WO2013153388A2

WO2013153388A2 - Improved underground coal gasification methods, systems and apparatus

Info

Publication number: WO2013153388A2
Application number: PCT/GB2013/050929
Authority: WO
Inventors: Alan BORROWMAN; Ian Porter
Original assignee: Portman Energy Limited
Priority date: 2012-04-10
Filing date: 2013-04-10
Publication date: 2013-10-17
Also published as: GB2501074A; GB2501074B; GB201206255D0; WO2013153388A3

Abstract

An underground gas transport and production system applicable to the process of coal gasification employing a novel single well approach in which air, oxygen or a mixture of these gases together with water (e.g. steam) is pumped from the surface, to supply a gasification process, via the same well casing through which gas produced by the gasification process is transported to the surface. A corresponding underground arrangement is also disclosed which complements the single well approach and its own advantages in terms of increased recovery of syngas by use of an array of delivery and recovery conduits. By providing multiple burn-fronts an averaging effect is achieved which results in a dilution effect and balancing of gas conditions in the coal seam.

Description

Improved Underground Coal Gasification Methods, Systems and Apparatus The present invention relates to underground coal gasification, and in particular improved methods, systems and apparatus for performing underground coal gasification processes. Background to the invention Underground coal gasification (UCG) is a process in which virgin coal is partially combusted and reacted with air or oxygen pumped into the coal. This enables energy to be extracted from in-situ underground coal deposits. UCG has been demonstrated and practiced for over a century to exploit coal deposits which are too difficult to mine or too deep for economic recovery using conventional methods. Typically, a UCG installation comprises a pair of wells drilled from the surface down into the coal deposit and connected within the coal deposit. In one approach parallel pairs of wells are separated usually by a distance of 10 to 50 metres. Air or oxygen is pumped into the coal through one of the wells and the gasification product, commonly referred to as synthetic gas or "syngas", is extracted through the other. The main economic use of syngas from the UCG process is the generation of electricity or the manufacture of chemicals or transport fuels on a relatively large scale. However, the output of each gasification chamber is limited so it is necessary to produce syngas from a chamber of larger size or a large number of chambers operating simultaneously. In another UCG approach, vertical or near vertical wells may be separated by a distance of 200 to 700 metres but linked by a common horizontal well extending through the coal seam in a configuration known as "linked vertical well" UCG. A further variant referred to as "continuously retractable injection point" involves a modification to the means by which an oxidising fluid of air or oxygen or a mixture of these gases and which may contain water or steam, is delivered to the coal. In this variant the well for oxidising fluid delivery is drilled into the coal seam and fitted with a perforated liner. An oxidising fluid is passed down a flexible tubing inserted within the perforated liner, and the flexible tubing is retracted as the coal is consumed by the gasification process to ensure that the oxidising fluid is delivered to the surface of the coal being gasified. Each of these UCG methods requires the drilling of two separate vertical (or inclined) wells from the surface into the coal deposit. A further alternative method requires the drilling of yet another well for the purpose of inserting an ignition device or system to initiate the gasification process. It is therefore an object of at least one embodiment of the present invention to obviate and/or mitigate one or more disadvantages associated with conventional underground coal gasification processes.

Summary of the invention According to a first aspect of the invention, there is provided an underground coal gasification well comprising; a delivery conduit configured to deliver an oxidising fluid to a coal deposit associated with the installation; and a recovery conduit configured to recover syngas produced from the coal deposit in a gasification process; wherein the first conduit and the second conduit are disposed within a single wellbore. The skilled person will understand the term fluid to include liquid, gas, liquid-like and gas- like materials. For example, fluid may also refer to gel or particulate material. The invention employs a novel single well approach in which an oxidising fluid is pumped from the surface, to supply a gasification process, via the same wellbore through which gas produced by the gasification process is transported to the surface; each via separate conduits. Preferably, the wellbore is cased. Optionally, the wellbore is sealed and contains an inert gas. The provision of an inert gas may serve to prevent corrosion and detect leaks or failures within the wellbore. The oxidising fluid may comprise air, oxygen, or a mixture of these gases. Preferably, the well further comprises an ignition and fuel conduit disposed within the wellbore to supply fuel and ignition service to initiate the gasification process in the coal deposit. Optionally, the ignition and fuel conduit is deployed alongside the delivery conduit. Alternatively, and preferably, the ignition and fuel conduit is disposed within the delivery conduit. Optionally, the well further comprises a water conduit disposed within the wellbore to deliver water into the delivery conduit. Water may be delivered in the form of steam or by a water spray arrangement. Preferably, the well further comprises at least one cooling fluid conduit disposed within the wellbore to supply cooling fluid to cool the recovery conduit. Preferably, at least one cooling fluid conduit supplies cooling fluid to the interior of the casing. Optionally, the well further comprises cooling means, such as a cooling jacket, mounted on the recovery conduit, to which the cooling fluid is supplied by at least one cooling fluid conduit. Preferably, the well is configured to control a temperature of the recovered syngas by controlling cooling fluid supply through one or more cooling fluid conduits. Preferably, the well further comprises a monitoring conduit disposed within the wellbore and arranged to transport material from the coal deposit. Most preferably, the well further comprises corresponding monitoring means configured to analyse the material. Such analysis may identify contaminants or the like present in the coal deposit. Optionally, the well is configured to adjust, or indeed cease, delivery of oxidising fluid to the coal deposit responsive to the analysis. Most preferably, the well comprises a wellhead, the wellhead comprising a plurality of interfaces corresponding and coupled to the plurality of pipelines disposed within the wellbore. Preferably, the well further comprises a vent to provide fluid communication with the interior of the wellbore. Preferably, the well further comprises corresponding monitoring means configured to analyse fluid from the interior of the wellbore. Such analysis may reveal casing leaks or leaks from one or more of the conduits disposed within the wellbore. Optionally, the well is configured to adjust, or indeed cease, delivery of oxidising fluid to the coal deposit responsive to the analysis. According to a second aspect of the invention, there is provided an underground coal gasification array comprising; a recovery conduit extending within a coal deposit and configured to recover syngas produced from the coal deposit in a gasification process; and plurality of delivery conduits associated with the recovery conduit, each of the delivery conduits configured to deliver an oxidising fluid to the coal deposit. Most preferably, the conduit array comprises a plurality of recovery conduits, each of the plurality having an associated plurality of delivery conduits. Most preferably, at least two of the delivery conduits are located at different distances from the recovery conduit. Optionally, at least one of the delivery conduits houses a seal. Advantageously the seal may be selected to open the delivery conduit dependent upon temperature. Accordingly, the seal may comprise a eutectic or fusible plug. Alternatively, the seal may be located at any position in the delivery conduit and configured to be drilled through to open the delivery conduit. Further alternatively, the seal may be located any position in the delivery conduit and configured to be opened mechanically, for example upon receiving a signal to open the respective delivery conduit. The signal may be transmitted by means of a direct communication with the seal - such as an electrical, hydraulic or optical connection - or by indirect means such as a pressure, acoustic or electromagnetic signal, or by any other means. Preferably, the seal is configured to be closed mechanically using same or similar methods. The seal may also be drilled through as required. Optionally, the recovery conduit or at least one of the recovery conduits comprises a seal. Similarly, the seal may be located any position in the recovery conduit and configured to be opened mechanically upon receipt of a corresponding signal. Preferably, the seal is also configured to be closed mechanically. Preferably, the conduits comprise one or more apertures. Most preferably, the conduits comprise perforated liners. Optionally, the conduits comprise one or more slotted guide tubes. Optionally, each recovery conduit and its associated plurality of delivery conduits are disposed substantially in a same plane. Alternatively, the array comprises a plurality of recovery conduits disposed at different vertical heights. Most preferably, the different vertical heights correspond to locations of different coal seams. Optionally, the array comprises a plurality of recovery conduits extending radially from a central location. In an embodiment of the third aspect of the present invention, this provides for coal to be gasified in an arc of up to 360 degrees around the wellbore. A particular advantage stems from the fact that the wellbore can therefore be drilled into the middle of a coal seam or field, rather than at an edge. Preferably, the conduit array comprises one or more monitoring conduits configured to transport material from the coal deposit for analysis. Most preferably, the one or more monitoring conduits are arranged around the periphery of the coal deposit. Optionally, the or each recovery conduit comprises a cooling jacket arranged to cool the syngas within the recovery conduit. Alternatively, the or each recovery conduit comprises one or more perforations through which a cooling fluid is injected directly into the syngas. Embodiments of the second aspect of the invention may include one or more features corresponding to features of the first aspect of the invention or its embodiments, or vice versa. According to a third aspect of the invention, there is provided an underground coal gasification installation comprising a well according to the first aspect and an array according to the second aspect; wherein the delivery conduit of the well is in fluid communication with the plurality of delivery conduits of the array to deliver oxidising fluid from the surface; and wherein the recovery conduit of the well is in fluid communication with the recovery conduit of the array to recover syngas from the coal deposit. Advantageously, the installation comprises a plurality of arrays according to the second aspect, each of the arrays disposed at a different vertical height. In this way, syngas can be recovered from several vertically separated coal seams again through a single wellbore. Optionally, the installation further comprises an ignition system deployed within the same casing of the well. Embodiments of the third aspect of the invention may include one or more features corresponding to features of the first and/or second aspects of the invention or their embodiments, or vice versa. According to a fourth aspect of the present invention, there is provided a method of performing an underground coal gasification process comprising:

delivering an oxidising fluid to an underground coal deposit;

gasifying at least a portion of the coal deposit; and

recovering syngas produced from the underground coal deposit;

wherein the delivery of oxidising fluid and recovery of syngas is performed via a single wellbore. Preferably, the method comprises delivering a fuel to the coal deposit and igniting the fuel. This provides a more furious ignition source for igniting the coal to be gasified. Optionally, the method comprises cooling the syngas as it is recovered. Preferably, the method comprises controlling a temperature of the syngas by controlling the cooling of the syngas as it is recovered. Preferably, the method comprises obtaining a material sample from the coal deposit during the gasification process and analysing the sample. Optionally, the method comprises obtaining a fluid sample from within the wellbore and analysing the fluid sample. The gasification process and/or syngas recovery may be controlled, or indeed halted, dependent on the analysis. This may be achieved by varying the supply of oxygen and/or water (or steam). Embodiments of the fourth aspect of the invention may include one or more features corresponding to features of the first to third aspects of the invention or their embodiments, or vice versa. According to a fifth aspect of the present invention, there is provided a method of providing an underground coal gasification well comprising:

drilling a wellbore; and

disposing an oxidising fluid delivery conduit and a syngas recovery conduit within the wellbore. Optionally, the method comprises casing the wellbore to provide a cased well. Embodiments of the fifth aspect of the invention may include one or more features corresponding to features of the first to fourth aspects of the invention or their

embodiments, or vice versa. According to a sixth aspect of the present invention, there is provided a method of providing an underground coal gasification pipeline array comprising;

drilling a syngas recovery bore within a coal deposit; and

drilling a plurality of oxidising fluid delivery bores associated with the syngas recovery bore within the coal deposit Optionally, the method is repeated at a plurality of depths. Optionally, the plurality of depths correspond with a series of coal deposits. Preferably, the method comprises lining at least one of the syngas recovery bore and the plurality of oxidising fluid delivery bores. Preferably, the at least one bore is lined with a perforated or slotted liner. Most preferably, the syngas recovery bore and the oxidising fluid delivery bore are drilled from the base of a single associated production well. Embodiments of the sixth aspect of the invention may include one or more features corresponding to features of the first to fifth aspects of the invention or their embodiments, or vice versa. According to a seventh aspect of the present invention, there is provided a method of generating electrical power comprising recovering syngas from a coal deposit according to the method of the fourth aspect and converting the recovered syngas to electrical power. Embodiments of the seventh aspect of the invention may include one or more features corresponding to features of the first to sixth aspects of the invention or their

embodiments, or vice versa. According to an eighth aspect of the present invention, there is provided a syngas or hydrocarbon recovered via an underground coal gasification well according to the first aspect, from an underground coal gasification pipeline array according to the second aspect, by an installation according to the third aspect, using a method according to the fourth aspect, from an underground coal gasification well provided by the method of the fifth aspect or from an underground coal gasification pipeline array provided by the method of the sixth aspect. Embodiments of the eighth aspect of the invention may include one or more features corresponding to features of the first to seventh aspects of the invention or their embodiments, or vice versa.

Brief description of the drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 illustrates in schematic form the top of an underground coal gasification well, in accordance with an embodiment of the present invention; Figure 2 illustrates in schematic form the bottom of an underground coal gasification well, in accordance with an embodiment of the present invention; Figure 3 illustrates in schematic form a well-head associated with the top of the

underground coal gasification well illustrated in Figure 1 , in accordance with an

embodiment of the present invention; Figure 4 illustrates in schematic form the layout of conduits in an underground coal gasification array, in accordance with an embodiment of the present invention; Figure 5 illustrates in schematic form the layout of conduits in an alternative underground coal gasification array, in accordance with an alternative embodiment of the present invention; Figure 6 illustrates in schematic form a multi array installation serviced via a common, single well, in accordance with an alternative embodiment of the present invention; and Figure 7 illustrates in schematic form an installation in which the array comprises a number of delivery conduits and recovery conduits extending radially from a central, single, common well, in accordance with a further alternative embodiment of the present invention. Detailed description of preferred embodiments Figures 1 to 3 illustrate various components of an underground coal gasification installation in accordance with one or more aspects of the invention, which comprises a single vertical or inclined well connected to a wellhead and drilled and completed (i.e. cased) below ground. The well contains multiple conduits that are connected to and in fluid communication with a horizontal array of bores within the plane of a coal seam. One conduit supplies a mixture of an oxidising agent and water (or steam) to a gasification chamber in the coal seam to fuel a gasification process and another conduit provides a means of recovering the syngas produced by the gasification process to the surface. The well also supplies a fuel gas or liquid for initiating the gasification process, supplies water to cool the syngas, and incorporates conduits for monitoring contaminants escaping from the gasification chamber. Figure 1 illustrates the top of an underground coal gasification well 1 in which, in contrast to conventional underground coal gasification installations, the oxidising agent pipeline 3 ("delivery conduit") and the syngas pipeline 5 ("recovery conduit") are deployed within a same single casing 7. Figure 2 illustrates the bottom of the well 1 and the interface with an underground coal gasification pipeline array 51 , and Figure 3 provides a top-down view of the corresponding wellhead 23. Note that the wellbore itself need not necessarily be cased to benefit from the invention, provided the pipelines are still deployed within the same wellbore. The delivery pipeline 3 conveys an oxidising agent, with water or steam, under pressure to a coal gasification chamber (not shown) associated with the well 1 for the purposes of initiating and maintaining the gasification process. Once the process is underway, the recovery pipeline 5 conveys the produced syngas, under pressure, from the gasification chamber to the surface for extraction and subsequent conversion, storage, or other syngas application. By housing the delivery pipeline 3 and the recovery pipeline 5 in a single cased well, the requirement to drill pairs of parallel (relatively vertical) wells is negated. One particular advantage stems from the ability to perform underground coal gasification processes in coal seams or deposits which are too deep to justify the drilling of two separate wells but may not be of a thickness or quantity to be commercially attractive for UCG. In addition, it may not be possible to site a second well due to geological or geographical constraints which would make a particular coal seam or deposit inaccessible or commercially attractive to conventional UCG methodologies. Another advantage is that the land area required for the surface installation is significantly decreased by deploying the delivery pipeline and recovery pipeline within a single wellbore (and wellhead) rather than separate wellbores (and their associated wellheads).

Surface conductor 29 and well casing 7 provide a barrier between the pipelines and the surrounding rock formation and are fixed in position by cement 31 which fills the void between the well 1 and the drilled hole in the rock formation. Furthermore, such an arrangement provides for local control of all of the parameters of the underground coal gasification process via a single well-head. Additional advantages thus stem from safety implications, such as being able to shut down a UCG operation or installation via a single well-head. Water pipeline 1 1 may be employed to convey water (or steam) under pressure into the delivery pipeline 3 whereupon the water (or steam) is mixed with the oxidising agent and conveyed to the gasification chamber for the purpose of maintaining the gasification process.

The exemplary single well casing 7 contains several additional pipelines to perform additional functions. For example, cooling fluid pipeline 9 conveys an aqueous or gaseous medium under pressure into the open space within the casing 7 for the purpose of assisting the cooling of syngas within the recovery pipeline 5. For additional cooling of the syngas within the recovery pipeline 5, a cooling jacket pipeline 13 conveys water under pressure to a cooling jacket 17 located around recovery pipeline 5 near the base of the well casing (see Figure 2). Supply to the water cooling jacket 17 may be regulated dependent on feedback from a temperature probe 19 mounted on the recovery pipeline 5. In this embodiment, an ignition pipeline 15 is located within the delivery pipeline 3 to convey fuel gas or liquid, under pressure, to the furthest end of the delivery pipeline 3 to assist in combusting the coal in the underground coal deposit to initiate the gasification process. A monitoring pipeline 21 conveys contaminants that may permeate from the gasification chamber through the surrounding coal and rock formations for the purpose of detecting and analysing such contaminants. The wellhead 23 provides an isolatable termination point at the surface for all the above pipelines, by way of appropriate interfaces, valves etc. as illustrated in schematic form in Figure 3. For example, recovery pipeline interface 27 is an isolatable connection to recovery pipeline 5, for the purpose (for example) of facilitating the cleaning out of solids that may have become deposited inside delivery pipeline 5, or for the occasional sampling or extraction of syngas from the delivery pipeline 5. Casing vent 25 provides access to the interior of the casing 7, for example to convey the flow of aqueous or gaseous medium from said open space in the well casing 7 for monitoring purposes. For example, medium extracted from the interior of the casing 7 via the casing vent 25 may be analysed for the purpose of detecting leakage from any of the pipelines into the well casing 7. Note that while an underground coal gasification well in accordance with the present invention, such as the exemplary embodiment described above, may be employed with a conventional underground coal gasification chamber, particular benefits of the well provide for complementary underground coal gasification chamber arrangements which in turn bring their own additional advantages. One such arrangement will now be described with reference to Figure 4 which illustrates the layout of conduits (or bores or liners) in an underground coal gasification array 51 in accordance with an embodiment of another aspect of the invention (the combination of well and array providing an installation in accordance with an embodiment of yet another aspect of the invention). Figure 4 shows the extension of pipelines 3, 5, 21 into a coal panel (shown in plan view) to create an array of corresponding conduits 53, 55, 71 within the coal deposit. The conduits 53, 55, 71 located in the coal deposit are perforated liners to allow the flow of gases while preventing blockage caused by creeping of the coal or ingress of impurities etc. It is particularly advantageous if the conduits 3, 5, 21 are disposed substantially in the plane of the coal panel; however it will be appreciated that a variety of deployments will provide the same effect. As illustrated, delivery conduit 53 is 'side-tracked' repeatedly to create multiple delivery conduits 53, 53a substantially (but not necessarily) in parallel to and to either side of the recovery conduits 55. The direction and terminal point of each conduit 53, 53a, 55 is arranged such that the effective gasification chamber extends in a pre-determined manner. While in the illustrated example the effective gasification chamber extends laterally in one direction away from the well, an alternative gasification chamber might extend in all directions; comprise a single or indeed several recovery conduits, or indeed any other equivalent arrangement. In operation, fuel gas or liquid and air or oxygen are supplied to the location where the gasification process is to be initiated via corresponding pipelines and conduits (first in-well then within the coal panel) and ignited for example by a piezoelectric sparking device fitted to the end of an ignition pipeline (or end of an appropriate delivery conduit or conduits). Any appropriate ignition means may of course serve this purpose. The resulting combustion forms a gasification chamber in the coal panel and establishes sufficient temperature for gasification to commence, at which time the supply of fuel gas or liquid is stopped and gasification continues. Delivery conduits 53 which supply the oxidising agent to the gasification are arranged on either side of each of the recovery conduits 55 within the coal seam to provide localised oxidation to assist the gasification where it is required. As the gasification chamber naturally enlarges as coal is consumed, parallel delivery conduits 53a begin to provide the required local oxidation. Accordingly, by providing an array of delivery conduits 53,53a etc. a gasification process that would otherwise die out due to lack of a sufficient oxidising agent supply is able to continue much longer and indeed for as long as there are corresponding delivery conduits. Furthermore, the provision of multiple recovery conduits 55 and associated multiple delivery conduits 53, 53a, means that syngas can be produced from multiple burn-fronts, which allows syngas production per recovery well to be increased significantly in comparison to conventional methods. In the described example, said benefits are enjoyed in addition to the benefits afforded by the above-described single-well installation. The skilled person will also appreciate that the averaging effect provided by multiple burn-fronts results in a dilution effect and balancing of gas conditions in the coal seam which are additional advantages of arrays according to the invention. The subsequent delivery conduits 53a may be provided with drillable plugs 54 which provide a fluid seal until drilled through, for example when the gasification process progresses to a point at which it is desirable to open the relevant pipeline 53a and permit additional oxidising agent to be supplied to the gasification chamber. As the gasification chamber thereby expands both perpendicularly to the delivery conduits 53 and in the direction of flow of the syngas, this ensures that the gasification reaction is sustained and that the dimensions of the gasification chamber are controllable. Figure 5 illustrates an alternative layout to that shown in Figure 4 in which fusible or eutectic plugs 154, 154a are disposed at the ends of delivery conduits 153,153a to initially prevent (and subsequently controllably allow) the flow of oxidising agent directly from the open end of the delivery conduit into the coal panel. Also illustrated is a packer 157 arranged at the end of one of the conduits 153a which is employed to prevent oxidising agent from bypassing the plug 154a via slots or perforations that might exist in the lining of the conduits 153a. Each conduit may be provided with such a packer. Note that monitoring conduit 21 is 'side-tracked' to create corresponding coal panel monitoring conduits 71 ,171 around the periphery of the coal deposit. Accordingly, in-coal panel conditions can be monitored topside by extracting fluids (gases, liquids, vapours etc.) and particulates via the corresponding interface in the wellhead. In the presence of multiple coal seams which may lie within the same field, multiple arrays of recovery and delivery conduits may be provided with appropriate vertical separation(s) between one another so as to service such additional coal seams. It is of course particularly advantageous if all of the arrays are serviced and in communication with a common vertical wellbore. Figure 6 illustrates an exemplary embodiment of such a multi- array installation in which several arrays 202a, b, c, d of different size, orientation and vertical depth are serviced via a common, single well 201. Figure 7 illustrates an alternative embodiment of an installation in which the array 302 comprises a number of delivery conduits 353 and recovery conduits 355 extending radially from a central, single, common well 301. In such an embodiment the well 301 may be drilled in the centre of a coal deposit and the array provide 360 degree coverage around the well within the coal deposit - servicing all of the conduits simultaneously or separately according to gas demand or the availability of gasifiable coal. Furthermore, it maximises access to the coal deposit for a given drilling range from the common well. When forming the array (as shown for example in Figure 4 or Figure 5) within the coal panel, at least one of the delivery conduits which supplies the oxidising agent and at least one of the recovery conduits which extracts the syngas during the gasification process are drilled to intercept at the location where the gasification is initiated. Once a sufficient number of bores have been drilled in the coal seam and perforated liners have been installed, the bores are pressurised and / or pumped out to remove water from the bore. In a similar manner to the optional use of eutectic or fusible plugs, ceramic plugs (such as indicated by reference number 56 in Figure 2 and Figure 4) can be inserted in the recovery pipelines and drilled through when ready for use. Since delivery of oxygen or air to the combustion zone is a specific objective in

underground coal gasification processes, any losses of oxygen into the coal seam prior to arrival at the combustion zone is undesirable due to the cost (e.g. compression of air or oxygen production). In highly porous coal types, it is desirable therefore to provide a barrier to such losses. Depending upon the porosity of the coal seam therefore, the delivery pipelines may need to be lined with an impervious barrier to prevent the absorption of oxygen or air into the coal formation. In a first embodiment, a polymeric or cement (or combination thereof) barrier 'casing' material that is impervious (or substantially impervious) to oxygen is applied during the drilling process onto the wall of the delivery conduit whereby such material adheres to the wall sufficiently to act as a barrier against the flow of oxygen into the coal seam. For this purpose, the drill-head for drilling the delivery conduit is fitted with a nozzle which sprays the casing material onto the face of the coal which has been drilled. A pumping unit on the surface or close to the surface is used to pressurise the barrier material within the drilling stem or within a conduit contained within the drilling stem and provides sufficient flow of the barrier material to "case" (or line) the exterior of the drilled-out cavity. Upon completion of the conduit drilling activity, the casing activity is actuated by the pressure of the polymeric or cement material within the drill stem. This treatment to prevent oxygen ingress also serves to act as a cave-in barrier for friable coals which may collapse due to the nature of the coal type and which cave-in may otherwise block the flow of

oxygen/steam to the combustion zone. In an alternative embodiment, following extraction of the drilling apparatus from the delivery conduit an oxygen delivery liner pipe manufactured from a polymeric plastic (or like material) is inserted into the conduit and, by means of an internal support or mandrel, progressed to the furthest extent of the bore from the surface. This delivery liner pipe acts both as a cave-in barrier to the coal - in particular where soft or friable coals may present a blockage to the flow of oxygen to the combustion zone and to the ingress of oxygen into the coal seam. The liner pipe is manufactured from a material which melts and/or volatises at a temperature below pyrolysis temperature, ensuring that it's structural integrity meets the desired objectives of supporting the surrounding coal body and preventing the ingress of oxygen into the seam. Upon commencing UCG operations, in the vicinity of the gasification chamber, the liner pipe would therefore (intentionally) melt and/or vaporise when subjected to the heat of gasification (pyrolysis temperature), thereby continuously allowing the free passage of oxygen to the gasification zone. The flow of oxygen or air through the liner pipe during gasification operations would provide a cooling means to prevent heat transfer from the gasification chamber from affecting the structural or mechanical properties of the liner pipe within the coal seam from being degraded. In a further alternate installation method to that above, a drill-bit with a modified open-able tip may be employed which would allow the insertion of the pipeline liner into the drilled pipeline and to retract the drill at completion of the drilling activity leaving the liner pipe behind in the coal seam for the purpose of delivery of oxygen to the combustion zone. As with the embodiment described above, the liner pipe would melt at or about gasification (pyrolysis) temperature in the locality of the gasification chamber. Note that while an underground coal gasification installation comprising the previously described well and the above described underground coal gasification array (or a plurality of arrays) is preferred, it will be understood by the skilled person that such arrays in accordance with the invention may be employed with existing underground coal gasification installations (e.g. comprising one or more pairs of parallel vertical wells) mutatis mutandis. That is, to benefit from the advantages of the array the delivery pipeline and the recovery pipeline need not be located within the same casing; however, as an installation it is particularly advantageous if they are so co-located. The invention provides an underground gas transport and production system applicable to the process of coal gasification employing a novel single well approach in which air, oxygen or a mixture of these gases together with water (e.g. steam) is pumped from the surface, to supply a gasification process, via the same well casing through which gas produced by the gasification process is transported to the surface. A corresponding underground arrangement is also disclosed which complements the single well approach and its own advantages in terms of increased recovery of syngas by use of an array of delivery and recovery conduits. By providing multiple burn-fronts an averaging effect is achieved which results in a dilution effect and balancing of gas conditions in the coal seam. Various modifications may be made within the scope of the invention as herein intended, and embodiments of the invention may include combinations of features other than those expressly claimed.

Claims

Claims: 1. An underground coal gasification array comprising; a recovery conduit extending within a coal deposit and configured to recover syngas produced from the coal deposit in a gasification process; and a plurality of delivery conduits also extending within the coal deposit and associated with the recovery conduit, each of the delivery conduits configured to deliver an oxidising fluid to the coal deposit, wherein the recovery conduit and the delivery conduits extend from a single wellbore.

2. The array according to claim 1 , wherein the array comprises a plurality of recovery conduits, each of the plurality having an associated plurality of delivery conduits.

3. The array according to claim 1 or claim 2, wherein at least two of the plurality of delivery conduits are located at different distances from the corresponding recovery conduit.

4. The array according to any of claims 1 to 3, wherein at least one of the delivery conduits comprises a seal which can be selectively opened to control the expansion of a corresponding gasification chamber.

5. The array according to any of claims 1 to 4, wherein each recovery conduit and associated plurality of delivery conduits are disposed substantially in a same plane.

6. The array according to any of claims 1 to 5, comprising a plurality of recovery

conduits disposed at different vertical heights.

7. The array according to any of claims 1 to 6, comprising a plurality of recovery

conduits extending radially from a central location.

8. The array according to any of claims 1 to 7, wherein the array comprises one or more monitoring conduits configured to transport material from the coal deposit for analysis.

9. The array according to claim 8, wherein the one or more monitoring conduits are arranged around the periphery of the coal deposit.

10. The array according to any of claims 1 to 9, wherein the or each recovery conduit comprises a cooling jacket arranged to cool the syngas within the recovery conduit.

1 1. The array according to any of claims 1 to 10, wherein the or each recovery conduit comprises one or more perforations through which a cooling fluid is injected directly into the syngas.

12. The array according to any of claims 1 to 1 1 , wherein the conduits comprise one or more apertures.

13. The array according to claim 4 or any of claims 5 to 12 when dependent on claim 4, wherein the seal may be selected to open the delivery conduit dependent on temperature.

14. The array according to claim 13, wherein the seal comprises a eutectic or fusible plug.

15. The array according to claim 4, wherein the seal is configured to be drilled through to open the delivery conduit.

16. The array according to any preceding claim, wherein at least one recovery conduit comprises a seal.

17. The array according to any of claims 1 to 16, wherein the conduits comprise

perforated liners.

18. The array according to any of claims 1 to 17, wherein the conduits comprise one or more slotted guide tubes.

19. An underground coal gasification installation comprising a well and an array

according to any of claims 1 to 18; the well comprising a single wellbore, a delivery conduit in fluid communication with the plurality of delivery conduits of the array to deliver oxidising fluid from the surface; and a recovery conduit in fluid communication with the recovery conduit of the array to recover syngas from the coal deposit;

wherein the delivery conduit and the recovery conduit are disposed within the single wellbore.

20. The installation according to claim 18, wherein the well further comprises an ignition conduit disposed within the wellbore to supply fuel to initiate the gasification process in the coal deposit.

21. The installation according to claim 20, wherein the ignition conduit is deployed

alongside the delivery conduit.

22. The installation according to claim 20, wherein the ignition conduit is disposed within the delivery conduit.

23. The installation according to any of claims 19 to 22, wherein the well further

comprises a water conduit disposed within the wellbore to deliver water into the delivery conduit.

24. The installation according to any of claims 19 to 23, wherein the well further

comprises at least one cooling fluid conduit disposed within the wellbore to supply cooling fluid to cool the recovery conduit.

25. The installation according to claim 24, wherein the at least one cooling fluid conduit supplies cooling fluid to the interior of the casing.

26. The installation according to claim 24 or claim 25, wherein the well further comprises cooling means mounted on the recovery conduit to which the cooling fluid is supplied by at least one cooling fluid conduit.

27. The installation according to any of claims 24 to 26, wherein the well is configured to control a temperature of the recovered syngas by controlling cooling fluid supply through one or more cooling fluid conduits.

28. The installation according to any of claims 19 to 27, wherein the well further

comprises a monitoring conduit disposed within the wellbore and arranged to transport material from the coal deposit.

29. The installation according to claim 28, wherein the well further comprises

corresponding monitoring means configured to analyse the material.

30. The installation according to claim 29, wherein the well is configured to adjust or cease delivery of oxidising fluid to the coal deposit responsive to the analysis.

31. The installation according to any of claims 19 to 30, wherein the well comprises a wellhead, the wellhead comprising a plurality of interfaces corresponding and coupled to the plurality of pipelines disposed within the wellbore.

32. The installation according to any of claims 19 to 31 , wherein the well further

comprises a vent to provide fluid communication with the interior of the wellbore.

33. The installation according to claim 32, wherein the well further comprises

corresponding monitoring means configured to analyse fluid from the interior of the wellbore.

34. The installation according to claim 33, wherein the well is configured to adjust or cease delivery of oxidising fluid to the coal deposit responsive to the analysis.

35. The installation according to any of claims 19 to 34, comprising a plurality of arrays according to any of claims 1 to 18, each of the arrays disposed at a different vertical height.

36. A method of performing an underground coal gasification process comprising:

delivering an oxidising fluid to an underground coal deposit via a plurality of delivery conduits extending within the coal deposit;

gasifying at least a portion of the coal deposit; and

recovering syngas produced from the underground coal deposit via a recovery conduit extending within the coal deposit;

wherein the delivery of oxidising fluid and recovery of syngas is performed via a single wellbore.

37. The method of claim 36, further comprising delivering a fuel to the coal deposit and igniting the fuel.

38. The method of claim 36 or claim 37, further comprising cooling the syngas as it is recovered.

39. The method of claim 38, further comprising controlling a temperature of the syngas by controlling the cooling of the syngas.

40. The method of any of claims 36 to 39, further comprising obtaining a material sample from the coal deposit during the gasification process and analysing the sample.

41. The method of any of claims 36 to 40, further comprising obtaining a fluid sample from within the cased well and analysing the fluid sample.

42. The method of claim 40 or claim 41 , further comprising controlling or halting the gasification process and/or syngas recovery dependent on the analysis.

43. A method of providing an underground coal gasification pipeline array comprising; drilling a syngas recovery bore within a coal deposit; and

drilling a plurality of oxidising fluid delivery bores associated with the syngas recovery pipeline within the coal deposit;

wherein the recovery bore and the oxidising fluid delivery bores are drilled from a single wellbore.

44. The method according to claim 43, further comprising providing one or more seals in one or more of the recovery bore and the plurality of delivery bores.

45. The method according to claim 43 or claim 44, wherein the method is repeated at a plurality of vertical depths.

46. The method according to any of claims 43 to 45, further comprising lining at least one of the syngas recovery bore and the plurality of oxidising fluid delivery bores with perforated liners.

47. A method of generating electrical power comprising recovering syngas from a coal deposit according to the method of any of claims 36 to 42 and converting the recovered syngas to electrical power.