Patent Description:
Either when a well is drilled/completed, or at some point later in the life cycle of a well, sections of the well infrastructure may be uncased or without liner. That is to say that that the well infrastructure may comprises regions that are "open hole". Such open hole regions may exist in a pilot hole, or side track, or otherwise at the bottom of a well structure without a liner.

Further, at the end of the lifecycle of a well, or at the end of an appraisal process, or the like, steps may be taken to permanently abandon a well. Each territory in which the well and associated infrastructure is located will typically have its own abandonment requirements that may require different procedures to be adhered to during and/or following the abandonment process. The process of abandoning a well may differ somewhat depending on whether the well is onshore or offshore.

That said, it is not uncommon for there to be similar or overlapping procedures adopted in each of the above circumstances, which include isolating any freshwater zones associated with the well; isolating from the well any future production zones; preventing leaks to/from the well; and, in addition to removing wellheads, etc., also cutting and removing all well structure such as casing strings, etc., to a particular level below the surface.

It will be appreciated that the surface or ground region associated with an onshore well may relate to the surface from which the well structure extends into ground and then down to the formation, whereas for an offshore well, the surface or ground region may relate to the mudline, or the like, again from which well structure extends down to the formation below.

In addition, a particular type of well is an appraisal (or exploration) well which may be drilled as part of an appraisal process to determine the extent and reserves at a particular field. Appraisal wells may comprise a section having a metallic well structure, such as a conductor or casing, and an open hole section having no metallic well structure. Once the appraisal process is complete, appraisal wells are typcailly abandoned also. The abandonment process may include pumping a first plug, which may comprise cement, into the open hole section and positioning a second plug, which may also comprise cement in the metallic well structure section.

The non-patent reference entitled "<NPL>et al. describes wireless reservoir monitoring technology.

The non-patent reference entitled "Wireless Well Solutions CaTS™ Cabless Telemetry System" authored by Exprogroup describes wireless reservoir monitoring and control.

The non-patent reference entitled "<NPL>et al. describes wireless telemetry technology. The non-patent reference entitled "4D Pressure Pilot to Steer Well Spacing in Tight Gas" authored by <CIT>, <CIT>, and <CIT> describe well installation communication systems.

This background serves only to set a scene to allow a skilled reader to better appreciate the following description. Therefore, none of the above discussion should necessarily be taken as an acknowledgement that that discussion is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the invention may or may not address one or more of the background issues.

In described examples, there are systems and methods for deployment in proximity to an abandoned well. The systems and methods may allow use of data collected from an abandoned well, in which a sensor is positioned in the open hole section, or a well having a discontinuous metallic well structure.

In some examples, there is described a communication system that is configured to be deployed in an abandoned well having a discontinuous metallic well structure that may be severed below a ground region.

According to an aspect, there is provided a communication system according to claim <NUM>.

Optionally, the communications unit is configured to be in contact with the metallic well structure for injecting the data signals into the metallic well structure.

Optionally, the communication unit is configured to modulate the wirelessly received data signals for injection into the metallic well structure for reception by the at least one receiver.

Optionally, the downhole apparatus is configured to wirelessly transmit the data signals up to <NUM> metres.

Optionally, the well is an abandoned well comprising a first plug, the downhole apparatus being configured to be positioned below the first plug and to wirelessly transmit the data signal through the first plug.

Optionally, the abandoned well further comprises a second plug, and wherein the communications device is configured to be positioned above the first plug and below the second plug.

Optionally, the metallic well structure is severed below a surface, and wherein the at least one receiver is configured to be deployed at a ground region in proximity to the well for receiving the data signals from the metallic well structure through the ground region.

Optionally, the at least one receiver is configured to receive the data signals from the metallic well structure through roughly <NUM> to <NUM> metres of ground region.

Optionally, the at least one receiver is configured to be fixed, or otherwise secured, to the ground region when deployed.

Optionally, the system comprises a plurality of receivers arranged spatially at the ground region in proximity to the abandoned well.

Optionally, the spacing between each of the receivers is at regular intervals.

Optionally, the system comprises a processing unit configured to receive and process data signals from the plurality of receivers so as to fuse the data signals from different receivers in order provide a data signal representative of the data signal injected to the metallic well structure of the well.

Optionally, the processing unit is configured to correlate the data signals received from different receivers in order provide a data signal representative of the data injected to the metallic well structure of the well.

Optionally, the plurality of receivers are configured to receive the data signals using at least two different receiving methods.

Optionally, the plurality of receivers comprises a receiver including an electrode configured to receive data signals using a first receiving method, and/or a receiver including a loop antenna configured to receive data signals using a second receiving method.

Optionally, the processing unit is configured to process data from one or more of the receiving methods.

Optionally, the at least one receiver is configured to be deployed in a body of water and is configured to be deployed at a seabed or mudline in proximity to the well.

Optionally, the system comprises a transmitter configured to transmit data received by the receivers for subsequent receipt at a remote location.

Optionally, the data signals are electromagnetic (EM) data signals.

Optionally, the at least one receiver is configured to receive EM data signals having a frequency in the region of a range from <NUM> to <NUM>.

Optionally, the downhole apparatus comprises a sensor configured to sense one or more of temperature and pressure within the well.

According to an aspect, there is provided a method according to claim <NUM>.

Optionally, the altered parameter comprises pressure, and wherein the pressure in the first reservoir is altered by injection of a substance into the first well or removal of a substance from the first well.

Optionally, altering the pressure in the first reservoir comprises injecting water into the first reservoir via the first well.

Optionally, the second well is an abandoned well and optionally an abandoned appraisal well.

Optionally, the second well comprises an open hole section that intercepts the second reservoir, and wherein the downhole apparatus is located in the open hole section.

According to an aspect, there is provided a method of claim <NUM>.

Optionally, the method comprises positioning a first plug above the downhole apparatus and optionally positioning a second plug above the communications device.

Optionally, the method comprises severing the metallic well structure of the well below a surface, and wherein deploying the at least one receiver comprises deploying the at least one receiver at a ground region in proximity to the well for receiving the data signals from the metallic well structure through the ground region.

A description is now given, by way of example only, with reference to the accompanying drawings, in which:.

For ease of explanation, the following examples have been described in relation to an offshore well and well structure extending below a mudline, or the like. However, systems and methods described herein may be equally used and applicable in respect of onshore wells. Similarly, while the following examples may be described in relation to oil and gas wells, and in particular production and appraisal wells, the same systems and methods, etc., may be used beyond oil and gas applications. A skilled reader will be able to implement those various alternative embodiments accordingly.

Similarly, some of the following examples have been described in relation to wells having sections that are open hole specifically with reference to appraisal wells, or the like. However, it will be appreciated that aspects of the following systems and methods may equally be used with other wells and well structures having open hole sections, such as production wells, injections wells, or the like, or pilot holes, side tracks, etc..

Generally, disclosed herein are methods and systems for communicating data signals from downhole to at least one receiver at a ground region near the well. In particular, methods and systems disclosed are arranged to communicate data signals from a well having a discontinuous metallic well structure meaning that the metallic well structure cannot be used as a sole medium to propagate the data signals from downhole to the receivers at the surface. For example, in wells having an open hole section, methods and systems disclosed may be arranged to communicate data signals from the open hole section to the at least one receiver. It is noted that the well structure need only be suitable for propagating EM signals.

<FIG> shows a simplified representation of a section of a well <NUM>, and in this case an offshore appraisal well <NUM>. A metallic well structure <NUM> extends from the surface - in this case the seabed or mudline <NUM> - to a subterranean formation, as will be appreciated. Such well structure <NUM> can include conductor, casing and other tubing used to recover product from the formation. In this example, the well <NUM> comprises a wellhead <NUM>, wet tree or the like, at a production platform <NUM>. In other examples, the wellhead/tree arrangement <NUM> may be provided at the mudline <NUM>. A lower section <NUM> of the well <NUM> is open hole, in that there is no well structure positioned within the well in this section.

Referring to <FIG>, and as explained briefly above, when the appraisal well <NUM> is abandoned, a first cement plug <NUM> is typically formed at or just above the open hole section <NUM> of the well <NUM>. The first cement plug may be formed by pumping wet cement into the well <NUM>. Typically, a second cement plug <NUM> is formed above the first cement plug <NUM>. An intermediate section <NUM> of the well <NUM> forms an enclosed space between the first and second plugs <NUM>, <NUM>.

Referring to <FIG>, a final stage of the abandonment process comprises severing the metallic well structure <NUM> below the seabed or mudline <NUM>.

Appraisal wells cost a significant sum of money to drill. In known arrangements, the value of an appraisal well for data gathering ceases on pumping cement. The inventors have appreciated that that more data can be extracted from an appraisal well after abandonment. For example, pressure and temperature within the appraisal well could be monitored post-abandonment, which would provide additional information about connectivity/compartmentalisation of a reservoir with follow-on appraisal wells or nearby production wells.

Exemplary methods and apparatus may be configured to wirelessly provide downhole data to a surface from or through an open hole section or sections of an abandoned well, which may be permanently abandoned and have one or more metallic well structures (e.g. casing strings) severed below the surface, as shown in the exemplary arrangement of <FIG>.

Therefore, exemplary methods and systems disclosed herein allow utilisation of an appraisal well beyond its abandonment. A communication system is disclosed that permits data signals transmitted wirelessly by a downhole apparatus, such as a sensor or gauge, positioned in an open hole section of the well to be communicated to systems and apparatus at or above the seabed.

Downhole data from the open hole section of the well may be communicated using an electromagnetic (EM) method. For example, an EM gauge or sensor in the open hole section may be configured to create a dipole antenna that wirelessly transmits data signals through the surrounding formation. The wirelessly transmitted data signal may be received by a communications device placed in the metallic well structure and re-transmitted through the metallic well structure to systems and apparatus at the surface. In some respects, the communications device may therefore be considered to be or to comprise a relay.

As used herein, the term "wireless" when applied to communications encompasses all transmission that is not through a guided transmission medium, such as a wire, other metallic structure or a material having high EM conductivity relative to a surrounding medium. Wireless communications may, for example, be through air, water, ground (or formation) or another medium that has substantially isotropic EM conductivity.

The EM signal from the communications device may be received by one or more surface/seabed receivers. In exemplary arrangements in which the metallic well structure is severed below the surface, the data signals re-transmitted through the metallic well structure may be received by a plurality of receivers arranged at the surface/seabed, as described below.

In other arrangements, the wireless data signals transmitted by the downhole apparatus may be received by the metallic well structure itself and communicated to the surface via the metallic well structure.

In exemplary arrangements, communications can be duplex. That is, the surface receiver(s) may be transceivers configured to transmit data signals to the sensor or other apparatus within the well, as explained in more detail below.

Referring to <FIG>, a well <NUM> intercepts a reservoir <NUM>. The reservoir <NUM> may comprise hydrocarbon material. The reservoir <NUM> is intercepted by an open hole section <NUM> of the well <NUM>. The well <NUM> has been abandoned and the metallic well structure <NUM> has been severed below the seabed or mudline <NUM>.

The well <NUM> has fitted therein a communications system comprising a downhole apparatus <NUM>, which in this case comprises a sensor, a communications device <NUM> and one or more receivers <NUM>. The downhole apparatus <NUM> is configured to wirelessly transmit data signals through the well <NUM>. The downhole apparatus <NUM> may, for example, be configured to sense temperature and/or pressure in the open hole section <NUM> of the well <NUM> and to transmit data signals indicative of the sensed temperature and/or pressure.

Therefore, in exemplary methods and systems, the downhole apparatus <NUM> comprises a sensor configured to sense a downhole parameter, such as temperature and/or pressure. The downhole apparatus may further comprise a transmitter configured to wirelessly transmit a data signal indicative of the sensed parameter for receipt by a communications device <NUM>. The transmitter may be configured to transmit the data signal indicative of the sensed parameter at frequencies up to <NUM>. Further, the transmitter may be configured to transmit the data signal indicative of the sensed parameter over a distance of up to several hundred metres, for example, up to <NUM> metres.

The downhole communication device <NUM> is configured to receive the wirelessly transmitted data signals and to communicate corresponding data signals to the metallic well structure <NUM> for transmission to a receiver <NUM>. In exemplary methods and systems, the communications device <NUM> may be configured to inject data signals into the metallic well structure <NUM>, thereby using the metallic well structure <NUM> as a signal path. Accordingly, the communications device <NUM> may comprise a data processing unit configured to process the wirelessly received data signals into a format suitable for transmission via the metallic well structure <NUM>.

In the example of <FIG>, the receiver <NUM> is positioned at the mudline <NUM>, and is in signal communication with the metallic well structure <NUM>. The downhole communications device <NUM> is arranged within the bore of the metallic well structure <NUM> and, as described above, may be configured to measure, or otherwise obtain from the downhole apparatus, well conditions such as temperature and/or pressure.

In exemplary arrangements, the downhole communications device <NUM> is configured to communicate electrical signals to well structures, and in particular to communicate signals to the metallic well structure <NUM> (e.g. tubing). In other words, the metallic well structure <NUM> may itself form the signal path, rather than a dedicated cabling system or the like. As such, in exemplary arrangements, the downhole communications device <NUM> is both in physical and electrical contact with the metallic well structure <NUM> so as to be able to propagate the data signals therethrough.

While the communications device <NUM> in <FIG> is shown as being within the well <NUM> itself, it will be appreciated that in other examples the communications device <NUM> may be formed as part of a downhole tool, barrier or the like (e.g. formed together with a plug). In any event, in use, the communications device <NUM> is configured to communicate data signals to the receiver <NUM> at surface <NUM>. The data signals may relate to well conditions downhole, which can then be processed and/or determined at the surface <NUM> in order to maintain appropriate operation of the well <NUM>, and/or to provide information permitting informed decisions regarding interventions or work overs, etc. In some examples, the data signals may additionally or alternatively be communicated from the surface <NUM> to the downhole communication device <NUM> and on to the downhole apparatus <NUM> in a similar manner. In some cases, the downhole apparatus <NUM> may be a downhole tool, or other actuation device, and operation thereof may be effected by communicating signals in this manner to the downhole communication device <NUM> and on to the downhole apparatus <NUM>.

After abandonment of the well <NUM>, some of the metallic well structure <NUM> may be severed at a depth below the surface <NUM>, and the severed well structure removed. As such, a ground region <NUM> extends from surface <NUM> to the severed metallic well structure <NUM> that remains after abandonment. A discontinuity in signal path provided by the metallic well structure is now apparent.

The system comprises one or more receivers <NUM> configured to be deployed at the ground region <NUM> in proximity to the abandoned well <NUM>, and in particular, in proximity to the severed metallic well structure <NUM>. In the example shown in <FIG>, one receiver <NUM> is deployed but, as will be described later, more may be used. The receiver <NUM> is configured to receive data signals from the metallic well structure <NUM> of the abandoned well <NUM> via the ground region <NUM>. The system further comprises a processing unit <NUM> in communication with the receiver <NUM> and configured to receive and process data signals from the receiver <NUM>. The processing unit <NUM> may comprise dedicated hardware and/or firmware configured to process data accordingly. The processing unit <NUM> may comprise a processor and memory arranged operatively together in a known manner.

The receiver <NUM> is configured to receive data signals from the metallic well structure <NUM> of the abandoned well through roughly <NUM> to <NUM> metres of ground region <NUM> (e.g. in this case from <NUM> to <NUM> metres of ground region <NUM>). The ground region <NUM> may comprise seabed, or other such material, that is used to cover the severed well structure <NUM>.

The receiver <NUM> may be configured to receive EM data signals from the metallic well structure <NUM> of the well via the ground region <NUM>. In particular, the receiver <NUM> may be configured to receive data signals having a frequency of in the region of a range from <NUM> and <NUM>, such as from <NUM> and <NUM>, or the like.

The receiver <NUM> is configured to be fixed, or otherwise secured, to the ground region <NUM> when deployed. In some examples, the system may comprise one or more earth spikes, or the like, configured to provide a grounded potential. This may help in relation to signal reference purposes for the receiver <NUM> (e.g. particularly when receiving EM data signals from the well structure <NUM>).

The communication system may comprise a plurality of receivers <NUM>. The system - and in this example the processing unit <NUM> - can be configured to process, or otherwise merge or fuse, data signals received using each of the plurality of receivers <NUM>. In the example shown, the processor <NUM> may be configured to correlate data signals received using different receivers <NUM>. By processing data signals received at multiple receivers <NUM>, a data signal representative of a signal having initially been communicated to the metallic well structure <NUM> of the abandoned well <NUM> (e.g. and subsequently received via the ground region <NUM>) can be obtained. In such a way, the signal-to-noise ratio can be improved, compared to using only a single receiver <NUM>, which may be helpful given that some of the signal path now comprises the ground region <NUM>. Further, the ease with which the system can be deployed, yet still being able to obtain a suitable signal is improved, compared to deploying a single receiver <NUM>, given that at least one receiver will be more likely to be favourably positioned relative to the (now covered) severed well structure <NUM>.

In this manner, data can be collected from an abandoned well <NUM> from data signals received from the metallic well structure <NUM> of the abandoned well <NUM> via a ground region <NUM>, specifically using a plurality of receivers <NUM> deployed in proximity to the abandoned well <NUM>. As such, conditions of the abandoned well <NUM> can be monitored using the collected data. It will be appreciated that the collected data may comprise data associated with temperature and/or pressure at regions within the abandoned well <NUM>, and in fact the conditions of the well may relate to barrier integrity, or the like, which may be an important consideration for long term monitoring of such wells. In specific exemplary methods and systems, the temperature and/or pressure data may have been collected by the downhole apparatus <NUM>, which is positioned in an open hole section <NUM> of the well <NUM>.

In exemplary arrangements, the at least one receiver <NUM> may be configured as a transceiver and may therefore comprise a transmitter configured to transmit data signals towards the downhole apparatus <NUM>. As such, the transmitter of the at least one transceiver <NUM> may wirelessly transmit data signals into the ground region <NUM>, which may be received by the communications device <NUM> after propagation through the metallic well structure <NUM> or may be received by a repeater <NUM> (explained below), which is configured to inject the data signals into the metallic well structure <NUM> for propagation therethrough and reception by the communications device <NUM>. The communications device <NUM> therefore comprises a receiver configured to receive data signals from the metallic well structure <NUM>. The communications device may also comprise a transmitter configured to wirelessly transmit the data signals to the downhole apparatus <NUM>.

While in <FIG> the system is shown as having one receiver <NUM>, it will be appreciated that some examples the system may comprise more than one receiver <NUM>.

In addition, a plurality of downhole apparatus <NUM> may be positioned in the open hole section <NUM> of the well <NUM>. In such arrangements, one or more of the downhole apparatus <NUM> may comprise sensors for sensing a parameter of the reservoir and/or the well, such as temperature and/or pressure. Further, one or more of the downhole apparatus <NUM> may be configured to act as a repeater comprising a receiver configured to receive wirelessly transmitted data signals from another of the downhole apparatus <NUM> and a transmitter configured to wirelessly retransmit the received data signals to another of the downhole apparatus <NUM>, a communication device <NUM> and/or the metallic well structure <NUM>.

Further, a plurality of communications devices <NUM> may be positioned within the well <NUM> and in specific arrangements in the metallic well structure section of the well <NUM>. Each of the communications devices <NUM> may be configured to act as a relay and may therefore comprise a receiver configured to receive data signals either wirelessly transmitted by a downhole apparatus <NUM>, the at least one receiver (when configured as a transceiver) <NUM> or transmitted by another of the communications devices <NUM>. The communications devices may also comprise a transmitter configured to retransmit the data signals via the metallic well structure to another of the communications devices <NUM> or the at least one receiver <NUM>, or may transmit the data signals wirelessly to the one or more downhole apparatus <NUM>.

By way of an example, <FIG> shows a plurality of receivers 226a-226f configured such that, when deployed, each of the plurality of receivers are arranged spatially at the ground region <NUM> in proximity to the abandoned well <NUM>. In other words, the system may be configured such that the plurality of receivers 226a-226f are configured in an array, or the like, at the ground region <NUM> in proximity to the abandoned well <NUM>. The relative spacing between each receiver 226a-226f, or otherwise the position of each receiver 226a-226f, may be known or predefined. In the example shown in <FIG>, the spacing between each of the receivers 226a- 226f may be considered to be regular (e.g. spaced at regular intervals from one another).

In <FIG>, each of the receivers 226a-226f may be configured to measure a potential difference between an electrode formed with the receiver 226a-226f and a common potential at the processing unit <NUM>, or the like. Alternatively, and as is shown in <FIG>, each receiver 226a-226f may comprise two electrodes, and be configured to measure the potential difference therebetween.

In some examples, the processing unit <NUM> may be further configured to store data for subsequent collection/processing. In some cases, the processing unit <NUM> may comprise a transmitter configured to communicate data, for example by acoustically, for subsequent receipt and analysis. The processing unit <NUM> may be configured to communicate via a body of water (e.g. wirelessly) for subsequent receipt at a remote location. That remote location may include a receiving vessel or the like.

It will be appreciated at that the processing unit <NUM> may be configured to communicate processed data when requested to do so, or automatically from time to time, e.g. at regular intervals or when the data is requested by another entity.

In some examples, the receiver(s) <NUM>, may be configured to receive data signals having been transmitted from the metallic well structure <NUM> via the ground region <NUM> using a repeater unit <NUM>. That repeater unit <NUM> may be positioned at the metallic well structure <NUM>. In such examples, the repeater unit <NUM> may be configured to receive data signals at the well structure <NUM>, and improve the data signal quality (e.g. amplify, reduce/cancel noise) prior to communication to the ground region <NUM>. In some examples, those data signals may be directly communicated to the ground region <NUM> using the repeater unit <NUM>, or otherwise the repeater unit <NUM> may be positioned such that signals are communicated back to the metallic well structure <NUM> for subsequent transmission to the ground region <NUM>.

While in some cases, such repeater units <NUM> may be provided during normal operation of the well, in other cases the repeater unit <NUM> may be deployed around the time of well abandonment. As such, the repeater unit <NUM> may be considered to form part of the overall communication system.

Either way, the repeater unit <NUM> may be configured to modify data signals being communicated in the metallic structure for transmission via the ground region <NUM>. For example, the repeater unit <NUM> may be configured to amplify and/or modulate data signals having been communicated in the metallic well structure <NUM> for improved communication via the ground region <NUM>. This may be particularly true for repeater units <NUM> that are deployed around the time of abandonment. In some cases, such repeater units <NUM> may be configured to convert the frequency of the signal, and/or convert the signal from one signal type (e.g. EM) to another signal type (e.g. acoustic) to assist with transmission, as will be appreciated.

While in some examples the receiver(s) <NUM> may be configured similarly, e.g. to receive similar data signals, similar frequencies, etc., in other examples this need not be the case.

<FIG> shows the plurality of receiver types <NUM>, <NUM> configured to receive data signals using at least different receiving methods. Here, at least one receiver 234a-234c is configured to receive data signals using a first receiving method while at least one further receiver 236a- 236b is configured to receive data signals using a second receiving method. In the example shown in <FIG>, there are two types of receivers provided, a first type 234a-234c provided as an electrode configured to measure a potential difference (e.g. between an electrode and an earth point), and second type 236a-236b configured as a loop antenna, or the like, configured to measure variation in magnetic field.

In <FIG>, and by way of an example, while the processing unit <NUM> is offset somewhat from the abandoned well <NUM>, it will be appreciated that the system may still be considered to be deployed in proximity to the well <NUM>.

When the system is configured to use at least two receiving methods, the processing unit <NUM>, in communication with the receivers 234a-234c, 236a-236b is configured to receive and process data signals having been received from two or more receivers using those different receiving methods. In such cases again, the system - and in particular the processing unit <NUM> - may be configured to process, or otherwise merge or fuse, data signals received using the different receiving methods. By using multiple methods in this manner, the outcome of such processing may provide a processed data signal more representative of a signal having initially been communicated to the metallic well structure <NUM> of the abandoned well <NUM>, and subsequently received via the ground region <NUM>. In some examples, it may be possible to selectively choose which data/receiver type to use in any subsequent analysis (e.g. based on signal/data quality).

While in the above examples, the system is shown as being deployed in proximity to single abandoned well <NUM>, it will be appreciated that in some examples, the system may be deployed in proximity to multiple abandoned wells, and may be configured to receive data signals therefrom. Further, while in the above examples, the system is configured to receive data signals it will also be appreciated that in other examples, the system may additionally or alternatively be configured to communicate data signals for transmission through a ground region <NUM> and metallic structure <NUM>, for subsequent receipt at a downhole communication device <NUM>. The downhole communications device <NUM> may be configured to transmit wirelessly the data signals to the downhole apparatus <NUM>. Further still, while each of the plurality of receivers are shown as discrete, it will be appreciated that they may be deployed together in a combined array.

While it has been described that the processing unit <NUM> performs some data processing, it will be appreciated that in other examples, the data may be processed at the processing unit <NUM> in as much as it is received at the processing unit <NUM>, and then additionally or alternatively stored/communicated in raw format, or close to raw format, for subsequent processing an analysis.

In any event, the collected (and processed data) may be used to monitor conditions at an abandoned well, by collecting data associated with an abandoned well, and looking for changes in that data that may relate to underlying changes in the conditions of the well (e.g. loss of barrier integrity, etc.). The collected data may comprise data associated with temperature and/or pressure at regions within the abandoned well <NUM>.

It will be appreciated that exemplary systems and methods may not require the use of the communications device <NUM>. In such arrangements, the downhole apparatus <NUM> may be configured to transmit wireless data signals for receipt by the metallic well structure <NUM>. The data signals propagate through the metallic well structure <NUM> and are received by the receiver <NUM>. The receiver <NUM> may be in direct electrical communication with the metallic well structure <NUM>, or may be separated from the metallic well structure <NUM> by the ground region <NUM> if the metallic well structure is severed below the surface <NUM>.

Further, the communications system may be used in any circumstance in which there is a discontinuous metallic well structure that cannot, therefore, act as a sole transmission medium from the downhole apparatus <NUM> to the receiver <NUM>, optionally via the communications device <NUM>. In the exemplary systems and methods described above, the discontinuous nature of the metallic well structure is represented by the end of the metallic well structure <NUM> and the open hole section <NUM> of the well <NUM>, but this is exemplary only.

<FIG> shows a flow diagram for a method of abandoning a well including an open hole section and a metallic well structure section. The method comprises positioning <NUM> a downhole apparatus <NUM>, such as a sensor or an EM tool (e.g. CaTS), in the open hole (i.e. no liner required) section.

Once the downhole apparatus <NUM> is positioned within the well <NUM>, a first plug <NUM> is placed <NUM> on top of the downhole apparatus <NUM>. The first plug may comprise an inflatable element (or equivalent) and a cement portion, wherein the cement is poured into the well <NUM> after the inflatable element is positioned.

In exemplary arrangements in which a communications device <NUM> is used, the communications device <NUM> is positioned <NUM> above the first plug <NUM>. The communications device <NUM> is positioned in the metallic well structure section, which comprises a casing, conductor or the like. As discussed above, the communications device <NUM> may be used to boost data signals transmitted wirelessly from the downhole apparatus <NUM> for transmission to the receiver <NUM> at the seabed.

A second plug <NUM> is placed <NUM> above the communications device <NUM> and the metallic well structure <NUM> is severed <NUM> below the surface <NUM>.

The receiver(s) <NUM> are deployed at the surface <NUM> for receiving signals propagated through the ground region <NUM>. Signal reception is through the ground region, i.e. there is no requirement for direct contact with the metallic well structure.

<FIG> shows a method for determining whether there is connectivity between subterranean reservoirs of hydrocarbon material intercepted by a plurality of wells. That is, reservoirs that are intercepted by separate wells may be connected together and/or may be part of the same reservoir. The method shown in <FIG> allows the determination of whether the reservoirs are connected. It is noted that the "reservoirs" intercepted by the two wells may in fact be a single reservoir, if it is determined that they are connected and the term "reservoirs" is used for ease of description only.

<FIG> can be viewed in conjunction with <FIG>, which shows a first well <NUM> and a second well <NUM>. In the exemplary arrangement of <FIG>, the first well <NUM> is an abandoned appraisal well and the second well <NUM> is a production well, although other well types may also be used. The first well <NUM> comprises a communication system as described herein. In particular, the first well <NUM> includes a downhole apparatus <NUM>, a communication device <NUM> and at least one receiver <NUM>, all configured to operate as disclosed herein. The first well <NUM> and the second well <NUM> each intercept a reservoir <NUM>.

Water is injected <NUM> into the second well <NUM>. This increases the pressure in the reservoir <NUM>. The pressure in the reservoir <NUM> is one of a number of parameters that may be altered in the reservoir <NUM>. Whichever parameter is altered, it should be detectable by the downhole apparatus <NUM>. That is, the downhole apparatus <NUM> should comprise a sensor configured to sense a change in the chosen parameter and/or an associated parameter. In the case of <FIG>, the parameter is pressure and the downhole apparatus therefore comprises a pressure sensor for sensing a change in the pressure in the reservoir <NUM>.

The parameter is altered via the second well <NUM>. The parameter, or a corresponding parameter, is detectable by the communications system fitted to the first well <NUM>. That is, the downhole apparatus <NUM> comprises a sensor configured to sense the parameter or a corresponding or related parameter. Accordingly, the downhole apparatus <NUM> senses <NUM> the pressure in the reservoir and communicates a data signal indicative of the pressure in the reservoir to the receiver <NUM> using any method disclosed herein. In the case of <FIG>, the downhole apparatus <NUM> wirelessly transmits the data signal to the communications device <NUM>, which injects it into the metallic well structure <NUM>. The data signal propagates through the metallic well structure <NUM> and then through the ground region <NUM> above the severed well structure <NUM> before being received at the receiver <NUM>.

Claim 1:
A communication system for use in conjunction with a well (<NUM>, <NUM>) having a metallic well structure (<NUM>, <NUM>) therein, the system comprising:
a downhole apparatus (<NUM>) configured to be positioned in an open hole section (<NUM>, <NUM>) within the well (<NUM>, <NUM>) below the metallic well structure (<NUM>, <NUM>), the downhole apparatus (<NUM>) comprising an electromagnetic sensor configured to create a dipole antenna to wirelessly transmit data signals from the open hole section (<NUM>, <NUM>), through surrounding formation, to be received by a communications device (<NUM>) placed in the metallic well structure (<NUM>, <NUM>) for propagation via that metallic well structure (<NUM>, <NUM>), the downhole apparatus (<NUM>) configured to sense temperature and/or pressure in the open hole section (<NUM>, <NUM>), and to transmit the data signals indicative of the sensed temperature and/or pressure;
at least one receiver (<NUM>) configured to be deployed at a top of the well (<NUM>, <NUM>), and further configured to receive the data signals from the metallic well structure (<NUM>, <NUM>); and
the communications device (<NUM>) configured to receive the wirelessly transmitted data signals from the downhole apparatus (<NUM>) and to inject the data signals into the metallic well structure (<NUM>, <NUM>) for propagation therethrough.