NO20160966A1

NO20160966A1 - Downhole Sonar

Info

Publication number: NO20160966A1
Application number: NO20160966A
Authority: NO
Inventors: John Davies; Hans Van Dongen
Original assignee: Maersk Olie & Gas
Priority date: 2013-12-05
Filing date: 2016-06-03
Publication date: 2016-06-03
Also published as: GB2520969A; WO2015082702A2; WO2015082702A3; GB201321452D0; DK201670396A1

Description

Downhole Sonar

Field of the Invention

The present invention relates to an apparatus and method for measuring geometry of a wellbore.

Background of the Invention

Well logging tools may be used for assessing the characteristics of production wellbores and the surrounding geological formation. Wellbore logging may be performed at all stages of the well's life cycle, for example, during drilling, testing, completing or production. Wellbore logging may be used to determine properties, such as the dimensions of the wellbore. The dimensions of a wellbore surrounding a liner or tubular may significantly change during stimulation treatments and this may impact the positionlng of the tubing within the well. At the same time these treatments may also affect the geological formation of the wellbore. Information on the properties of the wellbore and wellbore formation may be helpful for making decisions, such as whether to carry out further drilling or production operations. At the same time it may be useful to gain information on the wellbore properties as these may impact the exploitation of the gas or oil reservoir.

Summary of Invention

According to a first aspect of the present invention there is provided a method for measuring geometry of a wellbore, the method comprising: providing a measuring apparatus within a conduit that is located within the wellbore;

contacting an inner wall of the conduit with at least one sensor;

transmitting one or more signals through the conduit towards a wall of the wellbore that surrounds the conduit;

detecting one or more reflected signals.

The reflected signals may be reflected back from the wall of the wellbore and/or from a device, apparatus or material between the conduit and the wall of the wellbore.The method may comprise determining the geometry of the wellbore behind the conduit from the detected signal.

The method may comprise detecting the device, apparatus or material between the conduit and the wall of the wellbore, or determining the geometry or another property of the device, apparatus or material, using the detected signal. The device or apparatus provided between the conduit and the wall of the wellbore may comprise an outer tubing, casing, conduit or liner. The material provided between the conduit and the wall of the wellbore may comprise, for example, an obstruction, blockage, collapsed section or the like. The device or apparatus provided between the conduit and the wall of the wellbore may comprise a gauge or other downhole tool, sensor or device.

The method may comprise detecting perforations in the device or apparatus, e.g. in the outer tubing, casing, conduit or liner.

The method may comprise determining a thickness or thickness loss or variation or other geometrical property of the conduit and/or of the device, material or apparatus provided between the conduit and the wall of the wellbore.

The method may comprise determining one or more properties indicative of the geometry, e.g. size, shape or dimensions, of the wellbore or wellbore wall. The method may comprise determining properties indicative of near wellbore wall conditions or damage, such as fractures, cracking or deformation. The measuring apparatus may be configured to survey, log and/or sense the environment around the conduit, such as the wellbore walls and/or contents of the bore and/or the geological environment around the conduit. By positioning the at least one sensor into contact with the inner wall of the conduit the number of transmission paths may be reduced and impedance changes may be eliminated. In some examples, the at least one sensor may be brought into engagement or contact with an inner wall of the conduit.

The measuring apparatus may comprise or be comprised in a downhole tool or tractor.

The at least one sensor may be comprised in or mounted on the measuring apparatus.

The at least one sensor may be or comprise an acoustic sensor.

The method may comprise emitting the one or more signal(s) towards the inner wellbore wall. The one or more signal(s) may comprise acoustic signal(s). The sensor may comprise a transmitter configured to emit the signal. The method may comprise detecting the one or more signal(s) reflected back by the inner wellbore wall or the device, apparatus or material between the conduit and the wall of the wellbore. The sensor may comprise a receiver configured to detect the acoustic signal or refiections thereof.

At least a portion of the outer surface of the conduit may be spaced apart from the inner wall of the wellbore. A medium may be provided between the portion of the outer surface of the conduit and the inner wall of the wellbore. The medium may comprise a material håving unfavourable acoustic properties. The medium may be or comprise a gas or liquid. The portion of the outer surface of the conduit may comprise an uncemented portion. The method may comprise transmitting the one or more signals through the conduit and the medium towards a wall of the wellbore that surrounds the conduit. The method may comprise determining the geometry of the wellbore behind the conduit and the medium from the detected signal.

The method may comprise determining a time between emission of the signal and detection of the reflected signal.

The time between emission and detection of the one or more signal(s) may be indicative of a distance between the conduit and the inner wall of the wellbore or the presence or location of the device, apparatus or material between the conduit and the wall of the wellbore, or the geometry or another property of the device, apparatus or material.

The method may comprise determining material properties behind the conduit based on at least one reflection, for example, by measuring an amplitude of the emitted and/or detected signal. Attenuation of the amplitude of the detected signal with respect to the emitted signal may be indicative of the materials behind the conduit.

The method may comprise detecting a location of openings or entry points of fractures or cracks in the wellbore wall. The time between emission of the signal and detection of the reflected signal may be indicative of the presence of crack or fracture openings, for example, by measuring a large time or an increase in time until the signal returns to the detector. A strong attenuation of the signal amplitude may also be indicative of fracture opening within the wellbore formation.

The method may comprise rotating, e.g. continuously rotating, the apparatus and/or sensor. The sensor may be located radially outwardly of the apparatus.

The method may comprise measuring the one or more properties of the wellbore at multiple points along a circumference of the wellbore, which may lead, for example, to a circumferential map or scan of the wellbore. The circumferential map may be indicative of the size and/or shape of the wellbore at a position of the apparatus within the conduit. Alternatively, single point measurements may be performed.

The method may comprise translating the apparatus through the conduit. In use, translating of the apparatus may comprise moving the apparatus in an axial direction, e.g. in a longitudinal direction of the conduit. In use, translating of the apparatus through the conduit may comprise running the apparatus through the conduit, locating the apparatus in the conduit, and/or retrieving the apparatus. The method may comprise measuring multiple points along a length of the conduit, which may lead, for example, to a translational map of the wellbore. The translational map may be indicative of the size and/or shape of the wellbore along a wellbore section or length.

The method may comprise moving or extending the sensor(s) into contact with the inner wall of the conduit. The sensor(s) may be mounted directly on the apparatus, which may be capable of moving or extending the sensors into contact with the inner wall of the conduit. Alternatively, the apparatus may comprise an extending arrangement, which may be capable of extending the sensor(s) into contact with the inner wall of the conduit and/or retracting of the sensor(s) from contact with the inner wall. The retraction of the sensor(s) may prevent damage of the sensor(s) during location and/or retrieval of the apparatus.

The method may comprise transmitting the emitted and/or detected signals or data indicative of the emitted and/or detected signal for analysis of the wellbore geometry to the surface.

The method may comprise storing information or data relating to the properties, e.g. geometry, of the wellbore. The apparatus may contain a memory for storing the information or data

The data or information may comprise data indicative of the emitted and detected signals, emission of the signal and detection of the reflected signal and/or attenuation of the amplitude of the reflected signal with respect to the emitted signal.

The method may further comprise re-examining a region of the wellbore when the data is insufficient and/or an insufficient number of measurements were tåken.

The method may comprise supplying power to the apparatus for measuring geometry of the wellbore.

The method may comprise using an apparatus according to the second aspect.

According to a second aspect of the present invention there is provided an apparatus for measuring geometry of a wellbore and/or for detecting a device, structure or material between the conduit and the wall of the wellbore, or determining the geometry or another property of the device, apparatus or material; wherein the apparatus comprises: a tool body to be positioned within a conduit in the wellbore, and at least one sensor supported by the tool body, wherein the apparatus is configured such that the sensor can engage or contact an inner wall of the conduit when the tool body is located within the conduit.

The apparatus may be operable to determine properties indicative of the shape, size or geometry of the wellbore, bore wall and/or near bore wall conditions or damage, such as fractures, cracking or deformation. The apparatus may be configured to survey, log and/or sense the environment around the conduit, such as the bore walls and/or contents of the bore and/or the geological environment around the conduit.

The device or structure provided between the conduit and the wall of the wellbore may comprise an outer tubing, casing, conduit or liner. The material provided between the conduit and the wall of the wellbore may comprise, for example, an obstruction, blockage, collapsed section or the like. The device or structure provided between the conduit and the wall of the wellbore may comprise a gauge or other downhole tool, sensor or device.

The apparatus may be configured to detect perforations in the device or structure, e.g. in the outer tubing, casing, conduit or liner.

The apparatus may be configured to determine a thickness or thickness loss or variation or other geometrical property of the conduit and/or of the device, material or structure provided between the conduit and the wall of the wellbore.

The sensor may comprise one or more transmitters for emitting a signal towards an inner wall of the wellbore. The signal may comprise an acoustic signal.

The sensor may comprise one or more receivers for detecting a reflection of the signal from the inner wellbore wall and/or from a device, structure or material between the conduit and the wall of the wellbore. A time between emission and detection of the signal may be indicative of a distance between the conduit and the inner wall of the wellbore or the presence or location of the device, apparatus or material between the conduit and the wall of the wellbore, or the geometry or another property of the device, apparatus or material. The time between emission and detection of the signal may be used to determine the size and/or shape of the wellbore and/or the presence, location, size and/or shape of the device, structure or material. In some examples, the receiver and transmitter may be the same, for example, in piezo-electrical sensors. In other examples, the receiver and transmitter are separate, different or distinct from one another.

Respective transmitters may be arranged to emit the signal at different angles with respect to the tool body, i.e. the signal may be emitted in different directions.

Respective receivers may be arranged to detect the signal reflected at different angles or directions from the wellbore wall.

In use, the tool body and/or the sensor may be rotated, such as continuously rotated, or rotatable for circumferentially scanning the wellbore, i.e. emitting and detecting the signal. The scan may comprise single point measurements. Alternatively or additionally, the properties indicative of the geometry of the wellbore may be measured at multiple points along a circumference of the wellbore, which may lead to a circumferential map of the wellbore. The circumferential map may be indicative of the size and/or shape of the wellbore at a position of the apparatus within the conduit.

Optionally, the apparatus may not be fixed or rigidly coupled to the conduit. For example, the device may be acoustically coupled to the conduit but may not be permanently attached.

The apparatus may be configured to measure multiple points along a length of the conduit measured e.g. whilst the tool body is moved through the conduit, which may lead to a translational map of the wellbore. The translational map may be indicative of the size and/or shape of the wellbore and/or the presence or location and/or dimensions of any device, structure or material between the conduit and the wall of the wellbore along a wellbore section or length.

The sensors may be located radially outwardly of the apparatus or a body of the apparatus. The sensors may be circumferentially positioned around the apparatus. The sensors may be distributed in a longitudinal direction of the apparatus. The sensors may be positioned along a longitudinal axis of the apparatus. The sensors may be arranged periodically on the apparatus. At least two of the sensors may be arranged diametrically opposed to each other. At least two pairs of diametrically opposed sensors may be provided on the apparatus. At least two and preferably each of the sensors may be equally spaced from each other, e.g. the sensors may be mounted 90° azimuthally apart from each other around a longitudinal axis of the body. The sensors may be provided in a staggered arrangement or on a common circumference of the apparatus or body of the apparatus.

The sensors may be arranged in sets of sensors which may be positioned radially outwardly of the apparatus. Each set may comprise a plurality of sensors located on a circumference of the apparatus. The apparatus may comprise a plurality of sets of sensors. The sets of sensors may be longitudinally spaced to each other. Optionally, the sets of sensors may be provided in a staggered arrangement.

For example, the apparatus may comprise at least a first set of sensors, a second set of sensors and a third set of sensors. Each set of sensors may be longitudinally spaced from each other set. The second and third set of sensors may be located in positions rotated around the longitudinal axis of the body with respect to the position of the first set of sensors. The rotation of the position of the second set of sensors with respect to the first set of sensors may be in a direction opposite to that of the third set of sensors.

The sensors may be mounted directly on the apparatus, which may be capable of moving or extending the sensors into contact with the inner wall of the conduit.

Alternatively, the apparatus may comprise an extending arrangement, which may be capable of extending the sensors into contact with the inner wall of the conduit and/or retracting of the sensors away from contact with the inner wall. The retraction of the sensors may prevent damage of the sensors during location and/or retrieval of the apparatus.

The extending mechanism may comprise one or more arms to support the sensors. The arms may be configured to bias the sensors either radially outwards or radially inwards. For example, the one or more arms may bias the sensors radially outwards into contact with the inner wall of the conduit.

The sensor or sensors may be incorporated in tool systems such as wireline logging tools, permanent monitoring systems, centralisers, stabilisers and collars etc.

For example, the tool body may comprise or be comprised in a downhole tractor. The downhole tractor may be used to propel one or more objects through the conduit, such as a wireline.

The downhole tractor may comprise at least one wheel configured to engage the inner wall of the conduit. The at least one wheel may comprise the sensor or respective sensors. The wheel may be rotatable to propel the tractor through the conduit.

In use, propulsion of the tractor through the conduit may enable the sensor to log or scan different points along the wellbore, for example, to determine the translational map of the wellbore.

The at least one wheel may be movable radially outwardly and inwardly, for example, by being mounted on pivoting arms or other suitable movement mechanism. The wheel may be biased radially outwardly so as to be in contact with the inner wall of the conduit.

Optionally the at least one wheel may comprise a deformable or pliant portion that may be provided on at least a periphery or outward portion of the wheel.

The tractor may comprise a plurality of wheels. The wheels may be located radially outwardly of the tool body. The wheels may be circumferentially positioned around the tool body. The wheels may be positioned along a longitudinal axis of the tool body. The wheels may be arranged periodically on the tool body. At least two of the plurality of wheels may be arranged diametrically opposed to each other. At least two pairs of diametrically opposed wheels may be positioned on the tool body. The wheels may be equally spaced from each other, e.g. the wheels may be mounted 90° azimuthally apart from each other around a longitudinal axis of the body. The wheels may be provided in a staggered arrangement or on a common circumference of the tool body.

The wheels may be positioned on the tool body in sets. Each set of wheels may comprise a plurality of wheels. The sets of wheels may be longitudinally spaced to each other. Optionally, the sets of wheels may be provided in a staggered arrangement.

For example, the tractor may comprise at least a first set of wheels, a second set of wheels and a third set of wheels. Each of the first, second and third sets of wheels may comprise one or more wheels. The second set of wheels may be longitudinally spaced from the first set of wheels. The third set of wheels may be longitudinally spaced from the second set of wheels. The second and third set of wheels may be located at positions rotated around a longitudinal axis of the body with respect to the first set of wheels, e.g. by 5° to 45°, and preferably 10°. The rotation of the position of the second set of wheels relative to the first set of wheels may be in a direction opposite to that of the third set of wheels. For example, the second set of wheels may be located at positions rotated by -10° around the longitudinal axis of the tractor with respect to the first set whereas the third set may be located at positions rotated by +10° around the longitudinal axis of the tractor with respect to the first set.

The sensor may be externally and/or outwardly facing from the wheel. The sensors may be configured to survey, log and/or sense the environment around the tractor, such as the bore walls and/or contents of the bore and/or the geological environment around the tractor. Optionally, the wheel may comprise a plurality of sensors.

When the sensor is provided in one or more of the wheels, this arrangement may ensure proximity between the sensor and the bore walls, which may improve surveying of the borehole wall and geological structure surrounding the conduit.

The tool body may be an elongate body, such as a tubular or a logging tool body. The tool body may be lowered into the conduit on a wireline. Optionally, the sensors may be attached to the tool body. The tool body may be or comprise coiled tubing.

The apparatus may be configured to perform a scan of the wellbore geometry while the tool body is run through the conduit, positioned in the conduit or retrieved from the conduit, for example, to determine the translational map of the wellbore.

The tool body may comprise or be comprised in a centraliser adapted to be positioned or mounted on an inner tubular within the centre of the conduit. One or more sensors may be mounted onto the centraliser such that the sensors are biased outwardly into contact with the inner wall of the tubular.

A scan of the wellbore geometry may be performed while the inner tubing comprising the centraliser is run through the conduit and positioned at the desired position. Once the centraliser is in position, the sensor may indicate changes in the geometry of the wellbore and/or the environment around the conduit, which may occur over longer time periods.

The tool body may contain a control module for controlling the signal emission and/or detection. The control module may comprise a memory for storing or transmitting signals to the surface. The control module may provide the sensors with power. The control module may be configured to analyse the signal from the sensor. When the signal or data quality is insufficient and/or an insufficient number of measurements were tåken, the control module may initiate re-examination of a wellbore region.

Power may be supplied to the apparatus and/or sensor via the wireline.

The conduit may comprise or define a passage. In some examples, the conduit may comprise or define a liner, casing, tubular and/or tubing. The conduit may be provided inside an outer conduit, e.g. a pipe inside a pipe.

The apparatus may be configured to implement the method of the first aspect.

It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment of the invention. Furthermore, the present invention is intended to cover apparatus configured to perform any feature described herein in relation to a method and/or a method of using or producing or manufacturing any apparatus feature described herein.

Brief Description of the Drawings

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 (a) is a representation of an apparatus for measuring geometry of a wellbore in accordance with an embodiment of the present invention; Figure 1(b) shows a transverse cross-sectional representation of the apparatus of Figure 1(a); Figure 2 shows a longitudinal cross-sectional representation of a modified embodiment of the apparatus of Figure 1(a); Figure 3 shows a graphical representation of a signal transmitted and detected signal by the apparatus of Figure 1(a); Figure 4 shows a longitudinal cross-sectional representation of a modified embodiment of the apparatus of Figure 1(a), located within a production zone of the wellbore; Figure 5 shows a longitudinal cross-sectional representation of an apparatus according to an embodiment of the invention in an exemplary use on a centraliser located within a conduit; Figure 6(a) shows a longitudinal cross-sectional representation of an apparatus according to an embodiment of the present invention in another exemplary use as a downhole tractor; Figure 6(b) shows a transverse cross-sectional representation of the apparatus of Figure 6(a); Figure 7(a) shows a longitudinal cross-sectional representation of the downhole tractor of Figure 6 (a) comprising sets of wheels according to an embodiment of the present invention; Figure 7(b) shows a transverse cross-sectional representation of the apparatus of Figure 7(a); and Figure 8 illustrates a flowchart of a method for measuring geometry of a wellbore in accordance with the present invention.

Detailed Description of the Drawings

Embodiments of the present invention relate to apparatus that can "see" through a conduit or tubular and deduce the characteristics (shape, distance, fracture locations, etc.) of whafs on the other side. Advantageously, the apparatus works even if a gap that contains, for example, a medium with unfavourable acoustic properties such as a fluid or gas, is present between the conduit or tubular and the wall of the wellbore. In other words, the apparatus can work with uncemented completions across the reservoir sections.

Referring to Figures 1 and 2, there is shown an apparatus 10 for measuring geometry of a wellbore in accordance with an embodiment of the present invention. The apparatus 10 comprises a tool body 20 to be located within a conduit 30 positioned in the wellbore 2, and a plurality of sensors 40 attached to the tool body 20. The tool body 20 is configured to bring the sensors 40 into engaging contact with an inner wall 32 of the conduit 30 when the tool body 20 is located within the conduit 30. However, the apparatus 10 is movable relative to the conduit 30, i.e. the apparatus 10 is acoustically coupled to the conduit 30 but not rigidly coupled to the conduit 30.

The apparatus 10 is operable to determine properties indicative of the shape, size or geometry of the wellbore 2, wellbore wall 4 and/or near wellbore wall 4 and conditions or damage, such as fractures, cracking or deformation. The apparatus is configured to survey, log and/or sense the environment around the conduit, such as the wellbore walls 4 and/or contents of the wellbore 2 and/or the geological environment around the conduit 30.

Each sensor 40 comprises a transmitter 42 (see Figure 2) for emitting a signal towards an inner wall 4 of the wellbore 2. The sensor 40 further comprises a receiver 44 for detecting a reflection of the signal from the inner wellbore wall 4. The signal comprises an acoustic signal. The receiver and transmitter can be the same, for example, in a piezo-electrical sensors. In other examples, the receiver and transmitter are separate, different or distinct from one another.

With reference to Figure 1, there is shown an arrangement of sensors 40 on the tool body 20. The sensors 40 are positioned circumferentially around the tool body 20. In addition to the circumferential arrangement, the sensors 40 are also provided along a longitudinal axis A of the tool body 20. In the embodiment of Figure 1, the apparatus 10 is provided with an extending mechanism, wherein the extending mechanism comprises one or more arms 22 to support the sensors 40. The arms 22 can be configured to bias the sensors 40 either radially outwards or radially inwards. In some examples, the arms 22 bias or extend the sensors 40 radially outwards into engaging contact with the inner wall 32 of the conduit 30. The arms 22 can also be configured to disengage the sensors 40 from contact with the inner wall 32 of the conduit 30. By disengaging or retracting the sensors 40 from contact with the inner wall 32 for example when the apparatus 10 is installed or retrieved, damage to the sensors may be prevented. The arms 22 on which the sensors 40 are mounted can be pivoting arms biased by one or more springs, or other mechanisms.

Referring to Figure 2, the sensors 40 comprise one or more transmitters 42. The one or more transmitters 42 are arranged to emit one or more signals towards the inner wall 4 of the wellbore 2. In some embodiments, the one or more transmitters 42 can be arranged to emit the acoustic signal at different angles or directions with respect to the tool body 20.

As can be seen in Figure 2, the sensors 40 comprise one or more receivers 44. The one or more receivers 44 are arranged to detect one or more signals reflected from the inner wall 4 of the wellbore 2. In some embodiments, the one or more receivers 44 can be arranged to detect the one or more signals reflected at different angles or directions from the wellbore wall 4.

The tool body 20 of Figures 1 and 2 is a tubular or a logging tool body 20. The tool body 20 is lowered into the conduit 30 on a wireline 34. The tool body 20 and/or the one or more sensor 40 can be adapted to rotate for circumferentially scanning the wellbore 2. In some examples, the sensors 40 are arranged or located on a rotating component or part of the tool body 20, such as an outer rotating cylinder or the like. In other examples, the sensors 40 are arranged or located on a swivel or the like, so as to rotate the sensors 40 around the longitudinal axis A of the tool body 20. The circumferential scan can comprise single or multi point measurements. Multi point measurements along a circumference of the wellbore 2 can lead to a circumferential map of the wellbore 2. Such a circumferential map is indicative of the size and/or shape of the wellbore 2 and/or the centering of the conduit 30 within the wellbore 2.

In addition, or alternatively to the rotational movement of the tool body 20, the tool body 20 is translated through the conduit. For example, translating of the tool body 20 comprises moving the tool body 20 in an axial direction, e.g. in a longitudinal direction, of the conduit 30. Translating of the tool body 20 can comprise running the apparatus 10 through the conduit 30, locating the apparatus 10 in the conduit 30, and/or retrieving the apparatus 10 from the conduit 30. During the translational movement of the tool body, single or multiple points are measured. Multi point measurements, tåken along a length of the conduit 30, from a translational map of the wellbore 2. The translational map can be indicative of the size and/or shape of the wellbore 2 and/or changes in wellbore geometry along a wellbore section or length.

Referring now to Figure 3, there is shown an example of an emitted signal and a detected signal, which was reflected back by the inner wall 32 of the conduit 30. A time delay or difference between the two signals is indicative of a distance between the conduit 30 and the inner wall 4 of the wellbore 2. The time delay between emission of the signal and detection of the reflected signal is used to determine the size and/or shape of the wellbore 2. The centering of the conduit 30 within the wellbore 2 can also be determined. Correlation techniques such as the cross-correlation function can be used. The cross-correlation function is a measure of how much one signal resembles a time delayed copy of another signal. After calculating the cross-correlation between the two signals, i.e. the emitted and the detected signal, the maximum of the cross-correlation function can be used to determine the time delay between the two signals.

Properties of the material behind the conduit 30 can be determined by measuring and/or comparing the amplitude of the emitted and reflected signal. By determining the attenuation of amplitudes of the signal and the distance the signal travels from the emitter 42 to the receiver 44, absorption rates which can be indicative of the material behind the conduit 30 are determined. As can be seen in Figure 3, the amplitude of the detected signal is attenuated.

By positioning the sensor 40 into contact with the inner wall 32 of the conduit 30 the number of transmission paths is reduced and impedance changes are eliminated.

The time difference and/or differences in frequency between the emission and detection of the reflected signal can be indicative of factures 6 (see Figure 4). These fractures 6 may have natural or artificial origin. In the embodiment of Figure 4, the apparatus 10 is located within the production zone of the wellbore 2. As can be seen in Figure 4, the production zone is isolated by packers 8, which may create a seal between the conduit 30 and the wellbore wall 4. The conduit 30 comprises perforations 36 through which oil or gas may be produced. The perforations could be pre-formed in the conduit 30 or created in situ, for example, by using a perforation gun, casing gun or high-shot density gun, etc.

The perforation of the conduit and subsequent acid injection therein may, for example, lead to the formation of fracture 6 within the wellbore formation. A large time difference between emission of the signal and detection of the reflection of the signal (e.g. the time difference being above a threshold) or absence of the reflected signal can be indicative of the presence of fracture openings. Fractures can also cause differences in frequencies or frequency spectrum between the emitted and detected signal which are due to interference of the acoustic wave at the fracture opening. The interference can be caused, for example, by reflection of the signal from opposing faces of the factures or fracture openings. Translational mapping of the wellbore sections containing fractures can provide information about the number and position of fractures in the wellbore formation. The determination of the presence of fractures in one or more closely located wellbores, such as injection and production wellbores, can provide an indication of flow via fractures between the injection and production wellbores.

In the embodiment of Figure 5 there is shown a centraliser 50 which acts as an equivalent to the tool body 20. The centraliser 50 is disposed or mounted on an outer surface of an inner tubular 36 to keep the inner tubular in the centre of conduit 30. The centraliser 50 can be secured to the inner tubular 36 by one or more hinges or collars 52. One or more bowstrings 54 of the centraliser 50 are in contact with the inner wall

32 of the conduit 30. The sensor 40 is mounted or disposed in or upon one or more bowstrings 54 of the centraliser 50. The sensor 40 is placed upon on the bowstring 54 of the centraliser 50 such that it is in engaging contact with the inner wall 32. In use, locating, running and/or retrieving the inner tubular 36 through the conduit 30 can lead to a translational scan of parts or sections of the wellbore 2. Once the centraliser is in position, the sensor 40 can indicate changes in the geometry of the wellbore 2 and/or the environment around the conduit 30 which may occur over longer time periods.

In the embodiment shown in Figures 6 (a) and 6 (b), the tool body 20 comprises or is comprised in a downhole tractor 60. The downhole tractor 60 can be used to propel one or more objects through the conduit, such as a wireline.

As shown in Figures 6 (a) and 6 (b) the downhole tractor 60 comprises a number of wheels 62 which are configured to engage the inner wall 32 of the conduit 30. The at least one wheel 62 is adapted to comprise the sensor 40. The sensor 40 can be arranged so as to be externally and/or outwardly facing from the wheel 60. The sensors 40 are configured to survey, log and/or sense the environment around the tractor 60, such as the wellbore walls and/or contents of the wellbore and/or the geological environment around the tractor 60. Each wheel 62 of the tractor can comprise one or more of sensors 40.

The wheels 62 are rotatably attached to the downhole tractor 60 in order to propel the tractor 60 through the conduit 30. The wheels 62 are mounted or attached to the tractor 60 so as to be movable radially outwardly and inwardly with respect to the tractor 60. For example, the wheel can be mounted on pivoting arms 64. Other suitable movement mechanisms can comprise arms 64 or pads which are biased by one or more springs. The wheel is biased radially outwardly by the arms 64 so as to be in contact with the inner wall 32 of the conduit 30.

In some examples, the wheels 62 comprise a deformable or pliant portion 66 that is provided on at least a portion of a periphery or outward portion of the wheel 62.

In the embodiment shown in Figures 6(a) and 6(b) the tractor 60 comprises four wheels 62 which are located radially outwardly of the tool body 20. However, in alternative embodiments the tractor 60 may comprise more or less than four wheels 62. The wheels 62 are circumferentially positioned around the tool body 20. In addition or alternatively, the wheels 62 can be positioned along a longitudinal axis A of the tractor 60.

With reference to the embodiment shown in Figures 6(a) two of the four wheels 62 are arranged diametrically opposed to each other and the two pairs of diametrically opposed wheels are positioned on the tool body. The wheels 62 are equally spaced from each other. In this embodiment, the wheels 62 are mounted 90° azimuthally apart from each other around the longitudinal axis A of tractor 60.

In some examples the wheels are positioned on the tractor 60 in sets, wherein each set of wheels 62 comprises a plurality of wheels 62, as shown in Figures 7 (a) and 7 (b). The sets of wheels 62 are longitudinally spaced to each other and provided in a staggered arrangement.

For example, the tractor 60 can comprise at least a first set of wheels 62, a second set of wheels 62 and a third set of wheels 62, wherein each set comprises one or more wheels 62. The sets of wheels 62 are longitudinally spaced and distributed on the tractor and located at positions rotated around the longitudinal axis A of the tractor 60 with respect to each other. For example, the second and third set of wheels can be provided at a position azimuthally rotated 10° to the first set of wheels. As can be seen in Figures 7 (a) and 7 (b), the rotation of the position of the second set of wheels 62 is in a direction opposite to that of the third set of wheels 62 so that the second set of wheels 62 is located at positions azimuthally rotated by -10° around the longitudinal axis A of the tractor 60 with respect to the first set. The third set can be located at positions azimuthally rotated by roughly +10° around the longitudinal axis of the tractor 60 with respect to the first set. However, it will be appreciated that other rotation angles are possible.

In some examples, the tool body 20 or the tractor 60 contains a control module (not shown) for controlling the signal emission and/or detection. The control module comprises a memory for storing or transmitting signals to the surface. The control module provides the sensors 40 with power. The control module can be configured to analyse the signal from the sensor 40. When the signal or data quality is insufficient and/or an insufficient number of measurements were tåken, the control module can initiate re-examination of a wellbore region. Power can be supplied to the apparatus 10 and/or sensor via the wireline 34.

A method for measuring geometry of a wellbore 2 is depicted in Figure 8. In use, apparatus is located within the conduit 30 that is located within the wellbore 2. The sensor is brought into engaging contact with an inner wall of the conduit. Once the sensor 40 is in contact with the inner wall 4, one or more signals are transmitted through the conduit towards a wall of the wellbore that surrounds the conduit. The one or more signals reflected back from the wall of the wellbore are detected by sensor 40 and the geometry of the wellbore behind the conduit from the detected signal is determined. Determining the geometry of the wellbore 2 can include determining the size, shape or dimensions, of the wellbore or wellbore wall. Properties indicative of near wellbore wall conditions or damage, such as fractures, cracking or deformation can be determined using the apparatus 10.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention. For example, the number of sensors as well as the arrangement of the sensors 40 on the tool body 20 or the tractor 60 may be modified. In alternative embodiments the sensors may be located only along the longitudinal axis of the tool body or tractor.

In alternative embodiment, the sensors 40 may be incorporated in permanent monitoring systems, stabilisers or collars etc. In alternative embodiments, the sensors may be attached to coiled tubing and the wellbore 2 is scanned while the coiled tubing is run through the wellbore 2. Other suitable downhole devices, structures or members could be suitably provided with sensors so as to form apparatus falling within the scope of the present invention.

In some embodiments the conduit comprises or defines a passage. For example, the conduit comprises or defines a tubular, tubing, casing and/or liner. In some embodiments, the conduit is provided within an outer conduit, e.g. a pipe inside a pipe arrangement.

Although the specific example given above describes measuring geometrical properties of the well bore, it will be appreciated that the above method and apparatus may also be used to detect or determine the extent of a device or structure provided between the conduit and the wall of the wellbore, such as an outer tubing, casing, conduit or liner or an obstruction, blockage, collapsed section or a gauge or other downhole tool, sensor or device.

It will also be appreciated that the above principles can also be applied to detecting perforations in the device or structure, e.g. in the outer tubing, casing, conduit or liner, for example, similarly to the detection of openings or cracks in the borehole wall.

Beneficially, another potential application of the above method and apparatus is in determining a thickness or thickness loss or variation or other geometrical property of the conduit and/or of the device, material or structure provided between the conduit and the wall of the wellbore.

Claims

1. A method for measuring geometry of a wellbore, the method comprising: providing a measuring apparatus within a conduit located within the wellbore; contacting an inner wall of the conduit with at least one sensor; transmitting one or more signals through the conduit towards a wall of the wellbore that surrounds the conduit; detecting one or more signals reflected back from the wall of the wellbore and/or from a device, apparatus or material between the conduit and the wall of the wellbore; and determining the geometry of the wellbore behind the conduit from the detected signal or detecting the device, apparatus or material between the conduit and the wall of the wellbore, or determining the geometry of the device, apparatus or material, using the detected signal.

2. The method according to claim 1, comprising determining properties indicative of near wellbore wall conditions or damage, such as fractures, cracking or deformation.

3. The method according to claim 1 or claim 2, comprising determining a time between emission of the signal and detection of the reflected signal, wherein the time between emission and detection of the one or more signals is indicative of a distance between the sensor or conduit and the wall of the wellbore or the device, apparatus or material between the conduit and the wall of the wellbore.

4. The method according to any preceding claim, comprising determining material properties behind the conduit based on at least one reflection, by measuring an amplitude of the emitted and/or detected signal.

5. The method according to any preceding claim, comprising detecting a location of entry points of fractures or cracks in the wellbore wall, wherein the time between emission of the signal and detection of the reflected signal is indicative of the presence of crack or fracture openings.

6. The method according to any preceding claim, comprising rotating the apparatus and/or sensor.

7. The method according to any preceding claim, comprising measuring the one or more properties of the wellbore at multiple points along a circumference or length of the wellbore to form a map or scan of the wellbore.

8. The method according to any preceding claim, comprising translating the apparatus through the conduit.

9. The method according to any preceding claim, comprising moving or extending the sensors into contact with the inner wall of the conduit.

10. The method according to any preceding claim, comprising re-examining a region of the wellbore when the data is insufficient and/or an insufficient number of measurements were tåken.

11. The method according to any preceding claim, wherein the device, apparatus or material between the conduit and the wall of the wellbore comprises an outer tubing, casing, conduit or liner or an obstruction, blockage or collapsed section or a gauge or other downhole tool, sensor or device.

12. The method according to claim 11, wherein method comprises detecting perforations in the outer tubing, casing, conduit or liner.

13. The method according to any preceding claim, wherein the method comprises determining a thickness or thickness loss or variation or other geometrical property of the conduit and/or of the device, material or structure provided between the conduit and the wall of the wellbore.

14. An apparatus for measuring geometry of a wellbore comprising a tool body to be provided within a conduit positioned in the wellbore, and at least one sensor supported by the tool body, wherein the apparatus is configured such that the sensor can contact an inner wall of the conduit when the tool body is located within the conduit; wherein the at least one sensor comprises one or more transmitters for emitting a signal towards an inner wall of the wellbore; the at least one sensor comprises one or more receivers for detecting a reflection of the signal from the inner wellbore wall and/or from a device, apparatus or material between the conduit and the wall of the wellbore; and a time between emission of the signal and detection of the reflection of the signal is indicative of a distance between the sensor or conduit and the inner wall of the wellbore or the presence or location of the device, apparatus or material between the conduit and the wall of the wellbore, or the geometry of the device, apparatus or material.

15. An apparatus according to claim 14, wherein the tool body is configured to bring the sensor into engaging contact with an inner wall of the conduit.

16. An apparatus according to claim 14 or 15, wherein the apparatus is operable to determine properties indicative of the shape, size or geometry of the wellbore, bore wall and/or near bore wall conditions, damage, fractures, cracking and/or deformation.

17. An apparatus according to any of claims 14 to 16, wherein the apparatus is configured to survey, log and/or sense the environment around the conduit and/or the bore walls and/or contents of the bore and/or the geological environment around the conduit.

18. An apparatus according to any of claims claim 14 to 17, wherein the signal comprises an acoustic signal.

19. An apparatus according to claims 14 to 18, wherein the sensors are located radially outwardly of the apparatus or a body of the apparatus.

20. An apparatus according to claims 14 to 19, wherein the tool body comprises or is comprised in a downhole tractor.

21. An apparatus according to claim 20, wherein the downhole tractor comprises at least one wheel configured to engage the inner wall of the conduit and the at least one wheel comprises the at least one sensor.

22. An apparatus according to claims 20 or 21, wherein, in use, propulsion of the tractor through the conduit enables the sensor to log or scan different points along the wellbore.

23. An apparatus according to any of claims 21 or 22, wherein the wheel is biased or biasable radially outwardly so as to contact the inner wall of the conduit.

24. An apparatus according to any of claims 21 to 23, wherein the wheels are circumferentially positioned around the tool body and/or positioned longitudinally and/or along a longitudinal axis of the tool body.

25. An apparatus according to claims 21 to 24, wherein the wheels are positioned on the tool body in a plurality of sets of wheels, and at least one of the sets of wheels is longitudinally spaced from at least one other set of wheels and/or at least one set of wheels are located at positions rotated around a longitudinal axis of the body with respect to at least one other set of wheels.

26. An apparatus according to any of claims 14 to 25, wherein the apparatus is configured to continuously rotate the at least one sensor while the tool body is run through the conduit, positioned in the conduit or retrieved from the conduit to scan the wellbore geometry.

27. An apparatus according to claims 14 to 19 or 26, wherein the tool body comprises or is comprised in a centraliser adapted to position an inner conduit within the conduit.

28. An apparatus according to claim 27, wherein one or more sensor(s) is mounted onto the centraliser such that the sensors are biased outwardly into contact with the inner wall of the conduit.

29. An apparatus according to any preceding claim, wherein the device, apparatus or material between the conduit and the wall of the wellbore comprises an outer tubing, casing, conduit or liner or an obstruction, blockage or collapsed section or a gauge or other downhole tool, sensor or device.

30. An apparatus according to any of claims 14 to 29, wherein the apparatus is configured to implement the method according to any of claims 1 to 13.

31. An apparatus substantially as shown or described herein with respect to the drawings.