湖南省下寒武统牛蹄塘组页岩孔隙结构特征

Pore Geometry Features in Lower Cambrian Niutitang Formation Shale, Hunan Province

选取下寒武统牛蹄塘组作为湖南省页岩气勘探开发的目标层位，通过对典型页岩样品的有机碳含量、有机质成熟度、矿物形态、裂缝形态、孔隙结构特征等进行测试分析，结果表明：①从采集的65块黑色页岩样品的有机碳值分析，有机碳含量普遍较高，最高值达到17．7％。其中湘西北高值区主要在大庸、慈利、桃源和常德县等地，含量在6％～15％；湘南高值区主要分布在衡阳、郴州及江永；湘西、常德部分地区、龙山地区等热演化已达到成熟及过成熟阶段。②牛蹄塘组裂缝发育，孔隙类型有原生孔、外生孔、矿物质孔，矿物质含量高，矿物自形程度高。③牛蹄塘组储层微孔较多，且孔隙体积较大，具有较好的储气性。研究认为：湖南省下寒武统牛蹄塘组页岩储层微孔较多，且孔隙体积较大，具有较好的储气性；孔隙和喉道分布均匀，孔隙分布较均匀，有利于页岩气的排出；页岩吸附能力较强。据此得出牛蹄塘组是湖南省页岩气勘探开发的重点目标层位。

Taking the lower Cambrian Niutitang Formation as the target for shale gas exploration and exploitation in Hunan Province has carried out tests and analyses of organic carbon content, organic matter maturity, mineral form, fissure form and pore geometry for typical shale samples. The result has shown that： Analysis of organic carbon contents from 65 black shale samples has found that the contents are generally higher, the highest can be 17.7 %. The higher content areas have Dayong, Cili, Taoyuan and Changde counties in northwestern Hunan; the figure is about 6 % ~ 15 %; southern Hunan higher content areas have Hengyang, Chenzhou and Jiangyong; the thermal evolution in western Hunan, some parts in Changde area and Longshan area has reached mature and over mature stages. Fissures are well developed in Niutitang Formation, pore types have primary pore, exogenetic pore and mineral pore. The mineral con- tent and idiomorphic degree are high. Niutitang Formation reservoir has numerous micropores with larger pore volume, thus better gas storage capacity. The study has considered that the shale reservoir has better gas storage capacity, pores and pore throats uniformly distributed, thus in favor of shale gas drainage; adsorptivity of shale is strong. In view of the above, the Niutitang Formation can be the key target horizon for shale gas exploration and exploitation in Hunan Province.