The present invention relates to a deep drilling system, and in particular to a stabilizing system to be used in such a deep drilling system, and a method for drilling a hole utilizing such a deep drilling system.

2. Technical background

In a deep drilling system, a drill bit is typically connected via several drill pipes, forming a drill string, to a drilling motor. Such a setup is also generally illustrated in figure l. The drilling motor, provided on the earth’s surface, applies drilling forces (the longitudinal and rotational forces as illustrated by arrows in Fig. l) onto the drill string l such that the drill bit 3 advances further into the ground 4, thereby creating a bore hole 5. Since bore holes can reach depths of up to several kilometers, it is desired that the drill string 1 is centered in the bore hole. Particularly, the sections close to the drill bit are centered such that the drill bit 3 advances in a defined direction into the ground. For these reasons, stabilizers are typically utilized, which can be provided in form of blades 2 as illustrated in Fig. 1. These blades are fixed to the drill string 1 and extend to the walls of the bore hole 5.

During drilling operation, a water-based drilling fluid is commonly pumped

downwards through the drill pipes to the drill bit, such that it flows back in the space provided between the drill string 1 and the walls of the bore hole. Thereby the drill bit is cooled, and the cuttings are transported to the surface.

When advancing through certain materials, e.g. when advancing through shale formation, the shale reacts with the water, swells and becomes sticky. This sticky mud, or sticky cuttings, can adhere between the blades 2, forming a ball of mud or mud cake 7. This effect, exemplarily illustrated in Fig. 2, is known as“balling”. Thereby a cavity 6 of the bore hole 5 can be formed wherein the diameter of the mud cake 7 can become bigger than the inner diameter of the bore hole 5.

This balling can create problems, in particular during pulling-out-of-hole (POOH) and/or running-in-hole (RIH) operations. For example, as illustrated in Fig. 3, when trying to retrieve the drill string out of the hole (POOH), problems arise: The accumulated mud cake 7 can cause a severe drag, and even jam the movement of the drill string. Accordingly, POOH operations can take much longer due to balling, or in the worst case, the drill string cannot be removed from the hole at all and has to be cut off.

Typically, such balling is characterized by an increased necessary rotary torque and a reduced penetration rate during drilling. Accordingly, balling can be noticed by an operator. Several methods for unballing are known in the art. For example, when balling has been noted, the drill bit can be lifted off the bottom of the bore hole and the water flow rate can be increased for a certain amount of time. Further, by spinning the drill string as fast as possible, it can then be tried to fling off the mud cake.

Alternatively, it can also be tried to shake off the mud cake by lifting and dropping the drill string rapidly. It can also be tried to pump a relatively small volume of specially prepared fluid (a so called“pill”) placed or circulated in the bore hole and subsequently wash off the ball of mud. By pumping fibers in the drilling fluid, it is intended to provide a better hole cleaning. Other techniques for preventing balling are based on providing a special coating onto the drilling equipment. However, these techniques are either expensive in cost, suited for one-time use only, or are ineffective in solving the issue.

Reference WO 2016/055822 Ai relates to a stabilizing system adapted to be used in a drilling system, wherein the transversal diameter of the stabilizing system increases when drilling forces are applied onto the stabilizing system. The disclosure thereof is incorporated herein by reference. A need exists for an improved stabilizing system, particularly to more reliably perform POOH and/or RIH operations.

It is therefore an object of the present invention to provide an improved stabilizing system, with particularly deals with balling better than the prior art techniques or systems, so that POOH and/ or RIH operations can be performed easier, faster and/ or more reliable.

These and other objects, which become apparent to the person skilled in the art upon reading the following description, are achieved by the present invention according to the subject matter of the independent claims.

Summary of the invention

According to a first aspect of the invention, a stabilizing system is provided, which is adapted to be used in a deep drilling system. The stabilizing system thereby comprises a longitudinal housing, which may particularly be a hollow housing. Further, the stabilizing system comprises a spring which is arranged inside the housing. In a preferred embodiment, the spring is provided as a helical spring.

Furthermore, the stabilizing system is configured such that the stabilizing system is contracted and the spring is compressed along the longitudinal axis of the stabilizing system when an external load is applied in longitudinal direction onto the stabilizing system. The external load may, for example, be due to drilling forces, which may generally denote to any kind of forces applied during drilling operation, such as torques, i.e. rotational forces, and longitudinal forces applied from the outside of the borehole onto a drill string, preferably acting in drilling direction onto the stabilizing system. The external load may also be due to temporary longitudinal forces applied onto the drilling system and hence on the stabilizing system from outside the borehole. A component of the forces may thereby be in the longitudinal direction. The longitudinal direction may be parallel to the longitudinal axis of the stabilizing system, which may be defined by the overall elongated form of the stabilizing system, and the elongated form of the longitudinal housing. Hence, the longitudinal axis and the longitudinal direction may correspond to the main axis of the stabilizing system, or the borehole. The longitudinal direction may thereby correspond to the main drilling direction.

Furthermore, the stabilizing system is configured such that the transversal diameter of the stabilizing system increases when the stabilizing system is contracted. The transversal direction of the stabilizing system may thereby be

perpendicular/orthogonal to the overall drilling direction, and

perpendicular/orthogonal to the longitudinal direction of the stabilizing system.

Furthermore, the stabilizing system is configured such that the spring urges the stabilizing system to expand along the longitudinal axis when the external load is released. The external load must not necessarily be completely released in order to allow the spring to urge the system to expand, but at least partially, preferably at least up to a certain threshold value. The spring may constantly act on particular

components of the stabilizing system, but only when the external load is below the certain threshold value, the stabilizing system may expand along its longitudinal axis due to forces applied by the spring.

Furthermore, the stabilizing system is configured such that the transversal diameter of the stabilizing system decreases when the stabilizing system expands along the longitudinal axis. Accordingly, when releasing the external load, the stabilizing system expands along its longitudinal axis, and its transversal diameter decreases.

Thus, by using the external load in combination with the provision of the spring, it is possible to change the transversal diameter of the stabilizing system in a reliable manner, allowing for weakening or even breaking away at least parts of a mud cake formed around the stabilizing system when retracting it from the borehole. This allows for an unhindered and reliable operation of the drilling system, and particularly for easier and faster POOH and/or RIH operation. By means of the external load, the transversal diameter can be easily increased, allowing for a stabilizing function of the stabilizing system, and the external load can easily be applied by means of drilling forces, which are always available during drilling. The spring, in turn, allows for reliably decreasing the transversal diameter of the stabilizing system, so that eventually the drill string can be removed from the borehole in a smooth manner. As the spring may directly act on the stabilizing system to urge it to expand along the longitudinal direction, thereby restoring the extended state of the stabilizing system, the transversal diameter of the stabilizing system can be eventually decreased with reduced risk of jamming. By decreasing the transversal diameter in this manner, a mud cake formed around the stabilizing system can be reliably broken loose. By alternately increasing and decreasing the transversal diameter of the stabilizing system, it is possible to facilitate losing of mud cakes.

Preferably, the transversal diameter of the stabilizing system increases when pushing forces are applied on the stabilizing system during drilling. If pulling forces are applied onto the stabilizing system, in order to remove the drill bit, drill pipes, and the stabilizing system from the borehole, the transversal diameter of the stabilizing system may decrease. The spring thereby facilitates this removal process by urging the transversal diameter of the stabilizing system to decrease. Thus, the transversal diameter of the stabilizing system can be altered in an efficient and reliable manner to break off a mud cake formed thereon, in order to thereby eliminate balling, and to improve POOH and/or RIH operations.

Preferably, the spring is provided concentrically with the housing. Thus, the spring may be applied such a main axis of the spring may essentially coincide with a main axis of the longitudinal housing. Thus, the spring applies uniform forces, with regard to a radial transversal direction of the stabilizing system. This improves reliability of increasing and decreasing the transversal diameter of the stabilizing system. Preferably, the spring is provided parallel to the longitudinal axis of the system. Hence, spring forces may essentially act along the longitudinal axis. Thereby, expansion of the stabilizing system along the longitudinal axis is facilitated, essentially allowing for reliably decreasing the transversal diameter of the stabilizing system.

Preferably, the stabilizing system further comprises a column arranged inside the housing and being adapted to transfer drilling forces applied onto the stabilizing system. The column may thereby be provided in form of a piston. The column may thereby extend through the spring provided in the stabilizing system. Drilling forces applied by a drilling motor may be transferred to the drill bit via the stabilizing system. The column may thereby be movable relative to the housing between a drilling position and a pulling position (relative to the other components of the stabilizing system).

Preferably, a spring travel of the spring between its relaxed stated and its maximal compressed state is between 1 and 100 cm, further preferred between 5 and 50 cm, and further preferred between 10 and 20 cm. This spring travel may allow for a reliable operation of the spring in order to decrease the transversal diameter of the stabilizing system when desired. The spring travel thereby ensures proper movement of the individual parts of the stabilizing system to eventually increase or decrease the transversal diameter thereof as required.

Preferably, the external load is at least 5 kN, further preferred at least 10 kN, and further preferred at least 15 kN. By applying such external loads, the transversal diameter of the stabilizing system can be increased in a reliable manner. Thereby, preferably, the spring can be brought into a compressed state, preferably maximal compressed state, by applying these external loads. Accordingly, by releasing such external loads, the respective force applied by the spring in order to urge the stabilizing system to expand along the longitudinal axis is sufficiently high in order to provide for a reliable function of the stabilizing system.

Preferably, a spring rate of this spring is between 10 and 5000 kN/m, further preferred between 50 and 2000 kN/m, further preferred between 100 and 1000 kN/m, further preferred between 200 and 500 kN/m, and further preferred between 250 and

400 kN/m. Such spring rates allow for reliably increasing and decreasing the transversal diameter of the stabilizing system. A sufficient spring force is thereby provided, in order to allow for a reliable function of the stabilizing system, reducing the risk of jamming, which may occur for example due to strong balling effects.

In a preferred embodiment, the stabilizing system further comprises at least one spacer movable relative to the housing between a retracted position and an expanded position. Preferably, the spring is thereby adapted to act on the spacer along the longitudinal axes of the stabilizing system to urge the spacer to the retracted position. The extend of protrusion of the spacer may thereby increase when the spacer is moved from the retracted position to the extended position. For example, a column arranged in the stabilizing system may move the spacer to the expanded position, when the external load is applied onto the column of the stabilizing system. When drilling forces are applied onto the stabilizing system, the column may move to the drilling position. Further, the spacer maybe moved to the expanded position by the column when said column is moving to the drilling position. When retracting the drill bit, the column may be moved to the pulling position, thereby releasing the spacer. By means of the spring, the stabilizing system may thereby be urged to expand along the longitudinal axis, and the spacer may be urged to the retracted position.

Accordingly, the drilling forces, i.e. longitudinal and/or rotational forces, in

combination with the spring forces, are utilized to vary the extent of protrusion of the spacer, such that mud cakes formed on or in-between the spacers can get loose. There is no need to apply further energy, like electrical current or hydraulic pressure in order to vary the extent of protrusion of the spacer. The stabilizing system is thereby able to withstand heavy workloads as particularly the movable column is adapted to transfer the drilling forces to the drilling bit. Thus, the spacer, the housing, and the column are preferably made of hard, durable alloy.

The term“spacer” used herein is not limiting to any particular shape or structure. Accordingly, the spacer can for example be provided in a cylindrical or spherical shape. Preferably, however, the spacer is designed in form of a blade or fin.

Preferably, the maximal movement of one spacer relative to the housing is in the range of 5 to 50 mm, preferably in the range of 10 to 40 mm, more preferably in the range of 15 to 35 mm, and most preferred in the range of 20 to 30 mm. These movement ranges are preferred to loosen, weaken and to remove mud cakes from the stabilizing system.

Preferably, the spring is in a compressed state, when the spacer is in the expanded position. Thus, by applying the external load, the spacer can be moved to the expanded position, so that the stabilizing function of the stabilizing system is provided upon drilling a hole. The spring is thereby in a compressed state, so that when the external load is removed, the spring can urge the spacer to the retracted position. This allows for a reliable transition of the stabilizing system.

Preferably, the spring is adapted to act on the spacer in the expanded position with a force of 5 to 25 kN, further preferred of 10 to 20 kN, further preferred of 13 to 17 kN, most preferred of approximately 15 kN. Hence, when the spring in the compressed state, it may provide a sufficient force on the spacer in order to urge it to move into the retracted position, once the external load is released. As the forces applied by the spring is sufficiently large, jamming of the movement of the spacer is efficiently prevented, guaranteeing reliable functioning of the stabilizing system.

Preferably, the spacer comprises a tapered section at one end thereof. Particularly preferred, a tapered section is provided at both ends of the spacer. The tapered section may preferably be tapered relative to the longitudinal axis of the stabilizing system by 5 to 70 degrees, further preferred by 10 to 60 degrees, further preferred by 15 to 50 degrees, further preferred by 20 to 40 degrees, further preferred by 25 to 35 degrees, and further preferred by approximately 30 degrees. Such a tapered section of the spacer allows for a smooth movement of the spacer when the stabilizing system is contracted or expanded, and particularly when the spacer thereby moves between the retracted position and the expanded position. As a spring force may act along the longitudinal axis of the stabilizing system onto the spacer, the provision of the tapered section may allow for a resulting transversal movement of the spacer.

Particularly preferred, the housing of the stabilizing system comprises a counter- tapered section which is adapted to interact with the tapered section of the spacer. The tapered section of the spacer may thereby be adapted to slide along the counter-tapered section of the housing to move the spacer along the longitudinal axes of the stabilizing system when the spacer moves between the retracted position and the expanded position. Accordingly, a spring force may act along the longitudinal axis of the stabilizing system, and due to the particular interplay of the spacer with the counter- tapered section, this longitudinal spring force can provide for a movement of the spacer with a transversal component, as will be appreciated by the person skilled in the art. Hence, when the external load is applied or removed, the stabilizing system may expand or contract, and the spacer can thereby smoothly move between the retracted position and the expanded position to thereby increase or decrease the transversal diameter of the stabilizing system, with a reduced possibility of jamming or blocking thereby.

Preferably, the housing comprises one or more passages extending from an interior side of the housing to an exterior side of the housing, further preferred, the one or more passages connect an inner space occupied by the spring and the spacer to an outer space of the stabilizing system. The passages may thereby be provided in forms of holes or valves. By providing such passages, the reliability of the functionality of the stabilizing system is increased. For example, fluids in the space may flow out through the passages when the spacer retracts, i.e. when the spacer further enters the space. Further preferred, a screen filter is provided in each one of the one or more passages, further improving the reliability of the stabilizing system.

Preferably, the stabilizing system comprises at least two spacers, further preferred three spacers. The spring may thereby be adapted to act on each of the spacers along the longitudinal axes of the stabilizing system to urge each one of the spacers to the retracted position. The spacers may thereby be equally positioned around the housing, whereby each one of the spacers may be supported in a respective opening of the housing. Providing three or even more spacers allows for improved stabilizing support. The provision of the spring allows for uniformly and equally moving each one of the spacers, to uniformly and equally increase or decrease the overall transversal diameter of the stabilizing system. In further embodiments, a plurality of sets of three or more spacers are arranged at different lengths of the drill string. Thus, stabilization can be achieved at different positions of the drill string, preferably near the drill bit.

Particularly preferred, the stabilizing system further comprises a spring force transfer ring provided in the housing between the spring and each one of the spacers. The spring force transfer ring may thereby be provided in form of a ring, provided at one end of the spring, and encompassing a column, if provided. The spring force transfer ring may thus be provided around the longitudinal axis of the stabilizing system, and the spring may be in direct contact with the spring force transfer ring. The spring may thus directly engage the spring force transfer ring, which in turn may transfer the forces applied by the spring to all spacers. Thereby, a smooth operation of the stabilizing system is provided for, as the spring forces are efficiently provided to each one of the spacers in a uniform manner. Further, by blocking a movement of the spring force transfer ring, the spring maybe retained in the compressed state, allowing for inserting or removing one or more spacers, for example during maintenance operations.

Preferably the stabilizing system further comprises at least one blade being fixed to the housing such that it extends from an outer surface of said housing. In addition to movable spacers, the stabilizing system can further comprise one or more non-movable blades for stabilizing the drill string.

In a further preferred embodiment, at least one spring and a column is provided, as detailed above. The column may comprise a thin section with a first diameter and a thick section with a second diameter, whereby the second diameter is greater than the first diameter. Further, the spacer may comprise a recess which is adapted to receive the thick section of the column when said column is in the pulling position.

Furthermore, the thick section may be adapted to urge the spacer into the expanded position when the column is moved to the drilling position. When drilling forces are applied onto the stabilizing system and the column is moved into the drilling position, the thick section of the column may vacate the recess of the spacer at least partially, and may thereby urge the spacer into the expanded position. Accordingly, the spacer is moved into the expanded position in a straight forward manner, requiring only a minimal mechanical effort. Thereby, the spacer may act on the spring, bringing it into the compressed state. Further, as the thick section of the column cooperates with the interior of the spacer, very high displacement loads can apply. Additionally, if the spacer is in the extended position, no force is required to hold it in this position as any radial force onto the spacer is adopted by the column.

Preferably, the column comprises a Kelly section and wherein the hollow housing comprises a corresponding Kelly bushing in which the Kelly section of the column is supported such that torques are transferred between the column and the hollow housing, and wherein the Kelly section is movable relative to the Kelly bushing along the longitudinal axis of the housing. Due to the Kelly section and Kelly bushing drilling forces are transferred to the drill bit while allowing the stabilizing system to contract and extend to a certain amount in order to utilize the drilling forces.

Preferably, the housing has an abutting face adapted to transfer drilling forces acting in longitudinal direction onto the stabilizing system to a respective counter abutting stop provided on the column, when the column is in the drilling position. After the stabilizing system is contracted to the necessary amount for extending the stabilizers the longitudinal drilling forces are fully transmitted by the stabilizing system to the drill bit via the abutting face and abutting stop. This ensures an efficient drilling. Preferably the stabilizing system further comprises a first and a second drill pipe linkage, wherein the first drill pipe linkage is adapted to be connected to a drill bit via at least one preceding dill pipe, and wherein the second drill pipe linkage is adapted to be connected to a drilling motor via at least one succeeding drill pipe, and wherein the first and second drill pipe linkages are provided on opposing longitudinal ends of the stabilizing system. Thus, the stabilizing system can be integrated into an ordinary drill string, preferably near the drill bit. External energy sources for the stabilizing system are not required. Thus, the drill string can be the same as for rigid stabilizers.

According to a further aspect of the invention, a drilling system is provided. The drilling system thereby comprises a stabilizing system according to the above, and preferably a drill bit and drill pipes.

According to a further aspect of the invention, a method for drilling a hole utilizing a drilling system according to the above is provided for. The method comprises the step of applying a positive force onto the stabilizing system in longitudinal direction, causing the overall longitudinal length of the stabilizing system to shorten, the spring to compress, and the transversal diameter of the stabilizing system to increase. Preferably, one or more spacers may thereby be moved to the expanded position.

The method further comprises the step of applying a negative force onto the stabilizing system in longitudinal direction, causing the spring to decompress and to urge the overall longitudinal length of the stabilizing system to elongate, and the transversal diameter of the stabilizing system to decrease. Preferably, one or more spacers may thereby be moved to the retraced position.

Hence, the present invention allows for providing stabilization of the drill pipes and drill bit during drilling operation and RIH operation. Furthermore, the present invention allows for an efficient handling or losing off mud cakes formed around the stabilizing system during RIH and POOH operations, in a particularly reliable manner. 4, Description of preferred embodiment

In the following, the invention as further described exemplarily with references to the enclosed figures. Therein, similar components are provided with same reference signs.

Figures 1-3 illustrate schematically a drilling system in different configurations.

Figure 4 illustrates a cross section of a stabilizing system according to a preferred embodiment of the present invention.

Figure 5 illustrates the stabilizing system of the embodiment illustrated in figure 4 in a different configuration.

Figure 6 illustrates particular details of the stabilizing system of figure 4.

Figure 7 illustrates particular details of the stabilizing system of figure 5.

Figures 4 and 5 illustrates a stabilizing system 100 according to an embodiment of the present invention. The stabilizing system 100 is thereby adapted to be connected to drill pipes at each end thereof via respective drill pipe linkages. In the configuration illustrated in figure 4, the stabilizing system 100 is in a state with increased transversal diameter, and decreased overall length. In the configuration illustrated in figure 5, in turn, the stabilizing system 100 is in an expanded state along the longitudinal axis, and with decreased transversal diameter. Figures 4 and 5 thereby illustrates a cross- sectional view of the stabilizing system 100. Figures 6 and 7 illustrate particular details of figures 4 and 5, respectively.

The stabilizing system 100 comprises a hollow housing 110, in which a column 130 is arranged. The column 130 is linearly movable along the main longitudinal direction of the stabilizing system 100, relative to the housing 110. The column is adapted to transfer longitudinal drilling forces, for example to a downstream drive piston, as will be appreciated by the person skilled in the art. The stabilizing system loo further comprises three spacers 120, of which one is clearly visible in the cross section illustrated in figure 4. The spacers 120 are equally positioned around the stabilizing system 100. The spacers 120 are thereby positioned in respective openings provided on the housing 110. As the spacers 120 are positioned equally around the housing 110, they provide for an optimal centering of the stabilizer 100 within a bore hole, as will be appreciated by the skilled person. The spacers may have a width of about 5,8 cm, and a length of about 33,5 cm.

The spacers 120 are not directly connected to the housing 110, as apparent from the detailed views of figures 6 and 7. Each spacer 120 is partially sandwiched between the housing 110 and the column 130, preventing the spacer 120 from accidentally falling out of the stabilizing system 100. As the spacer 120 is not directly fixed to the housing 110 and column 130, the spacer 120 can move relative to the housing 110 and the column 130.

Furthermore, a helical spring 140 is provided inside the housing 110, through which the column 130 extends. The spring 140 may have a length of 45 cm in its relaxed state. At maximum compression, the spring length may be of about 29 cm. The spring 140 is thereby provided such that spring forces of the spring 140 are parallel to the overall longitudinal axis of the stabilizing system 100. The spring 140 is thereby provided concentrically within the housing 110, and parallel to the longitudinal axis of the stabilizing system 100. One end of the spring 140 is in direct contact with a blocking surface 112 of the housing 110. The other end of the spring 140 engages a spring force transfer ring 141. The spring force transfer ring 141 is in turn in direct contact with the spacers 120, and encompasses the column 130. The spring force transfer ring 141 can be moved by the spring 140 along the longitudinal axis of the stabilizing system 100.

Thereby, a movement of the spacers 120 can be evoked.

Furthermore, the column 130 comprises a thick section 131, which is arranged corresponding to respective recesses 121 of the spacers 120. In the configuration illustrated in figures 4 and 6, the thick section 131 is not provided in the recesses 121 of the spacers 120, i.e. the thick section 131 is at least partially provided apart from the recess 121 of the spacer 120, thereby urging the spacer 120 to the fully expanded position. In the configuration illustrated in figures 5 and 7, the thick section 131 of the column 130 is provided fully inside the recesses 121 of the spacers 120.

In the configuration illustrated in figure 4 (and figure 6), the transversal diameter of the stabilizing system 100 is expanded. In the configuration illustrated in figure 5 (and figure 7), the transversal diameter of the stabilizing system is decreased, contrary to the configuration illustrated in figure 4. As can be seen from figure 5, the column 130 is in a different longitudinal position with regard to the housing 110, and the thick sections 131 of the column are fully inside the recesses 121 of the spacers 120.

For changing the configuration of the stabilizing system 100 to increase in transversal diameter (i.e. from the configuration illustrated in figures 5, 7 to the configuration illustrated in figures 4, 6), an external load may be applied to the stabilizing system 100 along the longitudinal axis. Thereby, the housing 110 and the column 130 perform a relative moment to each other, whereby the thick section 131 of the column 130 now urges the spacers 120 into the expanded position, i.e. to protrude to the outside further from the openings provided on the housing 110. For this purpose, the thick section 131 as well as the recesses 121 of the spacers 120 feature respective tapered surfaces, which allow for the thick section 131 to slide along the spacers 120 and thereby push the spacers 120 to the outside.

At the same time, when applying the external load to the stabilizing system 100, the housing 110 directly interacts with one end of the spacer 120, thereby further promoting a transversal movement of the spacer. For this purpose, the respective end of the spacer 120 features a tapered section 123, and the housing 110 features a respective counter-tapered section which is in sliding contact with the tapered section 123 of the end of the spacer 120.

Upon movement of the spacers 120 from the retracted position (figures 5, 7) to the expanded position (figures 4, 6), the spacers 120 perform a transferal and longitudinal movement. Due to the longitudinal movement, the spacers 120 act on the spring force transfer ring 141, urging the spring force transfer ring 141 to move and the spring 140 to enter a compressed state. Hence, a spring force of e.g. 15 kN must be overcome in order to bring the spacers 120 into the expanded position. When removing the stabilizing system 100 from a bore hole, the external load may be released. As the spring 140 acts on the spring force transfer ring 141, which in turn acts on the spacer 120 to move along the longitudinal direction of the stabilizing system 100, and due to the particular shape of the spacer 120 and the opening of the housing 110, the spacers 120 are urged to perform a movement with a transversal and longitudinal component, whereby the spacers 120 move to the retracted position. Thereby, a tapered section 122 on another end of the spacer 120 may facilitate the transversal movement of the spacer 120, in addition to the longitudinal movement evoked by the spring 140. The tapered section 122 of the spacer 120 may thereby slide along a respective counter-tapered section of the housing 110. All tapering conditions mentioned with regard to this embodiment may be of about 30 degrees, relative to the main axis of the stabilizing system 100.

Further, as the column 130 moves back the recesses 121 of the spacers 120 receive the thick section 131 of the column 130. In this state of decreased transversal diameter of the stabilizing system 100, only the force from the spring 140 keeps the spacers 120 in the retracted position. Any mud or liquid, present in the space inside the hollow housing 110, may exit the hollow space through the passages 111.

A spring force transfer ring retainer 142 is further provided, with can be inserted to block a movement of the spring force transfer ring 141, allowing for insertion or removal of spacers 120, for example during assembly or maintenance.

For removing the spacers 12 from the stabilizing system 100, the spring 140 maybe brought into a compressed state, as illustrated in figures 4 and 6. In this state, the spring force transfer ring retainer 142 may be introduced, to block a movement of the spring force transfer ring 141, and hence to block a relaxation of the spring 140. Then, the column 130 can be removed. Thereafter, the spacers 120 can be removed from the housing 110, by tilting the spacers 120 and extracting them. In the reversed order, the stabilizing system 100 may be assembled. Accordingly, if any spacer 120 becomes worn or eroded, the operator can change one or all of the spacers 120 instead of replacing the whole stabilizer. Further, due to the versatility of the stabilizing system 100, different sizes of spacers can be utilized within the same hollow housing 110. Thus, the stabilizing system 100 can be used for different bore hole diameters.

List of reference signs:

1 drill string

2 blade

3 drill bit

4 earth

5 bore hole

6 cavity

7 mud cake

100 stabilizing system

110 hollow housing

111 passage

112 blocking surface of housing

120 spacer

121 recess

122, 123 tapered section

130 column

131 thick section

140 spring

141 spring force transfer ring

142 spring force transfer ring retainer