WO2002010548A1

WO2002010548A1 - Base for a subsea installation and application thereof

Info

Publication number: WO2002010548A1
Application number: PCT/NO2001/000327
Authority: WO
Inventors: Gunnar ØKLAND
Original assignee: Subscape As
Priority date: 2000-08-01
Filing date: 2001-08-01
Publication date: 2002-02-07
Also published as: EP1307631B1; NO20003908A; NO311185B1; EP1307631A1; NO20003908D0; AU2001280284A1; DE60119332D1; ATE325255T1

Abstract

A pad for an subsea installatin in connection with petroleum-related drilling operations, in which a flexible mat (10), or a number of flexible mats (10), arranged to prevent the whirling up of bottom sludge, is placed underneath the subsea installation (14), or around the subsea installation (14), and where the mat (10), or mats, cover an area of the ocean bed (12) which is larger than the installation (14) which is placed on the ocean bed (12).

Description

Base for an subsea installation and application thereof.

The present invention relates to a pad for subsea installations in connection with petroleum-related well drilling, and application thereof.

In most cases involving work on subsea installations, bottom sludge will be encountered. This sludge has a very low density and is easily whirled up when touched. Thus, this bottom sludge affects the daily working conditions to a large extent, especially with respect to sight, for example, for a remotely operated vehicle (ROV) .

This often leads to more time being required to complete important work tasks which in turn increases the costs for the oil companies. As focus on efficiency and practicability for all stages of the operation is always important, there will be a considerable improvement for the working conditions on the ocean bed if this bottom sludge does not influence the implementation of the work tasks. It will be equally important to be able to carry out all work tasks which can be necessary in emergency situations.

A standard subsea installation has a high specific weight because it shall sink into the ocean bed underneath the installation. In many cases the installation must be installed with a small deviation from the geologically best location, and with consideration of future wells. Therefore, to place the subsea installation correctly the first time round represents a challenge as an even greater effort would be required if it has to be re-installed. In today's installations, it is known to arrange a metal plate underneath the subsea installations. However, this plate is too small to prevent whirling up of the sludge, as the plate as a rule covers an area corresponding to the lower part of the pad of the ocean installation. The plate can possibly prevent the whirling up of sludge immediately underneath the plate area, although this is doubtful as the installation sinks down into the bottom sludge, such that the plate is covered by the bottom sludge. In all cases, the plate will not prevent the whirling up of sludge underneath the parts of the subsea installation which extend outside the plate and, additionally, not in the wider area around the installation. The object with this plate is not to prevent the whirling up of sludge, but to ensure that the subsea installation is stabilised so that it is standing steadily on the ocean bed. Neither will it be natural to expand the plate so that it covers a larger area, as this will make the whole underwater installation proportionally heavy, and in addition will probably also result in difficulties with placing of the installation correctly on the ocean bed.

Therefore, there is a need for a base pad around, or underneath, the subsea installations in connection with petroleum-related well drilling, which can prevent the whirling up of bottom sludge in a relatively large area around the installation. In addition there is a need for a base pad that helps reduce the time it takes for implementation of important tasks at subsea installations. This will lead to cost reductions for the oil companies. There will also be a considerable improvement in the working conditions on the ocean bed if this bottom sludge does not represent any influencing factors on the implementation of the tasks. This will be equally important for the carrying out of all tasks that can be necessary in emergency situations.

The pad according to the present invention provides a series of advantages, in addition to preventing the whirling up of bottom sludge from the ocean bed, in that the pad can function as a template for the installing of subsea installations, functions as an extra safeguard against washout of bore holes, functions as a cover over bottom sludge and prevents this reducing the working conditions on the ocean bed, captures items which get lost on the ocean bed, captures unintentional spillages and eases the identi ication of their extent, provides better light conditions for remotely operated vehicles and provides a better orientation environment for remotely operated vehicles.

The pad according to the present invention is characterised in that a flexible mat, or a number of mats, adapted to prevent the whirling up of bottom sludge, is arranged underneath the subsea installation, or around the subsea installation, and where the mat, or the mats, cover (s) an area of the ocean bed which is greater than the installation that is placed on the ocean bed.

Preferred embodiments are characterised in that the flexible mat comprises a flexible material which provides a specific weight heavier than water and which is arranged to be placed over the ocean bed as a covering means to prevent the whirling up of bottom sludge. The flexible mat can also comprise an opening, or openings, or adapted side edges, or a penetrable area, arranged to fit snugly to the pad of the subsea installation. The flexible mat can comprise a rubber material, such as nitrile rubber, including weight elements, such as, for example, pieces of vulcanised steel, and where the specific weight of the mat is heavier than water. The flexible mat can also comprise an elastic plastic material incorporating weight elements, so that the specific weight of the mat is heavier than water or the mat can comprise a stainless steel-fibre material. Furthermore, the mat can comprise a surface covering, such as, for example, a fluorescent material, arranged to provide improved light conditions.

The present invention also relates to application of a pad of a subsea installation in connection with petroleum- related drilling operations, where the pad is arranged underneath the subsea installation, or around the pad of the subsea installation, in an area on the ocean bed which is larger than the area covered by the subsea installation, and which is arranged to function as a cover over the bottom sludge to prevent this from whirling up so that the working' conditions on the ocean bed are not affected.

For an alternative application, the pad is placed on the ocean bed and covers an area of the ocean bed that is at least twice the size of the area covered by the installation which is placed on the ocean bed. The pad can also be adapted to function as a template for installing subsea installations, in that the mat is arranged to guide the placing of the subsea installations, future pipelines, cables, etc. In addition, the pad can also function as an extra safeguard against washout of drilling holes. Furthermore, the pad can be equipped with transmitters, such as acoustic transmitters, to transmit the position of the subsea installation to a receiver above the ocean, as for example a DP-vessel.

The invention shall now be explained further with reference to the enclosed drawings, in which:

Figure 1 shows an subsea installation placed on the ocean bed and a pad according to the present invention, viewed from the side.

Figure 2 shows, correspondingly to figure 1, an subsea installation and the pad according to the invention, viewed from above.

A preferred embodiment of the pad according to the present invention comprises a flexible mat 10 which comprises a flexible material that provides a specific weight heavier than water and which is adapted to be placed on the ocean bed 12 as a covering means to prevent the whirling up of bottom sludge. The flexible mat 10 can be manufactured from a rubber material, such as nitrile rubber. To increase the specific weight of the mat, weight elements can be vulcanised in. These weight elements can comprise pieces of steel, or another adapted material. The amount and weight of the weight elements which are vulcanised in can also be adjusted to the application area, i.e. the conditions at the bed where the subsea installation 14 shall be installed, by the flexible mat 10 being made heavier or lighter according to the amount of sludge, type of sludge, topography of the bed, etc.

In the preferred embodiment the weight elements are vulcanised in, but can in other embodiments be secured in different ways to the mat 10. What is important is that the flexible mat 10 has a specific weight which is heavier than water so that the mat lies as a cover over the bottom sludge on the ocean bed 12, and prevents the bottom sludge from being whirled up. It must also be so heavy that it is not affected by underwater currents or other external influences. If it is necessary, because of the topography of the bed, current conditions, etc., the flexible mat can, if desired, be fixed more securely to the ocean bed by the aid of securing means, such as plugs, or the like. Further- more, the flexible mat 10, must in one embodiment, withstand that the underwater installation 14 is placed on top of the mat 10 without this being affected or being moved too much. In another embodiment, the flexible mat 10 comprises one, or more, opening (s) approximately in the middle of the mat 10, through which the pad 16 of the subsea installation 14 is led for placing on the ocean bed 12. It is in this embodiment desirable that the opening in the flexible mat 10 fits closely to the pad 16.

Furthermore, the flexible mat 10 can, in another embodiment, comprise a penetrable area, for placing of the pad of the installation, which has a smaller thickness than the thickness of the surrounding section of the mat, or a more flexible or weaker area than the surrounding section of the mat. The object of this penetrable area with smaller thickness, which is more flexible or with lower tensile strength/elasticity limit, is that it shall give way when the installation is placed on top of the mat so that the pad is forced through the mat and down into the ocean bed. By forcing the pad through the mat, the opening edges of the flexible mat lie against the pad, preferably in a tight fit.

The flexible mat 10 can also be manufactured from material other than a rubber material, such as for example a flexible plastic material or a stainless metal-fibre material.

As shown in figure 2, a preferred embodiment of the mat is rectangular, but the flexible mat 10 can of course also take on other geometric shapes. The flexible mat 10 can be manufactured or cut to a desired shape according to the conditions at the ocean bed. When the flexible mat is to be placed on the ocean bed, it can for example, be rolled together from each side before being placed on the ocean bed, so that the mat consists of two rolled up parts where the centre, or the opening/the weaker area, of the mat is between the two rolled up parts. Thereafter, the flexible mat 10 is placed on the ocean bed with the centre/ opening, or the penetrable area, where the subsea installation shall be placed, and the two rolled up parts are rolled out in their opposite directions. The subsea installation 14 can now be placed exactly on the ocean bed 12. The pad 16 of the subsea installation can be led, or forced, through the opening, the penetrable area, in the flexible mat so that the pad plate 18 rests stably on the ocean bed, and the edges of the opening fit closely to the pad. It is preferred that the edges of the opening fit tightly to the pad, but this is not necessary.

If the bottom conditions and weight of the subsea installation allows it and the flexible mat 10 is large enough and flexible enough, the opening can be omitted and the subsea installation 14 can be placed directly onto the mat so that the mat lies underneath the installation 14, directly against the ocean bed 12. In another alternative embodiment of the pad according to the present invention, the pad comprises two or more flexible mats which are placed around and against the subsea installation. In this embodiment, the side edges of the mat 10 are shaped such that they fit against the pad 16 of the installation 14. This alternative embodiment can be applied on already existing subsea installations by the mats being placed against the pad and thereafter rolled out over the ocean bed. The flexible mats can be placed so that they overlap.

In a preferred embodiment of the present invention, the flexible mat comprises a surface covering of fluorescent material to improve the light conditions at the ocean bed. Furthermore, text can be added to the upper surface of the mat which gives important information about orientation conditions, well number, future pipelines, cables, etc. The coverage area of the mat will normally be at least 6-8 meters outside the existing base plate 18. This leads to the working area for remotely operated vehicle being nearly 100% covered.

In addition, the flexible mat can be equipped with acoustic transmitters which can transmit the position to DP-vessels which can easier locate it for subsequent and reoccurring work on the subsea installation.

The pad in the form of the flexible mat will provide many positive influences which are of decisive importance for the efficiency of the implementation of the production of oil wells, such as, for example; Function as a template for the installing of subsea installations; Function as an extra safe-guard against washout of drilling holes; Function as a cover over the bottom sludge and prevent .this from reducing the working conditions on the ocean bed; Capture items which are lost on the ocean bed; Capture unintentional leakages and easily identify their extent; Provide better light conditions for remotely operated vehicle; Provide better orientation ability for remotely operated vehicles.

Thus, a pad is provided which will considerably improve the working conditions at subsea installations.

Claims

1. A pad for an subsea installation in connection with petroleum-related drilling operations, characterised in that a flexible mat (10) , or a number of flexible mats

(10) , adapted to prevent the whirling up of bottom sludge, is arranged underneath the subsea installation (14) , or around the subsea installation (14), and that the mat (10), or mats, covers an area of the ocean bed (12) which is larger than the installation (14) which is placed on the ocean bed (12) .

2. A pad in accordance with claim 1, characterised in that the flexible mat (10) comprises a flexible material which provides a specific weight heavier than water and which is arranged to be placed on the ocean bed (12) as a- covering means against the whirling up of bottom sludge.

3. A pad in accordance with claim 2, characterised in that the flexible mat (10) comprises an opening, or openings, or adapted side edges, or a penetrable area for the pad (16) , arranged to fit against the base (16) of the subsea installation (14).

4. A pad in accordance with claims 1-3, characterised in that the flexible mat (10) comprises a rubber material, such as nitrile rubber, incorporating weight elements, such as, for example, vulcanised steel pieces.

5. A pad in accordance with claims 1-3, characterised in that the flexible mat (10) comprises a flexible plastic material incorporating weight elements.

6. A pad in accordance with claims 1-3, characterised in that the flexible mat (10) comprises a stainless steel- fibre material.

7. A pad in accordance with one of the preceding claims, characterised in that the flexible mat (10) comprises a surface covering, such as, for example, a fluorescent material, arranged to provide improved light conditions under water.

8. Use of a pad, according to the claims 1-7, at subsea installations (14) in connection with petroleum-related drilling operations, whereby the pad is arranged underneath the subsea installation (14), or around the subsea installation (14), and in an area of the ocean bed (12) which is larger than the area which the subsea installation (14) covers, and which is arranged to function as a cover over the bottom sludge and prevent this from whirling up, such that the working conditions on the ocean bed are improved.

9. Use of a pad in accordance with claim 8, in that the pad is arranged on the ocean floor (12) and covers an area of the ocean floor (12) which is at least twice the size of the area which the installation (14) that is placed on the ocean bed covers.

10. Use of a pad in accordance with claim 8, in that the pad is adapted to function as a template for installation of subsea installations (14), and in that the mat (10) is arranged to direct the placing of subsea installations, future pipelines, cables, etc.

11. Use of a pad in accordance with claim 8, whereby the pad, in addition, functions as an extra safe-guard against washout of drilling holes.

12. Use of a pad in accordance with claim 8, in that the pad is equipped with transmitters, such as acoustic trans^¬ mitters, to transmit the position of the subsea installation (14) to a receiver above the water such as, for example, a DP-vessel.