Diagenetic Controls of Sandstone Densification in the Lower Cretaceous Laiyang Group, Lingshan Island, Eastern China

The Lower Cretaceous Laiyang Group on Lingshan Island contains typical gas source and clastic reservoir rocks. The densification mechanism of clastic rock and its diagenetic connection have not been systematically studied, which significantly increases the risk associated with hydrocarbon exploration in eastern China. A comprehensive study was conducted on core samples obtained from the Scientific Drilling Borehole LK-1, utilizing core data in conjunction with a range of techniques, including microscopic observation, X-ray diffraction, physical property measurements, and low-temperature nitrogen adsorption. The results indicate that the sandstones are primarily composed of feldspathic litharenite, exhibiting a poorly to moderately sorted texture and a fine-to-medium grain size. The reservoir quality is quite poor, characterized by extremely low porosity and permeability. The reservoir space of tight sandstones is constituted by three main types of pores: residual primary pores, secondary dissolution pores, and intercrystalline pores. Tight sandstone reservoirs experienced notable diagenetic alteration during burial, with calcite, dolomite, quartz, and clay cements identified as the primary diagenetic minerals. Intense compaction and carbonate cementation are the principal mechanisms contributing to the densification of sandstones. Pore-filling clay minerals subdivide macropores into numerous micropores, significantly reducing reservoir permeability. The migration of dissolution products out of the system is a difficult process, which hinders the effectiveness of mineral dissolution in enhancing overall reservoir quality. This study may provide a valuable reference for the effective exploration of Lower Cretaceous clastic reservoirs in eastern Shandong.