川东北元坝地区长兴组层序地层及沉积相分析

Analysis of Sequence Stratigraphy and Sedimentary Facies of Changxing Formation in Yuanba Area of Northeast Sichuan

以Vail经典层序地层学理论为基础,根据露头、钻井、测井、地震等资料对川东北元坝地区长兴组进行单井层序地层划分。通过对单井层序地层特征的分析,结合三维地震,选择典型联井剖面进行了层序地层横向对比,并建立了层序地层格架;利用每个时期的古地貌图叠加地震相,得到沉积相平面展布图,最后分析各体系域的沉积相平面展布特征及演化规律。结果表明:元坝地区长兴组可划分为2个由海侵体系域和高水位体系域组成的三级层序,层序界面为Ⅱ型层序界面,层序向盆地方向逐渐减薄;2个三级层序中,海侵体系域厚度较薄,SQ2中高水位体系域在元坝X井中较元坝22井更为发育;礁滩主要在三级层序的高水位体系域中发育,海侵体系域中虽也有生长,但是规模小。

Based on the theory of Vail classical sequence stratigraphy, according to the outcrop, drilling, logging and seismic data, sequence stratigraphy of single well in Changxing Formation of Yuanba Area was divided; characteristic of sequence stratigraphy of single well was analyzed, and sequence stratigraphy of typical profiles in connected wells was laterally compared by the means of three-dimensional seismic, and sequence stratigraphic framework was established; sedimentary facies layouts were obtained by the overlay between palaeolandform map and seismic facies, and the characteristic and evolution rule of the layouts in different system tracts were discussed. The results showed that Changxing Formation in Yuanba Area could be divided into two third-order sequences which were composed by transgressive system tract（TST） and highstand system tract （HST）; the sequence boundary was type 1I , and sequence gradually thin toward the basin; the thickness of TST was thinner than that of HST, HST of SQ2 sequence developed in Well YuanbaX better than that in Well Yuanba22; reef and shoal mainly developed in HST of third- order sequence, and grew little in TST.