Shale gas geological characteristics and exploration potential of lower permian Taiyuan Formation in Linxing Area

Abstract

In order to reveal the geological characteristics and exploration potential of shale gas in Taiyuan Formation in Linxing area, eastern Ordos Basin, taking organic-rich mud shale as the research object, the distribution rules of mud shale cumulative thickness and single layer maximum thickness were found out based on field drilling and logging geological data. The organic geochemistry, physical properties, X-ray diffraction and isothermal adsorption experiments were carried out for shales, and the accumulation conditions and exploration potential of shale gas were studied. The results show that the distribution of mud shale in Taiyuan Formation in Linxing area is stable, the cumulative thickness is 10-50 m, the average thickness is 30 m, and the maximum thickness of single layer is 5−25 m. The Organic matter abundance is high, TOC content is 0.26%-12%, with an average value of 3.81%. Organic matter type is mainly II and III kerogen, and peak temperature of pyrolysis is between 443 ℃ and 576 ℃. The thermal maturity of shale near zijinshan rock mass increases obviously. The pores and fissures of nanoscale–micron scale are developed in shales. The pores of organic matter are mostly round, oval and honeycomb. Other types of pores such as the dissolution pores of clastic minerals are developed. The microcracks in mineral particles, the edge of clastic particles and the internal organic matter are relatively developed. The content of brittle minerals such as quartz and feldspar are 45%-65%, and the content of clay minerals is 28%-62%, which are mostly non-expansive minerals. The variation range of gas content in shale is large, ranging from 0.08 m3/t to 7.3 m3/t, with an average value of 1.41 m3/t. There is a significant positive correlation between gas content and TOC. Considering the factors such as shale thickness, organic matter abundance and thermal evolution degree, the central and northern shale in Linxing area has large thickness and high TOC content. The mineral assemblage is conducive to reservoir reconstruction and is a favorable area for shale gas exploration. Compared with marine shale gas exploration area in Sichuan Basin, Taiyuan Formation shale in Linxing area has the characteristics of shallow burial depth and low gas content. In the exploration and development of oil and gas resources, it is necessary to pay attention to the joint exploration and development of sandstone gas and coalbed methane in coal measure strata.

Keywords

• ordos basin
• geological characteristics
• shale gas
• marine-continental transitional facies
• exploration potential