Method and apparatus for generating seismic waves
AssigneePetrophysical Services, Inc.
InventorsWilliam S. Kennedy, Stephen J. Blumenkranz
Life of this patent
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Abstract
A method and apparatus for generating a seismic wave in a borehole in the earth is disclosed. A portion of the borehole, which may be the bottom of the hole or any other point along its length, is selected as the site for seismic wave generation. A device is provided to oscillate the borehole fluid in a selected portion of the borehole to establish a resonant standing pressure wave of desired frequency within the fluid. The wave is maintained by continuing to supply energy to the fluid to replace losses due to fluid friction, structural losses and radiated acoustic energy. The standing wave thus created is radiated through the borehole wall into the earth and is eventually received by seismic detectors located on the surface.
Claims23
A method for creating seismic waves in the earth from a borehole comprising the steps of:
- (a) providing first and second end means in said borehole, said first and second end means being vertically spaced apart a preselected distance to define a borehole space therebetween;
- (b) providing a fluid in said borehole space;
- (c) exciting said fluid into oscillation within the borehole space between said first and second end means, said fluid being oscillated at a frequency sufficient to create and maintain a resonant standing pressure wave between said first and second end means;
- and
- (d) varying the resonant frequency of oscillation over a range of frequencies.
An apparatus for generating a seismic wave in a borehole containing a fluid comprising:
- (a) a pair of end means positioned in said borehole and separated from each other by a preselected vertical distance;
- (b) means communicating with the fluid in said borehole space between said end means for inducing oscillations in said fluid whereby the fluid within said space generates a resonant standing pressure wave;
- and
- (c) means for varying the resonant frequency of oscillation of said fluid over a range of frequencies.
An apparatus for use in a borehole containing fluid for generating a seismic wave in the earth, said apparatus comprising:
- (a) first and second end means positioned in said borehole and separated from each other by a predetermined vertical distance, said first and second end means each including a compressible gas filled bladder;
- (b) connecting means between said first and second end means and including a central portion;
- (c) means housed within said central portion for inducing oscillations in said fluid between said first and second end means, whereby the oscillations of said drilling fluid generate a resonant standing pressure wave;
- and
- (d) means for varying the resonant frequency of oscillation of said fluid over a range of frequencies.
An apparatus for generating a seismic wave in the earth from a borehole containing fluid, said apparatus comprising:
- (a) first non-compressible end means positioned in said borehole in fluid tight position;
- (b) second end means vertically spaced from said first end means in said borehole, said second end means including a compressible gas bladder facing said first end means;
- (c) means located in said first end means for exciting said borehole fluid into oscillation between said first and second end means at a frequency of oscillation sufficient to create and maintain a resonant standing pressure wave between said first and second end means;
- and
- (d) means for varying the resonant frequency of oscillation of said fluid over a range of frequencies.
Dependencies are inferred from the claim text.