不同煤阶深煤层含气量差异及其变化规律

基于Langmuir 等温吸附方程式，开展不同煤阶不同温压条件下等温吸附模拟实验，实验结果表明：在煤岩镜质组反 射率Ro<3.0%时，Langmuir 等温吸附曲线随煤阶、温度、压力升高表现出明显的分带性。随着煤阶的升高，煤吸附能力逐 渐增强。温度小于55℃时不同煤阶Langmuir 体积受温度影响较小，之后影响逐渐增大。低煤阶在12 MPa、中高煤阶在 15 MPa以前随压力增加Langmuir 体积增大明显。根据实测含气量外推法结合高温高压等温吸附实验建立了深煤层含气量数 学模型，显示煤层含气量随埋深呈现快速增加—缓慢增加—不增加—缓慢减小的变化规律，其中低煤阶临界深度介 于1400~1700 m，中高煤阶临界深度介于1500~1800 m。该含气量数学模型对预测深部煤层含气量变化规律及煤层气资源评 价提供基础依据。

Variations of Gas Content in Deep Coalbeds of Different Coal Ranks

Based on Langmuir isothermal adsorption equation, we carried out isothermal adsorption simulation experiments under high temperatures and high pressures for different coal ranks. The results show that when vitrinite reflectance Ro less than 3.0%, the curves of Langmuir isothermal equation appear in a zone with the rising coal rank, temperature, and pressure. The adsorption capacity is enhanced with the rising coal ranks. The Langmuir volume of different coal ranks was less affected when the temperature was lower than 55℃, while more for temperatures above 55℃. The Langmuir volume increased obviously with the rising pressures when the low rank coal under 12 MPa and mid-high rank coal below 15 MPa. We established a mathematical model for determining gas content of deep coalbed based on the measured gas content extrapolation method and the high temperature and high pressure isothermal adsorption experiments. The modeled gas content shows variable outcomes, i.e., fast increase, slow increase, no increase, and slow decrease with the buried depth. The critical depth of low rank coal is located between 1400 m to 1700 m while the mid-high rank coal is located between 1500 m and 1800 m. The mathematical model of gas content provides a basis for forecasting gas content and evaluating deep coalbed methane resources.