扬子地区下寒武统与下志留统黑色页岩孔隙度与有机碳关系差异性及原因

下寒武统牛蹄塘组与下志留统龙马溪组页岩是扬子地区发育的两套富有机质黑色页岩，由于其分布面积广、厚度大、有机质丰度高而成为页岩气勘探的重点层位.然而牛蹄塘组孔隙度表现出了与龙马溪组截然不同的规律，两套页岩的孔隙结构、有机碳含量、密度也存在显著差异.结合测井、埋深（上覆压力）、孔隙度、有机碳及成熟度测试数据进行了对比分析.结果显示，牛蹄塘组过高的有机碳含量和热演化程度严重影响了页岩的孔隙结构，使有机质碳化，有机质孔发生坍塌和充填；牛蹄塘组埋深大、上覆压力也大，导致无机孔被压实，因此其总孔隙度明显小于龙马溪组. 

Relationship Differences and Causes between Porosity and Organic Carbon in Black Shales of the Lower Cambrian and the Lower Silurian in Yangtze Area

The black shales in lower Cambrian Niutitang and lower Silurian Longmaxi develop well in Yangtze area, which are the key horizons for shale gas exploration because of its wide distribution, large thickness, high organic matter abundance. The porosity of Niutitang Formation shows a distinct difference from Longmaxi Formation. There are also significant differences in the pore structure, organic carbon content and density of the two sets of shales. Based on the logging data, buried depth (overlying pressure), porosity, organic carbon and maturity test data, comparative analysis is conducted. Results show that pore structure has been affected by the high degree of thermal evolution and organic carbon of Niutitang Formation. Organic matter is carbonized, organic porosity is collapsed and filled. The depth of Niutitang Formation is deep and the overburden pressure is also large, causing the inorganic porosity to be compacted. These factors make the porosity of Niutitang Formation obviously less than Longmaxi Formation.