NO343296B1

NO343296B1 - Mobile wireline compensator

Info

Publication number: NO343296B1
Application number: NO20162072A
Authority: NO
Inventors: Tord Martinsen
Original assignee: Safelink As
Priority date: 2016-12-30
Filing date: 2016-12-30
Publication date: 2019-01-21
Also published as: NO20162072A1

Abstract

Mobile wireline compensator (100) for reduction ofdynamic loads and motion in offshore liftingoperations based upon a horizontal actuator (10)comprising:- a passive actuator cylinder (30), comprising a thirdpiston (31) connected to a piston rod (32), and hastwo volumes, designated V1 and V2, where V1 ison the piston side and V2 is on the rod side, thevolumes are filled differently, depending on if thepassive actuator cylinder (30) is working in tension or compression mode, where V1 is filled with hydraulic fluid and is connected to a gas accumulator (40) via conduit means and V2 is either filled with oil or filled with low pressure gas (including vacuum) when working in compression mode and where V2 is filled with hydraulic fluid and is connected to a gas accumulator (40) via conduit means and V1 is either filled with oil or filled with low pressure gas (including vacuum) when working in tension mode- an active actuator cylinder (20), including a piston rod (21), and the passive actuator cylinder (30) have collinear longitudinal axes that are horizontal, where their respective piston rods (21, 32) are fixed together in a stiff connection with actuator sheaves (14, 15) at the connection point- a position measurement means (33) to register the position of the third piston (31)- a gas accumulator (40), featuring a fourth piston (41) that separates fluid, containing two volumes designated V6 and V7, where V6 is connected to V1 in the passive actuator cylinder (30) if operating in compression mode and to V2 in the passive actuator cylinder (30) if operating in tension mode, via conduit means adapted with a control valve (CV1), filled with hydraulic fluid and where V7 is filled with gas- the actuator (10) further contains framework (11) joining the two actuator cylinders (20, 30) together in a stiff connection, where the framework (11) may partly consist of tanks and accumulators to reduce weight, the framework (11) is further fitted with connection means (12) used to connect the MWC (100) to a crane, or similar, located on a vessel (102), where the connection means (12) may be located in the centre of gravity of the MWC (100) or at other locations, the framework (11) further supports three secondary sheaves (17, 19a, 19b), used to support rope means (16, 18), such as steel wire rope, fibre rope, belt, chain or similar, connecting the actuator sheaves (14, 15) to the lower connection means (12), which in turn is connected to the payload (101), the rope means (16, 18) are reeved over the actuator sheaves (14, 15) and the secondary sheaves (17, 19a, 19b), with one end connected to a fixed point, such as the framework (11) and the other end connected to the payload (101) via a lower connection means (12), lowering of the payload (101) relative to the MWC (100) causes the actuator sheaves (14, 15) to move horizontally, the direction (i.e., towards or away from the active actuator cylinder (20)) depending on if the MWC (100) is compression- or tension-based- an accelerometer integrated into the MWC (100), adapted for measuring vertical motion- communication means, such as wireless communication while in air and acoustic communication while submerged, adapted for transmitting data from the vessel (102), such as commands and winch spooling speed, to the MWC (100)- a hydraulic motor (P), which is reversible, adapted to actuate the active actuator cylinder (30), based on measurement data from the position sensor (33), the accelerometer and the measurement data from the vessel (102), such as winch spooling speed.

Description

The mobile wireline compensator (MWC) is an installation tool designed to compensate heave motion during sensitive lifts in an offshore environment. The heave is typically induced by swells that cause floating objects, like installation vessels and barges, to move vertically up and down. The MWC is designed to operate in air or in water. The MWC is an inline tool that combines the principles of spring isolation with active cylinder control in order to generate an efficient compensation effect. The tool can operate like a traditional gas-over-hydraulic fluid spring-dampening device if the active control malfunctions. During offshore construction high and heavy structures are to be lowered by expensive working ships with big cranes of high carrying capacity. The structures have to be lifted from fixed or floating objects and be placed on either fixed or floating locations, topside or subsea. Irregular movements of working ships, barges and supply vessels generated by swell and wind can be increased a lot by the crane boom, so that even with average swell it is difficult or impossible to carry by the crane sensitive structures during violent ship and crane movements and to lower them subsea. Since daily costs of operation with working ships are very high, each delay causes enormous additional costs. Therefore, a strong demand exists to perform respective works also in less favourable weather and with average swell without damaging the structures to be moved. The prior art compensation devices, such as crane mounted active heave compensators, have a very high capital cost and have several weaknesses, where the biggest ones are, no mobility, insufficient splash zone crossing performance, fatigue of wire rope, lack of passive backup systems, high power demand and lack of models for heavy lifts.

Thus, the present invention relates to a mobile wireline compensator for reduction of dynamic loads and motion in offshore lifting operations based upon a horizontal actuator

EP 1795491 A1 describes a mobile wireline compensator for reduction of dynamic loads and motion in offshore lifting operations based upon a horizontal actuator, wherein it comprises an actuator cylinder with a piston connected to a piston rod, and has two volumes divided by the piston, a second actuator cylinder including a piston and a piston rod, the compensator further contains framework joining the two actuator cylinders together in a stiff connection, the framework is further fitted with connection means used to connect the compensator (4) to a crane (23) located on a vessel, and the framework and actuators is further fitted with sheaves used to support rope means, connecting the actuators to a lower connection means, which in turn is connected to a payload.

US 4593885 A describes a mobile wireline compensator for reduction of dynamic loads and motion in offshore lifting operations based upon a horizontal actuator, wherein it comprises an actuator cylinder with a piston connected to a piston rod, and a sheave connected to the end of the piston rod.

SUMMARY OF THE INVENTION

The main features of the present invention are given in the independent claim.

Additional features of the invention are given in the dependent claims.

The MWC consists of a special actuator connected to one or more gas accumulators, which further is connected to one or more gas tanks. The special actuator has a design that is naturally depth compensated, which is a large benefit for subsea usage. The actuator also allows for efficient usage of commercially available pumps for active actuator control. Other influences like temperature variations and load variations are handled by the active compensation system, which is able to increase or reduce gas pressure in tanks and accumulators individually by use of control valves and gas boosters. Active control (i.e., via a hydraulic motor) of the actuator is used to compensate for heave motion. The active control is controlled by a computer that calculates the control signal based on measurements from several sensors, where the most important ones are the piston position sensor, the accelerometer and the wire rope speed sensor. Information about the wire rope speed is transferred to the compensator via wireless signals while the compensator is in air and via acoustic transmission while it is submerged. The compensator can operate in several different modes with variable stiffness and damping with or without active control of the actuator and with or without active control of the pressure levels in the various gas volumes. The compensator is energy efficient due to the fact that passive part of the compensator carries the entire load of the payload weight and the actively controlled hydraulic motors(s) only have to compensate for gas compression effects and friction, which typically is maximum 15 % of the force compared to static force, and usually much less. Energy regeneration is also used so that only friction as well as oil leakage and mechanical losses in the hydraulic pump contributes to the energy consumption. When active control of the actuator is not required the MWC may use the active system to charge the internal battery pack.

Further, acoustic communication subsea and wireless communication topside allow for control and monitoring of the compensator, on-board sensors allow the user to verify performance after a lift is concluded.

The invention has the following advantages compared to the prior art: mobile construction, lower cost for same capacity, as good performance for long wave periods and better performance for short wave periods, excellent splash zone crossing performance, well-suited for resonance protection, reduced wear of steel wire rope, low energy consumption, reduced lifting height requirement, no upending required, native passive depth compensation.

The special actuator design allows for horizontal construction of the compensator, which gives two large benefits. One, the elongation of the compensator can be long without increasing the effective vertical length of the compensator. Two, troublesome upending of the compensator from horizontal position on the vessel deck to vertical position (hanging in the crane hook) is removed as it is ready to go when lifted straight up from the vessel deck. It also worth noting that the design is natively depth compensated without any additional means. The special actuator design allows for simpler construction at a lower cost compared to prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the actuator of a compression-based design with horizontally mounted sheaves on the actuator rod, viewed from a horizontal plane. Gas tanks and accumulators are not shown.

Figure 2 shows the actuator of a tension-based design with horizontally mounted sheaves on the actuator rod, viewed from a horizontal plane. Gas tanks and accumulators are not shown.

Figure 3 shows the actuator of a compression-based design with horizontally mounted sheaves on the actuator rod, viewed from a vertical plane. Gas tanks and accumulators are not shown.

Figure 4 shows a simplified hydraulic circuit for a compression-based system.

Figure 5 shows a simplified hydraulic circuit for a tension-based system.

Figure 6 shows a placement of the MWC in a topside lift, wherein it is located right above a payload located on a barge.

Figure 7 shows a placement of the MWC in a subsea lift, wherein it is located right above a payload.

Figure 8 is an illustration of a prior art active heave compensator, permanently installed topside.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following section will describe how a mobile wireline compensator (100), or MWC for short, according to the present invention works during different phases of an offshore subsea lift. One possible application is shown, where it is assumed that a payload (101) is initially on a barge (103) next to an installation vessel (102), as shown in figure 6. The payload (101) has to be retrieved by the vessel (102). Then the payload (101) needs to cross the splash zone. Next there is a descent of the payload (101) into deeper waters, and finally landing of the payload (101) on the seabed (106), as shown in figure 7.

There are different requirements to functionality during the different phases of the lifting operation. During the first phase, which is lifting of the payload (101), that is located on a floating barge (103), from a floating vessel (101), it is beneficial if the MWC (100) can compensate motion in such a way that the relative motion between the lower part of the MWC (100) and the barge (103) deck is zero, except for winch spooling. This functionality requires three things:

1. Velocity of the barge (103) deck

2. Velocity of the crane hook

3. Winch speed (i.e., wire rope spooling velocity)

The first requirement is handled by a wireless MRU (105), short for motion reference unit, placed on the barge (103) deck, preferably close to the payload (101). The second requirement is either handled by an accelerometer inside the MWC (100), or by a MRU (104) located on the vessel (102) or in the crane. The final requirement is normally given by the crane computer, and is transferred wirelessly while in air, or via acoustic signals when submerged, to the MWC (100).

Based on the information above the computer integrated into the MWC (100) is able to control the actuator (10) in such a way that the relative motion between the lower part of the MWC (100) and the barge (103) deck is close to zero while the crane winch is not spooling out wire rope. The computer will take spooling into account, to not cause any lag for the crane operator.

After successful connection and lifting of the payload (101) from the barge (103) deck, the payload (101) has to cross the splash zone (i.e., the border between air and sea), where different requirements apply. This phase is characterized by fast dynamics, where unpredictable forces from slamming and buoyancy occurs and is best suited for a passive heave compensator, which the MWC (100) basically is. Active actuator (10) control is turned off, stiffness and damping is adjusted to the best possible settings by use of control valves (CV). During the actual crossing of the splash zone, the actuator (10) equilibrium position tends to move towards the inner position, due to buoyancy forces acting on the payload (101). This effect is compensated by adjusting the internal gas pressure in one of the following ways:

1. Release gas to the surroundings

2. Transfer gas from the gas accumulator (40) to a tank with lower pressure 3. Transfer gas from the gas accumulator (40) to a tank with higher pressure by utilizing the gas booster (50)

The adjustment is performed automatically by the on-board computer based on changing equilibrium position of the actuator (10).

At a certain distance after crossing the splash zone, the MWC (100) will often switch to a softer setting with less damping. This is done to prevent resonance in the lifting arrangement. If the passive system alone is not enough to avoid resonance, then the actuator (10) can either be locked by closing control valves or actively controlled by the computer to prevent resonance.

Drop in temperature during transport from shallow waters to deeper waters influence the equilibrium position of the actuator (10). The water temperature often tends to decrease as the MWC (100) is lowered into deeper waters. This affects the actuator (10) equilibrium due to the fact that the gas pressure in all gas volumes are reduced due to lowered temperature. The MWC (100) compensates this either by transferring gas under higher pressure from one of the tanks to the gas accumulator (40) via control valves or from a tank under lower pressure to the gas accumulator (40) via the gas booster (50) and control valves (CV).

During the final phase of the lifting operation, which is the landing phase, the active actuator (10) control is again enabled, either by acoustic commands, water pressure triggering or by a ROV, to ensure that there is minimal relative velocity between the lower end of the MWC (100) and the seabed (106). The on-board computer uses the on-board accelerometer, the position sensor (33) as well as acoustically transmitted signals from the vessel (102) about wire rope spooling to actively control the actuator (10) to a high degree of accuracy and without crane operator lag. The water pressure sensor (indirectly measures distance) can also be used in improving the control signal.

Figure 1 and 3 illustrate an embodiment of a compression-based MWC (100) actuator (10) with horizontal sheaves (14, 15) attached to the actuator rods (32, 21) with all major sub-components numbered seen from the above and from the side, it does not depict accumulators, tanks or other components. Figure 2 shows a similar, but tension-based design. Horizontal sheaves (14, 15) reduces the vertical size of the MWC (100) as the other sheaves (17, 19a, 19b) can be mounted further up, hence reducing the minimum vertical size of the MWC (100).

The actuator (10) consists of an active actuator cylinder (20) and a passive actuator cylinder (30), that are collinear with each other as well as horizontal.

The active actuator cylinder (20) comprises a first hollow piston rod (21), connected to a first piston (23), a second hollow piston rod (24) connected to a second piston (22), where the second hollow piston rod (24) and the second piston (22) are mounted concentrically inside the first hollow piston rod (21) and fixed to one end of the active actuator cylinder (20). The active actuator cylinder (20) has three separate volumes, designated V3, V4 and V5. V3 is located between; the inside of the first hollow piston rod (21), the inside of the second piston rod (24), the top of the second piston (22) as well as the end of the actuator cylinder (20) and is filled with hydraulic fluid. V4 is located between; the inside of the first hollow piston rod (21), the outside of the second piston rod (24), the bottom of the second piston (22) and the first piston (23) as well as the end and inside diameter of the actuator cylinder (20) and is filled with a low pressure gas (including vacuum). V5 is located between; the outside of the first hollow piston rod (21), the top of the first piston (23) as well as the end and inside diameter of the actuator cylinder (20) and is filled with a hydraulic fluid. The passive actuator cylinder (30) comprises a third piston (31) connected to a piston rod (32) and has two volumes, designated V1 and V2, where V1 is on the piston side and V2 is on the rod side. The volumes are filled differently, depending on if the passive actuator cylinder (30) is working in tension or compression mode, where V1 is filled with hydraulic fluid and V2 is either filled with oil or filled with low pressure gas (including vacuum) when working in compression mode and where V2 is filled with hydraulic fluid and V1 is either filled with oil or filled with low pressure gas (including vacuum) when working in tension mode. At least one of the two volumes are connected to a gas accumulator (40).

The active and passive actuator cylinders (20, 30) have equal stroke length, the piston rods (21, 32) are joined together and should preferably have the same diameter to cancel water pressure effects. In the joint area between the piston rods (21, 32) a set of actuator sheaves (14, 15) are mounted. The actuator further contains framework (11) joining the two actuator cylinders together (20, 30) in a stiff connection. The framework (11) may partly consist of tanks and accumulators to reduce weight. The framework (11) is further fitted with connection means (12) used to connect the MWC (100) to a crane, or similar, located on a vessel (102), where the connection means (12) may be located in the centre of gravity of the MWC (100) or at other locations as shown in figure 3. The framework (11) further supports three secondary sheaves (17, 19a, 19b), used to support rope means (16, 18), such as steel wire rope, fibre rope, belt, chain or similar, connecting the actuator sheaves (14, 15) to the lower connection means (12), which in turn is connected to the payload (101). The rope means (16, 18) are reeved over the actuator sheaves (14, 15) and the secondary sheaves (17, 19a, 19b), with one end connected to a fixed point, such as the framework (11) and the other end connected to the payload (101) via a lower connection means (12). Lowering of the payload (101) relative to the MWC (100) causes the actuator sheaves (14, 15) to move horizontally, the direction (i.e., towards or away from the active actuator cylinder (20)) depending on if the MWC (100) is compression or tension-based. Lowering of the payload (101) will cause the pressure in the gas accumulator (40) to increase. The force acting on the actuator (10) is at least twice of the force in the rope means (16, 18), depending on the number of falls used.

Figure 4 and are very similar and shows simplified hydraulic circuits of compression and tension-based MWC (100). They are both described below:

- an actuator (10), comprising of an active actuator cylinder (20) and a passive actuator cylinder (30), which longitudinal axes are collinear

- the active actuator cylinder (20) comprises a first hollow piston rod (21), connected to a first piston (23), a second hollow piston rod (24) connected to a second piston (22), where the second hollow piston rod (24) and the second piston (22) are mounted concentrically inside the first hollow piston rod (21) and fixed to one end of the active actuator cylinder (20), the active actuator cylinder (20) has three separate volumes, designated V3, V4 and V5; V3 is located between: the inside of the first hollow piston rod (21), the inside of the second piston rod (24), the top of the second piston (22) as well as the end of the actuator cylinder (20) and is filled with hydraulic fluid; V4 is located between; the inside of the first hollow piston rod (21), the outside of the second piston rod (24), the bottom of the second piston (22) and the first piston (23) as well as the end and inside diameter of the actuator cylinder (20) and is filled with a low pressure gas (including vacuum); V5 is located between; the outside of the first hollow piston rod (21), the top of the first piston (23) as well as the end and inside diameter of the actuator cylinder (20) and is filled with a hydraulic fluid

- the passive actuator cylinder (30) comprises a third piston (31) connected to a piston rod (32) and has two volumes, designated V1 and V2, where V1 is on the piston side and V2 is on the rod side, the volumes are filled differently, depending on if the passive actuator cylinder (30) is working in tension or compression mode, where V1 is filled with hydraulic fluid and V2 is either filled with oil or filled with low pressure gas (including vacuum) when working in compression mode and where V2 is filled with hydraulic fluid and V1 is either filled with oil or filled with low pressure gas (including vacuum) when working in tension mode, one of the two volumes are connected to a gas accumulator (40)

- a position measurement means (33) to register the position of the third piston (31)

- a gas accumulator (40), featuring a fourth piston (41) that separates fluid, containing two volumes designated V6 and V7, where V6 is connected to V1 in the passive actuator cylinder (30) if operating in compression mode and to V2 in the passive actuator cylinder (30) if operating in tension mode, via conduit means adapted with a control valve (CV1), filled with hydraulic fluid and where V7 is filled with gas

- a gas booster (50), which can be of either single acting or double acting type, with or without area difference between gas and drive side, including means to drive it, which could be either hydraulic- or gas-based

- a number of tanks (T1, T2, …, TN) suitable for gas storage

- conduit means between V3 and V5 adapted with a hydraulic pump (P) adapted to transport oil under pressure between the respective volumes in any direction, adapted with control valves ( CV2, CV3) and a gas accumulator (60) suitable for handling pump leakage and providing low flow restriction when the MWC (100) is used in passive mode

- conduit means between V7 and the tank volumes (T1, T2, ..., TN) adapted with control valves (CVA1, CVA2, ..., CVAN) for adjustment of the volume size connected to V7

- conduit means between all gas volumes (V7, T1, T2, …, TN), the gas booster (50) as well as the surroundings, adapted with control valves (CV4, CV5, CV6, CVB1, CVB2, …, CVBN), suited for pressure adjustment, both up and down, in all volumes as well as filling from the surroundings or release of pressure to the surroundings.

Figure 6 shows the MWC (100) during a lift of a payload (101) from a barge (103). A wireless MRU (105) adapted for transferring motion data to the MWC (100) is used in combination with either an internal MRU (or accelerometer) or a second external MRU (104) as well as transmission of winch spooling data to calculate actuator rod (21, 32) speed to ensure that the relative motion between the lower end of the MWC (100) and the barge (103) deck is close to zero, except for winch spooling, this enables safe and efficient connection between the compensator and the payload as well as safe lift off. Passive actuator cylinder (30) pressure is adjusted, by transport of gas between tanks (T1, T2, …, T3) and the gas accumulator (40), to match the actual payload weight.

Figure 7 shows the MWC (100) during a subsea lift of a payload (101). For most of the time, while in transit from the splash zone to a short time before landing, the MWC (100) is in passive mode, i.e., there is no influence on the system from the pump (P) (i.e., free flow). The MWC (100) can be put into active mode by several means, e.g., based on water depth, time, turning a ROV switch or by acoustic communication. While in active mode the MWC (100) will minimize the relative motion between the lower end of the MWC (100) and the seabed (106) to ensure a safe and controlled landing. Winch spooling data is preferably transferred to the MWC (100) via acoustic communication or via an umbilical cable to remove crane operator lag.

The MWC (100) further features a sensing means adapted for measuring the vertical motion of the MWC (100), one or more sensing means adapted for measuring the pressure in one or more volume, a computer adapted for controlling the pump (P), the gas booster (50) and the control valves (CV) based on input from the sensing means, communication means adapted to transfer signals between the vessel (102) and the MWC (100), preferably with acoustic communication while subsea and wirelessly while in air and either a battery pack or an umbilical cable for energy supply.

Table 1

Claims

1. One mobile wireline compensator (100) for reduction of dynamic loads and motion in offshore lifting operations based upon a horizontal actuator (10) characterised by that it comprises:

a passive actuator cylinder (30), comprising a piston (31) of the passive actuator cylinder (30) connected to a piston rod (32) of the passive actuator cylinder (30), and has two volumes, designated V1 and V2, where V1 is on the piston side and V2 is on the rod side, the volumes are filled differently, depending on if the passive actuator cylinder (30) is working in tension or compression mode, where V1 is filled with hydraulic fluid and is connected to a gas accumulator (40) via conduit means and V2 is either filled with oil or filled with low pressure gas or vacuum when working in compression mode and where V2 is filled with hydraulic fluid and is connected to a gas accumulator (40) via conduit means and V1 is either filled with oil or filled with low pressure gas or vacuum when working in tension mode;

an active actuator cylinder (20), including a piston rod (21) of the active actuator cylinder (20), and the passive actuator cylinder (30) have collinear longitudinal axes that are horizontal, where their piston rod (21) of the active actuator cylinder (20) and piston rod (32) of the passive actuator cylinder (30) are fixed together in a stiff connection with actuator sheaves (14, 15) at the connection point;

a position measurement means (33) to register the position of the piston (31) of the passive actuator cylinder (30);

a gas accumulator (40), featuring a piston (41) of the gas accumulator (40) that separates fluid, containing two volumes designated V6 and V7, where V6 is connected to V1 in the passive actuator cylinder (30) if operating in compression mode and to V2 in the passive actuator cylinder (30) if operating in tension mode, via conduit means adapted with a control valve (CV1), filled with hydraulic fluid and where V7 is filled with gas;

the actuator (10) further contains framework (11) joining the two actuator cylinders (20, 30) together in a stiff connection, where the framework (11) partly consists of tanks and accumulators to reduce weight, the framework (11) is further fitted with connection means (12), on one side of the mobile wireline compensator (100), used to connect the mobile wireline compensator (100) to a crane, located on a vessel (102), where the

connection means (12) is located in the centre of gravity of the mobile wireline compensator (100) or at other locations, the framework (11) further supports three secondary sheaves (17, 19a, 19b), used to support rope means (16, 18), steel wire rope, fibre rope, belt, chain, connecting the actuator sheaves (14, 15) to the connection means (12), on opposite side of the mobile wireline compensator (100), which in turn is connected to a payload (101), the rope means (16, 18) are reeved over the actuator sheaves (14, 15) and the secondary sheaves (17, 19a, 19b), with one end connected to a fixed point, the framework (11) and the other end connected to the payload (101) via the connection means (12), lowering of the payload (101) relative to the mobile wireline compensator (100) causes the actuator sheaves (14, 15) to move horizontally, the direction, towards or away from the active actuator cylinder (20), depending on if the mobile wireline compensator (100) is working in tension or compression-mode;

an accelerometer integrated into the mobile wireline compensator (100), adapted for measuring vertical motion;

communication means, wireless communication while in air and acoustic communication while submerged, adapted for transmitting data from the vessel (102), as commands and winch spooling speed, to the mobile wireline compensator (100);

a hydraulic motor (P), which is reversible, adapted to actuate the active actuator cylinder (20), based on measurement data from the position sensor (33), the accelerometer and the measurement data from the vessel (102), winch spooling speed.

2. Mobile wireline compensator (100) according to claim 1, characterised by that it further comprises:

the active actuator cylinder (20) comprising the piston rod (21) of the active actuator cylinder (20), where the piston rod (21) of the active actuator cylinder (20) is a hollow piston rod, connected to a piston (23) of the active actuator cylinder (20), a second piston rod (24) of the active actuator cylinder (20), where the second piston rod (24) of the active actuator cylinder (20) is a hollow piston rod connected to a second piston (22) of the active actuator cylinder (20), where the second piston rod (24) of the active actuator cylinder (20) and the second piston (22) of the active actuator cylinder (20) are mounted concentrically inside the piston rod (21) of the active actuator cylinder (20) and fixed to one end of the active actuator cylinder (20), the active actuator cylinder (20) has three separate volumes, designated V3, V4 and V5; V3 is located between: the inside of the piston rod (21) of the active actuator cylinder (20), the inside of the second piston rod (24) of the active actuator cylinder (20), the top of the second piston (22) of the active actuator cylinder (20) as well as the end of the actuator cylinder (20) and is filled with hydraulic fluid; V4 is located between; the inside of the piston rod (21) of the active actuator cylinder (20), the outside of the second piston rod (24) of the active actuator cylinder (20), the bottom of the second piston (22) of the active actuator cylinder (20) and the piston (23) of the active actuator cylinder (20) as well as the end and inside diameter of the active actuator cylinder (20) and is filled with a low pressure gas or vacuum; V5 is located between; the outside of the piston rod (21) of the active actuator cylinder (20), the top of the piston (23) of the active actuator cylinder (20) as well as the end and inside diameter of the actuator cylinder (20) and is filled with a hydraulic fluid;

conduit means between V3 and V5 adapted with a hydraulic pump (P) adapted to transport oil under pressure between the respective volumes in any direction, adapted with control valves (CV2, CV3) and a gas accumulator (60) suitable for handling pump leakage and providing low flow restriction when the mobile wireline compensator (100) is used in passive mode,, there is no influence on the system from the pump (P);

a gas booster (50), which is of either single acting or double acting type, with or without area difference between gas and drive side, including means to drive it, which is either hydraulic- or gas-based;

a number of tanks (T1, T2, …, TN) suitable for gas storage; conduit means between V7 and each of the tank (T1, T2, ..., TN) volumes in parallel with V7 adapted with control valves (CVA1, CVA2, ..., CVAN) in each conduit means for individual adjustment of the volume size connected to V7;

conduit means between all gas volumes in V7, each of the tanks (T1, T2, …, TN), the gas booster (50) in parallel connection as well as the surroundings, adapted with control valves (CV4, CV5, CV6, CVB1, CVB2, …, CVBN) in each conduit means, suited for individual pressure adjustment, both up and down, in all volumes as well as filling from the surroundings or release of pressure to the surroundings.

3. Mobile wireline compensator (100) according to any one of claims 1-2, characterised by that it further comprises:

a first MRU (105) placed in a crane tip; and/or

a second MRU (104) placed in the vicinity of the payload (101), adapted for transmitting wireless signals to the mobile wireline compensator (100), to improve control over the active actuator cylinder (30).