祁连山冻土区天然气水合物岩性和分布特征

    Gas hydrate in the Qilian Mountain permafrost and its distribution characteristics

    • 摘要: 2008~2009年实施的“祁连山冻土区天然气水合物科学钻探工程”,已完成DK-1、DK-2、DK-3和DK-4孔的钻探任务。施工期间多次钻获天然气水合物实物样品,证实祁连山冻土区存在天然气水合物。祁连山冻土区天然气水合物主要以裂隙型和孔隙型2种状态产出。基于天然气水合物存在的10个方面的特征,认为天然气水合物赋存层位主要为中侏罗统江仓组,产于冻土层之下,主要储集于133.0~396.0m区间,储集层岩性多以粉砂岩、油页岩、泥岩和细砂岩为主,含少量中砂岩。钻孔中天然气水合物纵向分布不具有连续性,钻孔间横向分布规律不明显。岩石质量指标(RQD)统计结果显示,RQD低值区与天然气水合物储集层段具有较好的一致性,表明裂缝系统对于该区天然气水合物的分布具有重要的控制作用。

       

      Abstract: The Scientific Drilling Project of Gas Hydrate in Qilian Mountain permafrost,which covered the Juhugeng ore district of the Muli coalfield within Tianjun County, Qinghai Province, was implemented during 2008-2009. Four scientific drilling holes, i.e., DK-1, DK-2, DK-3 and DK-4 had been completed. The gas hydrate samples recovered from drillings have confirmed the existence of gas hydrate in Qilian Mountain permafrost. The drilling results show that "fracture-filling" and "pore-filling" are the main gas hydrate types existent in the permafrost. Based on a study of ten aspects of gas hydrate characteristics, the authors consider that gas hydrates mainly occur in Middle Jurassic Jiangcang Formation and hosted under the permafrost zone in the 133.0~396.0m interval. The reservoir rocks of gas hydrate are composed of siltstone, oil shale, mudstone, fine sandstone and a small amount of medium-grained sandstone. Vertical distribution of gas hydrate does not show continuity in individual holes, and lateral distribution is not apparent. Statistics of Rock Quality Designation Index(RQD)for cores show that the RQD lower value zone together with the gas hydrate reservoir segment has fairly good consistency. It is thus concluded that the fracture system plays an important role in the control of the distribution of gas hydrate in this area.

       

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