鄂尔多斯盆地西南部延长组6段重力流沉积特征及其油气地质意义

Sedimentary Characteristics and Petroleum Geological Significance of the Chang6 Gravity Flow in the Southwest Ordos Basin

鄂尔多斯盆地南部延长组长6油层组中发现大量块状无层理砂岩,属陡坡带处堆积的三角洲前缘沉积物沿斜坡滑塌形成的重力流沉积。综合岩芯、露头、测井及分析化验资料,认为延长组发育滑塌岩、液化沉积物流、砂质碎屑流和经典浊流等多种类型的重力流,不同类型重力流沉积特征差异明显;其中地形坡度、物源供给和一定的触发机制是形成长6重力流沉积的基本条件;在流动过程中由于水的混入和沉积物卸载,重力流沉积物发生浓度变化和流态转换,形成滑塌岩—砂质碎屑流、砂质碎屑流—浊流、浊流等不同组合类型;重力流砂岩延伸至半深湖—深湖相泥岩中,与长7烃源岩侧向连通,形成有利的成藏组合,是研究区延长组重要的勘探目标区。

There are a large number of massive sandstones in the Chang6 oil reservoir,Southwest Ordos Basin,which are gravity flows from sediments slumping along the slope in a delta front.We determined that there are differ-ent kinds of gravity flows,such as slumps,liquefied sediment flows,sandy debris flows,and turbidites,in the Yan-chang Formation based on cores,outcrops,logging,and testing data.The slope,sediment supply,and trigger mech-anism are the basic formation in the Chang6 gravity flow.Concentration and flow state change due to water maxing and sediment unloading during the flow process and form different kinds of combinations,such as slumps-sandy de-bris flow,sandy debris flow-turbidite,and turbidite.The gravity flow sandstone extends in the semi-deep lake and deep lake mudstone lateral connection with source rock in the Chang7 oil reservoir and develops favorable reservoir forming assemblages,which are the most important target zone of the Yanchang Formation in the study area.