AU2018214243A1

AU2018214243A1 - A wellbore water level measurement system

Info

Publication number: AU2018214243A1
Application number: AU2018214243A
Authority: AU
Inventors: Matthew BOLSOVER
Original assignee: Well Digital Ltd
Current assignee: Well Digital Ltd
Priority date: 2017-01-31
Filing date: 2018-01-31
Publication date: 2019-09-19
Anticipated expiration: 2038-01-31
Also published as: GB2559184B; WO2018142134A1; GB2559184A; GB201701531D0; AU2018214243B2

Abstract

Wells may be drilled down to a coal seam, for example substantially vertically. Groundwater will naturally tend to fill the well thus drilled, and removal of the water (i.e. dewatering of the wellbore) will tend to lower the level of water within the well. Removal of the water leads to a reduction of pressure that allows adsorbed gas (in particular methane) to desorb from the solid matrix of the coal, flow as a gas up the well and thus be collected at the surface. The more the pressure is reduced (by removing the water), the greater the rate of gas extraction possible. However, if water is removed from the well too quickly, the level of water in the well may decrease below some predetermined minimum level, which can cause problems. Thus, it is important to be able to monitor the level of water (15) within the well to ensure that as much as possible coal seam gas is allowed to flow (as a gas) up the well, and to minimise the possibility of the pump (11) burning out. Existing systems of monitoring water level in a wellbore use pressure sensors installed at the base of well and connected to the surface by cable. The present invention dispenses with the cable by providing a network of nodes (19, 21, 23, 25, 27, 29) fixed at respective locations within a well bore, with a master node configured to determine a level of water (15) in the wellbore from attenuation of wireless communication signals between adjacent nodes.

Description

SUREMENT SYSTEM [0001] The present invention relates generally to a wellbore water level measurement system and a method of a measuring a level of water within a wellbore and finds particular, although not exclusive, utility in extraction of coal seam gas.

[0002] Coal seam gas (also known as CSG, coal-bed methane, CBM, coalbed gas, coal-mine methane or CMM) is a form of natural gas, predominantly methane, adsorbed into the solid matrix of the coal (macerals). Macerals of coal generally include pores as well as open fractures (or cleats), which can also contain free gas or water at a pressure substantially above atmospheric pressure.

[0003] Water in fracture spaces in the coal may be pumped off by conventional means. For instance, a well may be drilled down to a coal seam, for example substantially vertically. Groundwater will naturally tend to fill the well thus drilled, and removal of the water (i.e. dewatering of the wellbore) will tend to lower the level of water within the well.

[0004] Removal of the water leads to a reduction of pressure that allows adsorbed gas (in particular methane) to desorb from the matrix, flow as a gas up the well and thus be collected at the surface. The more the pressure is reduced (by removing the water), the greater the rate of gas extraction possible.

[0005] However, if water is removed from the well too quickly, the level of water in the well may decrease below some predetermined minimum level. This can lead to at least two problems. The first is that if the dewatering pump being used runs dry, it may bum out very quickly, perhaps in a matter of seconds. This is extremely costly to repair. Secondly, gas may enter into the water pump line causing the well to become gassy. Pumping a gas-water mix is highly inefficient and is therefore undesirable.

[0006] Thus, it is important to be able to monitor the level of water within the well to ensure that as much as possible coal seam gas is allowed to flow (as a gas) up the well, and to minimise the possibility of the pump burning out.

[0007] Existing systems of monitoring water level in a wellbore use pressure sensors installed at the base of well. A higher volume of water above the sensor corresponds to a higher pressure. However, these systems are expensive and unreliable as the pressure sensor must be connected to the surface in order to (a) be powered and (b) relay its measurements back to the surface. Due to the high attenuation of electromagnetic waves in water, wireless systems are not practical and thus a cable must be run down the wellbore from the surface to the pressure sensor. Such cables are relatively fragile

WO 2018/142134 PCT/GB2018/050287 and easily damaged when running in hole, and are therefore very difficult to install. [0008] According to a first aspect of the present invention, there is provided a wellbore water level measurement system, comprising: a master node; and a plurality of repeater nodes, each repeater node fixed at a respective location within a well bore; wherein: the master node and each repeater node are configured to communicate with one another wirelessly to form a wireless network; water present between two adjacent nodes attenuates wireless communication signals therebetween; and the master node is configured to determine a level of water in the wellbore from attenuation of wireless communication signals between adjacent nodes.

[0009] In this way, when no water is present in the wellbore, all the repeater nodes will communicate at full strength with one another, and the master node will thereby be able to determine that no water is present in the wireless network.

[0010] In contrast, when the wellbore is full of water, wireless communications between all of the repeater nodes will be attenuated (e.g. at least some or all node pairs may not be able to communicate with one another, and/or signals between pairs of nodes may be of a lower strength than when no water is present in the wellbore), and the master node will thereby be able to determine that the wellbore is full of water.

[0011] In intermediate cases, that is, when the wellbore is partially full of water, wireless communications between some (but not necessarily all) of the repeater nodes will be attenuated, and the master node will thereby be able to determine that an intermediate quantity of water is present in the wellbore.

[0012] The level of water determined by the master node may be in relation to the repeater nodes. However, correct placement of the repeater nodes within the wellbore and/or calibration of the signal strength between nodes may allow the master node to determine a height of water within the wellbore relative to the surface, wellhead (at the top of the wellbore) and/or down-hole pump (at the bottom of the wellbore).

[0013] The wellbore may be between 10m and 2km deep, in particular between 100m and 1.5km deep, more particularly between 200m to 1km deep.

[0014] A drivehead or pumpjack may be provided at the wellhead and/or top of the wellbore for driving a down-hole pump at the bottom of the wellbore, for instance via rotation or reciprocation of a sucker rod, respectively. The master node may be configured to control the drivehead/pumpjack, or alternatively the drivehead/pumpjack may be manually controllable in response to an output of the master node, such that the water level within the wellbore may be adjusted. The down-hole pump may comprise a Progressive Cavity Pump [0015] The wellbore itself may be clad with cement and/or a casing. The casing may be metal.

[0016] The sucker rod may be provided within tubing within the wellbore and/or casing. Al

WO 2018/142134 PCT/GB2018/050287 ternatively, such tubing may be provided without a sucker rod. Water pumped out of the wellbore may be conveyed via the tubing. The tubing may be arranged in the wellbore to form an annulus between an outer surface of the tubing and an interior surface of the wellbore and/or casing.

[0017] The repeater nodes may be attached to the tubing. For instance, a repeater node may be attached to a section of tubing before insertion into the wellbore. The or each repeater node may be attached to an outer surface of the tubing.

[0018] The wireless network may be any suitable form of network, and may be in particular a mesh network. The network may be controlled by the master node.

[0019] The wireless network may be a radio-frequency wireless network. For instance, the nodes may be configured to communicate at a frequency of between approximately 300kHz and 300GHz, in particular between 3MHz and 30GHz, more particularly between 30MHz and 20GHz, for instance between 300MHz and 10GHz.

[0020] The system may be configured for communication signals between the nodes to propagate similar to those within a circular waveguide. The communication signals may operate in the transverse electric (TE) mode and/or transverse magnetic (TM) mode. Due to the size of the wellbore, and in particular the casing size, there may be a low frequency cut-off. Therefore, the nodes may be configured to communicate at a frequency of between approximately 1GHz and 10GHz.

[0021] The tubing may be electrically isolated from the casing. The tubing may comprise metal.

[0022] The system may be configured for communication signals between the nodes to propagate within the annulus. In this way, the system may be configured for communication signals between the nodes to propagate similar to those within a coaxial cable. The communication signals may operate in the transverse electromagnetic (TEM) mode. Accordingly, there may be substantially no low frequency cut-off. Therefore, the nodes may be configured to communicate at a frequency of less than approximately 1GHz. Accordingly, when the metal tubing is electrically isolated from the metal casing, a lower communication frequency may be used, extending the range of nodeto-node communication.

[0023] However, in some circumstances, a short circuit may accidentally form between the metal tubing and the metal casing. Therefore, in preferred embodiments, the master node and the repeater nodes are configured to communicate over the network at a frequency of less than 1GHz when the metal tubing is electrically isolated from the metal casing; and/or the master node and the repeater nodes are configured to communicate over the network at a frequency of between 1GHz and 10GHz when the metal tubing is in electrical contact with the metal casing. The master node and repeater nodes may be configured to select between the two frequencies ranges of

WO 2018/142134 PCT/GB2018/050287 operation in response to isolation and/or contact of the metal tubing with the metal casing.

[0024] The metal tubing may be electrically isolated from the metal casing using centralisers, for instance polymer based centralisers, or centralisers of any other electrically insulation material.

[0025] The repeater nodes may be uniformly spaced within the wellbore; however, in alternative arrangements, the repeater nodes may be spaced at arbitrary known distances within the wellbore.

[0026] The resolution of the system may be improved by decreasing the spacing between adjacent repeater nodes, for instance, by increasing the total number of repeater nodes. In cases where the spacing between adjacent nodes is such that water between the two nodes substantially inhibits communication between the two nodes, a change in the water level within the wellbore actually changes the size of the network under consideration (i.e. the number of repeater nodes present in the wireless network), and the master node may be configured to simply determine the water level within the wellbore by counting the number of repeater nodes present in the wireless network (or otherwise determining which repeater nodes are present in the wireless network). In this way, a substantially discrete (quantised) measurement system is provided.

[0027] In cases where the spacing between nodes (whether adjacent or not) is such that water between the nodes permits attenuated communication signals between nodes, resolution of the system may be improved by analysing the amount of attenuation between the nodes to determine the amount of water therebetween. In this way, a substantially continuous measurement system is provided.

[0028] This allows the repeater nodes to be spaced at arbitrary unknown distances within the wellbore, and analysis of signal strength between the nodes when the presence of absence of water is known, allows a level of each node within the wellbore to be determined.

[0029] According to a second aspect of the present invention, there is provided a method of determining a level of water in a wellbore, comprising: providing the system of any preceding claim in a wellbore; fixing each repeater node at a respective location within a well bore; forming a network between the master node and the repeater nodes by sending communication signals therebetween; providing water between two adjacent nodes in the wellbore and attenuating wireless communication signals therebetween; and determining a level of water in the wellbore from attenuation of wireless communication signals between adjacent nodes.

[0030] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles

WO 2018/142134 PCT/GB2018/050287 of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0031] [fig.l] Figure 1 is schematic view of a wellbore incorporating the present invention. [0032] [fig.2] Figure 2 is schematic view of a network of nodes as used in the present invention.

[0033] The present invention will be described with respect to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. Each drawing may not include all of the features of the invention and therefore should not necessarily be considered to be an embodiment of the invention. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0034] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other sequences than described or illustrated herein.

[0035] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other orientations than described or illustrated herein.

[0036] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0037] Similarly, it is to be noticed that the term “connected”, used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression “a device A connected to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B

WO 2018/142134 PCT/GB2018/050287 which may be a path including other devices or means. “Connected” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other. For instance, wireless connectivity is contemplated.

[0038] Reference throughout this specification to “an embodiment” or “an aspect” means that a particular feature, structure or characteristic described in connection with the embodiment or aspect is included in at least one embodiment or aspect of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, or “in an aspect” in various places throughout this specification are not necessarily all referring to the same embodiment or aspect, but may refer to different embodiments or aspects. Furthermore, the particular features, structures or characteristics of any embodiment or aspect of the invention may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments or aspects.

[0039] Similarly, it should be appreciated that in the description various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Moreover, the description of any individual drawing or aspect should not necessarily be considered to be an embodiment of the invention. Rather, as the following claims reflect, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0040] Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0041] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0042] In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter,

WO 2018/142134 PCT/GB2018/050287 coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

[0043] The use of the term “at least one” may mean only one in certain circumstances.

[0044] The principles of the invention will now be described by a detailed description of at least one drawing relating to exemplary features of the invention. It is clear that other arrangements can be configured according to the knowledge of persons skilled in the art without departing from the underlying concept or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

[0045] Figure 1 is schematic view of a wellbore incorporating the present invention. A shaft extends from the surface 1 and is clad with a casing 3 using conventional methods. Tubing 5 is passed down the interior of the casing 3, again using conventional methods, forming an annulus 7 therebetween. In some cases, centralizers are employed to space the tubing 5 from the casing 3; however, this is optional, and is not shown in the present figure for clarity.

[0046] A sucker rod 9 may be provided within the tubing, coupling a down-hole pump 11 to a drivehead/pumpjack (not shown) at the wellhead. In this way, water may be pumped from the wellbore out through the centre of the tubing 5 and removed by the water take-off means 13 (e.g. a pipe). In this manner, the water level 15 in the annulus may be controlled by adjusting the rate of pumping. Gas in the wellbore above the water level 15 may be drawn off via gas take-off 17.

[0047] A plurality of network nodes 19, 21, 23, 25, 27, 29 are coupled to the tubing 5, for instance prior to insertion of the tubing into the wellbore. The nodes 19, 21, 23, 25, 27, 29 are shown at a variety of spacings but could also be equally spaced along the tubing. Upper nodes 19, 21, 23 are located above the water level 15 and are therefore able to communicate wirelessly with one another. Lower nodes 25, 27, 29 are located below the water level 15 and are therefore unable to communicate wirelessly with one another.

[0048] The presence of only the three upper nodes 19, 21, 23 in the wireless network extending between them indicates to an up-hole user that the water level 15 in the wellbore must be somewhere between the lowermost upper node 23 and the uppermost lower node 25. The up-hole user is therefore free to determine that an increase in pumping rate may be made in order to lower the water level 15, thereby increasing the rate of gas extraction from the wellbore, without causing damage to the pump 11.

[0049] Figure 2 is schematic view of a network of nodes as used in the present invention. A master node 31 is provided at the top of a wellbore (not shown). A first repeater node

WO 2018/142134

PCT/GB2018/050287 is provided below the master node 31 in the wellbore. A second repeater node 35 is provided below the first repeater node 33, a third repeater node 37 is provided below the second repeater node 35, and a fourth repeater node 39 is provided below the third repeater node 37.

[0050] A water level 41 is shown in between the first repeater node 33 and the second repeater node 35. As there is no water present between the master node 31 and the first repeater node 33, wireless communication signals 43 may pass between the master node 31 and the first repeater node 33. Thus the master node 31 and the first repeater node 33 form part of a wireless network, that the master node 31 may use to determine the water level 41.

[0051] Some water is present between the first repeater node 33 and the second repeater node 35, such that wireless communication signals 45 therebetween are attenuated by the water. The amount of attenuation of these signals 45 may be used by the master node to infer the water level 41. Similarly, wireless communication signals 47 directly between the master node 31 and the second repeater node 35 are attenuated by the water. The amount of attenuation of these signals 47 may also be used by the master node to infer the water level 41.

[0052] Water is also present between the second repeater node 35 and the third repeater node 37, such that wireless communication signals 49 therebetween are attenuated by the water. The amount of attenuation of these signals 49 may be used by the master node to infer the water level 41. The spacing of the third repeater node 37 from the first repeater node 33 and the master node 31 is sufficiently great that no wireless communication signals are able to pass between the third repeater node 37 and either of the first repeater node 33 and the master node 31.

[0053] The spacing between the fourth repeater node 39 and the third repeater node is greater than the spacing between the third repeater node 37 and the second repeater node 35, such that no wireless communication signals are able to pass between the fourth wireless repeater node 39 and any other node when water is present therebetween as in this figure due to attenuation by water. Accordingly, fourth repeater node 39 does not form part of the wireless network formed by the mater node 31 and the first 33, second 35 and third 37 repeater nodes. Therefore the master node 31 is able to determine the water level 41 from attenuation of wireless communication signals 45, 47 from the second repeater node 35, attenuation of wireless communication signals 49 from the third repeater node 37, and attenuation of wireless communication signals 51 from the fourth repeater node 39.

Claims

1. A wellbore water level measurement system, comprising:

a master node; and a plurality of repeater nodes, each repeater node fixed at a respective location within a well bore;

wherein:

the master node and each repeater node are configured to communicate with one another wirelessly to form a wireless network;

water present between two adjacent nodes attenuates wireless communication signals therebetween; and the master node is configured to determine a level of water in the wellbore from attenuation of wireless communication signals between adjacent nodes.

2. The wellbore water level measurement system of claim 1, wherein the wireless network comprises a mesh network.

3. The wellbore water level measurement system of claim 1 or claim 2, further comprising a wellbore in which the system is provided, wherein the wellbore is clad by a metal casing and metal tubing is provided therein, electrically isolated from the metal casing.

4. The wellbore water level measurement system of claim 1 or claim 2, further comprising a wellbore in which the system is provided, wherein:

the wellbore is clad by a metal casing and metal tubing is provided therein;

the master node and the repeater nodes are configured to communicate over the network at a frequency of less than 1GHz when the metal tubing is electrically isolated from the metal casing; and the master node and the repeater nodes are configured to communicate over the network at a frequency of between 1GHz and 10GHz when the metal tubing is in electrical contact with the metal casing.

5. The wellbore water level measurement system of claim 3 or claim 4, wherein the metal tubing is electrically isolated from the metal casing using centralisers.

6. The wellbore water level measurement system of any preceding claim, wherein the master node is configured to determine the water level within the wellbore by counting the number of repeater nodes present in the wireless network.

WO 2018/142134 [Claim 7] [Claim 8]

PCT/GB2018/050287

7. The wellbore water level measurement system of any preceding claim, wherein the master node is configured to analyse the amount of attenuation between pairs of nodes to determine the amount of water therebetween.

8. A method of determining a level of water in a wellbore, comprising: providing the system of any preceding claim in a wellbore;

fixing each repeater node at a respective location within a well bore; forming a network between the master node and the repeater nodes by sending communication signals therebetween;

providing water between two adjacent nodes in the wellbore and attenuating wireless communication signals therebetween; and determining a level of water in the wellbore from attenuation of wireless communication signals between adjacent nodes.