湘西北下古生界海相页岩储层特征与含气性分析

基于野外地质和钻井资料，结合相关实验测试结果，对湘西北地区下古生界海相页岩储层特征进行了深入研究，并探讨了页岩甲烷含气性及影响因素。结果表明：牛蹄塘组黑色页岩以深水陆棚斜坡相沉积为主，厚度范围为50~250 m；龙马溪组为闭塞海湾沉积，底部黑色页岩发育。两组页岩有机质类型均属于Ⅰ型，有机碳含量平均为3.57%和1.16%，热演化程度较高，平均达2.61%和2.08%。受沉积环境和成岩作用影响，两组页岩均具有高石英、低黏土、少量碳酸盐矿物的组成特征。页岩储集空间可划分为3大类：矿物基质孔、有机质孔、微裂缝。受有机质和黏土矿物等因素影响，页岩内部孔隙结构参数各不同，但主体上孔径小于50 nm的微孔和中孔提供了大部分比表面积和孔体积，为气体存储主要场所。牛蹄塘组页岩甲烷最大吸附量平均为1.98 cm3/g；龙马溪组页岩甲烷最大吸附量较低，为1.16 cm3/g。其中有机质与黏土矿物对页岩甲烷吸附量均有一定的贡献，而过高的成熟度和含水量可导致页岩吸附能力下降。

Reservoir characteristics and gas-bearing capacity of the Lower Palaeozoic marine shales in Northwestern Hunan

Based on field geological and drilling data, the reservoir characteristics and gas bearing affecting factors of the Lower Paleozoic marine shale in the Northwestern Hunan were studied through the related experimental results. The results show as follows. The black shale of Niutitang Formation is formed in the deep water continental shelf margin slope sedimentary environment, with thickness of 50250 m. The Longmaxi Formation is stranded bay deposit and the black shale is mainly developed at the bottom. The organic matter type in both formations is predominantly sapropelic. The Total Organic Carbon (TOC) content of the black shale from the two formations is averaged at 3.57% and 1.16%, respectively, with high equivalent vitrinite reflectance (Ro) of 2.61% and 2.08%, respectively. Black shale in both formations are characterized by high content of quartz, low content of clay minerals, and small amounts of carbonate minerals which is controlled by sedimentation and diagenesis. Shale reservoir spaces can be divided into three broad categories: mineral matrix pore, organic pore and microfracture. Influenced by factors such as organic matter and clay minerals, the pore structure parameters of shales are different. The micropores (< 2 nm) and mesopores (250 nm) are mainly developed, which have massive contribution to the pore specific surface area and pore volume where the shale gas adsorption mainly occur. The average methane adsorption capacities of shales in the Niutitang Formation are 1.98 cm3/g, a little higher than that of shales in the Longmaxi Formation (1.16 cm3/g).The organic matter and clay minerals both play a role in the methane adsorption, and high maturity and water content can reduce shale adsorption capacity.