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FIELD OF THE INVENTION 
     This invention relates generally to water wells and more particularly to a method and apparatus for enhancing development of wells and rehabilitating existing wells that have lost capacity. 
     BACKGROUND OF THE INVENTION 
     Water wells and other wells that have been in production for a considerable length of time often lose capacity for a variety of reasons. One of the main reasons is that the well screen and/or the filter pack and surrounding formation fractures tend to become clogged with sand, clay, bacteria and other growths and materials that build up and impede entry of liquid into the well. 
     Various techniques have been used to restore lost capacity, including chemical injection, mechanical agitation, sonic energy application and electrical stimulation. None of these approaches has been entirely satisfactory. Chemical cleaning methods have typically involved pumping or gravity feeding chemicals into the well. The chemicals follow the path of least resistance which is usually not where the clogging takes place. Thus, conventional chemical injection has not been wholly effective. 
     Mechanical agitation of the well and screen from the inside dislodges scale and other built up material from the inside of the well. However, it does not affect the filter pack surrounding the well or the fractures in the surrounding formation, so deposit laden areas located outside of the well remain as a source of plugging. The use of sonic energy and electrical energy has been attempted but has not achieved widespread acceptance due largely to cost problems and lack of effectiveness. 
     SUMMARY OF THE INVENTION 
     Accordingly, a need remains for an effective way to remove material that clogs wells, well screens, and the surrounding filter pack and fractures, both in newly developed wells and in existing wells that have lost production capacity. It is the primary goal of the present invention to met that need. 
     In accordance with the invention, gas is applied under pressure in a sidewardly direction in the production zone of a well in controlled bursts. The pressurized gas creates shock waves that cause water and gas to flow outwardly and break down materials that have built up on the screen and also in the surrounding filter pack and formation fractures. At the end of each burst, a flushing effect ensues to draw the loosen particulate material into the well from the surrounding formation. These particles are then removed by a submersible pump or air lift assembly that forces water from the well to the surface. The gas bursts are generated throughout the entirety of the production zone of the well in order to thoroughly clean it and thereby significantly enhance its capacity. 
     Preferably, the gas bursts are controlled by a relief valve which is positioned down in the well and set to open when subjected to a selected pressure. When the relief valve opens, the gas is discharged sidewardly through side ports or through an open annulus so that the gas is applied directly to the well screen or louvers in a manner to maximize the dislodging of materials that plug the well. Mechanical agitation with agitating discs may be used along with the gas bursts. Chemicals may also be used and are particularly effective because they are carried by the gas outwardly into the formation where they can attack the deposits located there. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views: 
     FIG. 1 is a diagrammatic elevational view of a system that may be used to stimulate water well production in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a fragmentary sectional view similar to FIG. 1, but showing only part of the system and depicting a submersible pump in the well in place of an air lift assembly; 
     FIG. 3 is a fragmentary sectional view on an enlarged scale showing the detail identified by numeral  3  in FIG. 1; and 
     FIG. 4 is a fragmentary sectional view on an enlarged scale showing an alternative way of applying gas bursts in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in more detail and initially to FIG. 1, numeral  10  generally designates a well which may be used for the production of water or other fluids. The well  10  is bored into the surface  12  of the earth, and a casing  14  is installed in the well bore in a conventional manner. In the production zone or zones of the well  10 , a screen  16  is provided on the casing  14  in order to allow liquid from the surrounding formation to enter the well inside of the casing. 
     The well  10  is equipped with a production string which includes vertical piping  18  through which liquid from the well is delivered to the surface. A pipe  20  is connected with the lower end of the production piping  18  by a coupling  22 . At its upper end, the production piping  18  connects above the surface  12  with an elbow  24 . The elbow  24  connects through a valve  26  with a discharge hose  28  used to direct the water or other liquid from the well to a point of further use. 
     The water that is produced in the well  10  may be raised to the surface through the production string by an air lift assembly that includes an air lift line  30  connected with an air compressor  32 . Line  30  connects through a valve  34  with an elbow fitting  36 . The fitting  36  connects with a vertical line  38  that extends down through the production piping  18  in order to direct compressed air into the lower portion of the piping  18  to provide an air lift force for raising the water through the piping  18  and the discharge line  28 . 
     The elbow  24  may be provided with a lifting bracket  40  which allows the production piping  18  and the components carried on it to be raised and lowered in the well. A crane or boom (not shown) may be used for lifting of the bracket  40 . 
     FIG. 2 depicts an alternative arrangement in which the air lift assembly is replaced by a submersible pump  42 . The pump  42  may be an open or closed impeller pump having a housing  44  carried on the production piping  18  at a location immediately above pipe  20 . Within the housing  44 , the pump  42  is provided with a screen intake  46 . A pump cap  48  is provided at the upper end of the housing  44  where the pump connects with the production piping  18 . 
     In accordance with the present invention, compressed gas is supplied by a suitable source such as a bank of cylinders  50  (FIG. 1) containing a gas under pressure such as air, nitrogen or carbon dioxide. The cylinders  50  connect at their outlets with a supply line  52  leading to a fitting  54 . One outlet of the fitting  54  connects with an automatic flow loop  56  equipped with pressure gauges  58  and an automated flow control panel  60 . The loop connects with a cross-fitting  62  through a valve  64  which is controlled by the flow control panel  60 . 
     A manually operated flow path is connected with the other outlet of the fitting  54  in order to provide an alternative to the automatic flow control loop  56 . A flow line  65  connects with fitting  54  and extends to a cross  66  through a T-fitting  68  and a ball valve  70 . The T-fitting  68  is provided with a pressure gauge  72 . The cross  66  is similarly provided with a pressure gauge  74 . One of the connections for the cross  66  is provided with a ball valve  76 . A line  78  leading from the cross  66  to cross  62  provides a flow path along the manually controlled flow line. The cross  62  is provided with a relief valve  80  which opens in the event of application of excessive pressure. 
     In accordance with a preferred embodiment of the present invention, a flexible hose  82  extends from the outlet side of cross  62  down into the well  10  where it connects with a fitting  84  on the side of pipe  20 . The fitting  84  in turn connects with a vertical tube  86  extending downwardly inside of pipe  20 . As best shown in FIG. 3, tube  86  connects at its lower end with a bushing  88  on which a valve shroud  90  is carried. The shroud  90  contains a valve  92  which is capped at  94  on its lower end. The shroud  90  is provided with four (4) side ports  96  which are spaced equidistantly around the valve shroud. Gas nozzles  98  are threaded or otherwise secured in the ports  96 . 
     The valve  92  is a relief valve which may be of a type that is available commercially. The relief valve  92  can be set to open when a preset pressure is applied to it. For example, the valve may be set to open at any pressure setting between 50 and 1000 psi above hydrostatic pressure. When closed, the valve  92  is bubble tight to within 5 psi of the set pressure. When the valve  92  is closed, it blocks flow from the gas supply line  86  to the ports  96  and nozzles  98 . When line  86  is subjected to a pressure level equal to the setting of valve  92 , the valve opens and thereby applies air through ports  96  and  98  in bursts that are applied at the pressure level at which valve  92  is set to open. The flow rate of the bursts may be between 0.3 and 120 cubic feet per second. 
     The equipment in the well may include a double disk agitator assembly that includes a pair of agitating disks  100  located immediately above the nozzles  98  and another pair of agitators disks  102  located below the nozzles  98 . The disks  100  and  102  may be suitably carried on the lower end of the pipe  20 . The peripheries of the disks  100  and  102  are adjacent to the inside surface of the casing  14  and screen  16  so that the disks are able to provide mechanical agitation for removing scale and other deposits from the casing and screen. 
     Normally, liquid flows into the well through screen  16  and is delivered to the surface through the production string  18  by the air lift assembly or the submersible pump  42 . When the well becomes clogged to the extent that cleaning is desired, gas is applied from the cylinders  50  and flows to cross  62  along either the automatic flow control loop  56  or the manually controlled flow path provided by lines  65  and  78 . The gas is applied under pressure through the hose  82  to tube  86  and then to the relief valve  92  which remains closed until subjected to a pressure that exceeds its preselected pressure setting. When the gas pressure is sufficient to open the relief valve  92 , the valve pops open to provide a burst of gas through the nozzles  98  at a pressure equal to the setting of valve  92  and at a volume rate of flow between 0.3 and 20 cfm. 
     The gas bursts are applied directly to the side through the nozzles  98  to the screen  16 . The speed with which the gas is released by valve  92  generates a shockwave and a volume that forces the water outwardly to the side, thereby breaking down any materials that are built up on the screen or in the well, including sand, clay, bacteria, and other growths and materials. The energy of the gas bursts is sufficient to apply a shock wave to the surrounding filter pack and the fractures in the surrounding formation to loosen deposits in these areas as well. 
     When the valve  92  reseats due to the pressure dropping below the valve setting, the water displaced by the air bursts recovers and creates a flushing effect that draws the loosen particles from the filter pack and the fractures back into the well through the screen  16 . These particles are then carried to the surface by the rising gas bubbles or by the operation of the submersible pump  42  or the air lift assembly installed in the well. The sudden change in the water column that is generated by the burst of gas pulls additional particles into the well. 
     The cleaning assembly including the nozzles  98  is adjusted vertically up and down within the entirety of the production area of the well, and the procedure for cleaning involving the application of gas bursts is repeated so that the entire height of the production zone is subjected to gas bursts, thereby cleaning the entire screen  16  and applying the cleaning technique to the entirety of the producing area or zone of the well  10 . The lifting bracket  40  allows a crane or boom to move the cleaning equipment up and down. The entire production zone may be subjected to this cleaning procedure enough times to result in a situation where the discharge water is free of bacteria and/or fine materials built up in the well. The pumping by pump  42  and the air lift created by the air lift assembly, along with the agitation provided by the agitating disks  100  and  102 , enhances the ability of the cleaning equipment to dislodge the build up that may be encountered during development of a new well or rehabilitation of an existing well that is plugged. The velocities and pressure changes that result from the cleaning procedure facilitate removal of the materials that are dislodged from the well screen and adjacent areas. 
     Chemicals may also be injected into the well to enhance the cleaning effect. The chemicals may be applied by know techniques, and the chemicals are forced out through the screen  16  into the surrounding filter pack and formation fractures in order to dislodge materials from these deposit laden areas. The spent chemicals are eventually pumped or air lifted from the well for neutralization and disposal. After the chemicals have been removed, the well may be subjected to additional bursts of air and/or mechanical agitation followed by additional pumping and air lifting until the discharge water is substantially free of all traces of bacteria and particle matter. 
     FIG. 4 depicts an alternative arrangement that is used primarily for smaller diameter wells and/or wells that are provided with louvers  116  in place of screen  16 . Louver openings  116   a  are provided between adjacent louvers  116  which are typically inclined upwardly at an angle from the inside of the casing  14  to the outside of the casing. 
     In the arrangement shown in FIG. 4, the assembly of the nozzles  98  is replaced with a shroud  104  which includes on its upper portion a horizontal disc  106  and on its lower portion a conical plate  108 . The disc  106  and plate  108  are spaced apart to provide an interior chamber  110  between them. The outside edges of disc  106  and plate  108  are adjacent to the casing and louvers  116  and are spaced slightly apart to provide an annular discharge slot  112  through which the gas is applied. The chamber  110  is supplied with gas through ports  114  when the valve  92  is open. The plate  108  inclines upwardly as it extends toward the casing  14  and is preferably oriented at an incline that matches the upward incline of the louvers  116 . This allows gas flowing along the upper surface of the plate  108  and through the discharge slot  112  to flow in a direction to readily pass directly through the louver openings  116   a  to enhance removal of materials that may plug one or more of the louver openings. 
     The arrangement shown in FIG. 4 operates in substantially the same manner described previously. The principal difference is that rather than being discharged at discrete locations defined by the nozzles  98 , the gas is applied substantially continuously around the diameter of the well through the discharge slot  112 . Additionally, due to the incline of the bottom plate  108 , the air discharges from slot  112  at any desired angle matching the incline of the perforated openings  116   a.    
     From the foregoing it will be seen that this invention is one well adapted to attain all ends and objects hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.

Summary:
A method and apparatus for enhancing the production of newly developed water wells and existing wells that have suffered a reduction in capacity due to plugging. A gas line directs gas under pressure to a relief valve carried in the production string at a location in the production zone of the well. When the applied pressure reaches the pressure setting of the relief valve, the valve opens to apply air sidewardly in bursts which create shock waves to dislodge built up material from the well screen and the surrounding filter pack and formation fractures. Following each burst, the pressure conditions create a flushing effect which draws water back into the well along with the bacteria and particles that were dislodged. A submersible pump or airlift assembly in the production string then delivers the dislodged materials to the surface.