CN105064967A - Coal seam gas fracturing and mash gas driving method - Google Patents

Abstract

A coal seam gas fracturing and gas driving method includes two stages of hole sealing and fracturing and gas driving. First construct the drilling holes in the coal seam, then embed high-pressure rubber hoses in the drilling holes and seal the holes, select any drilling hole as the fracturing drilling hole, inject high-pressure gas into the fracturing drilling hole, and the coal seam can be fractured through the air pressure, increasing The gas permeability of the coal seam; while injecting high-pressure gas into the fracturing hole, the gas is extracted from other holes around the fracturing hole. If the gas fracturing effect is unsatisfactory such as hard coal or high ground stress, high-pressure water fracturing can be used first, and then high-pressure gas can be injected into the hole, and the drilling around the fracturing hole can be drained at the same time gas. This method takes into account the difference in the adsorption properties of coal to gas and fracturing gas, and combines the fracturing effect of gas with the gas driving effect, which can effectively improve the efficiency of gas drainage, reduce the number of gas drainage holes, and reduce the impact of water on gas. Inhibition of desorption. The method is simple, safe, reliable and effective.

Description

Coal seam gas fracturing and gas driving methods

technical field

The invention relates to a gas fracturing method, in particular to a method for coal seam gas fracturing and gas driving, which is applicable to coal seam gas fracturing and gas extraction rate improvement.

Background technique

Compared with hydraulic fracturing, gas fracturing has less influence on the gas permeability of coal seam, and has less influence on the gas adsorption and desorption effect of coal seam. Research on coal seam gas fracturing technology provides a new way of thinking for increasing the gas permeability of coal seams and improving the gas extraction efficiency of coal seams. In a single outburst coal seam, improving the gas permeability of the coal seam and improving the efficiency of gas extraction are the key to the mining of a single outburst coal seam. At present, the methods commonly used to improve the air permeability of a single coal seam are: hydraulic fracturing and hydraulic slotting. Although both methods have the effect of increasing the permeability of the coal seam, they both inevitably have the influence of water on the desorption of gas. At the same time, in the coal seam The residual water in the pores and fissures is likely to form a "water lock effect", which blocks the gas migration channel and is not conducive to gas extraction.

Contents of the invention

Technical problem: The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for coal seam gas fracturing and gas driving that is simple, safe, reliable and effective.

Technical solution: The method for coal seam gas fracturing and gas driving of the present invention includes two stages of sealing and fracturing and gas driving, and the steps are as follows:

a. According to the geological information parameters of the coal seam, determine the drill hole spacing, and construct a group of horizontally distributed drill holes in the pre-mined coal seam. The number of drill holes is set according to the fracturing range. Insert a high-pressure hose into the hole, and then seal the hole with a sealing material;

b. After the hole sealing is completed, select any drill hole as the fracturing drill hole, connect the high-pressure rubber hose in the fracturing drill hole with the high-pressure air pump, and connect the valve, gas pressure sensor and gas flow sensor in sequence in the pipeline Inject high-pressure gas into the fracturing borehole through a high-pressure air pump. The pressure energy of the high-pressure gas entering the borehole can destroy the integrity of the coal seam, open up the pores and fissures of the coal seam itself, and increase the gas permeability of the coal seam without affecting the coal seam’s gas resistance. Adsorption and desorption effect;

c. Connect the high-pressure rubber hoses of other drill holes adjacent to the fracturing drill hole injected with high-pressure gas to the gas drainage pipeline;

d. Since the gas in the coal seam moves from the position with high pore pressure to the position with low pore pressure, a higher pore pressure will be formed around the fracturing drilling hole injected with high-pressure gas, and a higher pore pressure will be formed around other adjacent drilling holes. With low pore pressure, a pore pressure gradient is formed between the higher pore pressure and the lower pore pressure, that is, the gas pressure gradient. At this time, it enters the stage of driving gas by air pressure, and the gas drainage system starts to extract gas from adjacent boreholes. Gas, the air pressure required for gas fracturing holes at this stage is smaller than that in the fracturing stage, which can reduce the pressure of gas injection into the fracturing borehole;

e. When the gas drainage concentration detector shows that the drainage concentration drops below the set value, complete the gas drive of a fracturing borehole, and inject high-pressure gas into the next borehole as a fracturing borehole for fracturing, and at the same time Turn the previous fracturing drilling into a drainage hole and connect it to the drainage pipeline for gas drainage;

f. Repeat step e several times until each of a group of horizontally distributed boreholes is used as a fracturing borehole and injected with high-pressure gas for fracturing, and gas drainage is performed on other adjacent boreholes while fracturing .

Use the downhole compressed air system to drive the air motor as the power source of the high-pressure air pump, or use the explosion-proof motor as the power source of the high-pressure air pump.

Multiple high-pressure air pumps can be connected in parallel according to the needs of the site to achieve the purpose of rapid fracturing with large displacement and high pressure.

The fracturing time for injecting high-pressure gas into the borehole is comprehensively determined according to the drilling distance, coal seam hardness, joint fissure development, and the parameters of detecting the air pressure and flow rate during the fracturing process; The change of gas concentration in the system is determined.

If the hardness of the coal seam is large or the ground stress is large, conventional high-pressure water fracturing is performed on the fracturing borehole first, and then high-pressure gas is injected into the fracturing borehole for fracturing.

The high-pressure gas is the air source provided by the downhole compressed air system, or nitrogen and _CO2 gas that are easily absorbed by the coal seam.

Beneficial effects: the present invention adopts the method of gas fracturing and gas driving, which can effectively avoid the influence of water on the coal seam in hydraulic measures such as hydraulic fracturing and hydraulic cutting, and the gas fracturing can not only fracture the coal seam, but also improve the air permeability of the coal seam It will not form a "water lock effect", block the gas migration channel, and will not affect the adsorption and desorption of gas. At the same time, the organic cooperation of gas fracturing and peripheral hole extraction in time and space, the "one extraction and one pressure" mode can increase the pore pressure gradient of the coal seam and improve the extraction efficiency. Gas fracturing does not affect the adsorption and desorption effect of coal on gas, and also avoids the blockage of gas migration channels by the moisture remaining in coal seams in other permeability enhancement measures. At the same time, the cooperation between gas fracturing and gas drainage in time and space can effectively improve the efficiency of gas drainage. Especially in a single outburst coal seam, the implementation effect of the method is more obvious. It can transform the structure of coal and rock mass and improve the gas permeability of coal and rock mass. For coal seams with high gas permeability, high-pressure air drives a large amount of free gas from the cracks and pores of the coal seam, so that the free gas in the coal seam can pass through the surrounding pores. Drainage not only reduces the gas pressure in the coal seam, reduces the risk of outburst, the gas in the pores of the coal seam is replaced by air, and greatly reduces the peak value of gas gushing out during coal mining, effectively avoiding the gas in the mining space Overrun. At the same time, the structural damage of the coal seam under the action of high-pressure air will reduce the elasticity of the coal seam, increase the plasticity of the coal seam, change the stress state of the coal seam, achieve the functions of pressure relief and gas discharge, and thus play a role in preventing outbursts. The method is beneficial to the extraction of coal seam gas, and has excellent effects on preventing and controlling coal and gas outburst, coal seam gas development, etc. The method is simple, convenient in construction, safe and reliable, good in effect, and has wide practicability.

Description of drawings

Fig. 1 is a schematic layout diagram of coal seam gas fracturing and gas driving method of the present invention;

In the figure: 1-coal seam, 2-drilling, 3-high-pressure rubber hose, 4-sealing material, 5-high-pressure air pump, 6-valve, 7-gas pressure sensor, 8-gas flow sensor, 9-downhole pressure air pipe 10-gas pressure sensor, 11-gas drainage pipeline.

Detailed ways

An embodiment of the present invention will be further described below in conjunction with accompanying drawing:

Embodiment 1: The method for coal seam gas fracturing and gas driving of the present invention includes two stages of sealing and fracturing and gas driving. For example, the average thickness of a coal seam in a certain mine is about 2.51m, and the buried depth is about 800m. The coal seam is stable. The structure is simple, and the inclination angle of the coal seam is about 0°～6°, with an average of 4°. It occurs in the middle and lower part of the Shanxi Formation, about 50m away from the limestone at the top of the Carboniferous Taiyuan Formation, 36.6m away from the sandstone at the bottom of the coal seam, and 51.51m away from the K ₄ aluminous mudstone at the top. The roof is sandy mudstone or sandstone, and the floor is sandy mudstone and Siltstone, the coal seam is relatively stable. The gas content is about 11.15m ³ /t, the gas drainage radius is 5m, and the coal seam permeability coefficient is 0.0861m ³ /(MPa ² .d). The damage type of the coal seam belongs to type III~IV coal, the relative gas pressure is 1.12~1.7MPa, the firmness coefficient is 0.22~0.4059, the initial gas emission velocity of the coal seam is 12.957~14.000, and the gas content of the coal seam is 6.15~17.59m ³ /t. The coal seam is an outburst coal seam with coal and gas, and the coal dust is not explosive. The method of coal seam gas fracturing and gas driving is used to extract gas from the coal seam, and the specific steps are as follows:

a. According to the coal seam geological information parameters, determine the borehole spacing, and construct a group of horizontally distributed boreholes 2 in the pre-mined coal seam 1. The number of 2 is set according to the range of fracturing, and there are at least 3, which is determined according to the driving radius of coal seam gas. Insert the high-pressure hose 3 into the drill hole 2 that has been constructed. The length of the high-pressure hose 3 is 25m, and then seal the gap between the drill hole 2 and the high-pressure hose 3 with cement roll or cement mortar sealing material 4. hole, the sealing depth is 20m, and the length of the high-pressure hose 3 should be greater than the length of the sealing section;

b. After the hole sealing is completed, select any drill hole 2 as the fracturing drill hole, connect the high-pressure rubber hose in the fracturing drill hole with the high-pressure air pump 5, and connect the valve 6 and the gas pressure sensor in sequence in the pipeline 7 and the gas flow sensor 8, use the downhole air pressure system to drive the air motor as the power source of the high-pressure air pump 5, or use an explosion-proof motor as the power source of the high-pressure air pump 5; multiple high-pressure air pumps 5 and one of the high-pressure air pumps 5 can be started according to engineering needs They are connected in parallel to achieve the purpose of rapid fracturing with large displacement and high pressure. Inject high-pressure gas into the fracturing borehole through the high-pressure air pump 5, and the pressure energy of the high-pressure gas entering the borehole 2 can destroy the integrity of the coal seam, open up the pores and fissures of the coal seam itself, and increase the air permeability of the coal seam 1 without affecting the coal seam Adsorption and desorption effects on gas; the fracturing time for injecting high-pressure gas into the borehole 2 is comprehensively determined according to the drilling distance, coal seam hardness, joint and fissure development, and the parameters for detecting the air pressure and flow rate during the fracturing process; The time required for the gas phase is determined according to the change of gas concentration in the drainage system; if the coal seam is hard or the ground stress is large, first implement conventional high-pressure water fracturing to the fracturing borehole, and then inject gas into the fracturing borehole The high-pressure gas is used for cracking; the high-pressure gas is the air source provided by the downhole compressed air system, or the nitrogen and CO2 gases that are easily absorbed by the coal seam _; nitrogen, _CO2 and other inert gases are used in the coal seam that is prone to spontaneous combustion.

c. Connect the high-pressure rubber hose 3 of other boreholes 2 adjacent to the fracturing borehole that injects high-pressure gas to the gas extraction pipeline 11, and use the negative pressure of the gas extraction pipeline to drain the gas in the surrounding drilling holes;

d. Since the gas in the coal seam 1 moves from the position with high pore pressure to the position with low pore pressure, a higher pore pressure will be formed around the fracturing drilling hole injected with high-pressure gas, and a higher pore pressure will be formed around other adjacent drilling holes 2. A lower pore pressure is formed, and a pore pressure gradient is formed between the higher pore pressure and the lower pore pressure, that is, the gas pressure gradient. At this time, it enters the stage of air pressure driving gas, and the gas drainage system starts to drain adjacent boreholes The gas in the gas fracturing hole at this stage requires less air pressure than the fracturing stage, which can reduce the pressure of gas injection into the fracturing hole; because the high-pressure gas in the pressure stage needs to fracturing the coal seam, the pressure required is higher , while in the driving stage, the gas in the fracturing area is driven to the adjacent fracturing boreholes, and the required pressure is lower than that in the fracturing stage;

e. When the gas drainage concentration detector shows that the drainage concentration drops below the set value, complete the gas drive of a fracturing borehole, and use the next borehole 2 as a fracturing borehole to inject high-pressure gas for fracturing, At the same time, the previous fracturing drilling is turned into a drainage hole and connected to the drainage pipeline for gas drainage;

f. Repeat step e several times until each of a group of horizontally distributed boreholes 2 is used as a fracturing borehole and injected with high-pressure gas for fracturing, and gas pumping is performed on other adjacent boreholes while fracturing mining, effectively improving the efficiency of gas extraction.

Working principle: Under the action of the in-situ stress field, the coal seam uses the drill hole to pump high-pressure gas into the coal seam. The in-situ stress field and the gas pressure together cause cracks in the coal seam. The pressure energy of the gas destroys the integrity of the coal seam and connects the pores and fissures of the coal seam itself. , while increasing the gas permeability of the coal seam, it does not affect the adsorption and desorption effect of the coal seam on gas. The gas in the coal seam always moves from the position with high pore pressure to the position with low pore pressure. The level of pore pressure affects the speed of gas movement. The combined effect of the two forms a higher gas pressure gradient, which can effectively improve the gas extraction efficiency.

Claims (6)

1. a coal seam gas pressure break and gas method of driveing, is characterized in that: the method comprises sealing of hole pressure break and gas drives two stages, and step is as follows:

A. according to coal geology information parameter, determine the spacing of wells, the boring (2) of construction one group of horizontal distribution in the coal seam (1) of pre-exploitation, the quantity of boring (2) is according to pressure break range set, have 3 at least, plug-in mounting high-pressure rubber pipe (3) in the boring of having constructed (2), then uses sealing material (4) to carry out sealing of hole;

B. after sealing of hole completes, any one boring (2) is selected to hole as pressure break, high-pressure rubber pipe in pressure break being holed is connected with high-pressure pump (5), in pipeline, access valve (6), gas pressure sensor (7) and gas flow sensor (8) successively simultaneously, in pressure break boring, gases at high pressure are injected by high-pressure pump (5), the pressure energy entering the gases at high pressure in this boring (2) destroys the globality in coal seam, the hole crack in conducting coal seam itself, does not affect the adsorption desorption effect of coal seam to gas while increasing coal seam (1) gas permeability;

C. be connected with the high-pressure rubber pipe (3) injecting other hole (2) that the pressure break of gases at high pressure is holed adjacent with methane gas extraction pipeline (11);

D. because the gas in coal seam (1) is moved to the position that pore pressure is low by the position that pore pressure is high, the pressure break boring of injecting gases at high pressure can form higher pore pressure around, other adjacent with it borings (2) then form lower pore pressure around, pore pressure grad is defined between higher pore pressure and lower pore pressure, i.e. methane pressure gradient, now enter air pressure and drive the gas stage, gas drainage system starts the gas in the adjacent boring of extraction, this air pressure needed for phase gas pressure break hole is little compared with the pressure break stage, the pressure of gas injection in pressure break boring can be reduced,

E. when gas extraction concentration detector showing extraction concentration and being reduced to below setting value, the gas completing a pressure break boring is driven, next one boring (2) is injected gases at high pressure capable pressure breaks as pressure break boring, pressure break boring is before become drainage holes simultaneously and be connected into extraction pipeline and carry out gas pumping;

F. repeat step e many times, until each boring (2) of one group of horizontal distribution is injected high pressure gas fracturing mistake as pressure break boring, and while pressure break, gas pumping is carried out to other adjacent borings.

2. coal seam gas pressure break according to claim 1 and the gas method of driveing, is characterized in that: utilize underground pressure air system drive air motor as the power source of high-pressure pump (5), or utilize fire-proof motor as the power source of high-pressure pump (5).

3. coal seam gas pressure break according to claim 1 and the gas method of driveing, is characterized in that: can need multiple stage high-pressure pump (5) in parallel according to scene, to realize the object that huge discharge hyperbar carries out pressure break fast.

4. coal seam gas pressure break according to claim 1 and the gas method of driveing, is characterized in that: described pressure break time of injecting gases at high pressure in boring (2) is according to the spacing of wells, seam hardness, developmental joint fissure situation and detect the air pressure of fracturing process and the parametric synthesis of flow is determined; Air pressure is driven gas stage required time and is determined according to the variation ofgas density situation of extraction system.

5. coal seam gas pressure break according to claim 1 and the gas method of driveing, it is characterized in that: if when seam hardness is large or geostatic stress is large, first conventional water under high pressure fracturing is implemented to pressure break boring, and then in pressure break boring, inject gases at high pressure carry out fracturing.

6. coal seam gas pressure break according to claim 1 and the gas method of driveing, is characterized in that: the air-source that described gases at high pressure provide for underground pressure air system, or for easily by nitrogen, CO that coal seam is adsorbed ₂gas.