Patent Publication Number: US-8122949-B2

Title: Tapered sleeve and fracturing head system for protecting a conveyance string

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a regular application claiming priority of U.S. Provisional Patent Application Ser. No. 61/012,732 filed on Dec. 10, 2007, the entirety of which is incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to improvements to a fracturing head. More particularly, a fracturing head having a tapered tubular sleeve for intercepting, deflecting, and redirecting fracturing fluid downhole, protecting a conveyance string from eroding and improving the fluid dynamics of the fracturing fluid inside the fracturing head. 
     BACKGROUND OF THE INVENTION 
     When completing wells that are drilled vertically, horizontally or kicked off horizontally (meaning first vertical then horizontal), several formations may be encountered. These multiple formations may be completed in one run, so as to produce fluids or gases from the multiple formations up the well to maximize the production of the several formations. To complete multiple formations in a single run, a conveyance string, such as coil tubing may be used. The coil tubing, having the appropriate downhole tools attached, such as perforating tools, would be inserted downhole to the lowest formation. 
     Typically, a downhole tool, such as a brazer jet, operatively connected to a conveyance string, such as coil tubing, is placed adjacent the lowest formation and is used to gain access to the formation. After gaining access to the lowest formation, the brazer jet is raised uphole of the lowest formation and the formation is stimulated or fractured by pumping fracturing fluids down the annular space between the conveyance string and the wellbore. 
     Upon completing stimulation of the lowest formation, the coil tubing, and thus the downhole tool, is positioned to the next formation or interval of interest and the process repeated. 
     Similarly, other apparatus could extend though a fracturing head which are vulnerable to introduced fracturing fluids. 
     Fracturing fluids are typically introduced into the well from the surface through a multi-port fracturing head. The multi-port fracturing heads may have either angled side fluid ports or right angled side fluid ports. 
     Current multi-port fracturing heads or fracheads, have a main bore which is in fluid communication with a wellhead, the wellhead having a bore of the production tubing or conveyance string extending downhole. The frachead includes side ports which can be angled downwardly or directed at right angles to the main bore. Typically the side ports are diametrically opposed, directing the fracturing fluid at each other and colliding in the main bore. 
     To reduce the overall weight of the fracturing head, and the compressive load placed on a wellhead, the size of the fracturing head is usually reduced. Typically, fracturing heads with right angled side ports are shorter in height than fracturing heads with angled side ports. The shorter height reduces the overall size of the fracturing head and thus reduces the overall weight and load placed on the wellhead by the fracturing head. Further, the shortened height of the fracturing head allows the entire wellhead assembly to be significantly lower to the ground, improving accessibility, and safety for operational purposes. 
     However, regardless of the angle of the side ports, fracturing fluid entering the frachead is known to cause significant erosive damage to the internal surfaces of the fracturing head. The abrasive nature of proppant in the fracturing fluid coupled with the velocity and fluid dynamics of the fracturing fluid causes erosion of the internal surfaces of the fracturing head and the conveyance string, such as coil tubing. This is especially evident at high pumping rates. 
     In circumstances where the main bore of the frachead includes apparatus passing through the main bore, the fracturing fluid would directly impinge the apparatus. Apparatus passing or extending through the frachead include tubular and conveyance strings, such as coil tubing, wireline, E-line, slick line and the like. Herein, such apparatus will be referred to as conveyance string. 
     Higher pumping rates result in higher velocities of the fracturing fluid traveling inside the fracturing head, thereby increasing the erosive damage to the conveyance string. Completions with fluids which vary from low erosion gels to high erosion slick water or straight water (combined with a sand proppant and nitrogen or carbon dioxide) for the fracturing fluid create much higher erosive damage. 
     US Patent Application Publication No. 2003/0221838 to Dallas discloses a blast joint to protect a coil tubing string from erosion when abrasive fluids are pumped through the fracturing head. However, the blast joint taught by Dallas only protects the coil tubing from direct impingement of the fracturing fluid and does not deflect and redirect fracturing fluid into a wellbore. 
     It is also known to introduce fracturing fluids through fracturing heads with angled side ports, however these fracturing heads are necessarily taller, significantly larger and heavier. Using embodiments of this invention, by intercepting, deflecting and redirecting the fracturing fluid stream within a fracturing head and minimizing fluid velocities, the overall size of the fracturing head is minimized. A smaller fracturing head requires less material to manufacture, is lighter and therefore is easier, more economical and safer to operate. Using right angle side ports, the overall profile of the fracturing head is reduced. The low profile also eliminates the need costs associated therewith for a man basket, additional scaffolds and third party crane units typically required for larger fracturing heads having angled side ports. 
     SUMMARY OF THE INVENTION 
     Apparatus and system is provided for receiving fracturing fluids entering a fracturing head from side ports and re-directing them downhole for protecting a conveyance string extending therethrough. 
     Generally, a tubular tapered sleeve is fit to the fracturing head, the sleeve having an inwardly and downwardly angled tapered outer surface and a bore adapted to pass a conveyance string therethrough. The sleeve has a top portion adapted to fit a main bore of the fracturing head and a downhole portion extending sufficiently downwardly and adapted to be at least juxtaposed across from the side ports. At least the downhole portion is tapered. To retain the sleeve within the main bore of the fracturing head, the top portion of the sleeve can have an upset that is fit to a shoulder in the main bore for limiting downhole movement of the sleeve through the main bore. The sleeve could itself be of erosion resistance material or the tapered outer surface could be coated or hardened to increase its wear resistance. 
     Further advantage is gained by synergistic system between the sleeve and an embodiment of the fracturing head. Such a system comprises a fracturing head having one or more side ports that are in fluid communication with a main bore extending therethrough. The tapered tubular sleeve is fit to the main bore from a top end of the fracturing head, and the downhole tapered portion extends downhole to a position below the one or more side ports. The main bore uphole of the side ports corresponds to the top portion for supporting the tapered sleeve therein. The main bore above the side ports can be formed with a shoulder and the tapered sleeve with an annular upset which engages the shoulder for ensuring support of the tapered sleeve. 
     The main bore can be tapered to correspond with the tapered sleeve, thereby maximizing annular cross-sectional area for the fracturing fluid therethrough and improve fluid dynamics thereof. The main body of the fracturing head is angled or tapered to be substantially parallel to and along the length of the taper or angle of the tapered sleeve thus minimizing or eliminating fracturing fluid acceleration as the fracturing fluid travels through the annular space formed between the outer surface of tapered sleeve and the main bore of the fracturing head. The stabilized fracturing fluid travels down into the wellbore without causing abrasive damage to the conveyance string. 
     In a broad aspect of the invention, a fracturing system, for introducing fracturing fluid to a wellbore through a conveyance string is disclosed. The system has a fracturing head with a main bore extending therethrough. The fracturing head further has one or more side fluid ports spaced around the fracturing head, in fluid communication with a tapered downhole end of the main bore for introducing fracturing fluid into the fracturing head. 
     The system further has a tapered tubular sleeve, the sleeve having a sleeve bore for receiving the conveyance string, and an outer surface. The outer surface has a top portion fit to an uphole end of the fracturing head&#39;s main bore, and a tapered downhole portion extending downwardly and tapering radially inwardly, downhole from the top portion and at least juxtaposed from the one or more side fluid ports for redirecting fracturing fluid down the wellbore. 
     In another aspect, the tapered downhole end of the main bore is substantially parallel to and along the tapered downhole portion of the outer surface of the sleeve. 
     In  FIGS. 1-3 ,  5 A,  5 B, and  7 , various bolt holes and bolt recesses are shown. Not all holes and recesses are shown and corresponding fasteners have all been omitted. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a cross-sectional view of an embodiment of the present invention illustrating a low-profile fracturing head having opposing and right-angled side fluid ports; 
         FIG. 2  is a cross-sectional view of an embodiment of the present invention illustrating a low-profile fracturing head fit to a tapered adapter; 
         FIG. 3  is a cross-sectional view of the fracturing head and tapered adapter of  FIG. 2 , the fracturing head having a regular straight main bore; 
         FIG. 4  is cross-sectional view of side elevation of an embodiment of a tapered deflecting sleeve having a straight sleeve bore; 
         FIG. 5A  is a cross-sectional view of an embodiment of the system illustrating a tapered deflecting sleeve within a fracturing head having a tapered main bore; 
         FIG. 5B  is a close up view of an upset and shoulder; 
         FIG. 6  is a cross-sectional view of side elevation of an embodiment of a tapered deflecting sleeve with radially outward flares at a distal end of the sleeve bore; and 
         FIG. 7  is cross-sectional view of an embodiment of the present invention illustrating a tapered deflecting sleeve within a fracturing head having a tapered main bore, the deflecting sleeve having a flared sleeve bore at a distal end. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a fracturing head  1  is shown fit with a tapered deflecting sleeve  3 . The fracturing head  1  has a main bore  5  which receives fracturing fluid (not shown) introduced from side ports  6 . The tapered sleeve intercepts the fracturing fluid, deflects and redirects the fluid downhole to a wellbore. The tapered sleeve has a sleeve bore adapted to receive a conveyance string, such as coiled tubing. By intercepting the incoming fracturing fluid, deflecting and re-directing it downhole, the tapered sleeve  3  prevents direct impingement of the fracturing fluid with the conveyance string. The fracturing fluid, which could include proppants, is deflected and redirected to avoid erosive effects of the fracturing fluid. The general deflection and redirection of the fracturing fluid downhole reduces the velocity of the fracturing fluid, as the fracturing fluid passes by the conveyance string  2 , to further mitigate the erosive effects of the proppants in the fracturing fluid. 
     With reference to  FIGS. 2 and 3 , in another embodiment, a fracturing head  1 , having a tapered deflecting sleeve  3 , is shown fit to a downhole adaptor  20  to reduce the bore diameter. The adapter  20  has a tapered bore  21  for reducing the fracturing head bore  5  to a reduced bore  30   d  of the wellbore, the reduced bore  30   b  being about that of the sleeve bore  30 . 
     With reference to  FIG. 4 , a tapered deflecting sleeve  3  has a sleeve bore  30  for receiving a conveyance string  2 , and an outer surface  31 . The outer surface  31  has a top portion  32  and a tapered downhole portion  33 . In one embodiment, the top portion  32  has an upset  8  at an uphole end of the top portion  32  of the sleeve  3 . 
     With reference also to  FIGS. 3 ,  5 A, and  5 B the upset  8  is adapted for engaging a shoulder  9  at an uphole portion of the fracturing head&#39;s main bore  5 , preventing any downhole movement of the sleeve  3 . The top portion  32  further has an annular sealing element  11  between the main bore  5  and the outer surface  31  for sealing against the uphole movement of fracturing fluids. 
     The tapered downhole portion  33  extends downhole and is at least juxtaposed from the one or more side fluid ports  6  for intercepting fracturing fluid. The tapered downhole portion  33  is of sufficient length to provide a protective sleeve for the conveyance string  2  such that it intercepts the flow of fracturing fluid, redirecting the fracturing fluid downhole, and typically terminates within the fracturing head  1 , at a point downhole from the side ports  6 , such that the deflecting sleeve  3  does not extend beyond the main bore  5  of the fracturing head  1 . The outer surface  31  of the tapered downhole portion  33  progressively narrows radially inward in the downhole direction, an uphole diameter being greater than a downhole diameter. 
     The fracturing head  1  has diametrically opposing right angle side ports  6  and a deflecting sleeve  3  for protecting the conveyance string  2  is illustrated. The angled or tapered sleeve  3  envelops the conveyance string  2 , such as coil tubing, running downhole through the fracturing head  1 . The deflecting sleeve  3  is positioned within the fracturing head  1  to envelop that portion of the conveyance string  2  that is in the direct path of fracturing fluid entering the main bore  5  from the side ports  6 . The deflecting sleeve  3  provides a first layer of physical protection to this portion of the conveyance string  2  by intercepting fracturing fluid that would otherwise directly impinge that portion of the conveyance string  2  adjacent the side ports  6 , causing excessive erosion. 
     The tapered deflecting sleeve  3  further provides an additional layer of physical protection by aiding in deflecting and redirecting the entering fracturing fluid downhole, reducing any erosive effects of the fracturing fluid to a downhole portion of the conveyance string  2  not directly enveloped by the deflecting sleeve  3 . By deflecting the direction of the entering fracturing fluid downhole, the abrasive flow of the proppants in the fracturing fluid imparts less energy on the conveyance string  2 , thereby reducing the erosive effects of the abrasive fracturing fluid. 
     The tapered deflecting sleeve  3  has an inner diameter sufficiently large enough to allow the conveyance string  2 , such as coil tubing, to pass therethrough. The sleeve  3  could be of erosion resistance material, or may be hardened with tungsten or a diamond coating to increase its wear resistant properties. One suitable coating is HVOF coatings by Hyperion Technologies, Calgary, Canada, providing upwards of 90 Rockwell hardness. The HVOF coating optionally replaces hexavalent chrome coatings. 
     Best shown is  FIG. 5B , the deflecting sleeve  3  has an annular upset  8  adapted to engage an annular shoulder  9  formed at an uphole portion of the main bore  5 . The upset  8  and shoulder  9  causes the deflector sleeve  3  to firmly position within the fracturing head  1 , concentrically aligned within the main bore  5 . 
     The upset  8  and shoulder  9  method of connection avoids conventional threading connections between the deflecting sleeve  3  and the fracturing head  1 , as threaded connections may be vulnerable to the effects of hardening processes. Further, the upset  8  and shoulder  9  method of connection allows for quick and easy removal of the deflecting sleeve  3 , when removal of the sleeve  3  is required. 
     A top end  40  of the top portion  32  can be flush with an uphole flanged interface  10  formed between the fracturing head  1  and generic upper equipment. An annular sealing element  11  can be fit about the top portion  32  of the sleeve  3 , between the main bore  5  and the outer surface  31 , preventing the upward movement of fracturing fluid to the uphole flanged interface  10 . 
     In a system embodiment, as shown in  FIGS. 5A and 7 , the fracturing head  1  can have a tapered main bore  12 , increasing the annular cross-section  4  of the main bore  12 . The increased annular cross-section  4  further decreases the velocity of the fracturing fluid as the fracturing fluid enters the main bore  12  from the side ports  6 . This further reduction of the velocity of the fracturing fluid cooperatively improves the fluid dynamics of the passing fracturing fluid, even further reducing the erosive effects of the fracturing fluid on the conveyance string  2 . 
     The fracturing head  1  comprises a tapered main bore  12  to improve the fluid dynamics of the fracturing fluid flowing downhole. The taper or angle of the main bore  12  is substantially parallel with the taper or angle of the tapered downhole portion  33  deflecting sleeve  3 . The taper extends from about the side ports  6  to about a downhole termination of the sleeve  3 . 
     The tapered main bore  12  increases the annular cross-section  4  of the main bore  12 . The increased annular cross-section  4  further decreases the velocity of the fracturing fluid as the fracturing fluid enters the main bore  12  from the side ports  6 . This further reduction of the velocity of the fracturing fluid cooperatively improves the fluid dynamics of the passing fracturing fluid, even further reducing the erosive effects of the fracturing fluid on the conveyance string  2 . 
     For example, using a nominal 4″ side port, the cross-sectional flow area is about 13 sq. inches. For a fracturing fluid flow rate of about 1 cu. meter/minute, the velocity is about 6.5 ft/sec. Using a tapered main bore and a tapered deflecting sleeve, the annular cross-sectional area about the deflecting sleeve increases to about 32 sq. inches, reducing the velocity advantageously to about 3 ft/sec. As the fluid flow passes the downhole portion of the deflecting sleeve, the fluid enters a larger annular area. For a conveyance string  2  of 2-inch coiled tubing, the remaining annular cross-sectional area increases to about 36 sq. inches for a further reduction in fluid velocity to about 2.3 ft/sec. 
     With reference to  FIGS. 6 and 7 , in another embodiment, a tapered deflecting sleeve  3  is shown having a sleeve bore  30  with radially outward flares  34  at a distal end to allow unimpeded upward movement of the conveyance string  2  and attached downhole tools.