鄂尔多斯盆地庆城油田延长组页岩层系层序地层与沉积相特征

Sequence stratigraphy and sedimentary facies characteristics of the shale strata of Yanchang Formation in Qingcheng Oilfield,Ordos Basin

鄂尔多斯盆地三叠系延长组页岩层系蕴藏着丰富的油气资源,但其层序格架及沉积相展布存在较大的争议,从而影响着页岩油气的精细勘探与开发。以庆城油田西233区块为例,应用岩心、测井及最新的三维地震资料重构了层序地层格架及沉积相分布。研究表明,在延长组原长81—长32砂组内,地层向湖盆中心呈进积叠置样式,可分为2个长期基准面旋回和10个中期基准面旋回。在每个中期旋回内,向盆地方向的古地貌依次为浅水带、斜坡带和盆底带。浅水带主要发育三角洲;斜坡带发育重力流水道,顺斜坡呈窄条带状分布;在盆底带近端发育重力流朵叶体沉积,砂体夹于泥页岩中,而盆底带远端主要为深湖页岩夹滑塌体沉积。原长7油层组页岩层系为1套穿时地层,由多个中期旋回的斜坡带下部、盆底带湖底扇砂体和半深湖—深湖泥岩组成。这一研究不仅对鄂尔多斯盆地夹层型页岩油的有效开发(开发区优选及水平井部署)具有重要的指导作用,亦对拗陷湖盆层序与沉积演化理论的发展具有一定的促进作用。

The shale succession of Yanchang Formation in Ordos Basin is rich in hydrocarbon resources,but its sequence framework and sedimentary facies distribution are controversial,which affects the exploration and development of shale hydrocarbon.Taking the Xi233 area of Qingcheng Oilfield as an example,this paper reconstructs the sequence stratigraphic framework and sedimentary facies distribution using core,logging,and the latest 3D seismic data.Research has shown that in the original Chang 81-Chang 32 interval of the Yanchang Formation,the strata represent a progradational superposition pattern towards the center of the lake basin,which can be divided into two long-term base-level cycles and ten mid-term base level cycles.In each mid-term cycle,the paleogeomorphology towards the basin is followed by shallow-water area,slope area and basin floor area.The shallow-water area mainly develops deltas.The slope belt develops gravity flow channels,which are distributed in narrow bands along the slope;the gravity flow lobe deposits are developed in the proximal basin floor,and the sand bodies are sandwiched in mud shale.The distal basin floor is mainly deep-lake shale interbedded with slump deposits.The original“Chang 7 interval”shale strata is a set of diachronous strata,which is composed of sublacustrine fan sand bodies and semi-deep to deep lake shale in the lower part of the slope belt and basin floor belt of multiple mid-cycles.This study not only plays an important guiding role in the effective development of interbedded shale oil in the Ordos Basin(optimization of development areas and deployment of horizontal wells),but also promotes the development of the theory of sequence and sedimentary evolution in depression lake basins.