Method for enhancing recovery ratio of coal-bed gas by injecting hot carbon dioxide into coal bed

Abstract

The invention provides a method for enhancing recovery ratio of coal-bed gas by injecting hot carbon dioxide into a coal bed, which comprises the following steps: 1) after implementing a coal-bed gas multi-branch horizontal well on the ground, draining water of a single well to reduce the pressure, and naturally generating gas until the yield is lower than the industrial gas flow standard; 2) draining water to reduce the pressure, and injecting hot carbon dioxide into the well, wherein the temperature of the injected hot carbon dioxide is 180-220 DEG C, and the injection pressure does not exceed 5 MPa; 3) shutting in the gas well for soaking; 4) draining water to reduce the pressure, and generating gas; 5) separating carbon dioxide and coal-bed gas from the generated gas; and 6) repeating the steps 2)-5) until the yield is lower than the industrial gas flow standard, and shutting in the well. The method provided by invention can effectively lower the coal-bed methane content and greatly enhance the coal-bed gas yield, thereby achieving the goal of industrialized development of coal-bed gas.

Description

technical field [0001] The invention belongs to the technical field of coal bed methane exploitation, and in particular relates to a method for increasing the recovery rate of coal bed methane by injecting heated carbon dioxide into a coal bed. Background technique [0002] my country's coalbed methane (coal mine gas) resources are very rich. According to the latest round of national coalbed methane resources evaluation results, the total coalbed methane resources in shallow coalbeds with a buried depth of 2000m are 36.81 trillion m 3 (equivalent to my country's onshore natural gas), mainly distributed in North China and Northwest China, the total recoverable resources of coalbed methane are about 10 trillion m 3 . The development and utilization of coalbed methane are of great significance to adjust my country's energy structure, reduce greenhouse gas emissions, improve coal mine safety production conditions, and solve the problem of coal mine gas disasters. [0003] For...

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Problems solved by technology

[0005] However, in the process of oil and gas exploitation, relying on the natural energy of the formation, the recovery rate is only about 30%.

Compared with conventional natural gas, the storage method of coalbed methane is mainly adsorption. Coalbed gas storage energy is low, permeability is poor, and mining is more difficult. At present, the national coal mine gas extraction rate is less than 20% on average

However, because the adsorption capacity of coal for nitrogen is weaker than that for methane, nitrogen cannot compete with methane for adsorption, that is, nitrogen cannot "squeeze" methane out of the matrix pores of coal, but after nitrogen is injected into the coal seam, Under isobaric conditions, by reducing the effective partial pressure of methane, the equilibrium pore pressure of adsorbed methane is reduced and desorbed

Therefore, the improvement of the recovery rate of coalbed methane by this method is also very limited.

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