WO2015038004A1

WO2015038004A1 - Computerized device for compensation of wave-caused distance variations on a drill string

Info

Publication number: WO2015038004A1
Application number: PCT/NO2014/050164
Authority: WO
Inventors: Tommy Andre Hognestad LILAND
Original assignee: Depro As
Priority date: 2013-09-12
Filing date: 2014-09-08
Publication date: 2015-03-19
Also published as: NO20131234A1

Abstract

Device (11) for compensation of wave-caused distance variations on a drill string between a floating drill rig and a seabed-fixed installation, comprising an extendable cylinder/ piston unit (12) which is arranged to be able to compensate when the load exceeds a pre-determined threshold value. The cylinder (13) of the cylinder/ piston unit (12) comprises in its base position a non-compressible liquid at both sides of a piston (14) positioned substantially in the middle of the cylinder (13) and is prevented from fluid communication with the surroundings. The device (11) is a complete, self-supported unit comprising cylinder (13), piston (14) on a piston rod (15), accumulator (17), and drainage tank (20). The device is arranged to be activated by a computer controlled solenoid valve (26) when a value measured by a load measuring sensor (24, 24') exceeds a defined, adjustable value.

Description

Computerized device for compensation of wave-caused distance variations on a drill string

The present invention relates to a device for compensation of wave-caused distance variations on a drill string between a floating rig and a seabed-fixed installation.

Background

When drilling offshore, it has become common to use floating units which at least during the actual drilling operation is fixedly attached to a fixed installation where the drill penetrates the seabed. For the purpose of compensating for wave-caused distance changes, i.e. vertical changes in distance from the seabed to the floating drilling rig utilized, so-cai ed heave compensation is in continuous operations. However, such compensation will fail sooner or later, and it is thus desirable, and has eventually become a requirement, that there is an extra device to ensure that the equipment is not torn apart by the forces of waves if the primary heave compensation for any reason ceases to work.

From WO publication 2011 074984 is known a system for dealing with the above problem, comprising a trigger module for attachment to a tubing string in a heave-compensated, load- bearing unit disposed on a floating installation, wherein two or more hydraulic cylinder units form an extendable connection between the heave-compensated, bad-bearing unit and a portion of the tubing string. The hydraulic cylinder unit must have fluid communication with an accumulator unit and there is a need for hydraulics and accumulator fluid pipes between the hydraulic cylinder unit and a gas reservoir in a suitable manner. A disadvantage with this solution is that the accumulator is not arranged on the heave compensated unit. This gives a higher risk of a safety failure, since the fluid communication pipe is exposed to external elements that might deform it or tear it apart.

The installation time For the described heave compensated unit can be extensive and there is a risk of erroneous installation due to the number of components of the system. Any errors might lead to a stop in the floating installation in question and damage to the equipment.

EP 1 428 973 describes a portable heave-compensator for use on a drill string between a floating drill rig and seabed-fixed installation. It provides a tensional force to support the drill string and allows the drilling vehicle to remain attached to the drill string under variations caused by waves or other changes of surface level. It comprises a hydraulic fluid accumulator, at least one chamber for pressurized air and a piston with a piston rod arranged to move in a cylinder. In one embodiment the accumulator surrounds the cylinder. The accumulator can include two ports, one for allowing fluid communication between the cylinder and the accumulator and one for allowing fluid communication between the accumulator and the container for pressurized air. The first mentioned port includes a closable valve. In base position a non-compressible fluid is present at both sides of the piston which is positioned substantially in the middle of the cylinder which is prevented from fluid communication with the surroundings.

US 2005/077 049 describes an apparatus and a method for protecting against problems associated with "heave" on a floating drill rig. The apparatus comprises an inline compensator which has a number of cylinders in a tube shaped housing and a number of low pressure and high pressure accumulators acting together in a system to compensate for heave in case the primary heave compensating system should fail or become inactive. The inline compensator utilizes a number of hydraulic cylinders acting in opposite directions and having different piston areas so that the cylinders are expanded or compressed at different pressure levels. The equipment is adapted for use together with coiled tubings.

There is thus still a need for a simple, robust, compact and reliable device that can ensure that the need for wave-caused distance variations between a floating rig and a seabed-fixed installation.

Objectives

It is thus an object of the present invention to provide a device which is capable of compensating wave-caused distance variations between a floating drill rig and a seabed-fixed installation, which also fulfills the criteria of being compact, robust, and comparatively inexpensive in production and which requires little maintenance.

It is also an object that the device is simpler to adapt to different areas of use and different operational conditions.

It is also important that the installation of the device is quick and safe.

The system as described is subject to regulations SIL 2 hit IEC 61508 to ensure reliable activation. The present invention

The above objects are achieved by the device according to the present invention.

By the term complete, self-supported unit is understood that the unit does not need external supply either in the form of electricity or other kind of energy, since the energy and the controlling mechanism needed for the unit to be operative, is supplied by the unit itself. There is thus no need for pipes or cables to the unit which is just mounted to the drill string in question and is then in a state of readiness, until the activation point defined by the separate floating unit is reached. The device according to the present invention has the advantage compared with the prior art technology in this area that it may be configured wireless, quickly and safe from a driller cabin. The load (tension) required to activate the system, in accordance with the weight of the system, can be readjusted in matter of seconds without requiring physical contact with the equipment.

An extra function or advantage is that when the drill string is attached to a seafloor-fixed structure and the operators want to test the connection, this is typically done by a so-called "overpull" test. With the device according to the present invention the activation can be overruled, something which is not possible with the prior art systems using valve activation at a certain pressure.

In addition the device according to the present invention is simple, easy and safe to install, since it is a free-standing heave compensating unit.

Figure 1 shows a perspectival drawing of the device according to the invention.

Figures 2a-2c show, in a simplified manner, the operation of the device according to the present invention in three different positions or phases.

Figure 3 shows an end cross-sectional view of the device shown in Fig. 1.

Figures 4a-4c show in principle the same as the figures 2a-2c, but in a slightly different technical embodiment.

Figure 1 shows a device 11 according to the present invention, comprising to extendable cylinders/ piston units 12 wherein the cylinders 13 have their closed end facing upwards while the piston rods 15 extends downwards from the cylinders. The pistons are in Fig. 1 hidden in the cylinders 13. Fig. 1 also shows accumulators 17, main valve 19, drainage tanks 20 and dump valve 21.

An upper attachment collar 22 is shown at the top of Figure 1 and a lower attachment collar 23 is shown at the bottom, for attachment to an element of a unit which provides heave compensation to a drill string on one side and either fixed equipment or another element of heave compensated drill string on the opposite side. Preferably the device according to the present invention is used at the surface, the upper attachment collar 22 being attached to a drill apparatus (not shown) while the lower attachment collar 23 is attached to a unit which heave compensates a drill string.

Figures 2a-2c illustrate the present invention's manner of operation in a simple way. While Figure 1 shows a realistic appearance for the device according to the present invention, Figure 2 only illustrates functional principles. Figure 2 shows the extendable cylinder/ piston unit 12, comprising cylinder 13, piston 14, piston rod 15 and an attachment ear 16 on the piston rod. The cylinder 13 has its closed end facing upwards while the piston rod 15 protrudes downwards from the cylinder 13. The piston 14 is shown about a middle vertical position within the cylinder 13. Accumulator 17, accumulator piston 18, main valve 19, drainage tank 20 and dump valve 21 are also shown. Finally a load measuring sensor in the form of a pressure transmitter 24, a computer unit such as a PLC 25 and a solenoid valve 26 are shown. The dotted lines to and from the pressure transmitter 24, the PLC 25 and the solenoid valve 26 represent communication signals that can be transmitted in any convenient manner and which preferably are wirelessly transmitted. The cylinder 13 is filled with a non-compressible liquid and the valves 19, 21 are closed; therefore piston 14 remains stationary within the cylinder 13 and compressional forces and tensional forces may be transmitted over the cylinder/ piston unit 12 without moving the piston.

Figure 2b shows a situation in which the pressure has exceeded a threshold value so that the pressure transmitter 24 has transmitted a signal to PLC 25 that the threshold value for allowable pressure has been exceeded. The PLC unit immediately ensures that the solenoid controlled valve 19 is opened by activating solenoid valve 26.

Then there is fluid communication from accumulator 17 to the bottom side of the cylinder 13. Optionally the dump valve 21 opens simultaneously with the main valve 19, in which case there is in this stage also open connection between the top side of cylinderl3 and the drainage tank 20.

With a tensional force to the cylinder/ piston unit 12, the piston 14 will now move downwards and expel liquid from the cylinder 13 to the accumulator 17, where an accumulator piston 18 that at all times separates gas from liquid, is displaced in an upwards direction in the accumulator against an increasing counter-force as the gas above the accumulator piston is compressed to higher and higher pressures.

The weight of the platform and its equipment will, however, be so large that the wave height determines to what extent the accumulator piston 18 is pushed upwards in the accumulator and thereby how far the piston 14 is pulled downwards in the cylinder 13. If the dump valve 21 remains closed in this stage, an underpressure is created above the piston 14 in the cylinder 13, which also contributes to slow down the movement of the pistons 14 and 18. A simpler function is to "force control" the dump valve 21 in a manner ensuring that it is always closed when main valve 19 is closed and always open when main valve 19 is open, since the unit functions excellent this way and no separate control mechanism is then required for the dump valve 21. It should be emphasized that even if main valve 19 and dump valve 21 are discussed in singular, there is typically one main valve per accumulator and one dump valve per drainage tank, so there may be two or more of each of these valves in one and the same device. It is worth noticing that the solenoid valve 26 and the main valve 19 in theory could be one and the same valve. Since, however, a rapid movement of significant volumes of liquid between the cylinder 12 and the accumulator 17, it is convenient to control one (main) valve 19 with large capacity by means of a solenoid valve having less capacity.

With regard to the main valve 19, this has, as the designation indicates, a built in trigger function that allows the valve to open at a certain pressure. Alternatively the valve may be in contact with one or more pressure sensors (not shown) included in the device, producing signal for opening of the main valve 19. When the main valve opens at a certain but adjustable threshold pressure, to thereby activate the device 11 so that open fluid communication is established between cylinder 13 and accumulator 17, the length of the cylinder/ piston unit 12 can be freely changed between mechanically determined limits.

When the platform passes a wave-top and moves towards a wave-bottom, the situation shown in Figure 2c occurs. The piston 14 in the cylinder 13 is forced upwards so that the length of the cylinder/ piston unit 12 is reduced. The piston 14 then sucks liquid back from the accumulator 17 into the cylinder 13 while liquid above the piston 14 is forced into the drainage tank 20 via dump valve 21, which, independent of whether having been open or closed in the above discussed stage, is open in this stage.

In general, after the main valve 19 has been opened and until it is manually or automatically closed, there is a dynamic balance in the system, determined by the wave variations influencing the floating construction and slowed or moderated by the pressure in the accumulator 17.

Figure 3 shows an end view of the device shown in Figure 1 (and which principally functions as illustrated in the Figures 2a-2c). Here an upper connection flange 22 is shown, two extendable cylinder/ piston units 12, eight accumulators 17 and two drainage tanks 20. It is worth noticing that the extendable cylinder/ piston units 12 typically are arranged in pairs, and that there may be two or more accumulators 17 and at least one drainage tank 20 for each respective cylinder/ piston unit 12. In general, the device typically comprises at least two extendable cylinder/ piston units 12 and at least one accumulator 17 and at least one drainage tank 20 per cylinder/ piston unit 12.

With regard to the illustrations 4a-4c, it is generally referred to the discussion of the figures 2a-2c. The course of events is the same, the only difference is that as load measuring sensor a strain gauge 24' is used rather than a pressure transmitter 24.

The specific manner of operation to pressure transmitter, strain gauge, PLC unit and solenoid valve is not described here, since these components individually are well known and frequently used in control engineering. Suitable components of said types can be acquired off the shelf.

The object with device of the present invention is primarily to provide a secondary or reserve compensation for wave-caused distance variations between a floating structure and a seabed- fixed construction which automatically is activated when a primary heave-compensation fails.

The genuine new concept is primarily how the activation is conducted as defined by the characterizing part of claim 1. By the changed operational conditions the load that calls for activation can rapidly and easily be controlled from a control room and if needed for testing purposes, the activation can be overruled correspondingly. Furthermore the possibilities for remote controlling and deactivation are improved by the present invention.

Claims

1. Device (11) for compensation of wave-caused distance variations on a drill string between a floating drill rig and a seabed-fixed installation, comprising an extendable cylinder/ piston unit (12) which is arranged to be able to compensate when the load exceeds a pre-determined threshold value, the cylinder (13) of the cylinder/ piston unit (12) in base position comprising a non- compressible liquid at both sides of a piston (14) positioned substantially in the middle of the cylinder (13) and being prevented from fluid communication with the surroundings, while the device (11) is a complete, self-supported unit comprising cylinder (13), piston (14) on a piston rod (15), accumulator (17), and drainage tank (20), the device being arranged to be activated by a computer controlled solenoid valve (26) when a value measured by a load measuring sensor (24, 24') exceeds a defined, adjustable value.

2. Device as claimed in claim 1, in which the computer controlled solenoid valve (26) is controlled by a PLC, programmable logic controller (25).

3. Device as claimed in claim 2, in which the load measuring sensor is a pressure transmitter (24) arranged to generate an electric signal to the PLC (25) at a measured load exceeding a defined, adjustable value.

4. Device as claimed in claim 2, in which the load measuring sensor is a strain gauge (24') arranged o generate an electric signal to the PLC (25) at a measured load exceeding a defined, adjustable value.

5, Device (11) as claimed in claim 1, in which the accumulator (17) in its base position is filled with gas under pressure and equipped with a main valve (19) which subsequent activation can release fluid into as well as out from the accumulator.

6. Device (11) as claimed in claim 1, comprising at least one drainage tank (20) arranged to temporarily receive surplus amount of liquid from the cylinder (13) when the device is activated, a dump valve (21) between the cylinder (13) and the drainage tank (20) being arranged to open for transferring the surplus amount of liquid.

7. Device as claimed in claim 1, being arranged to make use of non-compressible liquids.

8. Device as claimed in claim 1, the cylinder/ piston unit (12) in the base position having a fixed length and being rigid in the sense that in this position tension forces and compression forces can be conveyed along the length thereof without a change of its length.

9. Device as claimed in claim 1, the device subsequent activation remaining in the active state until it is manually reset to the base position.

10. Device as claimed in claim 1, the device comprising at least two cylinder/ piston units (12) and at least one accumulator (17) and at least one drainage tank (20) per cylinder/ piston unit (12).