CN101122222A - Down-hole horizontal hole exploitation system for mixing gas displacing coal gas, and the method - Google Patents
Down-hole horizontal hole exploitation system for mixing gas displacing coal gas, and the method Download PDFInfo
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Abstract
The invention discloses a system and a method for exploitation of mixed-gas coal-bed methane exploitation in a horizontal hole in an oil well, and relates to a coal-bed methane exploitation technology. The exploitation method comprises the following procedures: 1. various gases are integrated into a mixed gas; the mixed gas comprises a or a plurality of strongly exchanged gases, which comprises H2S, SO2 and CO2; the mixed gas also comprises a or a plurality of weakly exchanged gases, which comprises N2, H2 and He; 2. the mixed gas is injected into a coal bed (3) through an injection hole (1) with high pressure; 3. gas comprising the coal-bed methane is obtained from an drainage hole (2) with a drainage device, until the methane content is lower than the economic exploitation content and safety content. The invention promotes the exploitation rate and unit output of the coal-bed methane, and produces quite an obvious effect in reducing the greenhouse gas emission. Meanwhile, the invention is provided with the effect of reducing the outstanding risks of gas, and is applicable in the low-penetration exploitable coal-bed methane exploitation field.
Description
Technical Field
The invention relates to a coal bed gas exploitation technology, in particular to a system and a method for exploiting coal bed gas by displacing mixed gas in an underground horizontal hole.
Background
The coal bed gas belongs to unconventional natural gas, commonly called gas, consisting of CH 4 、CO 2 、O 2 、N 2 、CO、H 2 S、NO x Mixed gas composed of equal gases, the main component being CH 4 (methane), accounting for 80-90%. It is a natural gas that is produced during the coal formation process and then remains in the coal seam and surrounding rock strata in a sorbed and dissociated state.
In 2005, coal mine gas extracted underground in China is about 23 hundred million meters 3 Utilization amount is about 10 hundred million m 3 Gas release of about 150 hundred million m 3 . The direct consequence of a low pre-draw rate is: environmental pollution (about 150 hundred million m in coal mining, processing and transporting process 3 The coal bed gas is discharged to the atmosphere, which is equivalent to 2.3 hundred million of carbon monoxide (TCO) discharge 2e ) The resources are wasted, gas disasters are frequent, and the coal mining efficiency is low.
Most coal seams in China have high gas content, and the average gas content is 10m 3 The mining area above/t accounts for 41 percent; however, the permeability of the coal seam is low, generally 0.002-16.17 mD (millidarcy). Wherein, the permeability is less than 72 percent of 1.0mD, which is very unfavorable for the exploitation and utilization of coal bed gas. The common permeability of the coal seam in China is low, and the desorption speed is low, so that most coal seam test wells are low in yield, fast in attenuation and difficult to form stable industrial airflow.
The existing technology adopts a mature coal bed gas exploitation mode which comprises a ground vertical well, a ground exploitation region well, a underground horizontal hole (namely underground coal mine gas drainage) and a waste mine. The modes adopt pure extraction. In order to improve the single yield of the coal bed gas, a directional feather-shaped branch horizontal hole technology, a hydraulic fracturing permeation increasing technology, a liberation layer permeation increasing technology and the like are adopted, and a certain effect is achieved. Currently, the underground coal bed gas mining or the horizontal well extraction is mainly carried out, and the coal bed gas is extracted by adopting negative pressure; the recovery ratio of the coal bed gas is low, meanwhile, the depth of the horizontal hole is limited, the influence range of extraction is limited, a coal bed gas extraction blank zone is easily formed in the middle of an extraction area, and a large amount of coal bed gas resources are wasted.
The existing methods for displacement mining of coal bed gas are various, for example: water displacement, CO 2 Displacement, N 2 And (3) displacing coal bed gas. The effect of water flooding on coalbed methane remains uncertain; CO 2 2 Has good effect of displacing coal bed gas, but can leadGet upThe coal matrix expands, so that the permeability of the coal bed is reduced, the injectivity of the coal bed is influenced, the injection is difficult, and the coal matrix is not suitable for the low-permeability coal bed in China; n is a radical of 2 The effect of displacing the coal bed gas is better, but the displacement effect is limited; with CO 2 And N 2 The separation cost is high, and the economical efficiency of coal bed gas displacement exploitation is influenced.
Generally, the effect of underground coal bed gas exploitation needs to be improved. The development of a novel coal bed gas yield increasing technical mode has multiple meanings in the aspects of economy, safety, environmental protection and the like for coal enterprises in China, and an economic coal bed gas mining method with high recovery rate must be found.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings of the prior art, expand the application range of the prior art and provide a system and a method for mining underground horizontal hole mixed gas displacement coal bed gas.
The method is beneficial to improving the recovery rate, the recovery speed and the recovery range of the coal bed gas, and simultaneously, waste and greenhouse gas are stored in the unexploited coal bed.
The purpose of the invention is realized by the following steps:
1. underground horizontal hole mixed gas displacement coalbed methane mining system (this mining system for short)
As shown in fig. 1, the mining system comprises a coal seam (3), a roadway (4) consisting of a machine roadway and an air roadway and a pumping hole (2);
a roadway (4) is arranged around the plane of the coal seam (3), and a plurality of pumping and discharging holes (6) communicated with the roadway (4) are arranged in the coal seam (5);
an injection hole (1) is arranged in the coal seam (5);
the injection holes (1) and the pumping holes (2) are alternately arranged.
A conventional roadway pumping and drainage system is formed by a coal seam (3), a roadway (4) and pumping and drainage holes (2) in an underground coal bed gas mining area; the injection hole (1) is arranged, so that the underground horizontal hole mixed gas displacement coal bed methane exploitation system is formed.
2. Mining method (this mining method for short) for displacing coal bed gas by mixed gas in underground horizontal hole
The mining method takes the system as an operation platform and comprises the following steps:
(1) forming a mixed gas from the gases; the mixed gas comprises one or more of strong displacement gas including H 2 S、SO 2 、CO 2 (ii) a The mixed gas also comprises one or more of weak displacement gases, and the weak displacement gas comprises N 2 、H 2 、H e ；
(2) Injecting mixed gas into the coal bed (3) through the injection hole (1) by using high-pressure injection equipment;
(3) and simultaneously, gas containing coal bed gas is obtained in the pumping hole (2) by utilizing pumping equipment until the obtained methane concentration is lower than the economic exploitation concentration and the safe concentration.
The working principle of the invention is as follows:
aiming at low permeability coal seams in China, the invention provides a technology for displacing coal bed gas by mixed gas, namely, relative methane is used as strong displacement gas (such as H) to be injected into the coal seams through drill holes 2 S、SO 2 、CO 2 ) Or a weak replacement gas (N) 2 、H 2 ) The main mixed gas is used for replacing coal bed gas and driving the coal bed gas to flow to a production well. Relative to other displacement methods, the present invention mainly makes use of the following two aspects: the mixed gas displacement technology and the injection hole and the pumping hole are formed in the roadway, and the mixed gas displacement technology has the following effects:
one is displacement, strong displacement component and CH in the injected mixed gas 4 Competitive adsorption, replacement of CH 4 Molecules, promote desorption of coal bed gas and reduce CH 4 Partial pressure of (2), yet further promoting CH 4 Desorbing;
secondly, driving, the injection of the mixed gas is maintained to be higher than that of pure air extractionThe pressure gradient plays a role in increasing the flow velocity of the fluid, promotes the convection and dispersion of the coal bed gas, drives and carries CH 4 Flowing to a production well;
and thirdly, the variable permeability is realized, the mixed gas is injected to maintain higher pore pressure, the porosity and pore connectivity are increased, and the improvement of the coal bed permeability is facilitated. The different mixed gases may cause the coal seam to expand or contract (relative to when methane is adsorbed), which may reduce or increase the permeability of the coal seam and improve the injectibility of the coal seam.
In addition, an injection hole (1) is formed in the pumping and discharging roadway (4), and a horizontal pumping and discharging hole (6) is formed in the machine roadway (2) and the air roadway (3); the injection hole (1) and the pumping hole (6) are used for carrying out coal bed gas displacement mining, the coal bed gas displacement mining can be synchronous with a coal mining process, the influence on coal mining production of a coal mine is small, and the concentration of coal bed gas (coal bed gas) is reduced, so that the safety environment of the whole coal bed mining is improved; meanwhile, the coal bed gas is collected, and the emission of greenhouse gas is reduced.
The invention has the following advantages and positive effects:
1. the competitive adsorption capacity of strong replacement gas is exerted. Coal strongly displacing gas SO 2 、H 2 S、CO 2 Adsorption capacity ratio of (A) to (B) of 4 Strong, strong displacing gas injection can promote CH 4 Desorption of (3). Of course, the injected SO 2 、H 2 S、CO 2 Reduction of CH 4 Partial pressure in the coal seam also has certain promotion of CH 4 The effect of desorption.
2. The permeation enhancing function of weakly adsorbed gas is exerted. After the weakly adsorbed gas displaces the methane, the coal bed shrinks, and the permeability is increased. For example: weakly adsorbing gases (e.g. N) 2 、H e ) The permeability coefficient of the coal bed is increased by 1 order of magnitude. The method has important significance for the coal bed gas development of the low-permeability coal bed.
3. The mixed gas can be directly industrial waste gas, air, waste gas or the mixed gas of the industrial waste gas, the air and the waste gas added into the gas with the regulated components, the requirement on purification concentration is low or purification is not carried out, the gas source cost is greatly reduced, and the total cost of the mixed gas for displacing the coal bed gas is reduced; meanwhile, the waste gas is sealed in the coal bed which can not be exploited, and the atmospheric pollution is reduced.
4. The existing tunnel in the coal seam is exploited, so that the displacement exploitation construction cost is reduced, the mixed gas displacement coal bed gas is carried out by forming an injection hole in a pumping and discharging tunnel and forming a pumping and discharging hole in a mechanical tunnel air tunnel, the coal bed gas exploitation blank zone in the middle of the mining area can be eliminated, and most coal bed gas resources are utilized; meanwhile, the gas content of the coal seam of the mining area is reduced, the risk of gas outburst and coal seam outburst is reduced, and the safety of coal seam mining is improved.
In a word, the method improves the recovery rate and the single yield of the coal bed gas; for the coal seam to be mined, the mixed gas is finally released, but CH is pumped out in advance 4 Decrease CH 4 The discharge amount and the emission reduction effect are very obvious; meanwhile, the gas outburst risk is reduced; it is suitable for low permeability coal seam.
Drawings
FIG. 1 is a schematic (plan) view of the overall arrangement of the system;
FIG. 2 is a schematic representation (section) of mixed gas displacement coalbed methane;
FIG. 3 is CH 4 Cumulative yield is plotted against time.
Wherein:
1-an injection hole;
2-drawing and exhausting holes;
3-coal bed;
4-roadway.
X-time (days);
y-CH 4 cumulative yield (m) 3 )；
f-cumulative methane production versus time.
Detailed Description
The invention is further illustrated with reference to the following figures and examples:
1. this mining system
Forming an injection hole (1) in a coal seam roadway (4) by drilling, and sealing the hole by adopting a hole sealing measure (suitable for high pressure conditions); meanwhile, a coal bed gas pumping and discharging hole (2) is formed in the roadway (4). The distance between the injection hole (1) and the drainage hole (2) is 1-10 m, the specific distance depends on the width of a mining area, the time for discharging gas from the mining area and the permeability of a coal seam, and 3-5 m is an economic distance for the current state of the mining area of a coal mine.
2. The mining method
1. With respect to step (1):
mixing various gases according to a certain proportion to form a mixed gas;
the proportion is calculated according to the following formula:
p i the volume ratio of each gas;
R i the substitution rate for each gas:
The rate of substitution can be determined by reference to the following conclusions, in particular, based on the test results.
SO 2 ∶H 2 S∶CO 2 ∶CH 4 ∶N 2 ∶H 2 ＝5∶4∶2∶1∶0.2∶0.1；
Oxygen is added as additional gas, and the gas proportion control range is 0-21%.
When the parameter is 0.2, the partial pressure of methane is mainly reduced to promote desorption; when the parameter is 3, the adsorption competition is mainly used for promoting methane desorption, and the low-replacement-rate mixed gas displacement is generally adopted for most coal seams in China.
Is injected intoIn the process, the composition of the mixed gas is dynamically adjusted according to the pressure and temperature change of the coal seam, for example: starting to inject
The larger gas is adjusted according to the injection property of the coal bed
The composition (i.e. the ratio of various gases) is small
The mixed gas displacement of the value can improve the injection property, and the displacement speed can be improved by adopting a large displacement rate. In the injection process, mixed gas with different replacement rates can be alternately injected to displace the coal bed gas; or by averaging
The mixed gas is stably adopted to displace the coal bed gas.
O 2 The main functions are to destroy the surface of coal matrix, raise the temperature of coal bed and promote methane desorption, and the control standard is to avoid spontaneous combustion of coal bed and over oxidation of methane. Control criterion is O 2 The concentration is in the range of 0% to 21%, and the average substitution rate is 0 in consideration of the substitution rate of oxygen.
The proportion of various gas components can be changed in the injection process, the replacement rate of the whole mixed gas can also change in a fluctuating way, and weak replacement gas and strong replacement gas can be alternately injected to displace and exploit coal bed gas.
At present, CO is mainly used as the strong replacement gas 2 Weak replacement gas mainly adopts N 2 Other gases have certain side effects, and are preferably used at a minimum.
2. Concerning step (2)
The high-pressure injection equipment comprises a high-pressure injection pump, an air bottle, a high-pressure container and the like.
3. Concerning step (3)
And coal bed gas or mixed gas containing the coal bed gas is obtained from the pumping hole (6), and other gas components after the methane is separated can be recycled as components in the mixed gas.
3. Test results
As shown in fig. 3, in the test of displacing coal bed gas by mixed gas in the underground pumping and drainage roadway, the pumping and drainage holes (2) are adopted for pumping and drainage independently, and the increase of the coal bed gas is little after the coal bed gas reaches a certain amount; and then, a displacement method is adopted, the accumulated methane yield in the coal bed gas is greatly increased, and the fact that the coal bed gas yield and the recovery ratio can be increased in a coal bed gas displacement test of the mixed gas in the underground pumping and drainage roadway is proved.
Claims (4)
1. A mixed gas displacement coal bed methane mining system for an underground horizontal hole comprises a coal bed (3), a roadway (4) consisting of a machine roadway and an air roadway and pumping holes (2); a roadway (4) is arranged around the plane of the coal seam (3), and a plurality of pumping holes (2) communicated with the roadway (4) are arranged in the coal seam (5);
the method is characterized in that: an injection hole (1) is arranged in the coal seam (5);
the injection holes (1) and the pumping holes (2) are alternately arranged.
2. The system for mining mixed gas displacement coalbed methane in a downhole horizontal hole according to claim 1, which is characterized in that: the distance between the injection hole (1) and the pumping hole (2) is 1 m-10 m.
3. The mining method of the underground horizontal hole mixed gas displacement coal bed methane mining system based on claim 1 is characterized by comprising the following steps:
(1) forming a mixed gas from the gases; the mixed gas comprises one or more of strong displacement gas including H 2 S、SO 2 、CO 2 (ii) a The mixed gas also comprises one or more of weak displacement gases, and the weak displacement gas comprisesN 2 、H 2 、H e ；
(2) Injecting mixed gas into the coal seam (3) through the injection hole (1) by using high-pressure injection equipment;
(3) and simultaneously, gas containing coal bed gas is obtained in the pumping hole (2) by utilizing pumping equipment until the obtained methane concentration is lower than the economic exploitation concentration and the safe concentration.
4. The mining method of claim 3, wherein:
mixing various gases according to a certain proportion to form a mixed gas;
the proportion is calculated according to the following formula:
p i the volume ratio of each gas;
R i the substitution rate for each gas:
SO 2 ∶H 2 S∶CO 2 ∶CH 4 ∶N 2 ∶H 2 ＝5∶4∶2∶1∶0.2∶0.1；
oxygen is added as additional gas, and the gas proportion control range is between 0 and 21 percent.
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| Application Number | Priority Date | Filing Date | Title |
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| CNA2007100532681A CN101122222A (en) | 2007-09-19 | 2007-09-19 | Down-hole horizontal hole exploitation system for mixing gas displacing coal gas, and the method |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013056597A1 (en) * | 2011-10-19 | 2013-04-25 | 中国矿业大学 | Gas extraction method and device with alternating extraction and injection |
| RU2516674C1 (en) * | 2012-10-12 | 2014-05-20 | Федеральное государственное бюджетное учреждение науки ИНСТИТУТ ПРОБЛЕМ КОМПЛЕКСНОГО ОСВОЕНИЯ НЕДР РОССИЙСКОЙ АКАДЕМИИ НАУК (ИПКОН РАН) | Degassing of high coal at its processing in "layer-bed" |
| CN103982165A (en) * | 2014-05-21 | 2014-08-13 | 中国石油大学(北京) | Method for extracting natural gas hydrate by using gas mixture of CO2 and H2 |
| CN104234737A (en) * | 2013-06-21 | 2014-12-24 | 肖栋 | Enzymolysis-boosted coal-seam methane desorption technique and method |
| CN109577922A (en) * | 2018-11-29 | 2019-04-05 | 山西易高煤层气有限公司 | A kind of method of coal-bed-gas production-increase |
-
2007
- 2007-09-19 CN CNA2007100532681A patent/CN101122222A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013056597A1 (en) * | 2011-10-19 | 2013-04-25 | 中国矿业大学 | Gas extraction method and device with alternating extraction and injection |
| RU2516674C1 (en) * | 2012-10-12 | 2014-05-20 | Федеральное государственное бюджетное учреждение науки ИНСТИТУТ ПРОБЛЕМ КОМПЛЕКСНОГО ОСВОЕНИЯ НЕДР РОССИЙСКОЙ АКАДЕМИИ НАУК (ИПКОН РАН) | Degassing of high coal at its processing in "layer-bed" |
| CN104234737A (en) * | 2013-06-21 | 2014-12-24 | 肖栋 | Enzymolysis-boosted coal-seam methane desorption technique and method |
| CN103982165A (en) * | 2014-05-21 | 2014-08-13 | 中国石油大学(北京) | Method for extracting natural gas hydrate by using gas mixture of CO2 and H2 |
| CN103982165B (en) * | 2014-05-21 | 2016-08-24 | 中国石油大学(北京) | One utilizes CO2and H2the method of mixed gas exploitation of gas hydrate |
| CN109577922A (en) * | 2018-11-29 | 2019-04-05 | 山西易高煤层气有限公司 | A kind of method of coal-bed-gas production-increase |
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