Tectonic evolution of granite buried hill and its control on reservoir accumulation in Qiongdongnan Basin

Based on the gravity and magnetic, seismic, drilling, and age dating data of the Qiongdongnan Basin, combined with the tectonic evolution characteristics of the northern continental margin of the South China Sea, we analyzed the intrusion period and distribution law of granite in the basin, and discussed the development and evolution of granite buried hill and its reservoir control. Results show that the Indosinian and Yanshanian granite intrusions developed in the basin. The Indosinian granites were mainly distributed in NW (low) uplift zone, and the Yanshanian granites were distributed in NE (low) uplift zone. The tectonic type of granite buried hill in the basin is residual hill. The evolution of granite buried hill in the Indosinian and Yanshanian periods can be divided into magmatic intrusion period, exposure and denudation period, and final burial period. The evolution difference between them is mainly reflected in the intrusion time of magma. The granite buried hill in the basin has been exposed and eroded for a long time, and has experienced multi-stage tectonic movements. The grid-like faults were developed, which formed weathering crust reservoirs and fault-fracture reservoirs. The Songnan Low Uplift is surrounded by multiple concaves, in which fault + sand body composite transportation system is developed, forming a favorable oil and gas accumulation area.