A coalbed methane extraction method for complex old goaf areas formed by lower caving mining

Abstract

The invention discloses an extraction method for mining formed composite old mined-out area coalbed methane through a lower caving method. The method includes the steps that coalbed methane extraction is conducted by constructing a horizontal well at the position 1-5 meters above a lower goaf fissure zone; when the extraction amount of the coalbed methane is dropped to 10-20% of Q, segmented crushing is conducted, extraction is conducted on the goaf coalbed methane again, and when the extraction amount of the coalbed methane is dropped to 10-20% of Q again, supercritical carbon dioxide is injected to drive and replace the coalbed methane; extraction is conducted again till the extraction amount is dropped to 6 m<3> / min, and extraction is stopped. By means of the method, the problems that when a ground vertical drilling well is separately used to conduct extraction on a goaf originally, the effective contact area between the extraction drilling well and a goaf reservoir is small, and the extraction range is limited are solved; while the coalbed methane of the goaf on the lower layer is extracted, the coalbed methane resource close to the upper portion of the goaf is also extracted, and cost is saved; meanwhile, the horizontal well is located in the rock stratum, and therefore shaft collapse and blocking of the drilling well in a coal seam are avoided.

Description

technical field

[0001] The invention relates to a method for extracting coalbed methane in a composite old goaf formed by lower caving mining, and belongs to the technical field of extracting coalbed methane. 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 energy, and...

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