沉积体系与煤层气储盖特征之关系探讨

RELATIONSHIP BETWEEN DEPOSITIONAL SYSTEMS AND CHARACTERISTICS OF COALBED GAS RESERVOIR AND ITS CAPROCK

沉积作用通过聚煤特征、含煤岩系的岩性、岩相组成及其空间组合在一定程度上控制着煤层气的保存条件 ,我国存在具有一定时空展布规律的 6种煤储层 /盖层基本条件 :浅海 -障壁海岸体系对煤储层的封盖能力较强 ;浅海 -无障壁海岸体系多数导致对煤层气的封盖能力变差 ;近海三角洲体系的封盖沉积条件一般较好 ;河流体系如果沉积单元结构完整则封盖条件较好 ,若煤储层直接顶板为河道相或决口扇相粗 -中粒砂岩则对煤层气的保存十分不利 ;湖泊体系对煤储层的封盖能力较强 ;冲积扇体系的封盖能力总体上极差。沉积体系与煤层气储盖特征以及煤储层含气性之间的这种耦合关系 ,不仅在华南、华北聚煤区呈现出区域展布规律 ,而且对于特定矿区煤储层含气量分布具有控制作用 ,是煤储层含气性预测的重要参考依据。

The six fundamental conditions of the coal reservoir and its caprock assemblages with some regular occurrence in space time exist in China. The sealing capability of the shallow sea and barrier island system to coal reservoir is relatively high, that of the shallow sea and plane coast system becomes mostly poor, that of the littoral delta system is commonly good, that of the fluvial system is relatively good if the sedimentary unit is complete or very poor if the coal reservoir is directly overlaid by the channel or splay medium to coarse grained sandstone, that of the lake system is sufficiently high, and that of the alluvial fan system is generally very poor. The relationship between the sedimentation and coalbed roof condition not only occurs regionally in the North and South China, but also controls the distribution of the coalbed methane content in some given coalfields or coal mining districts, which provide the important reference for the prediction of the gas bearing coalbeds.