System and method for determining the start time of a pressure pulse from a downhole explosive device

Abstract

A system and method for use in determining the start time of a pressure pulse created by a downhole explosive device detonated by a firing signal includes a downhole tool with a pressure pulse detector that detects the pressure pulse and generates an input signal in response thereto, and a circuit path configured to output a signaling pulse distinguishable from the firing signal. A surface unit receives and discriminates the signaling pulse from the firing signal, and outputs a start time signal in response to receiving the signaling pulse. Alternatively, the downhole tool includes a processor that measures and stores the time that the pressure pulse detector generates the input signal.

What is claimed is: 
     
         1 . A system for creating a start time signal in response to a pressure pulse created by a downhole explosive device detonated by a firing signal, the system comprising:
 (a) a downhole tool comprising:
 (i) a pressure pulse detector for detecting the pressure pulse and generating an input signal in response to detecting the pressure pulse; and 
 (ii) a circuit path operatively connected to the pressure pulse detector, and configured to output a signaling pulse having a signal parameter distinguishable from the signal parameter of the firing signal, in response to the input signal; and 
   (b) a surface unit comprising a circuit path operatively connected to the downhole tool circuit path, and configured to discriminate the signaling pulse from the firing signal, and to output the start time signal in response to receiving the signaling pulse.   
     
     
         2 . The system of  claim 1 , wherein the downhole tool is powered solely by a power source located at the surface. 
     
     
         3 . The system of  claim 1 , wherein the downhole tool circuit path is further configured to amplify the input signal. 
     
     
         4 . The system of  claim 1  wherein the downhole tool circuit path is further configured to discriminate the input signal from the firing signal by comparing a parameter of the input signal to a predetermined parameter associated with the firing signal, and to output the signaling pulse only if the input signal is discriminated from the predetermined parameter associated with the firing signal. 
     
     
         5 . The system of  claim 1  wherein the downhole tool circuit path is configured to output the signaling pulse with a greater voltage, a greater current, or both a greater voltage and a greater current than the firing signal. 
     
     
         6 . The system of  claim 1  wherein the surface unit circuit path is configured to discriminate the signaling pulse from the firing signal by comparing a parameter of the signaling pulse to a predetermined parameter associated with the firing signal. 
     
     
         7 . The system of  claim 1  wherein the surface unit circuit path is configured to analogically attenuate electrical noise associated with the firing signal that is transmitted with the signaling pulse and/or is configured to digitally extract the firing signal from the signaling pulse to output the start time signal. 
     
     
         8 . The system of  claim 1  wherein the downhole tool circuit path is operatively connected to the surface unit circuit path by a transmission path that also transmits the firing signal to the downhole explosive device. 
     
     
         9 . A method for creating a start time signal in response to a pressure pulse created by a downhole explosive device detonated by a firing signal, the method comprising the steps of:
 (a) using a downhole tool for:
 (i) detecting the pressure pulse and generating an input signal in response to detecting the pressure pulse; 
 (ii) in response to detecting the pressure pulse, generating a signaling pulse distinguishable from the firing signal; 
   (b) using a surface unit for:
 (i) receiving the signaling pulse; 
 (ii) discriminating between the signaling pulse and the firing signal; and 
 (iii) in response to receiving the signaling pulse, outputting the start time signal. 
   
     
     
         10 . The method of  claim 9 , wherein the downhole tool is powered solely by a power source located at the surface. 
     
     
         11 . The method of  claim 9  wherein the downhole tool is further used for amplifying the input signal. 
     
     
         12 . The method of  claim 9  wherein the downhole tool is further used for discriminating the input signal from the firing signal by comparing a parameter of the input signal to a predetermined parameter associated with the firing signal, and wherein generating the signaling pulse is conditional on the input signal being discriminated from the firing signal. 
     
     
         13 . The method of  claim 9  wherein the signaling pulse is distinguishable from the firing pulse by a greater voltage, a greater current, or both a greater voltage and a greater current than does the firing signal. 
     
     
         14 . The method of  claim 9  wherein the surface unit discriminates the signaling pulse from the firing signal by comparing a parameter of the signaling pulse to a predetermined parameter associated with the firing signal. 
     
     
         15 . The method of  claim 9  further comprising, before receiving the signaling pulse at the surface unit, the step of analogically attenuating electrical noise associated with the firing signal that is transmitted with the signaling pulse to the surface unit and/or the step of digitally extracting the firing signal from the signaling pulse to output the start time signal. 
     
     
         16 . The method of  claim 9  wherein the surface unit receives the signaling pulse in a transmission path that also transmits the firing signal to the downhole explosive device. 
     
     
         17 . A downhole tool for creating a signaling pulse in response to a pressure pulse created by a downhole explosive device detonated by a firing signal, the downhole tool comprising:
 (a) a pressure pulse detector for detecting the pressure pulse and generating an input signal in response to detecting the pressure pulse; and   (b) a circuit path operatively connected to the pressure pulse detector, and configured to output a output the signaling pulse distinguishable from the firing signal, in response to the input signal.   
     
     
         18 . The downhole tool of  claim 17  wherein the downhole tool is powered solely by a power source located at the surface and used to create the firing signal. 
     
     
         19 . A downhole tool for determining the time of a pressure pulse created by a downhole explosive device detonated by a firing signal, the downhole tool comprising:
 (a) a pressure pulse detector for detecting the pressure pulse and generating an input signal in response to detecting the pressure pulse; and   (b) a processor operatively connected to the pressure pulse detector by a circuit path, the processor comprising an internal clock and a memory component storing a set of instructions executable by the processor to determine a time at which the processor receives the input signal, and store the time in the memory component.   
     
     
         20 . The downhole tool of  claim 19  wherein the set of instructions is executable by the processor to further store the input signal in the memory component in association with the time.