Repetitive low energy seismic source system controlled by digital timing means

Claim 1

A repetitive seismic source system comprising: a. an elongated pipe adapted for support within a borehole penetrating an earth formation at least partially filled with liquid: b. an elongated enlarged firing chamber attached, at one end, to a remote end of said pipe within said borehole and open at the other end so as to contact said liquid in said borehole and to form an impact surface for said chamber; c. lateral offset means connected to a near uphole end of said pipe; d. means connected to lateral offset means for delivering to said chamber through said lateral offset means and said pipe, a combustible gas mixture of a predetermined amount; e. ignitor means mounted in said offset tube means; f. means electrically connected with said ignitor means for energizing said ignitor means to initiate combustion of said mixture whereupon a combustion wave travels through said pipe through said firing chamber and strikes said impact surface to said liquid to generate a seismic disturbance; g. length/diameter ratio of said pipe being within a range to support said wave at supersonic speed; h. said firing chamber having a tapered end section connected to said pipe to re-establish said combustion wave therein after emergence from said pipe; i. time break indicating means attached to said firing chamber to indicate the occurrence of the passing of said combustion wave relative to said chamber; j. additional digital data responsive control means connected to parallel with said delivery means and said energization means connected to a time code generating means remotely positioned to said additional digital data responsive control means, for generating, in sequence, in accordance with a digital time source code, control signals for sequentially (1) controlling said delivery means to cause delivery to said elongated pipe and said elongated enlarged firing chamber of said predetermined amount of gas, and (2) actuating said energization means so as to energize said ignitor means, said digital source code constituting digital signals representative of multi-bit digital data timing words and a plurality of clock pulses, said remotely positioned time code generating means including gate means responses to said time break indicaTor means whereby said gate means is held in the enabled state for a predetermined duration to ensure detection of all significant seismic reflection signals after generation of said seismic disturbance, said additional digital data responsive control means including time decoding means for decoding said digital source code, first relay means electrically connected to said time decoding means and operative thereby to control said delivery means, so as to cause delivery along said elongated pipe and said firing chamber of said predetermined amount of said gas mixture, second relay means electrically connected to said decoding means and operated to control and cause actuation of said energization means in accordance with the occurrence of an operational coded event, said time decoding means of said additional digital data control means including: k. control means comprising start/stop/restart signal generating means and switch network means controllably connected thereto, said control means capable of generating digital signals for initiating, stopping and restarting delivery of gas and energization thereof within said system in accordance with the status of said switch network means; l. timing counter means connected to control means (k) and, including additional switch network means, said timing counter means accumulating clock pulses from a source of said pulses to provide a plurality of digital signals in accordance with switch conditions of said additional switch network means; m. control signal generating means including gate means selectively responsive to digital signals from control means (k) and timing counter means (l) as well as digital signals indicative of a multi-bit digital data timing word passing through control means (k) for generating at least first and second groups of control signals in which said first group sequentially controls said first and second relay means and hence the occurrence and duration of delivery as well as ignition of said gas within said pipe and chamber; n. cyclic record counting means including yet additional switch network means and gate and counter means responsive to digital signals from control means (k) which indicate each shooting cycle and compare the indicated cycle to an encoded ending cycle value in accordance with conditions of said yet additional switch network means, said record counting means also including a digital signal generating means responsive to digital signals from said gate and counter means thereof as well as to said second group of control means generated by control signal generating means (m) to provide a cycle reinitiation digital signal; o. reset logic means including a series of gate means responsive to at least said cycle re-initiation digital signal from record counting means (n) to provide a series of set and reset digital signals for circuitry (k)-(n) for setting said (k)-(n) circuitry to preselected initial conditions whereby the seismic shooting cycle can be automatically repeated without interruption until said ending cycle value encoded in record counting means (n) is attained.