GB2251307A

GB2251307A - Core orientation device

Info

Publication number: GB2251307A
Application number: GB9126009A
Authority: GB
Inventors: David Gowans
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-12-06
Filing date: 1991-12-06
Publication date: 1992-07-01
Anticipated expiration: 2011-12-06
Also published as: GB2251307B; AU1859792A; CA2072203A1; AU653827B2; GB9126009D0

Abstract

A device to enable the determination of the angular orientation of a core sample taken from an inclined bore hole includes an indicator (24) mounted upon an elongated body (21) for movement around the axis of the elongated body within a housing (18). The indicator is released by a trigger device (28) to permit it to move from a retracted position into an orientation-indicating position in which the indicator engages one of a multiplicity of apertures (27) in the lower end of the housing and thus indicates the relative orientation of the indicator and the housing at the time when the trigger device was operated. <IMAGE>

Description

Core Orientation Device The present invention is concerned with the taking of core samples of underground strata and is a device to enable the determination of the angular orientation of a core sample.

The practice of taking core samples for the purpose of identifying and analysing the orientation and thickness of underground rock and similar strata is well established.

Apparatus used for this purpose usually entails a rotating, hollow cylindrical cutting bit which cuts a continuous or discontinuous cylindrical core sample and feeds the core sample into a non-rotating inner tube or core tube. The core tube is subsequently withdrawn, either with the drill string or at the end of a cable or "wire line", and brings the core sample within it.

In order to interpret the information given by the core sample it is necessary not only to know the direction of inclination of the borehole relative to the vertical but also to understand how the strata under investigation are orientated relative to the axis of the borehole. Conventionally the latter feature is determined by drilling further boreholes, spaced from the first one, and repeating the core sampling exercise for each borehole. Such additional boreholes each represents a significant expense.

An alternative to the drilling of additional boreholes is to establish the rotational angular orientation of the core sample within a given borehole. In view of the considerable expense which is potentially to be saved in this way, many attempts have been made to determine this core orientation, using a variety of methods. For example, it has been proposed to scribe a line on the core itself while the sample is being taken and to hold the drill pipe without turning while it is being lowered into a borehole. However it is difficult to prevent the drill pipe twisting and also the core tube may turn relative to the drill pipe while the latter is being lowered. Thus the results obtainable by this difficult procedure are scarcely reliable.

Another method of attempting to determine the orientation of the core tube and core relative to the drill pipe is to lower into the drill pipe a device which takes an impression of the base of the borehole and then to attempt to match that impression to the face of the core sample. This determination not only involves non-productive time for the drilling rig but again takes no account of possible twisting of the drill pipe. When one recognises also that the surface of which the impression is to be taken may be caved-in or formed of silt, the unreliability of such prior art methods is imediately apparent.

It is therefore an object of the present invention to provide a device for determining the angular orientation of a core sample relative to the axis of a borehole, whereby at least sane of the disadvantages of prior methods of carrying out this determination are reduced or eliminated.

The core orientation device according to the present invention comprises an elongated, generally cylindrical housing, attachment means to connect the lower end of said housing to the upper end of the inner tube of a core sampling device, an elongated body adapted for linear axial movement within said housing between a retracted position nearer to the upper end of said housing and an orientation indicating position nearer to the lower end of said housing, retention means to releasably retain said elongated body in said retracted position, a trigger device, adapted to pass down the associated drill string and to cause said retention means to release said elongated body, a multiplicity of apertures in the lower end of said generally cylindrical housing and disposed substantially uniformly around the axial centre of said housing end, and an indicator, mounted upon said elongated body for movement around the axis thereof in response to gravity and adapted to remain above said housing end when the body is in its retracted position and to engage one of said apertures when the body is in its orientation indicating position.

In use, the core orientation device of the invention is attached to the inner tube of the core sampler and remains there during the core sampling. When the sample has been drilled, the device is activated by dropping or lowering the trigger device down the bore hole and the elongated body is thereby released so that it may move from its retracted to its orientation indicating position, in which the indicator, having adopted a position in response to gravity, engages one of the apertures in the end of the housing and thereby indicates the orientation of the core tube relative to the axis of the borehole.It is a significant feature of the device according to the present invention that the indicator, when subsequently withdrawn with the core tube, gives a direct indication of the orientation of the core sample last taken and can therefore be relied upon, since there is no significant operation between the core sampling and the activation of the indicator device during which disorientation of the sample could occur.

The generally cylindrical housing within which the elongated body is movable may very conveniently be of the same diameter, or approximately so, as the diameter of the inner tube or core tube of the core sampler. To accommcdate the cylindrical housing, an outer housing, of the same external dimensions as the outer tube of the core sampler, may be interposed and secured in position between the outer tube and the drill string, whereby the rotational drive to the cutter bit is transmitted fran the drill string. The generally cylindrical housing is attached at its lower end to the upper end of the core tube, such that the housing and core tube remain stationary together or rotate together, independently of the drill string.The attachment means may simply be a transverse pin, which may extend through a suitable cylindrical socket on the housing and into or through the spindle of the core tube.

Within the housing, the elongated body is retained for movement between its retracted upper position and its lower position in which it indicates the orientation of the core sample. The body may be releasably retained in its retracted position by one of various possible retention means. For example, a ball or other sprung latch within a radial bore in the elongated body may normally, under the spring pressure, engage a suitable socket in the inner wall of the housing, such that the elongated body may be released by sufficient axial pressure to overcome the spring. In another form of the invention, the retention means comprises one or more latches, which engage the housing in the region of its upper edge and may be disengaged by radially inward pressure on the latch(es).

The nature of the trigger device depends, at least to sate extent, on the form of the aforementioned retention means. Thus, when the retention means takes the form of a sprung latch releasable by axial pressure on the housing, then the trigger device may be a, preferably solid, body, which may be dropped or lowered down the borehole past the fluid contents of the borehole and release the elongated body by striking its upper end. In a preferred form of the invention in which the retention means comprises latches engaging the upper end of the housing, the trigger device may be a hollow cylinder which may be dropped or lowered into a position in which it surrounds the latches and disengages then fran the housing by urgina them radially inwardly.

At the lower end of the housing, a multiplicity of apertures are disposed substantially uniformly around the axial centre of the housing. The apertures may be discrete holes through the end of the housing or they may be radially elongated slots, which may in turn be discrete or may be interconnected at the aforementioned axial centre. Since the function of the apertures is each to provide a position for potential engagement by the indicator (depending upon the orientation of the core tube), they are preferably disposed at equal angular intervals around the centre. The accuracy of the determination is determined to a substantial extent by the number of apertures, so preferably there are a large number of such apertures, for example between 20 and 30 such apertures (at angular intervals of 18 to 12 degrees of arc) or more.

At the lower end of the elongated body, the indicator is mounted in such a way that it can adopt a position relative to the axis of the body which is in response to gravitational force.

The core orientation device according to the invention is used in inclined boreholes so the position adopted by the indicator will reflect the direction of inclination of the borehole.

That is, the indicator will adopt a position in which it (or at least its centre of gravity) will lie below the axis of the borehole. To achieve this result, the indicator may take the form of a weighted pointer, mounted for rotation afrt the axis of the elongated body and with its centre of gravity eccentric to that axis. In another form, the indicator may be a pointer, mounted with one end on a universal joint at the bottoms end of the elongated body, such that it swings rather like a pendulum belaw the body.

It will be apparent that the indicator, which adopts a position reflecting the direction of inclination of the borehole while the elongated body is retracted, is simultaneously indicating the rotational position of the core tube relative to the axis of the borehole. Thus, when the elongated body is released to enable it to enter its lower position, the indicator is immobilised by engaging one of the apertures and thus the core orientation is indicated in a manner which will not be misdirected by the withdrawal of the core tube and core sample fram the borehole.Further security may be achieved by providing for the elongated body to became retained in its indicating position until after the core sample has been removed. For example, a sprung latch or the like may became engaged autanatically when the body moves into that position. Alternatively or in addition, the body may be urged into its indicating position by a spring, for example a coil spring, acting between the elongated body and the cylindrical housing.

Other optional features of the core orientation device according to the present invention, and the advantages obtainable by means of that device, will become apparent from the following description with reference to the accompanying drawings. The drawings illustrate, by way of example, two preferred embodiments of the device.In the drawings Fig. 1 is a schematic longitudinal sectional view of the first embodiment of the core orientation device, with the elongated body in the retracted position; Fig. 2 is a view corresponding to Fig. 1 with the elongated body in the core orientation-indicating position; Fig. 3 is a schematic transverse sectional view of the lower end of the generally cylindrical housing for that body; and Fig. 4 is a longitudinal sectional view of the second embodiment of the device.

The device is illustrated vertically for the sake of clarity but in practice the borehole in which the device is used will be somewhat inclined to the vertical. Thus the broken lines 10 and 11 in Fig. 1 indicate the true horizontal and vertical respectively.

The device shown in Figs. 1 to 3 is contained in an outer tubular housing 12 which is interposed between the lower end of the drill string 13 and the upper end of the outer tube 14 of the core sampler. Thus the tube 14 rotates with the drill string in the usual way and cuts a generally cylindrical core sample 15, which is taken up in conventional manner into the sampler inner tube 16. The inner tube 16 is supported in bearings 17 and normally remains stationary while the outer tube 14 rotates.

The core orientation device comprises a generally cylindrical housing 18, secured by a diametrical pin 19 to the spindle 20 of the inner tube or core tube 16, so that the housing 18 rotates only if the core tube rotates. Within the housing 18 is an elongated body 21 which, subject to the effect of further features referred to below, is free to move a short axial distance in the housing. Upon a downward axial extension 22 of the body 21, an eccentrically mounted indicator 23 is free to rotate. The indicator 23 carries a needle 24 which, by virtue of the rotation of the indicator under the influence of gravity towards its lowest position, always indicates the position of the lowest side of the body 21 and of the core tube 16 to which that body is attached.

A compression spring 25 urges the body 21 downwardly within the housing 18 but the body in initially retained against the spring pressure by a pair of radially outwardlysprung latches 26, which are pivoted at the upper end of the body 21 and engage the adjacent end of the housing 18. The lower end of the housing 18 has a ring 27 of numerous countersunk circular apertures (see Fig. 3), each of which apertures is of a sufficient diameter to receive at least the tip of the needle 24. The dimensions of the body 21 are such that, when the body is held in its retracted position illustrated in Fig. 1, the tip of the needle 24 is spaced by a short distance above the ring of apertures 27.

In use of the core orientation device, when a core sampling run has been completed, an elongated tubular trigger 28 is dropped or lowered down the drill string.

The trigger 28 is able to pass over the latches 26 and press them radially inwardly, so that they may adopt the position illustrated in Fig. 2. Release of the latches in this way allows the body 21 to move downwardly under the influence of the spring 25 until a shoulder 29 on the body is stopped by an annular landing seat 30 on the housing 18.

Movement of the body 21 in this way allows the needle 24 to enter the angularly nearest of the apertures in the ring 27 and to project out through the end of the housing 18. Thus when the core sampler and the orientation indicator are subsequently withdrawn from the borehole to enable the core sample to be analysed, the needle 24 gives an immediate visual indication of which side of the sample was rotationally lowest in the underground location fran which the sample was taken.

The second embodiment of the core orientation device according to the invention, which is illustrated in Fig. 4 of the accanpanying drawings, comprises a short elongated body 40, mounted in a top member 41 for limited axial movement within a generally cylindrical housing 42. A bottom member 43 closes the lower end of the housing 42 and connects the housing in use, by means of a pin inserted in a bore 44 in the bottom member, to the upper end of a core sampler inner tube (not shown).

The body 40 is illustrated in its retracted, upper position in Fig. 4. It is retained in that position by a pair of latches 45, which engage the upper end of the top member 41.

The body 40 may be released fran the retracted position by means of a tubular trigger 46, which is dropped or lowered down the drill string and thus encircles the latches 45 and urges them inwardly towards the axis of the device.

A pendulum 47 is suspended by a universal joint 48 fran the lower end of the body 40 and is free to adopt any orientation within the housing 42. In practice, since the device is used in a location within an inclined borehole, the pendulum will invariably be inclined in use (relative to the axis of the housing) towards the lowest point of the housing circumference.

The housing bottan member 43 has in its flat face towards the pendulum a ring of apertures 49. There are 36 such apertures, uniformly spaced at angular intervals of 10 degrees of arc. When the latches 45 are released by the trigger 46, the body 40 is urged downwardly by a spring 50 and a pin 51 on the end of the pendulum 47 enters the nearest of the apertures 49, thus indicating the direction of relative inclination of the pendulum 47 and housing 42 at that instant.

The pin 51 remains in the relevant aperture 49, under pressure fran the spring 50, while the device and core sample are being withdrawn fran the borehole.

While the invention has been exemplified by two particular embodiments illustrated in the drawings, the core orientation device according to the invention is suitable for use with a wide variety of core sampling systems, including wire line systems, if necessary after modification of the core barrel backend.

Claims

1. A device to enable the determination of the angular orientation of a core sample, which device comprises an elongated, generally cylindrical housing, attachment means to connect the lower end of said housing to the upper end of the inner tube of a core sampling device, an elongated body adapted for linear axial movement within said housing between a retracted position nearer to the upper end of said housing and an orientation indicating position nearer to the lower end of said housing, retention means to releasably retain said elongated body in said retracted position, a trigger device, adapted to pass down the associated drill string and to cause said retention means to release said elongated body, a multiplicity of apertures in the lower end of said generally cylindrical housing and disposed substantially uniformly around the axial centre of said housing end, and an indicator, mounted upon said elongated body for movement around the axis thereof in response to gravity and adapted to remain above said housing end when the body is in its retracted position and to engage one of said apertures when the body is in its orientation indicating position.

2. A core orientation device as claimed in claim 1, wherein the generally cylindrical housing is of approximately the same diameter as that of the inner tube.

3. A core orientation device as claimed in either of the preceding claims, wherein said generally cylindrical housing is accommodated within an outer housing, which outer housing is of the same external dimensions as the outer tube of the core sampling device and is interposed and secured in position between said outer tube and the drill string.

4. A core orientation device as claimed in any of the preceding claims, wherein the attachment means is a transverse pin, extending through a socket on the housing and into or through the spindle of the inner tube.

5. A core orientation device as claimed in any of the preceding claims, wherein the retention means comprises a sprung latch within a radial bore in the elongated body engaging a socket in the inner wall of the housing.

6. A core orientation device as claimed in claim 5, wherein the trigger device is a body able to be dropped down the boreholeto strike the upper end of the elongated body.

7. A core orientation device as claimed in any of claims 1 to 4, wherein the retention means comprises one or more latches, which engage the housing in the region of its upper end and may be disengaged by inward pressure in a direction which is radial relative to the housing.

8. A core orientation device as claimed in claim 7, wherein the trigger device is a hollow cylinder able to be dropped down the borehole to surround the latch or latches and urge it/them inwardly.

9. A core orientation device as claimed in any of the preceding claims, wherein the apertures are discrete holes or slots, disposed at equal angular intervals around the axial centre of the housing.

10. A core orientation device as claimed in any of the preceding claims, wherein the indicator is a weighted pointer, mounted for rotation about the axis of the elongated body and with its centre of gravity eccentric to that axis.

11. A core orientation device as claimed in any of claims 1 to 9, wherein the indicator is a pointer, mounted with one end on a univeral joint at the bottom end of the elongated body.

12. A core orientation device as claimed in any of the preceding claims, wherein the indicator is retained in its orientation-indicating position by a sprung latch which becames engaged automatically when the body moves into that position.

13. A core orientation device as claimed in any of claims 1 to 11, wherein the indicator is urged into its orientation-indicating position by a spring, acting between the elongated body and the generally cylindrical housing.

14. A core orientation device substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 to 3 of the accompanying drawings.

15. A core orientation device substantially as hereinbefore described with reference to, and as illustrated in, Fig. 4 of the accompanying drawings.