Abstract:
A unitary pumping tree is provided for forming part of a wellhead assembly christmas tree. The tree integrates a bottom connector, shut-off valve, hydraulically actuated blow-out preventer, mechanically actuated blow-out preventer, flow tee and top connector, within a body formed as a single piece of steel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a composite pumping tree for use in a production wellhead assembly. The tree is formed using a unitary steel body. The body has appropriate side openings for integrating a shut-off valve, blow-out preventer and flow tee with bottom and top connectors, to form the tree. The bottom connector is adapted to connect with a tubing head and the top connector is adapted to connect with an upper segment of a production christmas tree, of which the composite tree forms a lower part. 
     BACKGROUND OF THE INVENTION 
     The present invention has to do with wellhead equipment used in connection with pumping oil wells. More particularly, as previously stated, it relates to a composite pumping tree. By “composite” is meant that the functional components referred to herein as top and bottom connectors, shut-off valve, production blow-out preventer and flow tee are integrated into a single steel body. The term “pumping tree” is used to generically encompass the body or housing, its component openings, its axial fluid flow bore and the functional components if they are mounted in the body openings. 
     For many years, a typical conventional production wellhead assembly for a pumping well was as shown in FIG.  1  and comprised, from the bottom up: a flanged casing bowl attached to the well casing; a flanged tubing head having an internal hanger from which the well tubing string was suspended; a tubing head adapter having a flanged connection at its bottom end and a threaded connection of smaller diameter at its top end; a production blow-out preventer (“B.O.P.”) body having top and bottom threaded connections and including side openings for receiving the B.O.P. ram components; a flow tee body having a threaded or flanged side opening for connecting with a flow line; and additional components (not shown), such as a polish rod stuffing box and the rotary drive assembly for rotating the well&#39;s rod string to power a downhole progressive cavity pump. (The overall assembly extending up from the top of the tubing head to the drive assembly is commonly referred to as the production christmas tree.) 
     The production christmas tree, as described in the previous paragraph, is designed for use in connection with a pumping well. Since the tree is subjected only to relatively low pressure in service, its parts are relatively thin-walled. 
     There are some pumping wells which, when shut in, can build up significant pressure at the wellhead due to the presence of gas in the produced fluid. When the rod string is pulled from the well, to service the downhole pump, it would be desirable to have a gate valve in place between the tubing head and the production tree, to provide a positive and reliable shut-off. 
     In the case of a naturally flowing well, where greater pressures would be expected, one or more high pressure shut-off valves are stacked between the tubing head and the flow tee and the production B.O.P. is usually not included. 
     A recent improvement in the production wellhead art is disclosed in Canadian Patent 2,197,584, issued Jul. 7, 1998 to the present applicant. More particularly this patent teaches integrating the tubing head adapter, B.O.P. and flow tee into a unitary structure or tree by forging or casting a single steel body or structure forming an axial vertical fluid flow bore and further comprising, from the bottom up: 
     a bottom connector or connection sized and designed to connect and seal with the top connection of the tubing head; 
     a B.O.P. housing section forming side openings connecting with the axial bore, for receiving the ram components of a B.O.P.; 
     a flow tee housing section forming a side opening and providing means for connecting with a flow line; and 
     a top connector sized and designed to connect with the upper section of the christmas tree (typically with the stuffing box). 
     In a preferred form, the generally tubular &#39;584 tree has a generally cylindrical outer configuration, thereby ensuring a relatively thick body side wall of consistent thickness. 
     The &#39;584 tree has been characterized by certain advantages, more particularly: 
     the unitary tree is significantly shorter and stronger as a result of removing the threaded or flanged connections between the functional components. This is particularly useful in the case where a vibrating offset rotary drive assembly is mounted on the top end of the christmas tree for rotating the rod string of a downhole progressive cavity pump; and 
     the thick side wall of the cylindrical body is amenable to drilling additional openings from the side, for example for insertion of an instrumentation string to measure bottom hole temperature or pressure. This feature permits the tree to be customized to meet the particular needs of a customer. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, the tree body of the &#39;584 patent has been lengthened and formed to provide an additional side opening, beneath the B.O.P. openings, for receiving a shut-off valve. Thus a shut-off valve and a production B.O.P. are combined in a pumping tree to provide a shut off capability whether the rod string is parted at the polish rod or not. 
     While a typical 2{fraction (9/16)} inch shut-off gate valve having flanged connections might have a length in the order of 16.6 inches, we find that the same valve components, when mounted into the tree body opening, will add only about 6 inches to the body length. The resulting composite pumping tree is still short enough and strong enough to permit a rod string rotary drive assembly to be mounted and operated thereon satisfactorily. 
     In a preferred embodiment, the blow-out preventer used immediately above the shut-off valve is hydraulically operated. This has led to a problem because the B.O.P. operator (which protrudes externally of the body) and shut-off valve hand wheel can interfere if stacked directly above each other. This difficulty has been resolved by staggering or relatively off-setting them about the perimeter of the body. 
     As a final preferred addition, the tree body can be formed to provide a second pair of opposed B.O.P. component openings above the first pair and beneath the flow tee opening. The ram components of a manually operated B.O.P. are mounted into these openings. The resulting composite pumping tree is still sufficiently short and strong enough to permit a rod string rotary drive assembly to be mounted and operated thereon satisfactorily. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a wellhead for a pumping well comprising a conventional pumping tree formed of interconnected separate functional components; 
     FIG. 2 is a perspective view of a pumping tree in accordance with the present invention, with some of the component parts exploded to show their detail. The tree comprises a bottom connector for connection with a tubing head, a shut-off valve, a hydraulic production B.O.P., a manual production B.O.P., a flow tee and a top connector for connection with a stuffing box (not shown); 
     FIG. 3 is a side view of the assembled tree of FIG. 2; 
     FIG. 4 is a top plan view of the tree of FIG. 2; 
     FIG. 5 is a side sectional view showing the body of the tree of FIG. 2 with the functional components removed, with all bores/openings shown on same orientation for simplicity; 
     FIG.  5   a  is a plan view taken along the line A—A of FIG. 5, showing the integral hydraulic line of the hydraulic B.O.P.; 
     FIG. 6 is a side sectional view showing a bleeder valve and passageway for monitoring pressure between the hydraulic and manual B.O.P.&#39;s; 
     FIG. 7 is a side sectional view showing the body of a tree employing only a single B.O.P.; and 
     FIG. 8 is a side view showing the tree of FIG. 2 incorporated into a wellhead assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The pumping tree  1  comprises an integral body  2  formed as a single piece of steel. It is generally tubular, having an axial, vertical fluid flow bore  3  extending therethrough. It is also generally cylindrical externally to provide a body side wall  4  of generally consistent thickness, having a wall thickness/bore diameter ratio in the range of 1 to 1 or greater. 
     The body  2  has a bottom connector  5  for connection with the flanged top connection  6  of a tubing head  7 . The bottom connector  5  is shown as a studded down connection. However it can be a flanged connection, clamp-hub connection or rotatable flange connection as well. The face  8  of the connector  5  forms a seal ring groove  9  extending around the bore  3 , so that when a seal ring (not shown) is inserted and the connector  5  is tightened against the tubing head connection  6 , a fluid tight seal is obtained. 
     A valve housing section  10  extends up from and is integral with the bottom connector  4 . The section  10  forms a body cavity or opening  11  for receiving a conventional gate valve  12 . The opening  11  communicates with the bore  3 . The gate valve  12  is operative to open or close the bore  3 , as required. Its hand wheel and bonnet assembly  13  protrude externally of the body  2 . 
     A first B.O.P. housing section  15  extends up from and is integral with the valve housing section  10 . The B.O.P. housing section  15  forms diametrically aligned or opposed side openings  16  communicating with the bore  3 . The side openings  16  are formed to receive the ram assembly components  17  of a conventional hydraulically actuated B.O.P.  18 . The operator  19  of the B.O.P.  18  protrudes externally of the body  2 . 
     The valve housing opening  11  and B.O.P. openings  16  are offset or staggered so that the hand wheel and bonnet assembly  13  and B.O.P. operator  19  do not interfere. 
     A second B.O.P. housing section  20  extends up from and is integral with the first B.O.P. housing section  15 . The housing section  20  forms diametrically opposed side openings  21  communicating with the bore  3 . The side openings  21  are formed to receive the ram assembly components  22  of a conventional mechanically actuated B.O.P.  23 . 
     The second B.O.P. openings  21  are offset relative to the first B.O.P. openings  16 . 
     A flow tee housing section  25  extends up from and is integral with the second B.O.P. housing section  20 . The flow tee housing section  25  forms opposed side openings  26  communicating with the bore  3 . Each of the side openings  26  are shown having a studded connector  27  for connection with a flow line (not shown), through which well fluid is produced. 
     An internally threaded, studded top connector  28  extends up from and is integral with the flow tee housing section  25 , for connection with the stuffing box. 
     From the foregoing it will be seen that by integrating functional components into a one-piece body and off-setting the body cavities, we have been able to incorporate a shut-off valve in combination with two B.O.P.&#39;s into the pumping tree without exceeding an acceptable wellhead height. 
     In another feature, an integral bleeder valve system is provided in the body side wall to test whether the bottom B.O.P.  18  is leaking and to return leaking fluid to the bore  3 . More particularly, a passageway  30  extends from the bore  3  from a point between the B.O.P.&#39;s  18 ,  23  and connects back with the bore above the second B.O.P.  23 . A port  31  leads from the passageway  30  to the outer surface  32  of the body  2 . A pressure gauge (not shown) can be attached at the port  31  to monitor pressure in the passageway  30 . A second port  33  connects with the passageway  30  from the body surface  32  and a needle valve  34  is positioned therein to open or close the passageway. 
     As previously mentioned, any of a variety of known connections can be substituted for the studded connections shown in the drawings.