Genesis of sandstone intrusion in Qiongdongnan Basin and their influence on gas hydrate accumulation

At present，there is less research on the role of sandstone intrusion in gas hydrate accumulation systems. There are geological conditions for sandstone intrusion and gas hydrate accumulation in the South China Sea，but the effect of sandstone intrusion on gas migration and gas hydrate accumulation is worth further study. Therefore，based on the seismic data and previous research results，the geological characteristics of the sandstone intrusion in Qiongdongnan Basin are finely characterized，and the genetic mechanism of the sandstone intrusion is determined in combination with the geological background，so as to establish the evolution model of the sandstone intrusion and summarize the role of the sandstone intrusion on gas migration and gas hydrate accumulation. The results show that：① Large sandstone intrusions are developed in the Lingnan low bulge of Qiongdongnan Basin，mainly located at the top of Huangliu Formation，with two wings extending diagonally upward into Yinggehai Formation，and a few small sandstone intrusions are located at the bottom of Yinggehai Formation. The sandstone intrusions present a U-shaped or wide V-shaped strong amplitude reflection in the seismic section. The transverse distribution range is 3-5 km，and the vertical height is about 350-750 m. The plane shape is circular or oval，with ring characteristics. ②The sedimentary source sand body in the middle Miocene and the sedimentary low permeability mud cover in the late Miocene provide the conditions for the overpressure of the sand body in Meishan Formation. Polygonal faults were formed in the Pliocene period，and the sand body in Meishan Formation is not consolidated due to undercompaction and is disturbed by volcanic activities after liquefaction. The trigger mechanisms of sandstone intrusions match each other in time and space and have good conditions for forming sandstone intrusions. ③Sandstone intrusions can be used as a relay migration channel for methane gas from deep to shallow layer，and a large number of deep thermal decomposition gas can migrate through sandstone intrusions to shallow stable regions to form hydrate reservoirs after deep diapirs and fractures，which is of great significance for hydrate exploration and development. © 2023 Editorial office of Oil Geophysical Prospecting. All rights reserved.