Subsea well assembly and assoicated method

Abstract

Subsea well assembly having a Xmas tree (107, 207) and wellhead (103). From a tubing hanger (113) a tubing extends into the well. A part of a production flow passage extends vertically from the tubing hanger (113) in a vertical bore (111) of the Xmas tree. A fail close production master valve (PMV) (117) is arranged in the production flow passage. The tubing hanger (113) is arranged below the Xmas tree (107), such as in the wellhead (103). The Xmas tree (107) exhibits a branch (115) that deviates from the vertical bore (111), which branch constitutes part of the production flow passage. The fail close type production master valve (PMV) (117) is arranged in the branch (115).

Claims

1. A subsea xmas tree configured to connect to at least one of: a wellhead located below the tree and comprising a tubing hanger, and a tubing spool located below the tree and comprising a tubing hanger; the tree comprising: a production flow passage having: a vertical bore extending through the xmas tree from the wellhead or tubing spool through an upper part of the tree, and a branch that deviates from the vertical bore, the branch located below the upper part; a plug profile in a top section of the vertical bore, the plug profile configured to lock an ESP plug such that the locked ESP plug seals the vertical bore, the ESP plug configured to control an Electric Submersible Pump (ESP); a fail-close type production master valve in the branch; and a production wing valve in the branch.

2. The tree of claim 1, wherein the production wing valve includes a fail-close type valve.

3. The tree of claim 2, further comprising a fail-in-place valve in the vertical bore below the branch.

4. The tree of claim 1, wherein the tree is configured to connect to a wellhead located below the tree and comprising a tubing hanger.

5. The tree of claim 1, wherein the tree is configured to connect to a tubing spool located below the tree and comprising a tubing hanger.

6. The tree of claim 1, further comprising a fail-in-place valve in the vertical bore below the branch.

7. The tree of claim 1, further comprising a tree cap installed in the upper part and configured to form a barrier between the vertical bore and an environment external to the tree.

8. The tree of claim 1, wherein the production flow passage does not comprise a sleeve, pipe, or tube within the vertical bore.

9. The tree of claim 1, further comprising a primary swab valve in the vertical bore above the branch.

10. A subsea production assembly comprising: a wellhead comprising a tubing hanger; a tree according to claim 4 connected to the wellhead; an ESP plug locked into the plug profile; and an ESP suspended downhole below the tree via a suspension string connecting the ESP to the ESP plug.

11. The assembly of claim 10, further comprising: a tree cap installed in the upper part of the tree; and an electrical wet-mate connector connecting the ESP plug to the tree cap.

12. A subsea production assembly comprising: a tubing spool connected to a wellhead and comprising a tubing hanger; a tree according to claim 5 connected to the tubing spool; an ESP plug locked into the plug profile; and an ESP suspended downhole below the tree via a suspension string connecting the ESP to the ESP plug.

13. The assembly of claim 12, further comprising: a tree cap installed in the upper part of the tree; and an electrical wet-mate connector connecting the ESP plug to the tree cap.

14. A method comprising: providing a tree according to claim 1 connected to a wellhead or a tubing spool; landing a BOP on top of the tree; suspending an ESP in a downhole position below the tree via a suspension string connecting the ESP to the ESP plug; and removing the BOP.

15. The method of claim 14, further comprising connecting a tree cap to the upper part of the tree.

16. A method comprising: providing a subsea assembly comprising: a wellhead comprising a tubing hanger, or a tubing spool connected to a wellhead and comprising a tubing hanger, and a subsea xmas tree connected to the wellhead or tubing spool and comprising: a production flow passage comprising: a vertical bore extending through the xmas tree from the wellhead or tubing spool through an upper part of the tree, and a branch that deviates from the vertical bore, a plug profile in a top section of the vertical bore, the plug profile configured to lock an ESP plug such that the locked ESP plug seals the vertical bore, the ESP plug configured to control an Electric Submersible Pump (ESP); an ESP plug locked into the plug profile; a fail-close type production master valve in the branch; a production wing valve in the branch; and an ESP suspended downhole below the tree via a suspension string connecting the ESP to the ESP plug; opening the production master valve and production wing valve; and activating the ESP to aid production through the production flow passage.

Description

EXAMPLE OF EMBODIMENT

(1) Having described the invention in general terms above, a non-limiting description of various embodiments will be given in the following with reference to the drawings, in which

(2) FIG. 1 is a principle sketch of a subsea well assembly according to a first embodiment of the invention;

(3) FIG. 2 is a principle sketch of a subsea well assembly according to a second embodiment of the invention;

(4) FIG. 3 is a principle sketch of a subsea well assembly according to yet another embodiment of the invention, wherein the assembly includes a tubing head spool;

(5) FIG. 4 is a principle sketch of a subsea well assembly according to yet another embodiment of the invention, wherein the assembly includes a tubing head spool;

(6) FIG. 5 is a principle sketch of the embodiment shown in FIG. 2, wherein an ESP (not shown) is suspended from the XT; and

(7) FIG. 6 is a principle sketch of the assembly shown in FIG. 1, however with the XT removed and with a blowout preventer landed on the wellhead.

(8) FIG. 1 shows a first embodiment of the present invention. A subsea well assembly 100 is installed on the seabed 101. It has a well head 103 from which a casing 105 extends into the seabed 101. A subsea Xmas tree 107 is connected to the well head 103 with a connection means 109. The Xmas tree 107 has a vertical bore 111 that aligns with the well head 103 and extends towards the top part of the Xmas tree 107.

(9) Within the well head 103 there is arranged a tubing hanger 113 from which a production tubing (not shown) can depend and extend into the well. When producing from the well, production fluid flows upwards through the tubing and into the vertical bore 111 of the Xmas tree 107.

(10) The vertical bore 111 of the Xmas tree 107 is in connection with a branch 115 that extends horizontally out from the vertical bore 111. The horizontal branch 115 constitutes part of the production flow passage through the Xmas tree 107. Hence, a fail close type primary master valve (PMV) 117 is arranged in the branch 115. As described above, the fail close type valve will close if hydraulic actuation pressure is lost, and thus close the flow passage. Downstream of the fail close type PMV 117 there is also arranged a production wing valve (PWV) 119 in the branch 115. The production wing valve 119 is also of the fail close type, and will constitute a back-up for the fail close type PMV 117.

(11) Above the branch 115, the vertical bore 111 of the Xmas tree 107 is provided with a primary swab valve (PSV) 121. This valve may be a hydraulically operated gate valve or a manual valve which will be closed during production. Above the PSV 121 the vertical bore 111 has a plug profile 123, adapted to be engaged by a plug (not shown in FIG. 1). During normal production, the PSV 121 will be closed and will constitute the primary barrier between the production fluid flowing in the production passage (bore 111 and branch 115) and the environment. As a second barrier, one may either arrange a plug in the plug profile 123 or install a tree cap on the top of the Xmas tree 107.

(12) In the left wing of the Xmas tree 107, opposite of the branch 115, there are various channels and valves associated with the annulus.

(13) FIG. 2 is a similar principle sketch illustrating a second embodiment of the present invention. This embodiment is also a subsea well assembly 200 according to the present invention. The assembly 200 is identical to the first embodiment described above with reference to FIG. 1, except that a lower production master valve 220 (lower PMV) is arranged, as an addition, in the vertical bore 111 of the Xmas tree 107, below the position of the branch 115. The lower PMV 220 is, for reasons to be described further below, not of fail close type. In stead, it is adapted to be opened and closed by the operator, such as by means of hydraulic control or by mechanical means.

(14) The comparable components of the various embodiments in this specification are given corresponding reference numbers, except for the first digit. For instance, in this second embodiment, as illustrated in FIG. 2, the various components are designated with a three digit number, the first of which corresponds to the numbering of the embodiment, such as 2 in this second embodiment. As an example, the PSV in the first embodiment (FIG. 1) is designated as 121 while the PSV in the second embodiment (FIG. 2) is designated as 221.

(15) FIG. 3 and FIG. 4 show a third and fourth embodiment of the present invention, which except for an added tubing spool 325, 425, substantially correspond to the first and second embodiment, respectively. As shown in FIG. 3 and FIG. 4, a tubing spool 325, 425 is added between the well head 303, 403 and the Xmas tree 307, 407. Furthermore, instead of landing the tubing hanger 313, 413 in the well head 303, 403, the tubing hanger 313, 413 is landed in the tubing spool 325, 425.

(16) Having described various embodiments of the subsea well assembly according to the invention above, an application of the assembly will now be described, wherein an electrical submersible pump (ESP) is used to increase the flow through the production tubing.

(17) ESP-assisted Production

(18) FIG. 5 illustrates the well assembly 200 described above with reference to FIG. 2, adapted for production with the aid of an ESP (not shown). In the plug profile 223 in the upper part of the vertical bore 211 of the Xmas tree 207, there is installed an ESP plug 227. From the ESP plug 227 a coiled tubing 229 is suspended. The coiled tubing 229 contains means by which to convey power and signal to the ESP. At the end of the coiled tubing 229 the ESP is arranged and adapted to pump fluid upwards through the tubing (not shown). The ESP is arranged within the bore of the tubing.

(19) When the coiled tubing 229 extends through the Xmas tree 207 and its vertical bore 211 in this manner, the lower PMV 220 and the PSV 221 will be in open position. To prevent the lower PMV 220 from closing while the coiled tubing 229 extends through it, it is not of the fail close type, as discussed above.

(20) When installing the ESP plug 227, a downhole safety valve arranged in the tubing, some distance into the well, is closed. A blow out preventer (BOP) (not shown) is landed on the Xmas tree 207. Then the ESP, suspended at the end of the coiled tubing 229, is lowered through the BOP, the vertical bore 211 of the Xmas tree, and down into the tubing suspended from the tubing hanger 213. At the upper end of the coiled tubing 229 is the ESP plug 227, which is locked to the plug profile 223 of the Xmas tree 207. The ESP plug 227 seals against the vertical bore 211 and makes, together with the closed downhole safety valve, two barriers. The BOP is then removed, and a tree cap 231 is landed and sealed to the upper part of the Xmas tree 207. Electrical wet-mate connectors (not shown) constitute an electrical interface between the ESP plug 227 and the tree cap 231. An electrical cable (not shown) extends from the tree cap 231, through which the operator can control the ESP.

(21) Opening the PWV 219 and the PMV 217 in the branch 215, which valves have been closed during installation of the ESP, opens the branch 215 for production flow.

(22) It should be noted that the described embodiment with the ESP also is employable with the first, third and fourth embodiment described above, that is without the lower PMV 220 and with or without a tubing spool 325, 425. In addition, the ESP could also be cable-suspended.

(23) FIG. 6 illustrates a situation wherein the tubing hanger 113 is being installed in the wellhead 103. In this situation the Xmas tree 107 is not yet landed onto the wellhead 103. Within the tubing hanger 113 there is arranged a removable wireline plug 113a. The tubing hanger 113 is installed through a blow out preventer (BOP) 135 landed on the wellhead 103.