| 摘要 |
1285985 Acoustic measurement of rock characteristics SOC NATIONALE DES PETROLES D'AQUITAINE 27 Oct 1969 [11 Dec 1968 30 Dec 1968 27 Feb 1969] 52545/69 Heading H4D [Also in Division G1] The characteristics of rock are measured during drilling as a function of the drilling depth by sensing vibrations of the drilling gear, clipping the electric signal thereby obtained to limit its voltage to between two predetermined values, passing the resulting signal through a band pass filter centred on a frequency equal to the frequency of rotation of the tool times the number of attacking elements on the tool, measuring the amplitude of the resulting signal and recording it on a chart driven in accordance with the drilling depth. Longitudinal and/or torsional vibrations may be sensed. As shown in Fig. 2, a sleeve 21 for connection in the drilling chain between the driving rod (9, Fig. 1, not shown) and the sludge injection head (7) carries two quartz accelerometers 31, 36 mounted diametrically opposite and axially offset as shown to respond to longitudinal vibrations. The accelerometers are connected via F.E.T.s 32, 37, slip rings 25 and brushes 27 to the clipping and filtering circuits (15). In a modification (Fig. 3, not shown) longitudinal vibrations are sensed by strain guages (47, 48) connected in a bridge circuit with compensating strain gauges (49, 50). Accelerometers or strain gauges may be mounted in recesses at the lower end of the driving rod (9). As shown in Fig. 8, strain gauges 123, 124 and accelerometers 125, 126, 127 are mounted on a sleeve at the bottom of the drill chain near the tool. Sludge pumped down the centre of the drill chain drives a turbine 135 to supply electricity to the clipping and filtering circuit 119, the output of which is arranged to operate a valve 117 to transmit pressure pulses through the sludge to a pressure detector (104, Fig. 7, not shown) and radio transmitter (114) at the top of the borehole. Accelerometer 127 senses the frequency of rotation of the drill and may be used to control the centre frequency of the band pass filter (Figs. 9, 10, not shown). Strain gauges 123, 124 enable longitudinal or torsional vibrations to be selected for measurement. Circuit details.-The voltage clipping circuit (Fig. 4, not shown) comprises a differential amplifier (56) having a diode connected across its input terminals, and a feedback circuit including pairs of oppositely poled, parallel connected diodes and a R.C. circuit for alternating high frequencies. An amplifier, band-pass filter and rectifier circuit are described with reference to Fig. 5 (not shown). The rate of drilling may be automatically controlled in dependence on the measured characteristics of the rock. |
