鄂尔多斯盆地东部府谷天生桥剖面上古生界下石盒子组8段辫状河储层构型表征

Characterization of braided river reservoir architecture of the Upper Paleozoic He 8 member on Fugu Tianshengqiao outcrop,eastern Ordos Basin

鄂尔多斯盆地苏里格东部地区上古生界下石盒子组8段(盒8段)为主力产气层,其储层内部构型是控制油气分布的关键地质因素。选取盆地东部与苏东地区具有相似物源体系与沉积环境的府谷天生桥剖面作为研究对象,对该剖面砂体构型进行精细解剖能为苏东地区地质模型的建立提供有效信息。通过剖面实测、岩相分析、构型解剖、砂体规模精确测量等方法,结合沉积学、岩石学特征分析,对府谷天生桥剖面上古生界盒8段辫状河储层构型特征进行了深入研究。结果表明:该剖面盒8段辫状河发育12种岩相类型;其储层内部可划分出复合河道带、单一河道带、单砂体、落淤层及增生体、层系组、层系及纹层等6级构型界面;共识别出河道充填(CH)、纵向砂坝(LB)、斜列砂坝(DB)、横向砂坝(TB)、废弃河道(ACH)和越岸沉积(OF) 6种储层构型单元,其中砂坝作为辫状河主要储层构型单元,纵向砂坝厚度介于2. 5～5. 8m,宽/厚比约为27. 6～37. 7;斜列砂坝厚度介于2. 2～6 m,宽/厚比约为34. 8～42. 1;横向砂坝厚度介于1. 5～3. 6 m,宽/厚比约为47. 0～61. 8。在对不同构型单元分析的基础上,总结了其空间叠置样式,建立了府谷盒8段辫状河复合砂体三维的构型模式,研究成果为苏东地区盒8段气藏精细描述提供了地质依据。

The major gas pay zone lies in the 8th member of the Upper Paleozoic Lower Shihezi Formation(He 8 member),eastern part of Sulige region,Ordos basin.Its reservoir architecture acts as a predominant geological factor for oil/gas distribution.Targeting at Tianshengqiao outcrop in Fugu county in eastern Ordos Basin,similar to eastern Sulige region in provenance and sedimentary setting,we finely studied the architecture of the outcropped sand body,which can offer critical information for the establishment of geological model of eastern Sulige region.Based on the outcrop survey,pe- trographic investigation,architecture analysis and fine measurement of sand body volume,combined with the sedimentary and petrologic analyses,we recognized twelve types of lithofacies in the braided river deposits of He 8 member.Six levels of architecture interfaces were classified within the reservoirs,namely composite channel-belt,single channel-belt,single sand body,silty layer accompanied with accretion,bed set,single bed and laminae.Six reservoir architecture units are indentified,that is,channel filling(CH),longitudinal bar(LB),diagonal bar(DB),transverse bar(TB),abandoned channel(ACH)and overflow deposits(OF).Among these,sand bar is a dominant reservoir architecture unit.The thickness of longitudinal bar ranges between 2.5m and 5.8m with the width/thickness ratio varying from 27.6 to 37.7;the thickness of diagonal bar ranges between 2.2m and 6m with a width/ thickness ratio varying from 38.4 to 42.1;while the thickness of transverse bar ranges between 1.5m and 3.6m with a width/ thickness ratio varying from 47.0 to 61.8.Based on the analyses of different architecture units,we summed up the spatial superimposition patterns of the reservoir, established the 3D architecture model of braided river composite sand body in the He 8 member of Tianshengqiao outcrop in Fugu county,both of which will provide geological evidences in the fine description of He 8 member in eastern Sulige region.