涪陵地区大安寨段页岩地球化学和储集特征变化规律

The Change Rule of Geochemistry and Reservoir Characteristics of Shale in Da'anzhai Section of Fuling Area

通过对涪陵地区大安寨段页岩有机质丰度、有机质类型、岩矿物组、微观孔隙结构和储集空间分析研究,探讨了涪陵大安寨不同亚段地球化学和储集特征及变化规律,为寻找页岩气开发"甜点"提供依据。结果表明:大安寨段总有机碳质量分数w(TOC)平均为0.79%,属低有机质丰度,但大二亚段属于好的烃源岩,平面上从东北往西南方向w(TOC)呈现减小趋势。烃源岩有机质处于高成熟的湿气演化阶段。石英在纵向上分布较稳定,黄铁矿和菱铁矿的普遍存在有利于有机质的保存,硅质含量与w(TOC)呈正相关,碳酸盐含量与吸附气含量呈负相关关系。大安寨段为低孔、特低渗储层,纵向上大二亚段物性好于大一和大三亚段,页岩构造微裂缝、黏土矿物间孔隙较发育。

According to analyses of the different shale organic matter abundance,organic matter type,rock and mineral composition,microscopic pore structure and reservoir space in Da'anzhai Section of Fuling Area,the change rules of geochemistry and reservoir characteristics in the formation were discussed in order to provide an evidence for the'dessert'in shale gas development.The results showed that the average content of organic carbon in Da'anzhai Section was 0.79%,it belonged to a good source rock in the second sub-segment of Da'anzhai Section,in which w(TOC)content decreased from the northeast to the southwest on the plane.The organic matter of source rock was at the high matured moisture evolution stage.Quartz remained a certain concentration vertically,the general distribution of pyrite and siderite was favorable for the reservation of organic matters,positive correlation was found between w(TOC)and silicon content,however,carbonate content showed negative correlation with absorbed gas concentration.Reservoir in Da'anzhai Section is of low porosity and extra-low permeability,and in the second sub-segment,the physical property is better than the first and third sub-segments,pore structure are mostly developed in micro cracks of shale and between clay minerals.