Vibrator and processing systems for vibratory seismic operations

• US 4,064,481 A
• Filed: 09/29/1975
• Issued: 12/20/1977
• Est. Priority Date: 10/18/1973
• Status: Expired due to Term

• Current Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Original Assignee: Daniel Silverman
• Inventors: Silverman, Daniel
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/617,857
• Time in Patent Office: 813 Days
• Field of Search: 340/15.5 DP, 340/15.5 TA, 340/15.5 CC, 340/15.5 SC, 340/17 R, 235/181, 360/8, 360/32, 324/77 G, 181/119
• US Class Current: 367/190
• CPC Class Codes: G01V 1/04 Details
• CPC Class Codes: G01V 1/375 Correlating received seismic signals with the emitted source signal
• CPC Class Codes: G01V 2210/127 Cooperating multiple sources

Abstract

Method and apparatus for carrying out vibratory seismic operations and processing seismic records, involving generating a square wave analog sweep signal for driving a vibrator, generating a square wave analog, or 1 bit digitized transmitted signal, digitizing the received signal to 1 bit, and correlating the 1 bit digitized received signal with the 1 bit digitized transmitted signal, and stacking a plurality of such 1 bit correlograms. Simple logic means are disclosed for performing a 1 bit × 1 bit correlation. Means are disclosed for generating a square wave analog sweep signal.

Claims

1. Apparatus for seismic prospecting, comprising;

a. a force generating means reference sweep signal comprising a square wave analog signal having succeeding plus and minus zero crossings, of variable frequency, of selected band width, and of selected time duration;

b. a force generating means responsive to said square wave reference sweep signal to create a train of alternately reversing forces on the earth, creating an oscillatory displacement of the earth at a first point on the earth;

c. means responsive to a sensor means to generate an oscillatory analog electrical signal responsive to said oscillatory displacement of the earth at said first point, and to provide a transmitted signal digitized to 1 bit;

d. means to detect the seismic wave generated by said force generating means after passing through the earth, at a second point distant from said first point, and, means to produce a detected signal.

2. The system as in claim 1 including means to digitize said detected signal to 1 bit and means to digitize said reference sweep signal to 1 bit and means to correlate said 1 bit detected signal with the 1 bit reference sweep signal.

3. The system as in claim 1 in which said force generator means includes means to generate alternately reversing impulsive forces on the earth, having constant delay time relative to the zero crossing times of said square wave reference sweep signal, whereby there is no variation in time delay between said force generating means and said square wave reference signal, as the frequency of said reference signal changes.

4. The system as in claim 1 in which said vibrator is driven electromagnetically with the current sequentially direct and reversed, responsive to the square wave reference sweep.

5. The system as in claim 1 including means to drive said force generating means explosively, first in one direction and then the other, responsive to plus and minus zero crossings of said square wave reference sweep signal.

6. The system in claim 1 in which said sensor is an accelerometer on the baseplate, and including means to doubly integrate the output, means to low-pass filter the integrated output, and means to digitize to 1 bit the the output of said filter.

7. The system as in claim 1 in which said sensor comprises displacement sensor means across a compliance between a truck weighting means and the baseplate.

8. The system as in claim 1 including a plurality of vibrators each having means to generate different sweeps and including programmable delay means to start each one at a different time after receiving a coded start signal from the recording truck.

9. The system as in claim 1 including hydraulic vibrator means, and including square wave valve means responsive to said square wave reference sweep signal, whereby said valve will change rapidly from full open to full closed, and vice versa.

10. The apparatus as in claim 1 including means to transmit said square wave reference sweep signal to said vibrator by radio, said means comprising;

means to generate a radio frequency carrier signal, and means to gate said carrier signal off and on in synchronism with said square wave reference sweep signal.

11. A seismic prospecting system comprising;

a. means to generate an oscillatory time function of ground motion in the earth, responsive to a square wave reference signal, of a variable frequency, of selected frequency content and time duration, at a first point on the earth;

b. means to provide an electrical transmitted signal of said oscillatory time function of ground motion, and wherein said electrical transmitted signal varies in phase from said reference signal due to phase shift in said means to generate, and means to digitize said electrical transmitted signal to 1 bit;

c. means at a second point distant from said first point to detect said ground motion after transmission through the earth, and to produce a received signal, and means to digitize said received signal to 1 bit; and

d. means to correlate said 1 bit electrical transmitted signal with said 1 bit received signal.

12. The system as in claim 11 including a square wave reference sweep signal to drive said means to generate, and means to correlate said transmitted signal with said reference sweep signal.

13. An improved seismic system comprising;

a. a vibrator comprising two parts relatively reciprocable, one part attached to a reaction mass, and the other part attached to a base plate positioned on the earth;

b. a reference sweep signal comprising a square wave signal of variable frequency of selected frequency range and time duration;

c. means responsive to said square wave reference signal to drive said vibrator so as to impress alternately reversing forces on the earth at a first point on the earth;

d. means to detect the alternating displacement of said baseplate, and to provide a transmitted signal representative of the seismic wave generated in the earth; and

e. means to digitize said transmitted signal to 1 bit.

14. The seismic system as in claim 13 including means to drive said vibrator impulsively by said square wave reference signal.

15. Apparatus for seismic prospecting comprising;

a. a timing means to generate a train of time-spaced unidirectional electrical pulses of continually changing time interval between adjacent pulses;

b. means to invert alternate pulses to provide a train of alternately reversing electrical pulses;

c. force generating means responsive to said train of alternately reversing electrical pulses to apply to the earth a corresponding train of alternately reversing forces, at a first point on the earth; and

d. means to detect the seismic wave generated by said force generating means after passing through the earth, at a second point distant from said first point, and means to produce a detected seismic signal.

16. The system as in claim 15 including means responsive to said timing means to generate a square wave analog electrical signal, each half cycle synchronous with said successive alternately reversing electrical pulses.

17. The system as in claim 16 including means to digitize said detected seismic signal to form a 1 bit digitized received signal, means to digitize said square wave analog signal and including means to correlate said 1 bit digitized received signal and said 1 bit digitized square wave analog signal.

18. The system as in claim 16 including means to transmit said 1 bit digitized transmitted signal to said second point.

19. The system as in claim 18 including means to convert said transmitted signal to a square wave transmitted signal, and means to gate a carrier signal in conformity with said square wave transmitted signal.

20. The system as in claim 15 in which said timing means includes a clock, adder means that is augmented by a fixed number of clock pulses for each cycle of operation, and a preset counter means which is preset to the count of said adder means and counts to zero in accordance with the pulses of said clock.