琼东南盆地深层源汇系统特征及富砂性预测:以松南低凸起中段陵三段为例

Characteristics of deep source-to-sink systems and sand prediction in Qiongdongnan Basin:A case study

针对琼东南盆地深层古近系扇体分布规律以及富砂性认识不清的问题,以松南低凸起中段陵三段为例,在源汇系统耦合分析思想的指导下,基于岩石学、锆石定年及平衡剖面确定物源体系及其演化;利用精细三维地震解释和古地貌刻画搬运通道类型及分布;通过井-震结合厘定沉积体系类型及分布规律;最后,利用多种地球物理方法开展沉积体系富砂性预测。研究表明:松南低凸起为继承性古隆起,主要岩石类型为花岗岩、二长花岗岩,含少量花岗闪长岩,基底年龄主要为239~250 Ma。陵水组三段沉积时期,松南低凸起中段发育一个东陡西缓的剥蚀区,面积约186 km^(2)。以分水岭为界,向西供源区面积约141 km^(2),并可进一步划分出3个次级汇水单元,发育3条自东向西发育的大型古断槽,断槽平均宽度2.88~3.23 km,平均深度0.25~0.5 km,宽深比6.4~10.3,是沉积物输送的良好通道;并在三个断槽之下识别出3个三角洲,地震剖面上顺物源方向见明显前积反射结构,垂直物源方向呈透镜状反射。此外,基于与已钻井区地震相特征类比,并结合波阻抗反演和深度学习等技术综合预测研究区陵水组三段发育富砂三角洲,可形成良好储层,并可作为深部潜山油气运移的良好通道。

To clearly understand the distribution patterns and sand richness in deep Paleogene fan bodies in the Qiongdongnan Basin,the third member of Lingshui Formation in the middle part of Songnan Low Uplift was studied in detail as an example by coupling analysis on the source-to-sink system.First,the provenance system and its evolution were determined by petrologic work,zircon dating,and tectonic balance profile.Secondly,the types and distribution of transport channels were characterized by utilizing fine 3D seismic interpretation for paleogeomorphological reconstruction.Thirdly,sedimentary system types and distribution patterns were clarified combining well and seismic data.Finally,multiple geophysical methods were used to predict sand richness in the sedimentary systems.Results show that the Songnan Low Uplift is an inherited paleo-uplift,where the main rock types were granite and monzogranite,plus a few granodiorite.The basement age spans 239~250 Ma.During the sedimentation period of the third member of the Lingshui Formation,an erosion area of 186 km2,being steep in the east flank and gentle in the west,was developed in the middle sector of Songnan Low Uplift.Separated by the watershed boundary line,the westward source area was about 141 km^(2),and could be divided into three secondary catchment units,in which three large ancient faulted troughs were developed from east to west correspondingly.The average width of the troughs is 2.88~3.23 km,the average depth is 0.25~0.5 km,and the width to depth ratio is 6.4~10.3.They are good channels for sediment transport,and three deltas were recognized in each trough.The seismic profiles show a clear progradational reflection structure along the source direction,and a lenticular reflection was observed perpendicular to the source direction.In addition,based on the comprehensive prediction of seismic facies,wave impedance inversion,and deep learning,the development of sand-rich deltas in the third member of the Lingshui Formation could form good reservoirs as a good pathway for deep buriedhill oil-and-gas migration,which is of great significance for deep oil-and-gas exploration in this area.