Sedimentary characteristics of nearshore subaqueous fans in steep slope of Dongying depression

The nearshore subaqueous fans have good reservoir potentiality and connect directly with oil source rock in deep water, which make them be favorable reservoirs. According to core observation ,stratigraphic division and the numerous data of seismic and logging, the nearshore subaqueous fans were studied in early and middle Shasan period of Paleogene in northern steep slope of Dongying depression. The sedimentary characteristics and controlling factors were analyzed in detail. The results show that the sandy-conglomerate sediments are mostly located among dark muds. The grain size becomes fine down to up in vertical. On the plane they are mainly located on the downcast side of the east Chennan fault and the southeast of Binxian salient. At the bottom of the fans there are thick psepholites and the thickness of conglomerates mostly accounts for more than 60% of the thickness of strata, the summation thickness of sand and conglomerate more than 90%. Because of the differences of the faults in active time and position, nearshore subaqueous fans are disjunctive on the plane and overlapped in vertical with the fan deltas. The formation of nearshore subaqueous fans is under the control of many factors, such as palaeotectonics, palaeoclimatologics, palaeotopography, palaeo-provenance, but the crucial factor is the intense activity of basin-control boundary faults in the north of Dongying depression during early and middle Shasan period of Paleogene.