Discussion on the origin of gas chimney and its relationship with the migration and accumulation of oil and gas hydrates into reservoirs in the northern South China Sea

In the exploration and evaluation of oil and gas and/or natural gas hydrate in the northern continental margin basins in the South China Sea, geophysical data, especially 2D/3D seismic profiles, commonly show seismic geological anomalies such as seismic reflection blurry zones of different types and characteristics that are closely related to oil and gas reservoirs and/or natural gas hydrate reservoirs, namely "gas chimney" or "fluid diapir" or "gas trap". This article focuses on the origin of the "gas chimney" and its relationship to the migration and accumulation of oil, gas, and natural gas hydrates. The oil and gas exploration practice manifests that gas chimneys are often associated with oil and gas reservoirs, especially natural gas hydrate reservoirs; and oil and gas hydrates are often located near their overlying or flanking areas. Previous extensive exploration practices and analyses of geological, geophysical, and geochemical data have confirmed that the gas chimney is closely related to the enrichment and accumulation of oil, gas, and natural gas hydrates on its overlying or adjacent sides. Gas chimney, as a channel connecting hydrocarbon/gas supply system with oil and gas or hydrate reservoir, is an important indicator to tracking the origin of oil and gas and/or hydrate reservoirs, and determining the activity of hydrocarbon/gas supply system. Therefore, in-depth study on the causes and types of gas chimney systems is necessary to clarify the migration and accumulation and control factors, and to guide the exploration. Meanwhile, geochemical analysis in this field will help determine the origin of gas chimneys and their impact on the migration and accumulation of oil and gas or hydrates in reservoirs.