VALVE ASSEMBLY

The invention concerns a gate valve assembly especially a gate valve assembly arranged for receiving an elongated member in its through bore. If necessary the elongated member is sheared in the through bore and the through bore is closed in a sealed manner. The invention may also be applicable to other kind of gate valves or valves.

The invention also concerns a method for operating a sealing in a gate valve assembly, a system providing temporary access to a well and a method for emergency shut down of an access to a well.

The elongated member as described in the application includes well related tubular formed elongated member such as a wire line or coiled tubing, pipes or drill pipes used in work over, drilling, completion, production or intervention operations.

Background of the invention To ensure safety the well access system equipment capable of cutting and sealing must be provided within the well access system for rapidly closing down the well should an emergency situation arise. Equipment available in the marked today are either based on rams (shear rams) with elastomeric ram seals or metal-to -metal gate valves. Rams are intended for shearing and sealing, but they have limitations to temperature and high speed flowing due to large elastomeric seals. Gate valves are designed as gas tight working valves, but are not designed particular for shearing. The cutting tool of the gate valve is often formed at a front edge of the movable gate element of the gate valve, arranged so that the gate valve is moved into closed position for sealing after conducting the cutting of the wireline or tubing. By adding sufficient force to the gate valve through the actuator, the gate might shear heavy coil tubing, but there is a risk that the cut parts of the tubular or wire line are stuck during the closing of the gate element, and/or that scratches are inflicted on the gate element and seats as a result of the shearing.

There is a possibility of leakage from the through bore of the gate valve assembly as result of insufficient sealing between the seal seat and the gate element due to damages or scratches in the sealing surface or small cutting parts getting stuck when closing the gate element.

To solve this problem various solution has been proposed. It is known within the prior art to coat the surface of the gate element or the seal seat with a hard material to prevent scratching. Further prior art solutions are described in the following publications; US 6545015 describes coating the sealing surfaces with an extremely hard material. In addition the publication describes the energizing of a sealing ring for preventing leakage between the gate valve housing and a seal seat. A ring with a rim protruding into a cavity of the sealing ring expands the sealing ring for sealing off between the leakage gap between the gate valve housing and the seal seat. The sealing ring has an orientation in the leakage gap receptive of the leakage of well fluid. The pressure of the well fluid leakage is utilized for expansion of the sealing element into sealing position in the leakage gap. US4997162 describes a solution to protect the seal seat form scratches and damages resulting in sufficient sealing against gate element, wherein the seal seat is preloaded in compression and is made of a hard material for protection against damage. US5370362 describes providing the sealing surface of the seal seat with a durable hard material to preserve sealing integrity and protect against scratching when opening and closing the gate element.

US 4625942 describes the problem with the entrapment of pressurized fluid within parts of the gate valve assembly and unwanted effect of urging the seal seat into a too tight engagement with the movable gate element. To facilitate the smooth movement of the gate element the sealing seat has a configuration which avoids the entrapment of pressurized fluid. The current invention suggests a solution to the problem with insufficient sealing around the throughbore as described above. An objective of the invention is to provide a gate valve arrangement with a compact construction, reliable working principles and a simple operation to preserve the integrity of the sealing functions of the gate valve assembly.

A further object is to provide an effective sealing arrangement for closing off the through bore even when the gate element or the sealing seat has scratches or even are more violently damaged.

Another objective of the invention is to provide the sealing arrangement

controllable so that sufficient sealing forces may be applied according to the specific need such as demanded by the operational condition of the gate valve assembly. Summary of the invention

The invention is defined in the independent claims and embodiments of the invention are defined in the dependent claims. The invention also include claims defining a system which provides temporary access to a well and method for emergency shut down of an access to a well.

In accordance with the invention the gate valve assembly comprises a gate valve housing having a through bore arranged for fluid flow and for receiving an elongated member. A gate element is arranged with a gate bore that is provided with a shear surface and arranged for receiving the elongated member. The gate element is movably arranged in the gate valve housing in a direction essentially transverse to the axial direction of the through bore between an open position essentially aligning the gate bore with the through bore, a shearing position for shearing the elongated member and a closed position preventing fluid from flowing through the through bore. The gate valve assembly further comprises at least one seal seat or element which is accommodated in the valve housing surrounding the through bore. The seal seat may be arranged in a recess in the valve housing or in a seal assembly. The seal seat is arranged with a sealing surface arranged to engage a sealing surface of the gate element. Further the gate valve assembly comprises a sealing force control system for regulating an activation force which works on the seal seat for providing a sealing force between the sealing surface of the seal seat and the sealing surface of the gate element in the closed position. The sealing force control system may comprise a source for providing an activation force and control means. The control means may be operable for regulation of the activation force which works on the seal seat for selectively sealing engagement with the gate element. The seal seat to be controlled by the sealing force control system in this manner may be an ordinary seal seat included in the gate valve assembly such as a first seal seat. The seal seat may also be a second seal seat or element provided in addition to the first seal seat. The second seal seat may also be accommodated in a recess in the valve housing positioned radially outside a first seal seat. Alternatively, the second seal seat may be arranged in a recess in the first seal seat. The first and second seal seats may form a seal assembly. The first seal seat may be arranged for providing a first sealing force and the second seal seat may be arranged for providing an additional or second sealing force. The sealing force control system may then be arranged to control the selectively sealing engagement between the first seal seat and/or the second seal seat and the gate element.

By providing the control means operable for regulation of the activation force which works on the seal seat for selectively sealing engagement with the gate element, the sealing force control system may in one embodiment be provided for a displaceably arranged seal seat. The control means may then be operable for regulation of the activation force for displacement of the seal seat between a position in sealing engagement with the gate element and a disengaged position away from the gate element.

The capability of the sealing force control system to selectively engage the seal seat with the gate element, may in another embodiment comprises a seal seat that is arranged in an initial engagement with the gate element. The control means may then be operable for regulation of the activation force for:

- provision of an initial sealing force in initial sealing engagement with the gate element in open and shearing position, - provision of an increased sealing force causing a tightened sealing engagement with the gate element in closed position.

By this arrangement the sealing engagement between the seal seat and gate element may be selected in accordance with the operational control conditions as provided by the sealing force control system. The sealing force control system may be provided for providing a sufficient sealing force during normal operation such as in open and closed position of the gate element. In the case where scratches occur or there is a risk for leakage between the gate element and the seal seat, the sealing force control system may be operable for providing an additional sealing force for ensuring sufficient sealing engagement between seal seat and gate. The control means may then be operable for regulation of the activation force for providing an increased sealing force thereby selecting a tightened sealing engagement with the gate element to ensure that scratches or damages do not result in a leakage. As mentioned above the seal seat may be provided as a second seal seat which is provided in addition to a first seal seat of the gate valve assembly. The first seal seat may then arranged so as to provide sufficient sealing force with the gate element during the normal operation of the gate valve assembly, whereas circumstances may demand the need for additional sealing with the gate element such as in a emergency mode, where the risk of scratching or damaging the seal seat is increased compared to a normal mode operation. The sealing engagement between the first seal seat and the gate element may be provided by the sealing force control system as explained above or by any conventional sealing force arrangement well known to the skilled person. In accordance with the embodiment where the gate assembly comprise a first and a second seal seat, the sealing force control system as described above may be provided for controlling the sealing engagement between the second seal seat and the gate element. The second seal seat may then be displaceably arranged or arranged in an initial sealing engagement with the gate element as explained when describing the seal seat above. When the second seal seat is displaceably arranged the sealing force control system control the displacement of the second seal seat by regulation of the activation force to select the sealing engagement with the gate element by moving the second seal seat into sealing engagement with the gate element or away from the sealing engagement with the gate element seal seat. In accordance with this embodiment the control means regulate the activation force for obtaining a disengaged position of the second seal seat away from the gate element when the gate element is in open and shearing position. And when in the gate element is in closed position the sealing force control system is arranged for displacement of the second seal seat into engagement with the gate element.

When the second seal seat is arranged in an initial sealing engagement with the gate element the sealing force control system may control the sealing force by regulation of the activation force to increase or decrease the sealing force to select the sealing engagement with the gate element. In accordance with this embodiment the control means regulate the activation force for provision of an initial sealing force in engagement with the gate element in open and shearing position. And when in the gate element is placed in a closed position the sealing force control system is arranged for provision of an increased sealing force causing a tightened sealing engagement with the gate element.

The ability of the displaceably arranged second seal seat to be moved between a position away from the gate element and into an engagement position disengaged with the gate element, reduces the risk of the second seal seat being inflicted during shearing. When moving the second seal seat into sealing engagement with the gate element such as in an emergency procedure, the second seal seat engages the gate element with a sealing surface which is likely to be intact and the sealing integrity of the gate valve assembly is thereby ensured.

The source of the sealing force control system may be a fluid pressure source or any other source capable of providing an activation force on the seal seat. Fluid lines may connect the fluid source to a fluid exposure area of the seal seat. The following explanations of the sealing force control system for controlling the operation of the seal seat may apply to a first and/or a second seal seat combined in the gate valve assembly or in an embodiment where the gate valve assembly has seal seat(s) configured as first seal seats or ordinary main seal seats. The control means may be arranged operable for control of fluid flow in the fluid lines between the fluid source and the fluid exposure area for regulation of the activation force working on the seal seat. The fluid pressure source may comprise a High Pressure Unit (HPU), an

accumulator bank or fluid bank that may be located on an ROV. The source provides an activation force such as a pressure force or for instance a suction force. If needed a pressure intensifier for instance a piston with a pressurizing effect may be included for pressurizing of the fluid providing the activation force.

In one embodiment the fluid lines may comprises two set of fluid lines. The control means may then be arranged operable for allowing pressurized fluid from the fluid source through the first set of fluid lines while preventing fluid flow through the second set of fluid lines and vice versa. In accordance with this embodiment the first set of fluid lines is dedicated to connect the fluid source to an upper exposure area of the seal seat. When the first lines are connected to the fluid source pressurized fluid flow through the first fluid lines to the upper exposure area of the seal seat exerting activation force on the seal seat for displacement of the seal seat into sealing engagement with the gate element. And when the second lines are connected to the fluid source pressurized fluid flow to a lower fluid exposure area of the seal seat for pressurized fluid to exert the activation force on the seal seat for positioning or displacement of the seal seat away from the gate element.

The control means may be provided as a valve arrangement such as for instance a valve unit controlling the fluid flow from the source through the fluid lines by the position of the valve unit. The valve unit may have a first position connecting the fluid source and the second fluid lines establishing fluid flow through the valve unit for instance to the lower exposure area of the seal seat to obtain a displaced position away from the gate element. In this first position, the valve unit may be arranged for disconnecting the fluid flow on of the first fluid lines from the fluid source for instance by venting the first fluid lines through a valve.

The valve unit may have a second position connecting the fluid source and the first fluid lines establishing fluid flow through the valve unit for instance to the upper exposure area of the sea seat to obtain a sealing engagement with the gate element. In this second position, the valve unit may be arranged for disconnection of the flow through the second fluid lines from the fluid source for instance by venting the second fluid lines through a valve. The valve unit may be provided with a spring and a control fluid flow line for supply of a control fluid to the valve unit for controlling the positions of the valve unit. The valve unit may be moved between first and second position by balancing the pressure of the control fluid with the spring force of the spring. The valve unit may be maintained in the first position when the pressure of the control fluid exceeds the spring force. The valve unit may be moved from the first position to the second position when the pressure of the control fluid in fluid line is reduced to a level where the spring force is not exceeded, such as when venting the control fluid line.

The valve unit as described here may also be arranged for controlling the sealing force of a seal seat arranged in initial sealing engagement with the gate element. By altering the positions of the valve unit between first and second position,an initial sealing force in engagement with the gate element and a tightened sealing engagement with the gate element may thereby be provided accordingly

corresponding to first and second position of the valve unit. As an alternative the sealing force control system may be provided for an electrified actuation of the seal seat such as a first and/or second seal seat. The source may be an electrical source with signal lines connecting the electrical source to a magnetic arrangement of the seal seat. The control means may then be provided for regulation of signals between the electrical source and magnetic arrangement of the seal seat in order to adjust the activation force working on the seal seat.

As the skilled person will realize the sealing force control system when employing the valve units or with alternative devices, may be provided in many ways in order to provide an activation force and regulate this activation force working on the seal seat for selectively sealing engagement with the gate element.

Another alternative is that the sealing force control system control a release spring unit for providing an activation force for actuation of the seal seat, such as first and/or second seal seat.

The seal seat may be provided with means for supply of a sealing fluid for instance a lubricating fluid, to be received between sealing surfaces of the seal seat and the gate element. Further means for pressurization the sealing fluid may be provided to seal for leakage that might occur due to scratching or damages on the gate element and or seal seat. The supply means may comprise a fluid passage for supply of the sealing fluid to the sealing area between the sealing surface of the seal seat and the sealing surface of the gate element. The sealing fluid should be pressurized to a pressure level which exceeds the pressure of the fluid flow in the through bore in order to avoid leakage from the through bore.

The means for supply of a sealing fluid may be provided for a seal seat such as a first seal seat and/or second seal seat. In one aspect at least one seal seat of a gate valve assembly may be provided by the means for supply of a sealing fluid either in the first or second seal seat or in both. One possibility is to combine a seal seat arranged with means for supply of a sealing fluid with a displaceable seal seat or a seal seat in initial sealing engagement arranged to be brought into sealing engagement with the gate element by the sealing force control system as described above. It should be mentioned that an arrangement comprising a seal seat provided with means for supply of a sealing fluid to be received between sealing surfaces of the seal seat and the gate element and means for pressurization the sealing fluid may work as a solution independent of the gate valve assembly as described earlier. The arrangement as such may represent an independepent solution for sealing leakage due to scratching and damages in the gate element/seal seat.

In one embodiment the seal seat such as the first and/or second seal seat may be arranged with a compressible portion at the sealing surface end of the seal seat facing the gate element. The compressible characteristic of this portion may provide sealing effect when the seal seat is arranged in sealing engagement with the gate element such as when the activation force positions the seal seat into sealing engagement with the gate element. The invention further concerns a system providing temporary access to a well comprising a gate valve assembly as described herein. The system may further comprise temporary access device such as a Riserless light Well Intervention (RLWI)-stack, landing string or similar equipment for providing temporary access to the well. An elongated member such as a wireline/drillpipe may be employed for deploying a RLWI stack at installation position without the need for using a riser.

The method in accordance with the independent method claim is for operating a sealing seat in a gate valve assembly. The gate valve assembly comprises a gate valve housing having a through bore arranged for fluid flow and for receiving an elongated member. Further the gate valve assembly comprises a gate element having a gate bore provided with a shear surface and arranged for receiving the elongated member and a seal seat accommodated in the valve housing surrounding the through bore, which seal seat is arranged with a sealing surface to engage a sealing surface of the gate element. The method comprises the steps of: -moving the gate element in the gate valve housing in a direction essentially transverse to the axial direction of the through bore for shearing of the elongated member and moving the gate element to a closed position,

- operating a sealing force control system for regulating an activation force working on the seal seat to provide a sealing force between the sealing surface of the seal seat and the sealing surface of the gate element in the closed position. The sealing force may be controlled by controlling the activation force using the sealing force control system.

The sealing force control system may comprise a control fluid source and control means which are operable for regulating the activation force, and the method may further comprise the steps of operating the control means and controlling fluid flow through fluid lines by connecting the control fluid source which is a fluid source to an exposure area of the seal seat for engaging the seal seat in sealing engagement with the gate element and disengaging the seal seat from sealing engagement with the gate element.

The invention also concerns a method for emergency shut down of an access to a well wherein the method comprises the steps of the method as presented above: -moving the gate element in the gate valve housing in a direction essentially transverse to the axial direction of the through bore for shearing of the elongated member and moving the gate element to a closed position,

- operating a control system comprising a source and control means which is operable for regulating an activation force working on the seal seat to selectively provide a sealing force for sealing engagement with the gate element in its closed position.

Further this method for emergency shut down of an access to a well may also comprise the steps of operating the control means and controlling fluid flow through fluid lines by connecting the source which is a fluid source to an exposure area of the seal seat for engaging the seal seat in sealing engagement with the gate element and disengaging the seal seat from sealing engagement with the gate element.

These and other characteristics of the invention will be explained in more detail with reference to the attached drawings showing a non-restrictive example

Brief description of the drawings Figs. 1 and 2 show an example of a gate valve assembly during working mode operation with the gate element shown in in an open position in Fig. 1 and a closed position in fig 2.

Figs. 3 and 4 show an example of the gate valve assembly with the gate element shown in a shearing position in Fig. 3 and in a closed position in Fig. 4. Figs. 5 6 show an example of operational steps for activation of a sealing arrangement when the gate element is in a closed position.

Figs. 7a to7c show examples of embodiments of a sealing seat.

Figs. 8 and 9 show an example of a sealing force control system for operation of the seal seat provided as a second seal seat.

Figs. 10 and 1 1 show an example of a set of a first and second seal seat arranged at one side of the gate element.

Fig. 12 shows an example of the gate valve assembly with the sealing force control system arranged for providing an activation force on a first seal seat with the gate element in a shearing position and in a closed position.

Figs. 13 to 14 show an example of the first seal seat arranged for supplying a sealing fluid to sealing surface between gate element and first seal seat.

Fig. 15 shows the gate valve assembly arranged with a combination of a seal seat as shown in Figs. 13 tol4 and a seal seat as shown in Fig. 12.

Figs. 16 to 19 show an example of an embodiment of a gate valve assembly according to the invention. Detailed description of an embodiment of the invention

Fig. 1 show a gate valve assembly 1 comprising a gate valve housing 100 with a through bore 3 extending through the gate valve housing 100. The through bore 3 is arranged for fluid flow and for receiving an elongated member, as illustrated by a wireline 5 in Figs. 3 and 4.

The gate valve assembly 1 is arranged with a gate element 2 which is

accommodated in the valve housing 100 and is movably arranged in a bore 101 of the gate valve housing in a direction transverse to the axial direction of the through bore 3.

The illustrated gate element 2 is formed with a gate bore 4 and has at least one shearing surface 15 for cutting of an elongated member such as a wireline 5 should an emergency situation arise.

In Figs. 1 and 2 the gate valve assembly 1 is shown during normal working operation. The through bore 3 is open for fluid flow when the gate element 2 is placed in an open position as shown in Fig. 1. In the open position of the gate element 2 the gate bore 4 is essentially aligned with the through bore 3 and the gate assembly is ready for receiving an elongated member in the through bore 3. It is further seen from fig 1 that the gate bore 4 has a diameter which corresponds essentially to the diameter of the through bore 3 extending through the gate valve housing.

The gate element 2 may also be moved into a closed position during normal working mode as illustrated in fig 2. The gate element 2 has then moved the gate bore 4 away from communication with the through bore 3, thereby preventing fluid flow to occur through the through bore 3. During normal working operation of the gate assembly the elongated member is removed from the through bore 3 before moving the gate element into closed position as shown in fig 2. In one embodiment the gate valve assembly 1 may be arranged with a first seal seat or element 6 accommodated in a first seal seat recess 70 in the gate valve housing 100, and in the shown example the first seal seat 6 is provided as an annular member with an opening having a diameter corresponding to that of the through bore 3. In the embodiments shown in Figs. 1-6 two first seal seats 6 are arranged at either side of the gate element 2; one first seal seat 6 at a downstream location and the other at an up stream location. The first seal seats 6 are provided for preventing leakage from the through bore 3 and consequently needs to perform sufficient sealing force against the gate element both in the open and in the closed position of the gate element 2. The gate valve assembly also includes a second seal seat or element 7 positioned radially outside the first seal seat in the valve housing. The second seal seat 7 in the shown embodiment is provided as an annular member arranged with an opening accommodating the first seal seat 6 to fit with the through bore 3. The second seal seat 7 is arranged at either side of the gate element 2 constituting an upstream seal and a downstream seal. In accordance with the shown embodiment the second seal seat 7 is arranged in the gate valve assembly in order to provide an additional sealing force against the closed gate element 2 in the cases where the sealing force between the first seal seat 6 and the gate element is not sufficient for preventing leakage of fluid from the through bore. The second seal seat 7 is located in the gate valve housing in a recess 170 that may be a continuation of the recess 70 for the first seal seat or a recess separate from the first seal seat recess.

As seen from Figs. 1 and 2 during normal working operation the second seal seat 7 is disposed in an inactive position where it does not exert a sealing force onto the gate element, neither in closed nor in open position of the gate element 2. When the gate element 2 is operated in accordance with normal operational mode, the first seal seat 6 is capable of providing sufficient sealing force in engagement with the gate element and thus activation of the second seal seat 7 is usually not necessary. This of course do not exclude the operation of the second seal seat 7 into sealing position with the gate element in closed or open position should the circumstances demand that this is necessary.

The second seal seat 7 is shown disengaged from the gate element 2 in a displaced position retracted away from the gate element 2. As an alternative or a supplement to the shown displaceable seal seat 7, the second seal seat 7 may be arranged with provisions to exert an initial sealing force in engagement with the gate element 2 in an open and shearing position as shown in Fig. 3 and with provision of an increased sealing force causing a tightened sealing engagement with the gate element in the closed position.

The gate element 2 in the figures are shown with a larger width and has a longer stroke compared to prior art solutions, in order to make room for the second seal seat 7 next to the first seal seat along the gate element.

Figs. 3 and 4 illustrate the shearing of an elongated member 5 such as a wire line as part of a emergency procedure where the gate element 2 needs to be closed quickly and there is no time to pull the wire line before closing the gate element 2.

The gate element 2 is shown in closed position in Fig. 4. A portion 16 of the cut off wireline is shown trapped in the gate bore 4. During the shearing procedure scratches may have been inflicted on the sealing surface of the first seal seat 6 facing the gate element 2 or on the gate element itself and/or cut off wireline might get stuck. These possible damages to the first seal seat 6 and the gate element 2 represent a possible risk for leakage in the sealing surfaces 80, 90 between the gate element and the first seal seat 6. To ensure that the sealing integrity of the valve assembly is kept intact also when the first seal seat 6 is damaged, the second seal seat 7 serves the purpose of providing additional sealing when arranged in sealing position against the closed gate element 2. The second seal seat 7 is shown in a position disengaged from the gate element 2 during the shearing of the wire line as illustrated in fig 3. In the closed position as illustrated in fig 4, the second seal seat 7 is also shown in a position disengaged from the gate element 2. The arrangement of the second seal seat 7 in a retracted position protects the sealing surface 95 of the second seal seat 7 during the shearing of the wireline.

Once the gate element 2 is closed the second seal seat 7 is operated for

displacement into sealing engagement with the gate element 2 as illustrated by arrow A, thereby contributing to the sealing of the through bore 3. As illustrated in Fig. 6, the second seal seat 7 may be operated for later disengagement from the gate element 2 by displacing the second seal seat 7 into a position retracted from the gate element 2. This may be necessary when the gate element 2 is to be moved to open position for resuming normal operation of the gate valve assembly 1.

The second seal seat 7 (and or the first seal seat 6), may be provided in metal and may be made up by a metal having the same hardness characteristics all through the seal seat or alternatively with a varying hardness characteristics. The second seal seat 7 (and or the first seal seat 6) may be provided in a soft or hard material. In another embodiment the second seal seat 7 (and or the first seal seat 6) may be made so that that one portion of the seal seat has a softer or more compressible part, preferably the portion of the second seal seat 7 intended to face gate element 2 when in sealing engagement, whereas the remaining part of the second seal seat 7 may have a harder part provided for enduring forces exerted on the second seal seat 7 when in sealing engagement with the gate element 2. Figs. 7a and 7b show examples of a configuration of the second seal seat 7 where at least a protruding portion 8 such as for instance a bump as shown in Fig. 7a or two bumps as illustrated in Fig. 7b are provided at the portion of the second seal seat 7 to face the gate element 2. In engagement with the gate element 2 the protruding portion(s) 8 will be pressed into the gate element 2 thereby establishing a tighter seal engagement with the gate element 2.

Fig. 7c shows an example of a second seal seat 7 with a configuration where an inner wall 96 and an outer wall 97is spaced from each other leaving room for receiving a sealing fluid 65 for instance a lubricator in the space 19 between the inner and outer wall. The inner and outer walls 96, 97 of the second seal seat 7 may be provided by two radially spaced annular elements 17, 18 as shown in the Fig. 7c. The second seal seat 7 is shown with two bumps, one bump provided one on each annular elements 17, 18. Alternatively the second seal seat 7 as shown in Fig. 7c may be provided with one bump or no pumps. When carrying out the sealing procedure for the second seal seat 7 shown in Fig. 7c, the second seal seat 7 as a whole, is first brought into sealing engagement with the gate element 2 as illustrated by arrows B in Fig. 7c, or alternatively the inner and outer walls are brought separately into engagement in a stepwise procedure. After the second seal seat 7 is set against the gate element 2, the sealing fluid 65 such as lubricator is supplied into the space as illustrated by arrow C in Fig. 7c and pressurized to provide an sealing effect between the seal seat and the gate element and prevent leakage from occurring due to scratches and damages on the seal seat and gate element. To avoid leakage from the fluid flowing in the through bore, the pressure of the sealing fluid may be set at a high pressure level to make sure that the sealing fluid pressure is larger than the pressure of the fluid flowing in the through bore 3. The configuration and workings of the second seal seat 7 as shown in Figs. 7a to7c may also be provided for an embodiment of a first seal seat 6, arranged in a valve assembly in combination with the second seal seat 7 or without the second seal seat7 .

The first seal seats and second seal seats 6, 7 arranged at both sides of the gate element may be provided clamped around the gate element as shown in the figs and ensures the establishment of two gas tight seal barriers. As shown in the figs the ability of the second seal seat 7 to be arranged in selectively sealing contact arrangement with the gate element is shown in the figures as a displaceably arranged seal seat. Figs. 8 and 9 show an illustrative example of a sealing force control system 20 for controlling the sealing engagement with the gate element. In the figs two set of fluid lines 10, 1 1 are illustrated schematically. As mentioned earlier the second seal seat 7 may alternatively be arranged in an initial sealing engagement with the gate element 2 and the sealing force control system 20 may provide an increased sealing force causing a tightened sealing engagement with the gate element 2. The sealing force control system 20 comprises a source 21 for providing an activation force working on the second seal seat 7. The fluid lines 10, 1 1 are provided with and control means 22 operable for regulation of the activation force working on the seal seat 7. In Figs. 8 and 9 the source 21 is a fluid source such as an accumulator bank for instance a hydraulic accumulator bank and a first set of fluid lines 10 is provided for forwarding the fluid from the source 21 to a seal seat control chamber 24 where the fluid works with an activation force on an upper exposure area 23 of the seal seat 7. A second set of fluid lines 1 1 is arranged for forwarding the fluid from the source 21 to the seal seat control chamber 24 for providing an activation force on a lower exposure area 25 of the seal seat 7.

Fig. 8 shows a situation where the control means is provided for directing pressurized fluid from the source through the second fluid lines 1 1 into to the seal seat control chamber 24 to work on the lower exposure area 25 of the second seal seat 7 for displacement of the second seal seat 7 in a position away from sealing engagement with the gate element as illustrated by arrow D. In the situation as illustrated in Fig. 8 control means 22 such a valve arrangement prevents pressurized fluid from entering the seal seat control chamber 24 at the upper exposure area 23 of the seal seat 7, for instance by the control means 22 closing the first fluid lines 10 or venting these fluid lines elsewhere. The second seal seat 7 will preferably assume this position when the gate element is in an open position as illustrated in Fig. 8 and during shearing of the wire line 5. In accordance with the illustrated arrangement of the sealing force control system 20 in Fig. 9, the control means 22 such a valve arrangement is provided for allowing pressurized fluid from the source through the first of fluid lines 10 into to the seal seat control chamber 24 after shearing of the wire line has been effectuated and the gate element 2 is moved to closed position. The pressurized fluid then works with an activation force on the upper exposure area 23 of the second seal seat 7 for displacement of the second seal seat 7 toward sealing engagement as illustrated by arrow C in Fig. 8. In the situation as illustrated in Fig. 9 the control means 22 such a valve arrangement prevents pressurized fluid from entering the seal seat control chamber 24 at the lower exposure area 23 of the seal seat 7, for instance by the control means 22 closing the second fluid lines 1 1 or venting these fluid lines elsewhere.

The control means 22 is shown provided as a valve arrangement illustrated by a valve unit 26 in Figs. 8 to 1 1. The valve unit 26 is movable between a first position as illustrated in Fig. 8 and a second position as illustrated in Fig. 9. The first position of the valve unit 26 as illustrated in Fig. 8 arranges for connecting the fluid source 21 and the second fluid lines 1 1 establishing fluid flow through the valve unit 26 as illustrated by a fluid flow direction symbol 40. The fluid flows from the fluid source 21 to the seal seat control chamber 24 to the lower exposure area 25, obtaining the displaced position of the second seal seat 7 away from the gate element 2. In the first position of the valve unit 26 the first fluid lines 10 are disconnected from the fluid source 21 and the first fluid lines 10 are vented through a valve 45 as illustrated by the position of the fluid flow direction symbol 41.

The second position of the valve unit 26 as illustrated in Fig. 9 establishes fluid communication between the fluid source 21 and the first lines 10 as illustrated by fluid flow direction symbol 42. The fluid then flows from the fluid source 21 and to the seal seat control chamber 24 to the upper exposure area 23, thereby moving the second seal seat 7 into sealing engagement with the gate element 2. In the second position of the valve unit 26 the second lines 1 1 are disconnected from the fluid source 21 and the second fluid lines 10 are vented through the valve 45 as illustrated by the position of the fluid flow direction symbol 43. As illustrated in Figs. 8 to 1 1 the valve unit 26 is provided with a spring 33 and a flow line 34 for supply of a control fluid to the valve unit 26. The positions of the valve unit 26 is controlled by the spring force of the spring 33 and the pressure of the control fluid supplied to the valve unit 26 through flow line 34. As illustrated in Fig. 8 the valve unit 26 is maintained in the first position with the pressure of the control fluid exceeding the spring force thereby keeping the second seal seat 7 retracted from the gate element. The fluid lines 10 are then arranged to vent through valve 45. When the pressure of the control fluid in fluid line 34 is reduced to a level where the spring force is not exceeded, the spring force of the spring 33 will switch the valve unit 26 to the second position as shown in Fig. 9, and the second seal seat 7 is brought into sealing engagement with the gate element 2 as shown in Fig. 9.

The valve unit 26 may of course also be provided so that the spring force switch the valve unit 26 between second and first position. As the skilled person will realize the positions of the valve unit 26 may be controlled by control pressure systems having configurations which are alternative to those illustrated in the figures or by any other control unit system, for instance an electric system or other valve actuating control systems.

In Figs. 1 to 9 the gate valve assembly is shown arranged with first seal seats and second seal seats both upstream and downside of the gate element 2. As an option to the arrangement including both the first and second seal set, the gate valve assembly may of course be arranged with only one set of first and second seal seat at the upstream or downstream side of the gate element. Figs. 10 and 1 1 illustrate an embodiment where the gate valve assembly 1 has first seal seats 6 arranged at both sides of the gate element 2. In addition a second seal is 7 arranged radially outside the first seal seat 6 at the downstream side. As seen from the illustrations in Figs. 10 and 1 1 , in this embodiment of the gate valve assembly the gate element 2 has an inclined inner surface 51 with cutting surface 50 arranged at a tip portion of the inclined inner surface for one cut shearing of the elongated member 5. In the embodiments of Figs. 1 to 9 the shearing surface 15 cuts the elongated member at two places as illustrated in Fig. 4. As the shearing of the elongated member 5 occurs with a pointed cutting surface 50 in the embodiment of Figs. 10 to 1 1 , the possible scratching and damaging of the gate element and/or the first seal seat is most likely to occur at gate element and/or the first seal seat adjacent to the cutting surface 50. Hence the second seal seat 7 is arranged outside the first seal seat 6 adjacent the cutting surface 50 at a downstream side of the gate element 2.

The sealing force control system 20 for controlling the displacement of the second seal seat 7 into and out from sealing engagement with the gate element 2 is similar to the sealing force control system 20 as illustrated in Figs. 8 and 9. Fig. 10 illustrates the second seal seat 7 displaced from the gate element 2, whereas the second seal seat 7 is shown in sealing engagement with the gate element 2 in Fig. 1 1. Fig. 12 is a schematic illustration of a gate valve assembly 1 in accordance with the invention where the sealing force control system, for instance one similar to that shown in Figs. 8 to 1 1 , may be arranged to control the sealing engagement between a seal seat such as the first seal seat 6 and the gate element 2. As illustrated by arrow G as shown in Fig. 12 the sealing force control system is provided for regulation of the activation force working on the first seal seat 6 for selectively sealing engagement with the gate element. The first seal seat 6 may be displaceably arranged or may be positioned in an initial sealing engagement with the gate element 2, and the sealing force control system provides an additional sealing force to the first seal seat 6 when the gate element 2 is closed.

In Fig. 12 the first seal seat 6 is arranged at the upstream side of the gate element and another first seal seat 6 is arranged at the downstream side of the gate element. One or both first seal seats 6 may arranged so that they have an initial sealing engagement with the gate element 2 and when necessary the sealing force control system provides additional sealing force to either or both first seal seats 6. In another embodiment one or both of the first seal seats 6 may be displaceably arranged wherein the sealing force control system then is arranged to move the first seal seat 6 into sealing engagement or away from sealing engagement with the gate element 2. Another possible combination is to arrange the gate valve assembly with a first seal seat provided for selectively sealing engagement with the gate element and then provide a set of the first and second seal seat 6, 7 at the other side of the gate element 2. Fig. 13 shows the first seal seat 6 arranged with means such a fluid passage 60 for supply of a sealing fluid to a sealing area between a sealing surface 80 of the first seal seat 6 and a sealing surface 90 of the gate element 2. As illustrated in Fig. 14 a sealing fluid 65 such as a lubricating fluid is supplied through the fluid passage 60 to the sealing area. The sealing fluid is pressurized as illustrated by arrow H in order to seal for leakage 86 that might occur due to scratching or damages 70. The sealing fluid should be pressurized to a pressure level which exceeds the pressure of the fluid flow in the through bore in order to avoid leakage from the through bore.

As illustrated in Fig. 15 the gate valve assembly may be provided with a first seal seat 6 arranged with fluid passage 60 for supply of sealing fluid to the sealing area between the first seal seat 6 and the gate element 2, and the first seal seat 6 at the other side of the gate element may be provided for selectively sealing engagement with the gate element 2 as shown in Fig. 12. Another option is to combine the first seal seat 6 provided for selectively sealing engagement with the gate element as shown in Fig. 12 with the means for supply of a sealing fluid to a sealing area as shown in Fig. 14. It is also possible to provide the second seal seat 7 with means for supply of a sealing fluid to a sealing area either alone or in combination with the second seal seat being 7 being displaceably arranged or in an initial sealing engagement arranged for further tightened sealing engagement with the gate element.

The fluid source for providing pressurized fluid exerted as an activation force on the first seal seat 6 and/or second seal seat 7 may be provided as a high pressure unit (HPU), an accumulator bank, some sort of fluid bank which in one embodiment of the invention may be located on a ROV. The fluid source may be capable of providing sufficient pressure for displacing of the seal seats into sealing

engagement with the gate element. If needed a pressure intensifier for instance a piston with a pressurizing effect may be included for pressurizing of the fluid to enter the seal seat control chamber. The sealing force control system 20 may be provided otherwise than illustrated in the embodiment in the figures. The seal seat may be operated by using one set of fluid lines connected to either the upper exposure area 23 or the lower exposure area 25 wherein the source provides an activation force as a pressure force or a suction force for sealing engagement or disengagement with the gate element.

Alternatively the sealing force control system may be provided for an electrified actuation of the seal seat. The source may be an electrical source with signal lines connecting the electrical source to a magnetic arrangement of the seal seat. The control means may then be provided for regulation of signals between the electrical source magnetic arrangement of the seal seat in order to adjust the activation force working on the seal seat.

Figs. 16 to 19 disclose another embodiment of a gate valve assembly 201 according to the invention.

As the above-discussed embodiments of gate valve assemblies according to the invention, the gate valve assembly 201 comprises a gate valve housing or body 200 having a through-bore 203 and a gate element bore 101 in which a gate element 202 is arranged to be operated between an open position and a closed position. In the open position, which is shown in Fig. 18, a gate bore 204 of the gate element 202 is arranged coaxially with the through-bore 203 so that a fluid is allowed to flow through the gate valve assembly 201 , as is indicated by arrow F in Fig. 18. In the closed position, which is shown in Fig. 19, the through-bore 203 is blocked. As is known within the art, an actuator (not shown) is arranged in the gate valve assembly 201 to move the gate element 202 between the open position to the closed position. The gate valve assembly 201 comprises an annular first seal assembly 230a, which is arranged in the valve body 200 adjacent and upstream the gate element 202, and an annular second seal assembly 230b, which is arranged in the valve body 200 adjacent and downstream to the gate element 202. Each seal assembly 230a, 230b is arranged coaxially with the through-bore 203.

Each seal assembly 230a, 230b comprises an annular first seal seat or element 206a, 206b and an annular second seal seat or element 207a, 207b, which is arranged in an annular recess in the first seal element 206a, 206b. Each first seal element 206a, 206b comprises an annular sealing surface 280 and each second seal element 207a, 207b comprises an annular sealing surface 295 (see Fig. 17), which sealing surfaces 280, 295 are arranged to seal against the gate element 202 when in the closed position. An annular locking plate 253a, 253b is arranged to lock each seal assembly 230a, 230b into position in the valve body 200.

When the seal assembly 230a, 230b is mounted in the valve body 200, the second seal element 207a, 207b is movable in the axial direction of the through-bore between a deactivated position, in which the sealing surface 295 is not in contact with the gate element 202, and an activated position, in which the sealing surface 295 is in contact with the gate element 202. In Fig. 19, second seal element 207b is in the activated position, and second seal element 207a is in the deactivated position. For moving the second seal elements 207a, 207b between the deactivated position and the activated position, the gate valve assembly 201 comprises a sealing force control system, e.g. a sealing force control system 20 of the above-disclosed type, i.e. comprising fluid lines 210a, 210b for providing hydraulic fluid for activating the second seal elements 207a, 207b and fluid lines 21 1a, 21 lb for providing hydraulic fluid for deactivating the second seal elements 207a, 207b.

In the present embodiment, as can be seen in Fig. 19, a control chamber 224a, 224b is formed between the first seal element 206a, 206b and the locking plate 253a, 253b in each seal assembly 230a, 230b, in which chamber 224a, 224b the second seal element 207a, 207b is axially movable, and with which chamber 224a, 224b the fluid lines 210a, 210b, 21 1a, 21 1b communicate to hydraulically activate and deactivate the second seal element 207a, 207b.

In order to activate the second seal element 207a, 207b, hydraulic fluid is provided to chamber 224a, 224b via fluid line 210a, 210b. In the chamber 224a, 224b, the hydraulic fluid will exert a hydraulic pressure onto the second seal element 207a, 207b forcing it towards the gate element 202. In order to deactivate the second seal element 207a, 207b, hydraulic fluid is provided to chamber 224a, 224b via fluid line 21 1a, 21 1b. In the chamber 224a, 224b, the hydraulic fluid will exert a hydraulic pressure onto the second seal element 207a, 207b forcing it away from gate element 202. It is understood that by controlling the hydraulic pressure in the chamber 224a, 224b, the pressure with which the second seal element 207a, 207b presses against the gate element 202, i.e. the sealing pressure, can be controlled.

As has been previously discussed, the second seal element 207a, 207b in each seal arrangement 230a, 230b is advantageously activated after the gate element 202 has closed, whereby the sealing surface 295 of the seal element 207a, 207b need not be exposed to potentially harmful abrasion caused by the moving gate element 202.

By contrast, the sealing surface 280 of the first seal element 206a, 206b will, in the present embodiment, be in continuous contact with the gate element 202. In order to facilitate shearing of any elongated member present in the through-bore 203 when the gate valve assembly 201 closes, i.e. when the gate element 202 is brought from the open position to the closed position, the inner circumference 212a, 212b of the sealing surface 280 of the first seal element 206a, 206b may be formed as a cutting edge (see Figs. 17 and 18).

By arranging the first and second seal elements 206a, 206b, 207a, 207b in a seat assembly 230a, 230b as disclosed above, it may be easier, in some applications, to assemble the gate valve assembly 201 with good tolerances. Also, it may enable a more simple geometry of the valve body 200. In the embodiment disclosed in Figs. 16 to 18, the second seal element 207a, 207b is arranged in an annular recess of the first seal element 206a, 206b. Consequently, the first seal element 206a, 206b will support and also guide the second seal element 207a, 207b when it is pressurised, i.e. activated. In order to facilitate the mounting of the seat assemblies 230a, 230b in the valve body 200, the gate valve assembly 201 may comprise hydraulic couplers 213 (see Fig. 17) allowing hydraulic communication between the seat assemblies 230a, 230b and the sealing force control system (not shown in Figs. 16 to 18) to be established in an efficient and reliable manner.

In the illustrated embodiments the activation of the seal seat is explained for a displaceable seal seat. However the sealing force control system may also be provided for operation of control means that are operable for regulation of an activation force for a seal seat that is positioned in a sealing engagement with the gate element. The sealing force control system may then be arranged for providing an initial sealing force in engagement with the gate element such as in open and shearing position. Further the sealing force control system may be arranged for provision of an increased sealing force causing a tightened sealing engagement with the gate element such as in closed position of the gate element.

The control means is shown as valve units in the figures. As an alternative to valve units such as control valves, the other suitable means for controlling the connection between the source and the second or fist seal seat may of course also be employed.

In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention as defined in the attached claims.