Method and apparatus to measure borehole pressure during blasting

Abstract

Pressure sensors and techniques are presented in which one or more piezoelectric discs are housed in a holder structure with a hole allowing exposure of the piezoelectric disc(s) to ambient pressure within a borehole, with wiring leads passing through the holder structure for conveying an electrical signal from the piezoelectric device to an external interface circuit or for conveying an electrical signal from an internal interface circuit to an external data acquisition system.

The following is claimed: 
     
         1 . A pressure sensing apparatus for measuring borehole pressure during blasting operations, comprising:
 a housing defining an interior cavity with at least one aperture extending from the interior cavity outside the housing;   at least one piezoelectric device within the interior cavity of the housing; and   a pair of wire leads electrically coupled with the piezoelectric device and extending from the interior cavity outside the housing.   
     
     
         2 . The pressure sensing apparatus of  claim 1 , wherein the at least one piezoelectric device at least partially faces the at least one aperture of the housing. 
     
     
         3 . The pressure sensing apparatus of  claim 1 , further comprising a filler material to protect against moisture penetration and/or to provide mechanical coupling to transfer a pressure wave to the at least one piezoelectric device. 
     
     
         4 . The pressure sensing apparatus of  claim 3 , wherein the filler material comprises silicone grease. 
     
     
         5 . The pressure sensing apparatus of  claim 1 , comprising a plurality of piezoelectric devices coupled with one another into a single circuit within the interior cavity of the housing. 
     
     
         6 . The pressure sensing apparatus of  claim 1 , comprising an interface circuit within the interior cavity of the housing, the interface circuit comprising:
 a rectifier with an input coupled with the at least one piezoelectric device and an output, and   at least one capacitor coupled with the output of the rectifier;   wherein the pair of wire leads is coupled with the output of the rectifier.   
     
     
         7 . The pressure sensing apparatus of  claim 6 , wherein the at least one capacitor has a capacitance value; wherein the at least one piezoelectric device has a longitudinal charge coefficient; and wherein the capacitance value is selected according to the longitudinal charge coefficient such that an output signal on the pair of wire leads of the pressure sensing apparatus for a rated pressure provides a maximum voltage output of about 3-5 V. 
     
     
         8 . The pressure sensing apparatus of  claim 1 , wherein the at least one piezoelectric device has a longitudinal charge coefficient of about 300 pC/N or more. 
     
     
         9 . The pressure sensing apparatus of  claim 8 , wherein the at least one piezoelectric device has a longitudinal charge coefficient of about 500 pC/N or more. 
     
     
         10 . The pressure sensing apparatus of  claim 1 , wherein the at least one piezoelectric device includes a ceramic perovskite material. 
     
     
         11 . The pressure sensing apparatus of  claim 10 , wherein the at least one piezoelectric device includes a lead zirconate titanate (PZT) material. 
     
     
         12 . The pressure sensing apparatus of claim one, wherein the at least one piezoelectric device is at least partially covered with a heat shrink material. 
     
     
         13 . A detonator for initiating a blasting operation, comprising:
 a housing defining an interior cavity;   at least one piezoelectric device within the interior cavity of the housing;   a first pair of wire leads for coupling to a blasting machine to activate the detonator; and   a second pair of wire leads electrically coupled with the piezoelectric device and extending from the interior cavity outside the housing.   
     
     
         14 . A booster assembly for facilitating a blasting operation, comprising:
 a booster housing; and   a pressure sensor for measuring borehole pressure during blasting operations, the pressure sensor comprising:
 a sensor housing mounted to the booster housing, the sensor housing defining an interior cavity with at least one aperture extending from the interior cavity outside the sensor housing, the at least one aperture facing at least partially away from the booster housing; 
 at least one piezoelectric device within the interior cavity of the sensor housing; and 
 a pair of wire leads electrically coupled with the piezoelectric device and extending from the interior cavity outside the sensor housing. 
   
     
     
         15 . A method of sensing pressure in a borehole during a blasting or seismic measurement operation, the method comprising:
 locating a pressure sensor apparatus within a borehole, the pressure sensor apparatus comprising:
 a housing defining an interior cavity with at least one aperture extending from the interior cavity outside the housing, 
 at least one piezoelectric device within the interior cavity of the housing, and 
 a pair of wire leads electrically coupled with the piezoelectric device and extending from the interior cavity outside the housing; 
   initiating a blasting operation;   measuring an electrical signal on the pair of wire leads contemporaneously with the blasting operation; and   determining a borehole pressure value at least partially according to the measured electrical signal.   
     
     
         16 . The method of  claim 15 , further comprising connecting the pair of wire leads to an interface circuit; measuring an electrical signal at the output of the interface circuit; and determining a borehole pressure value at least partially according to the electrical signal at the output of the interface circuit. 
     
     
         17 . The method of  claim 15 , further comprising locating the pressure sensor apparatus proximate to a detonator within the borehole. 
     
     
         18 . The method of  claim 15 , further comprising locating the pressure sensor apparatus proximate to a booster within the borehole. 
     
     
         19 . A pressure sensing apparatus for measuring borehole pressure during blasting operations, comprising:
 at least one piezoelectric device encapsulated inside a molded structure; and   a pair of wire leads electrically coupled with the piezoelectric device and protruding from the molded structure.   
     
     
         20 . The pressure sensing apparatus of  claim 19 , further comprising a metal shell at least partially surrounding the molded structure.