上覆地层对煤层气含量的控制机理

The Controlling Mechanism of Overlying Strata on CBM Content

在众多的煤层气含量控制因素中,上覆地层特征对煤层气含量起着至关重要的控制作用。根据煤田勘探和煤层气勘探积累的大量资料,将其控制机理分为两种。其一,上覆有效地层的岩性、裂隙发育程度决定着排替压力,致密的、高排替压力的厚层泥岩、砂质泥岩等对煤层气保存有利。其二,地质历史时期煤层埋深最浅时的储层温度压力决定了煤层气理论含气量。在一定深度范围内,上覆地层有效厚度越薄,储层压力越低,理论含气量越低,煤层气散失越严重。这一结论为大量含煤盆地、矿区或井田煤层气含量分布所证实。

There are many controlling factors on coalbed methane content, of which the overlying strata control the regional distribution of coalbed methane content. The investigation on the characteristics of overlying strata is the foundation of coalbed methane accumulation prediction. Based on plentiful data obtained from exploration for coal and coalbed methane, the controlling mechanism of the overlying strata on gas content can be divided into two parts： the lithology and fractures of the overlying strata dominate displacement pressure, and the compacted and thick strata which have high displacement pressure is favorable to preservation of coalbed methane; the temperature and pressure when the burial depth of coal seam was the shallowest during the geologic history controlled the theoretical gas content. Within a certain burial depth, the thinner is the overburdeu strata, the lower is the rese;cvoir pressure, the lower is the theoretical gas content, and the more the dissipation of eoalbed methane. The conclusion had been confirmed by the distribution of coalbed methane content in many coal-beating basins, coalfields, and coal mines.