The Study On Sedimentary Facies Of Pinghu Zone In Xihu Sag In The East China Sea Shelf Basin

The Xihu sag lies to the east of east China sea shelf basin, west from fish hill,sea reef, Hupi reef three heaves and the Changjiang river and Qiantang depressed, east to fishing island magma rock, north from Fujiang depressed, south to Jilong depressed. The direction of strike in it is NNE and the total area is about 4.27×104km~2. Five 2-class structure cell strip Baochu slope,Santan depressed,Zhedong center anticline, white bank depressed and Tianping break be setted off from west to east in Xihu sag. Pinghu zone lies in Baochu slope, subdivided to north Pinghu zone, middle Pinghu zone and south Pinghu zone.At the study of strata sequence stratigraphy in Xihu sag, colligate investigation production of the former, analyse the artesian well rock core, survey well, seism and analyse testing information in the research section, adopt P.R.Vail etc. sutra strata sequence stratigraphy theory, divided into nine third-class strata sequence from Eocene series Pinghu group to Miocene Liulang group. Based on the contrast of strata sequence stratum in Pinghu zone, we can discovered that every stratum have good comparison.The types of the rock in Xihu sag are richness and multiplicity, and the apiece rocks of terrigenous fragmentary are developed very well. The content of quartz is almost between 60%～70%, and the content of quartz in the Pinghu group is more than in the Huagang group in evidence. The content of quartz is descending from down to up, but the content of feldspar is increased by degrees. In the plane, the stabilization component of mineral in zhe west is lower zhan in the east, which shows that the collectivity of terrigenous sediment accommodate is from the west to the east. The mature degree of configuration of sandstone in Pinghu zone belongs to juvenility, which indicated that the sediment place is near by the terrigenous denudation place and the distance of convey is short.The sedimentary have 5 types which are half close down bay facies, tide-flat sedimentary facies,tide-controlled delta sedimentary fades,lake delta sedimentary facies and lake sedimentary facies. There also have some sedimentary subfacies and some sedimentary microfacies, such as supratidal zone,intertidal zone,subtidal zone,delta front,delta plain,prodelta,stream channel fill,stream channel edge and flood plain.The condition of mineral deposit in Pinghu zone is very good, and the break block oil trap developed very good and legion. There are 2 suits assembles of reservoir strata and capping formations which are Pinghu and Huagang assemble of reservoir strata and capping formation. In the sedimentary date of Pinghu group, the tide-flat sedimentary facies and tide-controlled delta sedimentary facies are developed very well. In this area the reservoir strata are main composed by the sand of tide-controlled delta and the capping formation are mud of bay and mud of swamp. In the paralic sedimentary date of Huagang group, main developed zhe lake delta sedimentary facies. In this area the sandstone of the distributary channel in delta and the river mouth bar are mainly reservoir strata and the capping formation are mud of bay and mud of swamp.