Acoustics – Geophysical or subsurface exploration – Seismic source and detector
Patent
1986-02-28
1987-06-23
Jordan, Charles T.
Acoustics
Geophysical or subsurface exploration
Seismic source and detector
181113, 181121, G01V 100
Patent
active
046745912
ABSTRACT:
Method and apparatus for downhole seismic exploration employing vibration emanating from a point deep in a well. An elastic steel column has an upper end extending above the top of the well. A reaction mass is attached vertically thereabove through a vertically mounted compression spring system, in parallel with it a vertically mounted servo-controlled hydraulic cylinder-piston assembly. The displacement of a spear or bit on the lower end of the column relative to earth develops a displacement signal. The piston in the hydraulic cylinder is under reciprocated servo control to apply vertical vibration to the upper end of the column and thereby to the spear, while developing an electrical, pressure-differential signal corresponding to the pressure across the cylinder-piston assembly. The vertical vibration is adjusted by feedback through the servo control in accordance with the displacement signal and the pressure differential signal, to seek and find an appropriate resonant frequency for the column in the range of 5 Hz to 250 Hz. The frequency is maintained at resonance to generate and transmit a downhole signal, which is detected at a location at a known distance from the spear so that the time differential between transmission and detection of the signal.
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Eldred John W.
Jordan Charles T.
URS Corporation
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