A well tool device and a method for temporary well isolation

Abstract

A well tool device (10) comprising a tubular housing (12) with a first house part (12a) and a second house part (12b), said tubular housing (12) having a through running boring (14). A first barrier comprising a solid first glass disc (16) is closing off the through running boring (14) upstream in the tubular housing (12). A second barrier 5 comprising a solid second glass disc (18) is closing off the through running boring (14) downstream in the tubular housing (12), wherein said first and second glass discs (16,18) are axially displaced from each other, with an atmospheric chamber (40) provided therebetween, and the first glass disc (16) is arranged to be shattered by applying a first hydraulic pressure and the second glass disc (18) is arranged to 0 be shattered by applying a second hydraulic pressure, wherein said second hydraulic pressure is less than said first hydraulic pressure.

Description

[0001] A well tool device and a method for temporary well isolation

[0002] Field of the invention

[0003] The present invention relates to a well tool device comprising a tubular housing with a first house part and a second house part, said tubular housing having a through running boring. The invention also relates to a method for temporary well isolation during a well completion phase.

[0004] The present invention relates to a well tool device for temporary well isolation during well completion phase. Typical activities are pressure test and packer setting.

[0005] Background of the invention

[0006] In different types of well operations, it is a need for well tool devices providing a temporary isolation of a tubing or casing string during well completion activities. A common solution is a frangible plug configured to break at a given differential pressure across the plug, in example 5 000 psi (35 MPa). In example if there are a hydrostatic pressure on both sides of the plug i.e., 3 000 psi (20,7 MPa), the differential pressure is zero across the plug. If pressure at wellhead / surface is increased to i.e., 5 000 psi (34,5 MPa), the pressure above the plug will be 8 000 psi (55,2 MPa), and the differential pressure across the plug will be 5 000 psi (34,5 MPa), at this point the plug will activate and open.

[0007] In some cases, there can be overbalance across the plug. I.e., 5000 psi (34,5 MPa) above the plug, and i.e., 4000 psi (27,6 MPa) below the plug. If the breaking pressure across the plug is set to 5000 psi (34,5 MPa), the well head pressure must be increased to 4000 psi (27,6 MPa) to break the plug. This can be a problem if it is required to pressure test the well to 4500 psi (31 ,0 MPa). The plug will break before test pressure level is reached.

[0008] In some cases, there can be underbalance across the plug. I.e., 4000 psi (27,6 MPa) above the plug, and i.e., 5000 psi (34,5 MPa) below the plug. If the breaking pressure across the plug is set to 5000 psi (34,5 MPa), the well head pressure must be increased to 6000 psi (41 ,4 MPa) to break the plug. This can be a problem if the wellhead equipment has a pressure limitation of i.e., 5000 psi (34,5 MPa), the pressure limitation is reached before the required differential pressure across the plug is reached, and the plug cannot be activated. Disclosure of the state of art

[0009] Barrier valves are known that isolates wellbore reservoir pressure utilizing two internal barrier devices. For instance, can a sub be run on the bottom of the tubing and / or below a packer BHA to isolate the tubing and act as a barrier to set hydraulic set packers. After all tests are performed, the barriers are knocked out using a drop bar, coiled tubing, slickline, or sand line. Once the barriers are removed, the wellbore fluids can then be produced up the production tubing.

[0010] Barriers that separate tubing and wellbore fluids when running tubing and completion BHAs is also known, wherein internal burst discs are designed to withstand high differential pressure before being removed.

[0011] WO2019 / 083376 A1 discloses a well tool device comprising a housing with a breakable ball seat, wherein a drop ball received in the ball seat partially or fully closes fluid communication in the through channel of the housing. The breakable ball seat is made of brittle and / or tempered glass, and the ball seat is broken by a pressure build up in the housing forcing the ball seat against one or more disintegrating means provided as inside protrusions in the through channel.

[0012] W02020 / 117069 A1 discloses packer setting device comprising a tubular with a breakable plug seated in a load ring axially movable within the boring the tubular between a first position in where the plug is with a distance to a breaking pin and a second position in where the plug is forced against the breaking pin.

[0013] US 2014 / 0083716 A1 discloses a down hole pressure isolation tool placed in a pipe string and includes a pair of pressure discs having one side that is highly resistant to applied pressure and one side that ruptures when much lower pressures are applied to it.

[0014] US 2014 / 0008085 A1 discloses a well barrier for sealing off a first portion of a wellbore from a second portion of the wellbore, the first portion having a higher fluid pressure than the second portion.

[0015] Objects of the present invention

[0016] It is an object of the invention to provide a well tool device having a tubular housing with a combination of two glass discs placed with some distance between them forming an atmospheric chamber. The atmospheric chamber below the upper disc, will make the upper disc breaking pressure inert to any pressure present below the lower glass disc. This way, there is no need to consider if the system is over- or underbalanced to calculate the required break pressure.

[0017] The lower glass disc will only need to hold pressure from below and can have a break setting pressure from above at a low value compared to the upper one. As soon as the upper glass disc is broken, the second disc will be broken by the residual differential pressure from above.

[0018] It is also an object to provide a method for temporary well isolation during a well completion phase, particularly for use during pressure testing and packer setting.

[0019] Summary of the invention

[0020] The above objects are achieved with a well tool device according to the invention, wherein the well tool device comprises a tubular housing with a first house part and a second house part, said tubular housing having a through running boring. A first barrier comprising a solid first glass disc is closing off the through running boring upstream in the tubular housing, and a second barrier comprising a solid second glass disc is closing off the through running boring downstream in the tubular housing. The first and second glass discs are axially displaced from each other, with an atmospheric chamber provided therebetween, and the first glass disc is arranged to be shattered by applying a first hydraulic pressure and the second glass disc is arranged to be shattered by applying a second hydraulic pressure, wherein said second hydraulic pressure is less than said first hydraulic pressure.

[0021] Alternative embodiments of the well tool device according to the invention are disclosed in the independent product claims.

[0022] The first glass disc is preferably resting on a first glass disc break mechanism.

[0023] The first glass disc can be supported in the through running boring between a shoulder on an inner wall of the first house part and the first glass disc break mechanism.

[0024] The second glass disc is preferably resting on a second glass disc break mechanism. The second glass disc can be supported in the through running boring between a support sleeve and the second glass disc break mechanism.

[0025] The support sleeve can be fixed in a lower part of the first housing part, and the support sleeve is facing an upper part of the second housing part.

[0026] The first glass disc break mechanism can in one embodiment comprise a load ring supporting the first glass disc, said load ring is axially movable by the applied hydraulic pressure within the through running boring of the tubular housing between a first position in where the first glass disc is with a distance to a breaking pin and a second position in where the glass disc is forced against the breaking pin.

[0027] Said load ring can be resting on a shear ring with an annular shear lip to prevent axial movement in the first position until the shear lip is subjected to a force higher than a predetermined force, wherein the annular shear lip of the shear ring extends radially inward in the through running boring of the tubular housing.

[0028] Further, the breaking pin can be resting on the shear ring, and said breaking pin can be accommodated in a pocket on an outside of the load ring.

[0029] Said shear ring can be resting on the support sleeve.

[0030] The load ring may also comprise a liner ring having a first contact load surface in contact with a substantially similar contact load surface of the load ring, and the liner ring includes a second contact load surface in contact with the first glass disc.

[0031] A fastening mechanism can be positioned between the load ring and the liner ring, said fastening mechanism is configured to prevent movement of the liner ring relative to the load ring.

[0032] The second glass disc break mechanism can comprise one or more break pins for shattering the second glass disc when the second glass disc is pushed axially by the applied hydraulic pressure.

[0033] Said break pins can be placed facing an underside of the second glass disc. Said break pins may also be axially embedded in an inner wall of an upper part of the second house part. The first and second glass discs can be solid, frangible glass discs made of brittle and / or tempered glass.

[0034] The first and the second glass discs can in one embodiment have a first flat side and second opposing flat side, which are parallel to each other, and a chamfered side edge.

[0035] Said object are also achieved with a method for temporary well isolation during a well completion phase, comprising running in hole a well tool device as disclosed, wherein the method comprises the steps:

[0036] - running a tubing or casing string including said well tool device into a borehole, providing temporary isolation with a hydrostatic pressure upstream the well tool device equal to a reservoir pressure downstream the well tool device and with an atmospheric pressure between the first and second barrier in a chamber therebetween,

[0037] - increasing pressure upstream the well tool device to a first high pressure higher than the hydrostatic pressure, and performing well completion activities in the borehole,

[0038] - increasing pressure upstream the well tool device to a second high pressure higher than the first high pressure,

[0039] - applying said second high pressure on the first barrier to shatter the first solid glass disc and allowing fluid communication into the atmospheric chamber,

[0040] - applying residual differential pressure on the second barrier to shatter the second solid glass disc, and

[0041] - open for fluid communication through the well tool device.

[0042] Alternative embodiments of the method according to the invention are disclosed in the independent method claims.

[0043] Prior to increasing pressure upstream the well tool device to a second high pressure higher than the first high pressure, the pressure upstream the well tool device can be decreased to a pressure lower than the hydrostatic pressure.

[0044] The step of decreasing pressure upstream the well tool device to a pressure less than the hydrostatic pressure can comprise displacing to a lighter fluid. The well completion activities in the borehole prior to open the first and second barrier can comprise activities such as setting packers and / or performing pressure tests.

[0045] It is possible to include one or more well tool devices in a production string.

[0046] Further, the first glass disc can be shattered at a shear value that is higher than the shear value of the second glass disc.

[0047] The first glass disc break mechanism and the second glass disc break mechanism can also be activated at different differential pressures.

[0048] Description of the figures

[0049] Embodiments of the present invention will now be described, by way of example only, with reference to the following figures, wherein:

[0050] Figure 1 shows a well tool device according to the invention in a first state and as run in hole.

[0051] Figure 2 shows the well tool device in a second state with a first barrier broken.

[0052] Figure 3 shows the well tool device in a third state with a second barrier broken.

[0053] Figure 4 shows an example of a first glass disc break mechanism.

[0054] Figure 5 shows an example of a second glass disc break mechanism.

[0055] Figure 6 shows a schematic example of a well.

[0056] Figures 7-12 show operational examples of the well tool device according to the invention.

[0057] Fig. 13 and 14 show a first glass disc and a second glass disc for use in the well tool device according to the invention.

[0058] Description of preferred embodiments of the invention

[0059] The present invention relates to a well tool device 10. The well tool device comprises a tubular housing 12, or sleeve, with an axial through running boring 14. In different types of well operations, it is a need for well tool devices to provide a temporary isolation of a tubing or casing string during well completion activities. The well tool device 10 according to the invention will provide such temporary isolation of the tubing or casing string 62. Hence, in order to provide said temporary isolation, the well tool device 10 comprises a first and a second barrier in the through running boring 14 of the tubular housing 12. The first and second barriers are preferably a first solid glass disc 16 and a second solid glass disc 18.

[0060] Fig. 6 shows schematically a subsea or subterrain well with a wellhead 60 and a borehole 68. A production tubing 62, with one or more well tool devices 10 according to the invention, extends from the wellhead 60 and into a reservoir 66 for production of oil and gas. Packers 64 are placed in the annulus surrounding the production tubing 62 in the borehole 68. The well tool device 10 with the first solid glass disc 16 creating the first barrier and the second solid glass disc 18 creating the second barrier closes off fluid communication in the production tubing 62, and a chamber 40 with atmospheric pressure is provided between said first and second glass discs 16,18. Operational examples of the well tool device is explained in relation to fig. 7- 12.

[0061] The atmospheric chamber 40 is provided and sealed during assembly of the well tool device 10. Hence, the chamber 40 is filled with air at atmospheric pressure. However, the chamber 40 could be filled with any compressible fluid (or vacuum) that has a known and lower pressure than the pressure down in the well.

[0062] Fig. 1 shows the well tool device 10 in a first state when run in hole (RIH) with both first and second glass discs 16,18 intact. Fig. 2 shows that pressure has been applied and that the first solid glass disc 16 has been shattered or broken. Fig. 3 shows that the second solid glass disc 18 has been shattered or broken. The applied pressures shall be explained later.

[0063] The tubular housing 12 comprises an upper or first house part 12a and a lower or second house part 12b. The two house parts 12a, 12b are in a known way threaded and screwed to each other, and packers are used to seal of the through running boring 14. Similarly, the first and second glass discs 16,18 are circumferentially enclosed by packers to prevent any fluid flow past the discs.

[0064] The first glass disc 16 is accommodated in the first house part 12a. The second glass disc 18 is also accommodated in the first house part 12a. More specifically, the second glass disc 18 is supported in a fixed carrier or support sleeve 42 in a lower part of the first house part 12a, and with one side facing the second house part 12b. However, the second glass disc 18 could possibly be arranged in the second house part 12b.

[0065] The first and second glass discs 16,18 are frangible glass discs made of brittle and / or tempered glass. The glass discs 16,18 can basically have similar shape and design. Both glass discs 16,18 have a first flat side 56 and an opposing flat side 58 with a chamfered side edge 54 (see also fig. 13 and 14).

[0066] Fig. 13 and 14 shows that the first and the second glass discs 16,18 can be basically flat discs, which in cross section have a circular shaped base part 53 and a trapezoidal shaped part 55. The first flat side 56 and the second opposing flat side 58 of the first and the second glass discs 16,18 are parallel to each other. The chamfered side edge 54 is running from the second flat side 58 and to the circular shaped base part 53. One or more seals 70, such as O-rings, is / are embedded in the housing 12 or in the support sleeve 42 and encloses the base part 53 of the glass discs 16,18.

[0067] The first glass disc 16 is resting on a first glass disc break mechanism 20 in the first house part 12a. The first glass disc 16 is supported in the through running boring 14 between a shoulder 50 in an inner wall 14a of the first house part 12a and the first glass disc break mechanism 20. The first flat side 56 of the first glass disc 16 is facing and supported against the shoulder 50, i.e., facing upstream in the through running boring 14, while the opposing flat side 58 with the chamfered side edge 54 is facing and supported by the first glass disc break mechanism 20.

[0068] The second glass disc 18 is resting on a second glass disc mechanism 30, and the second glass disc 18 is supported in the through running boring 14 between the support sleeve 42 and the second glass disc break mechanism 30. The first flat side 56 of the second glass disc 18 is facing and supported on the second glass disc break mechanism 30, i.e., facing downstream in the through running boring 14, while the opposing flat side 58 with the chamfered side edge 54 is facing and supported against the support sleeve 42. Hence, the support sleeve 42 can have a similar chamfered side edge 52 as the second glass disc 18.

[0069] The support sleeve 42 is fixed in a lower part of the first house part 12a, and the chamfered side edge 52 of the support sleeve 42 is facing an upper part of the second house part 12b. The first and second glass disc break mechanisms 20,30 are shown in more detail in figures 4 and 5. It should be noted that, as an alternative to what is shown in the enclosed drawings, it is possible to use two glass disc break mechanisms of the first type 20, or to use two glass disc break mechanisms of the second type 30.

[0070] The first glass disc break mechanism 20 is shown in more details in fig. 4, and comprises in the shown embodiment a load ring 24 supporting the first glass disc 16. The load ring 24 has a similar chamfered edge 28 as the first glass disc 16. The load ring 24 is axially movable within the through running boring 14 of the tubular housing 12 between a first position in where the first glass disc 16 is with a distance to a breaking pin 22 and a second position in where the first glass disc 16 is forced against the breaking pin 22. The second position will occur after build-up of sufficient pressure.

[0071] The load ring 24 can in one embodiment comprise a liner ring 72, as illustrative shown in fig. 4. The liner ring 72 has a first contact load surface in contact with a substantially similar contact load surface of the load ring 24. The liner ring 72 includes a second contact load surface (corresponding to the chamfered edge 28) in contact with the first glass disc 16. A fastening mechanism can be positioned between the load ring 24 and the liner ring 72, wherein the fastening mechanism is configured to prevent movement of the liner ring 72 relative to the load ring 24.

[0072] Such a liner ring could possibly also be implemented between the second glass disc 18 and the chamfered side edge 52 of the support sleeve 42.

[0073] The load ring 24 is further resting on a shear ring 26 with an annular shear lip 26a to prevent axial movement in the first position until the shear lip 26a is subjected to a force higher than a predetermined force. The annular shear lip 26a of the shear ring 26 extends radially inward in the through running boring 12. The breaking pin 22 is resting on the shear ring 26, and the breaking pin 22 is accommodated in a pocket on an outside of the load ring 24. The shear ring 26 can as shown be resting on the support sleeve 42.

[0074] The shear lip 26a can be dimensioned to break at a predetermined shear force, and hence the first glass disc break mechanism 20 can be activated at a different differential pressures than the second glass disc break mechanism 30, which shall be explained in more detail later. The second glass disc break mechanism 30 is shown in more details in fig. 5, and comprises in the shown embodiment one or more break pins 32 for shattering the second glass disc 18 when the second glass disc 18 is pushed axially by the hydraulic pressure. The one or more break pins 32 are facing the flat underside 58 of the second glass disc 18. The break pins 32 are embedded axially in an inner wall 14b of the upper part of the second house part 12b. However, the break pins 32 could possibly also protrude radially inwards in the through running boring 14.

[0075] The break pin 32 can be covered by a cap isolating the pin from the second glass disc 18, but which is compressed or ripped apart when the second glass disc 18 is sufficiently pressurized.

[0076] The method and operational examples with pressures shall now be explained with help av fig. 7-12.

[0077] In fig. 7 the well tool device 10 is run in hole as disclosed previously, by running the tubing or casing string 62 including said well tool device 10 into the borehole 68, providing temporary isolation with a hydrostatic pressure Ph upstream the well tool device 10 equal to a reservoir pressure Pr downstream the well tool device 10 and with an atmospheric pressure Po between the first and second barrier 16,18 in the chamber 40.

[0078] The upstream hydrostatic pressure Ph is for instance 12 000 psi (82,7 MPa) and the downstream reservoir pressure Pr is equally 12 000 psi (82,7 MPa). APi over the first barrier 16 is thus 12 000 psi (82,7 MPa) and AP2 over the second barrier 18 is similarly 12 000 psi (82,7 MPa).

[0079] Fig. 8 shows a well completion activity in the borehole 68 prior to open the first and second barrier 16,18, such as setting packers 64. Other activities can for instance be performing pressure tests.

[0080] After running the well tool 10 in hole, the pressure upstream the well tool device 10 is increased to a first high pressure Phigm by applying for instance 4 000 psi (27,6 MPa) from the surface. The first high pressure Phighi is higher than the hydrostatic pressure Ph. AP1 over the first barrier 16 is now 16 000 psi (110,3 MPa) and AP2 over the second barrier 18 is still 12 000 psi (82,7 MPa). Thereafter, as shown in fig. 9, the pressure upstream the well tool device 10 can be decreased to a low pressure Plow lower than the hydrostatic pressure Ph. This can for instance be done by displacing to a lighter fluid. The decreased low pressure Plow can for instance be 8 000 psi (55,2 MPa), while the reservoir pressure Pr still is 12 000 psi (82,7 MPa). APi over the first barrier 16 is now 8 000 psi (110,3 MPa) and AP2 over the second barrier 18 is still 12 000 psi (82,7 MPa).

[0081] Reducing the pressure by replacing the fluid with a lighter fluid can for instance be done by lowering a thin coil tubing pipe or by having a tool with ports between the tubing and the annulus and then circulating through them before closing the ports. The reason for changing the fluid to a lighter fluid is that during the previous operations during drilling of the well, among other things, the fluid in the well must be so heavy that the hydrostatic pressure is higher than the pore pressure / reservoir pressure. It is thus desirable to replace this fluid so that the oil / gas will flow to the surface when the well is finished and at start-up of the well.

[0082] In order to open the first barrier, i.e. , the first glass disc 16, as shown in fig. 10, pressure upstream the well tool device 10 is increased to a second high pressure Phigh2 that is higher than the first high pressure Phighi , wherein the second high pressure Phigh2 on the first barrier is used to shatter the first solid glass disc 16 and thus allowing fluid communication into the atmospheric chamber 40. The second high pressure Phigh2 can for instance be 18 000 psi (124,1 MPa) (8 000 psi (55,2 MPa) hydrostatic pressure plus 10 000 psi (68,9 MPa) applied from the surface). The reservoir pressure Pr is still 12 000 psi (82,7 MPa). Before the first glass disc 16 is shattered, AP1 over the first barrier is 18 000 psi (124,1 MPa) and AP2 over the second barrier 18 is still 12 000 psi (82,7 MPa).

[0083] Shear value of the first glass disc 16 can in this example for instance be similar to AP1, i.e., 18 000 psi (124,1 MPa).

[0084] After the first glass disc 16 is shattered, there is no longer an atmospheric chamber 40 and the residual differential pressure AP2 (Phigh2 - Pr) acting on the second barrier is used to shatter the second solid glass disc 18, as shown in fig. 11 .

[0085] Shear value of the second glass disc 18 can in this example for instance be less than AP2, i.e., less than 6000 psi (41 ,4 MPa). Hence, the shear values of the first glass disc 16 and the second glass disc 18 can thus be different.

[0086] However, the shear values of the first glass disc 16 and the second glass disc 18 can also be similar, but wherein the first glass disc break mechanism 20 and the second glass disc break mechanism 30 can be activated at different differential pressures, as previously explained.

[0087] As shown in fig. 12, the production tubing 62 is now open for fluid communication through the well tool device 10 after the first barrier and the second barrier are opened.

Claims

Claims1. A well tool device (10) comprising a tubular housing (12) with a first house part (12a) and a second house part (12b), said tubular housing (12) having a through running boring (14), wherein a first barrier comprising a solid first glass disc (16) is closing off the through running boring (14) upstream in the tubular housing (12), a second barrier comprising a solid second glass disc (18) is closing off the through running boring (14) downstream in the tubular housing (12), said first and second glass discs (16,18) are axially displaced from each other, with an atmospheric chamber (40) provided therebetween, and the first glass disc (16) is arranged to be shattered by applying a first hydraulic pressure and the second glass disc (18) is arranged to be shattered by applying a second hydraulic pressure, wherein said second hydraulic pressure is less than said first hydraulic pressure.

2. The well tool device (10) according to claim 1 , wherein the first glass disc (16) is resting on a first glass disc break mechanism (20).

3. The well tool device (10) according to claim 2, wherein the first glass disc (16) is supported in the through running boring (14) between a shoulder (50) on an inner wall (14a) of the first house part (12a) and the first glass disc break mechanism (20).

4. The well tool device (10) according to claim 1 , wherein the second glass disc (18) is resting on a second glass disc break mechanism (30).

5. The well tool device (10) according to claim 4, wherein the second glass disc (18) is supported in the through running boring (14) between a support sleeve (42) and the second glass disc break mechanism (30).

6. The well tool device (10) according to claim 5, wherein the support sleeve (42) is fixed in a lower part of the first housing part (12a), and the support sleeve (42) is facing an upper part of the second housing part (12b).

7. The well tool device (10) according to claim 2, wherein the first glass disc break mechanism (20) comprises a load ring (24) supporting the first glass disc (16), said load ring (24) is axially movable by the applied hydraulic pressure within thethrough running boring (14) of the tubular housing (12) between a first position in where the first glass disc (16) is with a distance to a breaking pin (22) and a second position in where the glass disc (16) is forced against the breaking pin (22).

8. The well tool device (10) according to claim 7, wherein said load ring (24) is resting on a shear ring (26) with an annular shear lip (26a) to prevent axial movement in the first position until the shear lip (26a) is subjected to a force higher than a predetermined force, wherein the annular shear lip (26a) of the shear ring (26) extends radially inward in the through running boring (14) of the tubular housing (12).

9. The well tool device (10) according to claim 8, wherein the breaking pin (22) is resting on the shear ring (26), and said breaking pin (22) is accommodated in a pocket on an outside of the load ring (26).

10. The well tool device (10) according to claim 5 and 8, wherein said shear ring (26) is resting on the support sleeve (42).11 . The well tool device (10) according to claim 7, wherein the load ring (24) comprises a liner ring (72) having a first contact load surface in contact with a substantially similar contact load surface of the load ring (24), and the liner ring (72) includes a second contact load surface in contact with the first glass disc (16).

12. The well tool device (10) according to claim 11 , wherein a fastening mechanism is positioned between the load ring (24) and the liner ring (72), said fastening mechanism is configured to prevent movement of the liner ring (72) relative to the load ring (24).

13. The well tool device (10) according to claim 4, wherein the second glass disc break mechanism (30) comprises one or more break pins (32) for shattering the second glass disc (18) when the second glass disc (18) is pushed axially by the applied hydraulic pressure.

14. The well tool device (10) according to claim 13, wherein said break pins (32) is / are placed facing an underside (58) of the second glass disc (18).

15. The well tool device (10) according to claim 14, wherein said break pins (32) is / are axially embedded in an inner wall (14b) of an upper part of the second house part (12b).

16. The well tool device (10) according to claim 1, wherein said first and second glass discs (16,18) are solid, frangible glass discs made of brittle and / or tempered glass.

17. The well tool device (10) according to claim 1, wherein said first and second glass discs (16,18) have a first flat side (56) and second opposing flat side (58), which are parallel to each other, and a chamfered side edge (54).

18. A method for temporary well isolation during a well completion phase, comprising running in hole a well tool device (10) according to any of claims 1-17, wherein the method comprises the steps:- running a tubing or casing string (62) including said well tool device (10) into a borehole (68), providing temporary isolation with a hydrostatic pressure upstream the well tool device (10) equal to a reservoir pressure downstream the well tool device (10) and with an atmospheric pressure between the first and second barrier in a chamber (40) therebetween,- increasing pressure upstream the well tool device (10) to a first high pressure higher than the hydrostatic pressure, and performing well completion activities in the borehole (68),- increasing pressure upstream the well tool device (10) to a second high pressure higher than the first high pressure,- applying said second high pressure on the first barrier to shatter the first solid glass disc (16) and allowing fluid communication into the atmospheric chamber (40),- applying residual differential pressure on the second barrier to shatter the second solid glass disc (18), and- open for fluid communication through the well tool device (10).

19. The method for temporary well isolation according to claim 18, wherein prior to increasing pressure upstream the well tool device (10) to a second high pressure higher than the first high pressure, the pressure upstream the well tool device (10) is decreased to a pressure lower than the hydrostatic pressure.

20. The method for temporary well isolation according to claim 19, wherein the step of decreasing pressure upstream the well tool device (10) to a pressure less than the hydrostatic pressure comprises displacing to a lighter fluid.

21. The method for temporary well isolation according to claim 18, wherein said well completion activities in the borehole (68) prior to open the first and second barrier comprises setting packers (64) and / or performing pressure tests.

22. The method for temporary well isolation according to claim 18, wherein one or more well tool devices (10) is / are included in a production string (62).

23. The method for temporary well isolation according to claim 18, wherein the first glass disc (16) shatters at a shear value that is higher than the shear value of the second glass disc (18).

24. The method for temporary well isolation according to claim 18, wherein the first glass disc break mechanism (20) and the second glass disc break mechanism (30) are activated at different differential pressures.

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