GB2123458A

GB2123458A - Improvements in or relating to apparatus for signalling within a borehole while drilling

Info

Publication number: GB2123458A
Application number: GB08317551A
Authority: GB
Inventors: Anthony William Russell; Michael King Russell
Original assignee: Sperry Sun Inc; NL Sperry Sun Inc
Current assignee: Sperry Sun Inc; NL Sperry Sun Inc
Priority date: 1982-07-10
Filing date: 1983-06-28
Publication date: 1984-02-01
Also published as: GB2123458B; GB8317551D0

Abstract

A down-hole signal transmitter for a mud pulse telemetry system comprises a flow constrictor defining a throttle orifice for the mud flow, a throttling member displaceable to vary the throughflow cross-section of the throttle orifice, and a pump 52 for displacing the throttling member against the mud flow in order to modulate the mud flow. The displacement of the throttling member is controlled by a hydraulic amplifier, comprising a main pressure relief valve 72 (Fig. 2) and a subsidiary control valve 74 (Fig. 3), and a solenoid 76 to which the output signal of a measuring instrument is supplied. When the main valve 72 is closed, the pump 52 displaces a ram 66 coupled to the throttling member upwardly. However, when the signal supplied to the solenoid 76 is such as to magnetically attract an armature 78, the control valve 74 is opened to conduct a small flow of oil between the pump input and the pump output, and this in turn causes the main valve 72 to open thus conducting a much larger flow of oil from the pump input to the pump output and allowing the throttling member to be displaced downwardly by the pressure of the mud flow. The power consumption required to modulate the mud flow with this arrangement is very low, and this is easily met by a down-hole electrical generator. <IMAGE>

Description

SPECIFICATION Improvements in or relating to apparatus for signalling within a borehole while drilling This invention relates to apparatus for signalling within a borehole while drilling, and is more particularly concerned with a down-hole signal transmitter for a mud-pulse telemetry system.

Various types of measurements-while-drilling (MWD) systems have been proposed for taking measurements within a borehole while drilling is in progress and for transmitting the measurement data to the surface. However to date only one type of system has enjoyed commercial success, that is the so-called mud-pulse telemetry system. In that system the mud stream, which passes down the drill string to the drill bit and then back up the annular space between the drill string and the bore wall with the object of lubricating the drill string and carrying away the drilling products, is used to transmit the measurement data from a down-hole measuring instrument to a receiver and data processor at the surface.This is achieved by modulating the mud pressure in the vicinity of the measuring instrument under control of the electrical output signal from the measuring instrument, and sensing the resultant mud-pulses at the surface by means of a pressure transducer.

The applicants' British Patent Specifications Nos. 2,082,653A and 2,087,951A disclose such a system in which the measuring instrument is powered by an electrical generator driven by an impeller disposed in the mud flow and magnetically coupled to the generator to apply driving torque thereto. Such an arrangement disposes of the need for batteries down-hole and does not require the use of a fault-prone rotating seal. However, very considerable restraints are imposed on the construction of such a system in view of the need for compactness and the ability to operate down-hole in a hostile environment.

It is an object of the invention to provide a generally improved down-hole signal transmitter which is compact and has low power consumption.

According to the invention there is provided a down-hole signal transmitter for a mud-pulse telemetry system, comprising a flow constrictor defining a throttle orifice for the mud flow passing along a drill string, a throttling member displaceable with respect to the throttle orifice to vary the throughflow cross-section of the throttle orifice, a pump for displacing the throttling member against the mud flow, and valve means switchable between a first state in which the throttling member is displaceable by the output pressure of the pump against the mud flow and a second state in which said output pressure is relieved so as to enable the throttling member to be moved in the direction of the mud flow by the pressure of the mud flow acting on the throttling member, whereby the pressure of the mud flow may be modulated.

Such an arrangement is particularly convenient as it reliably produces the required mud pulses for transmitting measurement data to the surface at low power consumption, whilst being compact and of relatively simple construction.

The invention also provides a down-hole signal transmitter for a mud-pulse telemetry system, comprising a flow constrictor defining a throttle orifice for the mud flow passing along a drill string, a throttling member displaceable with respect to the throttle orifice to vary the throughflow crosssection of the throttle orifice, actuating means for displacing the throttling member against the mud flow, and change-over means switchable between a first state in which the throttling member is displaceable by the actuating means against the mud flow and a second state in which the throttling member is movable in the direction of the mud flow by the pressure of the mud flow acting on the throttling member, whereby the pressure of the mud flow may be modulated.

Furthermore the invention provides a downhole signal transmitter for a mud-pulse telemetry system, comprising a flow constrictor defining a throttle orifice for the mud flow passing along a drill string, a throttling member displaceable with respect to the throttle orifice to vary the throughflow cross-section of the throttle orifice, and control means for displacing the throttling member to modulate the mud pressure, wherein the control means incorporates a hydraulic amplifier comprising a main valve and a subsidiary valve for controlling a main flow of fluid through the main valve by acting on a subsidiary flow of fluid of relatively low magnitude.

In order that the invention may be more fully understood, a preferred form of down-hole signal transmitter in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through an upper part of the transmitter; Figure 2 is a longitudinal section through an intermediate part of the transmitter, with the outer duct omitted; and Figure 3 is a longitudinal section through a lower part of the transmitter, with the outer duct omitted.

The signal transmitter 1 illustrated in the drawings is installed in use within a non-magnetic drill collar, and is coupled to a measuring instrument disposed in an instrument pressure casing also installed within the drill collar, immediately below the transmitter 1. The drill collar is disposed at the end of a drill string within a borehole during drilling, and the measuring instrument may serve to monitor the inclination of the borehole in the vicinity of the drill bit during drilling, for example. The signal transmitter 1 serves to transmit the measurement data to the surface, in the form of pressure pulses, by modulating the pressure of the mud which passes down the drill string.The transmitter 1 is formed as a self-container unit and is installed within the drill collar in such a manner that it may be retrieved in the event of instrumentation failure for example, by inserting a wireline down the drill string and engaging the wireline with a fishing neck (not shown) on the transmitter, for example by means of a per se known gripping device on the end of the wireline, and drawing the transmitter up the drill string on the end of the wireline.

Referring to Figure 1, in which an upper part of the transmitter is shown, the transmitter 1 includes a duct 2 provided, at its upper end, with an annular flow constrictor 4 defining a throttle orifice 6 for the mud flow passing down the drill string in the direction of the arrow 8. Within the duct 2 is an elongate casing 10 bearing at its upper end, in the vicinity of the throttle orifice 6, a throttling member 12 which is displaceable with respect to the casing 10 in the direction of the axis of the duct 2 to vary the throughflow cross-section of the throttle orifice 6.The throttling member 12 is provided with a shaft 14 which extends into the casing 10, the space within the casing 10 being filled with hydraulic oil in order to ensure hydrostatic pressure balance and being sealed at its upper end by a Viton diaphragm 1 6 extending between the inside wall of the casing 10 and the shaft 14. The casing 10 is rigidly mounted within the duct 2 by three upper support webs 18 and three lower support webs (not shown) extending radially between the casing 10 and the duct 2, so as to provide an annular gap between the casing 10 and the duct 2 for mud flow.

Figures 2 and 3 show intermediate and lower parts of the transmitter respectively in which the duct 2 has been omitted. It should be appreciated that the transmitter also includes further nonillustrated parts between the upper part and the intermediate part, between the intermediate part and the lower part and below the lower part respectively. An annular impeller 22 having a series of blades 24 distributed around its periphery and angled to the mud flow surrounds the casing 10, as shown in Figures 2 and 3, and is carried on a shoulder 26 of the casing 10 by means of a filled PTFE (polytetrafluoroethylene) thrust bearing 28. The blades 24 are mounted on a copper drive ring 32.A rare earth magnet assembly 34 is carried by an annular shaft 36 rotatably mounted within the casing 10 by means of bearings 38, and incorporates six Sm Co (samarium-cobalt) magnets distributed about the periphery of the shaft 36. Three of the magnets have their North poles facing radially outwardly and a further three of the magnets, alternating with the previous three magnets, have their South poles facing radially outwardly. As the impeller 22 rotates in the mud flow, eddy currents will be induced in the copper drive ring 32 by the intense magnetic field associated with the six Sm Co magnets, and the magnet assembly 34 and hence the shaft 36 will be caused to rotate with the impeller 32 by virtue of the interaction between the magnetic field associated with the magnets and the magnetic field associated with the eddy currents induced in the drive ring 32.

The annular shaft 36 drives a rotor 42 of an electrical generator 44 (Figure 3) for supplying power to the measuring instrument. The generator 44 is a three-phase a.c. generator comprising a wound stator 46 having six poles equally spaced around the axis of the generator 44, and the rotor 42 incorporates eight Sm Co magnets 48 also equally spaced around the axis of the generator 44, four of the magnets 48 having their North poles facing the stator 46 and a further four of the magnets 48, alternating with the previous four magnets 48, having their South poles facing the stator 46. In addition the annular shaft 36 drives a hydraulic pump 52 (Figure 2) by way of an angled swashplate 54 and an associated piston thrust plate 56.

The hydraulic pump 52 comprises eight cylinders 58 extending parallel to the axis of the casing 10 and arranged in an annular configuration, and a respective piston 60 associated with each cylinder 58. The lower end of each piston 60 is permanently biased into engagement with the thrust plate 56 by a respective piston return spring 62, so that rotation of the swashplate 54 with the shaft 36 will cause the pistons 60 to axially reciprocate within their cylinders 58, the eight pistons 60 being reciprocated cyclically so that, when one of the pistons is at the top of its stroke, the diametrically opposing piston will be at the bottom of its stroke and vice versa. Each cylinder 58 is provided with a non-return valve 63 at its upper end, and each piston 60 is provided with a bore 64 incorporating a further non-return valve 65.The valve 65 opens towards the bottom of each stroke of the piston 60 to take in hydraulic oil, and the valve 63 opens towards the top of each stroke of the piston 60 to output hydraulic oil to the lower side of a ram 66 disposed within a cylinder 68. The outputs of the cylinders 58 are supplied to the ram 66 cyclically, and the ram 66 is coupled to the shaft 14 of the throttling member 12 by an output shaft 70, so that the throttling member 1 2 may be displaced upwardly by the pump 52 to decrease the throughflow cross-section of the throttle orifice 6.

Furthermore, as the ram 66 reaches the top of its stroke within the cylinder 68, pressure-equalising apertures 69 in an inner sleeve 71 place the upper and lower parts of the cylinder 68 in fluid communication and the pressure is equalised on the two sides of the ram 66.

The throttling member 12 may be subsequently displaced downwardly, to increase the throughflow cross-section of the throttle orifice 6, under pressure of the mud flow acting on the throttling member 12 when the hydraulic pressure acting on the lower side of the ram 66 is relieved.

This pressure relief is achieved by feeding back the output of the pump 52 directly to the input by way of a central duct 92 under control of a hydraulic amplifier which comprises a main pressure relief valve 72 (Figure 2) and a subsidiary control valve 74 (Figure 3) interconnected by a duct 90. The control valve 74 is operable by an actuator in the form of a solenoid 76 under control of the output of the measuring instrument.

In order to show the internal construction of the control valve 74, this valve is shown in Figure 3 with the lower half of the valve, as seen in the drawing, sectioned along the same plane as the rest of the drawing, but with the upper half of the valve sectioned along a longitudinal plane at right angles to the aforementioned plane. Thus the valve 74 incorporates an axial conduit 77 which opens into two branch conduits 91 which are symmetrically arranged about the longitudinal axis but only one of which is visible in the figure in view of the fact that the plane along which the upper half of the valve is sectioned is at right angles to the plane in which the branch conduits 91 are disposed. The two branch conduits 91 lead into an axial blind bore 79 which is terminated by a valve seating 83 within which a valve ball 81 is seated.The ball 81 is acted upon by a generally U-shaped member 82 which incorporates a guide rod 85 extending into a guide bore 85A and two hollow arms 82A extending through bores 82B.

The bores 828 are symmetrically arranged about the longitudinal axes but only one of these is visible in the drawing in view of the fact that the plane in which the bores 82B are disposed is at right angles to the plane along which the lower half of the valve 74 is sectioned. The arms 82 are connected by screws 82C to an armature 78 which is mounted on a guide pin 78A so that the armature 78 and the U-shaped member 82 are capable of limited axial movement with respect to the remainder of the valve 74.

When the form of the output signal from the measuring instrument is such as to cause the solenoid 76 to magnetically attract the armature 78, the armature 78 and the U-shaped member 82 are in the position shown in the figure with the U-shaped member 82 acting on the ball 81 to keep the valve 74 closed. Although not shown in the drawing a slight gap exists between the armature 78 and an end plate 80 of the solenoid 76 in this position so as to ensure that the ball 81 is firmly held against its seating 83 when the valve 74 is in the closed position.

When the form of the output signal from the measuring instrument changes so as to break the magnetic attraction between the armature 78 and the end plate 80 of the solenoid 76, the U-shaped member 82 is axially displaced by the action of the ball 81 of the control valve 74 being raised from its seating 83 by fluid pressure, thereby opening the control valve 74. It will be appreciated that the degree to which the ball 81 is lifted off its seating 83 is limited by the travel of the armature 78.This has the effect of enabling a small flow of oil from the pump output to the pump input, this flow passing from the duct 92 along a bore 87 through a valve member 88 of the pressure relief valve 72 (see Figure 2) and through a constriction 86 within the bore 87 and to the control valve 74 by way of a duct 90, the return flow to the pump input being by way of the annular space 99 surrounding the duct 90.

The action of initiating a small flow of oil through the constrictor 86 causes the valve member 88 to be displaced downwardly against the action of a spring 89, by virtue of the pressure differential which is established across the pressure relief valve 72 by the flow of oil through the constrictor 86. This results in apertures 94 in the form of spark-eroded slits in an outer sleeve 95 of the valve 72 being uncovered by the valve member 88, thus placing the duct 92, which incorporates an insert 93, in direct fluid communication with the pump input and initiating a much larger flow of oil from the pump output to the pump input by way of the duct 92 and the apertures 94.It will be appreciated from what has been said above that a main flow of oil through the pressure relief valve 72 is controlled by the control valve 74 acting on a subsidiary flow of oil of relatively low magnitude, so that the two valves 72 and 74 act as a hydraulic amplifier controlled by the output of the measuring instrument.

When the pressure relief valve 72 is opened the output of the pump 52 is fed back directly to the pump input by way of the duct 92 and the apertures 94 in the outer sleeve 95 of the valve 72, and the hydraulic pressure acting on the lower side of the ram 66 is relieved. This enables the ram 66 to be displaced downwardly within the cylinder 68 by the mud flow acting on the throttling member 12 with oil being supplied to the upper part of the cylinder 68 by way of an aperture 96 in the sleeve 71, and an annular passage 97 surrounding the sleeve 71.

When the form of the output signal from the measuring instrument again changes in such a manner that the armature 78 is attracted to the end plate 80 of the solenoid 76, the U-shaped member 82 is axially displaced against fluid pressure so as to reseat the ball 81 of the control valve 74 within its seating 83, thus closing the control valve 74 and stopping the flow of oil through the constriction 86 in the valve member 88 of the pressure relief valve 72. This causes the valve member 88 to be displaced upwardly by the spring 89, so that the apertures 94 are again covered and the valve 72 is closed, thereby preventing feedback of oil directly from the output to the input of the pump 52. Thus the full output of the pump 52 is again applied to the underside of the ram 66 and the ram 66 is displaced upwardly.

it will be appreciated therefore that, if the measurement data from the measuring instrument is arranged to suitably vary the current passing through the solenoid 76 so as to intermittently attract the armature 78 to the end plate 80 of the solenoid 76, the throttling member 12 will be displaced in such a manner as to modulate the pressure of the mud flow upstream of the throttle orifice 6 in dependence on the measurement data.

Thus a series of pressure pulses corresponding to the measurement data will travel upstream in the mud flow and may be sensed at the surface by a pressure transducer in the vicinity of the output of the pump generating the mud flow.

The provision of the hydraulic amplifier and the fact that the direction of movement of the ram 66 is controlled by a small flow of oil through the control valve 74 means that the power consumption of the solenoid 76 is very low, so that the total power requirement of the measuring instrument is easily met by the electrical generator 44.

Claims

1. A down-hole signal transmitter for a mudpulse telemetry system, comprising a flow constrictor defining a throttle orifice for the mud flow passing along a drill string, a throttling member displaceable with respect to the throttle orifice to vary the throughflow cross-section of the throttle orifice, actuating means for displacing the throttling member against the mud flow, and change-over means switchable between a first state in which the throttling member is displaceable by the actuating means against the mud flow and a second state in which the throttling member is movable in the direction of the mud flow by the pressure of the mud flow acting on the throttling member, whereby the pressure of the mud flow may be modulated.

2. A transmitter according to claim 1, wherein the actuating means is a pump for displacing the throttling member against the mud flow.

3. A transmitter according to claim 2, wherein the change-over means comprises valve means switchable between a first state in which the throttling member is displaceable by the output pressure of the pump against the mud flow and a second state in which said output pressure is relieved so as to enable the throttling member to be moved in the direction of the mud flow by the pressure of the mud flow acting on the. throttling member

4. A transmitter according to claim 2 or 3, wherein the valve means comprises a pressure relief valve which, when open, couples the output of the pump directly to the pump input.

5. A transmitter according to claim 2,3 or 4, wherein the valve means comprises a hydraulic amplifier incorporating a main, pressure relief valve and a subsidiary, control valve for controlling a main flow of fluid through the main valve by acting on a subsidiary flow of fluid of relatively low magnitude.

6. A transmitter according to claim 5, wherein the pressure relief valve is adapted to open when the control valve is opened.

7. A transmitter according to claim 6, wherein the pressure relief valve comprises a spring-biased valve member having a bore extending therethrough for the subsidiary flow of fluid towards the control valve and movable by pressure of fluid acting against the spring force when the control valve is opened, to open the pressure relief valve.

8. A transmitter according to claim 7, wherein the valve member is disposed within an outer sleeve having at least one aperture extending therethrough, and is movable, when the control valve is opened, between a first position in which the or each aperture is covered by the valve member and a second position in which the or each aperture is uncovered by the valve member to enable the main flow of fluid therethrough.

9. A transmitter according to any preceding claim, wherein an electrical actuator is provided for controlling the change-over means in response to an electrical output signal from a measuring instrument.

10. A transmitter according to claim 9, wherein the electrical actuator is a solenoid.

11. A transmitter according to claim 10 when appended directly or indirectly to any one of claims 5 to 8, wherein an actuating member is movable by being magnetically attracted by the solenoid, when an appropriate switching signal is applied to the solenoid, in order to close the control valve.

12. A transmitter according to claim 2 or any one of claims 3 to 11 when appended directly or indirectly to claim 2, wherein a ram is provided for displacing the throttling member upwardly when the output pressure of the pump is applied to the underside of the ram, and at least one pressureequalising aperture serves to piace the upper side of the ram in fluid communication with the lower side of the ram when the ram approaches the top of its stroke.

13. A transmitter according to claim 2 or any one of claims 3 to 12 when appended directly or indirectly to claim 2, wherein the pump incorporates a plurality of cylinders having pistons arranged to be driven cyclically, and a valve arrangement for discharging the output of each cylinder at an appropriate point in the stroke of the associated piston.

14. A transmitter according to claim 13, wherein each piston has a bore extending therethrough for connecting the input of the pump to the associated cyclinder, and a further valve arrangement is provided for supplying an input to each cylinder by way of the bore in the associated piston at an appropriate point in the stroke of the piston.

1 5. A transmitter according to claim 2 or any one of claims 3 to 14 when appended directly or indirectly to claim 2, wherein the pump is disposed in a mud-free environment within a casing and is arranged to be driven by an impeller positioned in the mud flow passing along the drill string and magnetically coupled to the pump to impart driving torque thereto.

1 6. A transmitter according to claim 1 5, wherein an electrical generator disposed in a mudfree environment within the casing is also arranged to be driven by the impeller.

17. A down-hole signal transmitter for a mudpulse telemetry system, comprising a flow constrictor defining a throttle orifice for the mud flow passing along a drill string, a throttling member displaceable with respect to the throttle orifice to vary the throughflow cross-section of the throttle orifice, and control means for displacing the throttling member to modulate the mud pressure, wherein the control means incorporates a hydraulic amplifier comprising a main valve and a subsidiary valve for controlling a main flow of fluid through the main valve by acting on a subsidiary flow of fluid of relatively low magnitude.

18. A down-hole signal transmitter for a mudpulse telemetry system, substantially as hereinbefore described with reference to the accompanying drawings.