Patent Publication Number: US-9404332-B2

Title: Well system with an independently retrievable tree

Description:
BACKGROUND 
     Conventionally, wells in oil and gas fields are built up with various components: a wellhead housing, a tubing hanger, a casing hanger, etc. Below those components is the drilled borehole for the well. Concentric casing strings are successively installed into the well to reinforce the drilled borehole. These casing strings are typically cemented at their lower ends and sealed with mechanical seal assemblies at their upper ends. Once drilled, the well is typically converted for production by landing a tubing hanger that supports a production tubing string. The production tubing string extends to the reservoir and provides a fluid pathway for directing hydrocarbons to the surface. At the surface, flow of the produced hydrocarbons from the reservoir is controlled by a series of valves that is colloquially called a Christmas tree (or tree). 
     Traditionally, there are two primary categories of trees—vertical and horizontal—that typically sit on top of the wellhead to control flow. In a vertical tree arrangement, the tree sits on top of a wellhead that supports the tubing hanger and, in turn, the production tubing string. The vertical tree has one or more production bores and contains valves extending vertically to respective lateral production fluid outlet ports in the wall of the tree. 
     Alternatively, the well may have a horizontal tree arrangement in which the tubing hanger is landed in the tree rather than the wellhead. A lateral production fluid outlet port in the tubing hanger is aligned with a corresponding lateral production port in the tree that leads to a production line, allowing for production through the tubing hanger and into the tree. 
     Each of these conventional arrangements has certain disadvantages. For example, to remove the production tubing string, which is supported by the tubing hanger landed in the wellhead, in a vertical tree arrangement, the vertical tree would have to first be removed, which can be costly and time consuming. With a horizontal tree, the tubing hanger that supports the production tubing string may be removed without removing the tree. But if it necessary to remove the tree, the tubing hanger and associated production tubing string is also removed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the various disclosed system and method embodiments can be obtained when the following detailed description is considered in conjunction with the drawings, in which: 
         FIG. 1  shows illustrative components of the presented well system; 
         FIG. 2  is an illustrative sequence for construction of the well system; 
         FIG. 3  is a second, illustrative sequence for construction of the well system; 
         FIG. 4  is a third, illustrative sequence for construction of the well system; 
         FIG. 5  is a fourth, illustrative sequence for construction of the well system; and 
         FIG. 6  is an illustrative final construction with barrier removed from the tubing hanger. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. 
     Accordingly, disclosed herein is a well system and sequences for construction of such. Some embodiments for a well system include a wellhead, a tree, a tubing hanger, a tubing spool located between the wellhead and the tree, and a production isolator connecting the tubing hanger production bore with the tree production outlet. The tree and production stab combination can be set up to operate as a production or horizontal tree. The tree can be changed in combination with the production isolator to operate like a horizontal or vertical tree, depending upon user preference. This system is designed such that the central bore of the tree is large enough for the tubing hanger to be installed and removed through the tree. Thus, the tubing hanger can be removed or installed independent of the tree. Furthermore, the tubing hanger sits within the tubing spool, and thus the tree can also be removed or installed independently of the tubing hanger and associated completion. 
     This well system can be constructed in a number of ways, providing ample flexibility in maintenance and operation of the well. One method embodiment includes connecting a tubing spool to a wellhead, installing a tubing hanger within the tubing spool, and then installing a tree and a production isolator simultaneously to the tubing spool. 
     A second method embodiment includes connecting a tubing spool to a wellhead, installing a tubing hanger within the tubing spool, installing a tree to the tubing spool, and then installing a production isolator within the tree. 
     A third method embodiment includes connecting a tubing spool to a wellhead, installing a tree to the tubing spool, installing a tubing hanger within the tubing spool through the tree, and finally, installing a production isolator within the tree. The system can be set up to operate either as a vertical or horizontal configuration 
     A fourth method embodiment includes connecting a tubing spool to a wellhead, installing a tree to the tubing spool, and installing a production isolator and a tubing hanger simultaneously within the tubing spool through the tree. 
       FIG. 1  illustrates the multiple parts that supply the framework of the presented system, and are simply used to give a detailed explanation of the overall working environment. A tree  102  is used in this system and is an assembly of valves, spools, and fittings used to contain, control, and regulate the flow for an oil well or gas well. A tree as such can also be used for any type of well, including surface or subsea hydrocarbon well, a water injection well, a water disposal well, a gas injection well, a condensate well, and other types of wells. Trees are used on both surface and subsea wells. These trees can be identified as either a “subsea tree” or a “surface tree,” and each of these classifications has a number of variations. 
     The primary function of the tree is to control, contain, and/or regulate the flow of fluids out of the well. A tree may also be used to control the injection of fluids into a non-producing well in order to enhance production rates of oil from other wells. When the well and facilities are ready to produce and receive oil or gas, tree valves are opened and the formation fluids are allowed to be produced through a flow line. 
     A wellhead  104  can be used without a tree  102  during drilling operations, and also for riser tie-back situations that later would have a tree installed at the top of the riser. However, the present system provides the flexibility to use and install the tree  102  independently in a number of different ways. 
     The wellhead  104  is the component at the surface of the well that provides the structural and pressure-containing interface for the drilling and production equipment. The primary purpose of the wellhead  104  is to provide the suspension point and pressure seals for the casing strings that run from the bottom of the hole sections to the surface pressure control equipment. Once the well has been drilled, it is completed to provide an interface with the reservoir rock and a tubular conduit for the well fluids. The surface pressure control is provided by the tree  102 , which is normally installed on top of the wellhead  104 , along with isolation valves and chokes equipment to control the flow of well fluids during production. The wellhead  104  can be welded onto the first string of casing, which is usually cemented in place during drilling operations, to form an integral structure of the well. The wellhead  104  provides a mechanism for casing suspension, tubing suspension, pressure sealing, etc. 
     More importantly, the wellhead provides a mechanism for attaching the tree  102 . 
     The presented system also includes a tubing spool  106  connected to the top of the wellhead  104 . Landed within the tubing spool  106  is a tubing hanger  108  with associated production tubing  107 , as shown in  FIG. 2 . The tubing spool  106  includes a shoulder surface that the tubing hanger  108  lands on, making it possible to suspend a production tubing string  107 , as shown in  FIG. 2 . The tubing spool  106  has a lateral opening through which oil, water, gas, air, or other fluids is fed into or from the annulus between the production casing string (the innermost casing string) and the production tubing in order to carry out production processes. A sealing and/or lock-down assembly is typically installed above the tubing hanger  108  to lock the tubing hanger in place and to ensure that the production tubing and annulus are hydraulically isolated. 
     The well system also includes a production isolator  110 . The production isolator  110  can include production environmental barriers  112   a,    112   b,  and  112   c  but need not include all three. For purposes of this discussion only, it will be assumed that all three barriers are used. These environmental barriers can be plugs that installed in the tree  102 . The environmental barriers  112   a,    112   b,  and  112   c  can also be a single valve or valve type mechanism integral to the production isolator  110 . Retrieval of the production isolator  110  allows for retrieval of the environmental barriers  112   a,    112   b,  and  112   c  simultaneously should they need servicing or replacement. The seals on the outside of the production isolator  110  that seal to the tree are also retrievable. Thus, all primary and secondary production barriers are retrievable at once. The production isolator is connected to the tubing hanger via a stab connection and ring seals. It is also possible to use a locking mechanism or any other suitable device for connecting the tubing hanger to the production isolator  110 . Further, a fluid connection exists from the production tubing  107 , through the production isolator, and to the production flowline of the tree. 
       FIG. 2  represents one of the multiple sequences of construction for the presented well system. In one embodiment, with the wellhead  104  already installed, the tubing spool  106  is connected to the wellhead  104 , and the tubing hanger  108  is installed within the tubing spool  106 . Finally, the tree  102  and the production isolator  110  are installed simultaneously; the tree  102  being connected to the tubing spool  106  and the production isolator  110  stabbing into and connecting with the tubing hanger  108 . 
       FIG. 3  represents another method embodiment for constructing the well system. Here, the tubing spool  106  is connected to a wellhead  104 , and a tubing hanger  108  is installed within the tubing spool  106 . Next, the tree  102  is connected to the tubing spool  106 . Finally, the production isolator  110  is installed within the tree  102 . 
       FIG. 4  illustrates yet another method embodiment to constructing the presented well system. First, the tubing spool  106  is connected to a wellhead  104 . Next, the tree  102  is connected and installed on the tubing spool  106 . The tubing hanger  108  is then installed through the tree  102  and within the tubing spool  106 . Finally, the production isolator  110  is installed within the tree  102 . 
       FIG. 5  illustrates yet another method embodiment to constructing the presented well system. As shown in  FIG. 5 , first the tubing spool  106  is connected to a wellhead  104 . Next, the tree  102  is connected and installed on the tubing spool  106 . The tubing hanger  108  and the production isolator  110  are then both installed through the tree  102  and within the tubing spool  106  simultaneously. 
       FIG. 6  shows a detailed view of the final production stackup of the well system, with the barrier removed in the tubing hanger  108 . The lower barrier would have to be removed (in the case of a plug) or opened (in the case of a valve). Because of the multiple sequences, as presented in  FIGS. 2-4  above, the presented system allows for installation and retrieval of the tubing hanger  108  and the associated completion system independent of the tree  102 . The present system also allows for installation or retrieval of the tree  102  independent of the tubing hanger  108  and the associated completion system. Furthermore, the production isolator  110  can be run or retrieved with the tubing hanger  108  and associated completion system. 
     There are multiple advantages to the presented invention. The tree, as well as the tubing hanger, can be installed or retrieved independently of one another. This feature of the system saves both time and cost when only one of the two needs to be pulled. In addition, it minimizes interruption of the operation of the well. Additional safety barriers can also be utilized. Further, the system has the flexibility to be used in either a vertical or horizontal production setup. This system also allows direct access from the top of the vertical bore without removal of barriers. Direct access can be achieved through a fluid connection from the top of the tree that extends around and outside the production isolator and around (or outside) the tubing hanger into the annulus within the wellhead. The large bore of this system allows the ability to drill through the tree. Batch completions can be done before or after the tree is installed, and even allow for 7″ bore to be sent through the tree. 
     Furthermore, no alignment of the tree to the tubing hanger spool is required; and no alignment of the production isolator to the tubing hanger or the tubing hanger spool is required. The production isolator is concentric with the vertical bore of the tree and is connected to the tubing hanger via a stab connection and ring seals. Thus, no alignment is needed from the production isolator to the tubing hanger. The tree is landed on the tubing spool and sealed via a stab connection. 
     Different embodiments for a well system and methods for constructing such systems are presented. The method embodiments provide flexibility for constructing, maintaining, and running the well system. For example, the tree and production isolator can be installed together, after installation of the tubing hanger. Another method embodiment can include installing the tubing hanger, tree, and production isolator separately in that order. Another embodiment can include installation of the tree, installation of the tubing hanger, and then installation of the production isolator. Other embodiments can include alternative variations. 
     These and other variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.