AU2015100327A4 - Oxygen injection device and method - Google Patents

Abstract

The invention provides a device and method of carrying out oxygen-enriched underground coal gasification. <0 (0e LOn

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Applicant: Linc Energy Ltd Invention Title: OXYGEN INJECTION DEVICE AND METHOD The invention is described in the following statement: 1 OXYGEN INJECTION DEVICE AND METHOD TECHNICAL FIELD [0001] This invention relates to a device and method of carrying out underground coal gasification (UCG). In particular, a device and method for oxygen-blown UCG are disclosed. BACKGROUND ART [0002] Underground coal gasification is a process by which product gas is produced from a coal seam by combusting and gasifying the coal in situ in the presence of an oxidant. The product gas is typically referred to as synthesis gas or syngas and can be used as a feedstock for various applications, including clean fuels production, chemical production and electricity generation. [0003] Wells are drilled into the coal seam to allow for oxidant injection and product gas extraction. The wells are linked or extended to form a substantially horizontal wellbore (also referred to as an in-seam well channel/linkage channel) to facilitate oxidant injection, cavity development and product gas flow. [0004] The well allowing the injection of oxidant is called an injection well. The well from which product gas emerges is called a production well. Both horizontal and vertical well regions can be used for injection and production. Underground coal gasification may also utilise one or more substantially vertical wells (e.g., a service well and an ignition well) located between the injection and production wells. [0005] A coal seam having injection and production wells with a substantially horizontal wellbore linking the two is typically referred to as an underground coal gasifier. The gasifier will have a combustion zone within which coal is combusted in the presence of an oxidant, a gasification zone located downstream of the combustion zone in which coal is gasified and partially oxidized to produce product gas, and a downstream pyrolysis zone in which pyrolysis of coal occurs. Hot product gas flows downstream from the gasification zone and exits the ground from a well 2 head of the production well. As coal is consumed or gasified, a gasifier (gasification) cavity within the coal seam develops and grows in size. [0006] The product gas (raw syngas) generated by UCG typically includes syngas as well as other components, and the constituency will depend on various factors including the type of oxidant used for UCG (air or other oxidant, such as oxygen or oxygen-enriched air), water presence (both ground water and exogenous water), coal quality, and UCG operating temperature and pressure. [0007] Major challenges of UCG include controlled combustion and gasification of the coal seam, controlling the composition of the product gas, and the need to re ignite the coal seam one or more times following initial ignition of the seam. SUMMARY OF INVENTION [0008] An object of the present invention is to provide a device and method for UCG that minimises one or more of the problems of the prior art. [0009] In one aspect, the invention provides an oxygen lance including: a) a lance body having an internal passage with a check valve inserted therein, b) a coiled tubing adapter connected to the rear end of the lance body, said adapter including a bore hole for the passage of a thermocouple cable, c) at least one spacer tube connected to the forward end of the lance body, d) an injection nozzle connected to the forward end of the spacer tube, and e) a thermocouple for monitoring the temperature of the injection nozzle. [0010] In one embodiment, one or more components of the oxygen lance include a centraliser. For example, the lance body, the coiled tubing adapter, the at least one spacer tube, and/or the injection nozzle can include a centraliser. [0011] In another aspect, the invention provides a method of underground coal gasification in a coal seam provided with an injection well, a production well and a substantially horizontal wellbore linking the injection well and the production well, including the steps of: a) inserting a metal casing into the wellbore, b) injecting air 3 into the wellbore through the injection well, c) igniting the coal seam while continuing the injection of air into the wellbore through the injection well, d) introducing oxygen into the wellbore via an oxygen injection device positioned in the wellbore to establish a gasifier cavity in the coal seam, and e) withdrawing product gas from the production well. [0012] In one embodiment, the oxygen injection device is an oxygen lance as set forth herein. [0013] In another embodiment, the method further includes the step of retracting the oxygen injection device in the direction of the injection well to establish one or more additional gasifier cavities in the coal seam. [0014] In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying figures. BRIEF DESCRIPTION OF DRAWINGS [0015] Figure 1 is a perspective view of an oxygen lance according to an embodiment of the present invention. [0016] Figure 2 is a cutaway view of the oxygen lance shown in Figure 1. [0017] Figure 3 is a cutaway view of another oxygen lance according to an embodiment of the present invention. [0018] Figure 4 is a cutaway view of a further oxygen lance according to an embodiment of the present invention. DESCRIPTION OF EMBODIMENTS [0019] The present invention relates to a device and method for oxygen-blown

UCG.

4 [0020] Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to mean the inclusion of a stated integer, group of integers, step, or steps, but not the exclusion of any other integer, group of integers, step, or steps. [0021] In one aspect, the invention provides an oxygen lance including: a) a lance body having an internal passage with a check valve inserted therein, b) a coiled tubing adapter connected to the rear (i.e., uphole) end of the lance body, said adapter including a bore hole for the passage of a thermocouple cable, c) at least one spacer tube connected to the forward (i.e., downhole) end of the lance body, d) an injection nozzle connected to the forward end of the spacer tube, and e) a thermocouple for monitoring the temperature of the injection nozzle. [0022] The lance body can be of any suitable size, shape and construction, and can be made of any suitable material or materials. The lance body can be manufactured in shapes and sizes to suit the specific application. Preferably, the lance body has a round cross-section to provide an annular passage for the flow of oxygen, although other cross-section shapes are possible, as will be understood by one of ordinary skill in the art. [0023] The lance body can be of unitary construction or can include two or more connectable body segments/pieces. Where the lance body includes multiple connectable segments/pieces, these segments/pieces can be screwed and/or welded together to form a complete body. For example, the ends of each body segment can be threaded, and the full-length lance body can include one or more threaded collars for connecting the ends of adjacent segments together. Alternatively, adjacent body segments can be welded together to form a full-length lance body. [0024] The lance body can have any suitable outer diameter and length. For example, the lance body can have an outer diameter of about two to four inches, including, for example, 2.25 inches, 2.50 inches, 2.75 inches, 2.90 inches, 3.00 inches, 3.25 inches, 3.50 inches, and 3.75 inches. Preferably, the lance body has an outer diameter of about 2.00 to 2.90 inches. As will be understood by one of ordinary 5 skill in the art, the outer diameter of the lance body will not exceed the inside diameter of a wellbore into which the oxygen lance is to be inserted. [0025] The passage of the lance body includes a non-return/check valve (e.g., ball and spring, spring loaded flapper valve, or the like) fitted within the passage. As will be understood by one of ordinary skill in the art, a check valve can prevent oxygen and/or product gas reverse flow in the oxygen lance. More than one check valve can be included. For example, dual check valves can be included in the passage. [0026] In one embodiment, one or more components of the oxygen lance include a centraliser. For example, the lance body, the coiled tubing adapter, the at least one spacer tube, and/or the injection nozzle can include a centraliser. As described herein, by "centraliser" is intended a positioner, such as fins or vanes, that extend from the one or more components of the oxygen lance, and help position the oxygen lance within a wellbore. That is, the centraliser helps centralise the oxygen lance within the wellbore. In one embodiment, the centraliser is spring-loaded. [0027] In another embodiment, the at least one spacer tube includes two or more spacer tubes, including three, four, five, or six spacer tubes. Preferably, two spacer tubes are connected to the forward end of the lance body. As will be understood by one of ordinary skill in the art, where the oxygen lance includes two or more spacer tubes, the injection nozzle will be connected to the forward end of the spacer tube farthest from the lance body. [0028] The injection nozzle connected to the forward end of the spacer tube can be straight, bent, or side-ported (including spaced side apertures). Selection of the orientation of the oxidant injection nozzle connected to the forward end of the spacer tube and the oxygen exit velocity can be used to direct underground gasifier cavity growth in either horizontal or vertical directions. That is, gasifier cavity growth in a coal seam can be tailored by adjusting the axial and/or radial distribution of the injection nozzle (including spaced side apertures), as well as the oxygen exit velocity.

6 [0029] As disclosed herein, the oxygen lance includes a thermocouple for monitoring the temperature of the injection nozzle. As will be understood by one of ordinary skill in the art, inclusion of a thermocouple allows temperature information/data to be collected from the oxygen lance. This temperature information/data can be used to control the operating parameters of the oxygen lance, including oxygen injection rate and quantity, and optional fluid (e.g., water or carbon dioxide) injection rate and quantity. More than one thermocouple can be included on the oxygen lance. [0030] One or more parts of the oxygen lance (including centralisers) can be made of material that is resistant to high temperatures and corrosion, and/or undergoes controlled expansion at elevated temperatures, such as those found in an active underground coal gasifier (e.g., in the range of 400 to 1,200 0C). [0031] Exemplary metal, metal alloys, and ceramics suitable for the oxygen lance (including centralisers) include, but are not limited to, stainless steel (and alloys thereof), chromium-nickel alloys (including those containing silicon, cobalt, tungsten, molybdenum, and microalloying elements such as nitrogen, and rare earth metals such as cesium),the Inconel @ (predominantly nickel-chromium alloys), Monel @ (predominantly nickel-copper alloys), and Hastelloy @ (predominantly nickel containing alloys) families of high-performance alloys, zirconia toughened alumina, yttrium stabilised zirconia, zirconia di-oxide, and silicon carbide. [0032] Additionally, one or more parts of the oxygen lance (including centralisers) can be coated (e.g., via plasma coating) with a protective coating, including, for example, ceramic coatings, zirconia (zirconium oxide) coatings, alumina-zirconia coatings, and carbon composite coatings. [0033] The oxygen lance is positionable and retractable within a wellbore of an underground coal gasifier. Positioning and retracting of the oxygen lance can be achieved utilising coiled tubing connected to the lance body via the coiled tubing adapter and extendible within the wellbore (via an injection well or a service well) to position the lance at a desired location within the wellbore/retract the lance within the wellbore.

7 [0034] An electrical cable of one or more thermocouples can extend within the coiled tubing and externally (via the bore hole in the coiled tubing adapter) of the lance body, spacer tube(s), and injection nozzle of the oxygen lance. [0035] In another aspect, the invention provides a method of underground coal gasification in a coal seam provided with an injection well, a production well and a substantially horizontal wellbore linking the injection well and the production well, including the steps of: a) inserting a metal casing into the wellbore, b) injecting air into the wellbore through the injection well, c) igniting the coal seam while continuing the injection of air into the wellbore through the injection well (to maintain combustion of the coal seam), d) introducing oxygen into the wellbore via an oxygen injection device positioned in the wellbore to establish a gasifier cavity in the coal seam, and e) withdrawing product gas from the production well. [0036] In a preferred embodiment, the oxygen injection device is an oxygen lance as set forth herein. [0037] Preferably, the casing in the metal-cased wellbore extends from adjacent a heel of the injection well to adjacent a heel of the production well. [0038] The metal casing (also referred to as a well liner/metal liner) can be of any suitable size, shape and construction. Preferably, the casing has a round cross section to provide an annular passage. Exemplary metals suitable for the casing include, but are not limited to, stainless steel, carbon steel, copper, or aluminium, and combinations thereof. [0039] As will be understood by one of ordinary skill in the art, selection of the metal casing material and wall thickness of the casing influences combustion zone development and advancement, as well as gasifier cavity formation, in a coal seam when practicing the disclosed UCG method. [0040] The casing can be of any suitable diameter and length. Typically, the casing will have an outer diameter of anywhere between about 5 to 10 inches, more preferably about 5 to 8 inches, and even more preferably about 5.5 to 7 inches.

8 [0041] The casing can be of unitary construction or can include a plurality of connectable units (i.e., segments). The casing or segments can be of any suitable length, including, metres, tens of metres, hundreds of metres, and kilometres. Accordingly, casing segments can be connected together to form a full-length casing being tens of metres long, hundreds of metres long, or even several kilometres in length, depending on the length of the wellbore. Each casing segment can be, for example, about 1 to 10 metres in length, including about 3, 5, 6, 7, or 9 metres in length. [0042] The casing segments can be connected together in any suitable way. For example, the ends of each segment can be threaded, and the full-length casing can include one or more threaded collars for connecting the ends of adjacent casing segments together. [0043] In one embodiment, the metal casing inserted into the wellbore includes a perforated segment. The perforations in the perforated segment can be of any suitable size, shape and arrangement as required to achieve one or more desired outcomes. For example, the perforations allow ignition of a coal seam from within the metal-cased wellbore using an ignition tool located within the wellbore at the perforated segment to ignite the surrounding coal seam. [0044] In embodiments where the casing includes a perforated segment, the perforated segment can include a sheath configured to cover some or all of the perforations in the segment. The sheath can be of any suitable length as required by the perforated segment of the casing, including, metres and tens of metres. Each sheath segment can be, for example, about 1 to 12 metres in length, including about 3, 5, 6, 7, or 9 metres in length. [0045] The sheath can be of any suitable size, shape, and construction, and can be made of any suitable material or materials, including, for example, aluminium, fibreglass, carbon fibre, plastic, and combinations thereof. The sheath can be about 1 mm to about 20 mm thick, including about 2 mm, about 5 mm, about 10 mm, or about 15 mm thick.

9 [0046] The sheath can be, for example, a membrane, sheet, or film that wraps around the outer diameter or the inner diameter of the casing at least once and covers some or all of the perforations in the perforated segment of the casing. Alternatively, the sheath can be embedded in some or all of the perforations in the perforated segment of the casing. [0047] As will be understood by one of ordinary skill in the art, the sheath will degrade upon commencement of the ignition process in a coal seam, and can act as an accelerant during ignition of the coal seam. Preferably, the sheath is made of high density polyethylene (HDPE). [0048] The casing can include a firebreak material connected to the casing or forming part of the casing (e.g., a casing segment constructed of the firebreak material). Exemplary firebreak materials include, but are not limited to, the Inconel @ (predominantly nickel-chromium alloys), Monel @ (predominantly nickel-copper alloys), and Hastelloy @ (predominantly nickel-containing alloys) families of high performance alloys. The firebreak material and/or segment can be positioned adjacent the heel of an injection well. [0049] The casing can include associated instrumentation such as one or more sensors for sensing and reporting conditions in the wellbore. Any suitable type of sensor can be used. For example, the sensor can be a thermocouple for sensing the temperature. [0050] In one embodiment the casing includes a string of thermocouples connected to the casing so that temperature information/data can be collected from the casing at multiple points (particularly during operation of the gasifier). This temperature information/data can indicate the performance of the underground gasification process and can be used to control the operating parameters of the gasifier. [0051] The step of injecting air into the wellbore through the injection well can be achieved in any suitable manner. For example, a source of air (e.g., an air 10 compressor) can be connected directly or indirectly to a well head of the injection well, such that the air is injected/introduced into the wellbore via the injection well. [0052] The step of igniting the coal seam preferably includes using an ignition tool, whereby an ignition tool that includes ignition means is inserted into the coal seam via the injection well, a service well, and/or the production well. Once inserted into the coal seam, the ignition tool is used to ignite the coal seam and establish a combustion zone. [0053] In one embodiment, the ignition tool is positioned in the wellbore at a perforated segment of the metal casing. [0054] Inserting, positioning, and retracting the ignition tool within the coal seam can be achieved utilising coiled tubing. The coiled tubing can be of any suitable size, shape and construction and can be made of any suitable material or materials. More particularly, the coiled tubing can be of any suitable length and diameter. Preferably, the coiled tubing is made of metal, such as stainless steel, carbon steel, or copper. The coiled tubing can be of unitary construction or can include two or more connectable tube pieces. A preferred outer diameter for the coiled tubing is 1.75 to 3.5 inches. [0055] The ignition tool can ignite the coal seam in any suitable way. In one embodiment, the ignition tool includes ignition means such as an ignition fuel (e.g., hydrocarbon gases, such as methane, propane, butane, and mixtures thereof), an electrical spark generator (e.g., a spark plug), an electrical heat resistor (e.g., a glow plug), an ignition chemical, such as thermite (i.e., a pyrotechnic composition of a metal powder fuel and a metal oxide), a pyrophoric substance (e.g., a liquid, such as triethylboron (TEB), a gas, such as silane, a solid, such as phosphorus or an alkali metal), a pyrophoric substance and a hydrocarbon mixture, such as TEB vaporised in methane, or a pyrophoric substance and an inert gas, such as TEB and nitrogen, and combinations thereof. [0056] Once the coal seam has been ignited (or re-ignited), the ignition tool is retracted a safe distance while continuing the injection of air into the wellbore to 11 fuel/maintain combustion of the coal seam. Alternatively, the ignition tool can be withdrawn from the coal seam following successful ignition of the seam. [0057] As will be understood by one of ordinary skill in the art, establishment of a combustion zone (and, subsequently, a gasifier cavity) in a coal seam and the production of UCG product gas can be assessed in a number of ways, including monitoring the quality and/or composition of the product gas (e.g., the calorific value and/or the H 2 to CO ratio) emerging from the production well. [0058] The oxygen injection device used to introduce oxygen into the wellbore/coal seam can be inserted via the injection well or a service well. The oxygen injection device is positionable and retractable. As with the ignition tool, positioning of the oxygen injection device can be achieved utilising coiled tubing connected to the oxygen injection device and extendible within the wellbore to position the oxygen injection device at a desired location within the wellbore. [0059] The coiled tubing as described herein can include a single tube (line) connectable to a downhole tool (e.g., an ignition tool or an oxygen injection device). The coiled tubing can alternatively include at least one inner tube (inner line) extending within an outer tube (outer line), wherein one of the tubes is connected to one downhole tool while the other tube is connected to another downhole tube. That is, the coiled tubing can include at least one inner tube and an outer tube that extend concentrically relative to one another. More than one inner tube may extend within the same outer tube. A preferred diameter for the outer tube is 2.0 inches, whereas a preferred diameter for the inner tube is 0.75 inches. [0060] The step of introducing oxygen into the wellbore via the oxygen injection device positioned in the wellbore can be achieved by providing substantially pure oxygen (e.g., from an air separation unit or a tank/cylinder of liquid oxygen) to the injection device for delivery to the wellbore/coal seam. [0061] As will be understood by one of ordinary skill in the art, oxygen can be injected at any suitable injection rate and quantity. The injection rate/quantity can be chosen with respect to various design criteria, including ensuring that the quality 12 and/or composition of the product gas (e.g., the calorific value and/or the H 2 to CO ratio) emerging from the production well are as desired and/or the rate of combustion zone advancement/gasifier cavity formation is appropriate. One of ordinary skill in the art will be able to formulate the rate and quantity of oxygen injection necessary to achieve desired outcomes. [0062] The oxygen injection device can include a controller operable to control the release/injection of oxygen. The controller can be operated remotely from the oxygen injection device. Oxygen injection rate and quantity can be adjusted using flow controlling devices. The controller can include pressure safety devices, filtration devices, and flow metering devices, in addition to isolation valves. Control logic can allow the oxygen to flow as per the required settings. [0063] Injection of oxygen into the wellbore/coal seam via the oxygen injection device is carried out to achieve downhole oxygen enrichment in the range of about 30 mol% to about 80 mol%, including about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, and about 75 mol%. [0064] As discussed herein, the oxygen injection device is positionable and retractable. When used, in order to continue the UCG process through a coal seam, it will be necessary to reposition the oxygen injection device periodically to progress the combustion zone along the coal seam and provide optimum resource recovery of the underground coal resource. Thus, to support particularly the advancement of the combustion zone and gasifier cavity formation, the coiled tubing and oxygen injection device can be drawn along the cased wellbore that extends through the coal seam. A preferred method is utilising the controlled retracting injection point (CRIP) concept, as will be understood by one of ordinary skill in the art. [0065] Therefore, in one embodiment, the disclosed UCG method further includes the step of retracting the oxygen injection device in the direction of the injection well to establish one or more additional gasifier cavities in the coal seam.

13 [0066] According to an important aspect of the present invention, retracting the oxygen injection device positioned in the wellbore (continuously or intermittently) in the direction of the injection well causes the active UCG cavity to burn towards the oxygen injection device. Accordingly, re-ignition of the coal seam is not generally necessary to continue the UCG process. [0067] One of the advantages of the UCG method disclosed herein is lowered nitrogen content in the product gas. Accordingly, in one embodiment, the product gas withdrawn from the production well includes less than about 70% volume/volume nitrogen, including less than about 60% volume/volume nitrogen, less than about 50% volume/volume nitrogen, less than about 40% volume/volume nitrogen, less than about 30% volume/volume nitrogen, less than about 20% volume/volume nitrogen, less than about 10% volume/volume nitrogen, less than about 5% volume/volume nitrogen, and less than about 1% volume/volume nitrogen. [0068] In addition to injecting air into the wellbore through an injection well and introducing oxygen into the wellbore/coal seam via an oxygen injection device (e.g., an oxygen lance), the disclosed method optionally further includes the step of injecting carbon dioxide, water, and/or steam into the wellbore and/or the production well. The carbon dioxide, water, and/or steam can be injected into the wellbore via the injection well and/or a service well, using conventional equipment for the handling of fluids, as will be understood by one of ordinary skill in the art. [0069] The carbon dioxide can be recycled from a downstream processing facility that separates carbon dioxide from product gas. The water can be obtained from a naturally occurring water source such as surface water or ground water. The water can be either fresh water or brine. The water can be treated water, such as demineralised water or raw water separated from product gas. [0070] In one embodiment, the injected carbon dioxide, water, and/or steam acts as a quenching fluid to reduce the temperature of the product gas to less than about 200-600 0C, including less than about 550 C, less than about 500 C, less than about 450 C, less than about 400 C, less than about 350 C, less than about 300 C, and less than about 250 C.

14 [0071] As will be understood by one of ordinary skill in the art, localised downhole cooling/quenching can be used to influence combustion zone advancement and gasifier cavity formation. [0072] Reducing the temperature of the product gas via quenching fluid may require that the temperature of the product gas in-seam and/or within a well (e.g., the production well) be monitored, and the injection rate and quantity of quenching fluid be regulated according to the temperature reading. To that end, at least one thermocouple (located in-seam or within the production well) can provide temperature information for regulating the flow of the quenching fluid. [0073] In one embodiment, the injection of carbon dioxide, water, and/or steam can be used to adjust the composition of the product gas. For example, adjusting the ratio of injected carbon dioxide to air/oxygen can be used to maintain hydrogen to carbon monoxide ratio in the product gas of between about 1.5 and 4.0, including between about 1.6 and 3.0 and between about 1.8 and 2.5. [0074] As will be understood by one of ordinary skill in the art, adjusting the composition of the product gas via injection of carbon dioxide, water, and/or steam may require that the composition of the product gas be monitored, and the injection of one or more of carbon dioxide, water, and/or steam be regulated according to the product gas composition. To that end, a gas analyser coupled with a microprocessor can be employed to monitor the composition of the product gas and/or control the injection of one or more of carbon dioxide, water, and/or steam. [0075] In the figures, like reference numerals refer to like features. [0076] An embodiment of an oxygen lance 50 according to the present invention is shown in Figure 1. The oxygen lance 50 has a 2.0" outside diameter lance body 51 having an internal passage with a check valve inserted therein (which are not shown), a coiled tubing adapter 53 connected to the rear end of the lance body 51 and including a bore hole 54 for the passage of a thermocouple cable 55, a pair of 2.0" outside diameter spacer tubes 56 connected to the forward end of the lance body 51, a 2.0" outside diameter injection nozzle 57 connected to the forward end of 15 the spacer tube 56 farthest from the lance body 51, a thermocouple for monitoring the temperature of the injection nozzle (which is not shown), and a plurality of adapters 58 for joining the lance body 51, spacer tubes 56, and injection nozzle 57. The spacer tubes 56 include centralisers 59. [0077] A cutaway view of the oxygen lance 50 is shown in Figure 2, and illustrates the passage 63 in the lance body 51, with dual check valves 64 in the passage 63. As also illustrated, the passage 63 extends through the spacer tubes 56 and injection nozzle 57. [0078] Another embodiment of an oxygen lance 70 according to the present invention is shown in Figure 3. The oxygen lance 70 has a 2.0" outside diameter lance body 51 having an internal passage 63 with dual check valves 64 in the passage 63, a coiled tubing adapter 53 connected to the rear end of the lance body 51 and including a bore hole 54 for the passage of a thermocouple cable (which is not shown), a pair of 2.0" outside diameter spacer tubes 56 connected to the forward end of the lance body 51, a 2.0" outside diameter injection nozzle 57 connected to the forward end of the spacer tube 56 farthest from the lance body 51, and a thermocouple for monitoring the temperature of the injection nozzle (which is not shown). The coiled tubing adapter 53 and injection nozzle 57 include centralisers 59. As also illustrated, the passage 63 extends through the spacer tubes 56 and injection nozzle 57. [0079] A further embodiment of an oxygen lance 90 according to the present invention is shown in Figure 4. The oxygen lance 90 has a 2.9" outside diameter lance body 51 having an internal passage 63 with single check valve 64 in the passage 63, a coiled tubing adapter 53 connected to the rear end of the lance body 51 and including a bore hole 54 for the passage of a thermocouple cable (which is not shown), a 2.9" outside diameter spacer tube 56 connected to the forward end of the lance body 51, a 2.9" outside diameter injection nozzle 57 connected to the forward end of the spacer tube 56, and a thermocouple for monitoring the temperature of the injection nozzle (which is not shown). The bore hole 54 includes a compression fitting 65. Also shown is a plug 66, which prevents entry of 16 contaminants into the nozzle 57 upon initial downhole insertion of the oxygen lance 90. As also illustrated, the passage 63 extends through the spacer tube 56 and injection nozzle 57. [0080] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more combinations. [0081] Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. It will therefore be appreciated by those of skill in the art that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention.

Claims (15)

1. An oxygen lance comprising, a. a lance body having an internal passage with a check valve inserted therein; b. a coiled tubing adapter connected to the rear end of the lance body, said adapter including a bore hole for the passage of a thermocouple cable; c. at least one spacer tube connected to the forward end of the lance body; d. an injection nozzle connected to the forward end of the spacer tube; and e. a thermocouple for monitoring the temperature of the injection nozzle.

2. The oxygen lance of claim 1, wherein the passage comprises dual check valves.

3. The oxygen lance of claim 1 or claim 2, wherein the coiled tubing adapter comprises a centraliser.

4. The oxygen lance of any one of claims 1 to 3, wherein the at least one spacer tube comprises two spacer tubes and wherein the injection nozzle is connected to the forward end of the spacer tube farthest from the lance body.

5. The oxygen lance of any one of claims 1 to 4, wherein the at least one spacer tube comprises a centraliser.

6. The oxygen lance of any one of claims 1 to 5, wherein the injection nozzle comprises a centraliser.

7. A method of underground coal gasification (UCG) in a coal seam provided with an injection well, a production well and a substantially horizontal wellbore linking the injection well and the production well, including the steps of: a. inserting a metal casing into the wellbore; b. injecting air into the wellbore through the injection well; 18 c. igniting the coal seam while continuing the injection of air into the wellbore through the injection well; d. introducing oxygen into the wellbore via an oxygen injection device positioned in the wellbore to establish a gasifier cavity in the coal seam; and e. withdrawing product gas from the production well.

8. The method of claim 7, wherein the metal casing inserted into the wellbore comprises a perforated segment.

9. The method of claim 8, wherein the metal casing inserted into the wellbore comprises a sheath associated with the perforated segment.

10. The method of claim 8 or claim 9, wherein igniting the coal seam comprises positioning an ignition tool in the wellbore at the perforated segment of metal casing, providing an ignition fuel to the ignition tool, and igniting the coal seam using the ignition tool, wherein the ignition tool comprises ignition means.

11. The method of any one of claims 7 to 10, wherein one or more thermocouples are attached to the metal casing for collection of temperature data from the casing during underground coal gasification.

12. The method of any one of claims 7 to 11, wherein downhole oxygen enrichment is in the range of about 30 mol% to about 50 mol%.

13. The method of any one of claims 7 to 12, wherein the oxygen injection device is an oxygen lance as set forth in any one of claims 1 to 6.

14. The method of any one of claims 7 to 13, further including the step of retracting the oxygen injection device in the direction of the injection well to establish one or more additional gasifier cavities in the coal seam. 19

15. The method of any one of claims 7 to 14, further including the step of injecting carbon dioxide, water, and/or steam into the wellbore via the injection well and/or a service well.