Abstract:
The invention relates to an apparatus and method for imparting a precise amount of impulse energy to be delivered to the ground. The apparatus includes an anvil for operative deployment against the earth a hammer operatively connected to the anvil for striking the anvil; and a control system operatively connected to the hammer for controlling the impulse energy of the hammer striking the anvil. The control system includes a linear feedback system for measuring the linear position of the hammer with respect to the anvil during a force stroke and a processor for receiving linear position data from the linear feedback system for controlling the relative speed of the hammer with respect to the anvil during a force stroke through an actuation system.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to an apparatus and method for imparting a precise amount of impulse energy to be delivered to the ground.  
         [0002]     BACKGROUND OF THE INVENTION  
         [0003]     In the oil exploration industry, seismic data is obtained to enable scientists and engineers to develop a picture of underlying rock formations. The reflection seismic method attempts to image the top few kilometres of the earth&#39;s crust by artificially creating a wavefield at the earth&#39;s surface and then recording this wavefield at multiple locations as it returns to the surface via reflections from the rock layers of the earth&#39;s crust. These wavefields are then processed in order to obtain images of the subsurface that can be used to help locate hydrocarbons or other minerals. In order to obtain this data, a wavefield is created at the surface at a source location by setting off a percussive shock wave that imparts wave energy into the ground. The source is typically an explosive charge, Vibrator sinusoidal wave or a mechanical impulse system. A Vibrator creates a sinusoidal signal of changing frequency through shaking the earth, whereas an impulse or explosive source creates a single multiple frequency shock wave that travels into the earth.  
         [0004]     A series of receivers (geophones) located at previously surveyed points are set up to record the amplitude of wave energy reflected to each receiver point from underlying formations as a function of time, thus creating an array of time/amplitude data sets from each geophone array.  
         [0005]     As noted, shock waves can be imparted to the ground by either explosive or mechanical systems. While explosive systems can generate shock waves of a greater magnitude, there are many disadvantages in using explosives both in terms of regulations and efficiency. Thus, mechanical impulse systems are desirable due to: low deployment cost, high resolution data created by a greater number of source locations, increased safety and low environmental impact.  
         [0006]     In the past, however, mechanical shock wave generators have been disadvantaged in that the amount of impulse energy imparted to the ground cannot be accurately controlled thus leading to increased error margins in the interpretation of the collected seismic data. Thus, there has been a need for a mechanical impulse system that is capable of precisely controlling the amount of impulse energy for a given source location.  
         [0007]     A review of the prior art reveals that a system that enables a precise amount of energy to be delivered to the ground has not yet been deployed.  
         [0008]     For example, U.S. Pat. No. 4,271,923, U.S. Pat. No. 4,402,381 U.S. Pat. No. 3,905,446, U.S. Pat. No. 4,118,994 and U.S. Pat. 4,316,521 describe hammer/anvil pulse generator systems. However, none of these patents describe the use of a hydraulic actuation and control systems that provides linear velocity and position feedback to ensure that a repeatable output of energy is delivered to the earth.  
         [0009]     U.S. Pat. Nos. 4,341,282, 4,011,923, 4,114,722, 4,135,598, 4,116,300, 5,666,328, 6,065,562 and U.S. Pat. No. 4,492,285 each describe pulse generator that utilizing a vibrating energy source, U.S. Pat. No. 4,108,271 describes a pulse generator that releases pressurize gas to impart energy to the ground that does not utilize a hydraulic actuation and control system that provides linear velocity and position feedback to ensure that a repeatable output of energy is delivered to the earth. U.S. Pat. No. 3,557,900 describes a pulse generator that utilizes a chemical combustion process.  
       SUMMARY OF THE INVENTION  
       [0010]     In accordance with the invention, there is provided a system for imparting a mechanical impulse to the earth comprising: 
        an anvil for operative deployment against the earth;     a hammer operatively connected to the anvil for striking the anvil;     a control system operatively connected to the hammer for controlling the impulse energy of the hammer striking the anvil, the control system including a linear feedback system for measuring the linear position of the hammer with respect to the anvil during a force stroke, a processor for receiving linear position data from the linear feedback system and for controlling the relative speed of the hammer with respect to the anvil during a force stroke through an actuation system.        
 
         [0014]     In accordance with a further embodiment of the invention, the control system includes: 
        a hydraulic actuator operatively connected to the hammer, the hydraulic actuator having a retract side and a pressure side;     a hydraulic reservoir and hydraulic pump operatively connected to the retract side of the hydraulic actuator, the hydraulic pump for pumping hydraulic fluid from the hydraulic reservoir to the hydraulic actuator;     a hydraulic accumulator operatively connected to the pressure side of the hydraulic actuator, the hydraulic accumulator having a pressure system for storing hydraulic energy on the pressure side of the hydraulic actuator; and,     a linear transducer operatively connected to the hammer for measuring the linear position of the hammer with respect to the anvil;     wherein the actuation system is operatively connected between the hydraulic pump and the retract side of the hydraulic piston.        
 
         [0020]     In yet another embodiment, the invention provides a system for imparting a mechanical impulse to the earth comprising: 
        an anvil/platen/base plate assembly for operative deployment against the earth;     a hammer and mass assembly operatively connected to the anvil, the hammer/mass assembly for striking the anvil;     a control system including a servo valve, hydraulic actuator and accumulator assembly interconnected to the hammer/mass assembly for controlling the impulse energy of the hammer/mass assembly striking the anvil/platen/base plate assembly, the control system including a linear feedback loop for measuring the linear velocity and position of the hammer with respect to the anvil during a force stroke, a processor for receiving linear velocity and position data from the linear feedback loop and a proportional integrated derivative (PID) control loop to measure and correct the velocity of the hammer/mass velocity with respect to the anvil during a force stroke.        
 
         [0024]     In a still further embodiment, the control system includes: 
        a hydraulic actuator operatively connected to the hammer and mass assembly, the hydraulic actuator having a pressure side and a retract side;     a hydraulic reservoir and first and second hydraulic pumps, the first hydraulic pump operatively connected through a servo control valve to the retract side of the hydraulic actuator, the hydraulic pump for pumping hydraulic fluid from the hydraulic reservoir to the retract side and the second hydraulic pump for pumping hydraulic fluid to the pressure side;     a hydraulic accumulator operatively connected to the pressure side of the hydraulic actuator, the hydraulic accumulator having a pressure system for storing energy from the hydraulic actuator when hydraulic fluid is pumped to the pressure side of the hydraulic actuator; and,     a linear transducer operatively connected to the hammer for measuring the linear velocity and position of the hammer with respect to the anvil;     wherein the actuation system is operatively connected between the hydraulic pump and the retract side of the hydraulic accumulator.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The invention is described with reference to the following drawings wherein:  
         [0031]      FIG. 1  is a schematic diagram of an impulse system in accordance with the invention;  
         [0032]      FIG. 2  is a side view of one embodiment of an impulse system in accordance with the invention installed on a vehicle;  
         [0033]      FIG. 2A  is an isometric view of one embodiment of an impulse system in accordance with the invention installed on a vehicle;  
         [0034]      FIG. 3  is an isometric view of an impulse system assembly in accordance with one embodiment of the invention;  
         [0035]      FIG. 3A  is a front elevation view of an impulse system assembly in accordance with one embodiment of the invention shown in a deployed position; and,  
         [0036]      FIG. 3B  is a schematic view of an impulse system assembly in accordance with one embodiment of the invention shown in a retracted position.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]     With reference to the figures, an impulse system  8  and impulse system assembly for providing mechanical impulse (seismic impulse) energy to the ground  9  is described. The system  8  generally includes a mass/hammer and anvil/baseplate assembly  10  and a hydraulic actuation system  12  (HAS) configurable to a carrier such as a vehicle  9   a  or a trailer (not shown). In operation, during a seismic survey, the system  8  is transported to a location where a seismic impulse is required and the system is deployed and operated to impart a mechanical shock wave to the earth at multiple source locations and recorded for scientific interpretation.  
         [0038]     Mass/Hammer and Anvil/Baseplate Assembly  10   
         [0039]     The mass/hammer and baseplate assembly  10  includes a mass assembly  10   a  connected to a hammer  10   b  that is used to strike an anvil  10   c . The anvil  10   c  is mated to a base plate  10   e , through the intermediate plate  10   d  and forced against the earth  9  by a hydraulically actuated hold down system  100  ( FIG. 3A ). As the anvil  10   c  is struck by the hammer  10   b , impulse energy is imparted to the earth  9  through the base plate  10   e . In a preferred embodiment, the anvil  10   c  includes a convex surface  10   f  that is engaged against a corresponding concave surface in a platen plate  10   g  of the baseplate  10   e  which enables concentrated impulse energy to be imparted into uneven terrain. The mass assembly  10   a  is mechanically attached to the hydraulic actuation system  12  through a gimble  10   d.    
         [0040]     Hydraulic Actuation System  12   
         [0041]     The Hydraulic Actuation System (HAS  12 ) operates to control the linear movement of the mass assembly  10   a  against the anvil  10   c  during a force stroke and the linear movement of the mass assembly  10   a  away from the anvil  10   c  during a retraction stroke as well as charging and discharging of hydraulic accumulators  12   d  using hydraulic fluid.  
         [0042]     The HAS  12  generally includes a hydraulic reservoir  12   a , hydraulic pumps  12   b ,  12   b ′, a hydraulic actuator  12   c , hydraulic accumulators  12   d  having a gas-filled bladder  12   e , a charge valve  12   x , a discharge valve  12   y , an actuation valve  12   f  (preferably a servo valve), a linear transducer  12   h  and proportional integrated derivative (PID) control electronics  12   g.    
         [0043]     In operation, during the retraction stroke, hydraulic fluid is pumped by pump  12   b  from the reservoir  12   a  through the actuation valve  12   f  to the hydraulic actuator  12   c  which causes the actuator  12   c  to retract thus lifting the mass and hammer to a set position above the anvil. The actuation valve  12   f  is closed and the mass and hammer are held in the set position. The accumulators  12   d  are then charged by pumping hydraulic fluid from the hydraulic reservoir  12   a  through charge valve  12   x  into each hydraulic accumulator  12   d  against the gas-filled bladder  12   e . During the charge cycle, charge valve  12   x  is opened and discharge valve  12   y  is closed. Upon reaching a predetermined charge pressure, as measured by pressure transmitter  12   z , the charge valve  12   x  is closed and the system is ready to fire.  
         [0044]     Upon triggering the force stroke, the potential energy stored within the accumulators  12   d  is converted to kinetic energy by opening the actuation valve  12   f  enabling the compressed bladder  12   e  to cause movement of the hydraulic fluid back through the servo valve into the hydraulic reservoir  12   a  through port  12   i , thereby causing movement of the mass assembly  10   a  towards the anvil  10   c . As the oil is forcing the hydraulic actuator  12   c  and mass assembly toward the anvil, the oil flow is metered and provides input to the control system  12   g  to control the velocity of the mass assembly  10   a . In addition, during the force stroke, the linear transducer  12   h  provides linear velocity and position data to the control electronics  12   g  which uses the linear velocity and position data in conjunction with a PID loop to determine and control the desired speed (and hence energy output) of the impulse system  8 .  
         [0045]     Once the force stroke is complete, the discharge valve  12   y  is opened and any remaining oil within the accumulator  12   d  is re-cycled back to the reservoir  12   a  by any remaining stored energy in the hydraulic accumulator. It is preferred to that hydraulic oil is re-cycled back to the reservoir to ensure appropriate heat dissipation from the hydraulic oil during the charge/discharge cycle so as maintain stable temperatures within the system.  
         [0046]     The linear transducer produces a velocity signal by measuring the change in position over time and creates a voltage output proportional to the rate of change. By recalling predetermined system parameters from a digital library, the actuator stroke, the actuator/mass assembly velocity, or both, can be tailored to produce predetermined force outputs. Precise force outputs can then be delivered at specific source locations during a seismic survey based on resolution requirements for that particular area.  
         [0047]     Furthermore, using the linear transducer and the PID loop to control the speed accurately, it is possible to deploy more than one impulse assembly  8  in the field whereby each can be synchronized to produce one summed output timed to occur simultaneously. As a result, the system enables accurate and repeatable force output for application to a wide variety of practical circumstances.  
         [0048]     Testing from the prototype carried out by and certified by Verifi Inc. (United Kingdom) has resulted in the output in excess of 860,000 lbsf being delivered to the base plate carried out during field testing, with 1000 psi accumulator charge pressure and 22 in of mass stroke.  
         [0049]      FIGS. 2, 2A , and  3  are drawings of an impulse system assembly  8   a  in accordance with a preferred embodiment of the invention that is adapted for configuration to a vehicle  9   a .  FIG. 3A  is a front elevation view of the impulse system assembly in a deployed position and  FIG. 3B  is a schematic diagram of the impulse system assembly in a retracted position.  
         [0050]     As shown, the impulse system assembly includes a vehicle frame assembly  50  for attachment to a vehicle  9   a  and for supporting the impulse system. In operation, the impulse system assembly is maintained in a retracted position (as shown in  FIG. 3B ) while the vehicle is in motion and in a deployed position (as shown in  FIGS. 2, 2A ,  3  and  3 A) when it is desired to impart a seismic impulse to the ground.  
         [0051]     The vehicle frame assembly  50  includes support members  50   a  extending to the rear for supporting the impulse system and a rear bumper  50   b  to protect the system.  
         [0052]     As shown in  FIGS. 3A and 3B , the impulse system includes guide columns  52  between a top plate  54  and the intermediate plate  10   d  that are retained within a collar  56  attached to the support members  50   a . The guide columns  52  are housed within the collars  56 . A deployment system  58  (preferably hydraulic actuators) are connected between the intermediate plate  10   d  and support members  50   a  that is operable to lift and lower the impulse assembly  8  between the retracted and deployed positions. In the retracted position, a latch system  60  (preferably pneumatically actuated) is utilized to actively lock the impulse system in the retracted position. As shown in  FIG. 1 , lift actuators  58  are hydraulically connected to pump  12   b ′ and reservoir  12   a  through valve  12   w  for lifting and lowering the impulse system. Control is provided through pressure switch  12   u  and electronic control module  12   g.    
         [0053]     In a preferred embodiment, a series of air bags  70  are located between the baseplate  10   e  and the intermediate plate  10   d  and work in conjunction with isolation disks located above and below the intermediate plate  10   d  to provide an isolating effect between the baseplate  10   e  and intermediate plate  10   d . The air bags  70  assist in minimizing the transmission of vibration and impulse force to the chassis of the vehicle at the moment of impact when the hammer strikes the anvil. A series of chain spring assemblies  72  are attached to the base plate  10   e  and through the intermediate plate  10   d  suspending the baseplate in the retracted position and to allow independent movement of the baseplate with respect to the intermediate plate to accommodate for uneven terrain during deployment.  
         [0054]     In operation, during a seismic survey, the vehicle operator drives the vehicle to a desired location determined by the requirements of the seismic survey. The operator lowers the impulse assembly  8  to the ground at that desired location and the hammer mass assembly is armed and a predetermined force stroke triggered. The force stroke is repeated as necessary. The operator then lifts the impulse assembly  8  and drives to the next location.