Mineral characteristic of rocks and its impact on the reservoir quality of He 8 tight sandstone of Tianhuan area, Ordos Basin, China

Abstract

Tight sandstone reservoirs have low porosity, low permeability, and strong heterogeneity; therefore the reservoir quality becomes the main concern in an exploration. In this paper, the research on the effects of petrology and cementation on the quality of various types of tight sandstone reservoirs in the He 8 Member of Tianhuan area, Ordos Basin, is carried out by means of common casting thin sections, field-emission scanning electron microscopy (FESEM), and inclusion temperature analysis. Hence, this study is of great importance so as to realize potential gas reservoir explorations. The findings achieved show that quartz overgrowth, kaolinite, and illite are the main cementation that controls the quality of sandstone in the He 8 Member, while ductile rock fragment is another key factor that influences the quality. The main pore types of quartz sandstone are secondary pores, and it is worth noting that the reservoir quality is mainly controlled by quartz overgrowth as well as the development of kaolinite. The average porosity is 7.60%, while the permeability is 0.78 × 10−3 μm2. The main pore type of lithic sandstone is intercrystal pore. Additionally, the reservoir turns into tight sandstone very early due to illite cementation and the high content of ductile rock fragment. Herein, the average porosity is 4.31%, while the permeability is 0.07 × 10−3 μm2. The mineral component content of lithic quartz sandstone is between that of quartz sandstone and lithic sandstone. Early compaction and secondary pore development are the two main factors that control the reservoir quality. In this case, the average porosity is 6.64%, and the average permeability is 0.34 × 10−3 μm2. Keywords: Ordos Basin, Tight sandstone gas reservoir, Shihezi formation, Petrological components, Cement