HK1202912B - A method for shortening an injection pipe underground coal gasification - Google Patents

Description

Method for shortening injection pipe for underground coal gasification

B.E. davis

Orlistat.

Priority requirement

This application is a national phase application of and claims priority from PCT patent application No. US13/47173 filed 2013 on 21/6, in turn claims priority from US patent application serial No. 13/536,100 filed 2012 on 28/2012 in paris convention, the entire contents of both of which are incorporated herein by reference.

Technical Field

The present disclosure relates generally to underground coal gasification ("UCG"), and in particular to a method for automatically shortening an injection pipe.

Background

It is well known that: underground coal can be gasified and a coal gasification process (UCG process) produces syngas. The process involves the operation of a gasification reactor cavity (reactor) between parallel horizontal boreholes within a coal seam that is fed oxidant gas, exemplified by air, oxygen, steam or a combination of these gases, through one borehole (injection well). After ignition of the coal seam, the gasification reaction between the coal and the injected oxidant gas forms syngas (CO, CO)₂、H₂、CH₄And other gases) and the syngas is removed via a second borehole (product well).

In a coal gasification process, there are a number of reactions that occur that produce syngas. Those reactions include:

C+H₂0=H₂+ CO (multiphase water-gas conversion reaction)

CO+H₂0=H₂+CO₂(transformation)

CO+3H₂=CH₄+H₂0 (methanation)

C+2H₂=CH₄(hydro-gasification)

C+1/2O₂= CO (partial oxidation)

C+O₂=CO₂(Oxidation)

C+CO₂=2CO (Boudouard reaction).

In a typical UCG process, the cavity grows in size as the coal is removed by the gasification process, and the coal face gradually moves between two boreholes as the coal is removed by the hot gases flowing across the face. When the injection gas is fed into the reactor via the liner inside the injection well, the discharge point of the gas is fixed at the end of the injection well liner. As the reactor grows, the hot gasification reaction zone moves away from the point of oxidant gas injection, which reduces the efficiency of the gasification process, resulting in a reduction in product quality. There is a known injection point shortening process known as the Continuous Retraction Injection Point (CRIP).

The currently used method to maintain gas quality is to move the injection point of the oxidant gas to match the movement of the coal gasification face so that the injected gas is always close to fresh coal, so that product quality is maintained. The movement of the end of the injection well liner is typically achieved by: the liner is shortened by cutting off a length of the liner to reposition the delivery point for the oxidant gas, or the liner is retracted up the injection well, which moves the injection point. Cutting the injection well liner or retracting it from the injection well achieves the relocation of the injection point, but requires significant logistics and special equipment to operate from the surface to achieve these objectives. It would be desirable to be able to move the injection point of the oxidant gas with the movement of the gasification face without the use of devices inserted into the injection well and operated from the surface, such as cutters or liner retraction equipment.

It is therefore desirable to provide a method to automatically shorten a liner for underground coal gasification, and it is to this end that the present disclosure is directed. This sacrificial liner link process for foreshortening may be applicable to all UCG actions that require the injection point to be repositioned in a horizontal injection well within the coal seam.

Drawings

FIG. 1 illustrates an example underground coal gasification facility in which the injection well liner may be shortened;

FIG. 2 shows a close-up view of a reactor and injection well with a sacrificial liner for automatically shortening the liner;

FIG. 3 shows details of an underground coal gasification process in which oxidizing gas is injected down the annulus of the injection well;

FIG. 4 illustrates details of an underground coal gasification process in which a sacrificial liner coupling portion of the liner is impacted by a fire of the UCG process; and is

FIG. 5 shows the detail of the underground coal gasification process when the sacrificial liner tie is partially eliminated to automatically shorten the liner.

Detailed Description

The present disclosure is particularly applicable to underground coal gasification processes (UCGs) where injection well liners are automatically shortened for underground coal gasification, and it is in this context that the present disclosure will be described.

Fig. 1 shows an example underground coal gasification facility 10 in which the injection well liner can be shortened. Apparatus 10 may include an injection well 12, a production well 14, and an initiation well 16. During the UCG process, injection well 12 is used to inject an oxidizing gas (such as air, oxygen, steam, or a combination of these gases, as indicated by the light blue arrows) into reactor region 18 (also referred to as a gasification cavity), which is a cavity initially formed in the coal by drilling and subsequently expanded by gasification of the coal. The cavity is formed between the injection point and the roof of the coal seam and grows laterally to the limits of the gasification process. During the UCG process, production wells 14 are used to extract the syngas formed during the UCG process, as indicated by the green arrows, while initiation wells 16 are used to initiate the gasification process in the coal seam, as indicated by the red arrows in fig. 1. Each of the wells has: sleeve 20 (20)₁Is a casing for an injection well, 20₂Is a casing of a production well, and 20₃Is the casing of the initiating well, but is not shown in fig. 1); and a liner 22 (22)₁Is a lining of an injection well, 22₂Is a lining of a production well and 22₃Is lining the originating well, but not shown in fig. 1) at each casingInside the tube. Typical diameters for the casing are 250mm, while those for the liner are 100-130 mm. In the following disclosure, we focus on injection well liners 22₁. During the UCG process, coal is gasified and the gasification cavity moves away from the injection point, which is at the end of the injection well liner and injection well. In the example in fig. 1, the direction 24 of the gasification process is from right to left, as indicated by the arrow. A key aspect of the UCG process is to move the injection point of the oxidant gas to match the movement of the coal gasification face without having to cut or retract the injection well liner, as will now be described in more detail.

Figure 2 shows a close-up view of a sacrificial liner coupler and reactor for automatically shortening the liner. Injection well 12 has points 30 where oxidizing gas is injected into injection liner 22₁In the gasification chamber 18 at the end of (a). As shown in fig. 2, the injection well has a liner 22₁And an annulus 26 between the edge of the borehole and the liner. Injection liner 22₁May have one or more liner portions (such as 22a, 22b, 22c, 22d in the example of fig. 2) and one or more sacrificial liner links 32 (such as the liner portions 32 in the example shown in fig. 2) between the liner portions₁、32₂And 33₃). The liner 22 typically has sacrificial liner ties at periodic intervals of 6-8 meters. Injection liner 22₁May be made of steel (or similar material) to withstand the rigors of the UCG process. The steel may not melt/decompose at temperatures below 600 ℃. Each sacrificial liner portion 32 (which may also be referred to as a tie) may be made of a material that melts/burns/decomposes at a temperature below the melting/decomposition temperature of the steel liner. For example, each sacrificial liner portion 32 may be made of fiberglass or a resin material. A typical resin is a high temperature epoxy tool resin. The sacrificial liner coupler and the liner portion are joined together by a threaded joint. In one embodiment shown in fig. 2, the liner and liner portions have a circular shape (like a pipe), while each sacrificial liner portion 32 has a square or rectangular shape. However, each sacrificial liner portion 32 may also have itIts shape, including a circular shape, is similar to other liner portions. In the configuration shown in fig. 2, the temperature along the length of the injection well liner is less than 200 degrees celsius, and both the liner portion and the sacrificial liner portion allow the flow of oxidizing gas to a gasification cavity within the liner.

FIG. 3 shows details of an underground coal gasification process in which oxidizing gas is injected down the annulus of the injection borehole. During the UCG process, the oxidizing gas 40 is fed down the annulus 26 to the gasification chamber 18 (not the interior of the liner). The direction of the oxidizing gas through the annulus of the injection well causes the hot zone of the reactor to move up the injection well to a point where it impacts a sacrificial liner connector segment of the injection well liner, which becomes unstable and which shortens the injection well liner to the liner failure location. In this process, the operator can send oxidizing gas down the annulus of the injection well to pull the hot zone up the liner and shorten the liner, and then send oxidizing gas into the interior of the liner during normal underground coal gasification. The gasification chamber 18 has a temperature of about 800-. The portion of the liner 34 (as shown in figure 3) into which the hot zone has been flushed may be at a temperature of about 600 degrees celsius while the remainder of the injector well liner into which the hot zone has not been introduced is still less than 200 degrees celsius.

When the oxidant gas stream is returned into the injection well liner, the gas enters the reactor at a new injection point where it can access fresh coal and maintain high quality product gas.

Fig. 4 shows details of an underground coal gasification process in which a sacrificial liner portion of the liner is impacted by a hot zone of the UCG process. As shown in fig. 4, the portion of the sacrificial liner that has been encased by the hot zone of the gasification cavity deforms, burns or melts (possibly into the gasification cavity), which causes the length of the injection well liner to automatically shorten at the appropriate time (as shown in fig. 5) so that the injection point of the oxidant gas (at the end of the liner) automatically moves with the coal face. For example, in one embodiment, the sacrificial liner portion may melt/decompose at a temperature of approximately 350 degrees celsius.

While the foregoing is described with reference to specific embodiments of the invention, it will be appreciated by those skilled in the art that: changes may be made in this embodiment without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims.

Claims (7)

1. A method for shortening an injection well liner during an underground coal gasification process, the method comprising:

providing an apparatus for performing underground coal gasification in a gasification cavity, the apparatus having an injection well with casing and an injection well liner with an annulus in between through which oxidizing gas is injected, the injection well liner having one or more liner portions and one or more link portions between the one or more liner portions, and each of the one or more link portions having one of a different mechanical property and a different physical property than each of the one or more liner portions such that the one or more link portions decompose before the one or more liner portions during the underground coal gasification process;

injecting said oxidizing gas through a proximal end of said injection well;

outputting the oxidizing gas into a gasification chamber only through a distal end of the injection well;

relocating an injection point of the oxidizing gas into the gasification cavity because one of the different mechanical properties and the different physical properties of at least one of the one or more link portions is exceeded by the characteristics of the underground coal gasification process to shorten the injection well liner by breaking down the at least one of the one or more link portions of the injection well liner; and

outputting the oxidizing gas into a gasification cavity only at a new distal end of the injection well, the new distal end being generated when the at least one link portion disintegrates as a result of being during the underground coal gasification process and when the at least one link portion and a liner portion connected to the at least one link portion are disengaged from the distal end of the injection well.

2. The method of claim 1, wherein repositioning the injection point further comprises: feeding oxidizing gas down an annulus of the injection well, drawing a hot region of the gasification cavity up into the injection well liner, and melting at least one of the one or more link portions of the injection well liner to shorten the injection well liner.

3. The method of claim 2, wherein melting at least one of the one or more link portions of the injection well liner further comprises: encasing at least one of the one or more link portions of the injection well liner in the thermal zone that melts the at least one of the one or more link portions of the injection well liner.

4. The method of claim 1, further comprising: the underground coal gasification process is continued using a shortened injection well liner.

5. The method of claim 4, wherein continuing the coal gasification process further comprises: sending an oxidizing gas to the gasification cavity inside the injection well liner.

6. The method of claim 1, wherein repositioning the injection point further comprises: the repositioning of the injection point is controlled by feeding oxidizing gas down the annulus of the injection well.

7. The method of claim 1, wherein the characteristic of the underground coal gasification process is temperature, and decomposing at least one of the one or more link portions further comprises exceeding a melting temperature of the at least one of the one or more link portions.