Fracture characteristics of Triassic Yanchang Formation in Gufengzhuang Area, Western Ordos Basin, and its control on low permeability reservoirs

Objective The Triassic Yanchang Formation in Gufengzhuang area belongs to the low permeability reservoir with natural fractures, but in the past, there were few studies on its fracture characteristics. Therefore, it is of great significance for the exploration and development of low permeability reservoirs to study the characteristics and formation period of natural fractures.Methods In this paper, by means of outcrop, core, imaging logging, scanning electron microscope, fluid inclusion, fault activity and tectonic stress, the characteristics, formation stages and causes of natural fractures in Yanchang Formation in Gufengzhuang area are studied, and the influence of fractures on low permeability reservoirs is discussed.Results The research shows that natural fractures are all developed in each Member of Yanchang Formation, with Chang 7 being the most developed Member, followed by Chang 8 and Chang 6 Members. The fracture strike is mainly in NEE direction, followed by NE direction, and a few NW and NWW directions. Calcite filling and obvious oil marks can be seen on the surface of the crack. Natural fractures are closely related to the thickness of rock strata, fault activity and so on. Comprehensive analysis of fracture inclusions, faults and tectonic activities shows that the formation period of fractures is multi-stage, mainly in Yanshanian and Himalayan periods.Conclusions The development of natural fractures has improved the porosity and permeability and reservoir space of low-permeability reservoirs in the study area, and provided favorable conditions for the near source, short-distance migration, reservoir accumulation and enrichment of low-permeability reservoirs. The development degree and formation period of natural fractures affect the reservoir formation and productivity of low-permeability reservoirs.