Distribution characteristics of hydrocarbon source rock in Heshan Sag

Heshan Sag locates in the ultra-deep water area of northern continental margin in South China Sea,on the oceancontinent transition zone with strong crustal thinning.The special geological conditions such as high temperature gradient and lithospheric ductile deformation are different from the depressions which are in continental shelf area,so Heshan Sag has special hydrocarbon accumulation history.Using the method of regional contrast and through the study of sequence stratigraphic framework,seismic facies and sedimentary facies,the distribution characteristics of Paleogene hydrocarbon source rock are predicted early.It is considered that Heshan Sag is a continental margin rift basin deposition in the Eocene period.The thickness of deep lake facies deposition is large in the central part of the sag and the local area of sag-controlling faults downthrown,showing the seismic reflection characteristics of low frequency,continuous,strong amplitude and parallel to subparallel,which are similar to the lake hydrocarbon source rocks drilled and confirmed in Baiyun sag.Therefore,the hydrocarbon source rocks in Heshan Sag have good hydrocarbon potential.