Abstract:
A sound source for geophysical studies of the earth for oil, gas and other natural resource exploration and more specifically a streamlined design of a hydraulically controlled impulsive sound source that may be inserted into oil wells and bore holes and a system and method for obtaining high quality seismic records from the impulsive sound source by adjusting and maintaining pressures within the well or bore hole.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 14/052,731 filed Oct. 12, 2013 that claims the benefit of U.S. Provisional Application No. 61/713,945 filed Oct. 15, 2012 entitled Method and Apparatus for Producing Sound Pulses within Bore Holes which is incorporated herein by reference in its entirety. This application further claims the benefit of U.S. Provisional Application No. 61/987,081 filed May 1, 2014 entitled, System and Method for Energizing an Impulsive Type Down-Hole Source which are each incorporated herein by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is related to a system and method for obtaining high quality seismic records from an impulse type sound source for geophysical studies of geological structures surrounding bore holes. The present invention is further related to a system and method of artificially pressurizing the bore hole and to adjusting and maintaining pressures within the bore hole to obtain sufficient sound output levels and high quality seismic records. 
       BACKGROUND OF THE INVENTION 
       [0003]    Geophysical surveys provide a cross-sectional map of the geology below the surface of the earth. Using sound waves, the shape and character of the geology may be revealed to indicate pockets within the sedimentary layers where oil and gas may be trapped, indicating locations where exploratory wells may be drilled for further geological analysis. Geophysical studies between bore holes or between bore holes and the ground surface have been done in the past using small charges of explosive impulsive sources and vibratory sound sources, but none of these types of sound sources have proved to be either practical or robust enough to be used over extended periods of time. 
       SUMMARY OF THE INVENTION 
       [0004]    A system and method of providing high quality seismic records from an impulse type of down-hole sound source designed to be robust as well as provide a practical tool to provide sound pulses for geophysical studies of the earth surrounding bore holes is here-with provided. The present invention further provides a system and method of obtaining seismic records using an impulsive sound source within a bore hole comprising the steps of artificially pressurizing the bore hole to obtain acceptable high quality seismic records. The present invention utilizes a free piston which is accelerated by the hydrostatic pressure of a fluid. Upon actuation of the free piston, the free piston moves through an isolated partially fluid filled piston chamber and strikes a sound transmitting anvil sending a sound pulse into an adjacent sound transmission chamber that is filled with light weight oil and surrounded by an elastomeric bladder. The sound pulse from the accelerating anvil moves the elastomeric bladder producing a sound wave that is emitted out through the fluid and ambient walls of the bore hole and into geological surrounding structures. In preparation for firing, an electric motor powered hydraulic pump, pumps hydraulic fluid to move a reset piston assembly to position a latching seal flange of the assembly into a receiving cup of a free piston. A check valve assembly within the flange provides for the evacuation of fluid within the receiving cup forming a vacuum seal that allows the reset piston assembly to draw the free piston through a high pressure fluid filled chamber and into a ready to fire position. The free piston is drawn to a stop point that breaks the vacuum and allows high pressure fluid within the chamber to rapidly accelerate the free piston against the anvil piston with the impulse providing the sound transmission. 
         [0005]    The impulsive sound source is designed in sections aligned end to end with a first cable termination module housing an umbilical cable and providing for the cable to be attached to and detached from the source. The cable is terminated at a two piece connector that has a first half portion within the upper module detachable from a second half portion that is mounted within the next module, an expansion chamber. The expansion chamber is enclosed with an elastomeric bladder to provide for changes in pressures within the source and assist in the absorption of vibrations as the source is fired. The expansion chamber serves as a reservoir for hydraulic fluid to operate the reset piston assembly. The expansion chamber also houses a set of power cables that extend through the chamber and are affixed to run an electric motor housed in the next module. The electric motor drives a hydraulic pump housed within a next module. The hydraulic pump takes fluid from and returns fluid to the reservoir of the expansion chamber and provides fluid to move the reset piston assembly that prepares the source for firing. The reset piston assembly module also houses the high pressure fluid implosion chamber for the free piston. The impact chamber is an open cylinder that houses the anvil and receives the fired free piston from the implosion chamber that strikes the anvil forcing the anvil a short distance into the sound transmission chamber transmitting the sound pulse to the elastomeric bladder that encloses the transmission chamber. The bladder propagates the sound through the fluid of the bore hole and the surrounding geological structure. 
         [0006]    The reversible three phase or DC motor is capable of high temperature operation and provides for the source to be successively fired as the motor is rotated in a first direction to supply hydraulic fluid to move the reset piston down to retrieve the free piston and an opposite direction to draw the free piston up to a ready to fire position with the rate of firing controlled by the speed of the motor. The motor direction is reversed using a relay switch that switches the power leads when the motor amperage peaks due to the latching seal flange bottoming out within the receiving cup in an extended position of the reset piston assembly or to switch directions when abutting a bulkhead of the reset piston assembly housing in a fully retracted position. In further embodiments, the electric motor may be controlled remotely to set the speed of the motor and firing rate. 
         [0007]    The modular design of the impulsive sound source provides for the top surface of the anvil and bottom surface of the free piston cylinder to be interchanged with anvils and free pistons of different shapes and sizes to change the characteristics of the sound pulse and seismic data. By varying the weight and/or stroke of the free piston and/or the anvil shape or other characteristics, the output pulse may be varied or tuned. For example, two flat shapes of the piston and anvil surfaces may produce the sharpest energy transition with the greatest amplitude and highest frequency upon impact of the free piston and the anvil piston. However, if the free piston shape is instead shaped as a conical point mating with the anvil having a conical hole, the frequency content would change as the conical point enters the conical hole producing a longer pulse with lower frequency content in the sound pulse with various shapes producing a range of amplitudes and frequencies. 
         [0008]    The impact chamber is further partially filled with fluid to create a cushion for the free piston and the anvil preventing the contact of metal on metal and absorbing vibrations within the source. The sound characteristics may be further changed by the compressibility and type of fluid used within the impact chamber. Fluids of different viscosity and compressibility may change compression characteristics of the fluid. For example, a more compressible fluid may slow the acceleration of the free piston and therefore produce a lower frequency pulse. The impulsive sound source may further be of any diameter and length necessary to accommodate the diameter of the bore hole and requirements of the geological survey. 
         [0009]    The present invention is further related to an impulsive sound source comprising an umbilical cable extending through a cylindrical housing; a hydraulic fluid reservoir formed within the housing and supplying a hydraulic pump; an electric motor powered from the umbilical cable and controlling the hydraulic pump; a hydraulic cylinder controlled by the hydraulic pump; a reset piston movable within a fluid filled piston chamber using the hydraulic cylinder, the reset piston having a flange movable within an implosion chamber; a free piston having an annular rim and cup within the implosion chamber; an anvil within an impact chamber adjacent the implosion chamber; an elastomeric bladder enclosing a fluid filled sound transmission chamber adjacent the impact chamber; and wherein the free piston is accelerated by hydrostatic pressure within the implosion chamber to strike the anvil and transmit a sound pulse through the sound transmission chamber and the elastomeric bladder. 
         [0010]    The impulsive sound source further comprises a latching seal assembly surrounding the reset piston flange, the flange having an inlet passage and check valve to evacuate fluid from the free piston cup and thereby latch the reset piston and free piston to draw the free piston to a ready to fire position. The difference in cross-sectional area of the reset piston flange and free piston annular rim provides the clamping force for the reset piston to latch to the free piston. The impulsive sound source may be repeatably fired by having the reset piston retract to an uppermost position causing the electric motor to rotate in a first direction to control the delivery of hydraulic fluid from the hydraulic pump to a first chamber and return hydraulic fluid to the reservoir from a second chamber and move the reset piston to the free piston and wherein the reset piston and free piston latch triggering the electric motor to reverse direction and the delivery of hydraulic fluid from the hydraulic pump is to the second chamber and return of hydraulic fluid to the reservoir is from the first chamber to move the reset piston and free piston to the uppermost position where the free piston is fired and the electric motor is triggered to rotate in the first direction. 
         [0011]    The impact chamber of the impulsive sound source may be partially filled with fluid and changing the viscosity and compressibility of the fluid within the impact chamber changes the characteristics of the sound pulse. In the impulsive sound source, the shape of a bottom surface of the free piston and the shape of the top surface of the anvil changes the characteristics of the sound pulse where as an example the top surface of the anvil may be recessed in shape and the shape of the free piston may be conical. The impulsive sound source may further have a dashpot in the anvil. The implosion chamber of the impulsive sound source may further comprise an elastomeric bladder to conform to fluid movements within the impulsive sound source. The reservoir of the impulsive sound source may further comprise an elastomeric bladder to conform to fluid movements within the impulsive sound source. Components of the impulsive sound source may be arranged in the order of an umbilical termination module on the top, an expansion chamber module beneath, next an electric motor housing module beneath, next a hydraulic pump module beneath, next an hydraulic cylinder module beneath, next a free piston implosion module beneath, next an impact chamber module beneath, and next a sound transmitting module beneath. 
         [0012]    The impulsive sound source may further comprise a manifold block adjacent to the hydraulic pump and the manifold block may house two pressure relief valves and two check valves. The reset piston of the impulsive sound source may be directly attached to a hydraulic piston rod on the opposite side of a hydraulic cylinder bulkhead. The sound transmitting anvil of the impulsive sound source may have fluid flow passages for fluid volume control. 
         [0013]    The present invention is further related to a method of generating a sound pulse within a bore hole through a manual or automated process, comprising the steps of extending an umbilical cable to support a cylindrical housing of a sound source; storing hydraulic fluid in a reservoir within the housing; supplying a hydraulic pump from the reservoir; controlling the hydraulic pump using an electric motor powered from the umbilical cable; filling a hydraulic cylinder using the hydraulic pump; moving a reset piston within a fluid filled implosion chamber using the hydraulic cylinder; seating the reset piston within a cup formed in the upper portion of a free piston; evacuating fluid from the cup forming a vacuum to draw the free piston using the reset piston to a ready to fire position; preventing travel of the free piston and pulling the reset piston from the cup thereby breaking the vacuum and accelerating the free piston to strike an anvil within an impact chamber to generate a sound pulse; transmitting the sound pulse through a fluid filled sound transmission chamber to an elastomeric bladder to propagate the pulse out and through the fluid filled bore hole and into the surrounding geological structures. 
         [0014]    The method of generating a sound pulse within a bore hole may further comprise the steps of changing the viscosity and compressibility of fluid within the impact chamber to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of increasing or decreasing the weight of the free piston to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of increasing or decreasing the length of the stroke of the free piston to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the step of shaping a top surface of the anvil and the bottom surface of the free piston in reciprocal shapes to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of shaping the top surface of the anvil to be a recessed cone and shaping the bottom surface of the free piston to be conical in shape to change the characteristics of the sound pulse. The method of generating a sound pulse within a bore hole may also further comprise the steps of transmitting a sound pulse wherein the free piston and anvil having flat surfaces; and collecting geological survey data; transmitting a sound pulse wherein the free piston having a conical shape and the anvil having a recess; collecting geological survey data; and combining the geological survey data acquired. 
         [0015]    The method of generating a sound pulse within a bore hole may also further comprise the step of forming a dashpot in the anvil. The method of generating a sound pulse within a bore hole may also further comprise the step of enclosing the implosion chamber with an elastomeric bladder. The method of generating a sound pulse within a bore hole may also further comprise the step of enclosing the reservoir with an elastomeric bladder to form an expansion chamber. The method of generating a sound pulse within a bore hole may also further comprise the step forming the free piston with an annular rim. 
         [0016]    The present invention is further related to a system and method of obtaining acceptable high quality seismic records by adjusting and maintaining pressures within a bore hole that may be similar to initial pressures from the first acquisition data in the survey or to desired pressures based on the fluid of the bore hole or the intensity and characteristics of the recorded seismic data. In performing a seismic survey, the impulsive sound source may be lowered to a position within a bore hole and fired to acquire the seismic records. The impulsive sound source may then be moved set distances and fired to acquire seismic data within the prescribed region of the survey. Each time the impulsive sound source is moved, pressures surrounding the source change resulting in changes to the intensity and characteristics of the seismic data. 
         [0017]    The present invention is related to a method of obtaining seismic records using an impulsive sound source within a bore hole comprising the steps of lowering an impulsive sound source to a desired depth within a bore hole to begin a seismic survey; measuring pressure readings within the bore hole to determine an initial pressure; adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole based on the initial pressure and current pressure readings; firing the impulsive sound source; and acquiring seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole further comprising the step of adjusting the pressure within the bore hole to the initial pressure. The method is further related to the steps of determining the intensity and characteristics of the seismic records. The method further comprises the steps of adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole based on the determined intensity and characteristics of the seismic records. 
         [0018]    The method further comprises the steps of raising the impulsive sound source to a new depth within the bore hole; measuring pressure readings within the bore hole at the new depth; adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole to the initial pressure readings. The method further comprises the steps of raising the impulsive sound source to a new depth within the bore hole; measuring pressure readings within the bore hole at the new depth; adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole to a desired pressure based on the initial and current pressure readings. The method further comprises the steps of moving the impulsive sound source to another depth within the bore hole; measuring pressure readings within the bore hole; firing the impulsive sound source within the bore hole; determining the intensity and character of the seismic records; adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole based on the initial and current pressure readings and the intensity and characteristics of the seismic records. The method further comprises the steps of simultaneously moving the impulsive sound source while firing the impulsive sound source within the bore hole while measuring pressure readings within the bore hole while determining the intensity and characteristics of the seismic records and adjusting the supply of gas or fluid to the bore hole to adjust the pressure within the bore hole based on the initial and current pressure readings and the intensity and characteristics of the seismic records. 
         [0019]    The present invention is further related to a method of obtaining seismic records using an impulsive sound source within a bore hole comprising the steps of artificially pressurizing the bore hole to obtain enough pressure to operate the sound source to sufficient sound output levels to obtain acceptable high quality seismic records. In the method, the pressure levels are changed within the bore hole as the sound source is moved within the bore hole in order to adjust the pressure within the bore hole to a desired level. The present invention is further related to a method of moving an impulsive sound source up or down within a fluid filled bore hole, adjusting pressures within the bore hole and firing the source at a constant fluid pressure surrounding the source. 
         [0020]    The present invention is further related to a system for adjusting and maintaining pressure within a bore hole in order to obtain consistent quality seismic records using an impulsive sound source comprising an impulsive sound source; an umbilical cable for lowering the impulsive sound source to a desired depth within a bore hole to begin a seismic survey; a pressure sensor measuring readings within the bore hole; a gas or fluid pressure source; a pressure regulator adjusting the supply from the pressure source of gas or fluid to the bore hole to adjust the pressure within the bore hole based on an initial and current pressure readings; a controller for firing the impulsive sound source. The system for adjusting and maintaining pressure within a bore hole in order to obtain acceptable quality seismic records wherein the initial pressure is a pressure reading taken at an initial depth at the beginning of a seismic survey. The system for adjusting and maintaining pressure within a bore hole in order to obtain acceptable quality seismic records further comprises a computer processor for determining the intensity and characteristics of the seismic records from the firing of the impulsive source. In using the system for adjusting and maintaining pressure within a bore hole in order to obtain acceptable quality seismic records using an impulsive sound source, the adjustment of gas and/or fluid from the pressure source using the pressure regulator may be based on the determined intensity and characteristics of the seismic records. The impulsive sound source may then be moved to a new depth within the bore hole using the umbilical cable of the pressure source and using the pressure regulator of the system the supply of gas or fluid to the bore hole may be adjusted to the initial pressure or to a desired pressure at the new depth. Using the computer processor, the system for maintaining pressure within a bore hole in order to obtain acceptable quality seismic records using an impulsive sound source, the pressure regulator may adjust the supply of gas or fluid to the bore hole to the initial pressure or a desired pressure simultaneously while the impulsive sound source is moving and firing based on the initial and current pressure readings and the intensity and characteristics of the seismic records. The pressure within the bore hole may be adjusted automatically using the computer processor or by using a manually controlled pressure regulator or a manually operated fluid control valve. 
         [0021]    The present invention is related to an impulsive sound source for obtaining seismic records within a bore hole, comprising a hydraulic pump; a reset piston; a free piston; a movable anvil; and wherein the free piston is accelerated by hydrostatic pressure to strike the movable anvil and transmit a sound pulse through a bore hole to obtain seismic records. The impulsive sound source may comprise an umbilical cable. The impulsive sound source may comprise a hydraulic fluid reservoir. The impulsive sound source may comprise at least one elastomeric bladder. The free piston of the impulsive sound source may have an annular rim and cup. The reset piston may have a latching seal and check valves to expel fluid from the free piston cup to latch the reset piston and free piston. The impulsive sound source may comprise an electric motor and may be repeatably fired by having the reset piston move to a retracted position causing the electric motor to rotate in a first direction to control the hydraulic pump to move the reset piston to the free piston; and the reset piston and the free piston latch triggering the electric motor to reverse direction and move the reset piston and free piston to the retracted position to fire the free piston and trigger the electric motor to rotate in the first direction. The characteristics of the sound pulse of the impulsive sound source may be changed by changing the weight of the free piston. The characteristics of the sound pulse of the impulsive sound source may be changed by changing the stroke of the free piston. 
         [0022]    The present invention is further related to an impulsive sound source, comprising an impulsive sound source comprising modules, the modules comprising an umbilical termination module; an expansion chamber module; an electric motor housing module; a hydraulic pump module; a hydraulic cylinder module; a free piston implosion module; an impact chamber module; and a sound transmitting module. 
         [0023]    The components of the impulsive sound source are arranged in the order of the umbilical termination module on the top, the expansion chamber module beneath, next the electric motor housing module beneath, next the hydraulic pump module beneath, next the hydraulic cylinder module beneath, next the free piston implosion module beneath, next the impact chamber module beneath, and next the sound transmitting module beneath. 
         [0024]    The present invention is further directed to a method of obtaining seismic records within a bore hole, comprising the steps of delivering hydraulic fluid to move a reset piston to a free piston; latching the reset piston to the free piston; moving the reset piston and free piston to a ready to fire position; accelerating the free piston using hydrostatic pressure to strike a movable anvil to generate a sound pulse; transmitting the sound pulse through a bore hole to obtain seismic records. The method of obtaining seismic records within a bore hole comprising the steps of repeatedly firing the sound source comprising the steps of controlling the delivery of hydraulic fluid using an electric motor; moving the reset piston to a retracted position causing the electric motor to rotate in a first direction to deliver hydraulic fluid to move the reset piston to the free piston; latching the reset piston to the free piston causing the electric motor to reverse direction to deliver hydraulic fluid to move the reset piston and free piston to the retracted position to fire the free piston and trigger the electric motor to rotate in the first direction. 
         [0025]    The present invention is further related to a method of obtaining seismic records using an impulsive sound source within a bore hole comprising the steps of moving an impulsive sound source within a bore hole; adjusting pressures within the bore hole; firing the impulsive sound at an adjusted pressure surrounding the impulsive sound source; and acquiring seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole may further comprise the steps of measuring pressure readings within the bore hole at the a first depth to obtain an initial pressure; moving the impulsive sound source to a new depth within the bore hole; measuring pressure readings within the bore hole at the new depth; adjusting pressure within the bore hole to the initial pressure. The method of obtaining seismic records using an impulsive sound source within a bore hole may further comprise the steps of moving the impulsive sound source to a new depth within the bore hole; measuring pressure readings within the bore hole at the new depth; adjusting pressure within the bore hole to a desired pressure. The method of obtaining seismic records using an impulsive sound source within a bore hole may further comprise the steps of determining the intensity and characteristics of the seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole may further comprise the steps of adjusting the pressure within the bore hole based on a determined intensity and characteristics of the seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole may further comprising the steps of moving the impulsive sound source to another depth within the bore hole; measuring pressure readings within the bore hole; firing the impulsive sound source within the bore hole; determining the intensity and characteristics of the seismic records; adjusting the pressure within the bore hole based on pressure readings and the intensity and characteristics of the seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole may comprise the steps of simultaneously moving the impulsive sound source while firing the impulsive sound source within the bore hole while measuring pressure readings within the bore hole while determining the intensity and characteristics of the seismic records; and adjusting the pressure within the bore hole based on the pressure readings and the intensity and characteristics of the seismic records. The method of obtaining seismic records using an impulsive sound source within a bore hole may comprise the steps of artificially pressurizing the bore hole to obtain enough pressure to operate the impulsive sound source to sufficient sound output levels to obtain consistent quality seismic records. The pressure levels within the bore hole in the method of obtaining seismic records may be adjusted while the sound source is moving within the bore hole in order to keep the pressure within the bore hole at a desired level. 
         [0026]    The present invention is further related to a system for adjusting and maintaining pressure within a bore hole in order to obtain acceptable quality seismic records using an impulsive sound source comprising an impulsive sound source having at least one pressure sensor; a pressure source; and wherein the pressure source adjusts the pressure within the bore hole based on initial and current pressure readings from the at least one pressure sensor. The initial pressure in the system may be a pressure reading taken at an initial depth at the beginning of a seismic survey and current pressure readings are pressure readings taken during the seismic survey. The system for adjusting and maintaining pressure within a bore hole in order to obtain acceptable quality seismic records using an impulsive sound source may further comprise a computer processor for determining the intensity and characteristics of the seismic records from the firing of the impulsive source. The adjustment of pressure within the bore hole may be based on a determined intensity and characteristics of the seismic records. The impulsive sound source may be moved to a new depth within the bore hole and the pressure source may adjust the pressure within the bore hole to the initial pressure at the new depth. The impulsive sound source may be moved to a new depth within the bore hole and the pressure source may adjust the pressure within the bore hole to a desired pressure at the new depth. In using the computer processor, the pressure source may adjust the pressure within the bore hole at the current depth of the impulsive sound source simultaneously while the impulsive sound source is moving and firing based on one of at least the initial and current pressure readings and the intensity and characteristics of the seismic records. 
         [0027]    These and other features, advantages and improvements according to this invention will be better understood by reference to the following detailed description and accompanying drawings. While references may be made to upper, lower, vertical and horizontal, these terms are used merely to describe the relationship of components and not to limit the operation of the present invention to any one orientation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Several embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings in which: 
           [0029]      FIG. 1A  is a cross-sectional diagram of a first portion of a first embodiment of the impulsive sound source in an embodiment of the present invention; 
           [0030]      FIG. 1B  is a continuation of the cross-sectional diagram of  FIG. 1A  as a second portion of a first embodiment of the impulsive sound source of the present invention; 
           [0031]      FIG. 2A  is a cross-sectional diagram of a first portion of the first embodiment of the impulsive sound source of the present invention; 
           [0032]      FIG. 2B  is a continuation of the cross-sectional diagram of  FIG. 2A  as a second portion of the first embodiment of the impulsive sound source of the present invention; 
           [0033]      FIG. 3  is a cross sectional diagram of an embodiment of a cable termination of module A of the first embodiment of the impulsive sound source of the present invention; 
           [0034]      FIG. 4  is a cross sectional diagram of an embodiment of an expansion chamber of module B of the first embodiment of the impulsive sound source of the present invention; 
           [0035]      FIG. 5  is a cross sectional diagram of an embodiment of an electric motor of module C of the first embodiment of the impulsive sound source of the present invention; 
           [0036]      FIG. 6  is a cross sectional diagram of an embodiment of a hydraulic fluid pump of module D of the first embodiment of the impulsive sound source of the present invention; 
           [0037]      FIG. 7A  is a cross sectional diagram of an embodiment of a reset piston assembly and high pressure free piston chamber of module E of the first embodiment of the impulsive sound source of the present invention in a ready to fire; 
           [0038]      FIG. 7B  is a cross sectional diagram of the embodiment of the reset piston assembly and free piston chamber of module E of the first embodiment of the impulsive sound source of the present invention in a fired position; 
           [0039]      FIG. 7C  is a cross sectional diagram of an embodiment of the reset piston assembly and free piston chamber of module E of the first embodiment of the impulsive sound source of the present invention in an extension of the reset piston assembly to prepare the source for firing; 
           [0040]      FIG. 7D  is a top view cross section showing an embodiment of the communication ports in the implosion chamber of module E in a first embodiment of the impulsive sound source of the present invention; 
           [0041]      FIG. 7E  is a cross sectional diagram of an embodiment of a latching seal flange of the reset piston assembly of module E of the first embodiment of the impulsive sound source of the present invention; 
           [0042]      FIG. 8  is a cross sectional diagram of an embodiment of an impact chamber of module F of the first embodiment of the impulsive sound source of the present invention; 
           [0043]      FIG. 9  is a cross sectional diagram is a further embodiment of the free piston and anvil of the impact chamber of module F of the first embodiment of the impulsive sound source of the present invention; 
           [0044]      FIG. 10A  is a cross sectional diagram of an embodiment of a sound transmission chamber of module G of the first embodiment of the impulsive sound source of the present invention; and 
           [0045]      FIG. 10B  is a top view cross section showing an embodiment of the communication ports in the sound transmission chamber of module G in a first embodiment of the impulsive sound source of the present invention; 
           [0046]      FIG. 11A  is a cross-sectional diagram of an embodiment of a first portion of the impulsive sound source within a bore hole with an embodiment of a pressure regulating system of the present invention to adjust pressures within the bore hole in an embodiment of the present invention; and 
           [0047]      FIG. 11B  is a continuation of the cross-sectional diagram of  FIG. 11A  of an embodiment of a second portion of the impulsive sound source within a bore hole in an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    The present invention is an impulsive type sound source for creating sound pulses which can be used for seismic surveys between liquid filled bore holes in the ground such as water wells, oil wells and/or bore holes for geological studies. The present invention is further related to a system and method of artificially pressurizing the bore hole to obtain adequate and consistent pressures to operate the sound source to sufficient sound output levels to obtain acceptable high quality seismic records. 
         [0049]    The present invention provides a sleek modular design of an impulsive sound source  1  to make the system easier for transportation and insertion of the source into wells and bore holes for seismic analysis deep within the ground. The impulsive sound source  1  may be of any diameter and dimension suitable for the requirements of a geological survey with components of acceptable materials to withstand the high temperatures and pressures within water wells, oil wells and/or the bore holes used for geological studies. In a first embodiment, the impulsive sound source  1  is constructed with the series of modules as shown in  FIGS. 1A and 1B  with each of the modules A-G fixed end to end to one another along axis X using clamping rings and a series of bolt circles. Module A is the umbilical cable termination that as shown in  FIGS. 2A and 2B  has a housing  3  where the umbilical cable  2  aligns through the center of the housing and along axis X. The housing  3  may be of any shape, dimension or design with an upper termination head that is dependent on the size, design and construction of the umbilical cable  2 . The umbilical cable  2  carries the weight of the source  1  as well as shields and surrounds the electric cables for power to the motor, and for electrical and/or optical cables for control and sensors as required within the source  1  such as sensors to determine the instant of firing, the pressure, the temperature and structural conditions within the source and within the bore hole. 
         [0050]    As shown in  FIG. 3 , the connector  5  of module A provides a wire block  6  that distributes the electrical power, sensor and control cables throughout the source  1 . Module A is attached to module B using a series of bolts  7  and a stainless steel clamping ring  4  positioned around the lower end of the cylindrical housing  3 . Each of the upper and lower edges of the clamping ring  4  has a rim  8  extending completely around the ring  4  forming a channel  10  along a middle portion of the ring  4 . The housing  3  and the rim  8  of the ring  4  may have a series of bolt holes  9  that are evenly spaced around the outer edge of the cylinder to accept the bolts  7  that secure the ring  4  to the housing  3 . A groove  12  may be formed in the housing  3  to accept the rim  8  of the ring  4 . The shoulder  14  forming the groove  12  may extend at a distance from axis X that is greater than a tubular center casing  15  that mates and aligns with the housing of module B. The tubular casing  15  formed on the base of the housing  3  is of a slightly smaller diameter than the diameter of the cylindrical housing  16  of module B. The housing  16  of module B, in this embodiment, is similarly formed with a shoulder  14  and groove  12  to provide for the lower rim  8  of the clamping ring  4  to lock around the shoulders  14  and secure the modules together. An index pin  18  may provide for the proper alignment and orientation of the modules with respect to one another. As described herein, heat resistant seal and bearing assemblies  20  made of viton or other plastic materials typically used in high pressure fluid applications are installed at the tubular casing  15  and at other connections in the housing and at each fluid path throughout the source to prevent leakage of hydraulic fluid and to properly secure and seal all high pressure connections. 
         [0051]    Module B, as shown in  FIG. 4 , is an expansion chamber that is formed with a housing surrounded by an elastomeric bladder  21 . The second half of the cable distribution connector  5  is a connector receptor  22  that is positioned at the top of the electric cable and fluid flow passage  24  that is formed through the center of the housing  16 . The cable distribution connector  5  provides for the cable termination of module A to be disconnected from the rest of the impulsive sound source for transportation of the source separate from the umbilical cable  2 . The power cables  26  are properly shielded and extend down and through the fluid flow passage  24  to reach the motor cable connector  32  at the top of the motor  34  in module C. In a first embodiment, a combination time break pressure and temperature transducer  33  used to detect the firing of the source as well as monitor and transmit pressure and temperature is installed at the top of the fluid flow passage  24 . Other sensors may be positioned throughout the source  1  to determine temperature and pressure as well as monitor and collect system operational parameters and other information. Module B also has openings  31  through the housing  16  to allow fluid communication from the flow passage  24  to the expansion chamber bladder  21 . The flow passage  24  and expansion chamber  28  are filled with high temperature resistant hydraulic fluid to serve as a reservoir for the hydraulic pump  52  of module D of the source  1 . The bladder  21  is secured to the housing  16  using band clamps  36  that surround the housing  16  and affix the bladder  21  at only the upper and lower portion of the housing  16  to allow for the middle of the bladder  21  to expand as pressure changes occur within the flow passage  24  and other modules of the source  1 . A filler port  38  is provided to fill the flow passage  24 . A vent  30  may be provided along the filler port passageway  29 . A fluid passageway  40  is also provided at the base of module B to provide for communication of fluid between the flow passage  24  and the electric motor  34  of module C. 
         [0052]    A housing  44 , as shown in  FIG. 5 , surrounds the electrical motor  34  and an annular fluid flow compartment  42  is formed between the housing  44  and the module C outer housing  45 . The compartment  42  is filled with the system hydraulic fluid from the upper passageway  40  from module B to help maintain the motor  34  at acceptable operational temperatures. The upper passageway  40  also provides for fluid to flow from the compartment  42  back through to the expansion chamber flow passage  24  of module B as the source is fired and pressures change within the source. As temperature and pressure increase or decrease within the source and fluid moves through the hydraulic system, the expansion bladder  21  expands or contracts to prevent damage to components within the source due to fluid fluctuations. At the base of the enclosure  44  a flow passage  47  connects the reservoir of Module B to the manifold block  54  of module D and a rubber or other durable shock absorbing material cushion mount  48  is placed to help isolate the motor  34  from accelerations caused by the motions of the free piston  43 . The motor  34  is a reversible three phase or DC motor capable of high temperature operation. The motor housing  44  and other structural components of the source  1  may be of stainless steel or other comparable materials that are capable of sustaining the load and pressures of the firing of the source  1  and bore hole environment. At the base of the motor  34 , the shaft  49  of the electric motor  34  extends along axis X into module D to operate the hydraulic fluid pump  52 . The shaft  49  is aligned through the manifold block  54  and is affixed to the hydraulic pump  52  using a flexible coupling  56  as shown in  FIG. 6 . 
         [0053]    The manifold block  54  is in the upper portion of module D and contains two check valves  58  and two pressure relief valves  60  for supplying the bi-directional hydraulic pump  52  with hydraulic fluid and for setting the maximum pressure at which the hydraulic system may operate. The manifold block  54  has fluid by-pass passages  62  that connect the pump  52  to the pressure relief valves  60  and bores  64  that communicate with fluid by-pass tubes  66  for delivering hydraulic fluid to the reset piston assembly chambers  63  and  65  of module E. The by-pass tubes  66  extend from an upper portion  67  of the housing  68  of module D to a lower portion  69  that forms a shoulder for the tubing connection.  0 -rings  61  are rabbited into recesses within the upper and lower housing  68  and  69  and each end of the by-pass tubes  66  are installed. This design feature provides easy access to the tubing  66  for repair. The upper surface  70  of the lower housing portion  69  forms a seat for bolts  7  to be inserted through bolt holes that are evenly spaced around the cylindrical housing for attachment of module D to module E. 
         [0054]    As the motor shaft  49  rotates in one direction, fluid is delivered to one by-pass passage  62  and one by-pass tube  66  and fluid is returned through the other by-pass tube  66  and by-pass passage  62  thereby simultaneously filling one and evacuating the other of the reset piston chambers  63  and  65  to extend or retract the reset piston assembly of module E. The check valves  58  direct fluid flow based on the rotational direction of the motor  34 . The relief valves  60  provide for the release of fluid back to the reservoir of module B to prevent over pressuring the system as the reset piston assembly reaches a full point of extension and bottoms out in the receiving cup  130  of the free piston  110  or full retraction at an upper most point with the motor continuing to run in one direction until a peak in amperage triggers a relay switch (not shown) to change the direction of flow. 
         [0055]    As shown in  FIG. 6 , the rod  72  of the reset piston assembly extends into a cavity  74  formed by the housing  68  of module D. In order to slide smoothly a bearing and seal assembly is installed within bulkhead  75 . The bearing and seal assembly includes a seal  71  a bearing  73  and a backup ring  78  positioned to protect the seal  71  from extrusion. To secure the bearing and seal assembly in place a retainer ring  82  is installed between a preformed edge  77  at the base of the housing  68  and a ledge formed at the upper surface  79  of the upper housing  80  of module E. The seal  71  prevents fluid leakage from chamber  63  into cavity  74  as chamber  63  is pressurized. 
         [0056]    The reset piston  84  separates chambers  63  and  65  and is positioned along the piston rod  72  using a cylindrical sheath  83  and cap nut  85  that is tightened to hold the reset piston  84  in place along the rod  72 . The sheath  83  is set at a thickness t that when combined with the upper rod diameter d is equal to the lower rod diameter D below the piston  84  in order to maintain an equal volume in the actuation chamber  63  and refraction chamber  65  above and below the piston  84 . Hydraulic fluid from the hydraulic pump  52  is fed to and returned from the actuation chamber  63  through actuation feed bore  87 . Hydraulic fluid is fed to and returned from the retraction chamber  65  through feed bore  89 . A seal gland and ring bearing assembly  86  is affixed to the outer diameter of the reset piston  84  to seal and further assist in the reduction of friction as shown in  FIG. 7A . The housing  80  of module E encloses the reset piston actuation chamber  63  and retraction chamber  65  with bulkhead  76  forming the base of the refraction chamber  65 . The housing  80  is enclosed by an elastomeric bladder  102  forming the high pressure fluid implosion chamber  100  for the free piston  110 . The free piston  110  may be hollow to reduce the weight of the free piston  110  and the overall weight of the source  1 . 
         [0057]    The bladder  102  is affixed to the housing at each end of the module using band clamps  36 . The chamber  100  is sealed using a seal gland and ring bearing assembly  94  at bulkhead  76  that provides for reduced friction allowing the piston rod  72  to move smoothly between the reset piston chamber and implosion chamber. For the communication of fluid to and from the actuation and retraction feed lines  87  and  89  bores may be drilled through the housing and resealed with a brazed plug  96 . A fluid fill plug  98  that is for example 90 degrees away from the actuation and retraction feed lines  87  and  89  is provided to fill the implosion chamber  100  with hydraulic fluid. 
         [0058]    The housing  80  of the implosion chamber  100  may be tapered at either end to provide support structures for the attachment of bolts  7  to connect module D at the upper support structure  104  and to connect module F at the lower support structure  106  along the axis X. A seal gland ring bearing assembly  112  is installed at the lower support structure  106  to seal the implosion chambers and reduce friction to allow the free piston  110  to move smoothly within the impact chamber  120  of module F. The module F housing  118  surrounds the free piston  110  to form the impact chamber  120 . Additional seals  20  are installed between the support bulkhead  118  and lower structural support  106  of housing  80  to prevent leakage. A fluid fill plug  128  as shown extends from the impact chamber perpendicularly to axis X and through the support bulkhead  118  to fill the impact chamber  120  to an appropriate fluid level denoted as fin  FIG. 7A . 
         [0059]    As shown in  FIG. 7A , the piston rod  72  extends out and through the actuation and retraction chambers  63  and  65  and the chamber bulkhead  76 . Attached to the end of the reset piston rod  72  is the reset piston latching seal assembly  123  that using a vacuum seal retains and draws the free piston  110  to a ready to fire position at an uppermost point within the implosion chamber  100 . At the highest retraction point of the reset piston  84 , the upper circular surface  151  of the receiving cup  130  strikes a shoulder  152  of the housing  80  that pulls the latching seal  146  out of the cup  130  breaking the vacuum seal and providing for high pressure fluid to flow past the latching seal  146  to rapidly accelerate the free piston through the chamber  100  to contact the anvil  160  within the impact chamber  120  transmitting the sound pulse as shown in  FIG. 7B . A cross-sectional top view of the housing  80  showing the central portion of the implosion chamber  100  and the ports  90  that provide communication between the chamber  100  and the elastomeric bladder  102  is shown in  FIG. 7C . 
         [0060]    The source  1  is prepared for firing by filling the actuation reset piston chamber  63  with pumped pressurized hydraulic fluid to force the reset piston  84  and the latching seal assembly  123  from the upper retraction position after firing down and into the receiver cup  130  of the free piston  110  at the base of the implosion chamber  100 , as shown in  FIG. 7D . The latching seal assembly  123  plugs into the receiver cup  130  formed in the upper portion at the top of the free piston  110 , and is retained within the receiver cup  130  due to the evacuation of fluid that is trapped within the space between the bottom cylindrical surface  145  of the reset piston flange  138  that includes the reset piston latching seal assembly  123  and the upper cylindrical surface  148  of the cup  130 . The fluid within this space is purged out through a passageway  132  forcing check valve  134  to open and release the evacuated fluid into the implosion chamber  100  through the check valve outlet  135 . The evacuated space forms a vacuum to effectively lock the latching seal assembly flange  138  and free piston  110  together. Hydraulic fluid is then simultaneously removed from the actuation chamber  63  and fed to the retraction chamber  65  to draw the free piston  110  up to an uppermost retraction point in the implosion chamber  100 . 
         [0061]    The latching seal assembly  123 , as shown in  FIG. 7E , has a high pressure latching seal ring  146  that surrounds the flange  138 . The flange  138  has a diameter with a very close tolerance to and only slightly smaller than the diameter of the receiving cup  130  with the latching seal ring  146  seated within a groove formed around the outer diameter of the flange  138  and extending out beyond the edge  142  of the outer diameter of the flange  138 . In a first embodiment, the latching seal  146  is retained within this groove in the flange a hooked sealing surface  141  and using a seal retainer ring  143  with flat head screws  144  that may be inserted through the base  145  of the flange  138  and be countersunk to maintain a smooth surface of the base  145  to mate with the smooth surface  148  of the receiving cup  130 . Alternatively, the retaining ring  143  and screws  144  may be inserted through the upper surface  147  of the flange  138  to retain the latching seal  146 . The retainer ring  143  may have a similar hooked surface  139  to retain the seal  146 . Check valve  134  is mounted within the center and flush to the base  145  of the flange  138  by inserting a spanner wrench in slots  133  on either side of a central fluid passageway  132 . The outlet port  135  of the check valve  134  communicates with the implosion chamber  100  and provides for fluid in the space between the base  145  of the reset piston assembly flange  138  and the inner cylindrical surface  148  of the receiving cup  130  to be evacuated through the passageway  132  and open check valve  134  to create the vacuum seal that retains and draws the free piston  110  into the ready to fire position. A pressure relief outlet  92  may be formed through the reset piston assembly housing  80 . 
         [0062]    As an example, if all or nearly all of the fluid has been purged out of the space between the bottom surface  145  of the piston flange  138  and the inner surface  148  of the free piston cup  130  through the check valve  134  and given that the sealing diameter at the inside diameter ID of the receiving cup  130  of the free piston  110  is 8.9 cm (3.5 inches) and the diameter of the portion of the reset piston assembly flange  138  within the receiving cup  130  is 7.6 cm (3.0 inches), the difference in effective cross sectional area at the annular rim  149  of the receiving cup  130  is 6.5 cm 2  (2.56 square inches). Therefore, if the fluid pressure within the implosion chamber  100  is 20.6 MPa (3000 psi) then as the reset piston assembly flange  138  moves upward compressing the fluid within the implosion chamber  100 , the 6.5 cm 2  (2.56 square inch) difference in area produces a clamping force approaching 34.2 kN (7680 pounds of force) between the flat surfaces. This clamping force provides for the reset piston assembly to draw the free piston  100  to the full retraction point of the reset piston assembly. At the top of the retraction stroke of the reset piston  84 , the upper edge  151  of the receiving cup  130  of the free piston  110  is stopped against the bottom side of a shoulder  152  formed in the implosion chamber housing  80  and the latching seal assembly flange  138  begins to pull out of the receiving cup  130 . The expanded diameter of the latching seal  146  is pulled past a radius  154  formed in the vertical wall of the cup  130  releasing the vacuum and allowing fluid within the chamber  100  to flow past the latching seal  146  and fill the evacuated space between the upper and lower surfaces  145  and  148  accelerating the free piston  110  rapidly towards the impact chamber  120 . 
         [0063]    The impact chamber  120 , as shown in  FIG. 8 , is partially filled with fluid to cushion the impact between the metal impact surface or face  162  of the free piston  110  and the anvil impact face  164 . The compressibility and viscosity of the fluid within the impact chamber  120  and the shape of the impact surface  162  and anvil face  164  all contribute to the quality and characteristics of the sound produced by the impulsive sound source  1 . Upon impact, the anvil piston  160  within the cylindrical support bulkhead  118  of module F and partially into an upper portion  172  of the sound transmission chamber  170  of module G. The support bulkhead  118  includes two bolting flanges  124  and  125  that extend laterally to provide bolt holes that are evenly spaced around the circular upper flange  124  attaching module E to module F and the circular lower flange  125  attaching module F to module G. 
         [0064]    A dashpot nose  166  is formed at the cylindrical base  168  of the anvil piston  160 . The cushion profile of the dashpot  166  is formed to act as a damper to absorb the remaining energy of the anvil  160  as it stops moving at the bottom of its impulse stroke. A seal and bearing assembly  178  is installed on the anvil piston  160  to reduce friction and a ring seal  179  is installed on the bulkhead  118  to prevent fluid flow between the impact chamber  120  and sound transmission chamber  170 . 
         [0065]    After firing, the impact chamber fluid is forced through a channel  180  formed through the anvil piston  160  and into a by-pass passageway  181  and into the space  182  within the impact chamber  120  created by the movement of the anvil piston  160  of module F. In drawing the free piston  110  up to the reset position for firing, fluid is drawn from the space  182  and up through the channel creating a vacuum and drawing the lower anvil piston  160  up and into the impact position for firing. The source  1  may be of any acceptable shape and dimension to accommodate the shape and dimensions of the bore hole being surveyed. As shown in  FIG. 9 , the free piston  110  may be shaped as a conical point  163  and the anvil may have a cylindrical opening  177  that would cause the frequency content to change as the conical point  163  enters the opening  177  producing a longer pulse with lower frequency content in the sound pulse. The free piston  110  and anvil may be formed in various shapes to produce a range of amplitudes and frequencies. Also by varying the weight and stroke of the free piston and/or anvil, the shape, intensity, and characteristics of the output pulse may be varied or tuned. 
         [0066]    A fill valve  184  and passage  186  is provided for module G to fill and adjust the fluid within the sound transmission chamber  170 . A bladder  188  is affixed to the upper portion and lower portion of the sound transmission housing  176  as shown in  FIG. 10A  using band clamps  36 . Any number of ports  190  to transfer fluid from the sound transmission chamber  170  to the bladder  188  may be formed within the sound transmission chamber housing  176  with the number and dimensions dependent on the requirements of the geological survey. As noted, because of the modularity of the source  1 , module G may be replaced with a sound transmission chamber having more or less than the four ports shown from the top view of the sound transmission chamber in  FIG. 10B . A time break transducer or other sensors  33  may be installed in the sound transmission chamber  170  to detect the firing of the source or pressures and temperatures within the source  1 . In a first embodiment, the end  194  of module G may be conically in shape to prevent the source from being held or damaged on ledges within the bore hole as the source is inserted and hung from the umbilical cable  2 . 
         [0067]    In operation, the source  1  in its ready to fire position is shown in  FIG. 7A , in its fired position is shown in  FIG. 7B  and in its reset position is shown in  FIG. 7D  being picked up by the reset piston latching seal assembly  123 . As the latching seal assembly flange  138  plugs into the receiving cup  130  at the top of the free piston  110 , the latching seal  146  seals and slides within the bore of the cup  130 . Fluid within the cup  130  escapes out through the check valve  134  forming a partial vacuum with the clamping force of the high pressure fluid within the implosion chamber  100  holding the reset piston latching seal assembly  123  and the interior surface  148  of the cup portion  130  together to draw the free piston  110  to the refraction point where the upper edge  151  of the free piston  110  is stopped against the shoulder  152  formed within the reset piston assembly housing  80 . The latching seal assembly flange  138  is partially pulled from the cup  130 , fluid enters past the radius  154  formed in the outer edge of the cup  130  and past the latching seal  146  to fill the evacuated space between the flat surfaces  145  and  148  of the latching seal assembly flange  138  and the free piston  110  releasing the vacuum and accelerating the free piston  110  down to impact upon the sound transmitting anvil piston  160  sending a sound pulse into chamber  170 , through ports  190  to the bladder  188  and out through the ambient wall of fluid within the bore hole and into the surrounding geological structures. 
         [0068]    As the free piston  110  is accelerated when the impulsive sound source  1  fires the face  162  of free piston  110  impacts upon the face  164  of the movable anvil piston  160  and thereby causing the anvil piston  160  to rapidly accelerate downwardly creating the impulse which in turn rapidly expands elastomeric bladder  188  of the sound transmission chamber  170  creating a sound pulse within the well fluid F which propagates through the well casing  202  into the earth strata  204  as a seismic sound pulse within the earth, as shown in  FIGS. 11A and 11B . Because the elastomeric bladder  21  of the expansion chamber of Module B, the elastomeric bladder  102  surrounding the free piston chamber of Module E, and the elastomeric bladder  188  of the sound transmission chamber  170  of Module G are all tubular and flexible bladders the pressure of the fluid within these chambers denoted as Ps stands equal to the pressure within the well casing denoted as Pw. 
         [0069]    When the impulse type of down-hole sound source  1  of the present invention is suspended by the umbilical cable  2  there is a pressure seal gland  206  which seals the pressure within the well around the umbilical cable  2  within a pressure retaining well cap assembly  208  held in place and sealed at the top of the well casing  202  by bolt circle  210 . The bore hole  212  and well casing  202  may be either a shallow bore such as a few hundred feet or a deep bore such as 10,000 feet and the bore may be fully liquid filled or only partially filled with fluid. The intensity of the impulse the sound source  1  produces when fired is proportional to the static pressure within the bore hole  212  where the sound source  1  is located thus when the sound source  1  is immersed at a shallow depth in the well or bore hole  212  the intensity of the seismic data is lower than when immersed deeply within the bore hole fluid F such as when submerged in water, oil, or in drilling mud. 
         [0070]    When the sound source  1  within a bore hole  212  is used for seismic profiling, the sound source  1  may be raised and lowered within the well between shots from the sound source  1 . As the sound source  1  is raised or lowered in the bore hole  212 , the pressure within the well Pw changes depending on the location and depth of the sound source  1 . For acceptable quality in the records of the seismic survey, it is important that the intensity and character of the sound pulse remains constant as the sound source  1  is raised and lowered to a location and fired. Any changes in pressure within the well Pw during the collection of seismic data may affect the intensity and character of the sound pulse, thus the present invention provides for pressure within the well Pw to be adjusted as the impulsive sound source  1  is moved within the well casing  202  or bore hole  212 . 
         [0071]    For example, commonly in completing a seismic survey, the sound source  1  is lowered to a lowest point in the bore hole  212  and fired and is then raised to another depth and fired and this is repeated as the sound source  1  is pulled up through the bore hole  212 . One of more pressure sensors  214  on the sound source  1  as well as pressure sensors  216  at the well cap assembly  208  transmit pressure readings to a controller  218 . From these readings the pressure may be manually or automatically increased as the sound source  1  is moved within the bore hole  212  to keep the current pressure the same as the initial pressure readings that were recorded when the survey started at, in this example, the lowest point in the bore hole  212 . A fluid pressure source  220 , the controller  218 , a pressure regulator  222  and using hose or pipe  224  connected through the well cap assembly  208  may supply either high pressure gas, water or other fluid through an input fitting  226  to adjust the pressure within the bore hole  212 . The bore hole  212  may be filled with fluid nearly to the top of the bore hole  212  with a cushion or space of pressurized gas of a short length L such as 10 feet more or less from the pressure retaining well cap assembly  208  to the well fluid level D with the well fluid level D ending above ground level. The impulsive sound source  1  and pressure regulating system  200  may also be used with the fluid F within the bore hole  212  completely filling the bore. The well cap assembly  208  containing the umbilical cable sliding seal  206  and the fluid input fitting  226  and bolt circle  210  is illustrative of where a conventional well head device such as that which is called a lubricator may be used within actual use of the pressure regulating system  200  of the present invention. 
         [0072]    The top layer of earth  227  called overburden and the rock formations  204  beneath the overburden  227  are illustrated. A break B in the length of the well casing  202  and bore hole  212  which may be for instance from about one hundred feet to thousands of feet is also shown. The sound source  1  is operational at any depth within the bore hole  212 . However, if a bore hole  212  is too shallow to supply enough hydrostatic pressure for the impulsive sound source  1  to produce an adequate sound pulse, the bore hole  212  may be pressurized to different levels of pressures until a pressure level is reached which provides sound pulses from the sound source  1  with enough intensity and sound characteristics to obtain acceptable high quality seismic records. The pressure regulating system  200  of the present invention may further provide automated adjustments to the pressures to maintain an initial pressure that is recorded at the initial depth of the seismic survey and using a computer processor of the controller adjust pressures to the initial pressure or a desired pressure based on the current pressure readings and/or intensity and characteristics of the seismic data acquired from the impulsive sound source  1  at a location and depth within the bore hole  212 . 
         [0073]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.