Petrology, Physical Properties, and Diagenetic Characteristics of Glutenite Reservoir: An Example from the Upper Urho Formation in Zhongguai Salient, Junggar Basin, China

Abstract

Abstract The Upper Urho Formation on the northwest margin of the Junggar Basin is a key formation for oil and gas exploration. Based on the core observation, combined with the analysis of cast thin section, scanning electron microscope, energy dispersive spectrum, X-ray diffraction, fluid inclusion, and porosity-permeability test, the petrological characteristics, physical properties, diagenesis types, and their effects on the physical properties of the glutenite reservoir of Upper Urho Formation were studied systematically. The results show that the lithology of reservoir of the Upper Urho Formation in Zhongguai Salient is mainly conglomerate with a small amount of sandstone. The permeability of conglomerate is generally higher than that of sandstone, and the physical properties of granule conglomerate and fine pebble conglomerate are relatively better. The reservoir experienced complicated diagenesis, mainly including compaction, cementation, and dissolution, also including filler shrink seam and metasomatism. At present, the reservoir of Upper Urho Formation in Zhongguai Salient is mainly at the middle diagenetic stage A period and partly at the middle diagenetic stage B period. The original porosity lost by compaction is the largest, which is the fundamental reason for low porosity and low permeability of reservoir. The influence of cementation on reservoir physical properties has two sides. On the one hand, the development of cementation is the main reason for low porosity and low permeability of reservoir. On the other hand, the early cementation resists compaction to a certain extent and provides a material basis for the later dissolution. The reservoir of Upper Urho Formation in Zhongguai Salient is deeply buried and has experienced strong compaction and cementation, and the reservoir properties are poor, but the secondary pore space formed by dissolution improves the reservoir properties to some extent. The study concluded that the dense glutenite reservoirs of the Upper Urho Formation can develop relatively high-quality reservoirs on a local scale, which is of guiding significance for the exploration of the Upper Urho Formation.