Method for synergetic extraction of coal bed gas in caving type gob area and lower coal bed

Abstract

The invention discloses a method for synergetic extraction of coal bed gas in a caving type gob area and a lower coal bed. The method comprises the steps that firstly, a mine is explored, a horizontal well is constructed from the ground to a base plate of the gob area, carbon dioxide is compressed into the well for cleaning, and coal bed gas extraction is carried out; when the extraction amount of coal bed gas in unit time drops to 20%-40% of Qi, running and stopping circulate, the extraction pressure is reduced, and the re-extraction process is carried out again; when the extraction amount drops to be below 20% of Qi, carbon dioxide is injected for replacement, and extraction is carried out again; when the extraction amount drops to be below 20% of Q1 again, the horizontal well and a coal and rock strata of the lower coal bed are subjected to fracture, and coal bed gas discharge and extraction are carried out; when the extraction amount drops to be below 20% of Q2, supercritical carbon dioxide replacement is carried out; and when the extraction amount drops to 10% of Q2 through extraction, extraction is stopped. By means of the method, synergetic extraction of coal bed gas in the carving type gob area and coal bed gas near a low coal seam is achieved, cost is reduced, and the coal bed gas resource is extracted to the greatest extent.

Description

technical field [0001] The invention relates to a method for cooperatively extracting coalbed methane from caving old gobs and lower coal seams, and belongs to the technical field of coalbed methane extraction. Background technique [0002] Due to long-term industrialized mining, there are countless old empty areas with huge areas in our country. Taking Shanxi Province as an example, by the end of 2013, there were more than 4,700 abandoned mines in Shanxi Province, and the area of ​​old empty areas had reached 5,000 square kilometers. Coal technology, the coal recovery rate is generally 50% to 60%, or even lower, so there are considerable coalbed methane resources and gas reserves in the above-mentioned old empty areas. Relevant data show that only Shanxi Province is used as an example. Gas resources are about 3 billion cubic meters. Gas is a kind of clean energy, and the energy utilization of residual coalbed methane in the old empty area can effectively alleviate the sho...

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Problems solved by technology

[0004] However, the above-mentioned patents have problems such as the small contact surface between the vertical drilling on the ground and the coalbed methane reservoir, and the limited range of extraction. At the same time, the above-mentioned patents all drain the old empty space to retain the coalbed methane resources, and they do not combine the old empty area with the corresponding coalbed methane. Adjacent to exploit coalbed methane resources as a whole, consider coordinated extraction

[0005] In fact, coal seams in coalfields often exist in the form of multiple layers of coal at a certain distance apart. In view of the combination of geological conditions where the upper part is an old empty area and the lower part is a thinner coal seam, at present, excavation and mining from solid deposits (traditional excavation and mining) From the perspective of coal), the thin coal seam (0-1.5 meters) with large fluctuations in the thickness of the lower coal seam is often abandoned. , which has resulted in a considerable waste of a large part of coal (coal bed methane) resources

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