EP2843185A1

EP2843185A1 - Underground coal gasification method

Info

Publication number: EP2843185A1
Application number: EP12825017.2A
Authority: EP
Inventors: Yong Qin; Wenjiu CHANG; Wei JIAN
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-08-19
Filing date: 2012-09-26
Publication date: 2015-03-04
Also published as: CN102287177A; EA201400149A1; WO2013026421A1

Abstract

An underground coal gasification method. The method comprises disposing multiple injection wells (3) and gas collection wells (4) in a gasification operation zone; adding a catalyst and a propping agent into injection wells and gas collection wells by means of a fluid medium; fracturing and reforming the coal layer using a fracturing device to form large areas of fissures and cracks; forming gasification paths in the form of directional wells between the injection wells and gas collection wells; adding a gasification agent, a catalyst, and water through the injection wells to cause coal layer combustions and chemical reactions; collecting at the gas collection wells the gas produced by means of collection devices. The fissure paths between the wells formed by reforming large fractures, and the metal mineral particles used as a propping agent for the paths between wells effectively enable the maintenance of the effective communication in the injection well network for long durations; the metal mineral particles also function as a catalyst and an aggregating agent during gasification, thereby substantially enhancing the coal gasification volume.

Description

BACKGROUND

This application involves a gasification method of the underground coal, especially a gasification method of the coal layer with depth of 500 meters to thousands of meters underground.
The coal gasification underground is an energy collection manner to directly burn the underground coal with control, generate crude synthetic gas by thermal and chemical actions to the coal, and output the crude synthetic gas to the ground. This is a kind of coal exploitation technique which integrates shaft building, coal mining and coal conversion processes, especially being appropriate to unminable and uneconomical mining coal layers, and to secondary and repeated coal mining.
As to the underground coal gasification process, strong gas permeation capacity is needed for coal layers. However, since the natural gas permeation capacity is poor, it is needed to dredge gasification channel in coal layer before the underground coal gasification operation. General way thereof is to dig wells in different directions around a gasification agent injection well, then inject the high pressure gas into the gasification agent injection well to observe the amount of gas discharged from the wells around the gasification agent injection well. Then, a direction linearly connected a well with maximum amount of discharged gas and the gasification agent injection well is chosen as a direction of gasification channel. With this method, it is needed to dig at least three wells to roughly determine the gasification channel, which is of high cost. Further, the gasification channel determined with this method is of low efficiency. Also, it is often happened that the chosen gasification channel cannot be dredged through, and it is needed to redetermine a gasification channel to be dredged again.
To solve the problem on high cost and low dredging efficiency of the method of defining and dredging the gasification channel, in CN1014241181A , it is disclosed a method of defining and dredging the underground coal gasification channel, which includes: measuring horizontal coal layer crustal stress; determining coal fracture development direction according to the measured horizontal coal layer crustal stress; determining coal gasification channel direction according to coal fracture development direction. The defect of above method is that it is needed to install underground gasification channel dredging device mentioned in CN201802362U in order to improve the underground gasification dredging efficiency and to save dredging time. Also, with this method, the gasification reaction area is small and the gasification efficiency is low.
In CN101586915B , it is disclosed a gasifier of pilot scale test gasification of underground coal and its process, which includes gas supply system, gasifier, temperature-pressure-ingredient measurement system, high-temperature video system and gas purification system. The inner side of shell of the gasifier is coated with fire-proof materials. This gasifier with its process is only limited to be used with raw coal mine tunnel other than underground coal layer with depth of 500 meters and even 2000 meters.
In the underground coal gasification process, firstly, hydrogen, carbonic oxide and other products are generated in coal gasification, secondly, the synthesis gas is synthesized to methane under the action of catalyst. Alkali metal catalyst is mostly chosen, such as potassium carbonate, sodium carbonate or alkali metal composite catalyst, like potassium carbonate-sodium carbonate binary catalyst, or potassium carbonate-sodium carbonate-lithium carbonate ternary catalyst. Large usage, high cost and recycling equipment requirement cause the problems for above catalysts.

SUMMARY

In order to overcome shortages of the present technology, this invention offers a method of underground coal gasification, especially a method for the gasification of coal layer with depth of 500 meters or more. This method includes steps of:

1. determining gasification working areas according to survey results;
2. setting injection wells and gas recovery wells in gasification working areas ;
3. forming gasification channel as a directional well (which could be a horizontal well or tilting well) between injection wells and gas recovery wells;
4. injecting gasification agent, catalyst and water through the injection well to promote the coal layer to combust for chemical action;
5. recycling generated gas in gasification recovery wells by a recycling device.

The gasification working areas could be 0.5 square kilometers or above. Isolation areas with interval of 500 meters or above may be set among gasification working areas.
The distance between said injection and gasification wells may be 150 to 500 meters. After coal layer gas field starts to be mined, the original well patterns of injection and gasification wells can be used for underground coal gasification working.
With above gasification channel, before the directional drilling, it is used a fracturing device to fracturing coal layer, fluid medium added with catalyst and proppant is injected into the injection and gas recovery wells. The injection pressure needs to be greater than the fracture pressure of stratum to form a large area of fracture cracks, which, together with the gasification channel formed by directional drilling. constitute a gasification channel system.
Catalyst and proppant with small particle diameter of e.g. 1-2mm may be injected into above fracture cracks, and catalyst and proppant with big particle diameter of e.g. 10-20mm, can be injected into the gasification channel.
The above mentioned catalyst and proppant can be such kind of material as metal mineral particles or preferred iron mineral particles with low cost. This metal mineral particles are of functions of catalyst and propping gasification channel.
The above mentioned injection wells can be set up separately as gas injection wells and water injection wells, which is located between the gas injection well and gas recovery well.
The above mentioned gasification agent can be air or oxygen.
The above mentioned gas injection well, water injection well and gas recovery well can be arranged as square queue sequentially, with gas injection well on edge of the queue. In mining engineering, after burning the initial gas injection wells, water injection well and gas recovery well are gradually converted to gas injection well and water injection well, with propulsion of burning zone.
The above mentioned gas injection well, water injection well and gas recovery well can be arranged as queue of other shape, such as quincuncial piles shape, circle shape and etc.
For multi-layer coal mining area, the best way is to mine underlying coal bed first, then, in turn, continue mining with upward propulsion.
With embodiment of this invention, the relatively closed underground coal layer is treated as a whole gasification reaction container, using drilling engineering technique and new type of directional drilling, fracturing reconstruction engineering and so on as coal layer reconstruction and injection-production matching processing technology, to overcome the shortcomings of existing technology with small affected area and low displacement efficiency, and to render characteristics of mining technology of large area, high efficiency and high calorific value, so as to achieve highly efficient comprehensive development of coal resources. Specific advantages of the present invention are as follows:

1. coal gasification and conversion processes are completed underground, which will not cause the pollution of the environment, such as the dust, poisonous and harmful gas generated by traditional process on the ground.
2. It's capable to exploit deeply buried coal resources(with depth of 500 - thousands of meters), which makes effective implementation of coal resources with difficulty in mining, which renders a demonstration effect for such kind of coal resources comprehensive development in future.
3. It adopts large scale fracturing reconstruction to form the primary and secondary crack channels, and uses directional drilling to build directional injection channels, namely, combines recovery techniques of injecting fluid medium for displacement, fracturing, and orientation etc., used during the mining development, to form the largest affecting effect and displacement effect, which can maximize the conversion of coal resources to avoid waste of resources.
4. Since it adopts the manner of injecting water into the underground coal layer, making oxygen reduction reaction alternately, and using highly efficient injection-production connected well pattern, under the effect of high temperature and high pressure environment, the produced coal gas has larger yield and larger combustion value than those in the existing technologies, which has good energy saving effect on resource utilization and downstream production.
5. The fracturing reconstruction of coal layer in this invention exploits inter-well crack channel generated from the large fracturing reconstruction, uses metal mineral particles as inter-well channel proppant, which could effectively keep a long time effective connection between injection and recovery well pattern, which forms a good production base for long time and large scale mining; and metal mineral particles can play a role of catalytic polymerization in the process of gasification, which has significant effect to improve coal gas yield.
6. It takes gasification channel as gasification reaction zone to omit special gasification equipment to save the cost.
7. It benefits coal layer gasification reaction by separately setting gas injection well and water injection well to inject gasification agent and water separately;
8. It settles isolation areas among gasification working areas to effectively prevent the ground surface subsidence due to gasification operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1 is the schematic drawing of gasification working area and isolation area of this invention;
Fig.2 is the schematic drawing of one distribution of injection and gas recovery wells in gasification working area of this invention;
Fig.3 is the schematic drawing of another distribution of injection and gas recovery wells in gasification working area of this invention;
Fig.4 is the schematic drawing of another distribution of injection and gas recovery wells in gasification working area of this invention;
Fig.5 is the schematic drawing of injection device of the gas injection well of this invention;
Fig.6 is the schematic drawing of injection device of the water injection well of this invention;
Fig.7 is the schematic drawing of gasification channel between injection well and gas recovery well of this invention;
Fig.8 is the schematic drawing of recycling device of the gas recovery well of this invention;
Fig.9 is a flowchart of the recycling process on the ground of this invention.

DETAILED DESCRIPTION

Further details of specific embodiments of the invention with respect to the appended drawings.
Referring to Fig.1, isolation area(2) is set between the gasification working areas (1), injection well(3) and gas recovery well(4) in gasification. The width of the isolation area is over 500m.
Referring to Fig.2-4, injection wells(3) can be settled separately as gas injection well(5) and water injection well(6), wherein water injection well(6) is located between gas injection well(5) and gas recovery well(4). Gas injection well(5), water injection well(6) and gas recovery well(4) can be arranged as rectangle, in which gas injection well(5) located at edge, water injection well(6) and gas recovery well(4) are arranged in turn. During the mining engineering, after the initial burning of gas injection well(5), water injection well(6) and gas recovery well(4) gradually are converted to gas injection well(5) and water injection well(6) respectively with propulsion of burning zone. Gas injection well(5), water injection well(6) and gas recovery well(4) can be arranged to other shapes, such as quincuncial piles form, circle and etc.
Referring to Fig.5, the gasification agent of this invention can be air or oxygen, which can be injected into coal layer through gasification agent injection device consisted of gasification agent injection pipe(7), lubricator(blowout preventer pipe)(8), casing pipe(9), oil pipe(10), packer (11), valve(12) and one-way valve(13) of the gas injection well(5).
Referring to Fig.6, water is injected to coal burning zone and nearby by the water injection device consisted of casing pipe (14),oil pipe(15), valve(16) and one-way valve(17).
Referring to Fig.7, gasification channel is set between the injection well and gas recovery well.
Referring to Fig.8, the produced gas of this invention is recycled by the recycling device consisted of casing pipe(18), oil pipe(19), valve(20) and one-way valve(21).
Referring to Fig.9, the ground recycling process includes steps of: producing mixing fluids underground; separating gas, liquid and solid by three-phase separator; and further processing by water treatment and desulfurization and dust removal equipment.

Claims

A method of underground coal gasification, comprising:
setting injection wells and gas recovery wells in gasification working areas;

forming gasification channel in a manner of a directional well between the injection wells and the gas recovery wells;

injecting gasification agent, catalyst and water through the injection well to cause the coal layer combustion and chemical reaction; and

recycling generated gas in gasification recovery wells by a recycling device.
The method of underground coal gasification as claimed in claim 1, wherein before the directional drilling, catalyst and proppant is added into the injection wells and gas recovery wells through fluid medium, coal layer is subjected to fracturing reconstruction by a fracturing device, to form a large area of fracture cracks, which, together with the gasification channel formed by directional drilling, constitute a gasification channel system.
The method of underground coal gasification as claimed in claim 1 or 2, wherein catalyst and proppant with small particle diameter of 1-2mm is injected into the fracture cracks, and catalyst and proppant with big particle diameter of 10-20mm is injected into the gasification channel.
The method of underground coal gasification as claimed in claim 3, wherein the catalyst and proppant is metal mineral particles.
The method of underground coal gasification as claimed in claim 4, wherein the metal mineral particles are iron mineral particles.
The method of underground coal gasification as claimed in claim 1, wherein area of gasification working areas is 0.5 square kilometers or above, and isolation areas with width of 500 meters or above are set among gasification working areas.
The method of underground coal gasification as claimed in claim 1 or 6, wherein the distance between said injection well and gasification well is 150 to 500 meters.
The method of underground coal gasification as claimed in claim 1, wherein the injection wells is set up separately as gas injection wells and water injection wells, which are located between the gas injection well and gas recovery well.
The method of underground coal gasification as claimed in claim 1 or 8, wherein the gasification agent is air.
The method of underground coal gasification as claimed in claim 9, wherein the gasification agent is oxygen.
The method of underground coal gasification as claimed in claim 1, wherein the gas injection well, water injection well and gas recovery well are sequentially arranged as square shape, with gas injection well on edge, and during mining, after burning the initial gas injection wells, water injection well and gas recovery well are gradually converted to gas injection well and water injection well respectively, with propulsion of burning zone.
The method of underground coal gasification as claimed in claim 1, wherein the gas injection well, water injection well and gas recovery well are arranged as quincuncial piles shape.
The method of underground coal gasification as claimed in claim 1, wherein the gas injection well, water injection well and gas recovery well are arranged as circle shape.
The method of underground coal gasification as claimed in claim 1, wherein multi-layer coal mining starts from underlying coal bed first, then, in turn, continues with upward propulsion.