郴耒凹陷龙潭组页岩气基本地质特征

Sequence Stratigraphy and Formation Conditions of Shale Gas of Longtan Formation in Chenlei Depression

郴耒凹陷龙潭组作为湖南省重要烃源岩,一直没有得到充分重视。本文通过大量野外露头观测、剖面实测、钻孔收集,采集样品地化参数、孔隙结构特征、比表面积的实验测定分析,对该区页岩气沉积特征进行了详细研究。分析结果表明,上二叠统龙潭组可分为3个层序期次,其中层序Ⅲ沉积期随着海侵进一步扩大,整个研究区基本处于浅海陆棚环境,有利于有机质的聚集;上二叠统龙潭组黑色页岩沉积面积广、厚度大、有机碳含量高(最高可达3.45%)、成熟度高(大于1.0%以上);孔隙度变化差异大(0.7%~39.3%),平均孔径为12.5±3 nm,孔径分选好,对储层中页岩气的改造运移有利;孔隙以表面积大的微小孔为主,甲烷吸附能力强,有较好含气潜力。

The Longtan formation in Chenlei depression is important source rocks in Hunan Province, but has not received sufficient attention. In this paper, a large number of field observation, profile measurements, borehole were collected, based on experimental study of the geochemical parameters, pore structure characteristics and specific surface area foe the collected samples, we analysed the sedimentary characteristics in detail. The analysis results show that, the Upper Permian Longtan formation can be divided into three sequence stages, in which the sequence Ⅲ deposition period, with the further expansion of the transgression, the area we studied is basically in a shallow sea shelf environment, which is conducive to organic matter. The accumulation of black shale in the Upper Permian Longtan formation is characterized by wide sedimentary area, large thickness, high organic carbon content(up to 3.45%), high maturity(more than 1.0%), and large differences in porosity(0.7 %~39.3%), the average pore diameter is 12.5±3 nm, and the sorting property is good, which is beneficial to the migration after the gas-bearing shale reservoir transformation;the pore structure is mainly composed of micro-pores, large surface area and strong ability to adsorb methane, it has a good gas potential.