Diagenesis and its controls on reservoir properties and hydrocarbon potential in tight sandstone: a case study from the Upper Triassic Chang 7 oil group of Yanchang Formation, Ordos Basin, China

The sandstones in the Chang 7 oil group are typically recognized as unconventional tight clastic rock reservoirs. These sandstones are fine-grained and have low permeability and porosity and low textural and compositional maturity. In the present study, optical microscopy, SEM, cathodoluminescence, and wireline log, core analysis permeability and porosity, and production test data are applied to analyze the diagenesis and its controls on hydrocarbon potential in these tight sandstones. The results indicate that the sedimentary environment and diagenesis controlled the physical properties of the reservoir. Three different diagenesis processes were likely occurred in these sandstones. Early strong carbonate cementation is a key factor for other subsequent alterations and the final reservoir properties. The sandstones dominated by dissolution and compaction have more capacity for hydrocarbon preservation.