Core orientation module and method

Abstract

A core orientation module, comprising a tool body for connection to a core drilling assembly tool. The tool body 102 comprises a power supply; a sensor platform 104 carrying one or more gyroscopic sen

Description

BACKGROUND

[0001] The invention relates to core orientation modules and methods for performing gyroscopic core orientation measurements during core drilling operations.

[0002] In the mining and minerals exploration industry it is commonplace to map a geological resource by drilling a large number of boreholes to extract core samples. It is important during the core drilling process to establish the physical orientation of the core extracted from the borehole in order for geologists to build a picture of the geological make up of the area being drilled and its associated mineral content. As part of this process, it is also important to establish the direction of the core sample taken and at what depth it was taken. Instruments can be mounted to a core barrel assembly which receives the drilled core sample, and which is subsequently retrieved to the surface. These instruments are typically functionally restricted to basic sensor measurements of the orientation of the core as it is drilled. This restriction is due to the difficulty of exposing more sophisticated sensors to the core drilling environment. Additionally, basic orientation sensors can be packaged in a small housing, which means that the core orientation module has minimal physical impact on the core barrel assembly. Basic orientation sensors consume very little electrical power and so can be operated from batteries for extended periods, which minimises the impact on drilling operations. Directional survey instruments are typically used to determine the azimuthal direction and inclination of the boreholes from which the cores are extracted. Depth is typically established by measurement of the number of drill rods in the borehole. Such instruments can be sent downhole before retrieval of the core barrel or after retrieving the core barrel between drilling operations, alleviating the limitations on sensor exposure to the drilling environment but at the cost of expensive rig time. These instruments are typically also quite large when compared to basic sensor core orientation devices and require significantly more electrical power than basic sensor core orientation devices

[0003] There is a desire for directional survey instruments that can be mounted on a core barrel to save rig time while being rugged enough for the sensors to withstand the harsh core drilling environment.

[0004] GB2514077A describes a known method of gyro surveying a borehole. While gyroscopes are known to have certain advantages for directional surveys over other sensor types, such as magnetic sensors, they are relatively expensive and susceptible to damage when subjected to shock and vibration. Gyroscopes can also require more power than other sensor types. SUMMARY

[0005] One aspect of the invention provides a core orientation module, comprising a tool body for connection to a core drilling assembly tool. The tool body comprises a power supply mounted in the tool body; a sensor platform carrying one or more gyroscopic sensors mounted in the tool body used to establish azimuthal direction of the core orientation module; and a rotary drive system connected between the sensor platform and the power supply. The rotary drive system is configured to rotate the sensor platform relative to the tool body, and to rotate with the sensor platform.

[0006] The sensor platform can also carry accelerometers. The sensor platform can be a hollow tube, and the rotary drive system can be mounted inside the hollow tube sensor platform. The gyroscopic sensor(s) and other sensors can be mounted on the outside of the hollow tube sensor platform, concentric with the rotary drive system.

[0007] The power supply can comprise a battery, such as a rechargeable battery and associated regulation.

[0008] The rotary drive system can comprise a motor and gearbox mounted on a shaft fixed relative to the tool body.

[0009] A second aspect of the invention provides a method for determining the orientation and azimuthal direction of the core orientation module of any preceding claim during a core drilling operation, including: defining a data sampling time interval (DSI), a survey start time (STR), a noise threshold (NTH), and a calibration criterion; commencing the core drilling operation with the core orientation module in a low power mode in which the gyroscopic sensor(s) is not activated to make measurements; activating the sensor platform after each DSI during the drilling operation and determining whether the core orientation module is stationary by comparing a measured noise signal to the NTH; at the first occasion where the core orientation module is determined to be stationary, performing a baseline calibration by activating sensors on the sensor platform, rotating the sensor platform within the tool body, and making gyroscopic and accelerometer measurements to determine the orientation and direction of the core orientation module; at subsequent occasions where the core orientation module is determined to be stationary: where the calibration criterion is met, activating the gyroscopic sensor, performing gyroscopic and accelerometer sensor measurements for determining the orientation and direction of the core orientation module, and deactivating the gyroscopic and accelerometer sensors to the low power mode; where the calibration criterion is not met, activating the gyroscopic sensor, rotating the sensor platform within the tool body, and making and storing gyroscopic and accelerometer measurements to determine the orientation and direction of the core orientation module, and deactivating the gyroscopic sensor to the low power mode; and at subsequent occasions where the instrument is not stationary, deactivating the sensor platform to the low power mode.

[0010] The calibration criterion can be a platform rotation interval (PRI) not being exceeded. The calibration criterion can alternatively or additionally be a baseline calibration threshold (BLC) not being exceeded.

[0011] The method can further comprise an end of hole survey being performed as the core barrel assembly is retrieved from the drillhole. The end of hole survey includes activating sensors on the core orientation module to detect linear motion of the core orientation module along the axis of the drillhole but not associated with drilling a core; when linear motion is detected, activating the gyroscopic sensor to take measurements at fixed intervals during the period of linear motion; and defining a final direction reference at the end of the period of linear motion. Alternatively, the start direction for the end of hole survey could be based upon the known measured direction of the core orientation module within the drillhole.

[0012] The method can comprise performing a measurement defining an initial direction reference. The method can also comprise determining an initial time and depth reference. The method can further comprise determining an end of hole time and depth reference. The method can comprise obtaining the direction references by gyrocompass measurement.

[0013] The method can comprise determining end of hole by detecting the linear motion stopping for a predetermined period of time.

[0014] Further aspects of the invention will be apparent from the description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows a perspective view of one embodiment of the core orientation module. FIG. 2 shows a side view cross section of the core orientation module of FIG. 1. FIG. 3 shows a flowchart of a method for performing a gyroscopic core orientation measurement while drilling. FIG. 4 shows a flowchart of a method for performing an end of hole survey. DETAILED DESCRIPTION

[0016] FIGs. 1 and 2 show a core orientation module that can be used in a core drilling operation to determine the orientation of a core retrieved during the operation. The module can be attached at an upper end of a core barrel below a latching head assembly for use in retrieving the core barrel by a wireline or slickline.

[0017] The core orientation module of FIG. 1 comprises a tool body 102 housing a sensor platform 104 with a rotary drive system 106 mounted inside the sensor platform 104, which carries sensor circuit boards 105. The tool body 102 further houses a battery 108, and processing, memory, and communications electronics 110. The tool body 102 is substantially cylindrical, hollow, and can be connected to a core barrel through any suitable connecting means such as a screw thread connection. The tool body 102 provides a pressure-resistant housing for the various parts of the module.

[0018] As is shown in FIG. 2, the core orientation module comprises a sensor platform 104 comprising a hollow tube 103 with circuit boards 105 mounted on the exterior face of the tube 103. The sensor platform 104 carries one or more gyroscope sensors, such as MEMs devices, and other sensors such as accelerometers. The sensors are suitable for detecting vibrations (noise), drilling activity, and other motion. The sensor platform 104 is concentric with the rotary drive system 106.

[0019] The rotary drive system 106 comprises an electric motor and a gearbox 107 and is connected to the battery 108 via a slip ring 112. The rotary drive system 106 is mounted on a bearing 114, and a shaft 116 which is fixed to the tool body 102.

[0020] The rotary drive system 106 is mounted inside and fixed to the sensor platform 104 such that the rotary drive system 106 and the sensor platform 104 rotate with each other relative to the tool body 102. The slip ring 112 provides power to the rotary drive system 106 during rotation. The bearing 114 facilitates rotation within the tool body 102. The shaft 116 is connected between the rotary drive system 106 and the tool body 102 such that the rotary drive system 106 rotates relative to the tool body 102 when it is powered on.

[0021] The battery 108 provides power to the rotary drive system 106 and the sensor platform 104. The battery can be any suitable power supply, such as a rechargeable battery. A wired power connection is also possible.

[0022] Locating the drive system inside the sensor platform provides a compact arrangement that occupies less space within the tool body. This in turn leaves more space for the battery or allows a shorter module comparable to basic core orientation sensor modules. A larger battery can allow the module to operate for longer periods before it must be retrieved to the surface for recharge or replacement.

[0023] Gyroscope sensors typically require more power than accelerometers or magnetometers. While a larger battery can offset this extra power requirement to some degree, it will likely be necessary to actively manage the power consumption of the sensors if the battery life is to be comparable with the duration of core drilling operations. As is described in more detail below, this can involve cycling the sensor package between low power modes, in which the sensors are inactive, and high-power modes in which the sensors are active and make and record measurements.

[0024] FIG. 3 illustrates a method for determining the orientation of the module. The method of FIG. 3 starts with step 302 in which the core orientation module is initialised. The initialisation involves defining a data sampling time interval (DSI), a survey start time (STR), a noise threshold (NTH), and a calibration criterion.

[0025] The DSI is the time interval between measurements, during which the sensors are in a low power mode. The STR is the time at which the survey is started. The NTH is a threshold used to determine whether drilling activity has stopped, and hence whether the instrument is stationary. The calibration criterion can be a platform rotation interval (PRI) which is defines a maximum time interval between platform rotations for calibration of the sensors, or a baseline calibration threshold (BLC) which defines the maximum allowable measurement drift from the baseline calibration measurement. If either or both of these is exceeded, the measurement system will be recalibrated.

[0026] Drilling commences in step 304 with the core orientation module in a low power mode. In the low power mode the sensors are put to sleep and do not make any measurements, and there is no power provided to the rotary drive system.

[0027] Power is provided to the noise sensors after a DSI elapses in step 306. The sensors make measurements of noise indicating that drilling is still taking place. The noise sensor can be an accelerometer, motion sensor or any other suitable sensor capable of detecting drilling activity, for example from vibrations. It is not necessary to power the gyroscopic sensors at this stage.

[0028] In step 308 the noise measurement is compared to the NTH. If the noise measurement is below the NTH then drilling is determined to have stopped. Otherwise, drilling is determined to be ongoing, and the gyroscopic sensor cannot be powered up or calibrated so the noise sensors are put back to the low power mode. Steps 306 and 308 are repeated for successive DSIs until the measurements determine that drilling has stopped.

[0029] The first time that the module is determined to be stationary, in step 310, the gyroscopic sensor is powered up and is calibrated. The sensor platform is rotated, and gyroscopic measurements taken and stored. Multiple measurements can be taken at different positions and measurements by other sensors can similarly be taken and stored. This step establishes the baseline calibration of the gyroscopic sensor.

[0030] After a further DSI elapses in step 312 another noise measurement is taken as in step 306.

[0031] In step 314 the noise measurement form step 312 is compared to the NTH as in step 308. Where drilling is detected, the noise sensors are put back to the low power mode. Steps 312 and 314 are repeated for successive DSIs until the measurements determine that drilling has stopped.

[0032] The next time that the module is determined to be stationary, in step 316 the gyroscopic sensors are powered up and calibration criterion is checked. If the calibration criterion is met, then the gyroscopic sensor can be used to take measurements. Otherwise, the gyroscopic sensor must be recalibrated before being used to take measurements.

[0033] If the calibration criterion is not met and the gyroscopic sensor must be recalibrated. In step 318, the sensors are powered up, the sensor platform is rotated, and gyroscopic sensor measurements are taken and stored during the rotation period, and the sensors are returned to the low power mode as in step 310. Measurements from other sensors can similarly be taken and stored. The rotation can be a stepwise rotation whereby the measurements are taken when rotation has paused. Where the sensor platform carries more than one gyroscopic sensor and / or a gyroscopic sensor that is suitably stable, it may not be necessary to rotate the platform and recalibrate the sensors, resulting in further power savings.

[0034] If the calibration criterion is met, in step 320, the sensors are powered up, gyroscopic (and other) sensor survey measurements are taken, and the sensors are returned to the low power mode.

[0035] Steps 312 onwards are repeated until the survey is ended. The orientation module is then retrieved to the surface and the stored measurement downloaded and the battery can be recharged if required. However, the battery power life will have been significantly extended by the power management techniques described above.

[0036] An end of hole survey can be initiated at this stage to provide measurements along the drillhole as the tool is retrieved to surface.

[0037] FIG. 4 illustrates an end of hole survey that starts with step 402 in which linear motion sensors are powered up to monitor the motion of the module along the axis of the borehole. These sensors could be accelerometers or other suitable sensors.

[0038] The sensor measurement determines if the motion is linear and indicative that the tool is being moved axially along the drillhole to surface but not actively drilling in step 404. 7

[0039] If linear motion is detected, continuous logging mode is enabled in step 406. The continuous logging mode can comprise power being applied to all sensors and any sensor taking successive measurements at fixed time intervals as the module moves along the well. An initial direction reference can be taken during this step, obtained using any suitable means such as a gyrocompass measurement or established from the core orientation module survey. An initial depth and time reference can be can also be obtained during this step, by the surface operator noting the time at which tool retrieval from hole commenced. A continuous depth and time log on surface can be correlated with instrument data sample times.

[0040] A final direction reference is determined in step 408. The direction reference can be determined by performing a sensor measurement, such as a gyrocompass measurement. The direction reference can also be determined using any other suitable means, such as using the known rig direction.

[0041] Step 408 occurs at end of hole. End of hole can be determined by the linear motion stopping for a predetermined period of time or other suitable sequence of events recorded by the core orientation module. A final depth and time reference can also be obtained by any suitable means during this step.

[0042] The result of the end of hole survey is a continuous measurement along the well. This can be compared with the individual measurements taken between drilling steps for validation.

[0043] Further changes can be made within the scope of the invention.

Claims

:

1. A core orientation module, comprising:a tool body for connection to a core drilling tool, comprising:a power supply mounted in the tool body;a sensor platform carrying gyroscopic and other sensors mounted in the tool body, anda rotary drive system connected between the sensor platform and the power supply and configured to rotate the sensor platform relative to the tool body, wherein the rotary drive system is configured to rotate with the sensor platform, whereinthe sensor platform comprises a hollow tube and the rotary drive system is mounted inside the hollow tube.12 01 262. A core orientation module as claimed in claim 1, wherein two gyroscopic sensors are mounted on the outside of the hollow tube.

3. A core orientation module as claimed in any preceding claim, wherein the gyroscopic sensor is mounted concentrically with the rotary drive system.

4. A core orientation module as claimed in any preceding claim, wherein the power supply comprises a battery, which may be re-chargeable.

5. A core orientation module as claimed in any preceding claim, wherein the rotary drive system comprises a motor and gearbox mounted on a shaft fixed relative to the tool body.

6. A core orientation module as claimed in any preceding claim, wherein the sensor platform also carries accelerometers and / or vibration sensors for noise detection.12 01 267. A method for determining the orientation and azimuthal direction of the core orientation module of any preceding claim during a core drilling operation, including:defining a data sampling time interval, DSI, a survey start time, STR, a noise threshold, NTH, and a calibration criterion;commencing the core drilling operation with the core orientation module in a low power mode in which the gyroscopic sensor is not activated to make measurements;activating noise sensors after each DSI during the drilling operation and determining whether the core orientation module is stationary by comparing a measured noise signal to the NTH;at the first occasion where the core orientation module is determined to be stationary, performing a baseline calibration by activating the gyroscopic sensor on the sensor platform, rotating the sensor platform within the tool body, and making gyroscopic measurements;at subsequent occasions where the core orientation module is determined to be stationary: where the calibration criterion is met, activating the gyroscopic sensor, performing gyroscopic sensor measurements for determining the orientation and azimuthal direction of the core orientation module, and deactivating the gyroscopic sensor to the low power mode;where the calibration criterion is not met, activating the gyroscopic sensor, rotating the sensor platform within the tool body, and making and storing gyroscopic measurements, and deactivating the gyroscopic sensor to the low power mode; andat subsequent occasions where the instrument is not stationary, deactivating the sensor platform to the low power mode.

8. A method as claimed in claim 7, wherein rotating the sensor platform comprises rotating the sensor platform to predetermined positions.

9. A method as claimed in claim 7 or 8, comprising making accelerometer measurements at the same time as the gyroscopic measurements.

10. A method as claimed in claim 7, 8, or 9, wherein the baseline calibration comprises making gyroscopic measurements in at least two positions of rotation of the sensor platform.

11. A method as claimed in any of claims 7-10, wherein the calibration criterion is a platform rotation interval, PRI, not being exceeded and / or a baseline calibration threshold, BLC, not being exceeded.12 01 2612. A method as claimed in any of claim 7-11, further comprising an end of hole survey, comprising:activating sensors on the core orientation module to detect linear motion of the core orientation module along the axis of the drillhole but not associated with drilling a core;when linear motion is detected, activating the gyroscopic sensor to take and store measurements in tool memory at fixed time intervals during the period of linear motion; anddetermining a final direction reference at the end of the period of linear motion.

13. A method as claimed in of claim 12, wherein end of the period of linear motion is determined by detecting the cessation of linear motion for a predetermined period of time.

14. A method as claimed in claim 12 or 13, further comprising performing a measurement defining an initial direction reference, when activating the gyroscopic sensors to take measurements at fixed intervals during the period of linear motion.

15. A method as claimed in any of claims 12-14, wherein the direction references are gyrocompass measurements, including measurements previously taken to establish the core orientation module direction16. A method as claimed in any of claims 12-15, further comprising determining an initial time and depth reference when activating the gyroscopic sensors to take measurements at fixed intervals during the period of linear motion.

17. A method as claimed in any of claims 12 - 16, further comprising determining final depth and time reference at the end of the period of linear motion.

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