Method and device for controlling crack expansion by freezing low-rank coal seams

Abstract

The invention provides a method and device for freezing a low-order coal seam to control crack expansion. The method comprises the steps that water is injected into a wellbore to fracture a crushed zone to form hydraulic cracks; water continues being injected to form a saturated water coal seam in the crushed zone; then liquid nitrogen is injected into the wellbore, and water in the saturated water coal seam of the crushed zone is converted into ice under the ultra-low temperature effect of the liquid nitrogen, and a crushed zone frozen coal seam is formed; liquid nitrogen continues being injected to enable the crushed zone frozen coal seam around the wellbore to be broken, and thus the liquid nitrogen can successfully penetrates through the crushed zone frozen coal seam to reach a low-permeability coal seam at the far position; and when the pressure of the liquid nitrogen is higher than the breaking pressure of the far coal seam, the far coal seam is broken, a large number of cracks are generated, then the liquid nitrogen is injected, the cracks extend forward, and a series of artificial cracks are formed, and fracturing is stopped. According to the method and device, interferenceof natural cracks in the crushed zone of the low-order coal seam to the artificial cracks can be effectively eliminated or weakened.

Description

technical field [0001] The application relates to the field of hydraulic fracturing of coalbed methane production stimulation measures, especially the method and device for controlling crack expansion by freezing of low-rank coal seams. Background technique [0002] Coalbed methane, commonly known as gas, is mainly composed of methane and is a gas resource that is associated and symbiotic with coal. In the process of coal mining, coalbed methane is the main harmful source of gas explosions and coal and gas outburst accidents in coal mines. As a kind of clean energy, the rational development and utilization of coalbed methane can not only improve the conditions of safe production in coal mines, but also protect the environment. At the same time, it also has important strategic significance for the adjustment of energy structure. [0003] my country's coalbed methane resources are relatively rich, and its reserves rank third in the world. The development and utilization of co...

AI Technical Summary

Problems solved by technology

However, for some low-rank coal seams, their strength is relatively low. During the drilling of coalbed methane wells, due to the sudden release of gas around the well wall, a large number of fracture zones around the coalbed methane wells will often be generated.

The natural fractures in these fractured zones will seriously interfere with the hydraulic fracturing process, and it is easy to cause the hydraulic fractures to extend along the natural fractures in the fractured zone around the wellbore, so that a large amount of fracturing fluid will be lost, and it is difficult to detect the fractures far away. The low-permeability coal seam at the location will have the effect of fracturing, which will eventually lead to the fracturing stimulation range being limited to the fracture zone around the wellbore, and the fracturing effect is poor.

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