Abstract:
A vibratory impact tool for loosening downhole stuck objects in oil or gas wells, utilizing an internal piston spring which is repeatedly compressed by hydraulic pressure, and repeatedly released by lifting a dart valve from a valve seat on a flow-through piston. When the dart valve is lifted from the valve seat by a tripping spring, flow resumes through the piston, quickly lowering hydraulic pressure above the piston, allowing the piston spring to sharply drive the piston against the housing. The dart valve is then reseated on the valve seat, causing the piston to again be driven against the piston spring, rapidly repeating the process.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of downhole jarring devices used in oil and gas well drilling and downhole equipment recovery. More specifically, it is a device that imparts rapid impacts to the desired portion of the work string or a stuck object, often referred to as a “fish”, for the purpose of loosening the stuck object. 
     2. Background Art 
     In well operation, there is often a need for jarring, impact or vibration devices to move downhole stuck members. Jars are typically included in a pipe or work string to provide upward or downward impacts when activated. Jars are usually single impact devices which must be recocked each time before operation, limiting the number of impacts per minute, and therefore limiting the energy, that can be delivered to a stuck member. 
     Some known impact tools require the operator to pull up on the work string with a force sufficient to pre-stress the work string, thereby providing the motive force for an impact. The impact is typically initiated when some type of valve or other triggering device in the tool triggers an action which applies the energy stored in the pre-stressed work string in the form of an impact delivered to the stuck object. The force of the impact delivered by such a tool depends upon how much energy is stored in the pre-stressed work string. That is, a larger over-pull will deliver a harder blow to the stuck object. 
     Often, in the use of this type of tool, the weight of the fish itself can be significant enough to raise the tension in the work string to such a high level that the tool will cease to function. More specifically, the force which can be applied to the triggering device by the flow of fluid is limited by the available fluid flow rate. The higher the amount of pre-stress tension, the harder it is to make the tool function. If the weight of the fish is too close to the pre-stress limit of the tool, the tool will cease to function as the fish begins to loosen. The operator then has to reduce the pre-stress on the work string to make the tool resume functioning, thereby limiting the force available in each impact and making the tool less effective. 
     Further, a tool which relies on work string pre-stress often has a fluid flow path which allows well bore return fluid to enter the tool, which exposes the internal tool parts to well bore debris. This can clog or restrict the moving parts and render the tool inoperative, it can cause failure of the seals, or it can cause the tool to wear out prematurely. 
     BRIEF SUMMARY OF THE INVENTION 
     The device of the present invention uses hydraulic power from surface pumps to repeatedly compress an internal piston spring in the tool. The piston spring is repeatedly allowed to expand, to deliver continuous rapid impacts. The sustained energy that is delivered to the stuck member becomes a motivating force to free the stuck member. When the operator desires, the fluid flow rate through the tool is increased to a selected level, which will exert sufficient hydraulic pressure to move a dart valve to seal against a valve seat on a flow-through piston. This cuts off flow through the piston and drives the piston and the dart valve downwardly. As the piston moves downwardly, it compresses the piston spring. At a designed tripping point, the dart valve is lifted away from the valve seat on the piston by a tripping spring, allowing flow through the piston to resume, sharply decreasing the hydraulic pressure on the piston. This allows the piston spring to drive the piston sharply upward, delivering an impact to the tool housing. Movement of the dart valve away from the piston seat is arrested by a momentary increase in hydraulic pressure above the dart valve, caused by a momentary cutoff of fluid flow through the dart valve. The dart valve is then driven downwardly again, and the cycle repeats rapidly. 
     The motive force for the impact is generated entirely within the tool, eliminating any need for prestressing the tool from above. This allows the tool to function regardless of the weight of the stuck object. No return fluid flow passes through the tool, eliminating the danger of contamination by well debris. 
     The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a longitudinal quarter section view of the tool of the present invention; 
     FIG. 2 is a partial section view of the tool shown in FIG. 1, prior to movement of the dart valve; 
     FIG. 3 is a partial section view of the tool shown in FIG. 1, after movement of the dart valve to seal against the valve seat on the piston; 
     FIG. 4 is a partial section view of the tool shown in FIG. 1, after further downward movement of the dart valve and the piston to compress the dart valve spring and the piston spring; and 
     FIG. 5 is a partial section view of the tool shown in FIG. 1, after separation of the dart valve from the valve seat, and after upward movement of the piston to impact the housing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The vibratory tool  10  of the present invention is shown in quarter section in FIG.  1 . It is comprised of an outer housing assembly made up of a top sub  12 , a shoulder stop  14 , a clutch  16 , a clutch housing  18 , a piston housing  20 , and a bottom sub  22 . The outer housing assembly provides means of transmitting tension and torque through the tool  10 . As tension is applied at the top sub  12 , it is transmitted to the clutch  16  through connecting threads. The clutch  16  is free to travel axially on the clutch housing  18 . The clutch  16  contains one or more seals  24  which prevent communication of fluid from the interior of the tool  10  to the exterior of the tool  10  during axial movement of the clutch  16 . Upward axial travel of the clutch  16  is limited by shouldering up against the shoulder stop  14 , which is threaded tightly against the clutch housing  18 . The shoulder stop  14  is prevented from backing off during operation of the tool  10  by one or more set screws  26 . Axial tension is passed from the clutch  16 , through the shoulder stop  14 , then to the clutch housing  18 , the piston housing  20 , and the bottom sub  22 . 
     Torque applied through the top sub  12  is transmitted through threads to the clutch  16 . The clutch  16  transmits torque to the clutch housing  18  through meshed fingers on both the clutch  16  and the clutch housing  18 . Torque is transmitted from the clutch housing  18  to the piston housing  20  and the bottom sub  22  via threaded connections. The outer housing assembly is sealed by a plurality of seals  24 ,  28 ,  30 , and  32 . 
     The fingered slip joint between the clutch  16  and the clutch housing  18  isolates the top sub  12  and the shoulder stop  14  from longitudinal impacts traveling upward through the clutch housing  18 , and reflects longitudinal shock waves back down through the clutch housing  18 , the piston housing  20 , and the bottom sub  22 , to the lower portion of the string or to the fish, not shown. 
     One or more upper and lower piston springs  34 ,  36  bias a piston  38  upwardly. The upper and lower piston springs  34 ,  36  are initially preloaded to give a selected upward biasing force against the piston  38 . The two lower piston springs  36  are separated by a lower piston spring retainer  40 , containing a wear guide  42 . The spring force from the lower piston springs  36  is transmitted to a mandrel  44  through a lower piston spring stop  46 , containing another wear guide  42 . The mandrel  44  is threaded into the bottom portion of the piston  38  to transmit the spring force from the lower piston springs  36  to the piston  38 . The mandrel  44  also serves as a guide to the upper piston springs  34 . One or more set screws  47  serve to help retain the mandrel  44  to the piston  38 . 
     A sleeve  48  and an upper piston spring stop  50  act to isolate the spring forces of the upper piston springs  34 , so they can transmit spring forces directly to the piston  38 , independently of the lower piston springs  36 . The two upper piston springs  34  are separated by an upper piston spring retainer  52 , containing a wear guide  54 . The piston  38  is free to move axially inside the piston housing  20  and the clutch housing  18 . The piston  38  is centralized by at least two wear guides  56 ,  58 . Piston rings  60  provide dynamic sealing between the piston  38  and the clutch housing  18 . 
     An impact ring  62  separates the piston  38  from the clutch housing  18  and restricts the upward axial movement of the piston  38 . Importantly, when the piston  38  moves upwardly, the impact ring  62  also distributes impact forces from the piston  38  to the clutch housing  18 . 
     The piston  38  is hollow, to allow fluid flow therethrough. Contained within the upper end of the piston  38  is an annular valve seat  64 . The valve seat  64  is retained to the piston  38  by at least one set screw  66  which lies beneath the upper piston ring  60 , to prevent backing off of the set screws  66 . The valve seat  64  is sealed inside the piston  38  by two seals  68 . 
     Inside the clutch housing  18  is a dart valve mechanism comprising a sleeve retainer  70 , a dart valve sleeve  72 , and a dart valve body  74 . The sleeve retainer  70  has holes therethrough, and the dart valve body  74  is hollow, to allow fluid flow therethrough. Surrounding the dart valve body  74  is a valve spring assembly made up of a spring stop  76 , a valve trip spring  78 , a standoff sleeve  80 , a standoff spring  82 , and a dart valve guide  84 . The dart valve guide  84  is held in place by an o-ring  86 . The spacing of the valve spring assembly is such that the valve spring assembly and the dart valve body  74  are free to travel axially. 
     The standoff spring  82  is weaker than the valve trip spring  78 , and the standoff spring  82  is spaced so that the dart valve body  74 , the spring stop  76 , and the valve trip spring  78  can be allowed an initial shift in the downward axial direction without compressing the valve trip spring  78 . This initial downward shift allows the dart valve body  74  to seal against the valve seat  64  in the upper end of the piston  38 , stopping fluid flow through the piston  38 . The standoff sleeve  80  prevents overtravel of the valve spring assembly in the downward axial direction. Upward movement of the valve spring assembly is stopped by abutment of the spring stop  76  against the dart valve sleeve  72 . The dart valve body  74  is concentrically located within the valve spring assembly, the standoff sleeve  80 , and the dart valve guide  84 . 
     After the standoff sleeve  80  contacts the dart valve guide  84 , a shoulder on the upper end of the dart valve body  74  seats against the spring stop  76 , so that as the dart valve body  74  travels downwardly, the valve trip spring  78  is compressed. Downward axial travel of the dart valve body  74  is limited by abutment of the spring stop  76  with an annular internal shoulder  88  on the clutch housing  18 . 
     Operation of the tool  10  is illustrated in FIGS. 2 through 5. FIG. 2 shows a close up of the tool  10  in the configuration in which it is run into the well bore. The standoff spring  82  provides an initial biasing of the dart valve body  74  toward an open position, spacing the dart valve body  74  away from the piston valve seat  64 , allowing flow through the tool. When the fluid flow rate is selectively increased by the operator to a critical flow rate, the increased fluid resistance of the dart valve body  74  causes the dart valve body  74  to move downwardly, compressing the standoff spring  82 , until the standoff sleeve  80  contacts the dart valve guide  84 , and the dart valve body  74  comes into contact with the valve seat  64 , as shown in FIG.  3 . At this point, the fluid flow through the tool  10  is shut off, and pressure begins to build against the upper end of the piston  38  and the dart valve body  74 . 
     This increased fluid pressure pushes the piston  38  downwardly, compressing the upper and lower piston springs  34 ,  36 , as shown in FIG.  4 . As the dart valve body  74  moves downwardly with the piston  38 , the dart valve trip spring  78  is also compressed, providing an increasing upward force against the dart valve body  74 . At the point where the downward hydraulic pressure force on the dart valve body  74  equals the upward force created by the dart valve trip spring  78 , the dart valve body  74  separates from the valve seat  64 , and the valve spring assembly suddenly retracts away from the piston  38 , as shown in FIG.  5 . 
     The upward momentum of the valve spring assembly and the dart valve body  74  is used to temporarily shut off fluid flow through the dart valve body  74 , to stop the valve spring assembly and the dart valve body  74  from overtravel in the upward direction. This is accomplished by restricting the fluid that can bypass the valve spring assembly. As the dart valve body  74  moves upwardly, the flow passage through the dart valve body  74  is gradually restricted as the flow path through the outside diameter of the dart valve body  74  is shut off by the inner diameter of the dart valve guide  84 . As the flow becomes restricted, pressure is built up above the dart valve body  74 , slowing the dart valve body  74 , the dart valve trip spring  78 , the standoff sleeve  80 , and the standoff spring  82 , until the upward travel of the dart valve body  74  and the valve spring assembly is halted. The pressure then returns the dart valve body  74  and the valve spring assembly to its operating position. 
     As the dart valve body  74  moves upwardly, the seal between the dart valve body  74  and the valve seat  64  is lost, causing a rapid drop in pressure above the piston  38 . Since the downward hydraulic pressure force is lost, the upper and lower piston springs  34 ,  36  cause the piston  38  to rapidly return and strike against the impact ring  62 , causing a sharp upward impact to be delivered to the clutch housing  18 , as shown in FIG.  5 . The dart valve body  74  then reseats on the valve seat  64 , and the entire cycle repeats numerous times each second. This process continues for as long as a sufficiently high rate of fluid flow is maintained through the tool  10  by the operator. 
     While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.