大王北洼陷浅水漫湖砂质滩坝沉积微相特征

Microfacies Characters of Sandy Beach and Bar in Shallow Water Over-lake,with an Example from the Dawangbei Sag

通过岩心精细的观察,结合测井、三维地震以及岩石鉴定分析等资料的综合研究发现,大王北洼陷沙二段盆地断坳期为浅水漫湖砂质滩坝沉积,可分为:滩、坝主体、坝侧缘、坝间4种沉积微相,其中坝主体的成分成熟度和结构成熟度较高,且坝主体砂层最厚,滩、坝侧缘和坝间砂体次之。另外,沙二段时期盆地内河流三角洲不发育,大量坝砂呈条带状沿岸或斜交岸线发育,滩砂呈席状大面积覆盖于盆内与坝砂和其他沉积砂体相连,构成了洼陷"满盆砂"的浅水漫湖沉积的特征。这些砂体规律性地分布于洼陷内,并且与油源邻近(沙三段中部油页岩),是有利的油气储集体,与油气富集密切相关。

The careful observations of core data, logging and 3D-seismic and petrographic analysis reveal that the 2nd member of the Shahejie Formation in the Dawangbei Sag consists of sandy beach and bar of shallow water over-lake. The sandy beach and bar of shallow water over-lake can be divided into four microfacies：beaeh, key bar, side-portion of bar and between-portion of bar. Among them, the key bar has a very high textural maturity and compositional maturity and a little thicker than beach, side-portion of bar and between-portion of bar. The 2nd member of the Shahejie Formation in Dawangbei Sag contains less developed delta, and well developed long and oblique bars preading across the lake shore. The beach sandy body overlapped in the sag, connecting the bar and other sandy bodies. These sandy bodies are developed in the whole shallow water over-lake in Dawangbei Sag, distributed in regualrity next to the hydrocarbon source（oil shale in the middle of the 3rd member of the Shahejie Formation）. They form an important reservoir rock and a potential for the exploration of oil and gas.