GB1231752A - - Google Patents

Abstract

1,231,752. Borehole logging; piezoelectric transducers. CORE LABORATORIES Inc. 17 Jan., 1969 [22 Jan., 1968], No. 2948/69. Headings H4D and H4J. Apparatus for logging the lithology of underground formations being traversed by the drill bit of a rotary drilling rig comprises a vibration pick-up transducer 24 fastened to a part of the drilling rig, circuits 46, 48, 50, 52 for amplifying the transducer output signals, attenuating signals of frequency below a predetermined cutoff frequency, and rectifying and integrating the remaining signals, and an indicator 54 for presenting the integrated signals in visible form. Transducer 24 is a quartz or tourmaline crystal or a wafer of barium titanate or lead zirconium titanate and may be mounted, on the swivel which rotatably supports the drill-pipe string, by a direct resin bond or, as shown, by a detachable mount. This mount comprises a plate 36 welded or otherwise bonded to the swivel, a housing 34 bolted to plate 36, and a resilient seal 44. Transducer wafer 32 has a fixed electrode 40 integral with or brazed to plate 36, and a spring electrode 42. Filter 48 blocks low frequency spurious signals due to vibrations of surface equipment, pulsations in the drilling mud flow and rubbing of the pipe string against the borehole walls, and passes higher frequency signals generated by the drill bit cutting action; it has a low cutoff frequency of 10 to 30 kHz and also may have an upper cut off frequency of 40 to 130 kHz. Indicator 54 may be an oscilloscope or strip-chart recorder which registers on a time or depth scale.