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US H1,308 HGranted
Narrow band acoustic source
AssigneeExxon Production Research Company
InventorsGraham A. Winbow, Sen T. Chen
Life of this patent
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Abstract
A seismic source for downhole use is disclosed which is formed by an outer tubular member having weighted ends which carries within a coaxially mounted tubularly shaped piezoelectric element. The piezoelectric element is cyclically driven to produce a standing wave having a frequency in the range of 0.25 to 5 kHz and a narrow bandwidth in the range of 5-50 Hz.
Claims16
An acoustic source comprising:
- a. a tubular member having a first end and a second end and a length L as measured between the first end and the second end;
- b. a tubularly shaped piezoelectric element having a generally cylindrical outer surface, said tubularly shaped piezoelectric element being located within the tubular member such that the generally cylindrical outer surface of the tubularly shaped piezoelectric element is in contact with an inner surface of the tubular member along an entire circumference of the generally cylindrical outer surface of the tubularly shaped piezoelectric element and said tubularly shaped piezoelectric element is securely fastened to the inner surface of the tubular member, said tubularly shaped piezoelectric element having a length L which is in the range of 0.05 L to 0.5 L;
- c. a means for electrically exciting the piezoelectric element operatively associated with said piezoelectric element;
- d. a first end mass fastened rigidly to the first end of the tubular member;
- and
- e. a second end mass fastened rigidly to a second end of the tubular member.
3 more elements
A method of generating an acoustic signal, said method comprising:
- a. positioning a tubular member in a fluid, said tubular member having a first end and a second end;
- b. cyclically exciting a standing extensional wave having a resonance frequency F.sub.R in the tubular member, the resonance frequency of the standing extensional wave being related to a length of the tubular member by the relation:
- L=v.sub.e /2F.sub.R
- where L is the length of the tubular member in feet, as measured between the first end and the second end, v.sub.e is a velocity of the standing extensional wave in the tubular member, v.sub.e being measured in feet per second, and F.sub.R is the resonance frequency in Hz;
- and
- c. emitting an acoustic signal from the tubular member.
3 more elements
A method of acquiring seismic data, said method comprising:
- a. positioning a tubular member in a first fluid-filled wellbore, said tubular member having a first end and a second end;
- b. driving a generally cylindrical outer surface of a tubularly shaped piezoelectric element against an inner surface of the tubular member, said generally cylindrical outer surface of the tubularly shaped piezoelectric element being securely fastened to an inner surface of the tubular member;
- c. exciting a standing wave in the tubular member, a first node of the standing wave being fixed by a first mass affixed to the first end of the tubular member and a second node of the standing wave being fixed by a second mass affixed to the second end of the tubular member, thereby emitting a high frequency, narrow band acoustic signal from the tubular member;
- d. reflecting said high frequency, narrow band acoustic signal off an interface in a body of rock surrounding the first fluid-filled wellbore;
- and
- e. receiving the high frequency, narrow band acoustic signal at a plurality of seismic receivers.
3 more elements
Dependencies are inferred from the claim text.