四川盆地东北部元坝地区长兴组层序-沉积相特征

Sequence-sedimentary Characteristics of Changxing Formation in Yuanba Area of Northeast of Sichuan Basin

四川盆地东北部元坝地区二叠系长兴组(P2ch)沉积期继承了吴家坪组末期古地理格局,经历了早期浅滩到中晚期生物礁镶边台地的沉积演化。通过野外露头、钻井、三维地震资料综合研究,将P2ch划分为2个三级层序,4个四级层序,以四级层序界面与高位体系域压缩法相补充作为绘图单元,通过单井层序精细标定,运用等分地层切片、沿层属性提取以及生物礁手工追踪等技术方法,编制了层序-沉积相图。研究表明:SQ1沉积时期,台地-陆棚沉积分异,生屑滩的分布由零星发育逐渐演化为连片分布;SQ2沉积时期,对应2期生物礁生长,前期在礁后发育礁后澙湖、生屑滩、滩间沉积,后期在主体部位发育暴露浅滩储层,滩后形成滩后澙湖沉积。P2ch生物礁滩发育在时间上具有早滩、晚礁的特征,平面展布上具有前礁、后滩的特征。

In the sedimentary period of Permian Changxing Formation(P2c),it inherited the palaeogeographic pattern at the late stage of Wujiaping Formation,it experienced the deposition evolution from shoal in the early period to the reef rimmed platform in the late period.Through a comprehensive research on the field outcrops,well drilling and 3Dseismic data,Changxing Formation was divided into two third-order sequences,four fourth-order sequences,the mapping unit were established by using the fourth-order sequences boundaries and added by highstand system tract compression method,through the fine calibration of the single well sequence,aliquot strata slicing,the technique layer attribute extraction and the reef manual tracking,a sequence-sedimentary facies diagram was compiled.Study shows that in the sedimentary period of SQ1,platform-shelf deposit is different,the distribution of bioclastic beach is evolved from sporadic development gradually into a continuous distribution.In the sedimentary period of SQ2,it is correspond to growth of the two reefs,lagoon,bioclastic beach,beach sedimentary are developed after reefs,on the growth stage of the reef,the exposed Shoal Reservoirs are developed on its main part,and post-reef lagoon sediment is formed at the post-reef period.The reef-flat development of Changxiang Formation has the characteristics that the beach is developed early and reef is developed later,the planar distribution is characterized by fore reef and back beach