东营凹陷北部陡坡带近岸水下扇沉积特征

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

近岸水下扇砂砾岩体具有良好的储集物性,而且紧邻油源,是一种有利的油气储集体。在系统观察岩心和地层划分对比的基础上,结合地震、测井等资料,对东营凹陷北部陡坡带沙三早、中期近岸水下扇进行了研究,详细分析了该类砂砾岩体的沉积特征和控制因素。研究结果表明,这类沉积体多夹于深色泥岩之中,垂向上具有向上变细的正旋回,平面上主要分布于陈南断层东段下降盘和滨县凸起东南侧紧邻凸起的地区,其扇体根部为巨厚的砂砾岩沉积,砾岩体积分数超过60%,砂岩和砾岩总体积分数超过90%。受断层活动期次和横向活动差异的影响,近岸水下扇具有在平面上与扇三角洲间互出现,剖面上与扇三角洲相互叠置的特点。尽管近岸水下扇的形成受古构造、古气候、古地形和古物源等多种因素的控制,但东营凹陷北部陡坡带控盆边界断层在沙三早、中期的强烈活动可能是导致近岸水下扇形成的决定性因素。

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.