四川盆地西部新场地区须家河组四段9砂组地震沉积学

Seismic sedimentology of the 9th sand group in the 4th member of the Triassic Xujiahe Formation in Xinchang area of the western Sichuan Basin

90°相位转换及地层切片技术是地震沉积学的重要研究手段。但实际研究中,小级别地震等时界面难以对比,简单地进行90°相位转换,不能正确反映岩性和地震反射的关系。文中通过分频解释技术对比追踪小级别地震等时界面,在保证合理信噪比的前提下,利用钻井控制的混合相位子波反褶积技术有效地提高了地震分辨率;同时使地震剖面零相位化,明确了地震反射的地质信息。依据该方法对四川盆地西部新场地区须家河组四段9砂组(T3x4(9))展开地震沉积学研究,认为T3x4(9)砂组内砂体普遍发育,水下分流河道不断地迁移改道,致使砂体互相叠置;根据砂体的延展方向,判断物源主要为北部龙门山岛链,其中由于多期水下分流河道叠置,新场地区中部砂体厚度最大。由于砾岩抗压实性能够对砂体的孔隙起到保护作用,新场地区中部水下分流河道叠置区的砂体物性较好,为勘探有利区。

The 90° phase conversion and slicing techniques are two important seismic sedimentology research ap- proaches. However, tracing and correlation of small-scale isochronal seismic interfaces are challenging in reality, as the 90° phase conversion technique could not correctly reflect the relationship between lithology and seismic responses. The solution to the problem is to use SpecDecomp technology to trace the small-scale isochronal seis- mic interfaces and then improve seismic resolution with drilling-constrained mix-phase wavelet deconvolution technology while ensuring a rational signal-to-noise ratio. During the process, the seismic section is dephased and geological information is extracted from seismic responses. The new approach had been applied to the study of the 9th sand group of the fourth member of the Xujiahe Formation（ T3x4（9） ）in Xinchang area of western Sichuan Basin. The result shows that sandbodies are well developed inside the group and are superimposed with one another as the underwater distributary channels moved and shifted frequently. According to the extension direc- tion of the sandbodies,the authors judge that the Longmengshang island group in the north is the provenance. The central Xinchang area contains the thickest sandbody of all as a result of the superimposition of multiplephases of underwater distributary channels. As the compaction resistance of conglomerate can protect the pores of sandstone,the sandbodies in areas with superimposed underwater distributary channels have faw）rahle physical properties, therefore are considered potential exploration targets.