GB2168463A - A valve for a wellhead - Google Patents

Abstract

A valve for an oil well comprises a T-shaped valve housing (1) consisting of a horizontal valve cylinder (2) and a downwardly extending connection piece (3) adapted for connection to a wellhead (5). A valve piston (16) is arranged in the valve cylinder and has three distinct rest positions, which, respectively, provide "production" (BOP) modes of operation. In (PROD), "servicing access" (SWAB), and "blow-out preventer" the rest position of the valve required for the SWAB mode, the connection piece (3) aligns with a through-going transverse channel (20), formed in the valve piston, which in turn is aligned with a channel (12) extending through an upper wall of the valve housing and provided with means for connection to an upwardly extending service tube S. In the (PROD) position openings (25) and (26) connect wellhead (5) to output flange (10). In the (BOP) position all passages are closed. <IMAGE>

Description

SPECIFICATION A valve for a wellhead Technical Field This invention relates to a wellhead valve for use in the exploitation of sub-terranean hydrocarbon deposits. The invention has particular relevance to a wellhead valve employed in the extraction of oil and/or gas from an underwater oil well.

Discussion of Prior Art The wellhead of an underwater oil well is terminated at its upper end in a valve assembly (a so-called "tree"), which includes a wellhead valve which permits various valve functions to be performed namely, inter alia -a production (PROD) mode, -an access for service (SWAB) mode, -and a blowout preventer (BOP) mode.

A wellhead valve for an underwater oil well, comprises a substantially T-shaped valve housing having an elongated, substantially horizontally arranged valve cylinder with a first end section, a second end section and a midsection located between said end sections, as well as a substantially vertically arranged connection piece for connecting the valve housing to the wellhead. The connection piece extends downwardly from the mid-section, and the first end section is designed for connection to a production line ducting extracted hydrocarbon material away from the well. The internal surfaces of the valve cylinder define a cavity, which along a major part of the length of the valve cylinder has a symmetry axis and which includes a valve piston which can be located in a selected one of a first, second and third axial rest position.The wellhead valve also includes means for transmitting an axial operating force to the valve piston to move it into a selcted rest position.

The present invention seeks to provide the required valve modes in a sliding valve in a manner which has advantages from the points of view of operation of the valve and its manufacture.

Summary of the Invention According to the invention a wellhead valve of the kind discussed above is characterised in that the mid-section of the valve housing has a lower radially directed passage capable of providing a hydraulic connection between the cavity defined by the valve cylinder and the connection piece, and an upper radial passage which is connectible to a service tube, said radial passages and said connection piece having a common, substantially vertical center line, said valve piston having a first portion, which in the first axial position seals off both said radial passages, a second portion which contains a through-going radially directed channel, the radial center line of which in said second axial position substantially coincides with said common center line and places said radial passages into communication via said channel, and a third portion with a piston cavity which has an axially directed outlet opening and a radially directed inlet opening, said piston cavity, in said third axial position, being arranged in hydraulic connection with said connection piece via said inlet opening and said lower radially directed passage.

Desirably, when the valve is in its PROD mode, the production flow through the valve is accelerated in a throttle means prior to entry into the piston cavity, which is formed with its outlet at right angles to its inlet. The acceleration of the flow causes heavier particles (sand etc.) to continue straight on whereby their kinetic energy can become damped by impact against the upper surface of the piston cavity. This upper surface may be appropriately lined with a hard (ceramic) material or a soft (rubber) material. The entrained particles then continue with a reduced kinetic energy with the oil/gas flow out through the valve outlet. In this way the erosion of the sand particles can be reduced by virtue of the flow diversion which occurs in the valve.

In its SWAB mode, the valve provides a straight flowline without sharp edges which can interfere with the insertion of a service tool into the wellhead. If required, the access area to the wellhead can be improved to a pre-determined desired area by removing a withdrawable part of the valve housing. This enables the valve housing to be installed at an early stage of the preparation of the well and enables drilling to take place through the valve housing without the final sealing surfaces being damaged.

In its BOP mode, the valve piston is desirably positioned at the outermost part and such that the large piston area in the valve device is utilized when the valve assumes this position. In this way maximum force can be utilized, and also cutting of service tools in the SWAB position can be performed. The BOP mode should be able to be assumed independently of position transducers or other control equipment, since the BOP mode is ordered on the appearance of a pressure increase.

The wellhead valve is preferably designed so that the valve modes PROD and BOP are obtained when the valve piston is in its two outer positions, whereas the valve mode SWAB obtains by locating the piston in its central rest position by appropriate pressurization. Suitably some form of mechanical detent arrangement is available to locate the piston in its central position.

The valve piston is desirably provided with means which ensure that the slide adopts an orientated position in relation to the openings in the valve housing.

Brief Description of the Drawings The invention will be further described, by way of example, in the following with reference to the accompanying drawings, wherein Figure 1 shows a sub-sea wellhead valve according to the invention in perspective view, a horizontal top ring of the valve having been removed for the sake of simplicity; Figures 2, 3 and 4 each show a vertical section of the valve of Fig. 1 taken through the axis A shown therein and depicts the valve in its BOP mode, its SWAB mode and its PROD mode, respectively; and Figures 5, 6 and 7 each show a vertical section through the valve of Fig. 1 perpendicular to the axis A and through a vertical center line B shown in Fig. 1, these Figures, respectively, showing the same operating modes depicted in Figs 2, 3 and 4.

Description of the Preferred Embodiment In the drawings, 1 designates a substantially T-shaped valve housing of a wellhead valve.

The valve housing 1 has a horizontal, or substantially horizontal, valve cylinder 2 and a vertical, or substantially vertical, connection piece 3 cast integrally with the valve cylinder 2. The connection piece 3 has a flange 4 at its lower end which is intended to connect the valve housing 1 to a wellhead 5 of an underwater oil well. The valve cylinder 2 has a midsection 6 and two end sections 7 and 8. The end section 8 has a closure plate 9 flanged to it. The end section 7 terminates in a flange 10 for connection to a production line P (shown in dash lines in Fig. 1).

The valve housing 1 includes a body 11 removably located in the housing 1, the vertical external limiting surfaces of the body 11 lying in a circular cylindrical surface. The center axis of this cylindrical surface coincides with a symmetry line B of the connection piece 3. The body 11 is provided with a horizontally directed through-hole, the limiting surface of which constitutes part of the inner limiting surface of the valve cylinder 2. In addition, the body 11 has a passage 12 in its upper portion and a passage 13 in its lower portion. The passages 12 and 13 have circular cross-sections and their center lines coincide with the center line B of the connection piece 3. The radially outer surface of the body 11 is arranged with a very small play in relation to the confronting, curved surfaces of the valve housing 1.A plurality of circular sealing rings 14 are arranged one in each of a plurality of annular grooves in circular-cylindrical surface portions of the body 11, each groove being arranged to be coaxial with the line B. The lower end surface of the body 11 rests on an annular collar formed in the connection piece 3. Normally, the body 11 is retained in the position shown in Figs. 2 to 7 by means of a removable rop ring 15, which is secured to the mid-section 6 of the valve cylinder 2, for example with the aid of a plurality of vertical bolts (not shown) screwed into the mid-section.

A circular-cylindrical valve piston 16 is located in the valve cylinder 2. The valve piston 16 is in rigid mechanical connection, by way of a piston rod 17', with a drive piston 17, which can be driven in one direction along the symmetry axis A by being supplied with a pressure medium fed through a first fluid pressure connection 18', and in the other direction by being supplied with pressure medium fed through a second fluid pressure connection 19'. In a first axial position (see Fig. 2), the drive piston 17 makes contact with an annular shoulder surface 18, and a first end portion 19 of the valve piston 16 makes sealing contact with the passages 12 and 13, placing the valve in its "blowout preventer" mode (BOP).

In a second axial position of the valve piston 16 (see Fig. 3), a through-going channel 20, provided in the mid-section of the valve piston 16 and extending in the transverse direction thereof, is aligned with the radially directed passages 12 and 13 of the valve cylinder 2, which puts the valve in its "service acess" mode (SWAB). The passage 12 is provided with means (not shown) for connecting a service tube thereto. The service tube is shown in dash lines at S in Fig. 2. The required position of the valve piston 16 for the SWAB mode is defined when a piston ring 21 of the drive piston 17 engages in an annular groove 22 in the valve cylinder 2. The piston ring 21 has a circular or other suitable profile, which permits release of the ring 21 from the groove 22 and thus continued piston motion upon a moderate, but clearly indicated, pressure increase.

In a third axial position (see Fig. 4), the drive piston 17 makes contact with an axial projection 23 of the closure plate 9. A second end portion 24 of the valve piston 16 is then aligned with the passages 12 and 13. The end portion 24 has a cavity 24' formed therein which defines an axially directed outlet opening 25 leading to the line P and a radially directed inlet opening 26, communicating with the passage 13. In this piston position, the valve is in its "production" mode (PROD).

In this PROD mode, a spring 27, which surrounds the projection 23 (and is shown only in Fig. 3), is compressed, the spring force countering the axial force exerted on the valve piston because of the change in direction of the oil flow which occurs in the cavity 24 during extraction of oil from the well. The spring force preferably corresponds to at least 50% of the oil flow generated force. The spring 27 is advantageously dimensioned such that, in the event of a pressure loss from the hydraulic conduits connected to the connections 18' and 19', it is capable of moving the valve piston 16 to the position required for the BOP mode.

A telescopic rod 28 of non-circular crosssection is arranged with one end axially movable in a deep axially directed, non-circular hole 23' of the projection 23, and with the other end being arranged in a similar manner in a corresponding non-circular hole of the drive piston 17. The purpose of the rod 28 (shown only in Fig. 2) is to prevent rotation of the valve piston 16 about the axis A.

The cross-sectional area available for access to the wellhead 5 can be increased by partially dismantling the valve housing 1. This can be one by removing the closure plate 9, moving the valve piston 16 shown in Figs. 2-4 together with its drive piston 17 so far to the right as to clear the body 11, removing the top ring 15 and lifting the body 11 out of the valve housing by applying an upwardly-directed tensile force to the body.

The invention is not limited to the embodiment of wellhead valve illustrated since many modifications thereof are possible within the scope of the following claims.

Claims (8)

1. A valve for location between a wellhead of a well and a production line therefrom, which valve includes a substantially T-shaped valve housing having an elongated, substantially horizontally arranged valve cylinder having a first end section, a second end section and a mid-section located between said end sections, a substantially vertically arranged connection piece extending from said mid-section and adapted for connection of said valve housing to said wellhead, said first end section being adapted for connection to the production line, the internal surfaces of said valve cylinder defining a cavity which along a major part of the length of the valve cylinder has a symmetry axis, a valve piston slidably located in the said cylinder, means for defining a first, a second, and a third axial position of said valve piston within said cylinder, and means for transmitting an axial operating force to said valve piston to move the latter within the cylinder, wherein said mid-section has a lower radially directed passage capable of providing a hydraulic connection between said cavity and said connection piece, and an upper radial passage which is connectible to a service tube; said radial passages and said connection piece having a common, substantially vertical center line;; said valve piston having a first portion which in said first axial position seals off both said radial passages, a second portion which contains a through-going radially directed channel, the radial center line of which in said second axial position substantially coincides with said common center line and places said radial passages into communication via said channel, and a third portion with a piston cavity which has an axially directed outlet opening and a radially directed inlet opening; said piston cavity, in said third axial position, being arranged in hydraulic connection with said connection piece via said inlet opening and said lower radially directed passage.

2. A valve according to claim 1, in which said radially directed passages are provided in a body removably located in the valve housing.

3. A valve according to claim 2, in which the body providing the radially directed passages is a circular-cylindrical body having a center line coinciding with said common center line, said circular-cylindrical body being formed with a through-hole which is directed perpendicularly to said center line and the limiting surface of which constitutes part of the inner limiting surface of said valve cylinder.

4. A valve according to any preceding claim, in which two of said first, second and third valve piston positions correspond to axial outer positions of said valve piston.

5. A valve according to claim 4, in which said outer positions of the piston are determined by individual stop surfaces, which are fixed in relation to said valve cylinder, said stop surfaces in said outer positions making mechanical contact with, respectively, a first and a second surface portion, which are fixed in relation to said valve piston.

6. A valve according to claim 5, in which an intermediate position of said valve piston is determined as a position in which a resilient projection of the valve piston locates in a corresponding recess in the inner wall surface of said valve cylinder.

7. A valve according to claim 5, in which an intermediate position of said valve piston is determined as a position in which a resilient projection on the inner wall surface of the valve cylinder locates in a corresponding recess in the valve piston.

8. A valve for a wellhead substantially as hereinbefore described with reference to, and as illustrated in, the acompanying drawings.