摘要
本文用地震地层学的方法,对盐城凹陷地震剖面作了初步的分析.根据地震反射波的终止特征,将盐城凹陷新生界划分成11个地震亚层序,并根据各亚层序的区域意义,分别归属于3个层序或2个超层序。在地震层序划分的基础上,作者利用地震反射结构、振幅、连续性和层速度特征,着重对B3和B6亚层序进行了地震相分析。结合本区现有的钻井地质资料,进行综合转相工作,恢复了渐新统的沉积相和沉积环境,指出油气聚集的有利部位。文章认为:渐新世早期,盐城凹陷是向心充填式断陷湖泊沉积。多源水流自北向南,自西向东汇聚于南部深湖区。凹陷南陡北缓,从南向北呈湖泊——扇三角洲——三角洲平原相的沉积特征。南部陡坡带发育有洪积——冲积沉积。渐新世后期,向心式断陷盆地转为超越式以河流相沉积为主的沉积盆地。来自北、东北、西三个方向的水流,在凹陷中部汇聚后,沿盐城大断裂前缘向东流去。作者指出:小型的扇三角洲是B8亚层序沉积类型油气勘探的最有利部位。主河流砂相沉积,结合构造的有利部位是B6亚层序构造——沉积复合次生油气勘探的有利部位。
Abstract
In this paper, the authors have made a preliminary estimation on the application of the seismic stratigraphy to the seismic sections obtained from Yancheng Depression. In correspondence to the characteristics of the termination of seismic reflections, the sediments of Cainozoic group at Yancheng Depression were divided into 11 seismic subsequences. But from the viewpoint of regional geology, they were categorized into 3 sequences or 2 supersequences respectively.Based on the classified seismic sequences, the authors focused their attention on the seismic facies analyses of subsequences B8 and B6 through the medium of seismic reflection configuration, the amplItude, the continuity and the interval velocity. By combining the results from above analyses with the existing local well information, an integrated facies transformation has been made. The sidementary facies and the sedimentary environment of the Oligocene series were thus generated and the locations favourable for oil accumulation were also suggested.It is considered that in Yancheng Depression, at the early stage of Oligocene epoch, Polygeneous watercourses flowed from north to south, from west to east, and finally converged on the southern deep lake area. Thus, the deposition presents itself the centripetal fill downcast lake deposit. The depression is precipitous in the south and tends to slow down in the north. From south to north, the sediment is characterized by: lake facies→fan delta facies→deltaic plain fades. In southern precipitous zone, there are diluvial and alluvial deposits. In the late period of Oligocene epoch, the centripetal downcast basin has become such a basin with the lapped river facies deposition in the main. Watercourses from the north, northeast and west, converged on the central of the depression and then, flowed eastward along the front fringe of large Yancheng rift.At the end of this paper, the authors remarked that, for oil prospecting, the most favourable places of B8 subsequences is the small fan delta area. The places favourable for the exploration of the secondary enrichment of oil bearing reservoir in the composite sediment is the structures fo B6 subsequence, its sediment presents as the sand facies deposition.
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