Constructive Effect of Tuffaceous Filling Dissolution in Clastic Reservoir—A Case Study from Kuishan Sandstone in Permian of Gaoqing Buried Hill in Jiyang Depression, Bohai Bay Basin

Tuffaceous fillings are a significant component of the Permian Kuishan sandstone in the North China Platform, and their complex diagenetic processes have a notable impact on the development of clastic rock reservoirs. This study, based on microscopic analysis of reservoirs and combined with quantitative analytical techniques such as electron probe microanalysis, homogenization temperatures of fluid inclusions, micro-area carbon-oxygen isotope analysis, and laser Raman spectroscopy, investigates the influence of tuffaceous interstitial material dissolution on reservoir development in the Permian Kuishan sandstone of the Gaoqing buried hill in the Jiyang Depression, Bohai Bay Basin. The results indicate that the dissolution intensity of tuffaceous interstitial materials can be classified into three levels: strong, moderate, and weak. In the strong dissolution zone, associated fractures and dissolution pores significantly contribute to reservoir porosity, with a positive correlation between dissolution plane porosity and total plane porosity. The reservoir space is characterized by a network of dissolution pores and fractures. The moderate dissolution zone is marked by the development of authigenic quartz, feldspar, and clay minerals, which do not effectively enhance porosity and permeability. The weak dissolution zone contains well-preserved volcanic glass shards, crystal fragments, and clay minerals, representing non-reservoir development sections. Lithology, sedimentary facies, diagenesis, and fractures collectively control the quality of the Permian Kuishan sandstone reservoir in the Gaoqing buried hill of the Jiyang Depression, Bohai Bay Basin. The advantageous zones for reservoir development in this area can be effectively predicted using thickness maps of the Kuishan sandstone, planar distribution maps of sedimentary facies, and fracture prediction maps derived from ant-tracking and coherence algorithms.