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CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application claiming the benefit of the priority date of U.S. application Ser. No. 12/637,255 (now U.S. Pat. No. 8,381,807), filed Dec. 14, 2009, which is incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a well stimulation tool for oil and/or gas production. More specifically, the invention is a hydraulically-actuated propellant stimulation downhole tool for use in a hydrocarbon well. 
         [0005]    2. Description of the Related Art 
         [0006]    In hydrocarbon wells, fracturing (or “fracing”) is a technique used by well operators to create and/or extend a fracture from the wellbore deeper into the surrounding formation, thus increasing the surface area for formation fluids to flow into the well. Fracing may be done by either injecting fluids at high pressure (hydraulic fracturing), injecting fluids laced with round granular material (proppant fracturing), or using explosives to generate a high pressure and high speed gas flow (TNT or PETN up to 1,900,000 psi) and propellant stimulation. 
         [0007]    Gas generating propellants have been utilized in lieu of hydraulic fracturing techniques as a more cost effective manner to create and propagate fractures in a subterranean formation. In accordance with conventional propellant stimulation techniques, a propellant is ignited to pressurize the perforated subterranean interval either simultaneous with or after the perforating step so as to propagate fractures therein. 
         [0008]    For example, U.S. Pat. No. 5,775,426 (issued Jul. 7, 1998), which is incorporated by reference herein, describes a perforating apparatus wherein a shell of propellant material is positioned to substantially encircle a shaped charge. The propellant material is ignited due to shock, heat, and/or pressure generated from a detonated charge. Upon burning, the propellant material generates gases that clean perforations formed in the formation by detonation of the shaped charge and which extend fluid communication between the formation and the well bore. 
       BRIEF SUMMARY 
       [0009]    A preferred embodiment of the invention having a flowpath therethrough includes a first section having an internal sidewall, an outer sidewall, and at least a portion of a propellant volume within the first section. At least one chamber is disposed in an annular portion between the outer surface of the tool and the flowpath, with a first end of each chamber positioned adjacent to the propellant volume. A detonator assembly is positioned in each chamber proximal to the propellant volume to, when actuated, cause ignition of the propellant. Actuation of the detonator assembly is caused by impact of a primer by a firing pin, which is caused to move by the pressure differential between the flowpath and a portion of the chamber. Ignition of the propellant causes pressure waves to be directed radially away from the tool and into the surrounding formation. 
         [0010]    Also according to the preferred embodiment, a plurality of flow ports is disposed through the exterior surface to provide for fluid flow into and out of the flowpath. A moveable sleeve assembly operates to prevent and permit fluid flow through the flow ports, depending on its position. In a first position, an insert sleeve substantially prevents fluid flow through the flow ports, while in a second position fluid flow is substantially permitted. The moveable sleeve assembly also prevents or allows pressure communication between the flowpath and each chamber to cause application of a hydraulic force to the firing pin. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]      FIG. 1  is a partial sectional elevation of the preferred embodiment of the present invention. 
           [0012]      FIG. 2  is a sectional elevation of a portion of the preferred embodiment more fully disclosing the middle sub and piston sleeve. 
           [0013]      FIG. 3  is a sectional elevation through section line  3 - 3  of  FIG. 2 . 
           [0014]      FIG. 4  is a sectional elevation through section line  4 - 4  of  FIG. 2   
           [0015]      FIG. 5  is a sectional elevation of a pressure chamber and firing pin of the preferred embodiment. 
           [0016]      FIG. 6  is a sectional elevation of a portion of the preferred embodiment wherein the sleeve assembly is in a disengaged state in a second position. 
           [0017]      FIG. 7  is a sectional elevation of the firing assembly and pressure chamber shown in  FIG. 5  wherein the firing pin has been released and has impacted the primer. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0018]    When used with reference to the figures, unless otherwise specified, the terms “upwell,” “above,” “top,” “downwell,” “below,” and “bottom,” and like terms are used relative to the direction of normal production through the tool and wellbore. Thus, normal production of hydrocarbons migrates through the wellbore and production string from the downwell to upwell direction without regard to whether the tubing string is disposed in a vertical wellbore, a horizontal wellbore, or some combination of both. In the figures, the arrow depicting flowpath  30  is pointing in the “downwell” direction (i.e., opposite the normal direction of fluid flow in the tool during production). 
         [0019]      FIG. 1  depicts a partial sectional elevation of a preferred embodiment of the present invention, which comprises a first section  20  having a mandrel  22  with an internal sidewall  24  and a ported sleeve  26  having a ported outer sidewall  28 . A flowpath  30  through the tool is partially defined by the substantially cylindrical internal sidewalls of the mandrel  22 , a top connection  32 , a middle sub  34 , a ported housing  36 , and a bottom connection  38 . The mandrel  22  is threadedly attached to the top connection  32  and the middle sub  34  at its upper and lower ends, respectively. A cylindrical propellant volume  46  is adjacent to and between the mandrel  22  and the ported sleeve  26 . 
         [0020]    The ported sleeve  26  has a plurality of circular pressure ports  40  spaced equally radially around the outer sidewall  28 , and is attached to the top connection  32  with a plurality of low head cap screws  42 . The bottom end of the ported sleeve  26  is attached to the upper end of the middle sub  34  with a series of interlaced tabs  44  positioned in slots  45  disposed in the outer surface of the middle sub  34 . 
         [0021]    A second section  48  of the tool includes a plurality of oblong flow ports  50  that define a fluid communication path between the flowpath  30  and the exterior of the tool. The flow ports  50  are equally spaced around, and disposed through, the cylindrical ported housing  36 , which has an upper end connected to the lower end of the middle sub  34  with a plurality of circumferentially-aligned grub screws  52 , and a lower end threadedly attached to the bottom connection  38 . Sealing rings  60  are positioned throughout the embodiment to prevent undesired fluid communication between the various elements, except through the flowpath  30  and through the plurality of flow ports  50 . 
         [0022]    A cylindrical pressure chamber  54  is disposed longitudinally through a annular portion  56  of the middle sub  34 . A detonator assembly  58  and firing pin  90  are located within the pressure chamber  54 , with the detonator assembly  58  located proximal to the upper end of the pressure chamber  54 . 
         [0023]    The middle sub  34  and ported housing  36  enclose a moveable sleeve assembly  62  having an attached ball seat  64  for selectively allowing communication through the flow ports  50  to the surrounding formation, as will be described infra. The sleeve assembly  62  is anchored in a first position by a plurality of circumferentially-aligned shear pins  66 . 
         [0024]      FIG. 2  is a sectional view of a portion of the preferred embodiment including the middle sub  34  and sleeve assembly  62 , which comprises a piston sleeve  68  coupled to an insert sleeve  70 . The sleeve assembly  62  is moveable between a first position and a second position, wherein in the first position the sleeve assembly  62  prevents fluid communication between the flowpath  30  and the exterior of the tool through the flow ports  50 . In the first position, the upper end of the piston sleeve  68  abuts a bottom profile  72  of the middle sub  34  to define a portion of the flowpath  30 . A first plurality of ports  74  provides a fluid communication path to the exterior of the piston sleeve  68 . A radially contractible firing pin locking key  76  is disposed circumferentially around the piston sleeve  68 . 
         [0025]    A lower section of the piston sleeve  68  has a larger interior diameter than an upper section. In the first position, the upper end of the insert sleeve  70  initially abuts the shoulder  78  defining the top end of the second portion, and is coupled thereto with a circumferentially-positioned expandable piston locking key  80 . The insert sleeve  70  is initially secured to the ported housing  36  with shear screws  66 . Upper and lower sealing rings  84 ,  86  are circumferentially disposed around the insert sleeve  70  to isolate the flow ports  50  from the flowpath  30 , thus substantially preventing communication between the flowpath  30  and the exterior of the tool. 
         [0026]      FIG. 3  is a sectional view through section line  3 - 3  of  FIG. 2  more fully disclosing the positioning of the three pressure chambers  54  disposed longitudinally within the annular portion  56  of the middle sub  34 , and showing first ends  88  of firing pins  90  (see  FIG. 2 ), which are orientated in the upwell direction. 
         [0027]      FIG. 4  more fully discloses the positioning of the shear screws  66  to secure the insert sleeve  70  to the ported housing  36 . The flow ports  50  are spaced equally radially around the ported housing  36 . The ball seat  64  defines an orifice  65  composing a portion of the flowpath  30 . 
         [0028]      FIG. 5  is a sectional view of the detonator assembly  58  and firing pin  90 . The firing pin  90  is within pressure chamber  54  proximal to an inlet  55 , and is retained in position by the firing pin locking key  76  engaged with a retention groove  100  circumferentially disposed around the firing pin  90 . The first end  88  of the firing pin  90  is pressure isolated from the second end  89  with a sealing ring  102 . The inlet  55  of each chamber  54  provides a fluid communication path to the flowpath  30 . 
         [0029]    The detonator assembly includes a primer  92 , primer case  94 , shaped charge  96 , and an isolation bulkhead  98 . The primer  92  is spaced above the firing pin  90  within the primer case  94 . The shaped charge  96  is positioned above and adjacent to the primer case  94 . The isolation bulkhead  98  is positioned adjacent the shaped charge  94  and proximal to the propellant volume  46 . In this position, detonation of the shaped charge will cause corresponding ignition of the propellant volume  46 . 
         [0030]      FIG. 6  is a sectional elevation of the preferred embodiment wherein the sleeve assembly  62  comprising the piston sleeve  68  and insert sleeve  70  is in a second position to allow fluid communication between the flowpath  30  and the surrounding formation through the flow ports  50  of the ported housing  36 . To shift the sleeve assembly  62  to this second position from the first position shown in  FIG. 1 , an appropriately-sized ball  104  is caused to flow down the wellbore and to engage the ball seat  64 . Engagement of ball  104  with the ball seat  64  seals off the flowpath  30  to prohibit fluid flow in the downwell direction through the orifice  65 . Thereafter, the well operator can cause the pressure within the flowpath  30  to exceed the shear strength of the shear pins  66  attaching (in the first position) the insert sleeve  70  to the ported housing  36 , which causes the shear pins  66  to fracture and detach the insert sleeve  70 . In  FIG. 6 , the shear pins  66  are shown in a sheared state. 
         [0031]    After shearing the pins  66 , increased fluid pressure within the flowpath  30  causes the insert sleeve  70  and piston sleeve  68  to move downwell until the lower section of the piston sleeve  68  contacts an inner shoulder  82  of the piston housing  36 . In this position, the piston locking key  80  expands into an adjacent flanged section  81  and decouples the insert sleeve  70  from the piston sleeve  68 . The insert sleeve  70  is thereafter allowed to continue downwell under the flowpath pressure until it contacts the bottom connection  38  (see  FIG. 1 ). The ported housing  36  further includes a locking section  106  that engages a ratchet ring  108  circumferentially disposed around the insert sleeve  70  to prevent upwell movement of the insert sleeve  70  after moving into the locking section  106 . 
         [0032]    Movement the sleeve assembly  62  to the second position causes hydraulic actuation of the firing pin  90  as follows. Engagement of the piston sleeve  68  with the interior shoulder  86  positions an outer groove  110  to allow the firing pin locking key  76  to radially contract thereinto. This contraction causes the firing pin locking key  76  to disengage from the firing pin  90 . 
         [0033]    As shown in  FIG. 7 , pressure thereafter communicated into the pressure chamber  54  causes the firing pin  90  to move upwell because of the pressure differential above and below the sealing ring  102 . In other words, because pressure upwell of the sealing element  102  is atmospheric, hydraulic pressure below the sealing element applies a hydraulic force on the second end  89  of the firing pin  90  resulting in upwell movement. 
         [0034]      FIG. 7  shows the detonator assembly  58  with the pressure chamber  54  after the firing pin locking key  76  has released the firing pin  90  and at the point of contact of the firing pin  90  with the primer  92 . The sealing ring  102  between the first end  88  and second end  89  of the firing pin  90  isolates pressure in the pressure chamber  54  upwell of the sealing ring  102  from the pressure in the flowpath  30 . After ports  74  are aligned with the inlet  55 , pressure within the flowpath  30  is communicated through the ports  74  into the pressure chamber  54  at a position below the sealing element  102 , resulting in a pressure differential that moves the firing pin  90  upwell to contact and detonate the primer  92 . Detonation of the primer  92  is contained by the case  94  and causes detonation of the adjacent shaped charge  96 , which transfers explosive energy to the propellant volume  46 , causing ignition thereof. The explosive energy is directed radially outwardly in the form of pressure waves through the circular ports  40  (see  FIG. 1 ) and into the surrounding formation. 
         [0035]    The present invention is described above in terms of a preferred illustrative embodiment of a specifically described team roping training apparatus. Those skilled in the art will recognize that alternative constructions of such an apparatus can be used in carrying out the present invention. Other aspects, features, and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims.

Summary:
A hydraulically-actuated propellant stimulation downhole tool for hydrocarbon wells. According to one embodiment of the invention, the tool comprises a first section having an internal sidewall defining at least a portion of a flowpath, and a ported outer sidewall and a propellant volume having at least a portion within said first section. An annular portion has at least one chamber having an end positioned adjacent to the propellant volume and an inlet providing a communication path to said flowpath. A detonator assembly is located within each chamber proximal to the propellant volume such that detonation of the assembly causes detonation of the propellant volume. A firing pin is propelled toward the detonation assembly by providing communication between the chamber and the flow path, causing a pressure differential between the pressure isolated ends of the firing pin.