Experimental study on the effect of supercritical CO2 on bituminous coal type Ⅰ fracture toughness
In order to study the response characteristics of bituminous coal fracture mechanics in the process of intensive coal bed methane extraction with supercritical CO2(SC CO2-ECBM),three-point bending experiments and low-temperature nitrogen adsorption experiments with different adsorption times of ScCO2 were carried out on bituminous coal samples with three kinds of bedding directions,and the change law of bituminous coal type Ⅰ fracture toughness and its pore structure under the action of ScCO2 were studied.The results showed that the type Ⅰ fracture toughness of bituminous coal deteriorated continuously with the increase of ScCO2 adsorption time,when the adsorption time was extended to 30 days,the type Ⅰ fracture toughness of bituminous coal reached the lowest point,and the fracture toughness of bituminous coal with different bedding directions from high to low is:load orthogonal bedding type,load vertical bedding type,load parallel bedding type.At the same time,with the increase of adsorption time,the changes of specific surface area and total pore volume of bituminous coal were basically consistent with the fracture toughness,but the average pore size showed the opposite trend.These microstructure changes were closely related to the fracture toughness,which led to the weakening of the fracture resistance of bituminous coal.The research results can provide theoretical guidance for predicting the change of coal reservoir physical properties in the ScCO2-ECBM process and evaluating the stability of CO2 storage.
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