Abstract:
A method of manufacturing a flow block for use as a T-Block, tree block, manifold block or valve block, the method including: machining a main bore in a body; forming an opening in the body in a side wall of the main bore; providing an insert including a first bore intersecting with a second bore and being in fluid communication with each other; forming a substantially curved surface on at least part of the intersection between the first bore and the second bore; and inserting the insert into the opening, such that the first bore is substantially aligned with the main bore in order to provide a fluid flow path between the main bore and the second bore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of prior PCT Application No. PCT/GB2007/050501, filed 21 Aug. 2007, and entitled Flow Block, hereby incorporated herein by reference, which claims the benefit of EPO Patent Application No. 06119576.4, filed 25 Aug. 2006, and entitled Flow Block, hereby incorporated herein by reference. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND 
     In the art of oil exploration, a tree is a pressure safety device consisting of a tee-piece on a wellhead which allows vertical intervention and allows fluids to flow through a horizontal or angled lateral port into or out of the well bore. The flow junction in either a surface or subsea tree is achieved using a tree block. The junction is machined from a solid block because a welded junction would not meet the necessary integrity and bending moment requirements. The junction is generally at a 90° angle. 
     The parent metal of the body, usually steel, is rarely suitable to handle the range of fluids found and used in a production oil well. The possibility of corrosion, erosion, hydrogen or carbon dioxide embrittlement requires the wetted surfaces of the bores and the outer portions of the body itself to be protected. This protection is usually achieved by nickel alloy such as Inconel® lining the surfaces by continuous welding of a wall of nickel alloy material to the parent metal wall. When striking an arc, and until the weld is established, an inconsistent quality weld bead is laid which is not acceptable. The same occurs when the weld is stopped and started, which occurs when the weld gun has to traverse an opening or side port. To clad steel surfaces in nickel alloy is a complex welding procedure. To clad the surfaces of the bore using nickel alloy welding, an electric welding arc must be kept at a precise distance from the metal surface to ensure a consistent weld quality. At a junction on a tree block between a production bore and a side outlet, the rotating weld has to jump the bore and then resume once across. The quality when the weld arc is resumed can suffer. A known solution to this problem is shown in  FIGS. 1 a    to  c.    
       FIG. 1  shows a typical wellhead tubing hanger with its lower end on the right (the wellhead is not shown in  FIG. 1 ) at various stages in its manufacture.  FIG. 1 a    shows a cross section of a tubing hanger which has a substantially circular cylindrical body  10 . A bore  11  is machined in the body  10  which in use will provide a passage for production fluid or water injection fluid. An opening  12  is machined on the side wall of the body  10 . In use, either production fluid will flow from the bore  11  to the opening  12  or water or gas injection flow fluid will flow from the opening  12  to the bore  11 . The flow of fluid in  FIG. 1  is from the right hand side of the bore  11  to the opening  12 , or vice versa. 
     As described above, it is necessary to coat all well fluid wetted surfaces of the tubing hanger with nickel alloy. The surfaces that need to be clad are the inner surface  13  of the bore  11  and certain portions of the outer diameter  14  of the tubing hanger. To ensure a consistent well quality, a solid cylindrical nickel alloy plug  15  of circular cross section is inserted into the opening  12  as shown in  FIG. 1 b   . This results in the surface of the bore  11  and the outer diameter  14  of the body  10  having a substantially flush surface, all the way around the body  10 . In the next step, an electric arc is used to nickel alloy clad the body  10  to create cladding  16  on the surface of the bore  13  and cladding  17  on the outer diameter  14  of the body  10 . The nickel alloy plug  15  allows the electric arc to be kept at a constant distance from the outer diameter  14  of the body  10  when the arc rotates around the outside of the body, or the body is rotated around the arc. 
     The next step of the process is shown in  FIG. 1 c    where the center of the nickel alloy plug  15  is machined out leaving a sufficient amount of nickel alloy on the side walls of the opening  12 . As can be seen, all the well fluid wetted surfaces of the tubing hanger are now clad in nickel alloy. Although the process shown in  FIGS. 1 a  to 1 c    helps to provide a consistent weld quality, the use of a sacrificial nickel alloy plug is undesirable because it requires considerable machining time to bore out the plug. Alternatively, instead of using an insert plug, the opening  12  is welded solid using nickel alloy. 
     For pressure containing equipment, especially oil field hydrocarbon pressure containing equipment, the metallurgic consistency structure of the parent body to withstand the hydrostatic forces is paramount. The body must have an equal consistency throughout its shape. Precise geometric surfaces, which are required in this field, cannot be achieved by casting and hence the bores are machined in the solid forged body. 
     SUMMARY 
     According to at least one embodiment, there is provided a method of manufacturing a flow block for use as a T-Block, tree block, manifold block or valve block, the method comprising the steps of: machining a main bore in a body; forming an opening in the body in a side wall of the main bore; providing an insert having a first bore intersecting with a second bore and being in fluid communication with each other; forming a substantially curved surface on at least part of the intersection between the first bore and the second bore; and inserting the insert into the opening, such that the first bore is substantially aligned with the main bore in order to provide a fluid flow path between the main bore and the second bore. 
     The use of an insert reduces the machining time as described in relation to  FIG. 1 . In particular, the insert can be easily machined because of its compact size relative to the body. 
     The use of a curved surface reduced the level of turbulence in fluid when it flows around the junction in the body between the main bore and the opening. A reduction in turbulence allows the use of smaller bores. By “substantially curved surface” or “curved surface” we mean a smoothly curved surface or a series of sloped surfaces that approximate a curve. The curved surface may be formed by machining. 
     The intersection between the first bore and the second bore preferably defines a corner, about which fluid flows in use and the curved surface may be formed on the intersection at the inside of the corner of the fluid flow. 
     A substantially curved surface may be formed on the intersection at the outside of the corner of the fluid flow. 
     The curved surface may be formed around the entire intersection of the first bore and the second bore. The substantially curved surface may be formed as a convex surface. 
     The insert may be welded and sealed into the opening in the body. The welding may be nickel alloy welding. 
     The body and the insert may be formed from the same material or they may be formed from different materials. The insert portion may be formed from nickel alloy material. 
     The method may further comprise: forming a recess in the body in the side wall of the main bore, opposite the opening; and inserting the insert into the opening such that a part of the insert is located within the recess. 
     The insert may be inserted into the opening so that the main bore and the first bore are concentric; and wherein the insert is formed so that the diameter of the first bore is equal to the diameter of the main bore. 
     The insert may be inserted into the opening so that the main bore and the first bore are concentric; and wherein a part of the first bore has a larger diameter than the main bore such that the second bore extends into the recess. 
     The method may further comprise: forming a second opening in the body in the side wall of the main bore and inserting the insert into the second opening as well as the first opening. 
     According to at least a second embodiment, there is provided a flow block for use as a T-Block, tree block, manifold block or valve block, the block comprising: a body having a main bore machined in the body and a side bore, the body being formed in at least two portions, a first portion containing the main bore, and a second portion containing the side bore and the curved surface; wherein the side bore intersects the main bore and is in fluid communication with the main bore; and wherein a substantially curved surface is provided on at least part of the intersection between the main bore and the side bore. 
     The intersection between the main bore and the side bore preferably defines a corner about which fluid flows in use; and wherein the curved surface may be disposed on the intersection at the inside of the corner of the fluid flow. 
     The curved surface may be provided around the entire intersection of the main bore and the side bore. 
     The radius of the curved surface may be greater than 25% of the diameter of the side bore. 
     The radius of curvature of the curved surface may be approximately 50% of the diameter of the side bore. 
     The substantially curved surface may be a convex surface. At least one weld may be provided between the first portion of the body and the second portion of the body. 
     The first and second portions of the body may be formed from the same material or they may be formed from different materials. 
     The second portion may be formed from nickel alloy or Tungsten material. The side bore is perpendicular to the main bore or the side bore may be at a non-ninety degree angle to the main bore. 
     A recess may be provided in the body in a side wall of the main bore, opposite the side bore. 
     The block may further comprise a second side bore intersecting the main bore, the second side bore being in fluid communication with the main bore; wherein a substantially curved surface is provided on at least part of the intersection between the main bore and the second side bore. 
     According to at least a third embodiment, there is provided a flow block assembly for use as a T-Block, tree block, manifold block or valve block, the assembly comprising; a body having a machined main bore and an opening in the body in a side wall of the main bore; a preformed insert having a first bore intersecting with a second bore and being in fluid communication with each other; wherein, in use, the insert is inserted into the opening in the body such that the main bore and the second bore are in fluid communication with each other; wherein the insert is provided with a substantially curved surface on at least part of the intersection between the first bore and the second bore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be described with reference to the accompanying figures in which: 
         FIGS. 1 a  to  c    show cross sections of a prior art tubing hangar. 
         FIGS. 2 a  and 2 b    show cross sections of a block according to a first embodiment including a main bore and a side outlet. 
         FIG. 2 c    shows a cross section of a block according to the first embodiment including a main bore and a side outlet at a non-ninety degree angle to the main bore. 
         FIG. 3  shows a cross section of a block according to a second embodiment including a main bore and a side outlet. 
         FIG. 4  shows a cross section of a block according to a third embodiment including a main bore and two side outlets. 
         FIG. 5  shows a cross section of block according to a fourth embodiment including a main bore and a side outlet which forms an inlet for fluid injection. 
         FIG. 6  shows a cross section of a block according to a fifth embodiment including an enlarged body. 
         FIG. 7  shows a cross section of a block according to a sixth embodiment including an enlarged body. 
         FIGS. 8 a  and 8 b    show cross sections of a block according to a seventh embodiment including a main bore and a side outlet. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 2 a  and 2 b    illustrates a tree block in a tubing hangar comprising a body  20  having a main bore  21  for production fluid. The main bore  21  is machined in the body  20 . An opening  22  is machined in the side wall of the body  20  and extends into the main bore  21 . The tree block is formed when a side outlet (not shown) is connected to the opening  22  such that a fluid path is established between the main bore  21  and the side bore. The main bore  21  and the side bore are in this example, perpendicular, but there may be situations in which this is undesirable and they may be non-perpendicular as shown in  FIG. 2 c   . 
     In this example, a rectangular opening is formed in the side wall of the body  20  and this rectangular opening extends across the bore  21  into the opposite side of the bore  21  such that the diameter of the bore  21  is increased from an initial diameter shown at  21   a  to an enlarged diameter shown at  21   b . The insert  23  has a rectangular cross section which is why a rectangular opening is used. However, the insert can have a cross section of another shape and the opening in the body would be shaped to match that of the cross section of the insert. 
     An insert  23  having an outer shape corresponding to the opening  22  is then inserted into the opening  22 . The insert  23  is formed from nickel alloy material and consists of a machined first bore  24  and a machined secondary bore  25  formed at a right angle to each other. 
     The insert  23  is disposed in the opening  22  such that the insert&#39;s first bore  24  is aligned with the main bore  21 . This is achieved, as seen in  FIG. 2 a   , by the insert extending into the enlarged diameter formed by the opening  22  such that the insert&#39;s first bore  24  is aligned with and concentric with the main bore  21 . Fluid communication is thus established between the main bore  21  and the side outlet (not shown) via the first bore  24  and the second bore  25  of the insert  23 . 
     To meet corrosion and erosion requirements, the inner diameter  21   a  of the bore  21  is clad with Inconel®, by nickel alloy welding as shown at  26 . The nickel alloy cladding  26  extends from the insert  23  to each end of the tubing hangar. The insert  23  itself does not need to be clad because it is made of nickel alloy. The bore  21  is subsequently machined out to leave a smooth flush surface between the nickel alloy cladding  26  and the insert  23 . 
     The outer diameter  14  of the body  20  is also clad with nickel alloy at certain locations. To achieve a consistent quality weld bead on the outer diameter of the body, a sacrificial steel plug is located in the insert&#39;s second bore  25  in such a position that a surface of the sacrificial plug is substantially flush with the outer diameter of the body  20 , so that the entire circumference of the body  20  at the position of the insert  23  is solid. A nickel alloy cladding can then be welded onto the outer diameter of the body  20  with a consistent quality weld because there will be no breaks in the weld which will affect the quality of the weld. The sacrificial steel plug can subsequently be machined out. 
     The insert  23  also comprises a curved surface shown at  30  in  FIG. 2 a   . The curved surface  30  is disposed at the inside corner of the intended flow path of fluid between the main bore  21  and the side outlet (not shown). It has been found that the curved surface helps to reduce turbulence in the flow paths when compared to a conventional  900  inside corner used in prior tubing hangars. By 90° inside corner we mean that the inner surface of the bore  21  and the opening  22  meet at a right angle and form an edge. The curved surface  30  helps to prevent areas of recirculation around the corner when the fluid flows from the main bore  21  to the side outlet. The inventors of this application have investigated prior art tubing hangars and in particular the flow path between the main bore and the side bore which flows around the right angled edge of the 90° inside corner. A 90° inside corner is the norm in prior art tubing hangars because of the ease of machining. The inventors have learnt from computer modelling that the effective flow area in the prior art is reduced causing a maximum velocity increase of 79% because of the region of recirculated flow around the 90° inside corner and to achieve a suitable flow rate, the velocity of the flow actually has to increase. Therefore, a 90° flow path around the inside corner creates turbulent flow and the corresponding high velocity in the fluid causes high shearing within the fluid. In a multi-phased fluid (as is often found in oil production), foaming and emulsions are formed in the fluid. This is undesirable because the next process stage is often the separation of the phases. Because of the state of the fluid which has been subject to shearing, the fluid will require a long time to settle which results in a larger and more expensive separation infrastructure. 
     The use of curved surface  30  on the insert  23  allows the fluid to flow around the corner with only a 36% increase in maximum velocity and therefore with reduced turbulence and hence reduced shearing. Accordingly, the side outlet (not shown) can be manufactured with a smaller diameter (as compared to prior art side outlet) because all of the cross-sectional area of the side outlet is effectively used. This is particularly advantageous because it reduces weight and cost. Further improvements can be found by enlarging the diameter of the main bore  21  in the body  20  such that the maximum velocity of the fluid in the main bore  21  is reduced, which in turn reduces the turbulence in the fluid. This is shown in  FIGS. 8 a    and  8   b.    
     The insert  23  is machined from a solid block of nickel alloy during which the insert&#39;s first bore  24  and second bore  25  are formed. The corner between the bores  24 , subsequently machined by inserting a tool into the insert  23  (via the bores  24 ,  25 ) to create the curved surface  30 . It is only possible to machine the curved surface  30  because it is formed on the insert  23 . It is not possible to machine a curved surface on the body  20  of the tubing hangar directly because an appropriate angled machining tool can not be inserted through the main bore  21 . In this example the insert is machined, but it could also be forged or cast depending on the type of material used for the insert. 
     A further example is shown in  FIG. 3  where the insert  23  is provided with two curved surfaces  30  and  31  formed at the inside and outside corners of the flow path between the main bore  21  and the outlet bore. In use, when fluid flows from the main bore  21  to the outlet bore via the first bore  24  and the second bore  25  of the insert, the flow will tend to overshoot the second bore  25  (flowing towards the top of the tubing hangar as shown in  FIG. 3 ), and then doubles back on itself to flow out through side outlet via the second bore  25 . The provision of the second curved surface  31  helps to reduce the overshoot and the turbulence in the fluid that has “overshot” the second bore  25 . 
       FIG. 4  shows a further example of the invention where two side outlets will be provided, the insert  23  being modified to extend through the entire body  20  of the tubing hangar. The use of two lateral side outlets means that the two side outlets can each be of a smaller diameter compared to a single side outlet. For instance, if the diameter of the main bore  21  is seven inches (17.78 cm) then the diameter of each of the side outlets can be five inches (12.7 cm) each. An advantage of using smaller side outlet is that smaller valves can be used in the side outlets. 
       FIG. 5  shows a further example. In  FIG. 5 , the flow of fluid is from the side outlet to the main bore  21 , via the insert  23 . In this case, fluid is injected through the side outlet down the main bore  21 . The insert  23  is provided with a hydraulic buffer zone  40  opposite the second bore  25 . The hydraulic buffer zone  40  helps to prevent the injected fluid from damaging the interior surface of the bores. In this example, the insert  23  is machined in a similar manner to the insert shown in  FIG. 4 , that is with the second bore  25  extending completely through the insert. This allows the curved surface to be machined on both sides of the insert. Then the opening on the insert that is opposite the side outlet is plugged with an nickel alloy plug as shown at  41 . 
       FIG. 6  shows a further example. In this example the main bore  21  is located in a body  20   a  which has a greater cross sectional area than the bodies  20  previously described. The opening  22   a  in the body  20   a  therefore projects further into the body  20   a  than the openings  22  previously described. The insert  23  is inserted into the opening  22   a  and then a filler sleeve  50  is inserted into the opening  22   a  such that it abuts against the insert  23  as shown in  FIG. 6 . The filler sleeve  50  is typically fabricated from steel and forms a friction fit with the body  20   a . The wetted surfaces of the bores are clad with nickel alloy as previously described, along with the inner surface of the filler sleeve  50  such that nickel alloy cladding  26   a  forms a flush surface with the insert  23 . In  FIG. 6  a side outlet  51  is also shown. The side outlet is retained in place by bolts  52  and is sealed against the body  20   a  with a gasket  53 . 
       FIG. 7  shows a further example similar to the example shown in  FIG. 6 . In this example the main bore  21  does not extend completely through the body  20   a  and the insert  23   a  is modified such that the first bore  24  does not extend completely through the insert  23   a . A curved surface  54  is machined in the insert  23   a  on the outside corner of the fluid flow as well as the inside corner. 
     Further improvements can be found by enlarging the diameter of the main bore  21  in the body  20  such that the maximum velocity of the fluid in the main bore  21  is reduced, which in turn reduces the turbulence in the fluid. This is illustrated in  FIGS. 8 a  and 8 b    which shows a completion tubing of various diameters  27   a  and  27   b  connected to the body  20  at the end of the body  29 . The diameter of the bore at  27   a  is 5 inches and the diameter of the bore at  27   b  and within the body  20  is 7 inches. The diameter of the side outlet is 5 inches. The use of an enlarged main bore  21  also allows the curved surface  30  to be formed around the entire intersection of the main bore  21  and the side outlet. In this example, with an enlarged diameter bore and the curved surface formed around the entire intersection, the maximum velocity increase is only 15%. 
     The inserts described above are machined from a solid block of nickel alloy although they could also be formed from some other suitable material such as tungsten, Inconel®, Stellite®, or low alloy steel. If the insert is manufactured from tungsten it is not possible for the insert to be nickel alloy welded to the bore. Instead, the tungsten insert would have to be locked in by a flange on the side outlet or by a mechanical sleeve. A tungsten insert is hard enough to withstand the corrosion, erosion, hydrogen or carbon dioxide embrittlement caused by the production fluid or water injection fluid and so does not need to be clad. 
     The embodiments have also been described with reference to a tubing hanger. However, it should be noted that the invention is not limited to a tubing hanger and could equally be applied to any T-Block, tree block, manifold block or valve block. In the case of a tubing hanger, the insert should be made as compact as possible. This is because a tubing hanger is a critical structure support member in a wellhead and may have to support up to 500,000 pounds weight (227 tons). This load has to be supported by the parent metal of the tubing hanger and it is therefore desirable to minimize the amount of parent metal removed from the body of the tubing hanger.