NO346547B1 - A retrievable inner assembly of a directional drill - Google Patents

Description

A retrievable inner assembly of a directional drill

The present invention is related to a retrievable inner assembly of a directional drill, according to the preamble of claim 1.

Background

A directional drill is a type of rock drill where the drill bit is pointed or pushed in a controlled direction. To achieve this the directional drill needs to have a device or system that controls the direction the drill bit is oriented. There are many ways to solve this. Some systems rely on the drill string behind the directional drill being fixed in a set orientation. Some directional drills have mechanical rotation preventing devices that grips into the borehole wall by the force of pistons, springs, drilling fluid or other. This invention relates to directional drills using drilling fluid activated rotation preventing device or devices.

During deep hole drilling a water-based drilling fluid is used to cool the drill bit and flush drill cuttings out of the borehole. This fluid can also be used in a directional drill to create a pressure for activating a gripping mechanism that grips into the borehole wall in order for the drill bit to maintain a fixed orientation.

One such directional drill and rotation preventing device is described in US6516900B1, in the name of the applicant. This directional drill uses a restriction to build up pressure inside. This pressure expands a packer assembly that again acts on a gripping system. A set of valves built into the directional drill control the flow to the packer in order to maintain a stable pressure. This valve system was however designed for use with a conventional drilling technology, where core samples are retrieved by removing the whole drill string from the borehole. In the more modern wireline drilling technology such valve system cannot be used.

NO316286B1, in the name of the applicant, describes a directional core drill for use with the wireline drilling technology. This drill also uses a restriction the drilling fluid has to pass, and that way build up a pressure that expands a packer assembly. The disadvantage with such system is how the drilling fluid pressure is dependent on the flow rate, and large variations in flow rate may cause building up too much pressure or not enough pressure.

NO20171838A1/WO2019096990A1 describes another directional core drill where the drilling fluid restriction is a valve that is built into the retrievable core tube assembly. The valve stops the fluid from passing until a certain pressure is reached. The pressure expands a packer and when the set pressure is reached, the valve opens and allows the drilling fluid to pass by. There are however, several disadvantages with a system like this that increases the risk to the user and equipment, and make it less applicable in other types of directional drills.

● The pressure in the gripping system will still vary with the drilling fluid flow rate due to restricted area in the valve passage. This causes uneven gripping force and affects the drilling operation negatively.

● A blockage of drilling fluid flow in the drill bit or valve can cause the pressure to increase above the packer tolerance.

● It becomes difficult to detect leaks in the drill string as the valve builds up pressure, but the drilling fluid escapes through the leaks instead of past the valve. This will make it seem like everything is normal to the operator, but in reality, no drilling fluid flow will reach the drill bit and severe damages to the drilling assembly and drill string can occur.

● When drilling in holes without drilling fluid return it will not be possible to fill the drill string with fluid in order to control the pressure conditions and detect issues like core blocking. ● The strength of the spring controlling the valve must be frequently adjusted as the spring gradually loses its strength due to the continuous high impact.

● There is no option to have any pressure between zero and the set pressure on the packer.

This makes it impossible to use on other type of drills where more than these two pressure conditions are needed.

It is accordingly a need for a retrievable inner assembly of a directional drill enabling improved control of a rotation preventing device for the directional drills.

Object

The main object of the present invention is to provide a retrievable inner assembly of a directional drill partly or entirely solving the disadvantages of prior art.

It is an object of the present invention to provide a retrievable inner assembly of a directional drill providing improved control of a rotation preventing device for the directional drill.

An object of the present invention to provide a retrievable inner assembly of a directional drill that is independent of drilling fluid flow rate in the directional drill.

It is an object of the present invention to provide a retrievable inner assembly of a directional drill that is independent of fluid pressure in the directional drill after a desired/required fluid pressure is achieved in the directional drill.

An object of the present invention is to provide a retrievable inner assembly of a directional drill providing a pressure on the rotation preventing device that remains stable.

It is an object of the present invention to provide a retrievable inner assembly of a directional drill enabling separate controlling of the pressure on the rotation preventing device and in the directional drill.

An object of the present invention is to provide a retrievable inner assembly of a directional drill providing adjustable control of the rotation preventing device of directional drills.

It is an object of the present invention to provide a retrievable inner assembly of a directional drill that handles short-term pressure losses during drilling.

An object of the present invention is to provide a retrievable inner assembly of a directional drill providing adjustment of the rotation preventing device of directional drills to handle varying rock conditions and/or external pressure conditions.

It is an object of the present invention to provide a retrievable inner assembly of a directional drill enabling the possibility to detect and adjust for core blocks or other external factors influencing pressure conditions in the directional drill.

An object of the present invention is to provide a retrievable inner assembly of a directional drill enabling the use of multiple rotation preventing devices or other devices requiring pressure, where the pressure on each device may be set and adjusted independently.

Further objects of the present invention will appear from the following description, claims and attached drawings.

The invention

A retrievable inner assembly of a directional drill according to the present invention is disclosed in claim 1. Preferable features of the retrievable inner assembly are disclosed in the dependent claims.

A retrievable inner assembly of a directional drill according to the present invention comprises a two-valve assembly comprising first and second adjustable valve assemblies.

The first adjustable valve assembly of the two-valve assembly is according to the present invention arranged for controlling pressure on at least one rotation preventing device of the directional drill, while the second adjustable valve assembly is arranged for controlling drilling fluid pressure in the directional drill.

According to one embodiment of the retrievable inner assembly according to the present invention, the first adjustable valve assembly is designed as a pressure reduction valve that is open when drilling fluid pressure is lower than a pre-set value. In open condition the first adjustable valve assembly allows fluid passage from the directional drill and into the at least one rotation preventing device. If the drilling fluid pressure increases above the pre-set value, the first adjustable valve assembly closes and blocks further fluid passage to the at least one rotation preventing device.

If pressure in the at least one rotation preventing device reduces due to leakage, the first adjustable valve assembly opens up again and allows the pressure to build back up. If fluid pressure in the directional drill becomes lower than the pre-set value, the first adjustable valve assembly is arranged to slowly open and allow the pressure and drilling fluid from the at least one rotation preventing device to drain. If a short-term pressure loss occurs while drilling, the first adjustable valve assembly is providing a sufficient delay of the opening thereof to secure that the pressure on the at least one rotation preventing device will remain intact.

As the pressure needed on the at least one rotation preventing device will vary depending on rock conditions and external pressure conditions, the closing pressure of the first adjustable valve assembly can according to the present invention be adjusted freely to any suitable pressure.

The first adjustable valve assembly is further provided with a separate drilling fluid flow passage through the first adjustable valve assembly providing drilling fluid flow in the directional drill.

The second adjustable valve assembly is according to the present invention designed as a pressure relief valve arranged to build up pressure in the directional drill. According to a preferred embodiment of the retrievable inner assembly according to the present invention the second adjustable valve assembly is mounted downstream the first adjustable valve assembly, i.e. closer to a drill bit of the directional drill.

The second adjustable valve assembly is closed when the drilling fluid pressure is lower than a preset value. According to one embodiment of the retrievable inner assembly according to the invention, the second adjustable valve assembly comprises a nozzle or restriction that restricts, but does not fully block the drilling fluid flow in the directional drill and causes the fluid pressure above the second adjustable valve assembly to increase. When the drilling fluid pressure reaches a pre-set value, the second adjustable valve assembly opens and creates a by-pass passageway for the drilling fluid. This prevents the drilling fluid pressure from building up much higher than the pre-set value.

According to the present invention, the opening pressure for the second adjustable valve assembly is freely adjustable. In all situations the opening pressure should be higher than the closing pressure of the first adjustable valve assembly, but in most cases the difference should be small, e.g., but not limited to, between 5-15 bar.

In dry hole conditions, the difference may be significantly larger, as the second adjustable valve assembly can be used to retain drilling fluid in the drill string and give the operator control over the pressure conditions. This will be dependent on at which depth the water loss occurs. If e.g. the water loss is experienced approximately at 500 meters, a fluid pressure of 50 bar is built up in the directional drill by filling it with drilling fluid. If the pressure of the rotation preventing device is e.g.

20 bar, one should have at least 30 bar to be able to perform drilling with a fluid filled drill string.

With full control and knowledge of the pressure conditions inside the directional drill it is possible to detect and adjust for core blocks or other external factors influencing the pressure conditions in the drill.

The two-valve assembly of the retrievable inner assembly according to the present invention gives multiple benefits over existing solutions as the pressure on the rotation preventing device will remain perfectly stable and fully independent on drilling fluid flow rate in the directional drill, as well as independent of fluid pressure in the directional drill after a desired/required pressure is achieved. The pressure on the rotation preventing device will never exceed its pressure limitation, the force on contact/gripping parts of the at least one rotation preventing device will remain fully constant and improve drilling conditions, and the wear on bearings and seals will be minimized as the rotation preventing device pressure and force can be adjusted to the lowest possible without there being any risk of the pressure dropping. Leaks in the directional drill is also no issue, as some drilling fluid flow is always allowed to pass the first and second adjustable valve assemblies in order to cool the drill bit and directional drill.

The retrievable inner assembly according to the present invention also allows lower pressures to be used as the second adjustable valve assembly provides a restriction that will cause pressure buildup, but still allowing drilling fluid to pass through the two-valve assembly. The pressure in the at least one rotation preventing device will then equal the pressure created by the restriction of the second adjustable valve assembly, until this pressure increases to where the first adjustable valve assembly closes.

According to a further embodiment of the retrievable inner assembly according to the present invention, the two-valve assembly comprises multiple first adjustable valve assemblies, i.e. pressure reduction valves. The use of multiple first adjustable valve assemblies enables the use of multiple rotation preventing devices or other devices requiring pressure, where the pressure on each device may be set and adjusted independently by respective associated first adjustable valve assemblies.

Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

Example

The present invention will below be described in further detail with reference to the attached drawings, where:

Fig.1 is a principle drawing of a directional drill according to prior art,

Fig.2a-b are principle drawings of retrievable inner assemblies according to the present invention,

Fig.3a is a principle drawing of a two-valve assembly according to the present invention,

Fig.3b is a principle drawing of a first adjustable valve assembly according to the present invention,

Fig.3c is a principle drawing of a second adjustable valve assembly according to the present invention,

Fig.4 is a principle drawing of how the present invention works, and

Fig.5 is a hydraulic flow diagram of the present invention.

Reference is now made to Figure 1 illustrating an example of a directional drill 10 according to prior art the present invention is suitable for, wherein the directional drill 10 comprises numerous parts in the longitudinal direction forming the directional drill, also referred to as a bottom hole assembly. The directional drill 10 comprises, in order from below and up, a foremost diamond drill bit 20 with a reamer 30, drive shaft connection assembly 40, a thrust bearing assembly 50, a lower outer tube 60, a deflection assembly 70, an upper outer tube 80, stabilizer assembly 90, rotation preventing device 100, an optionally magnetic orientation assembly 150 and an orientation and connector assembly 200. The thrust bearing assembly 50, lower outer tube 60, deflection assembly 70, stabilizer assembly 90, rotation preventing device 100 and optional magnetic orientation assembly 150 being arranged for accommodating an inner drive shaft (not shown) for driving the drill bit 20, wherein the drive shaft is transferring feed and rotation forces from a drill rig onto the drill bit 20. The drill bit 20 may be a full-face drill bit or arranged for drilling a bore core. The drive shaft as well as the function of such a directional drill is well described in prior art, such as e.g. in NO316286B1, the enclosure of which is included herein by reference, and need no further description herein. A drill bit for drilling a bore core is shown in NO316286B1.

Reference is now made to Figure 2a-b which are principle drawings of embodiments of a retrievable inner assembly 300 according to the present invention, in the form of a retrievable survey assembly in Fig.2a and retrievable core tube assembly in Fig.2b.

The retrievable inner assembly 300 comprises numerous parts in the longitudinal direction. The retrievable inner assembly 300 according to the shown embodiment comprises, in order from top and downwards, a head assembly 400 comprising a spear head 401 for connection of the retrievable inner assembly 300 to a wireline with a quick snap connection (not shown), an optional instrumentation assembly 500 and a two-valve assembly 600 according to the present invention.

The retrievable core tube assembly 300 will further comprises a lower core catcher sleeve 910 attached to an inner tube 900 having space for receiving a bore core, wherein the inner tube 900 is arranged to lower end of the two-valve assembly 600.

Reference is now made in addition made to Fig. 3a-c showing principle drawings of a two-valve assembly 600 according to the present invention. The two-valve assembly 600 according to the present invention is formed by a first adjustable valve assembly 700 and a second adjustable valve assembly 800, in this embodiment arranged in series downstream the head assembly 400. Details of the first adjustable valve assembly 700 is shown in a cross-sectional view in Fig. 3b. The first adjustable valve assembly 700 comprises an elongated housing 710 provided with screw-in connections at ends thereof, arranged to the head assembly 400 or instrument assembly 500 at upper end and arranged to the second adjustable valve assembly 800 at lower end. The first adjustable valve assembly 700 in the shown embodiment is a (direct operated) adjustable pressure reduction valve, designed as a tight seat valve.

The elongated housing 710 of the first adjustable valve assembly 700 comprises a first 711a and second 711b interior spacing divided by a passageway 712 allowing fluid flow between the first 711a and second 711b interior spacing, wherein the first interior spacing 711a is arranged in the part of the elongated housing 710 facing the head assembly 400 or instrument assembly 500.

The part of the elongated housing 710 enclosing the first interior spacing 711a is provided with multiple openings 713 in circumferential direction thereof enabling flow of drilling fluid into the first interior spacing 711a of the elongated housing 710 and a separate fluid communication with openings 721 of a hollow stem 720 extending in longitudinal direction of the elongated housing 710.

The hollow stem 720 extends with a gap through the passageway 712 for allowing fluid to flow from the first interior spacing 711a at one side of the passageway 712 to second interior spacing 711b at the other side of the passageway 712.

The hollow stem 720 is at lower end, i.e. the end facing the second adjustable valve assembly 800, arranged to an adjustment screw 730, provided with a longitudinally through hole 731 for accommodating the hollow stem 720, which adjustment screw 730 is adjustable in longitudinal direction of the elongated housing 710 by means of corresponding threads 732 on exterior surface of the adjustment screw 730 and interior surface of the elongated housing 710.

The first adjustable valve assembly 700 further comprises a spool 740 arranged movably in longitudinal direction of the hollow stem 720 and elongated housing 710, wherein the spool 740 (valve seat housing) is provided with a longitudinally extending through hole 741 for receiving and accommodating the hollow stem 720. The adjustment screw 730 and spool 740 are further at facing ends provided with recesses 733 and 742, respectively, for receiving and accommodating ends of a spring 750 extending in longitudinal direction of the elongated housing 710 between the spool 740 and the adjustment screw 730, the spring 750 enclosing the hollow stem 720 in longitudinal direction thereof.

The first adjustable valve assembly 700 further comprises a closing member 760 formed by an elongated body 761 accommodating and enclosing the hollow stem 720, and provided with a flange 762 at one end thereof. The elongated body 761 is attached to the spool 740 at one end, extending through the passageway 712 and into the first interior spacing 711a wherein the flange 762 is positioned. The flange 762 has an exterior circumference that is larger than the interior diameter of the passageway 712.

The first adjustable valve assembly 700 further comprises sealing means 770 arranged in a circumferentially extending exterior recess of the elongated housing 710 sealing against the interior surface of the directional drill 10.

The first adjustable valve assembly 700 is further provided with at least one port 780 from the second interior spacing 711b in fluid communication with the at least one rotation preventing device 100.

The first adjustable valve assembly 700 according to the present invention accordingly provides a leakage-free pressure reduction of working pressure with no by-pass.

By means of adjustment of the adjustable screw 730 in longitudinal direction of the elongated housing 710, a desired pressure value is set for the first adjustable valve assembly 700 by adjustment of the compression of the spring 750.

The first adjustable valve assembly 700 is in initial position open, i.e. the flange 762 of the closing member 760 is positioned away from the opening in the passageway 712, enabling flow of fluid therebetween. When drilling fluid is supplied from the drill rig, the drilling fluid will flow into the first interior spacing 711a via the openings 713 and from the first interior spacing 711a to the second interior spacing 711b in front of the spool 740 via the passageway 712 and into the rotation preventing device 100 via the at least one port 780. When the fluid pressure at the at least one port 780 has increased above the set pressure, the fluid pressure acting on the spool 740 in the second interior spacing 711b will provide a higher force than the spring 750 provides on the spool 740 in the opposite direction, resulting in movement of spool 740 and thus the closing member 760 in longitudinal direction of the elongated housing 710, resulting in that the flange 762 will move to close the opening in the passageway 712, accordingly closing the flow of fluid from the first interior spacing 711a to the second interior spacing 711b, such that the drilling fluid will no longer influence the fluid pressure in the at least one port 780, thus providing a fluid pressure holding function for the at least one rotation preventing device 100.

If the fluid pressure drops at the at least one port 480 this will be compensated for by that the force in the spring 750 will gradually open the passageway 712 by moving the closing member 760 in longitudinal direction such that the flange 762 thereof moves away from the passageway 712 and flow of fluid is again allowed between the first 711a and second 711b interior spacing.

Reference is now made to Fig. 3c showing a cross-sectional view of the second adjustable valve assembly 800 according to the present invention. The second adjustable valve assembly 800 comprises an elongated housing 810 provided with screw-in connections at ends thereof, arranged to the first adjustable valve assembly 700 at upper end and arranged to the inner tube 900 at lower end, if present, or in the case of a retrievable survey assembly not connected to another component at lower end. The second adjustable valve assembly 800 is in the shown embodiment a (direct operated) pressure relief valve, designed as a tight seat valve.

The second adjustable valve assembly 800 is at upper part of the elongated housing 810, i.e. the part closest to the first adjustable valve assembly 700, comprising a valve seat 820 with an opening 821 allowing fluid flow from the first adjustable valve assembly 700.

The second adjustable valve assembly 800 further comprises an adjustment screw 830 provided with a longitudinally through hole 831 allowing flow of drilling fluid therethrough, which adjustment screw 831 is adjustable in longitudinal direction of the elongated housing 810 by means of corresponding threads 832 on exterior surface of the adjustment screw 830 and interior surface of the elongated housing 810.

The second adjustable valve assembly 800 further comprises a spool 840 arranged movably in longitudinal direction interior of the elongated housing 810, wherein the spool 840 is provided with holes 841 in circumferential direction thereof allowing fluid flow into the elongated housing 810. The adjustment screw 830 and spool 840 are further at facing ends provided with recesses 833 and 842, respectively, for receiving and accommodating ends of a spring 850 extending in longitudinal direction of the housing 810 between the spool 840 and the adjustment screw 830.

The second adjustable valve assembly 800 further comprises a nozzle 860 protruding from the end of the spool 840, wherein the nozzle 860 is provided with a through hole 861 in fluid communication with a center opening in the spool 840. The diameter of the through hole 861 of the nozzle 860 is considerably smaller than the opening 821 of the valve seat 820 and thus works as a restriction allowing a restricted/minimum fluid flow through the pressure relief valve 800 at all time.

According to a further embodiment, the spool 840 is provided with one or more channels 843 for directing/guiding fluid flow into the openings 841 of the spool 840.

The initial position of the second adjustable valve 800 is closed.

By means of the adjustment screw 830, the opening pressure of the second adjustable valve 800 may be adjusted to a desired pressure by controlling the compression of the spring 850. The second adjustable valve assembly 800 thus provides increased fluid pressure upstream the second adjustable valve assembly 800 and to the at least one rotation preventing device 100 by that the fluid pressure upstream the second adjustable valve assembly 800, and thus in the first adjustable valve assembly 700, is allowed to build up before the fluid pressure reaches the set pressure in the second adjustable valve assembly 800.

When the fluid pressure has reached the set pressure for the second adjustable valve assembly 800 the fluid pressure acting on the nozzle 860 via the opening of the valve seat 820 will be higher than the force of the spring 850 in the opposite direction, resulting in that the nozzle 860 and thus the spool 840 will move in longitudinal direction of the housing 810 opening a passage for fluid flow between the valve seat 820 and the spool 840, allowing fluid flow into the channels 843 and the spool 840, i.e. bypassing the opening 861 of the nozzle 860, further into the interior of the elongated housing 810 in addition to the fluid flow through the nozzle 860, and out of the elongated housing 810 at lower end through the opening 831 of the adjustment screw 830 and further to the drill bit 20. Accordingly, allowing considerably increased flow through the second adjustable valve assembly 800 without the fluid pressure in the directional drill 10 increasing of significance.

The nozzle 860 may be removable by design and be replaceable with a nozzle 860 containing a larger or smaller opening 861. A larger opening will increase the drilling fluid flow required to build up the pressure in the directional drill 10, whereas a smaller opening will reduce the drilling fluid flow requirement. Different rock conditions and drill bit designs will require different flow rates and setting the nozzle size accordingly will prevent unnecessary compression and wear on the spring 850.

A principle drawing of how the two-valve assembly 600 according to the present invention works is shown in Figure 4, showing a principle drawing, and Figure 5, showing a hydraulic flow diagram.

The rotation preventing device 100, shown in Figure 1, is e.g. formed by a packer pipe 101 including a packer housing having at least one pressure pad or packer element 102, lower 103 and upper 104 end pieces, respectively, and front 105 and rear 106 stuffing boxes, respectively. Accordingly, the rotation preventing device 100 is provided with sealings and connections at both sides thereof enabling arrangement into the directional drill 10. The at least one pressure pad or packer element pipe 101 and into engagement with a borehole wall for locking rotation of the rotation preventing device 100, as well as parts of the directional drill 10 between the orientation and connector assembly 200 and the drill bit 20, in relation to the borehole wall, the rotation preventing device 100 being arranged to be displaced axially along the borehole wall during drilling. The at least one pressure pad or packer element 102 is/are arranged to be pressed outward to the borehole wall by means of fluid pressure from the first adjustable valve assembly 700 of the two-valve assembly 600 of the retrievable inner assembly 300 according to the present invention when supplied with drilling fluid into the two-valve assembly 600/directional drill 10.

Accordingly, the pressure acting upon the rotation preventing device 100/pressures pad/element 102, is adjustable by the first adjustable valve assembly 700. In this way, it is possible to adapt the directional drill 10 in accordance with the present invention in a simple manner to different rock types requiring varying water quantities and varying pressure of the rotation preventing device 100.

By the two-valve assembly 600 according to the present invention the pressure on the rotation preventing device 100 will remain perfectly stable and fully independent on drilling fluid flow rate and pressure in the directional drill 10.

The first adjustable valve assembly 700 ensures that the pressure on the rotation preventing device 100 will never exceed its pressure limitation, as well as ensuring that the force on contact/gripping parts 102 of the at least one rotation preventing device 100 will remain fully constant and improve drilling conditions.

The first adjustable valve assembly 700 further ensures that the wear on bearings and seals will be minimized as the rotation preventing device 100 pressure and force can be adjusted to the lowest possible without there being any risk of the pressure changing.

Leaks in the drill string will with the use of the present invention be no issue, as some drilling fluid flow is always allowed to pass the first 700 and second 800 adjustable valve assemblies in order to cool the drill bit 20 and drill string.

The retrievable inner assembly 300 according to the present invention also allows lower pressures to be used as the second adjustable valve assembly 800 provides a restriction by the nozzle 860 that will cause fluid pressure build-up, but still allow drilling fluid to pass through the two-valve assembly 600 via the through hole 861 of the nozzle 860.

The pressure in the at least one rotation preventing device 100 will first equal the fluid pressure created by the nozzle 860 in the second adjustable valve assembly 800, until this fluid pressure increases to where the first adjustable valve assembly 700 closes.

According to a further embodiment of the present invention, the two-valve assembly 600 is provided with multiple first adjustable valve assemblies 700 arranged in series upstream the second adjustable valve assembly 800. The use of multiple first adjustable valve assemblies 700 arranged in series enables the use of multiple rotation preventing devices 100 or other devices requiring pressure, where the fluid pressure on each device may be set and adjusted independently by respective associated first adjustable valve assembly 700. Other devices requiring pressure may e.g. be locking/closing systems, actuators, mechanisms or instruments that may operate at different levels, where the spring force/pressure may be used to adjust between the different levels.

Even though the first adjustable valve assembly 700 in the shown embodiments are arranged upstream the second adjustable valve assembly 800, the second adjustable valve assembly 800 may be arranged upstream the first adjustable valve assembly 700 by mechanical adjustments/modifications.

Claims (6)

Claims

1. Retrievable inner assembly (300) for a directional drill (10) comprising a two-valve assembly (600) formed by a first adjustable valve assembly (700) and a second adjustable valve assembly (800) arranged in series downstream a head assembly (400) or instrument assembly (500), wherein the first adjustable valve assembly (700) is controlling fluid pressure of at least one rotation preventing device (100) of the directional drill (10), and wherein the second valve assembly (800) is controlling drilling fluid pressure in the directional drill (10),

characterized in that

the first adjustable valve assembly (700) is designed as a pressure reducing valve with a springloaded (750) closing member (760) held open by the spring (750) when drilling fluid pressure is lower than a pre-set value allowing fluid passage from the directional drill (10) and into the at least one rotation preventing device (100) and closed when the drilling fluid pressure in the at least one rotation preventing device (100) is above the pre-set value and the force of the spring (750) is overcome, as well as arranged to open if the pressure in the at least one rotation preventing device (100) is reduced below the pre-set value and lower than the force of the spring (750), and

the second adjustable valve assembly (800) is designed as a pressure relief valve with a valve seat (820) restricting drilling fluid and increasing drilling fluid pressure in the directional drill (10).

2. Retrievable inner assembly (300) according to claim 1, characterized in that the second adjustable valve assembly (800) is arranged to provide a minimum fluid flow through the second adjustable valve assembly (800) at all time.

3. Retrievable inner assembly (300) according to claim 1, characterized in that the valve seat (820) is spring-loaded (850).

4. Retrievable inner assembly (300) according to claim 1 or 3, characterized in that the spring-loaded first (700) and second (800) adjustable valve assemblies are adjustable by respective adjustments screws (730, 830).

5. Retrievable inner assembly (300) according to claim 1, characterized in that the first adjustable valve assembly (700) is arranged upstream the second adjustable valve assembly (800), or vice versa.

6. Retrievable inner assembly (300) according to claim 5, characterized in that the first adjustable valve assembly (700) provides a separate flow of drilling fluid through the first adjustable valve assembly (700).