The present invention relates to the provision of cooling water on an offshore platform, in particular to the provision of cooling water to topside equipment on an offshore platform.

Traditionally, offshore wellhead platforms have not required significant cooling, and any cooling requirements could be satisfied by air cooling. However, offshore production platforms are now becoming more common, and the topside equipment, including processing equipment, used on such platforms requires much greater levels cooling. One technique to provide such cooling has been to pump surrounding sea water through a cooling circuit to cool the processing equipment.

Cooling water is typically obtained on such platforms by running a caisson into the surrounding sea, which provides an effectively unlimited supply of cooling water. The cooling water is preferably taken from near to the seabed because the water is cooler than at the surface, and also because the water at these depths has fewer contaminants, such as shells, organic material, etc.

Whilst this technique is effective, it is expensive to install and maintain the cooling water caisson.

Viewed from a first aspect, the present invention provides a method of supplying cooling water to topside equipment on an offshore platform in a body of water, the method comprising supplying water from the body of water for use as the cooling water via an inside of a hollow, structural member of the offshore platform, wherein the hollow, structural member is open to the body of water.

By supplying water from inside of a structural member of the offshore platform, it is possible to avoid the need to install an expensive caisson extending deep into the body of water. Instead, the structural member provides this function. That is to say, the structural member provides the necessary passage between the body of water and the topside equipment to allow the provision of cooling water between the two. This both reduces initial installation requirements as well as provides a more robust structure, thereby reducing on-going maintenance and repair requirements.

The topside equipment is equipment on the offshore platform that is positioned above the waterline of the body of water in which the platform is situated. Thus, the topside equipment is not equipment that is submerged, either wholly or partly, below the waterline of the body of water. The water may be supplied to the topside equipment from inside of the hollow, structural member via a water supply conduit. The water supply conduit may supply water from inside of the hollow, structural member at a depth close to a surface level of the body of water. For example, a location less than 10m below the surface level, and preferably less than 5m below the surface level.

The body of water in which the platform is situated may be the sea. As such, seawater may be the cooling water.

The hollow structural member may be open to the body of water at a depth below a surface level of the body of water that is greater than 50% of the depth of the body of water at the offshore platform, and preferably greater than 75% of the depth of the body of water at the offshore platform.

The hollow structural member may be substantially closed to the body of water at depths below a surface level of the body of water that are less than 50% of the depth of the body of water at the offshore platform, more preferably less than 75% of the depth of the body of water at the offshore platform, and yet more preferably less than 90% of the depth of the body of water at the offshore platform.

The structural member may extend to a bed of the body of water. The structural member may be a leg of the offshore platform.

The offshore platform may be an offshore production platform. In such embodiments, the topside equipment may be processing equipment that is configured to, wholly or partly, process the hydrocarbon fluids produced at the production platform. Such processing equipment may include, for example, separators, scrubbers, compressors and/or pumps. Other processing equipment may additionally or alternatively be provided.

The platform may comprise a fluid cooler receiving the cooling water. The offshore platform may be a steel jacket offshore platform.

The water may be supplied using a pump. The pump may comprise a plurality of impellors for pumping the water. The pump may be located within the hollow body. The pump may be submerged below a water level within the hollow body. The pump may be driven by a motor. The motor may be an electric motor. The motor may be submerged below a water level within the hollow body. The motor may not be submerged. The motor may be accessible by a person from a deck of the platform. An access entry may be provided in the hollow body to permit a person to access the motor. The access entry may be above the surface of the water. The motor may drive the pump via a drive shaft. The drive shaft may extend within the hollow body.

The method may further comprise processing the water to remove contaminants before use as cooling water.

Viewed from a second aspect, the present invention provides an offshore platform in a body of water, the offshore platform comprising a hollow, structural member, wherein the hollow, structural member is open to the body of water, and wherein a water supply conduit supplies water from the body of water via an inside of the hollow, structural member for use as cooling water for topside equipment on the offshore platform.

The topside equipment is equipment on the offshore platform that is positioned above the waterline of the body of water in which the platform is situated. Thus, the topside equipment is not equipment that is submerged, either wholly or partly, in the body of water below the waterline of the body of water.

As for the method of the first aspect, the structural member provides the necessary passage between the body of water and the topside equipment to allow the provision of cooling water between the two. This both reduces initial installation requirements as well as provides a more robust structure, thereby reducing on going maintenance and repair requirements.

The water supply conduit may supply water from a depth close to a surface level of the body of water. For example, a location less than 10m below the surface level, and preferably less than 5m below the surface level.

The hollow structural member may be open to the body of water at a depth below a surface level of the body of water that is greater than 50% of the depth of the body of water at the offshore platform, more preferably greater than 75% of the depth of the body of water at the offshore platform, and yet more preferably greater than 90% of the depth of the body of water at the offshore platform.

The hollow structural member may be substantially closed to the body of water at depths below a surface level of the body of water that are less than 50% of the depth of the body of water at the offshore platform, more preferably less than 75% of the depth of the body of water at the offshore platform, and yet more preferably less than 90% of the depth of the body of water at the offshore platform.

The structural member may extend to a bed of the body of water. The structural member is a leg of the offshore platform. The offshore platform may comprise a pump to pump the water up the water supply conduit. The pump may be located within the hollow body.

The offshore platform may be an offshore production platform. In such embodiments, the offshore platform may have processing equipment that is configured to, wholly or partly, process the hydrocarbon fluids produced at the production platform. Such processing equipment may include, for example, separators, scrubbers, compressors and/or pumps. Other processing equipment may additionally or alternatively be provided.

The offshore platform may comprise equipment for processing the water to remove contaminants before use as cooling water. The offshore platform may comprise a fluid cooler receiving the cooling water. The offshore platform may be a steel jacket offshore platform.

Viewed from a third aspect, the present invention provides a method of retrofitting an offshore platform in a body of water to provide cooling water to topside equipment thereon, the method comprising installing a water supply conduit within a hollow, structural member of the offshore platform so as to supply water from the body of water via an inside of the hollow, structural member for use as cooling water for the topside equipment on the offshore platform.

The hollow, structural member may already be open to the body of water. Alternatively, the method may comprise forming an opening in the structural member so as to expose the interior of the hollow structural member to the body of water.

The method of retrofitting may result in an offshore platform according to the second aspect, optionally including any one or more of the optional features thereof.

Certain preferred embodiments of the present invention will now be described in greater detail, by way of example only and with reference to the accompanying drawing, in which:

Figure 1 illustrates a caisson for drawing water from within a leg of an offshore platform;

Figure 2 illustrates a first arrangement for pumping water up the caisson; and

Figure 3 illustrates a second arrangement for pumping water up the caisson.

Figure 1 illustrates the upper portion of a leg 2 of an offshore platform. In this example, the offshore platform has a steel jacket construction, but it will be appreciated that the techniques described herein are also applicable to other types of platform construction.

Typically the leg 2 of an offshore platform is constructed as a hollow tube, which is filled with a liquid, usually water. In some instances, the leg 2 will be a sealed tube filled with fresh water or an acid, so as to prevent corrosion of the interior surface of the leg 2. However, more commonly, the leg 2 will be provided with an opening 3 near to the seabed that allows the surrounding seawater to fill the leg 2. The present techniques are applicable to this type of construction.

As a result of the connection between the inside of the leg 2 and the surrounding body of water, the surface level of the water within the leg 2 will sit at approximately the same level as the surface level of the water outside of the leg 2. The surface level within the leg 2 will be affected by the tides. However, because it is only open to the body of water near the bed, the surface level within the leg will not be significantly affected by waves or weather conditions.

Provided within the leg 2 is a caisson 4, which acts as a water supply conduit. The caisson 4 extends from a location below the surface level of the water within the leg 2 up to a flange 6, which is exposed external to the leg 2. The flange 6 is shaped for connection to a further conduit for transporting water for use in cooling one or more systems on the structure.

The caisson 4 should extend to a depth within the leg 2 at least sufficient to ensure that it remains submerged at low tide. However, because weather and waves will not affect the surface level, it does not need to be overly deep. For example, it may extend only one or two meters below low tide surface level.

It is expected that a pump will be used to move the water from inside the leg 2 of the platform. The pump may be located within the leg 2, for example near or below the water level. Alternatively, it may be located at or beyond the flange 6, or even on the platform itself, provided of course that the pump is no more than 10m above the surface of the water, which is the maximum height that water can be drawn by suction.

Figures 2 and 3 illustrate exemplary arrangements for driving a pump 8.

The pump 8 is arranged within the caisson 4, and typically near or below a surface level of the water. In the illustrated embodiments, the pump 8 comprises a plurality of impellers, but it will be appreciated that any suitable pump 8 may be employed. When driven, the pump 8 drives water up a conduit 10 within the caisson 4. A filter 9 may be provided upstream of the pump 8 to reduce contaminants from damaging or fouling the pump 8.

In the Figure 2 arrangement, a motor 12 is provided that drives the pump 8 via a drive shaft 14. The motor 12 in this embodiment is provided above sea level and is not submerged. The motor 12 may be provided within the leg 2, and may be accessible from a deck of platform, for example via an access panel or door. Any suitable motor 12 may be used, for example the motor may be an electric motor or a combustion engine.

In the Figure 3 arrangement, a submersible motor 16 is used to drive the pump 8. The motor 16 is an electric motor capable of operating when fully submerged underwater. The motor 16 is provided below the pump 8 and below the water level within the leg 2. In the illustrated embodiment, the motor 16 is provided within the caisson 4. An electrical supply line 18 runs from a deck of the platform to the motor 16 to provide electricity to drive the motor 16. In the illustrated embodiment, the electrical supply line 18 runs within the caisson 4.

During operation, water will be drawn up the caisson 4 from within the leg of the platform. As the water is drawn out of the leg 2, it will be replaced by water from the surrounding body of water that enters at the base of the leg 2. Aside from the opening 3 at the base of the leg 2, the leg should be substantially closed to the surrounding body of water. That is to say, for example, substantially all of the water drawn through the caisson 4 (e.g. at least 90%, preferably at least 95%, more preferably at least 99%) has entered via the base of the leg 2.

By taking cooling water from inside of the leg, the advantages of drawing water from the seabed can be obtained without needing to run a separate caisson to the sea bed. This significantly reduced capital expenditure during installation. Furthermore, the platform leg 2 is a relatively large, structural member that is not easily damaged. This contrasts with the caisson, which is typically a relatively narrow and less robust. Thus, the likelihood of damage to the caisson is reduced and the costs for maintenance and repair are likewise reduced.

As discussed above, by taking seawater from close to the sea bed, the water contains far fewer contaminants than would be found in water closer to the surface. Nevertheless, it will be appreciated that the platform may include equipment for processing the water before being used as cooling water. Such processing may include, for example, filtration or chlorination. The leg 2 may comprise an inlet strainer near the sea bed for removing contaminants in the water. The inlet strainer may be located at any location between the opening 3 in the leg and an inlet of the caisson 4. The inlet strainer may be provided in addition to or instead of the inlet filter 9 described above.

The above technique is applicable to any offshore platform comprising equipment requiring cooling. However, it is particularly applicable to offshore processing platforms, i.e. in which oil, gas and water are separated from the well fluid. Such processing platforms may include wellhead production platforms or a central production platform. The processing equipment requiring cooling on such a platform may particularly include well fluid coolers, but may include any one or more of manifolds, separators, pumps, etc.

The above described caisson 4 may be installed at the same time as the offshore platform is constructed. Alternatively, it may be installed after installation of the offshore platform, i.e. during a retrofit operation. For example, this may be required if new equipment is installed on the platform having greater cooling requirements than the previous equipment.

In such a retrofit operation, a caisson 4 is installed inside the leg 2 such that it reaches the water within the leg 2. For example, a hole may be formed at the top of the leg 2, and the caisson 4 may be inserted through the hole. A flange 6 of the caisson 4 remains exposed from the leg 2. If the leg 2 is already open to the surrounding sea, then the caisson 4 can be used without further modification.

However, if it is not or if the opening 3 is not sufficiently large, then one or more further openings may be made in the leg 2 close to the seabed.