大川中地区须家河组二、四段地震相与沉积相研究

STUDY OF SEISMIC AND SEDIMENTARY FACIES OF THE 2ND AND 4TH MEMBERS OF THE XUJIAHE FORMATION IN THE GREAT CENTRAL SICHUAN

四川盆地上三叠统须家河组油气勘探开始于20世纪40年代,其中须二段、须四段是主要探目的层段,也是盆地周边地区寻找新气源最有利层位之一。依据地震地层学方法和理论,结合钻井与测井资料,将大川中地区须家河组划分成7个地震层序边界,分别为SB1—SB7,与之对应6个最大湖泛面,分别为MFS1—MFS6,并对层序界面的地震反射特征进行了总结。利用地震反射内部结构、外部形态和反射波终止类型,在大川中地区须家河组须二段与四段内共识别出平行—亚平行、前积、丘状、透镜状及发散状地震反射特征等5种地震相,并对18条二维地震测线进行了剖面地震相的综合解释,编制了须二段与四段的地震相平面分布图。通过地震相与沉积相的转换,分别划分出冲积扇、扇三角洲、辫状河三角洲以及湖泊等沉积体系,编制了大川中地区须家河组二段与四段沉积相平面图,对大川中地区须家河组构造格局的演化规律进行了分析。

Oil and gas exploration started in the 1940s in the Xujiahe Formation, Upper Triassic, Si- chuan Basin, of which the 2na , 4,h and 6th members are not only the maior targets, but also the most favorable horizons in search for new gas sources. According to the seismic and sedimentologieal studies, in combination with drilling data, there are seven seismic sequence boundaries in the Xujiahe Formation in the Great Central Sichuan area, namely SB1-SB7, corresponding to six large lake flooding surfaces, MFS1-MFS6 respectively. In this paper, the seismic reflection features of the sequence boundaries are summarized. Taking the advantage of seismic reflection internal structure, external form and reflection termination type, five kinds of seismic facies were identified and described, including the parallel, sub-parallel, foreset, hummocky, lenticular and divergent shaped seismic facies. Interpretation of seismic facies and sedimentary facies for 18 2D seismic sections was made and the distribution map of seismic facies for the 2nd and 4th members of the Xujiahe Formation compiled. Through the conversion of seismic facies to sedimentary facies, the Xujiahe Formation could be divided into several sedimentary systems, such as alluvial fan, fan delta, braided river delta and lakes. Based on the data, sedimentary facies maps of the 2nd and 4th members were compiled, and the history of tectonic evolution of the great central Sichuan area discussed.