Difference analysis of gravity decollement structures and its effect on hydrocarbon accumulation: By comparing analysis of Lower Congo-Congo Fan Basin and Niger Delta Basin

Gravitational decollement is a structural pattern commonly developed in passive continental marginal basins on both sides of the Atlantic Ocean.Two different types of gravity decollement structures with transitional salt and marine mudstone as decollement layers are developed.Based on the stress mechanism, it can be divided into extensional zone, transitional zone and compressional zone successively from the continent to the ocean.In order to clarify the difference between those two types of gravitational decollement structures and their influence on oil and gas accumulation, this paper makes a comparative analysis of two representative basins, the Lower Congo-Congo Fan Basin and the Niger Delta Basin.Through comparing, the differences of structure patterns, sedimentary reservoir distribution characteristics and hydrocarbon accumulation were clarified in the same zone.On the whole, salt gravitational decollement in extensional zone shows that the salt structures are highly active, the oil-gas accumulation conditions are superior, and there are many oil-gas discoveries in this zone.In transitional zone, the intensity of salt activity is moderate and the degree of oil-gas enrichment is the highest.In compressional zone, the salt activity is strong with a large scale salt accumulation, poor source rock and reservoir, and rare oil-gas discoveries.The extensional zone of marine mudstone gravitational decollement is the main oil-gas accumulation area with relatively weak structure activity and good match between the reservoir and source rock.In transitional zone, it has strong extrusion stress, and large amount of mudstone has been accumulated there.The mud diapir is magnificent, and deep-slow diapir structure is the favorable oil-gas accumulation area.The compressional zone is dominated by typical thrust imbricate structure with good match of source rock, reservoir and oil source faults.The oil-gas enrichment in this zone is relatively high.Based on the analysis of those two types of gravitational decollement in source rock, reservoir and hydrocarbon accumulation, this paper have provided some references for the research related to gravitational decollement