南黄海盆地二叠系地震地层特征与识别

南黄海盆地钻遇二叠系的井仅有4口,对大面积无井区(如崂山隆起)的地层特征认识不统一。从二叠系岩性特征和海陆钻井地层对比为出发点,结合二叠系内部及其上下地层的地震波组和速度特征,认为南黄海盆地二叠系分上下2段。上段为大隆—龙潭组含煤碎屑岩地层,煤系地层较薄且分布不稳定,存在相变特征,使得该组地层在地震反射特征上的规律性变差,地震上表现为较连续、中—高频反射和低速特征;下段为栖霞组灰岩夹泥页岩地层,地震上表现为较连续、中—低频反射和高速特征。在无井区识别二叠系时,抓住二叠系地层界面极性为"2负+1正"的强反射特征。下二叠统—中、上石炭统地震波组特征相似,由4~5个同相轴组成,厚度稳定(时间约为200 ms),地震波极性表现为"上正下负"的地层界面反射特征,可作为全区追踪的标准层。

SEISMIC STRATIGRAPHIC FEATURES AND RECOGNITION OF THE PERMIAN IN THE SOUTH YELLOW SEA BASIN

Only four wells have been drilled up to the Permian so far in the South Yellow Sea Basin, and the understanding is diverse concerning its stratigraphic features in the huge area without wells, e.g. the Laoshan Uplift. This article is supposed to be a starting point from lithology and land-sea correlation to drilled strata of the Permian for further study of seismic wave groups and velocity characteristics of its internal, Upper and Lower Permian strata in the South Yellow Sea Basin. Studies suggest that:the Permian is divided into upper and lower groups. The upper group includes the Dalong and Longtan Formations and is a coal-bearing clastic deposit. The coal seams are thin and distributed unstably, showing characteristics of phase transition, so the strata's regularity is deteriorated in seismic reflections. The seismic is slight continuous with middle-high frequency and low interval velocity; the lower section is the Qixia Formation containing limestone intercalating shale. The seismic is slightly continuous with middle-low frequency and high interval velocity. In the area in absence of wells, the Permian may be identified with the strong reflections of strata interface polarity of "2-negative and 1-positive" characteristics. The Lower Permian, Middle and Upper Carboniferous show similar seismic patterns, which consist of 4-5 seismic events, with rather stable thickness (about 200ms time thickness), and seismic wave polarity in "up-positive and down-negative" interface reflection characteristics. It can be used as the standard for regional correlation.