Method for joint-mining of coalbed gas and coal

Abstract

Provided is a method for joint-mining of coalbed gas and coal. The method comprises: a well-drilling step; a fracturing and penetration step; a coalbed gas extraction step: an ignition step, and an underground gasification step. The method combines an underground coal gasification technology and a coalbed gas extraction technology, not only allows for utilization of the high temperature of underground gasification to heat a coalbed. thus increasing the permeability of a coal seam. and increasing the recovery rate of the coalbed gas, but also allows for utilization of the coalbed gas to perform the drilling and the fracturing and penetration processes, thus increasing the efficiency of underground coal gasification for mining.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a novel process for mining underground carbon-containing organic mineral reservoir, in particular to a method for joint-mining of coalbed gas and coal.BACKGROUND OF THE INVENTION[0002]Coal, as a major source of energy in China, takes up about 70% of primary energy structure and is relatively rich in the total volume. It is predicted that the total volume of coal is about 4.5 trillion tons (within 2000 m), among which the volume of coal accumulated within 600 m is just about 25%. It is estimated from the present coal mining depth (400 m) that there is at least about 80% of the predicted total volume of underground coal in China not yet developed and utilized. The deeper development of coal resource is a long-term task. With the increase of the mining depth, an associated resource, i.e., gas (also referred to as coalbed gas) also increases in content. It is assessed in terms of coalbed gas resource that there is about 36 tri...

AI Technical Summary

Benefits of technology

The inventor has found that there are similarities between coalbed gas extraction and underground coal gasification technologies. By combining these technologies, the patent aims to improve the extraction rate of coalbed gas, adjust the gas composition for better production of methane, reduce production costs, and capture and utilize CO2. The invention also aims to use high-temperature generated by underground coal gasification to heat a coal seam for improved gasification and increased permeability of the coal seam. The fracturing technology is also combined to improve the permeability of the coal seam and subsequent gasification process. The use of gaseous, liquid, or supercritical CO2 as the fracturing medium is preferred. Overall, the invention allows for efficient utilization of coalbed gas and gasification of underground coal.

Problems solved by technology

Except for the Qinshui basin and the eastern margin of Ordos basin, it is difficult to realize scale and industrial development in other areas at present.

Furthermore, as there are many high-gas mines or coal & gas outburst mines, with the increase of the mining depth, both the geostress and the gas pressure further increase and the gas drainage becomes more difficult.

Nevertheless, with the increase of the mining depth, the geological environment becomes more complicated that the increased geostress, water influx and ground temperature cause the increase of sudden engineering disasters and serious accidents, for example, rock blast hazards, gas explosion, aggravated strata pressure behaviors, large surrounding rock deformation, rheologic phenomena, increase of ground temperature and the like, which cause great threats to the safe and efficient extraction of deep resources.

However, the existing coal underground technology only concerns the gasification of coal seams.

With the increase of the mining depth of coal, the content of coalbed gas will increase quickly and it is inevitable to have some problems in the extraction of coalbed gas, specifically including: (1) for a coal seam rich in coalbed gas, there may be problems such as safety challenge and waste of resources if gasification is directly implemented to the coal seam; (2) if the conventional coalbed gas mining means is employed without in combination with the underground gasification technology, the subsequent implementation of the underground gasification may cause overlapped functions such as drilling and increased investment cost; (3) injection of CO2 into a coal seam may increase the extraction ratio of CH4 from the coal seam, however, the yield of coalbed gas, which may be increased only in the initial stage of the extraction of coalbed gas, will drop quickly in the later stage as the fracture is likely to close; and (4) as the intermediate of the gasification process and one component of resulting products, CO2, participating in a series of redox reactions, is an important component (about 15-60%) of the output gas and an important factor influencing the calorific value and content of active components of the gas; however, the recycling of CO2 is not taken into consideration in the existing processes.

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