A method for the joint mining of coalbed methane in the old goaf area and the lower coal seam

Abstract

The invention discloses a method for combined mining of coal seam gas of a cutter column type old goaf and a lower coal seam. The method comprises the steps of first surveying a mine, constructing a horizontal well from the ground to the position which is 5-20 m under an old goaf base plate terrane, and performing coal seam gas extraction; when the coal seam gas extraction amount drops to 20%-40% of an initial value Q1, performing circulation of the extraction stopping-depressurization and extraction process; when the extraction amount drops to below 20% of Q1, performing fracturing of a coal and rock layer, performing horizontal well vertical section extension, installing a discharge and mining device, performing coal seam gas extraction, recording the extraction amount at the time as Q2; when the extraction amount drops to below 20% of Q2, injecting carbon dioxide gas for displacement, extracting the coal seam gas once again, and stopping the extraction until the coal seam gas extraction amount drops to 3 m3 / min. According to the method, the problems that an original extraction well drilling and old goaf contact area is limited and an extraction range is limited are solved, and the problems of high construction difficulty and low pore forming rate when the drilling construction is performed above a fissure zone are solved.

Description

technical field [0001] The invention relates to a method for combined mining of coalbed methane in a knife-pillar type old goaf area and a lower coal seam, and belongs to the technical field of coalbed methane mining. 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. Most of these old empty areas were excavated by old-style blasting with low recovery rate. Coal mining 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 an example of old empty areas Coalbed methane resources are about 3 billion cubic meters. Gas is a kind of clean en...

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Problems solved by technology

[0003] At present, the gas drainage of the old goaf is mainly aimed at the drainage of the old goaf on a single working face. The method is to drill the ground in the upper fracture zone of the old goaf to extract the gas from the old goaf. During the drilling construction process, the construction is difficult, the accident rate is high, and the hole formation rate is low

Moreover, a surface wellbore can only be used for drainage of an old empty area, and the output of the extracted coalbed methane is low and the cost is high

Chinese patent CN105114038A discloses a method relying on supercritical CO 2 A method for jet fracturing the coal pillars adjacent to the old goaf to extract gas from two old goats at the same level; Chinese patent CN104696006A discloses a method for penetrating the residual coal pillars of the multi-layer old goaf to extract the residual coalbed gas in the multi-layer old goaf method; the above methods are for the case of vertical well drainage of gas in multiple old empty areas; the above patents have the problems of small contact surface between the vertical drilling on the ground and the coalbed methane reservoir, limited range of extraction, etc. Coalbed methane resources remain in the empty area, but the coalbed methane resources in the old empty area and the adjacent unexploited coalbed methane resources are not coordinated, and joint development and coordinated drainage are considered

[0004] 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 ore deposits (traditional coal mining ) is often abandoned for the thin coal seam (0-1.5 meters) with a large change in the thickness of the lower coal seam. It has caused a considerable waste of a large part of coal (coal bed methane) resources

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