WO2011010099A1

WO2011010099A1 - A method for stimulating a subsurface target material and associated apparatus

Info

Publication number: WO2011010099A1
Application number: PCT/GB2010/001390
Authority: WO
Inventors: Wayne Rudd
Original assignee: Wayne Rudd
Priority date: 2009-07-24
Filing date: 2010-07-22
Publication date: 2011-01-27
Also published as: GB2472080A; GB0912878D0

Abstract

A method for providing for stimulating a subterranean target material (620) comprises: transmitting an inspection signal (615) comprising a plurality of frequencies to a subterranean target material; receiving a stimulated signal (627) in response to transmitting of the inspection signal, the stimulated signal indicative of at least one excitable frequency of the target material; analysing the stimulated signal to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material, and transmitting an excitation signal (645) to the target material for stimulation. The target material may be material ahead of a drill bit, or may be material at a contact location between tubing and a drill string.

Description

A METHOD FOR STIMULATING A SUBSURFACE TARGET MATERIAL AND ASSOCIATED APPARATUS

Technical Field The invention relates to a method for stimulating a target material and associated apparatus. In particular, but not exclusively, a method for stimulating a subterranean target material by exciting that target material, such as resonantly exciting that target material. Background

In certain industries, such as the oil and gas exploration and production industry, geological investigations are performed to determine, as accurately as possible, particular subterranean material characteristics and formations. For example, in the oil and gas industry it can be helpful to determine the presence and location of subterranean hydrocarbon bearing formations or reservoirs, as well as the type of materials that surround these formations. When these formations have been identified, bores are drilled into the earth in order to provide access to the hydrocarbons, and allow for production.

Such bores are commonly drilled in successive stages, using extending drill strings provided with a drill bit for drilling, which sometimes extend for thousands of feet into the earth. The bores are typically lined with casing for bore support and sealing. Drilling though hard and hardened materials can be detrimental to the life span of the drill bit, as the drill bit begins to ablate and/or fatigue.

Similarly, drill strings that extend though bores, such as open or cased bores, can become stuck, or jammed, as the drill string comes into contact with the bore wall. In such cases, it may not be possible to advance the drill string into the bore, and/or rotate the drill string.

Summary

According to a first aspect of the invention there is a method for providing for stimulating a subterranean target material, the method comprising:

transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material; receiving a stimulated signal in response to transmitting of the inspection signal, the stimulated signal indicative of at least one excitable frequency of the target material; and

analysing the stimulated signal to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material.

The method may comprise transmitting an excitation signal to the target material, such as directly to the target material. The method may comprise transmitting an excitation signal for further transmitting to the target material. For example, the method may comprise transmitting the excitation signal from a transmitter coupled to the earth or ground, seabed, sea, etc. Alternatively, the excitation signal may be transmitted for subsequent transmittal to the target material by further apparatus, such as a further transmitter/emitter/amplifier coupled to a further transmission path (e.g. coupled to the earth, ground, etc.).

The excitation signal may comprise the at least one identified excitable frequency for stimulating the subterranean target material. The excitation signal may be greater in amplitude than the inspection signal so as to stimulate the target material. The excitation signal may be greater in duration than the inspection signal so as to stimulate the target material. The excitation signal may be configured so as to agitate the target material. The excitation signal may be configured so as to heat the target material.

The method may comprise transmitting an excitation signal comprising a plurality of excitable frequencies of the target material so as to provide for stimulating of the target material. The excitation signal may comprise a plurality of frequencies, which may be discrete frequencies. The excitation signal may comprise a plurality of harmonic excitable frequencies. The method may comprise transmitting the inspection signal so as to transmit a plurality of discrete frequencies. The method may comprise transmitting the inspection signal so as to transmit a plurality of discrete frequencies sequentially or roughly sequentially. For example, the inspection signal may comprise a stepped chirp. The method may comprise transmitting the inspection signal so as to transmit a plurality of discrete frequencies simultaneously, or roughly simultaneously. For example, the inspection signal may comprise a ladder chirp. The method may comprise transmitting the inspection signal so as to transmit some of the plurality of discrete frequencies (roughly) simultaneously and some of the plurality of discrete frequencies (roughly) sequentially.

The method may comprise transmitting the inspection signal so as to transmit a plurality of frequencies contained within a particular bandwidth. For example, the inspection signal may be transmitted having a particular bandwidth over a range of frequencies, which may have little or no frequency separation/spacing. The inspection signal may be transmitted having a particular bandwidth over a range of frequencies, which has common frequency spacing (e.g. 50 Hz between central frequencies). The inspection signal may be transmitted having a particular bandwidth over a range of frequencies, which has irregular frequency spacing (e.g. 50 Hz, then

40 Hz, then 20 Hz, etc. between central frequencies).

The method may comprise transmitting a first inspection signal having a first particular bandwidth, and transmitting a second inspection signal having a second particular bandwidth. The first bandwidth may be greater than the second. The second bandwidth may be determined based on the at least one excitable frequency of the target material identified by analysing the stimulated signal. The method may comprise transmitting a third, four, fifth, sixth, etc. inspection signal. Each subsequent inspection signal may have a narrower bandwidth than a previous inspection signal.

The method may comprise receiving a stimulated signal after transmittal of each inspection signal so as to determine the bandwidth of subsequent inspection signals.

The inspection signal may be configured to oscillate the target material at a particular frequency (e.g. at an excitable frequency of the target material) after the inspection signal has ceased to be transmitted to the target material. For example, the inspection signal may be configured to be transmitted for the period of 1 second, 5 seconds, 10 seconds, 1 minute, 5 minutes, 10 minutes, or the like, or any time therebetween. Providing for transmitting of an inspection signal for such duration may allow the target material to begin absorb the inspection signal energy at an excitable frequency over a period of time and begin to oscillate, such as oscillate resonantly.

The stimulated signal may be generated or provided by an oscillating subterranean target material. For example, the stimulated signal may be generated by the oscillating target material after the transmittal of inspection signal has ceased to be transmitted to the target material. The stimulated signal may be provided by the excited oscillations of the target material being emitted back into the surrounding ground or earth, such as after the inspection signal has ceased to be transmitted to the target material. Whereby receipt and analysis of that stimulated signal may provide for identifying the particular excitable oscillations of the target material so as to provide for stimulating (e.g. further stimulation, agitation, heating, etc.) of the target material.

The method may comprise receiving a reflected signal. The reflected signal may be indicative of a reflected inspection signal, reflected from the target material. The receipt of the reflected signal may provide for evaluating the time of flight of the inspection signal and reflected inspection signal. The time of flight may provide for the relative distance from the target material to be estimated/approximated/evaluated, such as by using the estimate/approximate/known velocity of the inspection signal and reflected inspection signal in the transmission medium.

The stimulated signal may be at least partially defined by a reflected inspection signal. The stimulated signal may be a reflected inspection signal. In such cases, the stimulated signal (i.e. reflected inspection signal) may be analysed to identify at least one excitable frequency of the target material by analysing what frequencies the target material has absorbed. For example, analysing the stimulated signal may involve identifying certain frequencies that were comprised with the inspection signal, but which are absent/attenuated in the reflected inspection signal. Analysing the stimulated signal may involve identifying certain frequencies that were comprised with the inspection signal, but which are significantly attenuated in the reflected inspection signal with respect to other frequencies present in the reflected inspection signal, which may also be attenuated.

The stimulated signal, when provided partially/fully by a reflected inspection signal, may also provide for time of flight analysis, which may include relative distance analysis (as above).

The method may comprise receiving a stimulated signal, the simulated signal being provided by a stimulated transducer in the region of the target material, such as in close proximity, contact (e.g. touching contact) with the target material. The stimulated signal may be provided by a stimulated transducer integral/combined with the target material. The stimulated transducer may be configured to provide the stimulating signal in response to excitation of the target material as a result of transmitting the inspection signal The stimulated signal may comprise the excitable frequency(s) of the target material The stimulated signal may comprise communicable data to allow for identifying of the excitable frequency(s) The method may comprise receiving a stimulated signal, the stimulated signal being provided by two or more of a signal emitted from an excited target material, a reflected inspection signal, a signal transmitted from a stimulated transducer

The method may comprise transmitting/receiving the respective inspection sιgnal(s), stimulated sιgnal(s), excitation sιgnal(s) using one or more common transducers The method may comprise transmitting/receiving the respective inspection sιgnal(s), stimulated sιgnal(s), excitation sιgnal(s) using different transducers, which may be spaced from one another For example transmit/receive transducers may be spaced from one another so as to provide spatial resolution

The method may comprise transmitting an inspection signal so as to transmit a plurality of frequencies in a range up to 500 Hz to the target material (e g having bandwidth of 200 Hz, between 250 Hz and 450 Hz) The method may comprise analysing the stimulated sιgnal(s) to identify at least one resonant frequency of the target material so as to provide for stimulating of the target material, which may be resonant stimulating The method may comprise analysing the stimulated sιgnal(s) to identify at least one natural frequency of the target material so as to provide for stimulating of the target material The method may be for use with geological surveying, which may be underwater surveying The method may be for use with oil and gas exploration and production

The inspection sιgnal(s) stimulated sιgnal(s), and/or excitation sιgnal(s) may comprise acoustic signals, and/or electromagnetic signals, such as extremely low frequency (ELF) electromagnetic signals, super low frequency (SLF) electromagnetic signals, and/or ultra low frequency (ULF) electromagnetic frequency

The method may comprise transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material to a region associated with a drill bit, such as a region ahead of a drill bit The method may comprise transmitting an inspection signal comprising a plurality of frequencies for further transmittal to a subterranean target material associated with a drill bit For example, transmitting an inspection signal to a further device and/or transducer for further transmittal to a subterranean target material ahead of a drill bit, such as transmitting to a further apparatus associated with a drill bit, such that the further apparatus transmits the inspection signal to a target material ahead of a drill bit

The subterranean target material associated with the drill bit may be in the region of the drill bit, such as in proximal contact (e g within 2 metres, 5 metres, 10 metres, 20 metres, 50 metres, etc , or any number therebetween) The subterranean target material associated the drill bit may be in contact with the drill bit, such as touching contact ahead of the drill bit The subterranean target material ahead of the drill bit may be partially/fully surrounding the drill bit The subterranean target material ahead of the drill bit may be in the region of the drill bit, such as in proximal contact (e g within 2 metres, 5 metres, 10 metres, etc , or any number therebetween) The method may comprise identifying at least one resonant/excitation frequency of the target material ahead of a drill bit, so as to provide for simulation, agitation, heating, etc of target material and allow for improved drilling performance, such as reducing the wear on the drill bit The method may comprise transmitting the inspection signal from a region in association with a drill bit For example, the region may be a portion of the drill bit, or apparatus associated with a drill bit, such as a drill string The method may comprise receiving the stimulated signal at a drill bit, or at an apparatus associated with a drill bit (e g a bottom hole assembly comprising a drill bit) The method may comprise receiving the stimulated signal remotely from a drill bit

The inspection signal may be transmitted in a plurality of directions, such as being omnidirectional The inspection signal may be unidirectional The method may comprise directing the inspection signal in a particular direction, such as by using beamforming (e g using a phased array antenna), which may allow for directing of the inspection signal towards a particular target material

The method may comprise identifying a particular direction for a drill bit to adopt based on the excitation/resonant characteristics of different target materials in the region of the drill bit (e g ahead of the drill bit, to one side of the drill bit, etc ) The method may comprise identifying regions of material for avoiding For example, the method may comprise identifying regions of material to be avoided based on their stimulated characteristics.

The method may comprise transmitting the excitation signal from a drill bit. The method may comprise vibrating apparatus associated with a drill bit to provide for transmitting of the excitation signal. The method may comprise vibrating the drill bit to provide for transmitting of the excitation signal. The method may comprise configuring the performance of the drill bit so as to provide the excitation signal, which may be in addition to other frequencies being provided by the drill bit/apparatus. For example, the method may comprise modifying the speed of a drill bit in order to provide the excitation signal.

The method may comprise providing for modifying the direction of a drill bit based on received simulated signal(s). The method may comprise providing for modifying the direction of a drill bit based on received simulated signal(s).

The method may comprise transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material within a bore. The target material may be a material region at a location in which a first material is in contact with a second material provided within a bore, such as touching/rubbing/jamming contact of a drill string and tubing. The first and second materials may be the same materials, such as steel.

Tubing may be provided in a lined, or unlined bore. Tubing may be considered to comprise casing, liner tubing, etc.

The method may comprise transmitting the inspection signal through tubing. For example, tubing extending into the bore. The method may comprise transmitting the inspection signal through a drill string within a bore. The method may comprise transmitting the inspection signal through both the tubing of a bore and drill string.

The method may comprise receiving the stimulated signal from one or both of the drill string and tubing. The method may comprise transmitting the excitation signal to the target material using one or both of the tubing and drill string. The excitation signal may comprise the at least one identified excitable frequency for stimulating the target material (e.g. the target material being the location of a jam between a drill string and a tubing). The excitation signal may be configured to agitate the target material, for example so as to un-jam the target material. The excitation signal may be configured to heat the target material, for example using electromagnetic radiation.

The method may comprise attempting to move the drill string in addition providing the excitation signal.

The method may comprise using the time of flight of a reflected inspection signal (and/or stimulated signal) to identify the relative distance to the target material. The method may comprise using the phase relationship between two signals/reflected signals to identify the distance to the target material. The method may comprise identifying the relative distance using a technique such as that described in UK Patent Application, GB 0808189.5, which is incorporated herein by reference.

According to a second aspect of the invention there is a method comprising:

transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material;

receiving a stimulated signal in response to transmitting of the inspection signal, the stimulated signal indicative of at least one excitable frequency of the target material; and

analysing the stimulated signal to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material. The method may comprise any of the features of the first aspect.

According to a third aspect of the invention there is provided apparatus for providing for stimulating a subterranean target material, the apparatus comprising: an inspection transmitter configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material; a stimulation receiver configured to receive a stimulated signal in response to transmission by the transmitter of an inspection signal, wherein the stimulated signal is indicative of at least one excitable frequency of a target material; and an analyser configured to analyse a received stimulated signal and to identify at least one excitable frequency of a target material so as to provide for stimulating of a target material. The apparatus may comprise an excitation transmitter. The excitation transmitter may be in communication with the analyser, and may be configured to transmit an excitation signal to a target material, such as directly to a target material. The excitation transmitter may be configured to transmit an excitation signal that comprises the excitable frequency(s) identified by the analyser.

The excitation transmitter may be configured for coupling with the ground or earth, seabed, etc. so as to provide a communication path with a target material. The excitation transmitter may be configured to transmit an excitation signal to a further apparatus (e.g. a further transmitter) for further transmittal to a target material. For example, such a further apparatus may be coupled to the earth or ground, etc. for transmittal of an excitation signal to a target material.

The inspection transmitter may be configured to transmit an inspection signal directly to a target material, or may be configured to transmit of an inspection signal to a further apparatus for transmittal to a target material. Similarly, the stimulation receiver may be configured to receive a stimulated signal directly from a target material, or from a further apparatus. The apparatus may be configured to accommodate/correct for dispersive effects of particular frequencies in signal(s) when being communicated (transmitted and/or received) to/from further apparatus/target materials.

The apparatus may be configured to provide an excitation signal comprising the identified excitable frequency(s) for stimulating a subterranean target material. The apparatus may be configured to provide an excitation signal greater in amplitude than an inspection signal so as to stimulate a target material. The apparatus may be configured to provide an excitation signal greater in duration than an inspection signal so as to stimulate a target material. The apparatus may be configured to provide an excitation signal configured so as to agitate a target material. The apparatus may be configured to provide an excitation signal configured so as to heat a target material.

The apparatus may be configured to transmit a plurality of excitable frequencies of a target material so as to provide for stimulating of a target material. The apparatus may be configured to transmit a plurality of excitable frequencies, which may be discrete frequencies. The apparatus may be configured to transmit a plurality of harmonic excitable frequencies. The apparatus may be configured to transmit a plurality of discrete frequencies. The apparatus may be configured to transmit a plurality of discrete frequencies sequentially, or roughly sequentially. For example, the inspection signal may comprise a stepped chirp. The apparatus may be configured to transmit a plurality of discrete frequencies simultaneously, or roughly simultaneously. For example, the inspection signal may comprise a ladder chirp. The apparatus may be configured to transmit some of the plurality of frequencies (roughly) simultaneously and some of the plurality of discrete frequencies (roughly) sequentially. The apparatus may be configured to transmit an inspection signal comprising a plurality of frequencies contained within a particular bandwidth. For example, the apparatus may be configured to transmit an inspection signal having a plurality of frequencies having a particular bandwidth over a range of frequencies, which may have little or no frequency separation/spacing. The apparatus may be configured to transmit an inspection signal having a particular bandwidth over a range of frequencies, which have common frequency spacing (e.g. 50 Hz between central frequencies). The apparatus may be configured to transmit an inspection signal having a particular bandwidth over a range of frequencies, which has irregular frequency spacing (e.g. 50 Hz, then 40 Hz, then 20 Hz, etc. between central frequencies).

The apparatus may be configured to transmit a first inspection signal having a first particular bandwidth, and transmit a second inspection signal having a second particular bandwidth. The first bandwidth may be greater than the second. The second bandwidth may be determined based on the at least one excitable frequency of a target material identified by analysing a stimulated signal. The apparatus may be configured to transmit a third, four, fifth, six, etc. inspection signal. Each subsequent inspection signal may have a narrower bandwidth than a previous inspection signal. The apparatus may be configured to receiving a stimulated signal after transmittal of each inspection signal so as to determine the bandwidth of subsequent inspection signals.

The apparatus may be configured to provide an inspection signal configured to oscillate a target material at a particular frequency (e.g. at an excitable, and/or resonant, and/or natural frequency of a target material) after an inspection signal has ceased to be transmitted. For example, the apparatus may be configured to transmit an inspection signal for a period of 1 second, 5 seconds, 10 seconds, 1 minute, 5 minutes, 10 minutes, or the like, or any duration therebetween. Providing for transmitting of an inspection signal for such duration may allow for a target material to begin absorb inspection signal energy at an excitable frequency over a period of time and begin to oscillate, such as oscillate resonantly.

The apparatus may be configured to receive a stimulated signal generated or provided by an oscillating subterranean target material. For example, the stimulated signal may be generated by an oscillating target material after the transmittal of an inspection signal has ceased. The apparatus may be configured to listen for a stimulated signal, only after transmission of an inspection signal has ceased, or partially ceased. The apparatus may be configured to listen for a stimulated signal, during transmission of an inspection signal.

The apparatus may be configured to receive, as a stimulated signal, excited oscillations of a target material being emitted back into the surrounding ground or earth. The analyser may be configured to analyse such a stimulated signal to provide for identifying of particular excitable oscillations of a target material so as to provide for stimulating (e.g. further stimulation, agitation, heating, etc.) of a target material. The apparatus may be configured to receive a reflected signal, reflected from a target material. The apparatus may be configured to receive a reflected signal, wherein the reflected signal may be indicative of a reflected inspection signal, reflected from a target material. The apparatus may be provided with a reflection receiver, configured to receive a reflected signal/reflected inspection signal.

The apparatus may be configured to evaluate the time of flight of an inspection signal and reflected inspection signal. The apparatus may be configured to estimate/evaluate/approximate the relative distance of the apparatus from a target material, such as by using the estimated/approximated/known velocity of an inspection signal and/or reflected inspection signal.

The stimulated signal may be at least partially defined by a reflected inspection signal. The stimulated signal may be a reflected inspection signal. In such cases, the stimulated signal may be analysed to identify an excitable frequency of the target material by analysing what frequencies a target material has absorbed. For example, the apparatus may be configured to analyse a stimulated signal so as to identify certain frequencies that were comprised with an inspection signal, but which are absent/attenuated in the reflected inspection signal. The apparatus may be configured to identify certain frequencies that were comprised with the inspection signal, but which are significantly attenuated in a received reflected inspection signal with respect to other frequencies present in a received reflected inspection signal.

The apparatus may be configured to evaluate the time of flight of a stimulated signal, when provided partially/fully by a reflected inspection signal, which may also provide for time of flight analysis, which may include relative distance analysis (as above). The apparatus may be configured for use with a stimulated transducer, the stimulated transducer configured to be located at, or in the region of, a target material, such as in close proximity, contact (e.g. touching contact) with a target material. The stimulated transducer may be configured to be integral/combined with a target material.

The stimulated transducer may be configured to provide the stimulating signal in response to excitation of a target material as a result of transmitting an inspection signal. That is to say that the stimulated transducer may be configured to communicate a stimulated signal to the stimulation receiver for receipt thereof. The stimulated transducer may use a wired, or wireless, or combination of wired/wireless path so as to provide for communication of the stimulated signal. For example, the earth or ground may be used as a communication/transmission path. The stimulated signal may comprise the at least one excitable frequency of the target material. The stimulated signal may comprise communicable data to allow for identifying the at least excitable frequency.

The apparatus may be configured to receive a stimulated signal provided by two or more of: a signal emitted from an excited target material; a reflected inspection signal; a signal transmitted from a stimulated transducer.

At least two of the inspection transmitter, stimulation receiver and excitation transmitter may be provided by a common transducer All of the inspection transmitter, stimulation receiver and excitation transmitter may be provided by a common transducer. At least two of inspection transmitter, stimulation receiver and excitation transmitter may be provided by a spaced/displaced from one another, which may allow for the apparatus to evaluate spatial resolution The apparatus may be configured to transmit an inspection signal at a plurality of frequencies in the range up to 500 Hz to a target material The apparatus may be configured to identify at least one resonant frequency of a target material so as to provide for stimulating of a target material, which may be resonant stimulating The apparatus may be configured for use with geological surveying, which may be underwater surveying The apparatus may be configured for use with oil and gas exploration and/or production

The apparatus may be configured to use inspection/stimulated/excitation sιgnal(s) comprising acoustic signals, and/or electromagnetic signals, such as extremely low frequency (ELF) electromagnetic signals, super low frequency (SLF) electromagnetic signals, and/or ultra low frequency (ULF) electromagnetic frequency

The apparatus may be configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material associated with of a drill bit, such as ahead of a drill bit The apparatus may be configured to transmit an inspection signal comprising a plurality of frequencies for further transmitting to a subterranean target material associated with a drill bit For example, the apparatus may be configured to transmit an inspection signal to a further apparatus for further transmission to a subterranean target material ahead of a drill bit The apparatus may be configured to transmit an inspection signal having been conditioned for further transmittal by a further apparatus, such as by conditioning the signal to account for dispersive effects Subterranean target material associated with a drill bit may be in the region of a drill bit, such as in proximal contact (e g within 2 metres, 5 metres 10 metres, 50 metres, etc , or any number therebetween) Subterranean target material ahead of a drill bit may be in contact with a drill bit, such as touching contact Subterranean target material associated with a drill bit may be partially/fully surrounding a drill bit Subterranean target material ahead of a drill bit may be in the region of a drill bit, such as in proximal contact (e g within 2 metres, 5 metres, 10 metres, 50 metres etc , or any number therebetween) The apparatus may be configured to identify at least one resonant/excitation frequency of target material associated with a drill bit, such as ahead of a drill bit. For example, so as to provide for simulation, agitation, heating, etc. of target material to allow for improved drilling performance, such as reducing the wear on a drill bit.

The apparatus may be provided at a region in association with a drill bit. For example, the region may be a portion of the drill bit, or apparatus associated with a drill bit, such as a drill string, bottom hole assembly, or the like.

The apparatus may be configured to transmit an inspection signal in a plurality of directions, for example, in all/substantially all directions (i.e. omnidirectional). The apparatus may be configured to transmit an inspection signal unidirectionally. The apparatus may be configured to direct an inspection signal in a particular direction, such as by using beamforming (e.g. using a phased array antenna), which may allow for directing of an inspection signal towards a particular target material.

The apparatus may be configured to provide a directional signal, the directional signal based on the excitation/resonant characteristics of target materials, such as different target materials in the region of a drill bit (e.g. ahead of the drill bit, to one side of the drill bit, etc.). The directional signal may provide information/data to allow a drill bit to adopt a particular direction. The apparatus may be configured to identify (or provide for identifying) regions of material to be avoided by a drill bit. For example, the apparatus may be configured to identify regions of material to be avoided based on their stimulated characteristics, such as regions of clay, or the like, which may hinder the progress/efficiency of a drill bit.

The apparatus may be comprised with excitation apparatus, the excitation apparatus being associated with a drill bit so as to provide for transmitting of the excitation signal. The excitation transmitter may be comprised, at least partially, with a drill bit (e.g. configured such that vibrating a drill bit provides for transmitting of the excitation signal). The apparatus may be configured to modify/control the performance of a drill bit so as to provide the excitation signal, which may be in addition to other frequencies being provided by the drill bit/apparatus. For example, the apparatus may be configured to provide the excitation signal cumulatively and/or differentially with the vibration of a drill bit. That is to say, that the apparatus may be configured to modify the speed of a drill bit such that the vibratory output from a drill bit serves, at least partially, as an excitation signal

The apparatus may be configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material within a bore The target material may be a material at a location in which a first material is in contact with a second material provided within a bore, such as touching/rubbing/jamming contact of a drill string with tubing The first material may be the same as the second material, such as being provided by steel

Tubing may be provided in a lined, or unlmed bore Tubing may be considered to comprise casing, liner tubing, etc

The apparatus may be configured to transmit an inspection signal through tubing For example, tubing extending into a bore, etc The apparatus may be configured to transmit an inspection signal through a drill string within a bore The apparatus may be configured to transmit an inspection signal through both tubing of a bore and a drill string (e g a drill string passing at least partially through tubing, such as casing, of a bore)

The apparatus may be configured to receive a stimulated signal from one or both of a drill string and tubing The apparatus may be configured to transmit an excitation signal to a target material using one or both of tubing and drill string In such instances, the apparatus may be configured to provide an excitation signal comprising the at least one identified excitable frequency for stimulating a target material For example, the target material may be the location of a jam between a drill string and a tubing

The apparatus may be configured to provide an excitation signal configured to agitate a target material so as to remove/alleviate a jam The apparatus may be configured to provide an excitation signal configured to heat a target material, for example using electromagnetic radiation

The apparatus may be configured to move, such as vibrate, a drill string in addition providing an excitation signal to a target material, such a simultaneously move The apparatus may be configured to identify the time of flight of a reflected signal (such as a reflected inspection signal and/or stimulated signal) to identify the relative distance to a target material, such as the relative distance between the apparatus and a jam between drill string and tubing (e.g. by using the approximated speed of the signal in a tubing, and/or drill string). The apparatus may be configured to identify the phase relationship between two signals/reflected signals to identify the distance to the target material. The apparatus may be configured to identify the distance based on UK Patent Application, GB 0808189.5, which is incorporated herein by reference.

According to a fourth aspect of the invention there is provided apparatus comprising: an inspection transmitter configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material; a stimulation receiver configured to receive a stimulated signal in response to transmission by the transmitter of an inspection signal, wherein the stimulated signal is indicative of at least one excitable frequency of a target material; and an analyser configured to analyse a received stimulated signal and to identify at least one excitable frequency of a target material so as to provide for stimulating of a target material. The apparatus may comprise any of the features of the third aspect.

According to a fifth aspect of the invention there is a method comprising:

transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material ahead of a drill bit;

analysing the stimulated signal to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material and improved drilling performance.

The method may comprise transmitting an excitation signal directly to the target material. The method may comprise transmitting an excitation signal for further transmitting to the target material.

The method may comprise identifying a particular direction for the drill bit to adopt based on the excitation/resonant characteristics of different target materials in the region of the drill bit (e.g. ahead of the drill bit, to one side of the drill bit, etc.). The method may comprise identifying regions of material for avoiding. For example, the method may comprise identifying regions of material to be avoided based on their stimulated characteristics.

According to a sixth aspect of the invention there is a method comprising:

transmitting an inspection signal comprising a plurality of frequencies to a subterranean target material within a bore;

analysing the stimulated signal to identify at least one excitable frequency of the target material within the bore so as to provide for stimulating of the target material.

The method may comprise transmitting an excitation signal directly to the target material. The method may comprise transmitting an excitation signal for further transmitting to the target material. The method may comprise transmitting the inspection signal so as to identify a jam, interference or the like between an object, such as a tubing, within a bore, such as a cased or open bore. The transmitting of the excitation signal may provide for alleviating/removing the jam.

According to a seventh aspect of the invention there is a method for providing for stimulating a subterranean target material, the method comprising:

transmitting an inspection signal comprising a plurality of frequencies for transmittal to a subterranean target material;

The method may comprise transmitting an excitation signal for transmitting to the target material. The excitation signal may comprise the at least one identified excitable frequency for stimulating the subterranean target material. The excitation signal may be greater in amplitude than the inspection signal so as to stimulate/agitate the target material. The method may comprise emitting the excitation signal from a transmitter coupled to the earth/ground. The method may comprise transmitting the excitation signal for further transmittal to the target material. For example, the excitation signal may be transmitted from a controller for subsequent transmittal to target material by a transmitter/emitter/amplifier coupled to the earth/ground.

The method may comprise transmitting the inspection signal to the target material (e.g. directly to the target material). For example, the method may comprise emitting the inspection signal from a transmitter coupled to the earth/ground. The method may comprise transmitting an inspection signal for further transmittal to the target material. For example, the inspection signal may be transmitted from a controller for subsequent transmittal to target material by a transmitter/emitter/amplifier coupled to the earth/ground.

According to an eight aspect of the invention there is provided a method of oil and gas production/exploration, the method comprising any of the features of first, second, fifth, sixth, and/or seventh aspect of the invention. The method may be remote oil and gas production/exploration.

According to a ninth aspect of the invention there is provided oil and gas production/exploration apparatus, the oil and gas production/exploration apparatus comprised with the apparatus according to any of the features of the third and fourth aspects.

The oil and gas production/exploration apparatus may be any one or more of: tubing; a drill string; a drill bit; a bottom hole assembly; apparatus for an oil rig/platform; an oil rig/platform; apparatus for remote communication with an oil rig/platform.

According to a tenth aspect of the invention there is a method for providing for stimulating a subterranean target material, the method comprising:

transmitting a means for inspecting comprising a plurality of frequencies to a subterranean target material;

receiving a means for identifying an excitable frequency in response to transmitting of the means for inspecting, the means for identifying an excitable frequency indicative of at least one excitable frequency of the target material; and analysing the means for identifying an excitable frequency to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material. According to an eleventh aspect of the invention there is a method comprising:

receiving a means for identifying an excitable frequency in response to transmitting of the inspection signal, the means for identifying an excitable frequency indicative of at least one excitable frequency of the target material; and

analysing the means for identifying an excitable frequency to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material. According to a twelfth aspect of the invention there is provided a means for providing for stimulating a subterranean target material, the means for providing for stimulating a subterranean target material comprising: a means for transmitting configured to transmit a means for inspecting comprising a plurality of frequencies to a subterranean target material; a means for receiving configured to receive a means for identifying an excitable frequency in response to transmission by the means for transmitting of a means for identifying an excitable frequency, wherein the means for identifying an excitable frequency is indicative of at least one excitable frequency of a target material; and a means for analysing configured to analyse a received means for identifying an excitable frequency and to identify at least one excitable frequency of a target material so as to provide for stimulating of a target material.

According to a thirteenth aspect of the invention there is provided or providing for stimulating a subterranean target material comprising: a means for transmitting configured to transmit a means for inspecting comprising a plurality of frequencies to a subterranean target material; a means for receiving configured to receive a means for identifying an excitable frequency in response to transmission by the means for transmitting of a means for identifying an excitable frequency, wherein the means for identifying an excitable frequency is indicative of at least one excitable frequency of a target material; and a means for analysing configured to analyse a received means for identifying an excitable frequency and to identify at least one excitable frequency of a target material so as to provide for stimulating of a target material. According to a fourteenth aspect of the invention there is a method comprising:

transmitting a means for inspecting comprising a plurality of frequencies to a subterranean target material ahead of a means for drilling;

receiving a means for identifying an excitable frequency in response to transmitting of the means for inspecting, the means for identifying an excitable frequency indicative of at least one excitable frequency of the target material; and analysing the means for identifying an excitable frequency to identify at least one excitable frequency of the target material ahead of a means for drilling so as to provide for stimulating of the target material and improved drilling performance.

According to a fifteenth aspect of the invention there is a method comprising:

transmitting a means for inspecting comprising a plurality of frequencies to a subterranean target material within a means for a bore;

receiving a means for identifying an excitable frequency in response to transmitting of the means for inspecting, the means for identifying an excitable frequency indicative of at least one excitable frequency of the target material; and analysing the means for identifying an excitable frequency to identify at least one excitable frequency of the target material within the means for a bore so as to provide for stimulating of the target material.

According to a sixteenth aspect of the invention there is a method for providing for stimulating a subterranean target material, the method comprising:

transmitting a means for inspecting comprising a plurality of frequencies for transmittal to a subterranean target material;

receiving a means for identifying an excitable frequency in response to transmitting of the means for inspecting, the means for identifying an excitable frequency indicative of at least one excitable frequency of the target material; and analysing the means for identifying an excitable frequency to identify at least one excitable frequency of the target material so as to provide for stimulating of the target material.

According to a seventeenth aspect of the invention there is provided a method of oil and gas production/exploration, the method comprising any of the features of tenth, eleventh, fourteenth, fifteenth, and/or sixteenth aspect of the invention. The method may be remote oil and gas production/exploration.

According to an eighteenth aspect of the invention there is provided means for oil and gas production/exploration, the means for oil and gas production/exploration comprised with the or providing for stimulating a subterranean target material according to any of the features of the twelfth and/or thirteenth aspects.

According to a nineteenth aspect, there is a computer program, stored on a computer readable medium, the computer program comprising instructions to provide the method of any of the features of first, second, fifth, sixth, seventh, tenth, eleventh, fourteenth, fifteenth, and/or sixteenth aspect of the invention.

The invention includes one or more corresponding aspects, embodiments or features in isolation or in various combinations with of aspects whether or not specifically stated (including claimed) in that combination or in isolation. It will be appreciated that one or more embodiments/features/aspects may be useful in stimulating subterranean target material.

The above summary is intended to be merely exemplary and non-limiting.

Brief description of the figures

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 shows various exemplary embodiments of apparatus for providing for stimulating a subterranean target material;

Figure 2 shows an exemplary embodiment of apparatus in use with a stimulating transducer and target material;

Figure 3 shows exemplary plots of signals provided by the apparatus/stimulating transducer of Figure 2; Figure 4 shows a further exemplary embodiment of an apparatus in use with a target material; Figure 5 shows exemplary plots of signals provided by the apparatus/target material of Figure 4;

Figure 6 shows a further exemplary embodiment of an apparatus in use with a target material;

Figure 7 shows exemplary plots of signals provided by the apparatus/target material of Figure 6; Figure 8 shows exemplary embodiments of apparatus provided with a drill bit;

Figure 9 shows exemplary embodiments of apparatus provided with tubing and drill string; and Figure 10 shows a flowchart of providing for stimulating of a target material. Detailed description of the figures

Figure 1a shows an exemplary embodiment of an apparatus 100 for providing for stimulating a subterranean target material. The apparatus 100 comprises an inspection transmitter 110. The inspection transmitter 1 10 is configured to transmit an inspection signal 115 comprising a plurality of frequencies to a subterranean target material. The apparatus 100 further comprises a stimulation receiver 120 configured to receive a stimulated signal 125. A stimulated signal 125 is provided, by a target material or otherwise, in response to transmission by the inspection transmitter 110 of an inspection signal 115, as will be described. The apparatus 100 further comprises an analyser 130. The analyser 130 is provided by a frequency detector and is in communication with the stimulation receiver 120. The analyser 130 is configured to analyse a received stimulated signal 125 to identify at least one excitable frequency of a target material, and provide information regarding that at least one excitable frequency in order to provide for stimulating a target material. Here, the apparatus 100 further comprises an excitation transmitter 140, in communication with the analyser 130, and configured to provide an excitation signal 145 based on the at least one excitable frequency of a target material identified by the analyser 130. In the present embodiment, the excitation transmitter transmits that particular excitation frequency, identified by the analyser 130, to a target material.

Figure 1 b shows a further exemplary embodiment of an apparatus 200, comprising an inspection transmitter 210 configured to transmit an inspection signal 215 comprising a plurality of frequencies to a subterranean target material, stimulation receiver 220 configured to receive a stimulated signal 225, analyser 230, and excitation transmitter 240 configured to provide an excitation signal 245. Again, the analyser 230 is in communication with the stimulation receiver 220 so as to identify at least one excitable frequency of a target material. Similarly, the analyser 230 is configured to provide the at least one excitable frequency to the excitation transmitter 240 for excitable transmission of that frequency to a target material using the excitation signal 245. In addition, the analyser 230 is configured to provide the at least one excitable frequency to the inspection transmitter 210 such that the inspection transmitter 210 may modify subsequent transmissions of the inspection signal 215 based on the received excitable frequency(s).

In this embodiment, all of the inspection transmitter 210, stimulation receiver 220, and excitation transmitter 240 are configured for transmission or receipt of their respective signals 215, 225, 245 via further apparatus 210a, 220a, 240a (such as further acoustic transducers, or the like). That is, the apparatus 200 is configured to communicate remotely with further apparatus 210a, 220a, 240a so as to transmit/receive the respective signals 215, 225, 245. It will readily be appreciated that in some embodiments, the apparatus 200 may be configured to condition the respective signals 215, 225, 245 for communication with further apparatus 210a, 220a, 240a and/or target material. For example, the apparatus 200 in the present embodiment is configured to condition the respective signals 215, 225, 245 based on the transmission characteristics of the transmission lines to each of the further apparatus 210a, 220a, 240a, in order to account for anticipated dispersive effects of the transmission lines. Figure 1c shows a further exemplary embodiment of an apparatus 300, comprising an inspection transmitter 310 configured to transmit an inspection signal 315 comprising a plurality of frequencies to a subterranean target material, stimulation receiver 320 configured to receive a stimulated signal 325, and analyser 330. Here, the analyser 330 is again in communication with the stimulation receiver 320 and is configured to identify at least one excitable frequency of a target material. However, the apparatus 300/analyser 330 are configured to provide information regarding the identified excitable frequency(s) of a target material for use by a further device.

Figure 1d shows a further exemplary embodiment of an apparatus 400. Here, the apparatus 400 comprises an inspection transmitter 410, and stimulation receiver 420, similar to that described above. In this embodiment the inspection transmitter 410 and stimulation receiver 420 are provided by a transceiver 460. In other words, the inspection transmitter 410 and stimulation receiver 420 are provided by a common transducer.

The apparatus 400 again comprises an analyser 430. However, in the present embodiment the analyser 430 is provided with a frequency detector 430a, along with a processor 430b and memory 430c, the processor 430b and memory 430c being configured in a known manner. It will be appreciated that the analyser 430 may be provided by a microcontroller/microprocessor, such as that provided by a field programmable gate array, application specific integrated circuit, programmable intelligent computer, or the like.

The analyser 430 is in communication with the transceiver 460 and is configured to identify at least one excitable frequency of a target material from a received stimulated signal 425. The analyser 430 is further configured to provide the inspection transmitter 410 with information, or a signal, to provide as an inspection signal 415. In a similar manner to the embodiment in Figure 1c, the analyser 430 is configured to be able to provide information to a further device/apparatus, based on the identified excitation frequency(s) of a target material, so as to allow for stimulation of that target material.

Here, the apparatus 400 is configured to modify subsequent transmitted inspection signals 415 based on the received stimulated signal(s) 425. The apparatus 400 is additionally configured to evaluate time of flight of transmitted/received signals. In the above embodiments, the apparatus 100, 300, 400 (or further apparatus 210a, 220a, 240a) are configured to emit and/or receive acoustic signals, such as by using acoustic transducers (which may be any suitable acoustic transducer such as piezoelectric, hydrophonic, etc.), in alternative embodiments that need not be the case. In some embodiments the apparatus 100, 300, 400 (or further apparatus 210a, 220a, 240a) may be configured to emit and/or receive electromagnetic signals, by using electromagnetic transducer, antennas configured for emitting and/or receiving electromagnetic signals, or the like.

Similarly, while in the above embodiments particular configurations are described, it will readily be appreciated that these are exemplary only, and that various modifications can be made to incorporate and/or modify features of one embodiment with another. For example, the apparatus 100 of Figure 1a may be provided with a common transducer 460, which may be configured to transmit an inspection signal 115, receive a stimulated signal 125, and/or transmit an excitation signal 145. Similarly, the apparatus 400 of Figure 1d may not be provided with a transducer 460, but may be configured to communicate with further apparatus 210a, 220a, 240a similar to Figure 1 b. In such arrangements, the analyser 430 may be configured to provide, receive and/or analyse all the respective signals sent to/from further apparatus 210a, 220a, 240a, which may be communicated electrically (wired or wirelessly) and/or optically for remote communication to further apparatus 210a, 220a, 240b so as to provide for acoustic (or otherwise) stimulating of a subterranean target material. A skilled reader will readily be able to implement the various alternative embodiments accordingly.

Figure 2 shows an exemplary embodiment of stimulating a subterranean target material, using an apparatus 500 similar to the embodiments shown in Figure 1 (e.g. Figure 1a), the apparatus 500 configured to transmit an inspection signal 515, receive a stimulated signal 525, and transmit an excitation signal 545. Figure 2 shows the apparatus 500, coupled with the earth 510, or ground, (i.e. acoustically coupled). Embedded in the earth there is shown also a subterranean target material 520. The target material 520 may be a particular geological rock formation, hydrocarbon bearing formation, or the like.

In this embodiment, the target material 520 is comprised with a stimulated transducer 530, so as to be in touching contact with the target material 520. The stimulated transducer 530 is configured to observe the vibratory response of the target material 520 during, or after, the target material 520 has been subjected to an inspection signal 515 communicated from the apparatus 500. The stimulated transducer 530 is configured to transmit a stimulated signal 525 to the apparatus 500 based on the observed response of the target material 520. Here, the stimulated signal 525 comprises the excitable frequency response of the target material 520.

In use, the apparatus 500 is configured to transmit to the target material 520, via the earth 510, the inspection signal 515 comprising a plurality of frequencies. That is to say that the earth 510 acts as a transmission path/medium for the inspection signal 515, as well as for the stimulated signal 525/excitation signal 545.

Figure 3a shows a plot of frequency against amplitude of an exemplary inspection signal 515, where five discrete frequencies to be transmitted are shown. In this embodiment, the frequencies range from 100 Hz to 500 Hz, each of which have the same amplitude. In alternative embodiments, some particular frequencies may have differing amplitudes in order to account for anticipated transmission effects, such as attenuation effects.

The apparatus 500 is configured to transmit the inspection signal 515 as a so-called ladder chirp. That is to say that all the constituent frequencies are transmitted simultaneously, and, in this embodiment, for the same period of time. Here, the inspection signal 515 is transmitted for a period of 10 seconds. The inspection signal 515 can be considered as having a bandwidth of 400 Hz, comprising central frequency separations of 100 Hz. In alternative embodiments, a different bandwidth may be used, which may have differing discrete central frequency spacing and any number of discrete frequencies. For example, the inspection signal 515 may have a bandwidth of 10 Hz, 1000 Hz, 10 kHz, 100 kHz, 1 MHz, or the like. The inspection signal may have central frequency separations of 10 Hz, 1000 Hz, 10 kHz, 100 kHz, etc. The central frequency separation may be uniform, or may be irregular.

The mechanical characteristics of the target material 520 mean that it has a tendency to vibrate most at a frequency that is closest to one of its resonant frequencies, in response to being subjected to an inspection signal 515. In the present example, a resonant frequency of the target material 520 may be approximately 213 Hz. When the inspection signal 515 comes into communication with the target material 520, the target material 520 is stimulated such that it vibrates at a frequency closest to 213 Hz. Thus in the present example, the target material 520 is stimulated most by the component of the inspection signal 515 at 200 Hz. The stimulated transducer 530 is configured to observe this vibration and produce the stimulated signal 525 based on this vibration. Figure 3b shows a plot of frequency against amplitude of an exemplary stimulated signal 525 provided by the stimulated transducer 530. Here, the stimulated signal 525 is a signal frequency of 200 Hz configured to be transmitted to the apparatus 500. In alternative embodiments, the simulated signal 525 may be provided by a modulated signal, or the like, comprising information as to the particular excitable frequency of the target material 520, such as being frequency, amplitude, phase modulated, etc. Shown in dashed lines in Figure 3b are the frequency components of the inspection signal 515 that did not stimulate the target material 520. As described in relation to Figure 1 , the apparatus 500 is configured to receive the stimulated signal 525, analyse the stimulated signal 525 to identify at least one excitable frequency (i.e. 200 Hz) of the target material 520, and in this embodiment, provide an excitation signal 545 based on the identified excitable frequency. Figure 3c shows a plot of frequency against amplitude of an exemplary excitation signal 545 provided by an excitation transmitter of the apparatus 500. Here, the excitation signal 545 having a central signal frequency of 200 Hz is transmitted to the target material 520. Shown in dashed lines in Figure 3c are the frequency components of the inspection signal 515 that are not provided to stimulate the target material 520. As can be seen, the apparatus 500 is configured to provide the excitation signal 545 at greater amplitude than that of the amplitude of the inspection signal 515.

In such an arrangement, the apparatus 500 is able to provide for simulating of the target material 520 by identifying the excitable frequency(s) of the target material 520, and provide an excitation signal 545 at that frequency. Such an arrangement may be useful when providing for agitating the target material 520. For example, agitating the target material 520 so as to loosen for drilling, etc. during oil and gas production/exploration.

It will readily be appreciated that the process above may be repeated such that an excitation signal 545 that is closer to the resonant frequency of the target material 520 may be provided. For example, subsequent to the above process, the apparatus 500 is configured to transmit a second inspection signal 525 having a bandwidth of 50 Hz, ranging from 175 Hz to 225 Hz, having six discrete frequency components, with a central frequency separation of 10 Hz. That is, the secondary inspection signal 525 comprises discrete frequencies of 175 Hz, 185 Hz, 195 Hz, 205 Hz, 215 Hz and 225 Hz In such an arrangement, the stimulated signal 525 then shows that 215 Hz provides the greatest response by the target material 520 As such, the apparatus 500 is then configured to provide the excitation signal at 215 Hz A skilled reader will readily appreciate that such a method may be continued in order to provided for a closer match been the excitation signal 545 and the resonance of the target material 520, therefore providing for maximum agitation/stimulation of the target material 520

It will be appreciated that in Figures 3a to 3c, the frequency components of the respective signals are shown as having only a single, central, frequency, however a skilled reader will appreciate that this is representative of a central frequency, which may a spectrum of frequencies either side, which may be of reduced amplitude In some embodiments, each discrete frequency may comprise a spectrum of frequencies, of which, the central frequency occupies between 60 and 90 percent, for example

Figure 4 shows a further exemplary embodiment of stimulating a subterranean target material, using an apparatus 600 similar to the embodiments shown in Figure 1 and 2 The apparatus 600 is configured to transmit an inspection signal 615, receive a stimulated signal 625, and transmit an excitation signal 645 Figure 4 shows the apparatus 600, coupled with the earth 610, or ground, (e g acoustically coupled), along with a subterranean target material 620 Again, the target material 620 may be a particular geological rock formation, hydrocarbon bearing formation, or the like

In use, the apparatus 600 is configured to transmit to the target material 620, via the earth 610, the inspection signal 615 comprising a plurality of frequencies That is to say that the earth acts as a transmission path/medium for the inspection signal 615 Here, the target material 620 is not provided with a stimulated transducer

Figure 5a shows a plot of time against frequency of an exemplary inspection signal 615, where again five discrete frequencies to be transmitted are provided In this embodiment, the frequencies again range from 100 Hz to 500 Hz, each of which have the same amplitude (although this is not shown in Figure 4a) Again, in some embodiments particular frequencies may have differing amplitudes in order to account for anticipated communication effects, such as attenuation

Here, the inspection signal 615 is provided as a so-called stepped chirp That is to say that all the constituent frequencies are transmitted sequentially First a 100 Hz signal is transmitted for a period of time, then a 200 Hz signal, then a 300 Hz signal, then a 400 Hz signal, and then a 500 Hz signal. In the present embodiment, the period of transmission of each signal is around two seconds. That provides an inspection signal having a period of around 10 seconds.

As before, the inspection signal 615 can be considered as having a bandwidth of 400 Hz, comprising central frequency separation of 100 Hz. The mechanical characteristics of the target material 620 provide for a resonant characteristic are the same as above, approximately 213 Hz.

When the inspection signal 615 comes into communication with the target material 620, the target material 620 is stimulated such that it vibrates at a frequency closest to 213 Hz. Therefore, again the target material 620 is stimulated most by the component of the inspection signal 615 at 200 Hz. Due to the period of the inspection signal 615, the target material 620 continues to oscillate after the inspection signal 615 has ceased to be transmitted.

Here, the oscillatory behaviour of the target material 620 at its excited frequency provides a stimulated signal 625. That is to say that the vibratory nature of the target material 620 provides a stimulated signal 625 that is communicated to the apparatus 600, through the transmission path of the ground 610, which can be received by a stimulated receiver of the apparatus 600.

Figure 5b shows a plot of time against frequency of an exemplary stimulated signal 625 provided by the target material 620. Here, the stimulated signal 625 initially provides a single frequency; this frequency reduces as the energy accumulated in the target material 620 dissipates. The dashed line in Figure 5b shows that frequency. Although not shown, the amplitude of the stimulated signal 625 also decreases with time.

As described in relation to embodiments in Figure 1 , the apparatus 600 is configured to receive the stimulated signal 625, analyse the stimulated signal 625 to identify at least one excitable frequency (i.e. 200 Hz) of the target material 620, and in this embodiment, provide an excitation signal 645 based on the identified excitable frequency. Figure 5c shows a plot of frequency against amplitude of an exemplary excitation signal 645 provided by an excitation transmitter of the apparatus 600 Here, the excitation signal 645 having a central signal frequency of 200 Hz configured to be transmitted to the apparatus 500 As before, shown in dashed lines in Figure 5c are the frequency components of the inspection signal 615 that are not provided to stimulate the target material 620

In a similar manner to before, the apparatus 600 may be configured to provide a second, third, fourth, etc , inspection signal 615 in order to resolve further the resonant frequency of the target material 620, and to provide for improved stimulation

Again, frequency components of the respective signals 615, 625, 645 are shown as having only a single frequency, however a skilled reader will appreciate that this is representative of the central frequency, which may be of a spectrum of frequencies, of which, the central frequency may occupy between 60 and 90 percent, for example

Figure 6 shows a further exemplary embodiment of stimulating a subterranean target material, using the apparatus 600 of Figure 4 Figure 6 shows the apparatus 600, embedded in the earth 610, or ground, (e g so as to be acoustically coupled)

In use, the apparatus 600 is configured to transmit to the target material 620, via the earth 610, the inspection signal 615 comprising a plurality of frequencies, as before Figure 7a shows the plot of time against frequency of the exemplary inspection signal 615, where again five discrete frequencies (100 Hz to 500 Hz) to be transmitted are shown (a stepped chirp) This is the same as Figure 5a

In this embodiment, the inspection signal 615 is reflected from the target material 620 to provide a reflected inspection signal 627 Figure 7b shows a plot of time against frequency of an exemplary reflected inspection signal 627 As is shown, the reflected inspection signal 627 is shifted in time from the inspection signal 615 because of the time of flight of the signals

Shown also in Figure 7b is that some of the stepped frequency has been significantly absorbed by the target material 620 Figure 7b shows an approximate plot of frequency against amplitude for the period of the reflected inspection signal 627 As can be seen, the target material 620 has effectively absorbed most of the signal components comprising a frequency closest to the resonant frequency of the target material 620

In such an embodiment, the apparatus 600 is configured such that reflected inspection signal 627 serves, at least in part, as the stimulated signal 625 Whereby, the apparatus 600 is configured to identify at least one excitable frequency of the target material by identifying the absence, or attenuation, of a particular frequency in the reflected inspection signal 627 In a similar manner to before, an excitation signal 645 (not shown) may be provided at, or around that frequency in order to stimulate the target material 620 Additionally, the apparatus 600 may be configured to provide a second, third, fourth, etc inspection signal 615 of varying bandwidth so as to resolve further an excitation frequency of the target material 620

In the present embodiment, the apparatus 600 is further configured to identify the time of flight between the transmitted inspection signal 615 and the reflected inspection signal 627 so as to provide for an approximate of the relative distance between the apparatus 600 and the target material 620

It will readily be appreciated that while in the embodiments described in relation to Figures 4 to 7, each of the apparatus 500, 600 are described as transmitting and inspection signal 515, 615, receiving a stimulated signal 525, 625, and transmitting an excitation signal 545, 645, in alternative embodiments that need not be the case In alternative embodiments, the apparatus may be configured to communicate with further apparatus so as to transmit/receive the various signals

Figure 8a shows a further embodiment of an apparatus 700, similar to that described above Here, the apparatus 700 is comprised with a bottom hole assembly, which comprises a drill bill 750 The drill bit 750 is shown advancing a subterranean bore 760 for the purposes of oil and gas exploration/production Figure 8a further shows a target material 720, which in this embodiment is positioned ahead of the drill bit 750 That is to say that the drill bit 750 is expected to advance into the target material 720 In use, the apparatus 700 is configured to transmit an inspection signal 715 towards the target material 720 (ι e ahead of the drill bit 750) from time to time, using an inspection signal 715 similar to that shown in Figures 3a or 5a (or a combination of both signals 515, 615). The apparatus then receives a stimulated signal 725, the stimulated signal 725 being indicative of the vibratory response of the target material 720, so as to allow for identification of an excitable frequency of the target material 720. In other embodiments, the apparatus 700 may be configured to identify an excitable frequency by using a reflected inspection signal, or a combination of a reflected inspection signal and a stimulated signal 725. When the excitable frequency of the target material 720 has been identified (which may have been resolved further using the technique described above), the apparatus 700 is configured to provide an excitation signal 745 at that frequency in order to stimulate the target material 720.

It will readily be appreciated that by providing for stimulating of the target material 720 in such a manner, allows for the target material 720 to be agitated/loosened prior to, or during, the drill bit's advance into the target material 720, thus providing for reduced wear and/or improved drilling/exploration performance.

Figure 8b shows a further embodiment of an apparatus 800, similar to that described above. Here, the apparatus 800 is in communication with a speed and direction controller 780 of the drill bit 750. In this embodiment, the apparatus 800 is configured to identify the at least one excitable frequency of the target material 720 and provide this to the controller 780, such that (i) based on the identified excitable frequency of the target material 720, the drill bit 750 is able to modify its speed so as to provide a vibratory response that is similar to that identified, and/or (ii) based on the identified excitable frequency of the target material 720, the drill bit 750 is able to modify its direction, for example, so as to try and avoid a target material (e.g. because it is deemed too hard).

In such an arrangement, the drill bit may act to emit the excitation signal (e.g. when not in contact with the target material 720), and/or may be act to vibrate at the excitation frequency (e.g. when in contact with the target material 720).

Figure 9a shows a further exemplary embodiment of an apparatus 900, similar to that described above, in use. Here, the apparatus is in communication with tubing 950, which in the present embodiment is used as casing to case a deviated oil and gas production/exploration bore.

A drill string 960 extends through the tubing 950 and follows the deviation of the bore. It will be understood by those of skill in the art that the radius of curvature of the deviated bore has been exaggerated for clarity. Here, the drill string has become jammed against the tubing 950 in a known manner.

Here, the apparatus 900 is configured to transmit an inspection signal 915 comprising a plurality of frequencies to the point of contact 920 between the drill string 960 and the tubing 950 (i.e. the target material 920). In this embodiment the apparatus 900 is configured to transmit the inspection signal 915 using the tubing

950 itself. That is to say that the tubing 950 serves as a transmission path for the inspection signal 915. It will readily be appreciated that the tubing 950 and/or the drill string 960 can be provided by steel, or similar.

Due to the differing mechanical properties (e.g., stresses and strains) at the target material 920, the target material's 920 behaviour is different from the remainder of the tubing 950/drill pipe/drill string 960. The target material 920 therefore provides a stimulated signal 925 as before (and/or a reflected inspection signal), which allows the apparatus 900 to identify at least one resonant frequency of the target material 920.

In a similar manner to that described above, the apparatus 900 is configured to provided an excitation signal 945, as shown in Figure 9b. The excitation signal 945 is communicated to the target material 920 using the tubing 950 as a transmission path, and serves to stimulate the target material 920 so as to remove the jam.

In some embodiments, a user may additionally manipulate/agitate the drill string at a similar time so as to assist with removing the jam. In additional/alternative embodiments, the apparatus 900 may be configured to provide for moving of the drill string 960, for example by coupling an eccentric motor to the drill string to provide for additional/alternative stimulation. In some embodiments the apparatus 900 is configured to monitor the excitable frequency from time to time, such as every second, so as to modify the excitation signal 945 based on possible varying mechanical properties of the target material 920.

Figure 9c shows a further embodiment of the apparatus 900. Here, the apparatus 900 is in communication with the tubing 950 and the drill string 960. Again, the drill string has become jammed against the tubing 950 in a known manner. Here, the apparatus 900 is configured to transmit the inspection signal 915 comprising a plurality of frequencies to the point of contact 920 between the drill string 960 and the tubing 950 (ι e the target material 920) using the tubing 950 However, the apparatus 900 is configured to receive the stimulated signal 925 using the drill string 960 That is to say that the tubing 950 serves as a transmission path for the inspection signal 915, while the drill string 960 serves as the transmission path for the inspection signal This is possible due to the continuity at the target material 920 As before, the apparatus 900 is configured to provided an excitation signal 945, as shown in Figure 9d Here, the excitation signal 945 is communicated to the target material 920 using the tubing 950 and the drill string 960 to stimulate the target material 920 so as to remove the jam In some embodiments, the apparatus 900 is further configured to identify the time of flight of an inspection signal, stimulated signal, and/or reflected inspection signal By having a knowledge (or an estimate, or guess) of the speed of sound in a tubing, or drill string, the relative distance between the apparatus and the target material can be identified

It will readily be appreciated that the apparatus may be provided at the surface, for example on a drilling platform, or provided such that it communicates remotely with the tubing, and/or drill pipe string Figure 10 shows a flowchart 1000 of the method for providing for stimulating a subterranean target material, in which the method comprises providing for transmitting 1100 of an inspection signal comprising a plurality of frequencies to a subterranean target material The method further comprises receiving 1020 a signal based on a stimulated signal in response to transmitting of the inspection signal, the stimulated signal indicative of at least one excitable frequency of the target material The received signal is analysed 1030 to identify at least one excitable frequency of the target material There is provided for transmitting 1040 of an excitation signal 1040, wherein the excitation signal is based on the identified excitable frequency(s) and is for transmittal to the target material so as to provide for stimulating of the target material In some embodiments the excitation signal comprises as frequency similar, or the same as, a resonant frequency of the target material The method may be considered to transform the information provided in a stimulated signal into a useful excitation signal.

In addition, and in view of the foregoing description, it will be evident to a person skilled in the art that various modifications to either embodiment may be made within the scope of the invention. Similarly, the apparatus and/or methods disclosed may have other functions/steps, in addition to those described.

It will be appreciated to the skilled reader that the features of particular apparatus may be provided by apparatus arranged such that they become configured to carry out the desired operations only when enabled, e.g. switched on, or the like. In such cases, they may not necessarily have the appropriate software loaded into the active memory in the non-enabled (e.g. switched off state) and only load the appropriate software in the enabled (e.g. on state). The apparatus may comprise hardware circuitry and/or firmware. The apparatus may comprise software loaded onto memory.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

While there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. Furthermore, in the claims means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.

Claims

1. A method for providing for stimulating a subterranean target material, the method comprising:

2. The method according to claim 1 , further comprising transmitting an excitation signal to the target material for stimulation.

3. The method according to claim 1 or 2, comprising transmitting an excitation signal for further transmitting to the target material for stimulation.

4. The method according to claim 2 or 3, wherein the excitation signal comprises at least one identified excitable frequency for stimulating the subterranean target material.

5. The method according to any preceding claim, comprising transmitting the inspection signal so as to transmit a plurality of discrete frequencies.

6. The method according to claim 5, wherein at least two of the plurality of discrete frequencies are transmitted simultaneously.

7. The method according to any preceding claim, wherein transmitting the inspection signal provides that the target material oscillates at a particular frequency after the inspection signal has ceased to be transmitted to the target material.

8. The method according to any preceding claim, wherein the stimulated signal is generated by an oscillating subterranean target material.

9. The method according to any preceding claim, further comprising receiving a reflected inspection signal, reflected from the target material, and comprising evaluating the time of flight of the inspection signal and reflected inspection signal to provide for the relative distance to the target material.

10. The method according to any preceding claim, comprising receiving a reflected inspection signal, reflected from the target material, and comprising using the reflected inspection signal as the stimulated signal.

1 1. The method according to any preceding claim, comprising transmitting an inspection signal so as to transmit a plurality of frequencies in the range of up to 500 Hz to the target material.

12. The method according to any preceding claim, comprising analysing the stimulated signal to identify at least one resonant frequency of the target material so as to provide for resonant stimulating of the target material.

13. The method according to any preceding claim, wherein the transmitted and received signals comprise acoustic signals, and/or electromagnetic signals.

14. The method according to any preceding claim, comprising transmitting the inspection signal to a subterranean target material ahead of a drill bit.

15. The method according to claim 14, comprising identifying regions of target material to be avoided by the drill bit based on their stimulated characteristics.

16. The method according to claim 14 or 15, comprising configuring the performance of the drill bit so as to provide an excitation signal.

17. The method according to any preceding claim, comprising transmitting the inspection signal to a subterranean target material within a bore.

18. The method according to claim 17, wherein the target material is located at a portion of interference between a tubing and a wall of the bore.

19. The method according to claim 18, comprising transmitting the inspection signal and receiving the stimulated signal from one or both of the tubing and the wall of the bore.

20. The method according to claim 19, further comprising transmitting an excitation signal to the target material using one or both of the tubing and the wall of the bore, the excitation signal comprising at least one identified excitable frequency for stimulating the target material and alleviating the jam.

21. Apparatus for providing for stimulating a subterranean target material, the apparatus comprising: an inspection transmitter configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material; a stimulation receiver configured to receive a stimulated signal in response to transmission by the transmitter of an inspection signal, wherein the stimulated signal is indicative of at least one excitable frequency of a target material; and an analyser configured to analyse a received stimulated signal and to identify at least one excitable frequency of a target material so as to provide for stimulating of a target material.

22. The apparatus according to claim 21 , the apparatus comprising an excitation transmitter, in communication with the analyser, the excitation transmitter configured to transmit an excitation signal to a target material based on an excitable frequency identified by the analyser.

23. The apparatus according to claim 22, wherein the excitation transmitter is configured to provide an excitation signal for stimulating a subterranean target material

24. The apparatus according to claim 21 , 22 or 23, wherein the apparatus is configured to transmit/receive some, or all, of the respective signals to/from a further apparatus for communication with a target material.

25. The apparatus according to any of the claims 21 to 24, wherein the inspection transmitter is configured to transmit a plurality of discrete frequencies sequentially.

26. The apparatus according to any of the claims 21 to 25, wherein the inspection transmitter is configured to transmit an inspection signal configured to oscillate a target material at a particular frequency after an inspection signal has ceased to be transmitted.

27. The apparatus according to any of the claims 21 to 26, wherein the stimulation receiver is configured to receive a stimulated signal generated by an oscillating subterranean target material.

28. The apparatus according to any of the claims 21 to 27, wherein the stimulation receiver is configured to receive a reflected inspection signal, reflected from a target material, wherein the apparatus is configured to evaluate the relative distance of the apparatus from a target material.

29. The apparatus according to any of the claims 21 to 28, wherein the apparatus is configured to analyse a reflected inspection signal to identify an excitable frequency of the target material

30. The apparatus according to claim 29, wherein the apparatus is configured to identify certain frequencies that were comprised with an inspection signal, but which are significantly attenuated in a received reflected inspection signal with respect to other frequencies present in a received reflected inspection signal in order to identify an excitable frequency of the target material.

31. The apparatus according to any of the claims 21 to 30, configured to transmit an inspection signal at a plurality of frequencies in the range up to 500 Hz to a target material.

32. The apparatus according to any of the claims 21 to 31 , wherein the apparatus is configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material ahead of a drill bit.

33. The apparatus according to claim 32, configured to identify at least one resonant/excitation frequency of target material ahead of a drill bit so as to provide for simulation of the target material.

34. The apparatus according to claim 31 or 32 wherein the apparatus is configured to modify/control the performance of a drill bit so as to provide an excitation signal to a target material based on an identified excitable frequency(s) identified by the analyser.

35. The apparatus according to any of the claims 21 to 34, wherein the apparatus is configured to transmit an inspection signal comprising a plurality of frequencies to a subterranean target material within a bore.

36. The apparatus according to claim 35, wherein target material is located at a portion of interference between a tubing and a wall of the bore.

37. The apparatus according to claim 36, wherein the apparatus is configured to transmit/receive the respective signals through one or more of the tubing and/or the wall of the bore.

38. The apparatus according to any of the claims 21 to 37, configured to transmit/receive acoustic signals.

39. Oil and gas production/exploration apparatus comprising an apparatus according to any of the claims 21 to 38.

40. The oil and gas production/exploration apparatus according to claim 37, wherein the oil and gas production/exploration apparatus is any one or more of: tubing; a drill string; a drill bit; a bottom hole assembly; apparatus for an oil rig/platform; an oil rig/platform; apparatus for remote communication with an oil rig/platform.

41. A computer program, stored on a computer readable medium, the computer program comprising instructions to provide the method of any of the claims 1 to 20.

42. A method for providing for stimulating a subterranean target material substantially as described with reference to the accompanying Figures.

43. A apparatus for providing for stimulating a subterranean target material substantially as described with reference to the accompanying Figures.