CN101173604A - Method for horizontal well mixed gas displacing coal-bed gas - Google Patents

Abstract

The invention discloses a method for displacing coal seam gas via horizontal well mixed gas, relating to the method of coal seam gas coal mining, which comprises the following steps: 1. A plurality of horizontal wells (10) are formed in the coal seam (30) through the horizontal well craft, which comprise injection wells (11) and harvesting wells (12) alternatively arranged at intervals ; 2. A high-pressure injecting equipment is used to inject the mixed gas into the coal seam (30) with coal seam gas via injection wells (11); 3. The mixed gas with coal seam gas is acquired in harvesting wells (12) until the methane concentration is lower than the coal mining concentration and the preservation concentration. The invention has the advantages of considering both the competitive absorption of strong replacement gas and the effect of permeation increase and methane gas partial pressure of feeble replacement gas; improving the recovery factor and the single yield of the coal seam gas, and reducing the coal mining cost of the coal seam gas, simultaneously, mothballing the waste gas geologically, and reducing and sealing waste gas at a maximum.

Description

Method for horizontal well mixed gas displacing coal-bed gas

Technical field

The present invention relates to a kind of coal-bed gas exploitation method, relate in particular to a kind of method for horizontal well mixed gas displacing coal-bed gas.

Background technology

The most air content in China coal seam is higher, average air content 10m ³The mining area that/t is above accounts for 41%; But the permeability in coal seam is lower, is generally 0.002～16.17mD (millidarcy).Wherein, permeability accounts for 72% less than 1.0mD's, is unfavorable for very much the exploitation and the utilization of coal bed gas.The general permeability in China coal seam is low, desorption rate slow and cause most coal seams test well to yield poorly, decay soon, be difficult to form stable industrialness air-flow.

The coal-bed gas exploitation mode of current techniques comparative maturity has: ground peupendicular hole, ground minery well (Gobwell), down-hole horizontal hole (being the coal mine gas extraction) and abandoned mine all adopt simple extraction mode.In order to improve the coal bed gas single rate, also adopt technology such as directed pinniform branch lateral aperture technology, hydrofracturing anatonosis, the anatonosis of liberation layer, obtained certain effect.It is main that current down-hole coal bed air to open is adopted main still extraction, adopt the negative pressure extracting coal bed gas, but the recovery ratio of coal bed gas is lower, and the degree of depth of lateral aperture is limited simultaneously, and the influence basin of extraction is limited, has wasted a large amount of coal bed gas resources.

The method of displacement exploiting coal bed methane is varied at present, and for example: water drive is replaced, CO ₂Displacement, N ₂Gas drive is for the coal bed gas technology.Water drive remains to be discussed for the effect of coal bed gas; CO ₂Gas displacing coal-bed effect is better, but can cause that matrix of coal expands, and reduces the permeability in coal seam, influences the injection in coal seam, causes injecting difficulty, and is not suitable for the hypotonic coal seam of China; N ₂Gas displacing coal-bed effect is better, but its replacement result is limited, simultaneously CO ₂And N ₂Separation costs more expensive, influence the economy of coal bed gas displacement exploitation.

The displacement scope is subjected to the distribution influence of drilling well very big.As Fig. 1, there is displacement dead band (40) in (22) four layouts of producing well in traditional peupendicular hole displacement mode, and this part coal bed gas can't be gathered or fully gather, and has reduced the recovery ratio of coal bed gas; And peupendicular hole is in other rock stratum (non-coal seam) greatly, and minimum part has taken substantial contribution in the coal seam.

In a word, the effect of down-hole coal bed gas extraction is still waiting to improve, the coal bed gas yield-increasing technology mode of development of new has the multiple meaning of aspects such as economy, safety and environmental protection for coal enterprises in China, therefore must seek new coal-bed gas exploitation method economy, that recovery ratio is high.

Summary of the invention

Purpose of the present invention just is to overcome the above-mentioned shortcoming and defect that existing coal-bed gas exploitation technology exists, and enlarges the scope of application of prior art, and a kind of method for horizontal well mixed gas displacing coal-bed gas is provided; This method not only helps improving the recovery ratio of coal bed gas, the speed of gathering and recovering range, reduces the displacement cost, can not seal discarded gas or sequestration of greenhouse gases up for safekeeping in the working seam simultaneously.

The present invention includes the following step:

1. as Fig. 2,3,4, generate technology by horizontal well and in coal seam (30), form some horizontal wells (10), some horizontal wells (10) are made up of alternate intervals structure arranged the same injection well (11) and producing well (12), and each horizontal well (10) comprises vertical section (13) and the horizontal segment (14) that is interconnected;

2. adopt the high pressure injection device that mist is injected the coal seam (30) that contains coal bed gas by injecting well (11);

3. in producing well (12), obtain the mist that contains coal bed gas, till the methane concentration that obtains is lower than the economic exploitation concentration and safe concentration.

Operating principle of the present invention and characteristics:

Inject mist by injecting well (11) to coal seam (30), mist can comprise all gases composition, by mist displacement coal bed gas, and drives it and flows to producing well (12).

With respect to other displacement method, the present invention mainly contains following two characteristics:

1, utilizes mist

Mist has following effect:

The one, displacement, the strong substitution gas and the CH of injection ₄Competitive Adsorption, displacement CH ₄Molecule promotes the coal bed gas desorb, reduces CH simultaneously ₄Dividing potential drop, further impel CH ₄Desorb;

The 2nd, to drive, the injection of mist has been kept than the higher barometric gradient of bleeding merely, plays the effect that increases rate of flow of fluid, impels convection current, the disperse of coal bed gas, drives and carry CH ₄Flow to producing well (12);

The 3rd, become and ooze, higher pore pressure has been kept in the injection of mist, increases degree of porosity and pore communication, helps improving the coal seam permeability.In addition, the gas componant of different replacement ratios can cause to expand in the coal seam or shrink (with respect to adsorbed methane time) in the mist, can reduce or improve the coal seam permeability, but improve the injection in coal seam.

2, in horizontal well (10), form injection well (11) and the producing well (12) that alternate intervals is arranged

Utilize injection well (11) and producing well (12) to carry out coal bed gas displacement exploitation, reduce peupendicular hole quantity, reduce gas displacement cost of winning, increase the coal bed gas recovery ratio, reduce the concentration of coal bed gas, but for working seam, improve the security context of whole seam mining, the coal bed gas of gathering simultaneously; For can not working seam, reduce greenhouse gas emission.

The present invention has the following advantages and good effect:

1, the competitive Adsorption ability of the strong substitution gas of performance.Coal to strong substitution gas (as SO ₂, H ₂S, CO ₂, NO _x, SO _xDeng gas) adsorption capacity compare CH ₄Inject strong substitution gas and can promote CH by force, ₄Desorption.Certainly, the strong substitution gas of injection also reduces CH ₄Dividing potential drop in the coal seam also has certain promotion CH ₄The effect of desorption.The anatonosis effect of the weak substitution gas of performance.Behind the weak substitution gas displacement methane, the coal seam shrinks, and the infiltrative effect of increase is arranged.For example: weak substitution gas (as: N ₂, H ₂, H _e) make the coal seam transmission coefficient increase by 1 more than the magnitude, in general can be by the gas componant of different diadochies in the mist, the breathing of control matrix of coal, the permeability in control coal seam, this cbm development for the hyposmosis coal seam is significant.

2, utilize the horizontal well mixed gas displacing coal-bed gas exploitation method, can reduce displacement exploitation construction cost, increase the scope of displacement, improve the recovery ratio of coal bed gas, utilize most of coal bed gas resource.

3, horizontal well mixed gas displacing coal-bed gas has reduced the exploiting field seam gas content, reduces the risk that gas is outstanding and the coal seam is outstanding, has improved the safety of seam mining; Can not working seam then can discard gas geology seals up for safekeeping.

In a word, the present invention takes into account advantage competition absorption and the anatonosis of weak substitution gas and the effect of reduction methane gas dividing potential drop of strong substitution gas; Improve the recovery ratio and the single rate of coal bed gas, seal up for safekeeping and reduce discharging in the geology that can not working seam can discard gas simultaneously.

Description of drawings

Fig. 1 is a peupendicular hole displacement dead band coal bed gas schematic diagram;

Fig. 2 is multilayer horizontal well distribution schematic diagram of the present invention (main looking);

Fig. 3 is a multilayer horizontal well distribution schematic diagram of the present invention (side-looking);

Fig. 4 is a multilayer horizontal well mixed gas displacing coal-bed gas schematic diagram of the present invention;

Fig. 5 is one of mobile schematic diagram of mist of the present invention;

Fig. 4 is two of the mobile schematic diagram of mist of the present invention;

Fig. 7 is a multi-branched horizontal well horizontal arrangement schematic diagram of the present invention.

Wherein:

The 10-horizontal well,

11-injects well;

The 12-producing well;

The 13-horizontal segment;

The 14-vertical section.

The drilling well of 20-tradition,

The 21-tradition is injected well; 22-tradition producing well.

The 30-coal seam.

40-displacement dead band.

The specific embodiment

The present invention is further described below in conjunction with drawings and Examples:

1,1. about step

Horizontal well generates the technology art and exists in coal, coal-bed gas exploitation, oil field; China's horizontal well generates technology and is in rank first (mainly referring to oil, coal department), can directly adopt these technologies to carry out horizontal well and generate.Existing and ripe horizontal well generates technology to be had: technologies such as vertical water horizontal well, small curvature radius horizontal well, multi-branched horizontal well, pinniform horizontal well, overlength horizontal well.If there is the very thick situation of a plurality of ore beds or ore bed in the coal seam, just need the multilayer horizontal well.Generally speaking, adopt the overlength horizontal well can reduce effectively the drilling well vertical component repeat creep into; For the ore bed that buries more deeply, relatively approaches, overlength horizontal well displacing phase has incomparable cost advantage for traditional coal seam air to open mining method especially.Horizontal well generates technology and becomes the well technology to carry out with reference to oil, coal department horizontal well.Have only under the situation of main horizontal well, it is consistent with spacing system of selection and traditional coal seam air to open mining method between the producing well to inject well, and control range is 1m～1000m, and generally getting 100～300m according to the exploitation time is optimum distance; Have under the situation of Multilateral Wells, the spacing between Multilateral Wells and the Multilateral Wells is consistent with the system of selection of the spacing of general displacement method.

As Fig. 2,3,7, horizontal well (10) is divided into injection well (11) and producing well (12).Generally speaking, drilling well is distributed as alternately shape, during the multilayer horizontal well, can form the space well spacing on the ore bed space, forms the alternate intervals shape on the space.

Wherein, inject well (11) and producing well (12) and act in accordance with coal seam (30) direction, injecting the well (11) and the horizontal segment of producing well (12) and the angle of coal seam (30) direction is ± 40 degree scopes.

2,2. about step

1) all gases is mixed the formation mist according to a certain percentage, mist is injected coal seam (30) through injecting well (11) by high pressure injection device (as high-pressure gas injection pump, high-pressure bottle etc.).

2) mixed gas composition comprises extensivelyr, mainly comprises strong substitution gas, selects SO _x, NO _x, H ₂S, CO ₂Deng gas and weak substitution gas, select N ₂, H ₂Deng gas.Mix strong substitution gas and weak substitution gas, can comprise O simultaneously ₂, destroy the matrix of coal surface texture, cause the coal bed gas desorption.

The average replacement ratio of mist

Calculate with reference to following formula:

$\stackrel{\‾}{R}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{p}_i\×R_i=0.2~5---\left[1\right]$

Wherein:

The average replacement ratio of-mist;

p _iThe volume ratio of-all gases;

R _iThe replacement ratio of-all gases, promptly under uniform pressure, all gases to the matrix of coal adsorbance with respect to the ratio of methane to the matrix of coal adsorbance.

Main mist replacement ratio can be calculated according to following parameter:

SO ₂∶H ₂S∶CO ₂∶CH ₄∶N ₂∶H ₂＝5∶4∶2∶1∶0.2∶0.1；

Or determine and with reference to other data through overtesting.Other gas is directly determined by result of the test.

Be 0.2 o'clock, be mainly reduction methane dividing potential drop and impel its desorb;

Being 5 o'clock, mainly is that competitive Adsorption is impelled the methane desorb.

O ₂Main effect destroys the matrix of coal surface, improves the coal seam temperature, impel the methane desorb, but controlled condition is as the criterion not cause spontaneous combustion of coal seam.Oxygen is controlled separately, and its control criterion is O ₂Concentration adds in the coal seam as supplementary means in 0%～21% scope.

Dynamically adjust the formation of mist in the injection process according to the pressure, temperature variation in coal seam, for example: begin to inject

Bigger gas according to the injection in coal seam, is adjusted

Formation (that is: gas ratio), adopt little

The displacement mist displacement of value is alternately injected gas displacing coal-bed; Perhaps adopt average

Adopt the displacement mixed gas displacing coal-bed gas stably.

In addition, mist can directly adopt industrial waste gas, air, discarded gas, sulfur-bearing tail gas or their mist to add and regulate composition gas, mixed gas concentration requires low or does not require, reduces the total cost of source of the gas cost and reduction mixed gas displacing coal-bed gas significantly; To discard simultaneously gas seal up for safekeeping with can not working seam in, reduce atmosphere pollution.

For can not working seam, gas componant can be random; But but for working seam, consider and exploit this coal seam in the future that the gas of injection can not have very strong toxicity, generally adopts CO ₂And N ₂Combined drive is relatively good for effect.

3,3. about step

Obtain coal bed gas or contain the displacement mist of coal bed gas in producing well (12), other gas componant of isolating behind the methane can recycle as the composition in the displacement mist again.Mist displacement mixed gas displacing coal-bed gas can increase substantially the output and the exploitation rate of coal bed gas; Can realize that then the geology of discarded gas is sealed up for safekeeping on a large scale if discard the gas injection.

Claims (3)

1. a method for horizontal well mixed gas displacing coal-bed gas is characterized in that comprising the following steps:

1. in coal seam (30), form some horizontal wells (10) by the horizontal well technology, some horizontal wells (10) are made up of alternate intervals structure arranged the same injection well (11) and producing well (12), and each horizontal well (10) comprises vertical section (13) and the horizontal segment (14) that is interconnected;

2. adopt the high pressure injection device that mist is injected the coal seam (30) that contains coal bed gas by injecting well (11);

3. in producing well (12), obtain the mist that contains coal bed gas, till the methane concentration that obtains is lower than the economic exploitation concentration and safe concentration.

2. by the described a kind of method for horizontal well mixed gas displacing coal-bed gas of claim 1, it is characterized in that step is 1.:

The horizontal well (10) that forms in coal seam (30) is that its angle is in ± 40 degree scopes along coal seam (30) direction.

3. by the described a kind of method for horizontal well mixed gas displacing coal-bed gas of claim 1, it is characterized in that step is 2.:

Mist mainly comprises strong substitution gas composition and weak substitution gas composition;

Calculate with reference to following formula:

$\stackrel{\‾}{R}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{p}_i\×R_i=0.2~5$

Wherein:

The average replacement ratio of-mist;

p _iThe volume ratio of all gases in the-mist;

R _iThe replacement ratio of-all gases.

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