松辽盆地南部大布苏地区青山口组高频层序沉积微相分析与岩性圈闭预测

Sedimentary Facies Analysis and Lithologic Trap Prediction in High-resolution Sequence Framework of Qingshankou Formation, Dabusu Area,Southern Songliao Basin

松辽盆地大布苏地区的斜坡背景与青山口组一段、二段侧向发育的三角洲前缘砂体配合,具备形成构造—岩性圈闭的良好条件。运用高分辨率层序地层分析方法,将研究层段划分为9个砂组。通过沉积微相分析,确定研究区发育三角洲前缘、浊积扇和半深湖等沉积相类型,并进一步识别出分流河道、河口坝、席状砂、浊积水道、浊积席状砂和半深湖泥质沉积等微相类型。以高频层序划分的砂组为单元,分析了各砂组的沉积微相构成与分布特征,指出垂向上高频层序下降半旋回的砂组,河口坝较发育;上升半旋回的砂组,分流河道较发育;青一段、青二段中,下部砂体厚度大,上部砂体厚度薄。平面上砂体呈南西—北东方向展布,西南部三角洲前缘水下分流河道、河口坝、席状砂等砂体发育;东北部以半深湖泥质沉积为主,局部发育浊积扇;砂体向北西斜坡方向的侧向减薄、尖灭明显。研究认为,三角洲前缘砂体与斜坡背景上的鼻状构造背景相互匹配,易于形成构造—岩性圈闭,为研究区最有利的勘探领域;结合地震特征,进一步预测了3个岩性圈闭勘探目标。

Due to the slope background and delta front sandbodies, there are favourable conditions for lithologic trap in Qingshankou Formation of Dabusu area in Songliao Basin. Nine sand groups are divided in intended interval with the method of high-resolution sequence stratigraphy. Delta front, turbidite fan and semi-deep lake are recognized through facies analysis, which are further identified as distributary channel, mouth bar, sheetlike sand, turbidite channel, turbidite sheet-like sand and semi-deep lake mudstones. Constitution and distribution of sedimentary facies are analyzed in each sand group which are based on high-resolution sequence framework. As a result, there are more mouth bar in the sand groups which belong to base-level falling hemi-cycles, whereas more distributary channel in the sand groups which belong to base-level rising hemi-cycles. In studied section, the sandstones in middle and lower part are thicker than those in upper part. The sandbodies are distributed along SW-NE direction and mainly located at the south-western part of the study area. Laterally, the sandbodies turned to be thinner and extinguished to upper direction of NW slope. Based on sedimentary facies distribution and other which are formed due oil and gas forming conditions, we can draw a conclusion that structure-lithologic trap to combination of sandbody distribution and nose structures are the main plays; furthermore, three plays are predicted in Dabusu area, south of Songliao Basin.