Claims
- 1. In a system for generating seismic waves in a bore hole in an earth formation, said hole containing drilling fluid, a downhole apparatus comprising a generally cylindrical body having a lower end and an upper portion and having an outer wall, the diameter of said body being less than the diameter of said bore hole, said diameters defining a first annulus comprising a fixed volume of drilling fluid surrounding said body, means on said body for acoustically isolating a portion of said annulus from the remainder of the fluid in said bore hole without deforming said earth formation, a liquid-filled cavity within said body, said cavity having an acoustically transparent window through said outer wall into said portion of said annulus, means within said cavity for generating acoustic waves in said liquid in said cavity which are transmitted from said cavity in a direction through said window to said portion of said annulus and then into said formation, said means for generating acoustic waves comprising a hydraulically operated piston reciprocally mounted in said body and exposed to liquid in said cavity, said piston having a shaft, said shaft having two ends, one of said ends having a head and being a head end and the other of said ends being a shaft end, means for hydraulically operating said piston which comprises a pump producing pressurized hydraulic fluid, and a servo valve connected by an output line to said pump for applying high hydraulic pressure at low flow to said shaft end of said piston.
- 2. The apparatus in claim 1 wherein the distance between said packers in one half the wavelength of said acoustic waves in said fluid in said portion of said annulus.
- 3. The apparatus in claim 2 wherein said distance is from 3.75 to 7.50 meters.
- 4. The apparatus in claim 1 wherein said shaft end is of small cross-section relative to said head end such that the high pressure, low flow output of said servo valve when applied to said shaft end generates a lower pressure, high flow output in said cavity by displacement of said head end.
- 5. The apparatus in claim 4 wherein said body further comprises an equalizing piston and a gas cavity, said gas cavity being disposed between said piston head end and said equalizing piston.
- 6. The apparatus in claim 4 wherein said liquid-filled cavity comprises an area defined: (a) by a support for mounting said servo valve; (b) a base with a central opening allowing passage therethrough of said piston shaft, the ends of said cavity being defined by said support and said base; (c) a nut disposed below said opening in said base defining a second annulus around said piston shaft; (d) said head end of said piston and (e) said window.
- 7. In a system for generating seismic waves in a bore hole in an earth formation, said hole containing a drilling fluid, a downhole apparatus comprising a generally cylindrical body having a lower end and an upper portion and having an outer wall, the diameter of said body being less than the diameter of said bore hole, said diameters defining a first annulus comprising a fixed volume of drilling fluid surrounding said body, means on said body for acoustically isolating a portion of said annulus from the remainder of said fluid in said bore hole without deforming said earth formation, a liquid-filled cavity within said body, said cavity having an acoustically transparent window through said outer wall into said portion of said annulus, and means within said cavity for generating acoustic waves in said liquid in said cavity which are transmitted from said cavity in a direction through said window to said portion of said annulus and thence into said formation, said means for generating acoustic waves comprising a hydraulically operated piston reciprocally mounted in said body and exposed to said liquid in said cavity, said piston having a shaft end and a head end, and biasing means for said piston located at said lower end of said body comprising an equalizing piston and a gas cavity, said gas cavity being disposed between said piston head end and said equalizing piston.
- 8. The apparatus in claim 7 wherein said means for acoustically isolating said portion of said annulus comprises expandable packers spaced along said body.
- 9. The apparatus in claim 7 which further comprises means for hydraulically operating said piston which comprises a pump producing pressurized hydraulic fluid and a servo valve connected by an output line to said pump applying high hydraulic pressure at low flow to said shaft end of said piston.
- 10. The apparatus in claim 7 wherein said shaft end of said piston is of small cross-section relative to said head end such that the high pressure, low flow output of said servo valve when applied to said shaft end generates a lower pressure, high flow output in said cavity by displacement of said head end.
- 11. The apparatus in claim 7 wherein said liquid-filled cavity comprises an area defined: (a) by a support for mounting said servo valve; (b) a base with a central opening allowing passage therethrough of said piston shaft, the ends of said cavity being defined by said support and said base; (c) a nut disposed below said opening in said base defining a second annulus around said piston shaft; (d) said head end of said piston and (e) said window.
DESCRIPTION
This is a continuation of application Ser. No. 537,200, filed Sept. 29, 1983.
US Referenced Citations (13)
Foreign Referenced Citations (1)
Number |
Date |
Country |
2376422 |
Sep 1978 |
FRX |
Continuations (1)
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Number |
Date |
Country |
Parent |
537200 |
Sep 1983 |
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