The Study Of The Shale Features Of Wufeng Formation-Longmaxi Formation In Southwest Of Sichuan Basin

As one of the black shale developed formations, the Upper Ordovician Wufeng Formation-- Lower Silurian Longmaxi Formation is the most advantageous area for shale gas exploration in the Upper Yangtze Platform. Predecessors have done a lot of research about sedimentary characteristics and reservoir characteristics of Wufeng Formation-- Longmaxi Formation in Southern and Southwest Sichuan Basin. But it is relatively weak in Southwest Sichuan Basin. This article is based on experimental analysis of a large number of ground and upground samples Leibo section and Well 205, and studies the sedimentary characteristics, parameter characteristics of shale gas. Based on these conversations, the article discusses the controlling factors of reservoir nanoporosity development and the controlling factors of gas adsorption. At last, Compared with the shale of Jiaoshiba area that is the shale gas production reservoir, evaluating the exploration potential of research area. The study show that:Wufeng Formation-- Longmaxi Formation shale mainly contains two kinds of sedimentary components: rigid components and plastic components; It is composed of organic-rich black mudstone/shale, silty mudstone/shale, argillaceous siltstone and micrite. The SiO2 of silicon-rich mudstone/shale come from silica biological. In the study area, the Wufeng Formation-- Longmaxi Formation was mainly deposited in deep-water shelf and shallow shelf, organic-rich black mudstone/shale and silty mudstone/shale are mainly developed in deep-water shelf and anoxic environment. In contrast, argillaceous siltstone, micrite and a little silty mudstone/shale deposited in shallow shelf and anoxic environment. Deep-water shallow is in favor of black shale development.In the study area, the shale of the Wufeng-Longmaxi Formation dominated by I-II1 types of kerogen; In the longitudinal direction, the TOC of lower member of Wufeng Formation and Longmaxi Fongmation is generally higher than 2%; In the plane, the shale that TOC>2% is most developed in Changni-Yibin; Thermal evolution of organic matter is in the high maturity- over mature stage.In the study area,the quartz content of lower member of Wufeng Formation and Longmaxi Fongmation is higher than thatThe porosity of the lower member of the Wufeng-Longmaxi Formation black shale ranged from 2% to 10%. There are three types pore: organic pore, inorganic pore and fracture. They have tow shapes, one is ink bottle type pores and the other is parallel slits inside wall. The latter has more pore volume and specific surface area than the former. Microporous and mesoporous provide the main pore volume and pore surface area, but macropores contributed little.The pore development of shale gas reservoir is controlled by organic matter, mineral composition, diagenesis and so on. Organic matter is mainly controlled the development of microporous and mesoporous. Clay minerals to some extent is controlled the development of mesoporous. And the effect of carbonate is not obvious. As for quartz, the effect depends on the source of quartz. Biogenic silica is in favor of nanoporous development of shale, but terrigenous quartz is unfavorable for nanoporous development of shale. Diagenetic evolution of compaction, cementation and recrystallization is not conducive to the formation of pores, but dissolution and transformation of clay minerals in favor of the development of porosity. It mainly controlled the development of macropores.The volume of adsorbed gas shows positive correlation with pressure and negative correlation with temperature. Pore structure and TOC control the volume of adsorbed gas, the more TOC and more nanopores, the more volume of adsorbed gas.The shale characteristics of study area is similar to the reservoir of shale gas in Jiaoshiba area, It has good exploration potential.