Geological characteristics of shale and exploration potential of continental shale gas in 7th member of Yanchang Formation, southeast Ordos Basin

Abstract: As a large-sized petroliferous basin with many shale formations such as Benxi Formation, Shanxi Formation, and 7th and 9th member of Yanchang Formation, the Ordos basin has the basic geological conditions for shale gas development. In order to evaluate the shale gas exploration potential of 7th member of Yanchang Formation, the authors investigated the geological and geochemical characteristics of 7th member shale with the aid of organic geochemical and petrologic analysis, gas quantity test and isothermal adsorption curve test. On such a basis, the preliminary evaluation of 7th member shale gas exploration potential was carried out. The results show that the shale of 7th member has moderate burial depth and thickness. With high abundance of organic matters which are mainly of Ⅰ-Ⅱ type, the maximum gas quantity could be up to 1.25-6.45 ml/g. The kerogen type and TOC of the 7th member shale are similar to those of marine shales in North America. Compared with marine shales in North America, the 7th member shale has higher content of feldspar and clay minerals but lower content of quartz and carbonate content as well as lower maturity. The shale gas exploration potential in the study area is quite promising and could serve as an important supplement of conventional exploration. The favorable targets lie in the southwest of Zhidan-Ganquan area.