GB2181471A

GB2181471A - Improvements relating to subsea wells

Info

Publication number: GB2181471A
Application number: GB08520602A
Authority: GB
Inventors: Brendan Herd
Original assignee: Advanced Production Technology Ltd
Current assignee: Advanced Production Technology Ltd
Priority date: 1985-08-16
Filing date: 1985-08-16
Publication date: 1987-04-23
Also published as: GB8520602D0

Abstract

The first part 2 of an electrical connection is associated with a wellhead 8. The second part 4 is associated with a spoolpiece 5 which is mounted on the wellhead 8 before the Xmas tree 9 is connected. The first part 2 is carried by tubing hangers 3 and is the male part of the electric connection. The second part 4 is the female part and is carried by a square shaft axially movable and non-rotatably mounted in spoolpiece 5. The shaft is moved downwardly to make the connection by a threaded bonnet and square drive 7 operated by a diver or remotely operated vehicle. <IMAGE>

Description

SPECIFICATION Improvements relating to subsea wells This invention is concerned with improvements relating to subsea wells, and more particularly to an improved manner of electrical connection at the wellhead of a subsea well.

In a subsea gas/oil/water injection well, a steel casing depends from a wellhead located on the sea bottom, which casing contains the production tubing. Pressure/temperature gauges located at the bottom of the production tubing provide information which is transferred up the tubing by independent cables to the wellhead prior to terminating at a data acquisition system (DAS) located on the outside of the wellhead.

Due to the nature of the running procedure an electrical connection has to be made at the wellhead, which requires an underwater mateable connector. In the simplest case of a non-flowing well where the wellhead is initially open to the sea, conditions exist which enable a diver unrestricted access to perform this task providing the water depth is less than 350 m. However, when used on a live well unrestricted access is not available and this connection is made remotely by placing one half of the connector in the tubing hanger (which is set in the welihead) and the mating half in the underside of the so-called Xmas tree. An existing connector is available which is designed to perform this task on a live well; however, due to the critical tolerances involved it has a somewhat blemished reliability record.

Due to the time constraints and physical complexity involved in running a tree, if the connector does not mate first time the system is normally not retrieved for repair and is left in the dead state with the well in the production mode.

The present invention aims to overcome these problems by providing an improved manner of making an electrical connection at a wellhead.

Accordingly, the invention provides a means of electrical connection at a subsea welihead, wherein one part of the connection is associated with the wellhead, usually with the tubing hanger, and wherein the other part of the connection is associated with a spoolpiece provided on the welihead.

By providing the other part of the connection on a separate spoolpiece, which is a relatively lightweight component, instead of on the Xmas tree, which is a heavy component, it is possible to mate the two connection parts without misalignment or damage occurring.

The spoolpiece provided as an additional component will normally rest on the wellhead and support the Xmas tree, and may additionally function as an adaptor to enable an Xmas tree of different (smaller) size to be disposed on the wellhead.

The system according to the invention can be used for either live or non-flowing wells.

Thus, by means of the present invention, by separating connector mating and Xmas tree connection, controlled mating of the connector via manual or remote vehicle operation can be achieved and the system checked out prior to running the Xmas tree.

As direct control of the make up is available this will enable the optimum connection to be made. The electrical connectors used will most likely be those used for automatic mating, but mounted on 'wind down' stabs.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure la is a side view, illustrating the means according to the invention of making an electrical connection at a subsea wellhead; Figure ib is a schematic plan view showing a typical arrangement of stabs and penetrators in the tubing hanger; Figure 2 shows a modification of the invention as applied to the mating of a power connector to operate downhole pumps; and Figures 3a and 3b illustrate the application of an electrical connection in accordance with the invention to provision of information at the bottom of the production tubing to a data acquisition system located on the outside of the wellhead.

Fig. la shows an arrangement wherein instrument cables 1 from pressure/temperature gauges located at the bottom of a subsea well terminate in male stabs 2 of standard fio petrol tubing hanger connectors, the stabs 2 being located in a tubing hanger 3 set in the wellhead. The female stabs 4 of the connectors are located in a spoolpiece 5 provided on top of the wellhead 8 and in turn supporting the so-called Xmas tree 9.

The system according to the invention operates a follows.

The instrument cables 1 from the downhole equipment terminate in the male stabs 2 in the tubing hanger 3. The respective female stab 4 is held on the end of a square shaft which is restrained from rotation by a guide plate 6. Clearances are large to allow lateral movement. The shaft is driven up and down by a threaded bonnet and square drive 7 operable by diver or ROV. By rotating the bonnet the female stab is thus lowered until it mates with the male stab 2.

To ensure the shoulder of the female stab 4 finishes in the optimum location in a guide funnel 10 there is sufficient travel in the bonnet 7 to enable a spring assembly 11 to accept further downward movement of the drive shaft 12. Once the shoulder is in position this spring allows a constant thrust to be exerted on the shoulder thus locking it in position.

At this stage the complete system can be tested and restabbed or retrieved as necessary.

As indicated, Fig. 1 b illustrates a typical arrangement in the tubing hanger of stabs and penetrators.

Further developments include the mating of a power connector (1250A up to 5.5 Kv) to operate downhole pumps. This arrangement may suitably use the layout shown in Fig. 2.

Figs. 3a and 3b schematically illustrate the manner of electrical connection according to the invention wherein information from two pressure/temperature gauges located at the bottom of a gas/oil/water injection well is transferred up the hole annulus on independent cables which penetrate the wellhead prior to terminating in a data acquisition system located on the outside of the wellhead. Although Fig. 3a shows the tubing hanger 3 with which are associated the male stabs 2 disposed remote from the spoolpiece 5 with which are associated the female stabs 4, it is to be understoodd that the spoolpiece 5 is located on the tubing hanger 3 in the same manner as shown in Fig. 1a.

Claims

1. An arrangement for establishing an electrical connection at a subsea well, comprising an electrical connection having first and second parts which are mateable with each other, the first part being associated with a wellhead and the second part being associated with a spoolpiece provided on the wellhead.

2. An arrangement as claimed in claim 1, in which the second part is movable into and out of engagement with the first part.

3. An arrangement as claimed in claim 2, in which the second part is mounted on an axially movable, rotationally restrained shaft and means are provided on the spool for moving the shaft axially.

4. An arrangement as claimed in claim 3, in which the said means act on the shaft via a spring.

5. An arrangement as claimed in any preceding claim, in which the first part is mounted in a tubing hanger depending from the welihead.

6. A method of establishing an electrical connection at a subsea well, by means of an electrical connection having first and second parts which are mateable with each other, the first part being associated with a wellhead and the second part being associated with a spoolpiece, the method comprising mounting the spoolpiece on the wellhead and mating the first and second parts of the electrical connection before a Xmas tree is mounted on the spoolpiece.

7. A method as claimed in claim 6, in which the second part is moved into engagement with the first part after the spoolpiece has been mounted on the wellhead.

8. A method as claimed in claim 6 or 7, in which the firt and second parts are mated under a spring force urging them towards each other.

9. An arrangement for establishing an electrical connection at a subsea well, substantially as described with referece to, and as shown in, the accompanying drawings.

10. A method of establishing an electrical connection at a subsea well, substantially as described with reference to the accompanying drawings.