compensated for such that the wireline between vessel and wellhead is essentially isolated from the heave amplitude caused by wave motion.

Compensation can be achieved by the use of a heave compensated winch or alternatively a non-compensated wireline winch working via a separate compensation system between wireline winch and well head. The device described here is of the later type.

This compensation is normally required both when operating the wireline in the well and also when first entering the toolstring into the lubricator/wellhead during (for example) RLWI (RiserlessWireline Intervention) operations.

In addition to the above the well head stack components; in particular the PCH (Pressure Control Head) would typically be installed and removed using a heave compensated wire. Depending on the weight of the PCH, this wire could be the wireline itself or it could be a separate wire. In the case of a separate wire it would be an advantage to synchronize the PCH heave compensation with that of the wireline plus the associated tool or toolstring itself. The system described here can embody an inherently synchronized lifting wire system for the handling of items such as the PCH if required.

In some cases the available installation space for a vessel based wireline compensating device may be small. For this reason the device described here is arranged as a vertical column in order to minimize its effective footprint within the wireline operating area of the vessel.

In many cases the device may be required to fit between decks whilst still giving the necessary amplitude of heave compensation. The device therefore has embodiments that minimize vertical dimensions whilst maximizing

compensation stroke. Wireline lifetime is reduced by repeated bend cycles. For this reason the bend radius (sheave/roller) diameter should be maximized, and the number of individual rollers in the compensating system minimized. Various embodiments are shown.

A consequence of maximizing bend radius of the wireline is that the sheaves or rollers will have increased angular inertia. The total number of sheaves/rollers in contact with the wireline can be 2 or 3 depending on the layout. The input sheave/roller functions to turn the wire input from horizontal to vertical; the remaining 1 or 2 sheaves/rollers constitute the compensating (output) part of the device.

The sheaves/rollers that are involved in the compensation will be required to accelerate and decelerate in accordance with the heave motion. It would therefore be an advantage to have a minimum of angular inertia in order to avoid slip between the sheave/rollers and the wireline. Any tendency to slip will be governed by the friction between sheave and wire.

The following factors will govern the available friction:

1 . Wireline tension

2. Groove geometry (sheave)

3. Contact sector length

4. Surface contamination (lubricating fluid)

5. Wire (surface) type (slickline, braided line, material, smoothness etc.) One embodiment of the device described here utilizes actively driven

sheaves/rollers in order to avoid slip between sheave/roller and wireline.

It is often desirable (particularly for offshore wireline operations) to minimize the time on station. The ability to run as many operation sequences as possible in parallel is therefore an advantage. Typically this results in a requirement to have one or more complete wireline strings including PCH and toolstring rigged, tested and ready to run alongside the active wireline system.

In conventional heave compensation systems, in order to have the complete wireline string rigged, tested and ready, it is necessary to have the wireline threaded through the compensating unit. This implies one compensating system for the active wireline as well as one compensating unit for each of the "ready" parallel wireline systems.

The device described here does not require the wireline to be threaded through it. It can attach to a ready rigged and tested wireline string from the side. This ability allows a single compensating unit to service multiple wirelines,

Embodiments of this compensation device have similar sheave/roller sets on either side of the vertical machine column allowing the compensator unit to access wirelines from either side. In this case both sides are mechanically connected and therefore move together; however normally only one side would be in contact with a wireline at any one time. The compensator device can be mounted on a track system, skid system or some other traverse device to enable movement between alternate wireline positions.

General layout:

The system preferably uses a 2:1 sheave system with a fixed input sheave and a moving compensation sheave. The wire can exit from the compensating sheave and attach directly to the load as shown below. This is the preferred solution since it minimizes wire wear and fatigue by having only 2 sheaves and only one reversal of bend direction. This layout would be used where the compensator output could be placed directly above the load.

In cases where the compensator is placed remote from the load an exit sheave would be added as shown below. The load acting on the compensating sheave and its associated actuating system is 2 x the wire tension. The load on the compensating unit as a whole is the resultant of wire tension in the input and output directions. The compensator unit is therefore designed to withstand the external bending loads as well as internal compression loads from the sheave system.

Compensating principle

The compensator uses a 2:1 sheave system acting directly on the wire. The compensation sheave therefore has a travel of ½ the required heave amplitude. In order to allow the compensating device to be as compact as possible it is desirable to have the overall axial dimension of the device as close as possible to the necessary compensating sheave travel. Compensating actuator system

A number of alternative solutions are possible to drive the compensating sheave through the required travel distance. The embodiment described here uses a mechanical stroke multiplier system incorporating roller pinion meshing components for minimum backlash and hence maximum accuracy. The stroke multiplier is driven by a linear actuator (electric, pneumatic, hydraulic, electromagnetic or other). The stroke multiplication principle described in this embodiment can be produced in a range of stroke multiplication ratios. The actual ratio is dependent upon the relative diameters of driven and drive pinions.

The actuating stroke is actively controlled to synchronize with the actual heave motion of the vessel as measured by motion or relative position sensing instrumentation.

Sheave/roller system

The description below can apply to Compensation devices using either sheaves or rollers. Roller based systems might be appropriate for compensating hoses, umbilical lines or similar.

The input sheave is simply used to divert/guide the wire between winch output and compensator stroke axis. This sheave rotates as the wire is spooled onto or off the winch. It is not involved in the compensation, and is therefore not required to accelerate and decelerate as the compensation device operates. This is a freewheeling sheave.

The compensating sheave and the exit sheave (if used) rotate when the winch spools wire in or out. It also accelerates and decelerates as the compensation device operates.

This acceleration and deceleration makes it desirable that the compensating sheave has a low angular inertia in order to minimize any tendency for the wire to slip against the sheave.

An alternative embodiment of the sheave system incorporates a rotational drive system for the compensating sheave and also exit sheave if fitted. The drive system actively spins the sheave(s) in harmony with the stroke movement of the compensating system, in order to minimize slip between wire and sheave.

Synchronous compensation of multiple wires

The compensating system can operate on multiple wires, arm system as follows:

- sheaves on either side of the column allowing simultaneous, synchronized compensation of 2 wires.

- sheaves on either side of the column allowing machine to access wire(s) from different locations (by lateral movement of compensator on travers system).

- multiplelayers of sheaves either alongside, above or below one another.

As an example Synchronous compensation might be used during RLWI (Riserless Well Intervention when landing or removing a wirelinetoolstring together with a pressure control head down to a lubricator unit at a subsea wellhead.

The Pressure Control Head and the toolstring would then have synchronized compensation, but would each be able to move independently relative to one another by differential movement of one or both winches on the input side (wireline winch & PCH handling winch).

Description of the figures

Figures 1 - 5 show the compensator of the invention in its simplest form.

According to figure 1 it comprises a column 1 which contains a hydraulic cylinder (not visible). A compensation sheave 2 is coupled to the cylinder. It also comprises an output sheave 3 and optional input sheave 4.

The column 1 is attached to an arm 5 via a hinge 6. Thereby the column can be moved in the horizontal plane. The horizontal movement of the column is adapted to bring the heave compensator into and out of alignment with a wire 7 of a wireline tool or another type of wire that needs to be subject to heave compensation. The arrow denotes the input of the wire 7, the arrow 7b denotes a possible output of the wire 7, while the arrow 7c denotes an alternative output of the wire 7. In the position in figure 1 , the compensation sheave 2 is in its lowermost position, which allow the wire to pass between the sheaves 2, 3, 4 in a straight line without being engaged with the sheaves but while being aligned with the grooves of the sheaves. This makes it possible to set up the wireline tool completely before connecting it to the heave compensator.

In figure 2 the compensator sheave has been moved upwards by actuating the hydraulic cylinder. It has caught the wire and lifted the part of the wire extending between the input and the output sheaves. In figure 3 the compensator sheave has been lifted to the top of the column. The distance between the positions in figure 1 and 3 is the maximum extent of compensation by the compensator. Figures 4 and 5 shows the device in perspective view. As can be seen, the compensator device has a pair of output sheaves 3a, 3b, a pair of

compensation sheaves (only one 2a shown) and a pair of input sheaves 4a, 4b. This allows for compensating two wires or a wire and a hose simultaneously and in synchronicity. One of the wire can be attached to a pressure control head and the other to a wireline tool. Thereby the two devices can be lowered to the seabed wellhead without any relative movement between them.

Figures 6 - 9 shows an alternative embodiment. It is similar to the embodiment of figures 1 - 5 but has an additional set of output sheaves 71 a, an additional set of compensation sheaves 8a (only one shown) and a pair of auxiliary winches 10 a, 10b. Thereby one or two additional wires 70 can be

compensated. Because of the auxiliary winches, the additional wires can be spooled in and out independent of the first wires, despite being compensated synchronously.

The compensator device can also be mounted in tracks 1 1 above the working area, as shown in figure 1 1 . It can also be mounted in tracks 12 on the floor of the working area, as shown in figure 1 2.

Figures 13 - 16 shows the hydraulic actuator system of the invention. The compensation sheave is attached to a gear/sheave carrier 13, which is arranged moveable with the compensator housing 22. The compensator housing 18 is a rectangular box with a slit 19 on each side. The carrier 13 carries a pair of double gears 15. However, A single double gear 15 may also be used. These gears 15 can be toothed gears or roller pinions. They have a first gear 20 with a large diameter and a second gear 21 with a smaller diameter. The diameter ratio is preferably 2:1 , but may be varied dependent on the space available. The larger diameter gear is meshing with the sidewall of the compensator housing 22 and the smaller diameter gear is meshing with a dual rack frame 14. A driving cylinder 16 is attached to the housing 22. A piston rod 17 with a piston 18 is housed within the cylinder 16. The outer end of the piston rod is attached to the frame 14. When a hydraulic pressure is imposed within the cylinder 16 below the piston 18, the piston rod 17 will be pushed upward bringing the frame 14 along, as the frame is meshing with the double gears 15. The frame 14 will attempt to turn the gears 15. Since the frame is meshing with the smaller diameter gear 21 and the housing is meshing with the larger diameter gear 20, the torque imposed on the gear 15 from the housing is the greatest and therefore the gears 15 will start to climb within the housing 22. They will also start to climb the frame 14. If the diameter ratio is 2:1 , the ascent of gears 15 relative to the frame will be half the speed of the ascent of the gears 15 relative to the housing. If the ratio is, e.g., 3:1 the relative speed of the ascent of the housing will be trice the ascent of the frame.

Alternatively, a telescopic cylinder may be used, which will make the cylinder very compact in retracted state.

In stead of a hydraulic cylinder the actuator may be pneumatic, electric or any other suitable linear actuator.

The compensator sheave may be actively driven with substantially the same peripheral speed as the wire, in order to prevent slippage of wire relative to the sheave. Thereby, it can be ensured that the wire does not move relative to the sheave. This is especially useful if the friction between the wire and sheave is low. Any output sheaves may be also actively driven.

In order to protect personnel from injury a shield structure may be put around the column 1 , with slits to allow for the passage of the wire 7.