Formation conditions and exploration potential of marine shale gas in the Ordovician Wulalike Formation in the western margin of Ordos Basin

Key words: 
• marine shale gas /
• formation conditions /
• exploration potential /
• Wulalike Formation /
• Western margin of Ordos Basin

Abstract: Based on organic geochemistry, XRD, FE-SEM, combined with the regional structure and sedimentary evolution characteristics, through the comprehensive analysis of the distribution and development characteristics, reservoir characteristics and preservation conditions of shale in the Wulalike Formation (or Pingliang Formation), the formation geological conditions and exploration potential of shale gas in the Ordovician Wulalike Formation (or Pingliang Formation) in the western margin of the Ordos Basin have been systematically studied. The stratigraphic thickness of the Wulalike Formation(or Pingliang Formation) in the western margin of the Ordos Basin varies greatly, with the thickness of about 10 ~ 80m in the north and central parts and more than 1000m in the south part. The TOC is between 0.10% and 1.40%, and the organic matter type is mainly type I (sapropelic type). The shale in the north and middle part was deeply buried , with a high degree of thermal evolution, and is in the gas generation stage, while the southern part is affected by the thrust of the western margin, which generates both oil and gas. Various types of pores are developed in the Wulalike shale, including intergranular pores, intragranular pores, microfractures and a small amount of organic matter pores. Compared with the Longmaxi shales, although the overall porosity of the Wulalike shale is low, the content of brittle mineral is high, microfractures are relatively developed, and its permeability is better than that of the Longmaxi shales. In the western margin of the basin, the fault in Wulalike Formation is generally undeveloped, and the underlying Kelimoli Formation is mainly limestone and the overlying Lashizhong Formation is mainly shale and micrite limestone, which have good sealing capability and favorable for the enrichment of shale gas. From the stratigraphic distribution, gas generation potential, fracturing ability, preservation conditions and other parameters of the Wulalike Formation, it is believed that the south of Tiekesumao in the north part of the western margin and the west of Gufengzhuang in the middle part have good marine shale gas exploration potential.