Abstract
Abstract The impact of diagenetic minerals and the characteristics of pore structures on reservoir qualities has been studied separately in the past years. However, the difference in the reservoir quality with different pore structures and having same or similar content of diagenesis minerals has not been ascertained. In this study, based on the core samples derived from Chang 6 member in the Ordos basin, various tests were performed to examine the sandstone diagenesis and investigate the pore structure. The results showed that there were five diagenetic facies by diagenetic and pore structure analyses, and the best reservoir quality rocks were found to have relatively low percentage of illite, carbonate cement, pore-filling chlorite, authigenic quartz, and relatively high proportion of intergranular pores. Smectite-to-illite reaction and chemical compaction were main sources for quartz cementation at 60–120°C, and carbonate content was found to increase toward source rocks. The porosity depth trends significantly affected the diagenetic facies. The diagenetic and the pore structure pathways of various diagenetic facies were reconstructed by integrated petrographic, mineralogical, and pore system data. This study provides insights into the porosity evolution and diagenetic pathways of various diagenetic facies of tight sandstones, and the influence of diagenesis minerals and pore structures on their reservoir quality.
Highlights
The Upper Triassic Yanchang Formation is one of the most important unconventional stratigraphic units in Ordos Basin, China, where widely distributed hydrocarbons in major petroliferous members [1,2,3]
Carbon and oxygen isotope tests were based on the Peedee Belemnite (PDB) standard and the standard mean ocean water, respectively
To simulate the various types of void space, a multitype model was developed to simulate the pores between the detrital grains and the void space related to clay
Summary
The Upper Triassic Yanchang Formation is one of the most important unconventional stratigraphic units in Ordos Basin, China, where widely distributed hydrocarbons in major petroliferous members [1,2,3]. Several studies reported on depositional environment, tectonic setting, diagenesis, pore structure, and reservoir quality [4,5,6,7,8]. These studies confirmed that the Yanchang Formation had advantageous sedimentary facies for oil accumulation, and the hydrocarbon sources were distributed widely in the basin [9,10]. Diagenetic evolution, pore volume evolution, the mechanism of oil accumulation and pore structure, and their effect on reservoir quality are still being debated by scholars in different sedimentary basins [12,18,20,21]
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