1.School of Civil Engineering, Hebei University of Science and Technology, Shijiazhuang , China; 2.Department of Mining and Design, Tiandi Science and Technology Company Limited, Beijing , China;3.School of Mechanics and Engineering,Liaoning Technical University, Fuxin , China

为确定贫水煤层钻孔注水-注液氮增透煤层技术方法的设计技术参数，建立了钻孔注水润湿数学模型，提出了注水时间和润湿半径的计算公式；基于热力学理论，建立了钻孔煤注液氮冷冻润湿数学模型，给出了注液氮冷冻煤层的温度场演化解析解，给出了煤层注液氮冷裂半径计算公式。利用建立的模型分析了影响煤层工作面钻孔注水-注液氮技术方法效果的因素和规律，结果表明：注水压力8 MPa、储层压力1.1 MPa下，注水8.7 h，注水润湿半径可达1.2 m；液氮冷冻时间增加，冷裂半径增大，但增长速率减小；液氮冷冻240 h后，再增加冷冻时间，冷裂半径基本不变；液氮冷冻180 h，冷冻半径为1.2 m，说明煤层注水可提高液氮冷裂效果，有且于防治冲击地压和煤与瓦斯突出灾害。

In order to determine the design parameters of the cool fracturing and permeability improved seam with the water injection-liquid nitrogen injection in low water-content coal seam.A mathematical moistening model of the borehole water injection was established and a calculation formula of the water injection time and the moistened radius was provided. Based on the thermodynamics theory, a freezing mathematical model with a coal borehole liquid nitrogen injection was established. An analytic solution of the temperature filed evolution in the liquid nitrogen freezing seam was provided and the calculation formula of the fracturing and permeability enhancing radius by the liquid nitrogen injection was provided. The model established was applied to analyze the fracturing and permeability enhancing effect of the borehole water injection-liquid nitrogen injection. The results showed that when the water injection pressure was 8 MPa, with the reservoir pressure of 1.1 MPa,the water injection time was 8.7 h,and the moistened radius of the water injection could be 1.2 m. With the liquid nitrogen freezing time increasing, the freezing fracturing and permeability enhancing radius would be increased and but the increasing rate would be reduced. After 240 h of the liquid nitrogen freezing, even if the freezing time was increased and the freezing fracturing radius would not be varied basically.After liquid cooling for 180 h,the freezing radius was about 1.2 m.The research would help the design of the water injection-liquid nitrogen injection into coal seam to enhance the permeability.