深部煤层吸附行为及含气量预测模型

Adsorption Behavior and Abundance Predication Model of Deep Coalbed Methane

深部煤层含气量变化特征与浅部有所不同，实测数据极少，需要研发新的方法对其进行预测。本文以鄂尔多斯盆地东部主煤层为对象，分析了影响吸附常数的地质因素。基于煤样在不同温度条件下的高压甲烷等温吸附实验，采用主成分分析方法，探讨了深部煤层含气量预测方法。选取温度、镜质组反射率、水分含量、灰分产率、镜质组含量、惰质组含量6个因素进行主成分分析，提取出3个主成分，获得吸附常数与3个主成分之间的多元一次函数关系，根据朗格缪尔方程并结合含气饱和度建立了深部煤层含气量预测模型。采用这一模型，对鄂尔多斯盆地东部深部煤层进行了实例研究。结果表明，煤层含气量随埋深的变化存在一个临界深度，临界深度大致在750～1200m之间，随煤级及地层温度和地层压力而呈规律性变化。在临界深度以浅，煤层含气量随埋深的增大而增高；超过临界深度后，含气量随埋深的增大而减低。

Occurrence of coalbed methane （CBM） content in deep coal seam with rare measured data is different from that in shallow seam, and a new method is demanded to predicte deep CBM content. Based on the isothermal methane adsorption experiments of coal samples under various temperature and pressure, geological controls of coal adsorption constants was discussed and a prediting method for deep CBM content was established with principal component analysis in a case of the main coal seam in the eastern Ordos Basin. Three principal components were extracted from the six factors including temperature, maximum vitrinite reflectance, moisture content, ash yield, inertinite group and vitrinite group contents. A predicting model of coal adsorption constants was suggested. A predicating model of deep CBM content was set up based on the Langmuir equation combining with gas saturation. Using the models, deep CBM content in the eastern Ordos Basin was predicted. It was shown that there is a critical depth in the correlation of CBM content to depth of coal seam. The critical depth ranges roughly from 750 m to 1200 m, and changes with the coal rank, pressure and temperature. CBM content enhances with increasing the depth when the burial depth is shallower than the critical depth, and reduces with increasing the depth when the burial depth is deeper than the critical depth.