage of which triggers, via a multivibrator 52, a duodecade glow tube 54 whilst the latter, via a multivibrator 63 triggers a decade glow tube 53. (Detailed in Fig. 9, not shown.) The outputs of the two glow tube circuits are jointly fed/to control a second recording element in recorder 55 so that in the resulting traces, the time scale of which is determined by the frequency of oscillator 49, every tenth trace is of enhanced strength. In this embodiment the time-to-amplitude converter 43 and the glow tube circuit 54 are controlled via span control 61 depending on which of the receivers R2 or R3 is operative. The apparatus may be tested, when the winch is not operating by switching into the circuit via switch 14 a test oscillator 56. For calibrating the apparatus switch 18<SP>1</SP> (Fig. 3) is opened and the absence of master pulses on conductor 18 allows a crystal controlled calibration oscillator 57 (Fig. 2), otherwise held inoperative by a control bias derived by rectification of the master pulses in 28, to function and inject pulses into the receiving systems to simulate the normal operation of the system. In a further calibration arrangement operation of switch 90 (Fig. 3) allows oscillator 49 to be utilized, the travel time gate 48, normally held open by the output of multivibrator 42, being held open by switching in a potential source 34. A modification of Fig. 3 which provides a measure of the total travel time even when the transmitter is not pulsed according to the distance travelled by the apparatus in the bore is described with reference to Fig. 12 (not shown) and an embodiment which utilizes the time of travel of acoustic waves between the transmitter and a single receiver is described with reference to Fig. 14 (not shown).