A study of depositional characteristics of the Jurassic strata in Chaoshan Subbasin, northern South China Sea, and its control on reservoir beds

The Jurassic strata in the Chaoshan sub-basin of northern South China Sea have great potential for oil and gas exploration, and the sedimentary characteristics have obvious effect on the development of the reservoirs.Based on analyzing the latest seismic data of the study area, the authors recognized four typical seismic reflection interfaces and three seismic reflection layers and, according to the result of the sequence interface, figured out the Jurassic distribution and residual thickness. On the basis of the comparative analysis of the transformation of seismic facies-sedimentary facies, the authors determined the sedimentary facies types and distribution characteristics of the Jurassic strata in different periods and reshaped the sedimentary evolution history of the Jurassic sediments in the Chaoshan sub-basin. The study area has mainly developed five sedimentary facies and eight kinds of sedimentary subfacies, and the coastal delta front subfacies and deepwater middle-fan subfacies have controlled the development of high-quality reservoirs of the debris flow sandstone separately. In addition, the turbid sandstone reservoir is mainly controlled by the sediment supply, the more closer to the delta sand body leaves, the more the number of slump turbidite, and the larger the area. In general, the front subfacies of the delta, the subfacies of the deep water fan and the gravity flow slip turbulence constitute the facies of high-quality reservoirs in the study area. The reservoirs are fairly favorable for oil and gas accumulation due to the deep burial and the mudstone cover.