AU2014203158A1 - Multi-purpose drilling apparatus - Google Patents

Abstract

Abstract There is provided a multi-purpose drilling apparatus, comprising: a drilling actuator unit configured to rotate an outer drill string entering a borehole, wherein space between the outer drill string and the borehole define an outer annulus space and to provide a downward flow of drilling medium inside the outer drill string; and a releasable guiding member configured to guide an upward flow of the drilling medium upwards from the drill bit unit either: via the outer annulus space in order to perform direct circulation drilling, or inside an inner drill string locating concentrically inside the outer drill string in order to perform reverse circulation drilling. (Figure 5) ---- > AIR&SAMPLES 122 DRILLING 126 EXAMPLE LOCATION FOR GUIDING MEMBER 124 108 INNER DRILL STRINGDRILLING -yACTUATOR APERTURE(S) A * ANt Zr K130 iuWER 114 CONNECTING FLANG,, 1LW ACCOMMODATION FLANGE 100 OUTER DRILL STRING 108 INNER DRILL STRING EXTENDS SEE FIGURE 4 106 OUTER ANNULUS SPACE 101 GROUNDN- Y 104 BOREHOLE

Description

- 1 Multi-Purpose Drilling Apparatus Field of the invention [0001] The invention relates generally to drilling. More specifically, the invention relates to a multi-purpose drilling apparatus applicable for both, reverse circulation drilling and direct circulation drilling. Background to the invention [0002] In drilling different methods are used, such as, for example, reverse circulation drilling and direct circulation drilling. The applications of these types of drilling may vary. The reverse circulation is typically used at least for exploration drilling in order to acquire clean samples from the borehole. The direct circulation drilling, on the other hand, may be used for production drilling, in which the pureness of the samples is not an issue. Typically different drilling apparatuses are used for these drilling types. Summary of the invention [0003] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. [0004] To this end, a first aspect of the present invention provides a multi purpose drilling apparatus, comprising: a drilling actuator unit configured to: rotate an outer drill string entering a borehole, wherein space between the outer drill string and the borehole define an outer annulus space; and to provide a downward flow of drilling medium inside the outer drill string from the drilling actuator unit towards a drill bit unit located at a lower end of the outer drill string, wherein the multi-purpose drilling apparatus further comprises: -2 a releasable guiding member configured to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit. [0005] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". [0006] A second aspect of the invention provides a releasable guiding member for use in a reverse circulation drilling apparatus, wherein the reverse circulation drilling apparatus comprises: a drilling actuator unit configured to: rotate an outer drill string entering a borehole, wherein space between the outer drill string and the borehole define an outer annulus space; and to provide a downward flow of drilling medium inside the outer drill string from the drilling actuator unit towards a drill bit unit located at a lower end of the outer drill string, wherein the releasable guiding member is configured to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or -3 via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit. [0007] A third aspect of the invention provides a method of selecting an operation mode of a multipurpose drilling apparatus, wherein the operation mode is selected between a direct circulation drilling mode and a reverse circulation drilling mode, the method comprising: providing a downward flow of drilling medium inside an outer drill string towards a drill bit unit located at a lower end of the outer drill string, wherein the outer drill string is configured to enter a borehole and space between the outer drill string and the borehole define an outer annulus space; either attaching or removing a releasable guiding member to/from a preconfigured location in order to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit. Brief description of drawings [0008] In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which [0009] Figure 1A to 1 D present different drilling methods; -4 [0010] Figures 2 to 4 show how reverse circulation drilling is performed with multi-purpose drilling apparatus, according to some embodiments; and [0011] Figures 5 to 8 show how direct circulation drilling is performed with multi-purpose drilling apparatus, according to some embodiments. Description of embodiments [0012] The following embodiments are exemplary. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. [0013] As said, reverse circulation (RC) drilling and direct circulation (DC) drilling types vary in terms of their use cases, for example. As understood by a skilled person and shown in Figures 1A to 1C, drilling medium, such as air, (depicted with solid arrows) is inputted to the drilling apparatus and, more particularly, to a drill bit unit 102, e.g. to retrieve samples beneath the surface 101 of the ground. The drilling medium may also or instead comprise water, lubricants or other ingredients, as known by a skilled person. The drill bit unit 102 may comprise a rotating drill bit, for example. In addition the drill bit unit 102 may comprise other functional entities as well, such as an air-hammer, which hammers the drill bit 102 towards the ground. In another embodiment, the hammer may be located above the ground. [0014] As shown in Figure 1A for DC drilling, air (as an example drilling medium) may be conveyed to the drill bit unit 102 within a drill string 100 and taken out of the drill hole 104 (borehole) through an outer annulus space 106 between the drill string 102 and the walls of the borehole 104. However, in RC drilling, as depicted in Figure 1 B, the air circulation is reversed so that the air is inputted to the drill bit unit 102 via the outer annulus space 106 and the drilling -5 fluid possibly mixed with solid sample particles come back up inside the drill string 100. The force driving the air up to the surface may be due to high pressure pumps used for feeding the air to the drill hole 104. [0015] As one further option, there may be an inner drill string 108 inside the (outer) drill string 100, as depicted in Figure 1C. Then there may also be an inner annulus space 107, in addition to the outer annulus space 106. In this double- or dual-wall configuration used for RC drilling, the air may be inputted to the drill bit unit 102 via the inner annulus space 107 (between the inner drill string 108 and the outer drill string 100). The air may come back to the surface inside the inner drill string 108, as shown with solid arrows in Figure 1C. The differential pressure may thus create an air lift (of the water and cuttings) up the inner string 108. The air may come back to the surface via the inner pipe 108 because there is less resistance inside the inner pipe 108 than in the outer annulus space 106 (i.e. between the drill hole 104 and the outer drill string 100). Further, there may be a dedicated drill bit unit 102 used for the RC drilling, which may, for example, comprise appropriate arrangement of through holes which allow the air to pass inside the inner drill string 108. It may be even so that the outer annulus space is negligible in terms of volume, and the outer drill pipe 110 may be immediately against the walls of the drill hole 104 (although a space is shown in Figure 1C for clarity). [0016] Figure 1 D further shows a drilling apparatus applicable for RC drilling. As shown, there may be drilling actuator unit 112 above the ground 101 used for actuating, such as rotating, the outer drill string 100 and, consequently, the drill bit unit 102. An air pump may be comprised in the drilling actuator unit 112 for feeding the air to the borehole 104. The outer drill string 100 may be connected to the drilling actuator unit 112 with a connecting flange 114 with threads or screws, for example. The inner drill string 108 may run through the flange 114 to inside the drilling actuator unit 108. Above the ground level 101, the drill cuttings which are brought up from the borehole 104 may, in RC drilling, be moved through a (sample) conveying channel 116 and the inner -6 drill string 108 to a cyclone 118 for sample separation. The sample conveying channel 116 may a metal, or otherwise robust, tube, for example. Thus, the option illustrated in Figures 1C and 1 D for RC drilling may provide clean samples, for example. [0017] For the direct circulation illustrated in Figure 1A, no samples need to be collected. Further, the DC drilling has no use for the inner drill string 108 inside the outer drill string 100. Thus, for the DC drilling, the drill strings may, in an embodiment, be replaced. The drill bit unit 102 may also be different in the DC drilling than in the RC drilling. Typically, also the drilling actuator unit 112 is switched to a drilling actuator unit dedicated for DC drilling. [0018] However, often it may be that both the RC drilling (e.g. for exploration drilling) and the DC drilling (e.g. for production drilling) are needed, possibly in turns. Typically there is specific drilling apparatus/unit/machinery dedicated for each drilling type. Thus, when there is a need to employ different type of drilling, one is required to change the drilling apparatus. This is neither efficient nor cheap. Thus, more efficient solution for performing both drilling types is needed. [0019] Therefore, it is provided a multi-purpose drilling apparatus, which comprises, as shown in a cross-sectional Figures 2 and 5, the drilling actuator unit (DAU) 112. The DAU may be configured to rotate the outer drill string 100 entering the borehole 104. As said, the space between the outer drill string 100 and the borehole 104 define the outer annulus space 106. Figure 2 shows a configuration of the multi-purpose drilling apparatus when used in the RC drilling and Figure 5 shows a configuration of the multi-purpose drilling apparatus when used in the DC drilling. Both Figures are cross-sectional views of the multi-purpose drilling apparatus. [0020] The DAU 112 may further be configured to provide a downward flow of drilling medium, as depicted with dotted arrows, inside the outer drill string -7 100 from the DAU 112 towards the drill bit unit 102 (not shown in Figure 2A). The drilling medium may be air, for example. As shown, the drilling actuator unit 112 may comprise apertures in the casing of the DAU 112 for allowing the air (as the drilling medium in this example) to be fed inside the drilling actuator unit 112. The DAU 112 may comprise a rotating axle 120 for rotating the outer drill string 100. The wall of the axle 120 may also comprise apertures for allowing the air to pass inside the hollow axle 120. The air may then be directed in the hollow axle 120 between the inner surface of the axle and the inner drill string 108, which may locate at least in the DAU 112 along the drilling (rotation) axis 122 of the DAU 112. The air may then be passed downwards via an annulus space between the connecting flange 114 and the inner drill string 108. Thus, the air may then reach the inside of the outer drill string 100, which is connected to the connecting flange 114. [0021] In RC drilling, the air may then further travel down towards the drill bit unit 102 in the inner annulus space 107 defined by the space between the outer drill string 100 and the inner drill string 108, as shown in Figure 2. Thus, in the RC drilling the inner drill string 108 may extend/continue from the DAU 112 inside the outer drill string 100 all the way to the drill bit unit 112. [0022] In DC drilling, on the other hand, the inner drill string 108 may not extend inside the outer drill string 100 to the drill bit unit 102. This is because the inner drill string 108 may provide no benefit to the production drilling. Thus, in this case, the air may continue downwards inside the outer drill string 100 towards the drill bit unit 102. Thus, the air may in DC drilling expand throughout the full diameter of the outer drill string 100 as the air goes downwards. This DC drilling case is shown in Figure 5. However, in one embodiment, the inner drill string 108 extends towards the drill bit unit 102 also in the DC drilling. [0023] It should be noted that the drill strings 100/108 may comprise one or more drill pipes/rods attached to each other with threads, as known by a skilled -8 person. Each drill pipe may of a predetermined length. In an embodiment, a length of 3 of 6 meters is used. [0024] At least for the RC drilling case of Figure 2, the inner drill string 108 may comprise several drill rods connected together in order to reach the drill bit unit 102. The drill rods of the inner drill string 108 may comprise a centering flange around the inner drill string 108, wherein the centering flange centers the inner drill string 108 with respect to the outer drill string 100 and further comprises at least one through-hole for passing the drilling medium (e.g. air) downwards towards the drill bit unit 102 in the inner annulus space 107. [0025] In one embodiment, the drill rod of the inner drill string 108 locating inside the DAU 112 may be a dedicated, DAU-specific drill rod. The dimensions of the DAU-specific drill rod may be adjusted by the dimensions of the DAU 112. The DAU-specific drill rod may be connected to the other drill rods of the inner drill string 108. In an embodiment, in case of DC drilling, the inner drill string 108 may comprise only the dedicated, DAU-specific drill rod locating substantially inside the DAU 112. The dimensions of the DAU-specific drill rod may be adjusted by the dimensions of the DAU 112. In one embodiment though, the drill pipe inside the DAU 112 is of the same type/dimensions as the other drill rods, such as 3 meters. [0026] The part of the inner drill string 108 (e.g. the DAU-specific drill rod), which is inside the DAU 112, is depicted in Figures 3 and 6 for the RC drilling and for the DC drilling, respectively. As shown, in an embodiment, the depicted part of the inner drill string 108 may comprise an upper and a lower accommodation flanges 128 and 130 for accommodating the part of the inner drill string 108 with respect to the DAU 112. The upper accommodation flange 128 may be set against a part of the DAU 112, as shown in Figures 2 and 5. The lower accommodation flange 130 may likewise be set against a part of the DAU 112 and comprise aperture(s), such as through-hole(s), which allow the -9 air to flow downwards from the hollow axle 120 of the DAU 112 towards the inside of the outer drill string 100 and towards the drill bit unit 102. [0027] The multi-purpose drilling apparatus further comprises the connecting flange 114 configured to connect the outer drill string 100 and the drilling actuator unit 112 together so that rotation of the outer drill string 100 by the drilling actuator unit 112 is enabled. In an embodiment, the connection between the outer drill string 100 and the connecting flange 114 may be formed with threads or screws, for example. In an embodiment, the connection between the outer drill string 100 and the connecting flange 114 is typically detachable so that new drill pipes/rods may be added to the drill strings 100/108 as the drill bit unit 102 enters deeper into the borehole 104, or to remove drill pipes/rods from the drill strings 100/108 as the drill bit unit 102 is retrieved to ground level 101 from the borehole 104. In an embodiment, the DAU-specific drill rod of the inner drill string 108 may be fixed in the DAU 112 and additional drill rods may be attached to the lower end of the DAU-specific drill rod as the drill bit unit 102 enters deeper into the borehole 104. [0028] The multi-purpose drilling apparatus may further comprise a releasable guiding member 124 configured to guide an upward flow of the drilling medium, depicted in the Figures with dashed arrows. The guiding is performed such that the drilling medium flows upwards from drill bit unit 102 to the ground level 101 either: * inside the inner drill string 108 through the drilling actuator unit 112 in order to perform reverse circulation drilling, in which case the guiding member 124 is removed from a predefined location 126 and wherein the inner drill string (108) locates concentrically inside the outer drill string 100, or e via the outer annulus space 106 in order to perform direct circulation drilling, in which case the releasable guiding member 124 is attached to the predefined location 126 and configured to prevent -10 the upward flow of the drilling medium through the drilling actuator unit 112. [0029] Thus, the releasable guiding member 124 is used for selecting an operation mode of the drilling between the reverse circulation drilling (Figure 2) and the direct circulation drilling (Figure 5). Further, it may be noted that the drilling actuator unit 112 may be a reverse circulation drilling actuator unit (RC DAU) for both operation modes. As known by a skilled person, in RC drilling the drilling medium and the drill cuttings flow upwards through the RC DAU 112 inside the inner drill string 108 to the cyclone 118, whereas in a direct circulation DAU, the drilling medium does not flow upwards through the DC DAU but emerges from the outer annulus space 106 to the ground 101. Thus, instead of changing the DAU 112 when switching from the RC drilling to the DC drilling or vice versa, the DAU 112 need not be changed but only the guiding member 124 needs to be attached to the predefined location, such as to the location 126. This may provide an advantage achieved by the proposed multi-purpose drilling apparatus. [0030] As shown for the RC case, in Figures 2 and in more details in Figure 4, the downward flow of the drilling medium (depicted with the dotted arrows) is via the space between the connecting flange 114 and the inner drill string 108 and further via the inner annulus space 107. The upward flow (depicted with the dashed arrows), on the other hand, is via/inside the inner drill string 108 through the DAU 112 to the cyclone 118. This is because the path via the inner drill string 108 is not closed/blocked with the guiding member 124, but is open. The upward flow of the air may be mixed with ground samples, drill cuttings, drill dust, etc. As the drilling medium and the drill cuttings emerge from the drill bit unit 102 towards the ground level 101, the air and cuttings may be directed through the DAU 112 inside the inner drill string 108 and the conveying channel 116 to the cyclone 118, as explained with reference to Figure 1 D.

- 11 [0031] In Figures 5 and 7A to 7C for the DC case, the downwards flow of the drilling medium (depicted with the dotted arrows) is via the space between the connecting flange 114 and the inner drill string 108 and further via the outer drill string 100. It may be noted that there may not be inner drill string 108 extending to inside the outer drill string 100 in DC drilling. However, in case there is the inner drill string 108 extending to inside the outer drill string 100, the downward flow of drilling medium may be, just as in RC drilling, between the inner annulus space 107. [0032] However, the upward flow (depicted with the dashed arrows) in the DC drilling, on the other hand, is via the outer annulus space 106. This is because the path through the DAU 112 is closed/blocked with the guiding member 124 being set in the predefined blocking position 126. Thus, the drilling medium and the drill cuttings/dust are not allowed to flow upwards through the DAU 112, but are forced to emerge to the ground 101 via the outer annulus space 106. In an embodiment, if the inner drill string 108 providing the path to the DAU 112 exists, the path via the inner drill string 108 may be blocked with the guiding member 124. In case there is no inner drill string 108, the path to the DAU 112 may be blocked otherwise, such as by applying the guiding member 124 in the connecting flange 114. In an embodiment, the upward path via/inside the outer drill string 100 is blocked with the guiding member 124, thus preventing the upward flow of the drilling medium inside the outer drill string 100. [0033] As explained earlier, there may not be any need to collect the samples in DC drilling, such as in production drilling, and therefore, the drill cuttings need not be conveyed through the DAU 112 nor collected by the cyclone 118. It may be noted though, that the cyclone 118 may be comprised in the multi-purpose drilling apparatus and connected to the DAU 112. However, in DC drilling, the guiding member 124 is used advantageously to block the path to the cyclone and thus force the drilling medium to go to the outer annulus space 106.

-12 [0034] The multi-purpose drilling apparatus may further comprise an attaching mechanism or means configured to releasably attach the releasable guiding member 124 to the predefined location 126 i. Such attaching means may comprise, e.g. threads or screws. Therefore, in an embodiment, the releasable guiding member 124 is attached to the predefined location 126 with at least one of the following: screws, bolts and/or nuts, screw threads matching with opposite screw threads, locking mechanism. The guiding member 124 may be comprise threads on its surface and the threads may be used to thread the member 124 air-tightly, e.g., against the inner surface of the inner drill string 108 in case the predefined location 126 is in the inner drill string 108. Thus, the inner surface of the inner drill string 108 may comprise the matching threads. In another embodiment, the screws may penetrate the walls of the inner drill string 108 and the guiding member 124 in order to attach the guiding member 124 securely and air-tightly in the predefined location 126. In yet one embodiment, there is a locking mechanism arranged in the predefined location 126, such as in the inner surface of the wall of the inner drill string 108, and in the guiding member 124 which securely lock the member 124. Such locking mechanism may comprise, e.g. bracket(s) projecting from the inner wall of the inner drill string 108 and matching recess(es) or cavities in the member 124, or vice versa. A twist of the guiding member 124 may lock the guiding member 124 securely and air-tightly in the predefined location 126. In an embodiment, the member 124 is fitted to the predefined location 126 with the help of hot air so that the member 124 expands against, e.g. the walls of the inner drill string 108. [0035] The releasable guiding member 124 may be also called a stopper or a sealing plug, as the member 124 prevents (stops) the air from passing upwards to the cyclone 118. The releasable guiding member 124 may be made of metal or rubber, for example. The shape of the air-tight releasable guiding member 124 may be a cylinder, such as a circular cylinder to match with the inner walls of the inner drill string 108. The guiding member 124 may further comprise a sealing in order to make sure that the attachment of the - 13 member 124 to the predefined location is air-tight. The guiding member 124 may not be hollow and it may be impenetrable to the drilling medium, such as to the air. Figure 6 shows the guiding member 124 attached to the inner drill string 108. The shape of a circular cylinder may provide ease in providing an air-tight attachment, e.g., to the inner drill string 108, i.e. to one of the one or more drill rods of the inner drill string 108. [0036] In an embodiment, the connecting flange 114 is replaceable without changing the DAU 112. In an embodiment, a direct circulation connecting flange may be used which is configured to accommodate the outer drill string 100. In another embodiment, a reverse circulation connecting flange may be used which is configured to accommodate the outer drill string 100 and further to provide a path for ground samples from the inner drill string 108 to the cyclone 118, or to any sample separation unit. As said, the DC drilling applicable connecting flange and the RC drilling applicable connecting flange are mutually replaceable without changing the DAU 112. The flange 114 may be connected to the DAU 112 with bolts and nuts, or threads. It may be noted that the outer drill rods forming the outer drill string 100 may be different in RC drilling and in the DC drilling. [0037] In an embodiment, the inner drill string 108 is at least inside the drilling actuator unit 112 and configured to provide a path for ground samples from the drill bit unit 102 to the cyclone 118 through the drilling actuator unit 112 in the RC drilling. In such embodiment, the predefined location 126 for attaching the releasable guiding member 124 may be in the inner drill string 108 in order to close the path to the cyclone 118. The location 126 may be anywhere in the inner drill string 108, not necessarily in the location as shown in Figures 2 and 5. [0038] In an embodiment, in case of DC drilling, the DAU-specific drill rod of the inner drill string 108 may be the only drill rod in the inner drill string 108. In an embodiment, the location 126 is in the DAU-specific part of the inner drill - 14 string 108, thus in the multi-purpose drilling apparatus and more particularly inside the DAU 112. [0039] However, in another embodiment, also in the DC drilling the inner drill string 108 extends to the borehole 104. In such case, the predefined location 126 may be in the inner drill string 108 even outside the DAU 112, for example, under the ground level 101 in the borehole 104, as shown in Figure 7C. One example location may be just above the underground air hammer of the drill bit unit 102. This is shown in Figure 7C. In an embodiment, an adapter drill rod is attached between the drill bit unit 102 and the inner drill string 108, wherein the adapter drill rod is seen as the replaceable guiding member 124. For example, the adapter drill rod may be of solid material and not hollow. Thus, the adapter drill rod may stop the air flow via the inner drill string 108 and guide the air to the outer annulus space 106. This embodiment may be useful for frequent change of the drilling mode between the RC drilling and the production drilling (DC drilling). This may be because then the switch from the RC drilling to the DC drilling may be performed by replacing the RC drill bit unit (comprising, e.g., an RC drill bit and an RC hammer) with the DC drill bit unit and by adding the adapter drill rod (as the guiding member 124) between the DC drill bit unit and the inner drill string 108. There may be threads in the adapter drill rod so that the adapter drill rod may be threaded to the drill bit unit 102 and to the inner drill string 108. Thus, it may not be necessary to change the RC drill rods into DC drill rods. [0040] However, in an embodiment, the RC drill rods are replaced with DC drill rods. A reason for this may be that typically RC drilling rods are more expensive. In such case, the inner drill string 108 may only comprise the DAU specific drill rod inside the DAU. In an embodiment, the guiding member 124 may be then added to the DAU specific drill rod, as shown in Figure 5, for example. Alternatively, a solid adapter drill rod (serving as the replaceable guiding member 124) may be attached, for example, at the top of the DC - 15 drilling rods in order to block the path to the DAU-specific drill rod (i.e. to the inner drill string 108). [0041] In an embodiment, the multi-purpose drilling apparatus comprises the inner drill string 108, which may comprise only one drill rod (the one inside the DAU 112) or many drill rods. [0042] In an embodiment, the connecting flange 114 has an aperture penetrating the connecting flange 114 along the drilling axis 122 in order to provide a path for ground samples from the drill bit unit 102 to the cyclone 118 via the inner drill string 108 in the RC drilling. In this case, the predefined location 126 for attaching the releasable guiding member 124 may be in the connecting flange 114 in order to close the path in order to perform DC drilling. In such case, there may not be any inner drill string 108 in the multi-purpose drilling apparatus when performing DC drilling. This is shown in Figure 7B in which the guiding member 124 is attached so that it closes the path via the flange 114. As a result, the upward flow of the air is forced via the outer annulus space 106, as shown. In such embodiment of Figure 7B, the downward flow of the drilling medium is guided to pass the connecting flange 114. In an embodiment, such guiding may be performed by the connecting flange 114 or the releasable guiding member 124 comprising apertures for enabling the downward flow of drilling medium to enter the outer drill string 100, as shown with the dotted arrow. The apertures may be designed not to pass air in the upwards direction, or the apertures may be so small that the (constant) downward flow of air prevents the air to come up via the apertures, for example. [0043] In an embodiment, there is no inner drill string 108 applied. In such case the predefined location 126 for attaching the releasable guiding member may in this case be upwards from the location at which the downwards flow of drilling medium is provided. An example location may be inside the conveying channel 116 to the cyclone 118.

-16 [0044] In an embodiment, the multi-purpose drilling apparatus further comprises the cyclone 118, as depicted in Figure 8. Figure 8 also shows how the releasable guiding member 124 is used to prevent the upward flow of drilling medium vie the inner drill string 108 to the cyclone 118 and, thus, to guide the upwards flow of the drilling medium by closing the path via the outer and inner drill strings 100, 108. [0045] In an aspect of the invention, there is provided the releasable guiding member 124 for use in a RC drilling apparatus, wherein the RC drilling apparatus comprises the drilling actuator unit 112 (which may be a drilling actuator unit suitable for RC drilling). The DAU 112 may be configured to rotate the outer drill string 100 entering the borehole 104, wherein space between the outer drill string 100 and the borehole 104 define the outer annulus space 106, and further to provide a downward flow of the drilling medium inside the outer drill string 100 from the DAU 112 towards the drill bit unit 102. The RC drilling apparatus further comprises the connecting flange 114 configured to connect the outer drill string 100 and the drilling actuator unit 112 together so that rotation of the outer drill string 100 by the drilling actuator unit 112 is enabled. The releasable guiding member 124 may be configured to guide an upward flow of the drilling medium upwards from drill bit unit 102 to the ground level 101 either * inside the inner drill string 108 through the drilling actuator unit 112 in order to perform reverse circulation drilling, in which case the guiding member 124 is removed from a predefined location 126 and wherein the inner drill string (108) locates concentrically inside the outer drill string 100, or e via the outer annulus space 106 in order to perform direct circulation drilling, in which case the releasable guiding member 124 is attached to the predefined location 126 and configured to prevent the upward flow of the drilling medium through the drilling actuator unit 112.

- 17 [0046] In an aspect of the invention, there is provided a method of selecting an operation mode of a multipurpose drilling apparatus, wherein the operation mode is selected between a direct circulation drilling mode and a reverse circulation drilling mode, the method comprising: providing a downward flow of drilling medium inside an outer drill string 100 from a ground level 101 to a drill bit unit 102 located at a lower end of the outer drill string 100, wherein the outer drill string 100 is configured to enter a borehole 104 and space between the outer drill string 100 and the borehole 104 define an outer annulus space 106; either attaching or removing a releasable guiding member 124 to/from a preconfigured location 126 in order to guide an upward flow of the drilling medium upwards from the drill bit unit 102 to the ground level 101 either: via the outer annulus space 106 by preventing the upward flow of the drilling medium inside the outer drill string 100 in order to perform direct circulation drilling, in which case the releasable guiding member 124 is attached to the predefined location 126, or inside an inner drill string 108 locating concentrically inside the outer drill string 100 in order to perform reverse circulation drilling, in which case the guiding member 124 is removed from the predefined location 126. [0047] In an aspect of the invention, there is provided a multi-purpose drilling apparatus, comprising: means for rotating an outer drill string 100 entering a borehole 104, wherein space between the outer drill string 100 and the borehole 104 define an outer annulus space 106; means for providing a downward flow of drilling medium inside the outer drill string 100 towards a drill bit unit 102 located at a lower end of the outer drill string 100, means for connecting the outer drill string 100 and the means for rotating together so that rotation of the outer drill string 100 is enabled, and guiding means for guiding an upward flow of the drilling medium upwards from the drill bit unit 102 to the ground level 101 either: evia the outer annulus space 106 in order to perform direct circulation drilling, or - 18 * inside an inner drill string 108 locating concentrically inside the outer drill string 100 in order to perform reverse circulation drilling. [0048] The multipurpose drilling apparatus may further comprise at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code, are configured, with the at least one processor, to cause the multipurpose drilling apparatus perform drilling according any one of the above-described processes. The multipurpose drilling apparatus may also comprise a user interface comprising, for example, at least one keypad, a touch display, a display, a speaker, etc. The user interface may be used to control the multipurpose drilling apparatus by the user. [0049] Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims (13)

1. A multi-purpose drilling apparatus, comprising: a drilling actuator unit configured to: rotate an outer drill string entering a borehole, wherein space between the outer drill string and the borehole define an outer annulus space; and to provide a downward flow of drilling medium inside the outer drill string from the drilling actuator unit towards a drill bit unit located at a lower end of the outer drill string, wherein the multi-purpose drilling apparatus further comprises: a releasable guiding member configured to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit.

2. The drilling apparatus according to claim 1, wherein the releasable guiding member is used to select an operation mode of the drilling between the reverse circulation drilling and the direct circulation drilling, wherein the drilling actuator unit is a reverse circulation drilling actuator unit for both operation modes.

3. The drilling apparatus according to any one of claims 1 to 2, wherein the multi-purpose drilling apparatus further comprises: an attaching mechanism configured to releasably attach the guiding member to the predefined location. - 20

4. The drilling apparatus according to any one of claims 1 to 3, wherein the shape of the releasable guiding member is a circular cylinder and the releasable guiding member is impenetrable by the drilling medium.

5. The drilling apparatus according to any one of claims 1 to 4, wherein the multi-purpose drilling apparatus further comprises: the inner drill string located at least inside the drilling actuator unit and configured, in the reverse circulation drilling, to provide a path for ground samples from the drill bit unit to a cyclone through the drilling actuator unit, wherein the predefined location for attaching the releasable guiding member is in the inner drill string in order to close the path, thereby enabling the direct circulation drilling.

6. The drilling apparatus according to claim 5, wherein the part of the inner drill string located inside the drilling actuator unit is a drilling actuator unit -specific inner drill rod, which is connectable to other inner drill rods of the inner drill string.

7. The drilling apparatus according to any one of claims 5 to 6, wherein the releasable guiding member is a solid drill rod attached to the inner drill string so as to close the path via the inner drill string.

8. The drilling apparatus according to any of claims 1 to 4, further comprising: a connecting flange configured to connect the outer drill string and the drilling actuator unit together so that rotation of the outer drill string by the drilling actuator unit is enabled, wherein the connecting flange has an aperture penetrating the connecting flange along the drilling axis in order to provide a path for ground samples from the drill bit unit through the drilling actuator unit to a cyclone via the inner drill string in the reverse circulation drilling, and wherein the predefined location for attaching the releasable guiding member is in the connecting flange in order to close the path. - 21

9. The drilling apparatus according to claim 8, wherein the multi-purpose drilling apparatus further comprises: at least one channel configured to channel the downward flow of the drilling medium to pass the connecting flange to the outer drill string.

10. The drilling apparatus according to any one of claims 1 to 9, wherein space between the outer drill string and the inner drill string define an inner annulus space, and the downward flow of the drilling medium to the drill bit unit is via the inner annulus space.

11. The drilling apparatus according to any one of claims 1 to 10, further comprising: a connecting flange configured to connect the outer drill string and the drilling actuator unit together, wherein the connecting flange is either: a direct circulation connecting flange configured to accommodate the outer drill string, or a reverse circulation connecting flange configured to accommodate the outer drill string and to provide a path for ground samples via the inner drill string to a cyclone, wherein the direct circulation connecting flange and the reverse circulation connecting flange are mutually replaceable without changing the drilling actuator unit.

12. A releasable guiding member for use in a reverse circulation drilling apparatus, wherein the reverse circulation drilling apparatus comprises: a drilling actuator unit configured to: rotate an outer drill string entering a borehole, wherein space between the outer drill string and the borehole define an outer annulus space; and to provide a downward flow of drilling medium inside the outer drill string from the drilling actuator unit towards a drill bit unit located at a lower end of the outer drill string, - 22 wherein the releasable guiding member is configured to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit.

13. A method of selecting an operation mode of a multipurpose drilling apparatus, wherein the operation mode is selected between a direct circulation drilling mode and a reverse circulation drilling mode, the method comprising: providing a downward flow of drilling medium inside an outer drill string towards a drill bit unit located at a lower end of the outer drill string, wherein the outer drill string is configured to enter a borehole and space between the outer drill string and the borehole define an outer annulus space; either attaching or removing a releasable guiding member to/from a preconfigured location in order to guide an upward flow of the drilling medium upwards from the drill bit unit either: inside an inner drill string through the drilling actuator unit in order to perform reverse circulation drilling, in which case the guiding member is removed from a predefined location and wherein the inner drill string locates concentrically inside the outer drill string, or via the outer annulus space in order to perform direct circulation drilling, in which case the releasable guiding member is attached to the predefined location and configured to prevent the upward flow of the drilling medium through the drilling actuator unit.