US 4,147,228 A · Methods and apparatus for the generation and transmission of seismic signals

Abstract

Methods and apparatus for generating and transmitting seismic signals for the purpose of seismic exploration are disclosed. The signals are force pulses shaped to have a spectrum constrained to the range of frequencies which are necessary for penetration to desired depths within the earth and for resolution of the geological reflection surfaces therein. These pulses are provided in a non-repetitive or aperiodic train, constructed to produce a transmitted energy spectrum whose mean energy extends smoothly at a substantially constant level over the spectrum frequency range, notwithstanding that the repetition frequency of the pulses may be swept over a frequency band much narrower than the spectrum range. The transmitted spectrum can exhibit an auto-correlation function having a major lobe which is predominant over any side lobes, corresponding to a desired level of resolution of the geological reflection surfaces.

Claims37

Dependent claims

The method of generating a seismic transmission having an energy spectrum extending over a frequency range for use in a seismic exploration system, comprising the steps of

(a) generating a plurality of sequences of pulses which are transmitted, which pulses are swept monotonically in repetition frequency, each sequence having a different lower pulse repetition frequency and a different upper pulse repetition frequency, said repetition frequencies falling within said frequency range, each of said pulses in any one of said sequences having a useful energy spectrum which extends beyond the highest repetition frequency of the sequence in which it is contained, and
(b) controlling the variation of the energy and timing of said pulses within any one of said sequences, and with respect to all of said sequences, such that the mean variation in the energy spectrum level over said frequency range is minimized for said transmission of all said sequences.

Seismic signal generation apparatus for producing in a receiving medium a transmission consisting of a sequence of pulses, said sequence being useful in a correlation process for high resolution seismic exploration, said apparatus comprising

a housing
a hammer mounted for reciprocation in said housing for oscillation over a trajectory away from and toward an impact position,
means for receiving impacts from said hammer and for applying controlled force pulses to said receiving medium, said means including an impact spring for controlling the spectrum of individual ones of said pulses,
said housing and hammer defining cavities for pressurized hydraulic fluid which is applied to said hammer for displacing said hammer over said trajectory,
valve means in communication with at least one of said cavities for switching the pressure of the hydraulic fluid applied to the hammer, and
control means for said valve means to time said sequence of pulses such that the autocorrelation function of said transmission exhibits low side lobes.

3 more elements

Dependencies are inferred from the claim text.

Methods and apparatus for the generation and transmission of seismic signals

Life of this patent

Methods and apparatus for the generation and transmission of seismic signals

Life of this patent

Abstract

Claims37