A well tool device and a method for well stimulation in a subterranean wellbore

Abstract

A method for well stimulation in a subterranean wellbore and a well tool device (10) with a tubular housing (12), the well tool device (10) further comprises an axially displaceable closing sleeve (24) having an axial and internal through running boring (38) with internal apertures (26), said closing sleeve (24) is axially displaceable in the through running boring (14) of the housing (12). A first glass ball seat (16) is provided downstream in the internal through running boring (38) of the closing sleeve (24), and the first glass ball seat (16) is open and arranged for receipt of a first drop ball (60) to close fluid flow through the first glass ball seat (16), wherein the first glass ball seat (16) is resting on a first glass seat break mechanism (20). A second glass ball seat (18) is provided upstream in the internal through running boring (38) of the closing sleeve (38), and the second glass seat ball seat (18) is open and arranged for receipt of a second drop ball (62) to close fluid flow through the second glass ball seat (18), wherein the second glass ball seat (18) is resting on a second glass seat break mechanism (30). A closing sleeve restraining means (34) is placed downstream of the closing sleeve (24), said restraining means (34) is arranged to restrain movement of the closing sleeve (24) in the housing (12) to hold the closing sleeve (24) in open position.

Description

[0001] A well tool device and a method for well stimulation in a subterranean wellbore

[0002] Field of the invention

[0003] The present invention relates to a well tool device comprising a tubular housing with an axial through running boring, and with a closing sleeve axially displaceable in the through running boring of the housing, and a method for well stimulation in a subterranean wellbore, as disclosed in the independent claims.

[0004] The present invention relates to a well tool device for opening and closing a fluid passage to annular side in a production tubing in an oil producing well, for the purpose of stimulation the well reservoir in preparation for oil and gas production.

[0005] Background of the invention

[0006] In different types of well operations, it is a need for well tool devices having a valve function, i.e. the well tool device needs to be reconfigured between a first closed state, an open state and a second closed state for fluid communication between tubing inside to tubing outside.

[0007] Typically, the first closed state is used for installing the production tubing in the well, and it is needed that the tubing is intact for well barrier reasons.

[0008] Once the tubing is installed, it is desired to be able to open up a production zone, and pump in stimulation fluid in the production sone to enhance the production efficiency of the zone. Once the stimulation of the zone is complete, it is desired to re-close the zone while stimulating other zones in the well.

[0009] Disclosure of the state of art

[0010] There is a lot of prior art in the field of stimulating a well or zone with multiple sleeves utilizing graded ball seats, for instance as disclosed in WO2019 / 088849 A. The document discloses a stimulation sleeve for well intervention in a subterranean wellbore, comprising a housing having flow ports, and a sliding sleeve disposed axially movable within the housing to open or close said flow ports. Said sliding sleeve A time delay mechanism is used to allow the sliding sleeve to axially travel in the housing at a predetermined speed to open or close said flow ports.

[0011] WO 2019 / 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] WO 2020 / 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 11306562 B1 discloses a stage tool used in a wellbore that has a housing consisting of two sub-housings that couple together. A first sleeve is movably disposed in the housing bore and is held closed with a temporary connection relative to a side port of the housing. The first sleeve has a first seat of millable material. A second sleeve is also movably disposed in the housing bore and is held opened with a temporary connection relative to the side port. An opening plug is landed on the first seat so pressure can break the connection and shift the first sleeve open relative to the side port.

[0014] US 11359453 B2 discloses a packer setting device, comprising a tubular with a plug housing, said plug housing having an internal, through running boring with an internal wall. A breakable plug seated in a load ring is axially movable within the boring 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.

[0015] Objects of the present invention

[0016] It is an object with the invention to combine two graded ball seats in the same sleeve, to manipulate the sleeve from a first closed position to an open position, and then to a second closed position using breakable ball seats in glass. The benefits with this are that when the glass seat breaks, it will instantly leave a full-bore production ID.

[0017] It is also an object to utilize a shear ring to hold the sleeve in the open position while stimulating the well. The shear ring has an activation pressure above the pore pressure and / or the hydraulic resistance pressure of the reservoir at the given flowrate while stimulation the zone. Also, by combining several sizes of drop balls and balls seats, it is possible to achieve the same feature over several zones in combination in the same well.

[0018] It is desired to open only one zone at a time, to be able to control exactly how much stimulation fluid is pumped into each zone.

[0019] Summary of the invention

[0020] According to a first aspect of the invention, a well tool device is provided, comprising a tubular housing with an axial through running boring, the well tool device further comprises: a closing sleeve having an axial and internal through running boring with internal apertures, said closing sleeve is axially displaceable in the through running boring of the housing, a first glass ball seat is provided downstream in the internal through running boring of the closing sleeve, and the first glass ball seat is open and arranged for receipt of a first drop ball to close fluid flow through the first glass ball seat, wherein the first glass ball seat is resting on a first glass seat break mechanism, a second glass ball seat is provided upstream in the internal through running boring of the closing sleeve, and the second glass ball seat is open and arranged for receipt of a second drop ball to close fluid flow through the second glass ball seat, wherein the second glass ball seat is resting on a second glass seat break mechanism, the closing sleeve is arranged to be axially displaceable in the through running boring of the housing dependent on pressure build-up in the housing, wherein the apertures of the closing sleeve are arranged to be shifted in and out of alignment with flow ports in the housing, and a closing sleeve restraining means is placed downstream of the closing sleeve, said restraining means is arranged to restrain movement of the closing sleeve in the housing to hold the closing sleeve in open position.

[0021] The second glass ball seat can have a doughnut shape, and the first glass ball seat can have a doughnut shape, wherein an internal diameter of the doughnut opening in the second glass ball seat is larger than an internal diameter of the doughnut opening in the first glass ball seat.

[0022] The restraining means can in one embodiment comprise a shear ring arranged to hold the closing sleeve in an open position with the apertures aligned with the flow ports in the housing during well stimulation. The shear ring of the restraining means can comprise an internal shear lip, wherein the shear lip of the shear ring is arranged to break when the closing sleeve is subjected to a predetermined hydraulic pressure.

[0023] A snap ring can be accommodated in a snap ring groove provided on and between an outer surface of the closing sleeve and an inner surface of the through running boring in the housing.

[0024] The closing sleeve can comprise a first snap ring groove and a second snap ring groove provided on and between an outer surface of the closing sleeve and an inner surface in the through running boring of the housing, and a snap ring, wherein the snap ring is arranged to travel from the first snap ring groove and to the second snap ring groove when the closing sleeve is displaced axially in the housing.

[0025] The glass seat break mechanism can in one embodiment comprise a load ring supporting the glass ball seat, said load ring is axially movable within the through running boring of the closing sleeve between a first position in where the glass seat is with a distance to a breaking pin and a second position in where the glass seat is forced against the breaking pin.

[0026] 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 closing sleeve, and the breaking pin is resting on the shear ring, and said breaking pin is accommodated in a pocket on an outside of the load ring.

[0027] The apertures of the closing sleeve are in a first position closed and out of alignment with the flow ports in the housing, and in a second position are the apertures open and in alignment with the flow ports in the housing, and in a third position are the apertures out of alignment with the flow ports.

[0028] According to a second aspect of the present invention, a method for well stimulation in a subterranean wellbore is provided. The method comprises the steps: running one or more well tool devices as disclosed into the wellbore, wherein a closing sleeve of the well tool device is in a first closed position with apertures of the closing sleeve out of alignment with flow ports in the housing of the well tool device, landing a first drop ball in a first glass ball seat, and to build up pressure to shift the closing sleeve from the first closed position to an open position wherein the apertures of the closing sleeve are aligned with the flow ports in the housing of the well tool device, starting well stimulation in a zone while restraining movement of the closing sleeve using a restraining means placed downstream of the closing sleeve, when zone stimulation is completed, landing a second drop ball in a second glass ball seat, and building up pressure to break the restraining means and to shift the closing sleeve from the open position to a second closed position wherein the apertures of the closing sleeve are out of alignment with the flow ports in the housing of the well tool device, and shattering the first and the second glass ball seats, allowing travel of the first and second drop balls down in the wellbore.

[0029] After the second drop ball has landed in the second glass ball seat, pressure can be built up to activate a second glass seat break mechanism to break the second glass ball seat and to activate a first glass seat break mechanism to break the first glass ball seat.

[0030] The restraining means breaks at a pressure that is less than the pressure needed to active said first and second glass seat break mechanism.

[0031] The method comprises dropping a second drop ball that has a larger diameter than the diameter of the first drop ball.

[0032] The method may further comprise the steps of running a tubing string with multiple well tool devices into the wellbore, and successive complete well stimulation for multiple zones.

[0033] The method can comprise the steps of running a tubing string with two or more well tool devices into the wellbore, wherein the closing sleeves of the well tool devices are set in the first closed position, landing the first drop ball in the first glass ball seat of a downstream well tool device, and building up pressure to shift the closing sleeve in the downstream well tool device from the first closed position to the open position in order to stimulate a lower zone in the wellbore, landing the second drop ball in the second glass ball seat of the downstream well tool device, and building up pressure to shift the closing sleeve in the downstream well tool device from the open position to the second closed position, landing a third drop ball in the first glass ball seat of an upstream well tool device, and building up pressure to shift the closing sleeve in the upstream well tool device from the first closed position to the open position in order to stimulate an upper zone in the wellbore, and landing a fourth drop ball in the second glass ball seat of the upstream well tool device, and building up pressure to shift the closing sleeve in the upstream well tool device from the open position to the second closed position.

[0034] The method can be repeated for well tool devices over several zones using increasing sizes of drop balls and internal diameter glass ball seats in the well tool devices in the tubing string.

[0035] The method may further comprise the steps of installing a snap ring in a snap ring groove provided between an outer surface of the closing sleeve and an inner surface in the through running boring of the housing, said snap ring provides resistance or friction between the closing sleeve and the housing preventing unwanted axial displacement of the closing sleeve.

[0036] The snap ring can travel from a first snap ring groove and to a second snap ring groove when the closing sleeve is allowed axial displacement in the housing.

[0037] Description of the figures

[0038] Embodiments of the present invention will now be described, by way of example only, with reference to the following figures, wherein:

[0039] Figure 1 shows a well tool device according to the invention as it is run in borehole position, with a closing sleeve in a first closed position.

[0040] Figures 2-8 show operation of the well tool device according to the invention.

[0041] Figure 9 shows details of a second ball seat and a second glass break mechanism in the well tool device.

[0042] Figure 10 shows details of a closing sleeve retaining shear ring in the well tool device.

[0043] Figure 11 shows details of a first ball seat and a first glass break mechanism in the well tool device. Figure 12 shows a production tubing / string with several well tool devices according to the invention.

[0044] Figures 13-23 show multiple zone operation utilizing several well tool devices according to the invention.

[0045] Description of preferred embodiments of the invention

[0046] Figure 1 shows a well tool device 10 according to the invention. The well tool device 10 can also be called a stimulation sleeve, and is intended for stimulating a well by pumping in stimulation fluid in a production zone to enhance the production efficiency of the zone.

[0047] As further seen in figure 1 , the well tool device comprises a tubular housing 12, or sleeve, with an axial through running boring 14. Within the through running boring 14 of the housing 12 is a closing sleeve 24 placed axially displaceable. The closing sleeve 24 comprises an axial and internal through running boring 38 with internal apertures 26.

[0048] The closing sleeve 24 comprises a first glass ball seat 16 in the through running boring 38. The first glass ball seat 16 can also be called a lower glass ball seat and is placed downstream in the closing sleeve 24. The first glass ball seat 16 is internally open and has for instance a doughnut shape and is arranged for receipt of a first drop ball 60 to close fluid flow through the first glass ball seat 16. The first glass ball seat 16 is resting on a first glass seat break mechanism 20. The first glass seat break mechanism 20 can similarly be called a lower glass seat break mechanism.

[0049] The closing sleeve 24 further comprises a second glass ball seat 18 in the through running boring 38. The second glass ball seat 18 can also be called an upper glass ball seat and is placed upstream in the closing sleeve 24. The second glass ball seat 18 is internally open and has for instance a doughnut shape and is arranged for receipt of a second drop ball 62 to close fluid flow through the second glass ball seat 18. The second glass ball seat 18 is resting on a second glass seat break mechanism 30. The second glass seat break mechanism 30 can similarly be called an upper glass seat break mechanism.

[0050] The glass ball seats 16,18 are breakable and preferable made of brittle and / or tempered glass, and the glass ball seats are broken by a pressure build up in the housing 12 forcing the ball seat against one or more disintegrating means of the glass seat break mechanism 20,30.

[0051] An internal diameter of the second glass seat 18 is larger than an internal diameter of the first glass ball seat 16. Correspondingly, the second drop ball 62 has a larger diameter than the first drop ball 60.

[0052] The closing sleeve 24 is axially displaceable in the through running boring 14 of the housing 12 depended on applied pressure, wherein the apertures 26 are arranged to be shifted in and out of alignment with flow ports 28 in the housing 12. Hence, the well tool device 10 can be reconfigured between a first closed state, an open state and a second closed state for fluid communication between tubing inside to tubing outside, as shall be explained in more detail later. Typically, the first closed state is used for installing a production tubing in the well, and it is needed that the tubing is intact for well barrier reasons. Once the tubing is installed, it is desired to be able to open up a production zone, and pump in stimulation fluid in the production zone to enhance the production efficiency of the zone. Once the stimulation of the zone is complete, it is desired to re-close the zone while stimulating other zones in the well.

[0053] The housing 12 of the well tool device 10 further comprises a closing sleeve restraining means 34 placed downstream of the closing sleeve 24. The restraining means 34 is arranged to restrain movement of the closing sleeve 24 in the housing 12. The restraining means 34 is used to hold the closing sleeve 24 in the open position while stimulating the well. The restraining means 34 preferably has an activation pressure above the pore pressure and / or the hydraulic resistance pressure of the reservoir at the given flowrate while stimulation the zone.

[0054] The well tool device 10 may further comprise a snap ring 22 to provide resistance or friction between the closing sleeve 24 and the housing 12, to prevent that the closing sleeve 24 moves axially due to flow through the first or second glass ball seats 16,18, or possible due to other objects that can push on the closing sleeve 24. The snap ring 22 is accommodated in a first snap ring groove 40a provided between a groove on an outer surface of the closing sleeve 24 and a groove on an inner surface of the through running boring 14 in the housing 12, and the snap ring 22 is arranged to move together with the closing sleeve 24 to a second downstream snap ring groove 40b similarly provided between a groove on the inner surface of the housing 12 and a groove on the outer surface of the closing sleeve 24. The first and second snap ring grooves 40a, 40b are provided with a distance to each other.

[0055] Fig. 1 shows the snap ring 22 and the two snap ring groves 40a, 40b. In fig. 2 the snap ring 22 is accommodated and resting in the first snap ring groove 40a, and in fig. 5 the snap ring 22 has travelled with the closing sleeve 24 to the downstream and second snap ring groove 40b, where it is accommodated and resting. The snap ring 22 can be provided in upper part of the closing sleeve 24. The snap ring 22 is accommodated in the upstream and first snap ring groove 40a when the closing sleeve 24 is in the first closed position, and the snap ring 22 enters the downstream and second snap ring groove 40b when the closing sleeve 24 has been displaced to the second closed position.

[0056] Seals or seal stack 32 are provided between the closing sleeve 24 and the inner surface of the through running boring 14 in the housing 12.

[0057] The first and second glass seat break mechanism 20,30 are shown in more detail in figures 9 and 11 .

[0058] Both glass seat break mechanism 20,30 comprises in the shown embodiment a load ring 46 supporting the glass seat 16,18. The load ring 46 is axially movable within the through running boring 38 of the closing sleeve 24 between a first position in where the glass seat 16,18 is with a distance to a breaking pin 42 and a second position in where the glass seat 16,18 is forced against the breaking pin 42. The second position will occur after receipt of the drop ball 60;62 and build-up of pressure.

[0059] The load ring 46 is further resting on a shear ring 44 with an annular shear lip 44a to prevent axial movement in the first position until the shear lip 44a is subjected to a force higher than a predetermined force. The annular shear lip 44a of the shear ring 44 extends radially inward in the through running boring 12. The breaking pin 42 is resting on the shear ring 44, and the breaking pin 42 is accommodated in a pocket on an outside of the load ring 46.

[0060] Figure 10 shows the restraining means 34 in more detail. In one embodiment, the restraining means 34 can comprise a shear ring 36 arranged to hold the closing sleeve 24 in the open position with the apertures 26 aligned with the flow ports 28 in the housing during well stimulation.

[0061] The shear ring 36 of the restraining means 34 may for instance comprise an internal shear lip 36a, wherein the shear lip 36a of the shear ring 36 breaks when the closing sleeve 24 is subjected to a predetermined hydraulic pressure, thus allowing axial displacement of the closing sleeve 24.

[0062] Operation

[0063] Figures 1-8 show operation of one well tool device 10 according to the invention.

[0064] Figure 1 shows the configuration of the well tool device 10 when it is run in borehole position. The closing sleeve 24 is in the first closed position with the apertures 26 of the closing out of alignment with the flow ports 28 in the housing. No drop balls have been dropped and the first and second glass ball seats (16,18) are open. The snap ring 22 provides sufficient resistance against unwanted axial displacement of the closing sleeve 24.

[0065] In figure 2, a first drop ball 60 has been pumped down and landed in the first glass ball seat 16, and pressure is built up to shift the closing sleeve 24 to the open position.

[0066] As seen in figures 1 and 2, the apertures 26 of the closing sleeve 24 are upstream of the flow ports 28 in the housing.

[0067] In figure 3, the closing sleeve 24 has shifted to the open position, with the apertures 26 of the closing sleeve 24 aligned with the flow ports of the housing 12. Further displacement of the closing sleeve 24 is restrained by the restraining means 34 placed downstream of the closing sleeve 24. The restraining means 34 can as an example be designed to withstand a pressure of 4000 psi (27,5 MPa) before breaking.

[0068] In figure 4, zone stimulation is completed and a second drop ball 62 has been pumped down and landed in the second glass ball seat 18, and pressure is built up to shift the closing sleeve 24 to the second closed position. As seen in figures 3 and 4, the apertures 26 of the closing sleeve 24 are aligned with the flow ports 28 in the housing.

[0069] In figure 5, the closing sleeve 24 has shifted to the second closed position, with the apertures 26 of the closing sleeve 24 out of alignment with the flow ports 28 of the housing. As seen in figure 5, the apertures 26 have moved downstream and passed the flow ports 28. To allow the shifting, i.e., the axial displacement, of the closing sleeve 24, a breaking pressure higher than the force the restraining means 34 can withstand is applied. For instance, a breaking pressure of 4000 psi (27,5 MPa) or higher.

[0070] In figure 6, pressure is increased to activate the first and the second glass seat break mechanism 20,30. The second glass ball seat 30 supporting the second drop ball 62 is shattered first, for instance by applying a pressure of 5000 psi (34,5 MPa), and then the same pressure is applied to the first glass ball seat 16.

[0071] In figure 7, both glass ball seats 20,30 have been shattered and the two drop balls 60,62 can be pumped down in the well.

[0072] Figure 8 shows that the closing sleeve 24 is in the closed position, the glass ball seats 16, 18 are removed, the drop balls 60,62 have traveled down in the well, and the tubing is ready for production.

[0073] As seen in figures 5-8, the apertures 26 of the closing sleeve 24 are downstream of the flow ports 28 in the housing.

[0074] Multiple zone option

[0075] Two or more well tool devices 10 according to the invention can be operated in series by having size increments in glass ball seats and drop ball sizes. Each well tool device 10 is operated as previously disclosed.

[0076] Figure 12 shows a tubing string 70 with two well tool devices 10 in series. Four drop balls 60,62,64,66 can as shown be used. However, it should be noted that more well tool devices and drop balls can be used than shown, taking into account size increments in glass ball seats and drop ball sizes. The drop balls 60,62,64,66 have increasing diameter, with the first drop ball 60 having the smallest diameter, the second drop 62 diameter is larger than the first drop ball 60, a third drop ball 64 diameter is larger than the second drop ball 62, and a fourth drop ball is largest and having a diameter larger than the third drop ball 66.

[0077] Correspondingly, the internal diameter of at least the doughnut opening in the first and second glass ball seats 16,18 have increasing diameter. In the lower well tool device 10, the internal diameter of the second glass ball seat 18 is larger than the internal diameter of the first glass ball seat 16, as previously disclosed. In the upper well tool device 10, the internal diameter of the first glass ball seat 16 is larger than the second glass ball seat 18 in the lower well tool device 10, and the internal diameter of the second glass ball seat 18 in the upper well tool device 10 is larger than the internal diameter of the first glass ball seat 16 is the upper well tool device 10.

[0078] Figure 13 shows that the tubing string 70 can be run in the borehole with both closing sleeves 24 in the first closed position.

[0079] In figure 14, the first drop ball 60 has landed in the first glass ball seat 16 in the lower well tool device 10.

[0080] In figure 15, the closing sleeve 24 is in the open position, with the apertures 26 of the closing sleeve 24 aligned with the flow ports 28 of the housing 12, and a lower well zone can be stimulated using the lower well tool device 10.

[0081] In figure 16, the second drop ball 62 has landed in the second glass ball seat 18 to close the closing sleeve 24 in the lower well tool device 10, and in figure 17 the closing sleeve 24 is in the second closed position, with the apertures 26 of the closing sleeve 24 out of alignment with the flow ports 28 of the housing 12.

[0082] In figure 18, the closing sleeve 24 of the lower well tool device is in the second closed position, while the closing sleeve 24 of the upper well tool device 10 is the first closed position. The glass ball seats 16,18 in the lower well tool device 10 has been shattered, and the drop balls 60,62 in the lower well tool device 10 have been pumped down in the well. Figure 19 shows that a third drop ball 64 has landed in the first glass ball seat 16 in the upper well tool device 10.

[0083] In figure 20, the closing sleeve 24 of the upper well tool device 10 is in the open position, with the apertures 26 of the closing sleeve 24 aligned with the flow ports 28 of the housing 12, and stimulation can start.

[0084] In figure 21 , stimulation is completed, and a fourth drop ball 66 has landed in the second glass ball seat 18 in the upper well tool device 10.

[0085] In figure 22, the closing sleeve 24 of the upper well tool device 10 is in the second closed position, with the apertures 26 of the closing sleeve 24 out of alignment with the flow ports 28 of the housing 12.

[0086] As shown in figure 23, the glass ball seats 16,18 in the upper well tool device 10 has been shattered, and the drop balls 64,66 in the upper well tool device 10 have been pumped down in the well. Both well zones have been stimulated and the closing sleeves 24 of the upper and lower well tool devices 10 are in the second closed position.

Claims

Claims1. A well tool device (10) comprising a tubular housing (12) with an axial through running boring (14), the well tool device (10) further comprises: a closing sleeve (24) having an axial and internal through running boring (38) with internal apertures (26), said closing sleeve (24) is axially displaceable in the through running boring (14) of the housing (12), a first glass ball seat (16) is provided downstream in the internal through running boring (38) of the closing sleeve (24), and the first glass ball seat (16) is open and arranged for receipt of a first drop ball (60) to close fluid flow through the first glass ball seat (16), wherein the first glass ball seat (16) is resting on a first glass seat break mechanism (20), a second glass ball seat (18) is provided upstream in the internal through running boring (38) of the closing sleeve (24), and the second glass ball seat (18) is open and arranged for receipt of a second drop ball (62) to close fluid flow through the second glass ball seat (18), wherein the second glass ball seat (18) is resting on a second glass seat break mechanism (30), the closing sleeve (24) is arranged to be axially displaceable in the through running boring (14) of the housing (12) dependent on pressure build-up in the housing (12), wherein the apertures (26) of the closing sleeve (24) are arranged to be shifted in and out of alignment with flow ports (28) in the housing (12), and a closing sleeve restraining means (34) is placed downstream of the closing sleeve (24), said restraining means (34) is arranged to restrain movement of the closing sleeve (24) in the housing (12) to hold the closing sleeve (24) in open position.

2. The well tool device (10) according to claim 1 , wherein the second glass ball seat (18) has a doughnut shape, and the first glass ball seat (16) has a doughnut shape, wherein an internal diameter of the doughnut opening in the second glass ball seat (18) is larger than an internal diameter of the doughnut opening in the first glass ball seat (16).

3. The well tool device (10) according to claim 1 , wherein the restraining means (34) comprise a shear ring (36) arranged to hold the closing sleeve (24) in an open position with the apertures (26) aligned with the flow ports (28) in the housing during well stimulation.

4. The well tool device (10) according to claim 3, wherein the shear ring (36) of the restraining means (34) comprises an internal shear lip (36a), wherein the shear lip (36a) of the shear ring (36) is arranged to break when the closing sleeve (24) is subjected to a predetermined hydraulic pressure.

5. The well tool device (10) according to claim 1 , wherein a snap ring (22) is accommodated in a snap ring groove (40a;40b) provided on and between an outer surface of the closing sleeve (24) and an inner surface of the through running boring (14) in the housing (12).

6. The well tool device (10) according to claim 1 , wherein the closing sleeve (24) comprises a first snap ring groove (40a) and a second snap ring groove (40b) provided on and between an outer surface of the closing sleeve (24) and an inner surface in the through running boring (14) of the housing (12), and a snap ring (22), wherein the snap ring (22) is arranged to travel from the first snap ring groove (40a) and to the second snap ring groove (40b) when the closing sleeve (24) is displaced axially in the housing (12).

7. The well tool device (10) according to claim 1 , wherein the glass seat break mechanism (20;30) comprises a load ring (46) supporting the glass ball seat (16;18), said load ring (46) is axially movable within the through running boring (38) of the closing sleeve (24) between a first position in where the glass seat (16; 18) is with a distance to a breaking pin (42) and a second position in where the glass seat (16; 18) is forced against the breaking pin (42).

8. The well tool device (10) according to claim 1 , wherein said load ring (46) is resting on a shear ring (44) with an annular shear lip (44a) to prevent axial movement in the first position until the shear lip (44a) is subjected to a force higher than a predetermined force, wherein the annular shear lip (44a) of the shear ring (44) extends radially inward in the through running boring (38) of the closing sleeve (24), and the breaking pin (42) is resting on the shear ring (44), and said breaking pin (42) is accommodated in a pocket on an outside of the load ring (46).

9. The well tool device (10) according to claim 1 , wherein the apertures (26) of the closing sleeve (24) in a first position are closed and out of alignment with the flow ports (28) in the housing (12), and in a second position the apertures (26) are openand in alignment with the flow ports (28) in the housing (12), and in a third position the apertures (26) are out of alignment with the flow ports (28).

10. A method for well stimulation in a subterranean wellbore, characterized by comprising the steps: running one or more well tool devices (10) according to one or more of claims 1-9 into the wellbore, wherein a closing sleeve (24) of the well tool device (10) is in a first closed position with apertures (26) of the closing sleeve (24) out of alignment with flow ports (28) in the housing (12) of the well tool device (10), landing a first drop ball (60) in a first glass ball seat (16), and to build up pressure to shift the closing sleeve (24) from the first closed position to an open position wherein the apertures (26) of the closing sleeve (24) are aligned with the flow ports (28) in the housing (12) of the well tool device (10), starting well stimulation in a zone while restraining movement of the closing sleeve (24) using a restraining means (34) placed downstream of the closing sleeve (24), when zone stimulation is completed, landing a second drop ball (62) in a second glass ball seat (18), and building up pressure to break the restraining means (34) and to shift the closing sleeve (24) from the open position to a second closed position wherein the apertures (26) of the closing sleeve (24) are out of alignment with the flow ports (28) in the housing (12) of the well tool device (10), and shattering the first and the second glass ball seats (20,30), allowing travel of the first and second drop balls (60,62) down in the wellbore.11 . The method according to claim 10, wherein, after the second drop ball (62) has landed in the second glass ball seat (18), to build up pressure to activate a second glass seat break mechanism (30) to break the second glass ball seat (18) and to activate a first glass seat break mechanism (20) to break the first glass ball seat (16).

12. The method according to claim 10, wherein the restraining means (34) breaks at a pressure that is less than the pressure needed to active said first and second glass seat break mechanism (20;30).

13. The method according to claim 10, wherein the method comprises dropping a second drop ball (62) that has a larger diameter than the diameter of the first drop ball (60).

14. The method according to claim 10, wherein the method comprises the steps: running a tubing string (70) with multiple well tool devices (10) into the wellbore, and successive complete well stimulation for multiple zones.

15. The method according to claim 10, wherein the method comprises the steps: running a tubing string (70) with two or more well tool devices (10) into the wellbore, wherein the closing sleeves (24) of the well tool devices (10) are set in the first closed position, landing the first drop ball (60) in the first glass ball seat (16) of a downstream well tool device (10), and building up pressure to shift the closing sleeve (24) in the downstream well tool device (10) from the first closed position to the open position in order to stimulate a lower zone in the wellbore, landing the second drop ball (62) in the second glass ball seat (18) of the downstream well tool device (10), and building up pressure to shift the closing sleeve (24) in the downstream well tool device (10) from the open position to the second closed position, landing a third drop ball (64) in the first glass ball seat (16) of an upstream well tool device (10), and building up pressure to shift the closing sleeve (24) in the upstream well tool device (10) from the first closed position to the open position in order to stimulate an upper zone in the wellbore, and landing a fourth drop ball (66) in the second glass ball seat (18) of the upstream well tool device (10), and building up pressure to shift the closing sleeve (24) in the upstream well tool device (10) from the open position to the second closed position.

16. The method according to claims 14-15, wherein the method is repeated for well tool devices (10) over several zones using increasing sizes of drop balls (60,62,64,66) and internal diameter glass ball seats (16,18) in the well tool devices (10) in the tubing string (70).

17. The method according to claim 10, wherein the method comprises the steps: installing a snap ring (22) in a snap ring groove (40a;40b) provided between an outer surface of the closing sleeve (24) and an inner surface in the through running boring (14) of the housing (12), said snap ring (22) provides resistance or friction between the closing sleeve (24) and the housing (12) preventing unwanted axial displacement of the closing sleeve (24).

18. The method according to claim 17, wherein the snap ring (22) travels from a first snap ring groove (40a) and to a second snap ring groove (40b) when the closing sleeve (24) is allowed axial displacement in the housing (12).

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