Accumulation of natural gas hydrate based on migrating system: a case study of H zone of Qiongdongnan Basin

Abstract

Gas hydrate is greatly developed in the Qiongdongnan Basin which is one of the key exploration targets in the South China Sea, but the geological study of gas hydrate is insufficient. With 3D seismic data interpretation, geochemical data analysis and a large number of investigations, a related research work of H zone in the Qiongdongnan Basin was carried out in this paper, with accumulation system as the main line and focused on migration and transportation system. According to the analysis of 48 sets of geochemical data, the hydrate decomposition gas in H zone has a methane carbon isotope value (δ13C1) of -48.2‰ and a higher content of ethane and propane (C2+=21%), indicating that the gas is mainly thermogenic, and some are mixed gas. Seismic interpretation showed that the Quaternary tectonic activity in H zone was weak, and the NNE-trending gas chimney structure group, polygonal fault-silt complex and submarine slump body constituted the main migrating system and high-quality reservoir in the study area. Based on the gas source characteristics and migrating system of natural gas hydrate in H zone, three accumulation types were proposed, including the gas chimney type hydrate rich in thermogenic gas, the polygonal fracture-silt composite hydrate rich in thermogenic gas, and the submarine slump hydrate rich in thermogenic gas and mixed genetic gas.

Keywords

• gas chimney
• polygonal fault
• thermogenic gas
• gas hydrate
• hydrate accumulation
• qiongdongnan basin