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The Upper Permian Changhsing Formation is one of the most important gas-bearing formations in the Eastern Sichuan Basin. Nonetheless, the primary factors controlling the reef-shoal gas reservoirs of different regions are diverse. Clarifying the controlling factors for the formation of intra-platform reef-shoal reservoirs will promote the exploration and development process of the Changhsing Formation. By using outcrop data, core observation, thin section identification, scanning electron microscope analysis, physical property study, and logging interpretation, this paper analyse the characteristics and factors controlling the reef-shoal reservoir in Dianjiang area of the Eastern Sichuan Basin. The results show that the reef cap and reef base microfacies fine-to-medium crystalline dolomite reservoir have the best physical properties, and the reservoir spaces are primarily composed of intercrystalline pores, intercrystalline solution pores, karst caves, and fractures. The main lithology of reservoir formation is reef-shoal facies. The results for the carbon and oxygen isotopes show that dolomites of different particle sizes are formed in three environments. Affected by regression in the late Changhsingian Age, the reef-shoal of the Changhsing Formation were subaerially exposed to meteoric water diagenesis environments, resulting in the highly dispersed particles in rocks that formed a honeycomb karst system, which greatly improved the physical properties of the reservoirs. After reflux dolomitization, the honeycomb karst system was well preserved due to strong resistance to pressure and dissolution of dolomite. Therefore, dolomitization in the Changhsing formation contributed to reservoir porosity. Later, tectonic fracturing has adjusted and modified the reef-shoal reservoir. In summary, penecontemporaneous karstification was the key to the formation of the reef-shoal reservoir. [ABSTRACT FROM AUTHOR]

Detrital zircon grains were collected from six samples of sedimentary rock from the Middle Jurassic Zhiluo Formation in the western Ordos Basin of China. U–Pb isotopic geochronology data were measured and used to assess the provenance and directions of sediment transport of these grains. Five age populations were recognised amongst the U–Pb age spectra: 2700–2034 Ma, 1999–1426 Ma, 1296–636 Ma, 556–323 Ma, and 315–207 Ma. Each of these groups corresponds to one or several potential sediment sources around the western Ordos Basin. Based on these data and the spatial distribution of the six collected samples, we interpret that the material of the Middle Jurassic Zhiluo Formation in the western Ordos Basin was mainly derived from the northern margin of the North China Craton and the Qilian Orogenic Belt. In addition, the eastern margin of the Alxa Block contributed as a sediment source for certain regions. Detritus was transported via two major supply directions to the western Ordos Basin, and this basin was connected to the Hexi Corridor during the Middle Jurassic. In conclusion, our results are consistent with the closure of Palaeo-ocean and the formation of the orogenic belt. [ABSTRACT FROM AUTHOR]