CN103912302A - Seam-penetrating drilling hydrofracturing gas extracting method - Google Patents

Abstract

A gas drainage method through bed drilling hydraulic fracturing, by presetting the target borehole and hole through the coal seam as the free surface of hydraulic fracturing; enlarging the reaming section of the target borehole, fixing the casing, and setting the casing The tube is connected to the separation chamber. After the high-pressure water enters the fractured borehole, the coal body is broken, and the cracked crack gradually expands until it is connected with the hole; the water pressure and water volume are increased to wash away the coal body around the crack; Pump out to realize the separation of gas; after flushing, interpenetrating macro-cracks are formed between the fractured borehole and the target borehole. During drainage, the gas seeps into the fractures, and then flows into the target borehole and hydraulic fractured borehole, which fundamentally changes the gas flow pattern; the existence of cracks is equivalent to extending the length of the target borehole and hydraulic fractured borehole in the coal seam, increasing The larger contact area with the coal body can improve the gas drainage effect.

Description

A gas drainage method by hydraulic fracturing of drilling through layers

technical field

The invention relates to a layer-crossing drilling gas drainage method, in particular to a hydraulic fracturing networked layer-crossing drilling method suitable for coal seam gas extraction.

Background technique

With the increase of mining depth, the pressure and content of coal seam gas increase, the coal quality is soft, the gas permeability of coal seam is low, it is difficult to extract coal seam gas before mining, and the danger of coal and gas outburst is becoming more and more serious. my country has become the most serious outburst in the world. coal-producing countries. In order to eliminate the outburst risk of coal seams before mining and transform high gas outburst coal seams into low gas coal seams, regional gas drainage methods are required. At present, the regional coal seam gas pre-extraction method widely used in the coal mine field is the pre-extraction of the densely penetrated bed drilling strips in the floor rock roadway and the pre-extraction of the bedding drilling. Most of the coal seams in my country have experienced strong tectonic movement, poor permeability, and small drainage radius. In order to shorten the pre-extraction time of gas, the spacing of drilling holes is usually 3-5m. The "Regulations on the Prevention and Control of Coal and Gas Outbursts" control the pre-pumping range of the coal roadway strip at more than 35m, so the layer-crossing drilling holes for the protection of the coal roadway strip are usually arranged in more than 7 rows.

In addition, there are two deficiencies in the pre-extraction of the through-bed drilling: 1) the rock section of the drilled hole is long, the coal seam section is short, and the utilization rate of the drill hole is low; It enters the borehole in the form of seepage, and each borehole extracts the coal body within its own control range, and there is no direct connection between the boreholes, resulting in a large amount of work and low extraction efficiency. Therefore, when using this method, it is necessary to cooperate with the corresponding coal seam permeability enhancement measures.

Contents of the invention

Technical problem: The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a simple method, which reduces the engineering quantity of gas drainage through layer drilling and improves the efficiency of gas drainage through layer drilling hydraulic fracturing. method.

Technical solution: The gas drainage method for hydraulic fracturing of drilling through layers of the present invention comprises the following steps:

a. Construct a target borehole with a diameter of 100mm in a rock roadway that is 20m to 30m away from the coal seam floor and has a stable occurrence, and ream the coal seam section of the target borehole according to conventional techniques to form the target hole;

b. Reaming the opening of the target hole with a length of 1.5m, the diameter of the reaming is 130mm, a casing with a diameter of 100mm is placed in the reaming section, and the casing is fixed with quick-setting cement. Connect with the separation chamber with a high pressure hose;

c. Construct a hydraulic fracturing borehole in the direction of the coal seam on both sides of the target borehole, the diameter of the hydraulic fracturing borehole is 90mm, and the distance between the end point of the hydraulic fracturing borehole and the target hole 3 is 15-20m;

d. Place a high-pressure water injection pipe with a diameter of 50mm in the hydraulic fracturing borehole, and the high-pressure water injection pipe enters 1/3 of the thickness of the coal seam; inject cement mortar into the annular gap between the high-pressure water injection pipe and the hydraulic fracturing borehole, and fix the high-pressure water injection pipe ;

e. Connect the high-pressure water injection pipe and the high-pressure water pump with a high-pressure hose, turn on the high-pressure water pump, provide high-pressure water to the coal seam, and break the coal body;

f. Record changes in water pressure and water flow. When the water pressure drops by 30% or water flows out of the target borehole, increase the water pressure and water volume of the high-pressure water pump to flush the coal body. The water flow carries gas and coal body through the hole and target Drilling holes enter the separation chamber, and the gas is pumped away by the extraction pipeline to separate the gas in the separation chamber to realize the separation of coal, gas and water;

g. When no coal continues to rush out, turn off the high-pressure water pump and stop hydraulic fracturing; calculate the amount of gas extracted according to the flow and concentration of the extraction pipeline, weigh the amount of coal deposited in the separation chamber, and analyze the effect of hydraulic fracturing;

h. Close target boreholes and hydraulic fracturing boreholes, and connect them to gas drainage pipelines to extract the gas in the coal body within the range of hydraulic fracturing.

The water supply pressure of the high-pressure water pump is above 25MPa, and the water volume is above 15m ³ /h.

Beneficial effects: the present invention aims at the low utilization rate of drilling holes for pre-pumping coal seam gas, and the low pre-pumping efficiency due to the isolation between the drilling holes. surface; a hydraulic fracturing borehole is arranged at a distance of 15-20m from the target borehole (the distance within the coal seam), and high-pressure water is injected to break and scour the coal body, forming interconnected macro-fracture channels between the hydraulic fracturing borehole and the target borehole, Improve the gas permeability of the coal body in the area affected by hydraulic fracturing, change the gas flow pattern, and improve the gas drainage effect. This method creates macroscopic cracks between the drilled holes, which is convenient for construction and can be completed by ordinary workers; it overcomes the adverse effects of low utilization rate of drilled holes for pre-extraction of coal seam gas by drilled holes, and the isolation of drilled holes. Gas desorption first enters the macroscopic cracks between the target borehole and the hydraulic fracturing borehole, and then enters the interlayer borehole, which prolongs the length of the interlayer borehole in a disguised form, and fundamentally changes the gas flow pattern, which can significantly improve the gas extraction rate. mining efficiency.

Description of drawings

Fig. 1 is a schematic diagram of the hydraulic fracturing gas drainage method of the present invention.

In the figure: 1-coal seam; 2, 2'-crack; 3-target hole; 4, 4'-hydraulic fracturing drilling; 5-target drilling; 6-high pressure water injection pipe; 7-reaming section; 8-bottom plate Rock roadway; 9-high pressure water pump; 10-separation chamber; 11-drainage pipeline.

Detailed ways

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

As shown in Figure 1, the method for extracting coal seam gas by hydraulic fracturing of the present invention, concrete steps are as follows:

a. Construct a target borehole 5 with a diameter of 100mm that penetrates the coal seam 1 in a rock roadway 8 that is 20m to 30m away from the bottom plate of the coal seam 1 and has a stable occurrence. The coal seam section of the target borehole 5 is reamed according to conventional techniques to form target hole 3;

b. Reaming the hole section of the target borehole 5, the reaming length is 1.5m, the reaming diameter is 130mm, a casing 7 with a diameter of 100mm is placed in the reaming section, and the casing 7 is fixed with quick-setting cement, Then connect the sleeve pipe 7 and the separation chamber 10 with a high-pressure rubber hose;

c. Construct a hydraulic fracturing borehole 4 in the direction of the coal seam on both sides of the target borehole 5, the diameter of the hydraulic fracturing borehole 4 is 90mm, and the distance between the end point of the hydraulic fracturing borehole 4 and the target hole 3 is 15-20m;

d. Place a high-pressure water injection pipe 6 with a diameter of 50 mm in the hydraulic fracturing borehole 4 until the high-pressure water injection pipe 6 enters 1/3 of the thickness of the coal seam. Inject cement mortar to seal the hole, and fix the high-pressure water injection pipe 6;

e. Connect the high-pressure water injection pipe 6 and the high-pressure water pump 9 with a high-pressure hose. The water supply pressure of the high-pressure water pump 9 is above 25MPa and the water volume is above 15m ³ /h. Turn on the high-pressure water pump 9 to provide high-pressure water to the coal seam 1 to break the coal body; after hydraulic fracturing, the flow state of coal seam gas changes, and coal seam gas seeps into fracture 2, and then flows into target borehole 5 and hydraulic fracture borehole 4. The existence of fracture 2 is equivalent to extending target borehole 5 and hydraulic fracture borehole. The length of hole 4 in the coal seam increases the contact area with the coal seam, which can improve the gas drainage effect;

f. Record changes in water pressure and water flow. When the water pressure drops by 30% or the target borehole 5 has water flowing out, it indicates that a through-crack has formed between the ruptured borehole 4 and the target borehole 5. At this time, increase the high-pressure water pump 9 The water pressure and water volume flush through the coal around the crack, and the water flow carries the gas and coal through the hole 3 and the target borehole 5, and finally enters the separation chamber 10, and is sucked out of the separation chamber 10 through the gas extraction pipeline 11 gas, realize the separation of gas, coal and water;

g. With the increase of the amount of coal washed out from the target borehole 5, interconnected macro-cracks are gradually formed between the ruptured borehole 4 and the target borehole 5, and the high-pressure water pump 9 is turned off to stop hydraulic fracturing; according to the extraction pipeline Calculate the amount of extracted gas from the flow rate and concentration displayed on the pressure gauge 11, and analyze the effect of hydraulic fracturing by weighing the amount of coal deposited in the separation chamber 10;

h. Close the target borehole 5 and the hydraulic fracturing borehole 4, and connect them to the gas extraction pipelines respectively to perform gas drainage in the coal body within the hydraulic fracturing range.

As shown in Fig. 1: the solid line arrow is the water flow direction; the dotted line arrow is the flow direction of water, gas and coal; the hydraulic fracturing borehole 4' has been ruptured and the construction has been completed, and an inter-hole crack 2' has been formed; the hydraulic fracturing borehole 4 is Hydraulic fracturing is in progress and Fissure 2 is forming.

Claims (2)

1. A gas drainage method through bed drilling hydraulic fracturing, characterized in that it comprises the steps: a. Construct a target borehole (5) with a diameter of 100mm in a rock roadway (8) that is 20m to 30m away from the floor of the coal seam (1) and has a stable occurrence, and ream the coal seam section of the target borehole (5) according to conventional techniques , forming the target hole (3); b. Reaming the opening of the target borehole (5) with a length of 1.5m and a diameter of 130mm, placing a casing (7) with a diameter of 100mm in the reaming section, and fixing the casing with quick-setting cement (7), then connect the separation chamber (10) with a high-pressure rubber hose at the port of the casing (7); c. Construct a hydraulic fracturing borehole (4) in the direction of the coal seam on both sides of the target borehole (5). The diameter of the hydraulic fracturing borehole (4) is 90mm. ) at a distance of 15-20m; d. Place a high-pressure water injection pipe (6) with a diameter of 50mm in the hydraulic fracturing borehole (4), and the high-pressure water injection pipe (6) enters 1/3 of the thickness of the coal seam; The annular gap between (4) is filled with cement mortar, and the high-pressure water injection pipe (6) is fixed; e. Connect the high-pressure water injection pipe (6) and the high-pressure water pump (9) with a high-pressure hose, turn on the high-pressure water pump (9), supply high-pressure water to the coal seam (1), and break the coal body; f. Record changes in water pressure and water flow. When the water pressure drops by 30% or the target borehole (5) has water flowing out, it indicates that a through crack has formed between the ruptured borehole (4) and the target borehole (5). Increase the water pressure and water volume of the high-pressure water pump (9) at the same time to flush the coal around the crack, and the water will carry the gas and coal through the hole (3), the target borehole (5) and finally enter the separation chamber (10). The gas in the separation chamber (10) is pumped away through the gas extraction pipeline (11) to realize the separation of gas from coal and water; g. The water flow washes out the coal body, gradually forming interconnected macroscopic cracks between the fractured borehole (4) and the target borehole (5), and when no coal body continues to rush out, the high-pressure water pump (9) is gradually closed to stop hydraulic fracturing; Calculate the amount of extracted gas based on the flow rate and concentration of the extraction pipeline (11), weigh the amount of coal deposited in the separation chamber (10), and analyze the effect of hydraulic fracturing; h. Close the target borehole (5) and the hydraulic fracturing borehole (4), and connect them to the gas extraction pipeline (11) to extract the gas in the coal body within the hydraulic fracturing range. 2. The gas drainage method of cross-layer drilling hydraulic fracturing according to claim 1, characterized in that: the water supply pressure of the high-pressure water pump (9) is above 25MPa, and the water volume is above 15m ³ /h.