Development Mechanism of Composite Igneous Rock Buried-Hill Reservoir in Huizhou Sag, the Pearl River Mouth Basin

The composite igneous rock buried hill in Huizhou Sag of the Pearl River Mouth Basin, experienced multi-stage tectonic evolution from Yanshanian to Himalayan, and developed fracture dissolution type reservoirs. In order to clarify the mechanism of buried hill reservoirs, the author conducted a detailed study on the fracture cause, phase and diagenetic evolution of Huizhou 26-6 buried-hill reservoir with zircon U-Pb dating and casting thin section observation. Huizhou 26-6 buried-hill is composed of granite, diorite and basaltic andesite, which have undergone at least six stages of tectonic magmatic activity.Granites suffered cataclastic, diorite and basaltic andesite are schistotized. At 166 to 145 Ma, basaltic volcanic rocks erupted. At 145 to 134 Ma, regional metamorphism occurred under the influence of the mid-Yanshan tectonic movement, resulting in gneissic and gneissic mineralization of basaltic volcanic rocksand early fractures. At ~134 Ma and 120 to 110 Ma, acidic magma invaded of basaltic volcanic rocks in two stages with extension, and granite, siliceous and carbonate veins developed. Actinization, epidotization and chlorite occurred at the volcanic passage.A first phase of tensile fissure developed between 110 and 100 Ma, and magmatic hydrothermal upwelling between 102 and 87 Ma, and the fissure was half-filled with dolomite and turbidite. Large scale uplift of the area affected by Late Cretaceous tectonic transfor Mation, strong weathering, and developed weathering cracks and dissolution cracks; During the rifting period, there were two periods of Mag Matic hydrother Mal activity influenced by the movements of the first and second episodes of Zhuqiong, and the cracks were filled with chlorite and turbidite; During the South China Sea Movement and neotectonics, micro fractures were generated to connect Source rock. Organic acids entered the reservoir for further dissolution and transfor Mation. The fractures were not filled or half filled. Large scale oil and gas filling and accumulation took place at 5 to 13 Ma. This study provides a basis for comprehensive evaluation of reservoir characteristics and clarification of natural gas enrichment patterns in the study area.