APPARATUS AND METHOD FOR MEASURING BOREHOLE DEVIATION

Abstract: Apparatus for measuring the deviation of a borehole (12) comprises a plurality of rods (10), connected together in constant angular alignment, at least the first of which contains inclination sensing means. When inserted in the borehole (12) the apparatus measures the inclination of the hole at regular depth intervals in one or more axes. The measurements are stored electronically and may be processed to provide numerical and/or graphical information about the deviation of the borehole in three dimensions. Alternative embodiments and methods of deployment are described.

Description: Apparatus and Method for measuring borehole deviation This invention relates to a method and apparatus for measuring the deviation of boreholes, particularly (but not exclusively) boreholes of generally vertical disposition used for placing explosives in quarrying. It is normal practice in quarrying to drill a series of boreholes behind the existing roc face, from above. The boreholes generally have a slope of some degrees chosen to match the profile of the rockface. It has hitherto been customary to assume that the borehole lies in a straight line. In fact, however, boreholes tend to curve towards the foot of the rockface as viewed in vertical cross-section, and to deviate sideways when viewed in plan. This makes it more difficult to achieve consistency in blasting, and to achieve maximum efficiency of use of explosive. Accordingly, an object of the present invention is to provide an apparatus which enables the deviation of boreholes to be readily determined. In accordance with a first aspect, the invention provides apparatus for measuring the deviation of boreholes, comprising I a plurality of elongate rods having a cross-section suitable for insertion in a given size of borehole, each rod being of a predetermined length and each having end faces provided with means for mechanical connection to an adjacent rod so as to position the rods in a predetermined angular relationship, wherein at least the first of said rods contains at least one inclination sensor, the apparatus further including means for transmitting signals from said at least one sensor to the surface. Preferably, the apparatus includes means adapted to be mounted in use on the topmost rod for determining the length * of rod protruding from the borehole. The inclination sensor may suitably be an electrolytic angle sensor, and each rod containing a sensor suitably also includes microprocessor-based electronics for converting the output from the sensor to digital form for transmission of inclination signals from the or each sensor. Preferably, the apparatus further includes portable data capture means connectable to said signal transmission means, for storing inclination and file data for subsequent processing off-site β In a first embodiment of the invention, each rod contains at least one inclination sensor, and means are provided for electrical interconnection of the rods to provide a signal path between the sensors and the surface. Preferably, such electrical connection means provide a common signal path formed through the rods. It is further preferred, in this embodiment, that each rod contains one single-axis sensor, said axis being at right angles to the long axis of the rod. In a second particularly preferred embodiment, only the first of a series of rods contains an inclination sensor. In this case it is preferred that the first rod is provided with sensors for measuring inclination in two axes mutually at right angles to one another and to the long axis of the rod. According to a second aspect of the invention, a method of measuring the deviation of a borehole comprises introducing a series of elongate rods, of known length into the borehole, at lea >st the first of which contains at least one inclination sensor, into the borehole, and measuring and recording the inclination of at least said first rod in at least one axis at a plurality of known depth intervals down the borehole. Where a single-axis sensor is used, a first set of measurements is preferably performed with the rods in a first position, and a second set of measurements performed with the rods rotated through 90° into a second position. This is not necessary where sensors are provided for measuring the inclination in two axes. Preferably, the method further includes measuring the distance by which the last rod projects from the top of the borehole when the first rod is at the bottom thereof. Once the measurements are complete, the deviation of the borehole in three dimensions can be calculated for each measurement point from the measured angles and known lengths of the rods. Embodiments of the invention will now be described, by way of example, with reference to the drawings, in which:- Fig. 1 is a schematic side view of apparatus according to the invention in use; Fig. 2 is a perspective view of the apparatus in use in combination with another apparatus; Fig. 3 is a perspective view, partly broken away, of part of the apparatus; Fig. 4 illustrates a display produced by the apparatus; and Figs. 5 to 8 similarly illustrate the construction and deployment of a second apparatus embodying the invention. Referring to Figs. 1 and 2, the apparatus comprises a number of rods 10 which are fitted together and inserted down the-borehole 12. The rods 10 may conveniently be, for example, 2 m long by 63.5 mm outside diameter. The rods are of exact length and their ends are precisely machined to lock toget'her and to index together in rotational alignment. As seen in Fig. 3, each rod 10 comprises a tubular casing 14 containing an angle sensor 16 and an electronics package 18. One end face is provided with three spigots 20 which mate with recesses (not shown) at the opposite end of the adjacent rod to form a mechanical connection and to align the angle sensors in the mated rods. A 3-pin waterproof electrical connector 22 is also provided. The angle sensor 16 may suitably be an electrolytic angle sensor (ie an electrolytic gravity sensor) such as that used in the "TRIM" (Trade Mark) inclination sensor by Measurement Devices Limited. The electronics package 18 is suitably based on an Intel 8048 microprocessor, and is arranged to read the voltages from the angle sensor, condition and digitise these signals, and pass the resulting encoded signal up the line to the next electronics package 18 (daisy chaining). Such technology will be apparent to those skilled in the art and will not be further described herein. Reverting to Figs. 1 and 2, the rods 10 are connected together and lowered into the borehole 12. When sufficient rods have been inserted to fill the hole, leaving the last section protruding, a sighting/alignment section 24 is mounted on top. The sighting/alignment section 24 includes a sighting telescope 30, and electrical connections from the rods 10 to a battery 26 and electronic notebook 28. The system is switched on via the electronic notebook 28-. A software driven menu LCD display prompts the operator to enter file information such as date, face number, profile number and "rod offset". The rod offset is the amount of rod assembly protruding from the borehole, and can be measured by use of the sighting telescope 30 and a level staff 32. The"display then fills with the readings from the electronic packages. The readings indicate the angle of inclination 0 between each rod and the vertical as it lies in the hole. The rods 10 are first aligned towards the face; when the displayed readings have settled, a simple keystroke stores the values within the notebook memory. The rods 10 are then rotated to 90° (3 o'clock), 180° (6 o'clock) and 270° (9 o'clock) positions, the procedure being repeated for each. The rods 10 are then recovered, and the same procedure ensues for the next borehole. The entire process takes about 20 minutes per hole. In this embodiment each rod is provided only with one, single-axis inclination sensor, (the measurement axis being at right angles to the long axis of the rod 10). Accordingly, it is necessary to take readings with the rods in a first position and then rotated by 90° into a second position in order to measure the deviation in two axes. The further two readings (at 180° and 270°) referred to above are not strictly necessary, but assist in compensating for any errors. It will be apparent that by providing, for example, 2-axis sensing in each rod the procedure could be speedier, although at the expense of added complexity and cost. The data logged is preferably analysed remotely using a standard personal computer 34. Since the length, pitch and roll angle of each rod is known, the computer can calculate the X, Y and Z offset of each sensor. Summing the offsets gives the end position of the borehole. As indicated in Fig. 2, the apparatus of the invention may be integrated with a quarry face surveying system indicated at 36. A suitable system is "QUARRYMAN" (Trade Mark) from Measurement Devices Limited. This uses a laser rangefinder and angle sensors to derive information defining the spatial co-ordinates of selected points on the rockface. This information can be combined with the information from the apparatus of the present invention, to provide a display as shown in Fig. 4, giving a section at any selected borehole and plan of any part of the face, showing graphically the intended lines of the boreholes, the actual lines of the boreholes, the minimum burden and its depth for each borehole, and the minimum horizontal spacings between boreholes. Figs. 5 to 8 illustrate an alternative, particularly preferred embodiment of the apparatus. In this case there is a single "active" rod section 40 containing inclination sensors (again, preferably electrolytic gravity sensors, not shown) for measuring the inclination of the rod 40 in two axes mutually at right angles to one another and to the long axis of the rod 40, and an electronics package (not shown) as in the first embodiment. The active section is attached to the end of a series of "dummy" rod sections 42 which are pivotably attached to one another, as shown in Fig. 7, by PTFE hinge yokes 44 and a link member 46. This "knuckle" type joint allows the rods 44 to pivot about a single axis only so that constant angular alignment is preserved throughout the series, and also allows them to be folded into a convenient bundle for storage or transportation. The active rod 40 may be detachably connected to the adjacent dummy section 42 in a similar manner, using a lynch pin or the like. The apparatus further includes a sighting piece, including a telescope 48, battery 50 and electronic notebook 52 similar to those of the first embodiment. In this case the electrical connection of the battery 50 and notebook 52 can be made directly to the active section 40 by means of a cable 54, thus obviating the need for electrical connections between the rods 42. In this embodiment the method of operation involves inserting the active section 40 into the hole and aligning it with a reference or index direction as before. Readings of the inclination in the two measurement axes are then taken and recorded at known, regular depth intervals as the active section 40 is lowered to the bottom of the hole, whereafter the rod offset may be measured as before. The dummy sections 42 remaining outside the hole may be used like a tiller to maintain the correct orientation of the apparatus as it is lowered (see Fig. 8). The accumulated data may be processed and analysed to provide numerical and/or graphical information regarding the deviation of the borehole as before. The active section 40 is preferably fabricated from stainless steel and aluminium, whilst the dummy sections 42 may be made from lighter materials such as fibre glass or carbon fibre. This allows a 100 foot (30.48 metres) system to be constructed weighing approximately 251bs (11.36kg). The active and dummy sections 40 and 42 are preferably 6 feet (1.83 metres) long and 1 1/2 inches (3.81 cm) in diameter. This embodiment allows the number of electronic components, the structural complexity and the overall weight of the apparatus to be reduced, and is also more flexible in use since the depth intervals at which readings are taken can be varied at will, (given suitable software) rather than being fixed as in the first embodiment.

Claims: AMENDED CLAIMS [received by the International Bureau on 21 April 1989 (21.04.89) original claims 1 and 13 amended; other claims unchanged (3 pages)] 1. Apparatus for measuring the deviation of boreholes, comprising a plurality of elongate rods having a cross-section suitable for insertion in a given size of borehole and connected end to end in sufficient quantity that the total length thereof is sufficient to extend to a required depth, each rod being of a predetermined length and each having end faces provided with means for mechanical connection to an adjacent rod so as to position the rods in a predetermined angular relationship, wherein at least the first of said rods contains at least one inclination sensor, the apparatus further including means for transmitting signals from said at least one sensor to the surface. 2. Apparatus as claimed in claim 1, further including means adapted to be mounted in use on the topmost rod for determining the length of rod protruding from the borehole. 3. Apparatus as claimed in claim 1 or claim 2 wherein the inclination sensor is an electrolytic angle sensor. 4. Apparatus as claimed in any of claims-1, 2 or 3, wherein each rod containing a sensor further includes microprocessor- based electronics for converting the output from the sensor to digital form for transmission of inclination signals from the or each sensor. 5. Apparatus as claimed in any of claims 1 to 4, further including portable data capture means connectable to said signal transmission means, for storing inclination and file data for subsequent processing off-site. 6. Apparatus as claimed in any of claims 1 to 5, wherein each rod contains at least one inclination sensor, and means are provided for electrical interconnection of the rods to provide a signal path between the sensors and the surface. 7. Apparatus as claimed in claim 6, wherein said electrical connection means provide a common signal path formed through the rods. 8. Apparatus as claimed in claim 6 or claim 7 wherein each rod contains one single-axis sensor, said axis being at right angles to the long axis of the rod. 9. Apparatus as claimed in any of claims 1 to 5 wherein only the first of a series of rods contains an inclination sensor. 10. Apparatus as claimed in claim 9 wherein said first rod is provided with sensors for measuring inclination in two axes mutually at right angles to one another and to the long axis of the rod. 11. Apparatus as claimed in claim 9 or claim 10, wherein the second and subsequent rods are hingeably connected to one another. 12. Apparatus as claimed in any of claims 9, 10 or 11, wherein said second and subsequent rods are made from a light¬ weight material such as fibre glass or carbon fibre. 13. A method of measuring the deviation of a borehole comprising introducing a series of elongate rods of known length into the borehole, the total length of said rods being sufficient to extend to a required depth, and at least the first of said rods containing at least one inclination sensor, and measuring and recording the inclination of at least said first rod in at least one axis at a plurality of αiown depth intervals down the borehole. 14. The method of claim 13, wherein a single axis sensor is utilised and wherein a first set of measurements is performed with the rods in a first position, and a second set of measurements performed with the rods rotated through 90° into a second position. 15. The method of claim 13, wherein at least said first rod contains sensors for measuring inclination in two axes mutually at right angles to one another and to the long axis of the rod, and wherein the inclination in both said axes is measured in a single set of measurements. 16. The method of any of claims 13 to 15 wherein each rod contains at least one sensor, and wherein the rods are inserted to the full depth of the borehole prior to making said measurements. 17. The method of any of claims 13 to 15 wherein only the first of said rods contains a sensor, and wherein said measurements are made at regular depth intervals as the first rod is lowered into or raised from the borehole. 18. The method of any of claims 13 to 17, further including measuring the distance by which the last rod projects from the top of the borehole once the rods have been inserted to the full depth thereof.

Inventors: BALL STEVEN, BALL, STEVEN
Applicants: MEASUREMENT DEVICES LTD, MEASUREMENT DEVICES LIMITED
Application year: 1988
Main classification: E21B47
IPC codes: E21B47