A combined mining method for collapsed old goaf and lower coal seam coalbed methane

Abstract

The invention discloses a method for exploiting coal bed methane in collapse old goafs and lower coal beds in a combined manner. The method includes surveying mines, constructing horizontal wells from the ground to intermediate rock strata of the old goafs and the lower coal beds, carrying out fracturing and extracting the coal bed methane; circularly carrying out extraction stopping-decompression extraction procedures when the unit-time coal bed methane extraction quantities are reduced and reach 20%-40% of Q<1>, and continuing to extract the coal bed methane; carrying out secondary fracturing when the extraction quantities are lower than 10% of the Q<1>, constructing drainage straight wells and arranging equipment to drain the coal bed methane; carrying out carbon dioxide gas displacement when the extraction quantities are reduced and are lower than 20% of Q<2>, and draining the coal bed methane; carrying out supercritical carbon dioxide displacement when the extraction quantities are reduced again and are lower than 20% of the Q<2>, draining the coal bed methane until the extraction quantities are reduced and reach 10% of the Q<2>, and stopping extracting the coal bed methane. The method has the advantages that coal bed methane resources in the old goafs and the adjacent coal beds can be extracted together by the aid of the method, accordingly, the cost can be saved, and the coal bed methane resources can be extracted to the greatest extent.

Description

technical field [0001] The invention relates to a method for joint mining of caving old goaf and lower coal seam coal bed gas, and belongs to the technical field of coal bed gas 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%~60%, or even lower, so the above-mentioned old empty areas have considerable coalbed methane resources and gas reserves. 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 shortage of natural gas supply in m...

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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 from each other. 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, currently 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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