Abstract:
This paper is the result of oil−gas exploration engineering.
Objective The Triassic Yanchang Formation in the Gufengzhuang area of the western Ordos Basin develops low−permeability reservoir with abundant natural fractures, and few investigations have focused on the features of the fractures that are of great significance for the exploration and development of low−permeability reservoirs.
Methods In this paper, by means of fracture identification from the outcrops, cores, imaging logging, scanning electron microscope and fluid inclusion, fault activity and tectonic stress analysis, the fracture characteristics and influence on low permeability reservoirs are studied.
Results The results show that natural fractures are all developed in each Member of the Yanchang Formation, with Chang 7 being the most developed Member, followed by Chang 8 and Chang 6 Members. The fracture mainly orients in the NEE direction, secondly in the NE direction, and lastly in the NW and NWW directions. Calcite filling and obvious oil migration marks can be seen on the surfaces of the cracks. The development degree of natural fractures is closely related to the thickness of rock layers and intensity of fault activity. Comprehensive analysis of the fluid inclusions in fractures, faults and tectonic activities shows that the formation period of fractures is multi−stage, mainly in the 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 oil migration, accumulation and enrichment in low−permeability reservoirs. The development degree and formation period of natural fractures affect the reservoir forming and productivity of low−permeability reservoirs.
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