Abstract:
The present invention relates to a jetting tool and method useful for inserting coiled or stick tubing further into subterranean wells, to permit additional production capacity to be realized from the well. The tool is located near a distal end of the tubing and can be used to generate and insertion thrust that facilitates insertion of the tubing.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims benefit of and priority to U.S. provisional application Ser. No. 61/359,978, filed Jun. 30, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to devices and methods for conveying a tubing work string, such as coiled tubing or stick pipe further into production or other subterranean wells, and in particular into lengthy and horizontal wells. 
       BACKGROUND 
       [0003]    Subterranean wells, such as oil and gas production wells, can be very deep and long extending, e.g., 12,000 feet underground. A production zone in such a vertical well might be only a few hundred feet in length or vertical height. 
         [0004]    Some production wells, e.g., wells in the Haynesville Shale area of Louisiana, can be 8,000 to 12,000 feet deep followed by, e.g., 5,000 to 10,000 feet of additional horizontal run. 
         [0005]    When setting a well up for production, tubing is inserted into the well, and sometimes into a well casing. Coiled tubing is commonly used for this purpose. A ported sub (also known as a ported nipple) is mounted at the end of the tubing, through which fluid is pumped as the tubing is inserted into the well. As the tubing is inserted into the well the fluid is pumped into the tubing, travels to the ported sub, and is generally discharged from ports in the ported sub in a transverse direction, i.e., in a direction that is at a right angle to the longitudinal axes of the tubing and/or the casing. The discharged fluid then returns to the surface via the annular space between the outside of the tubing and the inside of the well or casing. 
         [0006]    When coiled tubing is used, the coiled tubing (pipe) is unrolled from a spool. As long lengths of the tubing are inserted into the straight well or casing, friction develops between the external walls of the tubing and the internal wall of the casing. This friction can cause the tubing to buckle as long lengths are inserted. Additionally, radial rotation of the tubing to eliminate or prevent the buckling is not practical since in the case of coiled tubing the tubing is mounted on a supply spool, and rotating the spool for this purpose is not readily achievable. 
         [0007]    Substantial friction is also developed as straight tubing (stick pipe) is inserted into long horizontal runs. 
         [0008]    However, in many wells merely pumping the fluid down the tubing is insufficient to prevent buckling of the tubing when the tubing runs are very long, even when the fluid includes friction reducers, glass beads, and the like, in an attempt to free the tube. In such situations, when the tubing cannot be inserted sufficiently near the bottom or end of the casing, lost production opportunities result as reserves near the far end of the casing cannot be produced by the well. 
         [0009]    What is needed are devices and techniques to permit tubing, such as coiled tubing, to be further inserted into the casing of lengthy production wells so additional reserves can be produced. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention includes a jetting tool that can be mounted at a distal end (the far end, or lower end) of the tubing to further draw the tubing into the well. The jetting tool includes ports that have their discharge angled back towards the entrance of the well. The amount of angle is chosen to maximize the amount of downward thrust generated by the jetting tool, so it can assist with pulling the tubing further into the casing. Preferably the jetting tool has between four and eight jets, each directed toward the well head. The amount of fluid being pumped down the tubing can be about 2 barrels (bbl) per minute, with a differential pressure of about 400 to 500 psi (e.g., as measured at the surface). This amount can be varied to change the amount of insertion thrust provided. For example, flow rates up to about 10 bbl/minute can be used. This flow provides thrust that helps pull the tubing straight, assists in overcoming frictional force between the tubing and the casing, and helps move the tubing further into the well. 
         [0011]    One aspect of the invention features a jetting tool for inserting a tubing work string into a subterranean well, such as a hydrocarbon production well. The jetting tool is sized for insertion into the well and has a generally cylindrical body. The body has a proximal and a distal end, the distal end of the tool for insertion into the subterranean well, followed by the proximal end. The proximal end is configured to be attached to a tubing work string, such as coiled tubing or stick tubing. 
         [0012]    The jetting sub can have an interior supply channel within the body that is configured to receive a flow, e.g., from the tubing work string. It can also have a plurality of jets located at an exterior surface of the body, the jets being configured to receive the flow from the interior channel and angled to impart an insertion thrust to the tubing work string. The discharge flow from the jets creates the insertion thrust. 
         [0013]    The jets of the jetting tool can have a discharge angle J of between about 15 and 35 degrees, and there can be between about 4 and about 8 discharge jets on the jetting tool. 
         [0014]    The outer body of the jetting tool can have an outer diameter of between about 2 and about 4 inches. An inside diameter of the jets can be between about ⅛ and ½ inch, or about ⅜ of an inch. It can have between about 4 and 8 jets, and they can be configured in one row, or more than one row (e.g., two rows having four jets each). An embodiment has one row of six jets, having and inside diameter of ⅜ of an inch. The distal end of the jetting tool can be attached to a perforating gun, and the proximal end can be attached to a tubing work string, e.g., that provides the flow to the jetting tool. 
         [0015]    The invention also includes a method of inserting a tubing work string into a subterranean well through a surface well control head, such as a well head or a blow out preventer (BOP). The method facilitates insertion of a tubing work string into a subterranean well. It includes the steps of positioning a jetting tool near a distal end of a tubing work string, inserting the tubing work string through a surface well control head of the subterranean well (such as a BOP), and establishing a flow through the tubing into an interior of the jetting tool, such that the flow discharges the exterior of the jetting tool through a plurality of jets in the jetting tool. 
         [0016]    A discharge flow from the plurality of jets of the jetting tool is directed towards the surface well control head, thereby producing an insertion thrust that further advances the tubing work string into the subterranean well. The flow can be about 3 barrels/minute, which establishes a thrust of about 4800 lb/square foot. The flow can be from about 0.5 to 5 barrels per minute, or more, depending upon the needs of the well and the design parameters of the jetting tool (such as size and number of jets). A discharge velocity of the flow can be between about 20 to 60 feet per second, or more, depending upon the design conditions chosen for the well. It is possible to use more than one jetting tool for a well application, and the jetting tool can be machined from a combination of parts that are subsequently assembled. 
         [0017]    Use of this method can overcome sufficient frictional resistance to enable at least an additional 5 to 15% of additional tubing work string length to be inserted into the subterranean well. 
         [0018]    Another aspect of the invention includes a ported nipple for an in-ground production well, the ported nipple configured to be mounted at a distal end of a tubing work string, and including discharge jets. The improvement of the ported nipple includes angling the discharge jets at an angle of between 15 and 35 degrees toward a surface well control head of the production well, such that a flow exiting the discharge jets imparts an insertion thrust to the tubing work string. 
     
    
     
       SUMMARY OF THE FIGURE 
         [0019]    The foregoing discussion will be understood more readily from the following detailed description of the invention, when taken in conjunction with the accompanying drawings. 
           [0020]      FIG. 1  is a cross-sectional view of a subterranean well. 
           [0021]      FIG. 2  shows a demonstration of fluid being discharged through the ports of a jetting tool. 
           [0022]      FIG. 3  is a close-up view of a jetting tool according to an embodiment of the invention. 
           [0023]      FIG. 4  is a cross-sectional view of an embodiment of the jetting tool. 
           [0024]      FIG. 5  shows an end view of an embodiment of a jetting tool, which depicts a thread connection for mating directly with coiled tubing, without the need of a crossover (adapter). 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  is a cross-sectional view of a subterranean well. As explained in Example 1 below, such wells can be 12,000 feet deep and have a horizontal run of 5,000 feet. A perforating gun  105  can be near the end of the tubing work string, attached to a jetting tool  100 . 
         [0026]      FIG. 2  shows a demonstration of fluid being discharged through the ports of a jetting tool  100 . Depicted at a distal end of the jetting tool  100  is a perforating gun  105 . In some embodiments the perforating gun is replaced with a plug, such as a bull plug (not shown). An insertion thrust  125  is provided by a flow of fluid from a tubing working string (not shown), that supplies the flow to a proximal end of the jetting tool. 
         [0027]      FIG. 3  is a close-up view of a jetting tool  100  according to an embodiment of the invention. The jetting tool can have a generally cylindrical body  200  with an OD, e.g., of 2″ to 3″ (nominal). The jetting tool at the proximal end P is connected to the tubing, and can be machined to have threads that correspond with and mate to the threads of the tubing, such as a 2⅜″ PAC thread box. The other, distal end D of the jetting tool can have a common bull plug thread such that it can be connected directly to a perforating gun  105 . Alternatively, the second end of the jetting tool can be threaded, e.g., having a 2⅜″ 8rd (8 round) thread pin. 
         [0028]    The jets  225  in the jetting tool can have machined ports that extend inwardly toward the ID of the tool at the pin connector end. These ports are steeply angled at an angle J (e.g., 15 to 35 degrees from the longitudinal axis  250  of the jetting tool) toward the proximal end P to maximize downward thrust imparted to the tubing work string. More than one row of jets can be included about the circumference of the body, although only one row is depicted. 
         [0029]    The tubing can be, e.g., 1.25 to 2⅜″. A perforating gun mounted below the jetting tool can have a diameter, e.g., of 2.125 to 3.375″, so substantial friction can also be developed between the outside surface of the gun and the inside surface of the casing. 
         [0030]      FIG. 4  is a cross-sectional view of an embodiment of the jetting tool of  FIG. 3 . A plurality of jets  225  (only one is shown) can receive a flow from an interior flow channel  350 . The flow is then discharged through the plurality of jets at an angle J, thereby creating a downward insertion force due to the insertion thrust that is generated by the discharge flow. 
         [0031]      FIG. 5  shows an end view of an embodiment of a jetting tool, which depicts a thread connection  305  for mating directly with coiled tubing, without the need of a crossover (adapter). An interior flow channel  350  is depicted, through which a flow can enter the jetting tool at the proximal end P, before discharge of the flow through the jets  225  towards the proximal end P of the jetting tool. As shown, a bracket  360  supports the jetting sub at a distal end D of the jetting sub, before insertion into a well. 
       Example 1 
       [0032]    When running TCP (tubing conveyed perforation) guns on coiled tubing, or regular tubing (stick pipe) in long horizontal runs, large amounts of friction are created as the tubing is used to push the tools toward the bottom of the well. This friction causes the tubing to buckle and “stack out,” such that additional tubing cannot be inserted into the well. 
         [0033]    During the process fluid is constantly pumped down the tubing and circulates back to the surface on the outside of the tubing. This energy is available and can be used advantageously. This concept was tested in November, 2009 on a natural gas production well in the Haynesville Shale field in Louisiana. The well had been drilled to about 12,000 feet true vertical depth, followed by a horizontal run of an additional about 5,000 feet. The horizontal run is used to produce additional gas in the section, as it approaches the boundary of the next section (of land). 
         [0034]    A producing section in wells in this field can vary from about 300 to 800 feet of casing length. Thus, after perforation is complete, the horizontal portion of the well can have the production capability of 10 to 20 vertical wells. 
         [0035]    For the test on this particular production well, the tubing could not inserted beyond a length of 16,000 feet due to buckling/friction of the tubing work string within the casing. Another 550 feet of production length remained at the far end of the casing, into which the tubing could not be inserted. When a jetting tool using the present invention was installed on the tubing (between the end of the tubing and the perforating guns) insertion of the tubing for the additional 550 feet was achieved, representing a total insertion length of between 16,500 and 17,000 feet. The extra 550 of tubing insertion represents the production capacity of an additional vertical production well, offsetting substantial additional drilling costs to permit production of this portion of the gas field. 
       Example 2 
       [0036]    Testing has shown that for a jetting tool with six jets having jet inside diameters of ⅜ of an inch, a flow of 1 barrel per minute generates a thrust of about 670 lbs/square foot. Two barrels/min generates a thrust of about 2100 lb/square foot, and 3 barrels/min generates a thrust of about 4800 lb/square foot. In this embodiment, a flow of 1 bbl/min corresponds to a discharge velocity of about 20 feet per second from the jets. A flow of three bbl/min corresponds to a discharge flow of about 60 fps. These large insertion forces are responsible for obtaining the types of results exemplified above. 
         [0037]    The invention is useful for all types of subterranean wells, including wells being drilled that do not have a casing installed, and for wells for producing non-hydrocarbon products, such as water or hot water. 
         [0038]    While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made wherein without departing from the spirit and scope of the invention.