Extraction method for coal bed gas in composite old mined-out area formed through lower tool post method

Abstract

The invention discloses an extraction method for coal bed gas in a composite old mined-out area formed through a lower tool post method. The method comprises the steps that a horizontal well is constructed at a middle rock layer between an upper old mined-out area and a lower old mined-out area, extraction is carried out, and the coal bed gas extraction amount within the unit time is recorded as Q1; when the extraction amount is decreased to be below 10-20% of Q1, fracturing is carried out for extraction again, and the coil bed gas extraction amount is recorded as Q2; when the extraction amount is decreased to be below 10-20% of Q2, fracturing is carried out again, and the extraction amount is recorded as Q3; when the extraction amount is decreased again to be 10-20% of Q3, carbon dioxide displacement is carried out; then, extraction is carried out again and not stopped until the extraction amount is decreased to 6 m<3> / min. By means of the method, the problems that only a ground vertical well drilling method is adopted for extracting the old mined-out area in the prior art, the effect contact area of an extraction drilling well and an old mined-out area storage layer is small, and the extraction range is limited are solved; sources near the upper old mined-out area coal bed layer are extracted together with lower old mined-out coal bed gas, and the cost is saved.

Description

technical field [0001] The invention relates to a method for extracting coalbed methane in a composite old goaf area formed by mining with a lower knife column method, 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 ...

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Problems solved by technology

[0006] In view of the above-mentioned problems, the present invention proposes a compound old void area formed by the upper caving method and the lower knife column method mining from the perspective of maximizing the exploitation of coalbed methane resources while considering the economic cost, and the upper and lower sections are formed by the knife column method mining. Combined with the method of simultaneous extraction of coalbed methane in old empty areas, it solves the phenomenon of a large amount of waste of resources caused by the abandonment of existing coalbed methane resources

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