Seismic sedimentology of sand-gravel bodies on the steep slope of rift basins---a case study of the Shahejie Formation, Dongying Sag, Eastern China

A variety of genetic types of reservoirs with good hydrocarbon accumulation conditions have been developed in petroliferous rift basins. The near-provenance, coarse-grained depositional system on the steep slopes of rift basins has become an important oil and gas exploration area. However, due to the large changes in lithologies and difficulties in its identification and characterization, the challenges in oil/gas exploration are significant. Seismic sedimentology, in this case, provides an effective means of identifying and characterizing the complex, coarse-grained sediments. We use a large number of cores, logs, and seismic data and establish the third- and fourth-order sequence frameworks in the Shahejie Formation on the steep slope of the northern Dongying Sag in eastern China Three types of lithofacies, including conglomerates, sandstones, and mudstones with 12 subspecies facies types have been identified and the relationship between different lithofacies types and depositional systems is determined. The relative changes of the lake level control the distribution of depositional systems in a sequence framework. Lowstand system tracts of SQ3 and SQ4 in the Shahejie Formation mainly developed near-shore subaqueous fans and a small number of slump turbidite fans. Smallscale offshore fans mainly develop in lacustrine transgressive systems tracts, and fan deltas, flood-type sublake fans, slump turbidite fans, and near-shore subaqueous fans mainly developed in highstand systems tracts. The study of seismic sedimentology, based on the theory of seismic lithology and seismic geomorphology, have been carried out. Stratal slices are used to identify and characterize the morphology and temporal-spatial distributions of various types of sand-gravel bodies on the steep slopes of the Dongying Sag based on core calibration and establish the model of seismic sedimentology for various types of sand-gravel bodies in different systems tracts.