Abstract:
Disclosed is a fluid hammer tool with two separate fluid hammers in separate sections of the tool. The tool includes an upper poppet valve assembly along one fluid flow path, and a lower poppet valve assembly along a separate outer flow path. Both fluid flow paths are fed from an upper sub and both exit through a lower sub. Both poppet valves include spring return mechanisms. Sealing of each poppet valve propagates an upstream shock wave. The lower poppet valve assembly encounters greater fluid flow and generates a larger shock wave. In the period when the upper poppet valve is closed, the lower poppet valve cannot open.

Description:
BACKGROUND 
     When the movement of a fluid is suddenly obstructed, e.g., by valve closure, the kinetic energy of the moving fluid causes the fluid to be compressed in the immediate vicinity of the obstruction. The local expansion of the fluid which follows the maximum compression appears as a reversely directed pressure or shock wave that propagates through the fluid. This phenomenon is commonly referred to as a water hammer, even though carrier fluids other than water can be used to generate the same effect. 
     In oil and gas well drilling, it is common to use a down hole motor which is driven by a flow of incompressible fluid (preferably high specific gravity fluid drilling mud) which rotates an attached drill bit. The mud can also act to clear cuttings from the hole and provide down hole pressure control (and thereby inhibit blow outs). 
     However, particularly when drilling in rock and hard materials and when directional (i.e. non-vertical) drilling, there may be insufficient down hole weight on the drill bit to fracture rock and achieve an economically feasible rate of progress. A fluid hammer drill may be used to increase the rate of progress. Water is preferred for the fluid hammer because mud, with its high viscosity, tends to rapidly wear the internal surfaces of the hammer. 
     It may be preferred to have mud driving the drill bit rotation, and to also have a flow of water or other less dense fluid to drive the fluid hammer. A fluid hammer with impacts in more than one section, and where the impacts can form additive shock waves, is more preferred—including where drilling is done with coil tubing. 
     SUMMARY 
     A fluid hammer tool with two separate fluid hammers in separate sections of the tool is described. The tool includes an upper sub with a fluid inlet end and a longitudinal bore, and passages connecting the longitudinal bore to an outer bore, where the outer bore is defined by the interior of an outer barrel which connects the upper sub with a lower sub. A diffuser is downstream of the upper sub and has a main bore communicating with the longitudinal bore of the upper sub. The diffuser further includes exit passages having a smaller diameter than the main bore in fluid communication with the main bore. The exit passages feed a first chamber housing an upper poppet valve assembly. 
     The upper poppet valve assembly has a valve stem which can move downstream to seal a longitudinal bore of a lower poppet valve assembly, by contacting an upstream edge of a lower poppet valve assembly, and thereby prevent fluid flow from the first chamber into the longitudinal bore of the lower poppet valve assembly. Closing of the upper poppet valve generates a first fluid hammering impact, which is immediately followed by opening of the upper poppet valve assembly due to the lower pressure in the expansion zone which is generated, cavitation generated by the diffuser and the action of a first spring return mechanism. 
     The longitudinal bore of the lower poppet valve assembly is in fluid communication with a longitudinal bore of the lower sub—from which fluid exits the tool. The greatest outer diameter of all portions of the lower poppet valve assembly is less than the inner diameter of the outer barrel, such that there is a restricted flow path between the outer barrel and the lower poppet valve assembly. The lower poppet valve assembly can move downstream against a second spring return mechanism within the outer barrel to seal against the upstream edge of the lower sub, whereby a second fluid hammering impact is generated, immediately followed by opening of the lower poppet valve assembly due to the lower pressure in the expansion zone which is generated, cavitation generated by a restricted portion of the flow path between the lower poppet valve assembly and the inner surface of the outer barrel, and the action of the second spring return mechanism. 
     Where the first and second fluid hammering impacts are simultaneous (or nearly simultaneous, as there is a spatial separation between where they are generated which the second shock wave must travel through to add with the first), the shock waves will be additive and have increased energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a first embodiment of a dual impact fluid driven hammering tool provided by the present invention. 
         FIGS. 2A, 2B and 2C  are cross-sectional views of the first embodiment (as assembled) taken along its axis during various stages of its operation, but with the diffuser, nut, and all springs shown in perspective and not sectional view. 
         FIG. 3  illustrates a cross-sectional view of the diffuser used in the first embodiment. 
     
    
    
     It should be understood that the drawings and the associated description below are intended and provided to illustrate one or more embodiments of the present invention, and not to limit the scope of the invention. Also, it should be noted that the drawings are not be necessarily drawn to scale. 
     DETAILED DESCRIPTION 
     A first embodiment of a dual impact fluid driven hammering tool of the invention is shown in  FIGS. 1, 2A, 2B and 2C . As illustrated in  FIG. 1 , the dual impact fluid driven hammering tool  100  comprises an upper sub  102 , an outer barrel  104 , a lower sub  106 , a diffuser  108 , an upper valve body  110 , and an inner valve barrel  112 . In an assembled and operating dual impact fluid driven hammering tool  100 , pressurized fluid enters through upper sub  102  and exits through lower sub  106 . The term “upstream,” as used herein, denotes the direction opposite to flow of pressurized fluid i.e. from the lower sub  106  towards the upper sub  102 ; and the term “downstream” indicates fluid flow in the opposite direction—with the flow of pressurized fluid. 
     A lower poppet valve assembly within the dual impact fluid driven hammering tool  100  includes an upper piston  114 , a set of O-rings  116  which seal upper piston  114  against the interior of inner valve barrel  112 , a pilot shaft  118 , a compression spring  120 , an inner lower sub  122 , and a lower valve head  124 . Upper valve body  110  houses an upper poppet valve assembly, which includes upper poppet valve (valve stem)  126 , an inner spring  128 , an outer spring  130 , a valve frame  132 , a locking nut  134 , and washers  156 . In comparison with outer spring  130 , inner spring  128  is preferably shorter, has a smaller diameter (measured across the helical dimension), and offers higher resistance to compression. Thus, material of inner spring  128  may preferably have a greater gauge and/or resistance than that of outer spring  130 . 
     Upper poppet valve  126  is formed from a cylindrical portion  136  and a valve stub  138 . At the opposite end of cylindrical portion  136  from valve stub  138 , end  140  is externally threaded for being screwed with locking nut  134 . 
     An externally threaded end  186  of diffuser  108  is screwed into a threaded interior slot  142  (illustrated in  FIGS. 2A-2C ) of upper valve body  110 , which lies within the bore of outer barrel  104 . An internally threaded end  180  of upper valve body  110  is screwed together with externally threaded region  144  of upper sub  102  (lying near end  146  of upper sub  102 ). An externally threaded portion  182  proximal to end  184  of upper valve body  110  is screwed with internally threaded end  158  of inner valve barrel  112 . The valve frame  132  is screwed with an internally threaded portion of end  184  of upper valve body  110 . The other internally threaded end of  160  inner valve barrel  112  is screwed together with an externally threaded cylindrical portion  162  of the inner lower sub  122 . Upper sub  102  and lower sub  106  are screwed to opposite ends of outer barrel  104 . While threaded region  152  of the upper sub  102  is screwed with internally threaded end  164  of outer barrel  104 , the other internally threaded end  166  of the outer barrel  104  is screwed with externally threaded region  154  of the lower sub  106 . 
     Valve stub  138  and externally threaded end  140  lie on opposite sides of valve frame  132  with externally threaded end  140  proximal to upper sub  102 . Within upper valve body  110 , cylindrical portion  136  can slide within a central passage of valve frame  132 . Inner spring  128  and outer spring  130  surround cylindrical portion  136  and their assembly is locked between valve frame  132  and locking nut  134 , through washers  156  (as illustrated in  FIGS. 2A-2C ). The locking nut  134  is screwed with externally threaded end  140 . In the upper valve body  110 , downstream movement of upper poppet valve  126  (i.e. in a direction away from upper sub  102 ) initially requires overcoming compression resistance from outer spring  130  (which is longer than inner spring  128 ), and when the outer spring  130  is compressed to reduce its length below that of the uncompressed inner spring  128 , the compression resistance of both outer spring  130  and the inner spring  128  has to be overcome to continue to move upper poppet valve  126  in such direction. 
     The upper piston  114  is secured within inner valve barrel  112  by screwing its internally threaded end  168  with externally threaded end  170  of the pilot shaft  118 , which extends through the assembly of inner valve barrel  112  and inner lower sub  122 . Compression spring  120  surrounds the portion of pilot shaft  118  lying between upper piston  114  and inner lower sub  122 . Over the pilot shaft  118 , the ends of compression spring  120  are bounded by the upper piston  114  and inner lower sub  122 . The externally threaded distal end  172  of pilot shaft  118  lies exterior to inner lower sub  122  and is screwed with internally threaded end  174  of lower valve head  124 . The upper piston  114  along with the portion of pilot shaft  118  lying between upper piston  114  and inner lower sub  122  (which is also surrounded by the compression spring  120 ), slides within the internal cavity of inner valve barrel  112  and inner lower sub  122 . To provide a sealed interface between upper piston  114  and the internal surface of inner valve barrel  112  when the former slides through the latter, three O-rings  116  are provided on a grooved surface of upper piston  114 . Within inner valve barrel  112 , longitudinal displacement of upper piston  114  is restricted at one end by valve stub  138  of upper poppet valve  126  and at the other end, by end  162  of inner lower sub  122 . Similarly, longitudinal displacement of lower valve head  124  within outer barrel  104  is restricted between end  176  of inner lower sub  122  and end (or the upstream edge)  148  of the lower sub  106 . 
     When positioned as in  FIG. 2A , the assembly of upper piston  114 , pilot shaft  118  and lower valve head  124  can freely slide downstream, but movement towards lower sub  106  can be made only by overcoming compression resistance of compression spring  120 . When springs  128  and  130  are compressed (either partially or fully) such that upper poppet valve  126  is closed (valve stub  138  is in contact with the upper piston  114  at its upper surface  192 , sealing the bore along upper piston  114  etc., as illustrated in  FIGS. 2B and 2C ), the assembly of upper piston  114 , pilot shaft  118  and lower valve head  124  cannot freely move upstream towards valve frame  132 . However, closure of upper poppet valve  126  (and lower valve head  124 ), when the tool is operating, is momentary (see below). 
     The force to propel downstream movement of the assembly of upper piston  114 , pilot shaft  118  and lower valve head  124  is from pressure resulting from liquid entering upper sub  102 , which is then forced out of ports  194  and into chamber  204 , where the pressure on the uppermost surface  174  of lower valve head  124  forces the entire assembly downstream. The pressure downstream of lower valve head  124  is relatively lower than on its upstream side because fluid must flow through the relatively narrow passage between the outer surface of valve head  124  and the inner surface of outer barrel  104 , generating a reduced pressure zone downstream of valve head  124  and upstream of lower sub  106 . 
     Compression of compression spring  120  is at a maximum when end  178  of the lower valve head  124  closes and seals against end  148  of lower sub  106  (as illustrated in  FIG. 2C ), propagating a shock wave in the upstream direction. A low pressure zone following the shock wave, coupled with the force provided by decompression of spring  120 , moves lower valve head  124  (and its end  178 ) away from end  148  of the lower sub  106  (breaking the seal and allowing fluid to exit through lower sub  106 ), after which the cycle can repeat. As noted, the lower poppet valve assembly (including upper piston  114 , pilot shaft  118  and lower valve head  124 ) cannot move upstream if upper poppet valve  126  is closed, due to the pressure in chamber  202 . The fact that the outer diameter of lower valve head  124  is smaller than inner diameter of the outer barrel  104  generates cavitation (i.e., zones of wide pressure variation) due to a venturi effect during sliding of the lower valve head  124  within the outer barrel  104 . 
     In operation of dual impact fluid driven hammering tool  100  (which can take place sub-surface and preferably in conjunction with coiled tubing drilling operations), pressurized fluid enters through upper sub  102  and exits through lower sub  106 . Each of upper sub  102 , outer barrel  104 , inner valve barrel  112 , upper piston  114 , pilot shaft  118 , lower valve head  124 , and lower sub  106  include a longitudinal bore to permit fluid flow. The upper valve body  110  and inner lower sub  122  also include a longitudinal bore. Cylindrical portion  136  of upper poppet valve  126  resides in the longitudinal bore of valve frame  132 , and pilot shaft  118  extends through the longitudinal bore of inner lower sub  122 . While the interfaces of the longitudinal bores of valve frame  132  with cylindrical portion  136  and of inner lower sub  122  with pilot shaft  118  are sealed, pressurized fluid can flow from first chamber  200  into second chamber  202  through a set of passages  150  in valve frame  132 . The passages  150  in valve frame  132  are preferably distributed symmetrically around its axis. From second chamber  204  (unless valve stem  138  is sealed against upper surface  192 ) pressurized fluid get delivered into the longitudinal bore of lower valve head  124  by travelling through the continuous bore through upper piston  114  and pilot shaft  118 . 
     Fluid enters first chamber  200  through diffuser  108 , and more specifically, after fluid enters into diffuser  108 &#39;s longitudinal bore  300  which connects with four narrowed passages  302  (illustrated in  FIG. 3 )—causing cavitation within first chamber  200 , due to the venturi effect. The pressure is higher in first chamber  200  than in chamber  202  (which is fed through passages  150 ) which forces upper poppet valve  126  downstream and causes valve stub  138  to momentarily seal against upper piston  114 , generating a shock wave upstream. Thereafter, the following low pressure zone and the force from springs  128  and  130  force upper poppet valve  126  and valve stub  138  upstream—breaking the seal and thereby draining the fluid from second chamber  202  into the bore of upper piston  114 , and plunging the pressure within second chamber  202  and first chamber  200 . The continuous fluid flow into upper sub  102  then causes the cycle to repeat. 
     The dimension of longitudinal bore within each component may vary to provision a desired type of flow path within the component and/or to facilitate its alignment with other components. For example, the outer diameter of portion of pilot shaft  118  which slides through the inner lower sub  122  matches the diameter of the longitudinal bore of the inner lower sub  122 . Similarly, the diameter of outer surface of the upper piston  114  matches with the diameter of inner surface of the inner valve barrel  112  (and that surface is sealed with O-rings  116 ). 
     Within outer barrel  104 , the portion of the upper sub  102  covered by outer barrel  104  but exterior to upper valve body  110  includes multiple fluid flow passages  194  branching from the longitudinal bore of the upper sub  102 . Passages  194  feed chamber  204  formed between outer barrel  104  and the outer surface of upper valve body  110  and the connected portions including inner valve barrel  112 . Thus, fluid entering upper sub  102  follows one of two different fluid flow paths. 
     The first fluid flow path is formed along the longitudinal bores of upper sub  102 , diffuser  108 , upper valve body  110 , inner valve barrel  112 , passages  150 , upper piston  114 , pilot shaft  118 , inner lower sub  122 , lower valve head  124  and lower sub  106 . The second fluid flow path is formed by passages  194 , which permit flow into the chamber  204 , and then into lower sub  106 . Both flow paths merge into the longitudinal bore of lower sub  106 . In operation of fluid driven hammering tool  100 , a larger volume of fluid entering the upper sub  102  flows through the second fluid flow path. Since sealing of lower valve head  124  and end  148  of the lower sub  106  halts flow of a larger volume of fluid than does sealing of valve stub  138  of upper poppet valve  126 , it generates a larger pressure on sealing, and a larger hammering impact than does sealing of valve stub  138  of upper poppet valve  126 . 
     The fluid driven hammering tool  100  is connected in a coiled tubing set-up through upper sub  102  and lower sub  106 . Water or other fluid enters it through the end  188  of the upper sub  106 , and exits through end  190  of the lower sub  106 . 
     The hammering impacts generated by the sealing of lower valve head  124  and upper poppet valve  126  can take place at different intervals. But when impacts are simultaneously produced by both, or near simultaneously, a resonant or amplified impact having a larger amplitude shock wave and greater energy may be produced. As such, increasing the frequencies of hammering impacts generated by making and breaking of seals formed by lower valve head  124  and the upper poppet valve  126  will generally result in a greater frequency of simultaneous impacts and greater frequency of higher energy shock waves. Impact frequencies can be adjusted, especially increased, by increasing the fluid flow through adjusting the internal dimensions of passages  194 ,  300  or  302 , or the gap between the outer diameter of lower valve head  124  and the inner diameter of the outer barrel  104 . The fact that the lower poppet valve assembly (including upper piston  114 , pilot shaft  118  and lower valve head  124 ) cannot move upstream when upper poppet valve  126  is sealed (as shown in  FIGS. 2B and 2C ), may assist in bringing both these poppet valves into simultaneous closure (resulting in a greater frequency of higher energy shock waves) more often than would otherwise take place. 
     The foregoing description and embodiments are intended to merely illustrate and not limit the scope of the invention. Other embodiments, modifications, variations and equivalents of the invention will be apparent to those skilled in the art and are also within the scope of the invention, which is only described and limited in the claims which follow, and not elsewhere.