A method for cooperatively extracting coalbed methane from the knife-pillar type old goaf area and the lower coal seam

Abstract

The invention discloses a method of synergetic extraction of coal bed gas of a tool post type mined area and a lower coal bed. The method comprises the steps that firstly, a mine is surveyed; after the floor failure depth is determined, a horizontal well is constructed; the coal bed gas of the mined area is extracted; when the extraction amount of the coal bed gas during unit time is decreased to 20-40% of Q1, the extraction pressure is decreased circularly so that coal bed gas extraction can be continued; when the extraction amount is decreased to 10-18% of Q1, supercritical CO2 is injected for displacement; when the extraction mount is decreased below 20% of Q1 again, oriented fracturing is conducted, a vertical discharge well is arranged on the other side of the horizontal well, and discharging equipment is arranged for conducting coal bed gas extraction; and when the extraction amount of the coal bed gas is decreased below 20% of Q2, the supercritical CO2 is used for displacement again, and extraction is stopped till the extraction amount is decreased to 10% of Q2. By the adoption of the method, coal bed gas resources close to a thin coal seam is extracted along with the coal bed gas in the tool post type mined area, and recovery of gas resources in abandoned still coal seams is achieved.

Description

technical field [0001] The invention relates to a method for cooperatively extracting coalbed methane from a knife-pillar type old goaf area and a lower coal seam, 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. Most of these old empty areas were excavated by old-style blasting with low recovery rate. Coal mining technology Most of the coal mining methods are knife column mining, and its coal recovery rate is generally 50%~60%, or even lower. Therefore, there are considerable coalbed methane resources and gas reserves in the above-mentioned old empty areas. Relevant data show that Taking Shanxi Province as an example, the coalbed me...

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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 coordinated extraction is considered

[0004] In fact, coal seams in coalfields often exist in the form of multiple layers of coal at a certain distance. Considering the combination of geological conditions where the upper part is an old empty area and the lower part is a thinner coal seam, the thickness of the lower coal seam often varies greatly from the perspective of mining. The adjacent thinner coal seam (0-1.2m) was abandoned, mostly because it was not technically feasible or technically feasible but abandoned from the perspective of economic cost, which resulted in a considerable part of the coal (coalbed methane ) massive waste of resources

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