GB2334732A

GB2334732A - Downhole telemetry system

Info

Publication number: GB2334732A
Application number: GB9820078A
Authority: GB
Inventors: Jonathan Symons
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-09-19
Filing date: 1998-09-16
Publication date: 1999-09-01
Also published as: GB9720024D0; GB9820078D0

Abstract

A downhole tool 10, 10a, of the well-logging/telemetry/drift/survey type. A downhole apparatus 5,5a employing the tool 10,10a, and a method of surveying a borehole 15,15a using the tool 10,10a is also disclosed. The tool 10, Fig 1 generates a pressure pulse(s) in a fluid contained in the borehole 15, the tool comprising means for measuring a characteristic of the borehole 15, such as inclination, and means for generating a pressure pulse in the fluid representative of the measure characteristic by altering a fluid throughflow area in the borehole 15. The tool has sleeves 105, 110 each having apertures 115, 120 therein. The apertures are aligned or not aligned so that pressure pulses can be produced. Movement of one of the sleeves is by a solenoid controlled by a measuring means. The movement may be via a ratchet mechanism. The outer sleeve may have blades thereon so that fluid flow can produce rotation of the sleeve.

Description

IMPROVEMENTS IN OR RELATING TO DOWNHOLE TOOLS The present invention relates to an improved downhole tool, and in particular, though not exclusively, to an improved well-logging/telemetry/drift/survey tool. The invention also relates to an improved downhole apparatus using such a tool, and further to an improved method of surveying a borehole of an oil/gas well using such a tool.

In the oil/gas industry, boreholes are drilled through layers of soil and rock to extract oil and/or gas from reservoirs or seams. To comply with safety regulations and to monitor the inclination of the borehole, among other reasons, the hole may be surveyed periodically during drilling. It is important, for example, that the location of the drill bit relative to the mouth of the hole is known so that a relief well can be drilled in the event of a blow-out.

It is presently known to measure the inclination of a drilled hole using one of four types of devices. The first type of device is a drift indicator, the second is a magnetic single shot device, the third is a mechanical measuring-while-drilling device (MMWD), and the fourth is a directional measuring-while-drilling device (DMWD).

The first two types of device (the drift indicator and the magnetic single shot device) have been used for more than 50 years. They require a person drilling a well to lower the device into the hole, wait for the device to perform a reading, raise the device from the hole, and then check the measurement taken by the device. Frequently, a second measurement is required to confirm the accuracy of the first measurement. These devices are very expensive to use because the drilling procedure is halted while the device is being used to survey the hole.

The third type of device (the MMWD) has been used for more than 40 years. It is located above the drill bit in a purpose-built collar. This device uses a swinging mechanical pendulum to measure the inclination of the device with reference to the vertical plane. This inclination reading is linked to a mechanically activated plunger which, when activated, produces a pulse which is transferred to the surface. Each pulse represents 0.5 degrees of inclination. This provides a measurement of the verticality (the downhole inclination) of the hole.

The fourth type of device (the DMWD) is similar to the MMWD but conveys information about the inclination of the hole by means of binary code rather than by mechanically activated pressure pulses. At the drilling console, the code is received, decoded and the results are displayed to the drill operators. The DMWD has a number of disadvantages associated with it. For example, it usually needs at least one trained engineer to operate it correctly and it is more expensive than the other devices.

Presently, the most commonly used device is the MMWD device. It is relatively inexpensive to run and does not require an additional trained engineer to operate it.

However, these devices are not very accurate or reliable.

They are also very expensive to make because they are housed in collars which can cost more than the combined cost of the component parts inside them. A further disadvantage of these devices is that they are sometimes lost downhole, that is, they have to be abandoned, because e.g. the bottom hole assembly becomes stuck.

It is an object of at least one aspect of the present invention to obviate or mitigate one or more of the above mentioned disadvantages in the prior art.

Advantages of one or more embodiments of a tool according to the present invention over known tools include: a) increased accuracy; b) increased reliability; c) retrievable, e.g. by wireline, e.g., in the event of breakage downhole or loss of the Bottom Hole Assembly (BHA); d) reduced possibility of Lost in Hole (LIH); e) portability (e.g. helicopter moveable).

According to a first aspect of the present invention there is provided a downhole tool for generating a pressure pulse(s) in a fluid contained in a borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole.

The means for generating a pressure pulse may include actuation means for controlling throughflow area varying means, such that, in use, the fluid throughflow area is changed to create a fluid pressure change.

Advantageously, the pressure pulse generating means may comprise a first tubular body.

Advantageously also, the pressure pulse generating means may comprise a second tubular body, one of the bodies being located within the other.

Advantageously each body provides at least one hole therethrough.

One of the bodies may be moveable relative to the other body from first to second position(s), wherein in the/a first position respective holes in the first and second bodies are not in alignment such that the tool is closed and fluid cannot pass therethrough, and wherein in the/a second position respective holes in the first and second bodies are in alignment such that the tool is opened and fluid can pass therethrough.

Thus by controllably moving the first and second bodies between the first and second positions a pressure pulse(s) can be generated in the fluid.

A first position wherein the tool is closed may comprise a dormant position, wherein the tool is not in use.

In this case a pressure reduction is caused by using the tool causing a negative pressure pulse.

Alternatively, a second position wherein the tool is opened may comprise a dormant position, wherein the tool is not in use.

In this case a pressure increase is caused by using the tool causing a positive pressure pulse.

Said one of the bodies may be rotatable relative to the other body about a longitudinal axis.

Alternatively/further, said one of the bodies may be moveable relative to the other body along a longitudinal axis.

The first and second bodies may be retained in association with one another by first and second bearings.

The actuating means may include a solenoid controlled by the measuring means.

The solenoid may provide a piston associated with a ratchet mechanism for controlling rotation of one of the first or second bodies.

The ratchet mechanism preferably controls rotation of the first, outermost body.

In a first embodiment the first body may carry one or more blades on an outermost surface thereof, which blade(s) tend to cause the first body to rotate when, in use, fluid passes thereby downhole.

In said first embodiment the one or more blades may be spiral blades.

In a second embodiment the first body may be provided with one or more recesses (flutes) and/or blades (impellers) on an outermost surface thereof, wherein, in use, when impinged upon by a rotational fluid flow the recess(es) and/or blades tend to cause the first body to rotate.

Preferably, each recess is provided substantially longitudinally on the first body.

Preferably a plurality of recesses are provided substantially equally spaced circumferentially upon the first body.

Advantageously the second body carries a nose cone, the nose cone having one or more holes formed therein.

In this way, in use, fluid passing into the tool when in the second position via the holes formed in the first and second bodies can exit the tool via the hole(s) in the nose cone.

The fluid may be a drilling fluid.

Advantageously, the characteristic of the borehole may be the inclination of the borehole from the vertical.

The time for which the pressure pulse is generated may be indicative of the measured characteristic, eg the deviation of the borehole from the vertical.

The means for measuring may be a strain gauge, inclinometer or accelerometer.

Where a strain gauge is provided, the gauge may be an electronic strain gauge.

Alternatively, inclination may be measured using a swinging pendulum, such as in the MMWD tool mentioned above.

Advantageously, the tool is of a retrievable type.

Advantageously further, the tool may be retrieved by wireline.

The at least one hole in at least one of each body may be longitudinally elongate.

According to a second aspect of the present invention there is provided a borehole survey or logging apparatus comprising: a downhole tool for generating a pressure pulse(s) in a fluid contained in the borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole; and means for detecting the pressure pulse.

The detection means may be provided on surface.

The detection means may include a pressure sensor.

The detection means may also include means for analysing the pressure pulse, so as to determine the measured characteristic.

The borehole logging apparatus may further comprise a baffle carried within a drillstring.

The baffle may include means for receiving the tool.

The baffle may further comprise one or more fluid throughflow orifices.

The baffle may be carried within the drillstring at or near a lowermost end thereof, e.g. at or near a drill bit.

In one embodiment the apparatus may include means for generating a rotational fluid flow around at least part of the tool.

Advantageously, the rotational fluid flow is a spiral or helical type flow down the borehole.

Preferably, the means for generating a rotational fluid flow comprises one or more baffles.

The one or more baffles may be distributed around the tool.

Preferably, the one or more baffles may be provided on a third tubular body, which body is securedly received within an upper portion of a fourth tubular body.

In such an embodiment the third and fourth tubular bodies surround the tool.

Preferably also, the fourth tubular body provides a mid portion having a reduced internal diameter.

Preferably further, the first body is provided with one or more recesses on an outermost surface thereof, facing the mid portion of the fourth tubular body.

Advantageously, a lowermost portion of the fourth tubular body is connected to the baffle. In this way the fourth tubular body upstands dependently from the baffle.

According to a third aspect of the present invention there is provided a method of surveying a borehole comprising: providing a downhole tool for generating a pressure pulse(s) in a fluid contained in the borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole; providing means for detecting the pressure pulse; measuring the characteristic; generating the pressure pulse; and detecting the pressure pulse.

Advantageously the time length of the pressure pulse is related to the value of the measured characteristic.

Advantageously also, so that the pressure pulse detection means detects when a measurement has been taken the pressure pulse relating thereto may be prefaced by a predetermined train of pressure pulses of selected duration and/or magnitude, and/or followed by a predetermined further train of pressure pulses of selected duration and/or magnitude.

According to a fourth aspect of the present invention there is provided a downhole tool for generating a pressure pulse(s) in a fluid contained in a borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid, the time for which the pressure pulse is generated being indicative of the measured characteristic.

According to a fifth aspect of the present invention there is provided a borehole survey apparatus including a tool according to the fourth aspect.

According to a sixth aspect of the present invention there is provided a method of surveying a borehole comprising providing and using a tool according to the fourth aspect.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, which are: Fig. 1 a schematic sectional side view of a first embodiment of a borehole survey/logging apparatus having a tool according to a first embodiment of the present invention within a borehole; Figs. 2(a) and (b) cross-sectional views of the tool of Fig. 1 along line A-A to an enlarged scale; Figs. 3(a) and (b) a partial cross-sectional views of the apparatus of Fig. 1; Fig. 4 a timing diagram showing the pressure detected by a pressure detecting means forming part of the apparatus of Fig. 1; Fig. 5 a more detailed schematic side view of the tool of Fig. 1; Fig. 6 a side view of a first body comprising part of the tool of Fig. 1; Fig. 7 a cross-sectional side view of the first body of Fig. 6; Figs. 8(a), (b) and (c) a series of cross-sectional views of the first body of Fig. 6 along lines A-A, B B, and C-C, respectively.

Fig. 9 a view from the top of the first body of Fig.

6; Fig. 10 a cross-sectional side view of a second body comprising part of the tool of Fig. 1; Figs. 11(a), (b) and (c) a series of cross-sectional views of the second body of Fig. 10 along lines A-A, B-B, and C-C, respectively; Fig. 12 a cross-sectional side view of a nose cone comprising part of the tool of Fig. 1; Fig. 13 a view from the bottom of the nose cone of Fig. 12; Figs. 14(a), (b), (c) and (d) a series of views of a cam ring being part of the tool of Fig. 1 comprising a view from a bottom side, a view from a top side, a cross-sectional side view, and a developed view; Figs. 15tea) and (b) a top view and a cross-sectional side view of a first, lower bearing comprising part of the tool of Fig. 1; Figs. 16 (a) and (b) a top view and a cross-sectional side view of a second, upper bearing comprising part of the tool of Fig. 1; Fig. 17 a side view of a solenoid piston comprising part of the tool of Fig. 1; Fig. 18 a partial side view of the solenoid piston of Fig. 17 to an enlarged scale; Fig. 19 a side view of a first, lower stop bar carried by the piston of Fig. 17; Fig. 20 a side view of a second, upper stop bar carried by the piston of Fig. 17; Fig. 21 a side view of the piston of Fig. 17, first, lower stop bar of Fig. 19, and second, upper stop bar of Fig. 20 in an assembled state; Fig. 22 a view from the bottom of a baffle comprising part of the apparatus of Fig. 1; Fig. 23 a cross-sectional side view along line A-A of the baffle of Fig. 22; Fig. 24 a cross-sectional side view along line B-B of the baffle of Fig. 22; Fig. 25 a view from the bottom of a baffle retaining ring comprising part of the apparatus of Fig. 1; Fig. 26 a cross-sectional side view along line A-A of the ring of Fig. 25; Fig. 27 a part cross-sectional side view of part of the tool of Fig. 1; Fig. 28 a schematic diagram of downhole electronic components of the tool of Fig. 1; Fig 29 a schematic diagram of electronic components of the pressure detecting means of the apparatus of Fig.

1; Fig. 30 a sectional side view of part of a second embodiment of a borehole survey/logging apparatus having a tool according to a second embodiment of the present invention within a borehole; Fig. 31 a side view of a first body comprising part of the tool of Fig. 30; Fig. 32 a cross-sectional side view of the first body of Fig. 31; Figs. 33(a), (b) and (c) a series of cross-sectional views of the first body of Fig. 31 along lines A-A, B-B, and C-C, respectively; Fig. 34 a side view of a second body comprising part of the tool of Fig. 30; Fig. 35 a cross-sectional side view of the second body of Fig. 34; Figs. 36(a), (b) and (c) a series of cross-sectional views of the second body of Fig. 34 along lines A-A, B-B, and C-C, respectively; Figs. 37(a), (b) and (c) a series of views of an upper cam ring being part of the tool of Fig. 30 comprising a view from a top, a cross-sectional side view, and a developed view; Figs. 38(a). (b) and (c) a series of views of a middle cam ring being part of the tool of Fig. 30 comprising a view from a top, a cross-sectional side view, and a developed view; Figs. 39(a), (b) and (c) a series of views of a lower cam ring being part of the tool of Fig. 30 comprising a view from a top, a cross-sectional side view, and a developed view; Fig. 40 a view from the bottom of a baffle comprising part of the apparatus of Fig. 30; Fig. 41 a cross-sectional side view along line D-D of the baffle of Fig. 40; Figs. 42(a), (b), (c) and (d) a series of views of a third tubular body comprising part of the apparatus of Fig.

30 comprising a side view, a cross-sectional side view, a top view, and a partial developed view.

Figs. 43(at and (b) a cross-sectional side view and a top view of a fourth tubular body comprising part of the apparatus of Fig. 30.

Referring to Figs 1 to 29, and initially to Fig. 1, there is illustrated a first embodiment of a borehole survey apparatus, generally designated 5, including a first embodiment of a downhole tool 10 for generating pressure pulses in a fluid contained in a borehole 15. This first embodiment of the tool 10 described herein is particularly advantageous in operation in the drilling of vertical boreholes since this embodiment of the tool 10 measures deviation of a borehole 15 from the vertical. The tool 10 is further particularly advantageous being retrievable, e.g. by wireline.

The tool 10 comprises means for measuring a characteristic of the borehole - in this embodiment deviation from the vertical - and means for generating a pressure pulse in the fluid representative of the measured characteristic which will be described hereinafter in greater detail.

The time for which the pressure pulse is generated is indicative of the deviation of the borehole 15 from the vertical.

The apparatus 5 further comprises means 20 for detecting the pressure pulse; the detection means being provided on surface. The detection means 20 include a pressure sensor 25. The detection means 20 also include means 30 for analysing the pressure pulse so as to determine the measured characteristic.

The apparatus 5 further comprises a baffle 35 carried within a drill string 40. The baffle 35 includes means for receiving the tool 10 comprising a substantially centrally formed aperture 36 thereon. The baffle 35 provides one or more fluid throughflow orifices 45.

As can be seen from Fig. 1, the main baffle 35 is carried within the drillstring 40 at or near a lowermost end 46 thereof, at or near a drill bit 50.

In use, the fluid - normally drilling fluid (drilling mud) - will in a conventional manner be pumped by means (not shown) down an internal bore 55 of the drillstring 40 through the baffle 35 - and optionally controllably through the tool 10 as hereinafter described - thence through drill bit 50 and up an annular passage 60 (in the direction of the arrows) formed between an outermost surface of the drillstring 40 and borehole 15.

Referring now to Fig. 5 in this embodiment of the tool 10, the means for measuring a characteristic of the borehole comprises a strain gauge inclinometer/magnetometer 65, while the means for generating a pressure pulse in the fluid includes actuation means in the form of a solenoid activator 70 including a ratchet mechanism and a throughflow area varying means in the form of a pulsar module 75. The tool 10 further includes upper and lower centralisers 80,85, along with a battery module 90, capacitor stack 95, CPU memory module 100, and generator 105.

The strain gauge 65 may be an electronic strain gauge. The means for measuring may alternatively be an accelerometer. Alternatively, inclination may be measured using a swinging pendulum, such as in the MMWD mentioned above.

The solenoid activator 70 and pulsar module 75 will now be described in greater detail with reference to Figs. 2(a) to 20 and Fig. 27. The pulsar module 75 comprises first and second elongate tubular bodies 105, 110, one of the bodies 110 being located within the other body 105, and one of the bodies 105 being rotatable relative to the other body 110 about a longitudinal axis.

Each body 105, 110 provides a plurality of holes 115, 120 therethrough. The first body 105 is rotatable relative to the second body 110 from first to second and back to first position(s), wherein in a first position respective holes 115, 120 in the first and second bodies 105, 110 are not in alignment such that the tool 10 is closed and fluid cannot pass therethrough, and wherein in a second position respective holes 115, 120 on the first and second bodies 105, 110 are in alignment such that the tool 10 is opened and fluid can pass therethrough.

The first and second bodies 105, 110 are retained in longitudinal rotatable relation with one another by first and second bearings 125, 130.

Thus by controllably moving the first and second bodies 105, 110 between first and second positions pressure pulse(s) can be generated in the fluid as will be later described in detail.

The first position wherein the tool 10 is closed comprises a normal, dormant position, wherein the tool 10 is not in use.

As can be seen from the drawings, in this embodiment, a plurality of circumferential substantially equally spaced groups of holes 115, 120 are provided on each of the first and second bodies 105, 110. Each group of holes 115, 120 consists of three holes substantially equally spaced around the respective body 105, 120, such that adjacent holes 115, 120 of each group are spaced from one another around the circumference of the body 115, 120 by substantially 120 .

Each group of holes 115 has a corresponding group of holes 120 at substantially the same longitudinal level.

The solenoid activator 70 includes a solenoid 116 providing a piston/indexing rod 120 associated with a ratchet mechanism for controlling rotation of the first body 105.

The first body 105 carries a plurality of spiral blades 121 on an outermost surface thereof, which blades 121 tend to cause the first body 105 to rotate when, in use, fluid passes thereby downhole.

The second body 110 carries a nose cone 131, the nose cone 131 having one or more holes 132 formed therein. The second body 110 and nose cone 131 may be interconnected by co-acting threaded portions on each. In this way, in use, fluid passing into the tool 10 when in the second position via the holes 115, 120 formed in the first and second bodies 105,110 can exit the tool 10 via the holes 130 in the nose cone 125.

Referring particularly to Figs. 18 to 21 and Fig. 27 the ratchet mechanism includes a lowermost end of the piston 120. The lowermost end of the piston 120 rigidly carries an upper stop bar 125 and further floatingly carries in a longitudinal slot 130 a lower stop bar 135.

The lowermost end of the piston 120 includes a stepped lip 140. A first spring 145 is provided between the lip 140 and lower stop bar 135, such that the lower stop bar 135 is loaded by the first spring 145. A second spring 146 is further provided on the piston 120 above the upper stop bar 125.

Referring to Figs. 14(a)-(d) and Fig. 27, the ratchet mechanism further includes a cam ring 150 having six substantially equally spaced slots 155 formed on an uppermost side thereof and further having six substantially equally spaced slots 160 formed on a lowermost side thereof. Each slot 155, 160 is suitably shaped to provide a lead-in portion, each slot 155, 160 being capable of receiving the respective bar 125, 135. As can be seen from Fig. 14(d) slots 155,160 are offset from one another.

The cam ring 150 has a threaded portion on an outer surface thereof allowing the ring 150 to be connected to the first body 105 via a corresponding threaded portion formed on an inner surface of the first body 105.

Referring now to Figs. 22 to 24 there is illustrated in more detail the baffle 35. As can be seen from these drawings, the baffle 35 includes substantially centrally formed aperture 36 and a plurality of fluid throughflow orifices 45 spaced therearound. The baffle 35 may be mounted on the drillstring 40 by means of baffle rotating ring 170, as can be seen from Fig. 27.

The baffle 35 and ring 170 may comprise the known Totco Ring/Baffle plate.

In use, the tool 10 can be lowered within the drill string 40 and received within the aperture 36 of the baffle 35. The tool 10 is received within the aperture 36 - such that the first body 105 is free to longitudinally rotate under the control of the ratchet mechanism relative to the baffle 35.

The tool 10 may be fabricated from materials conventionally suitable for use in downhole tools. The first body 105 may be made from stainless steel, the second body 110 from the CrMo steel, the nose cone 135 from CrMo, the cam ring 150 from CrMo steel, the bearings 125, 130 from Devlon, the piston 120 from high permeability nickel iron alloy, and the stop-bars 125, 135 from silver steel.

Further the retaining ring 120 and further the baffle 35 may be made from cast steel.

Referring to Fig. 28 there is illustrated a schematic diagram of downhole electronic components of the tool 10, comprising a connector board 170 connected to the inclinometer 65, a strain gauge amplifier 175, flash memory 180, CPU 100, power supply board 185, battery 90, communication connection 190, static RAM 195, optional compass 200, and further power amplifier board 205 connected to solenoid 115, and position sensor 210 for detecting rotation of the first body 105.

Referring now to Fig. 29 there is illustrated a schematic diagram of the pressure detecting means of the apparatus 5 - including pressure sensor 25 and analysing means 30. The analysing means 30 comprise a CPU 215, ROM 220, amplifier 225 and static RAM 230. The pressure detecting means further provides a battery 235, solar cell 240, LCD display 245, and keyboard 250.

The following particular points should be noted. The capacitor stack 95 will be used to power and activate the solenoid 115. The stack 95 stores the electrical charge necessary to activate the solenoid piston 120, up and down.

The capacitor stack 95 will be fed by a small generator or turbine which comprises vanes which are rotated as the mud flows past the tool 10. This type of stack 95 is found on a number of tools including MMWD, pressure gauge flow meters etc. The stack 95 would have an RPM sensor so that when the mud flow is reduced, for example to 400 gpm, the RPM sensor would "tell" the CPU 100 to take the readings and activate the solenoid 115 thereby creating the pulse.

An inclination/magnetometer would be used to measure azimuth and would be part of a second tool (Electronic Multi-shot - EMS) which would "piggy-back the tool 10, i.e. the tool would be two tools in one. Thus, as the drillstring 40 is pulled up hole to effect a bit change or run casing the tool 10 would automatically record an electronic multi-shot survey. This information would be stored in a memory chip and then downloaded on surface.

The obvious savings in terms of running and paying rental on conventional electronic multi-shot systems is obvious.

The only additional cost to the tool 10 would be in the form of the software package in the CPU 100, the magnetometer to record azimuth, memory chip and surface package to download the information. The CPU 100 memory unit is the tool's 10 brain and will contain the chips/electronics/software to control when and how readings are taken, when to activate the solenoid 115, length of activation time, etc.

In use, the tool 10 can be lowered down the drill string 40 and received by baffle 35. Drilling may then be carried out in a conventional manner. Alternatively. the tool 10 can be inserted within the drillstring 40 prior to insertion into the borehole 15.

Referring to Figs 27, 2(a), 2(b), 3(a), 3(b) and 4, once the tool 10 is in position the tool 10 can be opened and closed by the following procedure. The tool 10 is normally in a first, closed position where the holes 115, 120 of the bodies 105, 110 are not aligned - see Fig. 2 (a). In this position fluid passing down the drillstring 40 can only pass through the apertures 45 in the baffle 35.

The tool 10 incorporates a flow meter (not shown).

The flow meter may control the inclinometer 65 such that when an inclination reading is desired the fluid flow is reduced, for example to 400 gpm. This reduction in fluid flow causes the inclinometer 65 to take an inclination reading. The downhole electronics convert the inclination reading to an electronic signal controlling the piston 120, which in turn controls opening and closing of the holes 115, 120, the time T2-Tl for which the holes 115, 120 are aligned being proportional to the measured inclination.

Aligning of the holes 115, 120 causes a reduction the fluid pressure detected by the pressure sensor 25 spring loaded lower stopbar 135 to engage with a pair of lowermost slots. Downward movement of the piston 120 thereafter causes the upper stop bar 125 to engage with a next pair of uppermost slots 115.

The holes 115, 120 are then aligned, the first body 105 having rotated by 60". This causes a negative pressure pulse, the duration of which is proportional to the measured inclination. For example, the apparatus 5 can be calibrated prior to use, such that, e.g. 5 seconds = 0.5 degrees of inclination.

Once the duration of the desired pulse has elapsed, the piston 120 is again moved down to up causing the first body 105 to rotate by 600 relative to the second body 110 such that the holes 115, 120 are again out of alignment.

So that the pressure pulse detection means 20 detects when an inclination measurement has been taken, the pressure pulse related thereto may be prefaced by a selected train of pressure pulses of selected duration and also followed by a selected further train of pressure pulses of selected further duration.

Referring to Figs 30 to 43(b), and initially to Fig 30, there is illustrated a second embodiment of a borehole survey apparatus, generally designated 5a, including a second embodiment of a downhole tool 10a for generating pressure pulses in a fluid contained in a borehole 15a.

The second embodiments of the apparatus 5a and tool 10a are similar in certain respects to the first embodiment shown in Figs. 1 to 29, like parts being identified with the same numerals but suffixed with 'a'.

In the second embodiment of the tool 10a, the blades 121 are replaced by a plurality of recesses 200a (termed scallops) on an outermost surface of the first tubular body 105a. Each recess 200a is provided substantially longitudinally on the first body 105a, the recesses 200a being provided substantially equally spaced circumferentially upon the first body 105a.

Further, in the second embodiment of the apparatus 5a, there is included means for generating a rotational fluid flow around the recesses 200a of the tool 10a. In this embodiment the rotational fluid flow is of a spiral/helical nature down the borehole.

The means for generating the rotational fluid flow comprises a plurality of baffles 205a distributed around the tool 10a. The baffles 205a are provided on an outer surface of a third tubular body 210a, which body 210a is securedly received by suitable means relative to an inner wall in an upper portion 215a of a fourth tubular body 220a. As can be seen from Fig. 30 the tool 10a is received within the third and fourth tubular bodies 210a, 220a.

The fourth tubular body 220a provides a mid portion 225a having a reduced internal diameter. As can be seen from Fig. 30, the recesses 200a of the first body 105a face the mid portion 225a of the fourth tubular body 220a.

A lowermost portion 230a of the fourth tubular body 220a is connected by suitable fixing means to baffle 35a.

In this manner the fourth tubular body 220a upstands dependently from the baffle 35a. The fourth tubular body 220a may be provided within a drill string 40a or may comprise part of the drill string 40a.

In this embodiment the ratchet mechanism comprises upper and lower index rings 235a, 240a fixedly carried in an internal bore at an upper end of the first body 105a, and a middle index ring 245a fixedly carried on a solenoid piston 120a. The arrangement of rings 235a, 240a, 245a works in an analogous manner to the upper stop bar 125, lower stop bar 135 and cam ring 150 of the first embodiment.

In use, as fluid is pumped down the borehole 15a past baffles 205a, a swirling fluid flow is created. The combination of the third and fourth tubular bodies 210a, 220a, and the baffles 205a is conveniently termed a swirl baffle. The swirling fluid flow then passes down between the recesses 200a and the mid portion 225a, impinging upon the recesses 200a thereby tending to urge the first body 105a to rotate, which the first body 105a will do, if rotation thereof is allowed by the ratchet mechanism.

This second embodiment of the tool 10a described hereinbefore is particularly advantageous in operation in the surveying/logging of the inclination of a borehole.

The tool 10a may also be retrievable, eg. by wireline.

It will be appreciated that the embodiments of the present invention hereinbefore described are given by way of example only, and are not meant to limit the scope of the invention in any way.

Claims

CLAIMS 1. A downhole tool for generating a pressure pulse(s) in a fluid contained in a borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole.
2. A downhole tool as claimed in claim 1, wherein the means for generating a pressure pulse includes actuation means for controlling throughflow area varying means, such that, in use, the fluid throughflow area is changed to create a fluid pressure change.
3. A downhole tool as claimed in either of claims 1 or 2, wherein the pressure pulse generating means comprises a first tubular body.
4. A downhole tool as claimed in claim 3, wherein the pressure pulse generating means comprises a second tubular body, one of the bodies being located within the other.
5. A downhole tool as claimed in claim 4, wherein each body provides at least one hole therethrough.
6. A downhole tool as claimed in claim 5, wherein one of the bodies is moveable relative to the other body from first to second position(s), wherein the/a first position respective holes in the first and second bodies are not in alignment such that the tool is closed and fluid cannot pass there through, and wherein in the/a second position respective holes in the first and second bodies are in alignment such that the tool is opened and fluid can pass therethrough.
7. A downhole tool as claimed in claim 6, wherein, in use, by controllably moving the first and second bodies between the first and second positions a pressure pulse(s) is/are generated in the fluid.
8. A downhole tool as claimed in claim 7, wherein a first position comprises a dormant position, wherein the tool is not in use, and wherein, in use, movement to a second position causes a pressure reduction resulting in a negative pressure pulse.
9. A downhole tool as claimed in claim 7, wherein a second position comprises a dormant position, wherein the tool is not in use, and wherein, in use, movement to a first position causes a pressure increase resulting in a positive pressure pulse.
10. A downhole tool as claimed in any of claims 4 to 9, wherein one of the bodies is rotatable relative to the other body about a longitudinal axis.
11. A downhole tool as claimed in any of claims 4 to 10, wherein one of the bodies is moveable relative to the other body along a longitudinal axis.
12. A downhole tool as claimed in any of claims 4 to 11, wherein the first and second bodies are retained in association with one another by first and second bearings.
13. A downhole tool as claimed in any of claims 2 to 12, wherein the actuating means includes a solenoid controlled by the measuring means.
14. A downhole tool as claimed in claim 13, wherein the solenoid provides a piston associated with a ratchet mechanism for controlling rotation of one of the first or second bodies.
15. A downhole tool as claimed in claim 14, wherein the ratchet mechanism controls rotation of the first, outermost body.
16. A downhole tool as claimed in any of claims 4 to 15, wherein the first body carries one or more blades on an outermost surface thereof7 which blade(s) tend to cause the first body to rotate when, in use, fluid passes thereby downhole.
17. A downhole tool as claimed in claim 16, wherein the one or more blades are spiral blades.
18. A downhole tool as claimed in any of claims 4 to 17, wherein the first body is provided with one or more recesses on an outermost surface thereof.
19. A downhole tool as claimed in claim 18, wherein each recess is provided substantially longitudinally on the first body.
20. A downhole tool as claimed in either of claims 18 or 19, wherein a plurality of recesses are provided substantially equally spaced circumferentially upon the first body.
21. A downhole tool as claimed in any of claims 4 to 20, wherein the second body carries a nose cone, the nose cone having one or more holes formed therein.
22. A downhole tool as claimed in claim 21, wherein, in use, fluid passing into the tool when in the second position via the holes formed in the first and second bodies exits the tool via the hole(s) in the nose cone.
23. A downhole tool as claimed in any preceding claim, wherein the fluid is a drilling fluid.
24. A downhole tool as claimed in any preceding claim7 wherein the characteristic of the borehole is an inclination of the borehole from vertical.
25. A downhole tool as claimed in any preceding claim, wherein the time for which the pressure pulse is generated is indicative of the measured characteristic.
26. A downhole tool as claimed in any preceding claim, wherein the means for measuring is selected from a strain gauge inclinometer or accelerometer.
27. A downhole tool as claimed in claim 26, wherein the means for measuring is an electronic strain gauge.
28. A downhole tool as claimed in any of claims 1 to 25, wherein the means for measuring is a swinging pendulum.
29. A downhole tool as claimed in any preceding claim, wherein the tool is of a retrievable type.
30. A downhole tool as claimed in claim 29, wherein the tool is retrievable by wireline.
31. A downhole tool as claimed in claim 5 or any of claims 6 to 30 when dependent upon claim 5, wherein the at least one hole in at least one of each body is longitudinally elongate.
32. A borehole survey or logging apparatus comprising: a downhole tool for generating a pressure pulse(s) in a fluid contained in the borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole; and means for detecting the pressure pulse.
33. A borehole survey apparatus as claimed in claim 32, wherein the downhole tool comprises a tool as claimed in any of claims 1 to 31.
34. A borehole survey apparatus as claimed in either of claims 32 or 33, wherein the detection means is provided on surface.
35. A borehole survey apparatus as claimed in either of claims 33 or 34, wherein the detection means includes a pressure sensor.
36. A borehole survey apparatus as claimed in any of claims 32 to 35, wherein the detection means includes means for analysing the pressure pulse so as to determine the measured characteristic.
37. A borehole survey apparatus as claimed in any of claims 32 to 36, wherein the apparatus further comprises a baffle carried within a drillstring.
38. A borehole survey apparatus as claimed in claim 37, wherein the baffle includes means for receiving the tool.
39. A borehole survey apparatus as claimed in either of claims 37 or 38, wherein the baffle provides one or more fluid throughflow orifices.
40. A borehole survey apparatus as claimed in any of claims 37 to 39, wherein the baffle is carried within the drillstring at or near a lowermost end thereof.
41. A borehole survey apparatus as claimed in any of claims 32 to 40 wherein the characteristic of the borehole is the inclination of the borehole from vertical.
42. A borehole survey apparatus as claimed in any of claims 32 to 41, wherein the apparatus includes means for generating a rotational fluid flow around at least part of the tool.
43. A borehole survey apparatus as claimed in claim 42, wherein the rotational fluid flow is a spiral or helical type fluid flow.
44. A borehole survey apparatus as claimed in either of claims 42 or 43, wherein the means for generating a rotational fluid flow comprises one or more baffles.
45. A borehole survey apparatus as claimed in claim 44, wherein the one or more baffles are distributed around the tool.
46. A borehole survey apparatus as claimed in claim 45, wherein the one or more baffles are provided on a third tubular body, which body is securedly received in an upper portion of a fourth tubular body.
47. A borehole survey apparatus as claimed in claim 46, wherein the fourth tubular body provides a mid portion having a reduced internal diameter.
48. A borehole survey apparatus as claimed in claim 47, wherein the first body is provided with one or more recesses and/or one or more blades on an outermost surface thereof.
49. A borehole survey apparatus as claimed in claim 48, wherein the one or more recesses face the mid portion of the fourth tubular body.
50. A borehole survey apparatus as claimed in any of lowermost portion of the fourth tubular body is connected to the baffle.
51. A method of surveying a borehole comprising: providing a downhole tool for generating a pressure pulse(s) in a fluid contained in the borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid representative of the measured characteristic by altering a fluid throughflow area in the borehole; providing means for detecting the pressure pulse; measuring the characteristic; generating the pressure pulse; and detecting the pressure pulse.
52. A method of surveying a borehole as claimed in claim 51, wherein the characteristic of the borehole is the inclination of the borehole from vertical.
53. A method of surveying a borehole as claimed in either of claims 51 or 52, wherein the time length of the pressure pulse is related to the value of the measured characteristic.
54. A method of surveying a borehole as claimed in any of claims 51 to 53, wherein, in use, so that the pressure pulse detection means detects when a measurement has been taken, the pressure pulse relating thereto is prefaced by a predetermined train of pressure pulses of selected duration and/or magnitude and/or followed by a predetermined further train of pressure pulses of selected duration and/or magnitude.
55. A downhole tool for generating a pressure pulse(s) in a fluid contained in a borehole, the tool comprising means for measuring a characteristic of the borehole and means for generating a pressure pulse in the fluid, the time for which the pressure pulse is generated being indicative of the measured characteristic.
56. A borehole survey apparatus including a tool according to claim 53.
57. A method of surveying a borehole comprising providing and using a tool according to claim 55.
58. A downhole tool for generating a pressure pulse(s) in a fluid contained in a borehole as hereinbefore described with reference to Figs. 1 to 29 or Figs. 30 to 43 (b)
59. A borehole survey apparatus as hereinbefore described with reference to Figs. 1 to 29 or Figs 30 to 43 (b)
60. A method of surveying a borehole as hereinbefore described with reference to Figs. 1 to 29 or Figs. 30 to 43 (b)