AU2017248082B2

AU2017248082B2 - A core drilling system and method for obtaining an orientated rock core sample using said core drilling system

Info

Publication number: AU2017248082B2
Application number: AU2017248082A
Authority: AU
Inventors: Eirik Borg
Original assignee: Huygens As
Current assignee: Huygens As
Priority date: 2016-04-08
Filing date: 2017-04-07
Publication date: 2021-08-19
Anticipated expiration: 2037-04-07
Also published as: AU2017248082A1; NO342901B1; CA3014270A1; EP3440304A1; NO20161581A1

Abstract

It is disclosed a system and method for drilling rock cores, and in particular to determine their orientation in the subsurface. The core drilling system includes a drill string with a drill bit at an end thereof, a core sampling arrangement mounted inside the drill string at said end thereof, the core sampling arrangement including a core tube ( 100) for holding a core sample, the core tube having a first end located near the drill bit and a second end distant from the drill bit, a core catcher ( 101) fixed at the first end of the core tube ( 100), a core tube head (102) fixed to the second end of the core tube ( 100), the system further including a rotational joint (104) connecting the core tube head to a latching unit (105) adapted to releasable lock to the drill string, wherein said rotational joint (104) allows the latching unit (105) to rotate independently from the core tube (100). The system further includes an orientation unit (103) that is rotationally free from the core tube through being located at the opposite side of the rotational joint ( 104) relative to the core tube, fixed at or integrated into the latching unit ( 103) or placed as a separate freely rotational section between the rotational joint (104) and a second rotational joint fixed to the latching unit.

Description

WO 2017/176127 PCT/N02017/050087 1

A CORE DRILLING SYSTEM AND METHOD FOR OBTAINING AN ORIENTATED ROCK CORE SAMPLE USING SAID CORE DRILLING SYSTEM

This application claims priority from Norwegian patent application No. 20160580 filed on April 8, 2016 with the title of "Core orientation tool", as well as from Norwegian patent application No. 20161581 filed on 30 September 2016 with the title of "A core drilling system and method for obtaining an orientated rock core sample using said core drilling system", the content of both of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to core sampling during drilling operations in the bedrock, and in particular an apparatus and method for determining the orientation of a core sample.

BACKGROUND

In mining and engineering operations, it is regularly necessary to obtain samples of the rock in the subsurface. For this end, core drilling equipment is used. Some of the most common equipment for rock core drilling includes a tubular drill string terminated in a tubular drill bit. Inside the front section of the drill string, there is a retractable core sampling arrangement including a core tube holding the core sample, and a core catcher mounted at the lower end of the core tube. Furthermore the core sampling arrangement includes a rotational joint followed by a latching unit. The latching unit is arranged to ensure that the core sampling arrangement is fixed at a specific distance from the drill bit, preventing the core sampling arrangement from moving forward from its designated position inside the drill string as well as being pushed upward as the core sample enters the core tube. The latching unit will normally rotate with the drill sting due to frictional forces between the latching unit and its designated seat inside the drill string, and if necessary the latching unit can be rotationally physically locked to the drill sting. The rotational joint allows the latching unit to rotate independently from the core tube, thus allowing the core tube to be stationary due to frictional forces between the core sample and the core catcher and core tube, while the latching unit and drill string is rotating.

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When a core sample is to be retrieved, the rotation of the drill string is ceased and the drill string lifted until the core catcher clamps the core and breaks it loose from the subsurface. Then, a fishing unit attached to a wire line is lowered into the interior of the drill string until it connects to the latching unit located at the rear end of the core sampling arrangement. By pulling in the wire line, the latching unit locking means will retract, thus core sampling arrangement will disconnect from the drill string allowing the whole core sampling arrangement to be hoisted to the surface.

In situations where it is interesting to know the physical orientation of the core sample as it was when situated in the subsurface, an orientation unit is traditionally mounted at the rear end of the core tube, between the core tube and the core tube head or as an integrated part of the core tube head. The orientation unit is adapted to measure the physical orientation of the core sample, and store the measurements. The term orientation or physical orientation of a core sample are here related to determinate the position the core sample as it was when situated in the subsurface, traditionally this would be rotational position (also known as toolface) and inclination relative to earth gravity, but sensors to determinate direction relative to magnetic north, true north or an artificial grid can also be implemented, thus a part of the term orientation. Furthermore the orientation unit can be adopted to collect a wide varity of other down hole information, such as but not limited to temperature, pressure and flow. At the surface, the stored measurements are retrieved and the part of the core sample fixed in the core catcher marked accordingly while still inside the core catcher. In some cases the core catcher or core tube is equipped with a core marking device, making a mark along the core as it enter the core tube, in order to make it possible to assemble the core sample to its original state, if broken in several pieces, thus making it possible to tell the orientation of parts or the whole core sample based on a single reference position.

An orientation unit traditionally includes sensors such as accelerometers, a memory unit to store the readings from the sensors, a processor to control the measuring process and a communication interface. The measurements and storing are either performed continuously or in an event driven process.

In the first case, measurements are taken and stored in the memory at even intervals, e.g. each 30 seconds. The measurements and storage can be done continuously as long as the core orientation arrangement is in the hole or a time delay can be implemented to shorten the number or measurements stored in the

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memory. When the core sampling unit has been retrieved to the surface, the measurement of interest has to be identified, i.e. the measurement taken before or after the core is broken from the sub surface, after ceasing rotation at the end of a drilling run. Thus, the drilling operator will normally note the moment in time of such event with a timer device, said timer device is synchronized with the clock in the orientation unit during initial activation of the orientation unit at surface, or when the orientation unit is back at surface after a drilling run, and compare this moment of time with the time matching measurements stored in the memory.

In the second case, one embodiment relies on that measurements are taken at even intervals, e.g. each 30 seconds, the said measurements being stored in the memory continuously or stored if a specific input is given, and in a second embodiment the electronics inside the orientation unit is on standby and activated to preform measurements and storing if a specific input is given. The orientation unit includes a sensor which detects the vibrations or movements created by the drilling process, intentional movements of the drill string done by the operator or landing of the fishing device on top of the latch unit. When the coring operation has come to its end and the rotation of the drill string is ceased, such events can be registered by the sensor leading the processor to initiate processes that make the operator able to download data about orientation of the core at the time of the event. Such processes may include that the stored measurements at the time of event are marked with a time or number stamp, or that the measurements is only stored at the time of an event, or that the measuring and storing is only activated at the time of an event. The drawback with this approach is that the sensor may be fooled and not detect the correct time of event, e.g. due to disturbance or unexpected movements of the drill string, repeated stop and start of the drill string caused by normal handling of a drill rig, drill chuck taking a new grip on the rods or adding a new drill rod all with potential to be interpertated as an event mentioned above, thus causing readings at in-correct time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device and method for determining the orientation of a core sample which is time saving, provide less risk for working accidents, reduce wear on equipment and is more reliable than the devices and methods mentioned above or found in other prior art.

This is achieved in a device and method according to the appended claims.

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According to a first aspect, the invention relates to a core drilling system including a drill string with a drill bit at an end thereof, a core sampling arrangement mounted inside the drill string at said end thereof, the core sampling arrangement including a core tube for holding a core sample, the core tube having a first end located near the drill bit and a second end distant from the drill bit, a core catcher fixed at the first end of the core tube, a core tube head fixed to the second end of the core tube, the system further including a rotational joint connecting the core tube head to, a latching unit adapted to releasable lock to the drill string, wherein the said rotational joint allowing the latching unit to rotate independently from the core tube. The core drilling system further includes an orientation unit that is rotationally free from the core tube through being located at the opposite side of the rotational joint relative to the core tube, fixed at or integrated into the latching unit or placed as a separate freely rotational section between the said rotational joint, and a second rotational joint fixed to the latching unit, wherein the orientation unit is rotationally free from the core tube.

With this invention, the orientation unit is not rotationally fixed to the core tube as in conventional systems, but instead free to rotate relative to the core tube. In the preferred embodiment the latch unit is collocated with the orientation unit, thus both units will rotate with the drill string. The relocation of the orientation unit offers several advantages, such as providing direct access to the latching unit locking and hoisting means, thus making it possible to directly monitor the position of the latch unit locking means and presence of any hoist mechanism, as well as facilitate for direct readings of drill string rotational position and speed. As a result the invention will provide more robust and accurate means for initiating the orientation unit to log the orientation of the core sample at the correct moment of time, compared to prior art. Furthermore the relocation make it possible to conserve space in such degree that the total length of the core sample arrangement can be similar to conventional core sample arrangements, thus eliminating the need for the time consuming, equipment wearing and risk related work of hoisting and lowering the rods twice to install and later dismantle an extension sub on the drill string to accommodate the extra length an orientation unit fixed to the core tube will give to the core sample arrangement, seen in prior art. The orientation unit may include means to determine at least the rotational position of the core sample relative to earth gravity and the inclination of the core sample relative to earth gravity, as it where when situated in the subsurface. The means for determining the rotational position of the core sample relative to earth gravity includes a

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reference point connected to the core tube or any couplings fixed to the core tube and a sensor connected to the orientation unit.

Further, the sensor may be a Hall-effect sensor, while the reference point may be a magnet.

Further, the reference point may be in near proximity of the sensor for direct reading of the reference point position, or is located at a distance from the sensor, wherein the position of the reference point is transferred to suitable near proximity of the sensor by means of a transmission device.

Further, said transmission device may be a shaft and/or magnetic coupling.

Further, the orientation unit may include means to detect the rotation of the drill string by measuring the rotational position of the orientation unit. Thus, the orientation unit is able to directly measure that the drill string is rotating, instead of inferring this from vibration, as in prior art system.

Still further, the orientation unit may include means to determine the presence of a hoist mechanism, or said hoist mechanism landing or latching into the core sampling arrangement.

According to another embodiment of the invention, the orientation unit may include means to detect the position of the locking means on the latching unit, thus tell the moment of time they lock into the drill string as well as retract and core sample arrangement free to move upward.

This is another consequence of the arrangement of the orientation unit in fixed or integrated relationship with the latching unit; the orientation unit may actually directly detect the position of the latch unit locking means or the hoisting mechanism engaging the hook on top of the latching unit, both not seen in prior art.

The orientation unit may also include means to detect movements or vibrations in the drill string or core sampling arrangement.

Further, the orientation unit may include an integrated display and operation means for activation as well as reading of measurements.

According to a second aspect, the invention includes a method for obtaining a rock core sample using the above-mentioned core drilling system. The method includes

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the steps of: a) activating the orientation unit and lowering the core sampling arrangement to its designated seat at the bottom end of the drill sting, b) operating the drill string to drill a rock core, with the latching unit and orientation unit rotating with the drill string, c) ceasing coring operation when a suitable length of core is obtained, d) measuring at least the rotational position and inclination of the core sample relative to earth gravity, as it was when situated in the subsurface, before and/or after breaking the core from the subsurface, e) storing said measurements in the orientation unit, f) retrieving the core sampling arrangement with a core sample fixed inside the core tube to the surface, and g) reading said measurements from the orientation unit and mark the core sample accordingly.

According to an embodiment of the invention, step d) includes the orientation unit detecting if an interesting down hole event occurs, the orientation unit performing a measurement when such an event is detected, step e) includes either only storing said measurement each time when such an event is detected or storing a number of measurements related to the event, storing all or a specific number or measurements and storing time of the events, or storing a number of measurements within a pre-set time frame and storing the time of event happening within the time frame.

According to one embodiment of the invention step d) includes detecting said interesting event by the orientation unit by monitoring changes in the rotational speed of the drill-string by measuring the rotational position of the orientation unit.

According to another embodiment of the invention, step d) includes detecting said interesting event by the orientation unit by monitoring if the hoist mechanism is engaged with the core sampling arrangement.

According to another embodiment of the invention, step d) includes detecting said interesting event by the orientation unit by monitoring when the locking means on the latching unit retract andthe core sample arrangement being free to move upward.

These are the three methods that may be used to positively detect an interesting event in an event driven process. Due to the particular arrangement of the orientation unit collocated with the latching unit, wherein it is rotating along with

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the drill string and in fixed proximity of locking means and hoist mechanism , these methods will be more accurate in determining said interesting event, than prior art

According to one embodiment, the orientation unit when activated is measuring and storing the measurements continuously at even intervals, step a) includes starting a timer device at the surface, synchronizing or time link the timer device with the orientation unit, step d) includes using the timer device to log the time of interestingdownhole events, such event being suitable time for preforming measurement of the orientation of the core step g) includes correlating the logged time of interesting events in the timer device, with the matching measurements stored in the orientation unit memory.

According to another embodiment the orientation unit when activated is measuring and storing the measurements continuously at even intervals, step d) includes starting a timer device at the surface and to log the time of interesting events during the drilling run, such event being suitable time for preforming measurement of the orientation of the core, step g) includes synchronizing or time link the timer device with the orientation unit and correlating the logged time of measurement in the timer device with the matching measurement(s) stored in the orientation unit.

In this way, the timer device may be started at any time during the drilling process, and synchronized with the orientation unit in behind.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features of the present invention will be apparent from the following detailed description of the invention with reference to the drawings, wherein:

Figure 1 is a schematic view of a prior art core sampling system, Figure 2 is a schematic view of a core sampling system wherein the invention is implemented, Figure 3 is an external view of an embodiment of the inventive core drilling system, Figure 4 is a schematic cross-sectional view of the core drilling system, and Figure 5 is a schematic block diagram of an electronic recording arrangement to be included in the core orientation tool.

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DETAILED DESCRIPTION

Fig. 1 shows prior art core sampling arrangement, i.e. the inner arrangement that is actually collecting the core sample wherein the orientation unit is mounted as a fixed extension to the core tube. The arrangement is intended to be mounted inside a tubular drill string (not shown), with the lower (left hand) end of the arrangement adjacent to the drill bit. The arrangement includes a core tube 100 with a core catcher 101 at the lower (left) end. At the right end of the core tube, there are in succession: a core tube head 102, an orientation unit 103, and a latching unit 105 mounted on a rotatable joint 104. The latching unit 105 includes a number of locking means in form of retractable latches 106 adapted to engage a corresponding shoulder in the interior of the drill string. At the end of the latching unit there is a hook 107 adapted to be engaged by a hoist mechanism, such as a wire-line. The hook 107 is connected to the latches 106 and by pulling in the line the hook 107 will disengage the latches 106 from the said drill sting shoulder, allowing the whole assembly with core sample to be retrieved to the surface.

This arrangement has a number of disadvantages, of which one is that the orientation unit will extend the total length of the core sample assembly causing need for a sub to be installed on the drill string to accommodate the extended length. Alternatively the core tube can be shorten to accommodate the orientation unit within the original length of the core sample assembly, thus leading to shorter drilling runs due to less space for core sample inside the core tube. Both alternatives are time consuming, cause extra wear on the equipment and involve work hazards for the operators. Another disadvantage is that it may be difficult to obtain reliable readings from the orientation unit about down hole events such as cease of drill string rotation, due to the collocation with the core tube, since the core tube preferably will not rotate during drilling, thus making it necessary to instead interpret volatile vibrations or longitudinal movements.

Fig. 2 shows a core sampling arrangement according to the invention, i.e. the inner arrangement that is actually collecting the core sample wherein the orientation unit is collocated with the latching unit and rotational free from the core tube. The arrangement is intended to be mounted inside a tubular drill string (not shown), with the lower (left hand) end of the arrangement adjacent to the drill bit. The arrangement includes a core tube 100 with a core catcher 101 at the lower (left) end. At the right end of the core tube, there are in succession: a core tube head 102, a rotatable joint 104 and an orientation unit 103 collocated with a latching unit

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105. The latching unit 105 includes a number locking means in form of retractable latches 106 adapted to engage corresponding shoulder in the interior of the drill string. There may also be an optional second rotatable joint 108 between the orientation unit 103 and the latching unit 105. At the end of the latching unit there is a hook 107 adapted to be engaged by a hoist mechanism, such as a wire-line. The hook 107 is connected to the latches 106 and by pulling in the line the hook 107 will disengage the latches 106 from the said drill sting shoulder, allowing the whole assembly with core sample to be retrieved to the surface.

This arrangement has a number of advantages, of which one is that the orientation unit will not extend the total length of the core sample assembly eliminating need for a sub to be installed on the drill string to accommodate the extended length found in prior art. Consequently shorten the core tube seen as an alternative in prior art, is also not an option needed to be considered. The invention provide through the said advantages a system that providing direct access to the latching unit locking and hoisting means, thus making it possible to directly monitor the position of the latch unit locking means and presence of any hoist mechanism, as well as facilitate for direct readings of drill string rotational position and speed. As a result the invention will provide more robust and accurate means for initiating the orientation unit to log the orientation of the core sample at the correct moment of time, compared to prior art. Furthermore the relocation make it possible to conserve space in such degree that the total length of the core sample arrangement can be similar to conventional core sample arrangements, thus eliminating the need for the time consuming, equipment wearing and risk related work of hoisting and lowering the rods twice to install and later dismantle an extension sub on the drill string to accommodate the extra length an orientation unit fixed to the core tube will give to the core sample arrangement, seen in prior art.

Figure 3 is a schematic partial view of an embodiment of the inventive core sampling arrangement, i.e. orientation unit 103 with a core tube head (102) and a and rotational joint 104 excluding the lower parts with core catcher and core tube and the upper latching unit with its hoisting means. The devices shown are substantially cylindrical with a longitudinal axis. The end of the partial view of the core sampling arrangement shown to the left in Fig. 2 is arranged to be connected to the core tube which holds the core sample. The end of the partial view of the core sampling arrangement shown to the right is arranged to be connected to the latching unit.

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Fig. 4 is a schematic cross-sectional view of the core sampling system shown in Fig. 3. From left to right, the figure shows the core tube head 102 with a one way valve 504 allowing fluids trapped inside the core tube to escape through ports 502. The core tube head 102 is connected to a rotational joint 104 with a screw connection 505. The screw connection 505 allows the length of the assembly to be adjusted. The screw connection is fixed with a locking nut 506. The rotatable joint 104 is connecting the core tube head to the orientation unit 103, and includes an inner shaft 534 and an outer housing 535 connected by means of first 540 and second 532 thrust bearings with a slide bearing 536 there between. Lubrication channels 537 conduct grease from the grease nipple 552 to the bearings. This arrangement provides for a very robust joint.

The orientation unit 103 includes an electronic circuit board 522 with several accelerometers and a magnetometer. The inner shaft 534 of the rotational joint 104 includes an indication magnet 529 installed at its right hand end, the magnet acting as an indication point for the position of the core tube. In the orientation unit there is a corresponding idler magnet 530 mounted in a ball bearing 531. This idler magnet 530 is free to rotate and will closely follow the position of the indication magnet 529. The position of the idler magnet 530 is detected by a Hall-sensor 528 on the circuit board 522. The Hall-sensor 528 may be used to read out the position of the idler magnet 530 and thus the position of the core tube, but may also be used to detect rotation of the rotating parts to the right in the figure (on the right hand side of the rotational joint 104) relative to the static core tube. The orientation unit 103 is meant to be connected to a latching unit (not shown) locking it to the outer drill-string. The figure also shows a plunger rod 516 extending from the latch unit. This plunger 516, which is connected to the hook 107 and the latches 106 in the latching unit, includes a magnet 514 mounted at the end thereof. This magnet 514 is adapted to operate a magnetic proximity sensor 518 in the orientation unit. When the wire line is pulling in the latching unit, it will retract the plunger 516 causing the magnet 514 to move away from the magnetic proximity sensor 518, thus creating a signal that can be used by the processor to determinate exact time the time of the event, in order to process measurements and storing of such measurements accordingly.

This particular arrangement of the orientation unit above the rotation joint offers several advantages. The correct moment for taking the orientation reading may be determined in several ways: Stopping of the drilling operation may be detected by the Hall-detector, i.e. that the rotation ceases. Stopping of the rotation may also be

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detected by the accelerometers in the orientation unit. When the orientation unit is rotating, the accelerometers will provide a continuous alternating signal. Lastly, the operation of the magnetic proximity sensor may also be used to initiate an orientation reading. Another advantage of this setup is that due to the orientation unit being located on the upper side of the rotating joint, it is now possible to combine the orientation unit into the latch unit to conserve space, thus allowing room for a core orientation system that can be installed on any core sample arrangement without extending the total length or shorten the length of the core tube.

Thus, the method for obtaining the orientation readings of the core sample may either be an event driven process or a continuous process with readings taken at even periods, the readings being read when the orientation unit is retrieved to the surface.

In case of the event driven process, readings are obtained when an interesting event occurs, this event being detected by the orientation unit itself when measuring that the rotation of the drill string ceases, or measuring that the hoisting gear has engaged the core sampling unit or the latch locking means are retracted. These methods for detecting the interesting events are fully reliable.

However, the readings may also be retrieved in the conventional way, either by detecting vibrations or longitudinal movements of the drill string or core tube, or by using a timer device that is started and synchronized with the clocks in the orientation unit when the process begins. When the core sampling unit is retrieved to the surface, interesting events logged in the timer unit may be correlated with the corresponding readings logged in the orientation unit. In this embodiment, the orientation unit will take readings continuously at even intervals during the process, e.g. each 30 seconds.

In an alternative embodiment of the later method, the timer unit is not initially synchronized with the orientation unit. It is started at will when an interesting event occurs during the drilling of the core. Several interesting events may be logged. When the orientation device is retrieved to the surface, the clocks of the timer and orientation units are synchronized, e.g. using the moment of final cessation of the rotation of the drill string as a point of synchronization, and then correlating the readings in the orientation unit with the interesting events logged in the timer unit.

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Fig. 4 is a schematic block diagram illustrating principles of an electronic recording arrangement to be included in a core orientation tool.

The electronic recording arrangement 200 includes a digital bus 210 which interconnects a microprocessor 220 and a memory 230, which may be a non volatile memory such as Flash, ROM, PROM, EPROM, EEPROM memory or similar, which contains executable processor instructions to be processed by the processor.

The memory 230 is a processor-readable memory or data storage. During operation, the memory 230 contains a set of processing instructions which, when executed by the processing device such as the microprocessor 220, causes the processing device to perform a method as disclosed above with reference to figure 1.

The electronic recording arrangement 200 further comprises a volatile memory 240 for storage of temporary and intermediate data, which is also connected to the bus 210. The memory 240 may i.a. store logged drilling data associated with the drilling operation and orientation data associated with the core sample that is obtained from the subsurface.

The electronic recording arrangement 200 further comprises an I/O device 250 which interconnects the bus 210 and a drilling data sensor 260, in particular a rotation sensor 260. The rotation sensor 260 may be external to the electronic recording arrangement, but still included in the core orientation device.

The electronic recording arrangement 200 further comprises a wireless communication interface 270, connected to the bus 210 and also connected to antenna 290. In an aspect, the wireless communication interface may operate in accordance with the Bluetooth protocol, although numerous alternatives exist.

The electronic recording arrangement 200 further comprises a power supply device 280, such as a battery, which may be rechargeable or non-rechargeable.

Also shown in figure 4 is a remote operating device 292 which is arranged to be communicatively operable with the core orientation tool, and in particular with the electronic recording arrangement 200. To this end, the remote operating device 292 includes a wireless communication interface (not shown) connected to an antenna 294. The remote operating device 292 may also include operating

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elements and display elements. The remote operating device 292 is configured to operate in accordance with the same data communication protocol as the wireless communication interface 270 included in the core orientation device's electronic recording arrangement 200, in order to enable digital communication there between. Hence, the remote operating device 292 may e.g. be configured to operate in accordance with the Bluetooth protocol, another appropriate wireless communications protocol or cable.

Instead of using a magnet as an reference point and a Hall-sensor to read its position, other solutions may be used, such as but not limited to other types of magnetic sensors, optical sensor, selsyn sensor or any other suitable means for reference point and matching sensor for reading rotational position of a shaft of coupling.

Another option is to avoid fixing the orientation unit to the latching unit and instead arrange another bearing there between. Then, the orientation unit is free to rotate freely from both the core tube and the latching unit.

Claims

l-uI international Application r2 1w u0 u 25-05-2018 1 Claims

1. A core drilling system with a drill tube terminated in a drill bit, the drill tube including a core sampling arrangement mounted inside thereof, the core sampling arrangement including a core tube (100) for holding a core sample, the core tube 5 having a first end located near the drill bit and a second end distant from the drill bit, a core catcher (101) fixed at the first end of the core tube (100), and a core tube head (102) fixed to the second end of the core tube (100), the system further including a rotational joint (104) connecting the core tube head (102) to a latching unit (105) adapted to releasable lock to the 10 drill tube, wherein said rotational joint (104) allows the latching unit (105) to rotateindependently from the core tube(100), characterized in * an orientation unit (103) rotationally free from the core tube, fixed to or integrated within the latching unit (106) in near proximity of the rotational joint (104), e one or more detectable reference members (529) fixed to the core tube (100) or to an element fixed to the core tube (100) such as the rotational joint (104), • wherein the orientation unit (103) includes at least one sensor (528) that can determine the rotational position of said reference member (529), and thus determine the rotational position of the core tube (100) relative to the orientation unit (103), * wherein the orientation unit (103) includes at least one sensor for determining the direction of earth gravity, - wherein the orientation device compromise means to process data collected from the said reference device sensor (528) and said earth gravity sensor, in order to calculate and store the rotational position of the core tube (100) relative to earth gravity, and thus determine the rotational orientation of the core sample relative to earth gravity when situated in the sub-surface, * wherein the orientation device includes means for accessing said stored rotational position data with a suitable interface.

2. A core drilling system according to claim 1, wherein the reference device sensor is a Hall-effect sensor (528), while the reference member is a magnet (529).

3. A core drilling system according to claim 2, wherein the reference member (529) is in near proximity of the reference device sensor (528) for direct reading of the reference point member (529) position, or is located at a distance from the reference device sensor (529), wherein the position of the reference point member (529) is transferred to suitable near proximity of the sensor by means of a

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transmission device.

4. A core drilling system according to claim 3, wherein said transmission device is a shaft (534) and/or magnetic coupling (530).

5. A core drilling system according to claim 1, wherein the orientation unit (100) s Includes means to detect rotation or rotational speed of the drill string.

6. A core drilling system according to claim 1, wherein the system Includes means for determining the presence of a hoist mechanism latched to the core sampling arrangement, or for determining the position of locking means in the latching unit.

7. A core drilling system according to claim 6, wherein the means is linked to the latching unit (106), and thus may be operated by a wire line connected to the latching unit.

8. A core drilling system according to claim 7, wherein the means creates a signal that can be used by the processor to determine exact time to process measurements and storing of such measurements.

9. A method for obtaining a rock core sample using a core drilling system as claimed in any of the claims 1-8, the method Including the steps of:

a) activating the orientation unit and lowering the core sampling arrangement to its designated position at the bottom end of the drill sting, b) operating the drill string to drill a rock core, with the latching unit and orientation unit rotating with the drill string, c) ceasing coring operation when a suitable length of core is obtained, d) measuring the orientation and inclination of the core relative to earth gravity when situated in the subsurface, before and/or after breaking the core from the subsurface, e) storing said measurements in the orientation unit, f) retrieving the core sampling arrangement with a core sample fixed inside the core tube to the surface, and g) reading said measurements from the orientation unit and mark the core sample accordingly.

10. A method according to claim 9, wherein step d) includes that the means for 3o determining the presence of a hoist mechanism latched to the core sampling arrangement, or for determining the position of locking means in the latching unit activate a command related to the measurement and logging of core tube orientation data of interest.

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11. A method according to claim 9, wherein the orientation unit, when activated, is measuring and storing the measurements continuously at even intervals, step a) includes starting a timer device at the surface, synchronizing or time link the timer device with the orientation unit, s step d) Includes using the timer device to log the time ofinteresting downhole events, such event being suitable time for performing measurement of the orientation of the core, step g) includes correlating the logged time of interesting events in the timer device, with the matching measurements stored in the orientation unit memory.

12. A method according to claim 9, wherein the orientation unit when activated Is measuring and storing the measurements continuously at even intervals, step d) includes starting a timer device at the surface and to log the time of interesting events during the drilling run, such event being suitable time for performing measurement of the orientation of the core, is step g) Includes synchronizing or time link the timer device with the orientation unit and correlating the logged time of measurement in the timer device with the matching measurement(s) stored In the orientation unit.

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