Tectonic evolution of buried hills and the main controlling factors of fractures in the fault step zone of the Pearl River Mouth Basin, northern South China Sea

Buried hills are an essential offshore oil and gas exploration direction. Based on the new three-dimensional (3D) seismic data, formation micro scanner images (FMI), and zircon chronology data, the stratigraphic structure, structural characteristics, and fracture reservoir characteristics of the buried hills in the fault step zone in the Pearl River Mouth Basin in the northern South China Sea were analyzed. Then, the tectonic evolution of buried hills and the controlling factors of fracture development were discussed. From the results, the target buried hill is composed of Mesozoic volcanic rocks, and the primary reservoir types are medium-high angle structural fractures. The buried hill underwent a multi-stage tectonic evolution during the Mesozoic-Cenozoic period. Mesozoic extrusion and Cenozoic extension processes controlled the fractures in the buried hill. Shear and extensional fractures developed against Mesozoic extrusion, while shear and tensional fractures developed during Cenozoic tensional processes and magma intrusion. Tectonic movements control the development of fractures in the interior of the buried hill. Groups and types of fractures cut into each other to form network fractures, providing good reservoir space for oil and gas.