库车坳陷下侏罗统阿合组高分辨率层序地层特征

High-resolution sequence stratigraphy in Lower Jurassic Ahe Formation in Kuqa depression

通过钻井岩芯、测井资料分析,库车坳陷下侏罗统阿合组可识别出6个长期基准面旋回以及20～23个中期基准面旋回。阿合组区域性隔层一般发育在长期基准面旋回上升到下降的转换位置或非对称型长期基准面旋回(只有上升半旋回)的上部。长期基准面旋回是该区建立高分辨率层序地层对比格架的基础和关键。根据层序界面特征和相序的不同,可将中期基准面旋回大致划分为三种结构明显不同的类型(向上"变深"的非对称型旋回层序,向上"变浅"的非对称型旋回层序,对称型旋回层序);中期基准面旋回是进行储层非均质性研究、储层预测与生储盖组合分析的基本单元;中期基准面旋回明显地控制了储集体的岩性和物性的变化以及沉积微相的变化。中期基准面上升的早期易形成辫状河道砂体,岩性由粗变细,孔渗由高变低;中期基准面上升的中期一般为心滩坝沉积,岩性粗细和孔渗无规则变化;中期基准面下降的中晚期易形成河口坝、远砂坝砂体,其岩性由细变粗,孔渗由低变高;基准面下降的晚期易形成水下分流河道砂体。

Based on the analysis of drilling core and well log data, 6 long-term stratigraphic base-level (circles) and 20~23 mid-term stratigraphic base-level circles can be distinguished in the Lower Jurassic Ahe Formation in the Kuqa depression. The huge thick mudstone section deposited at the transfering position from uprising to subsiding of the long-term stratigraphic base-level circles or at the upper part of (nonsymmetric) long-term stratigraphic base-level. It is the main regional confining bed in the Ahe (Formation). According to the long-term stratigraphic base-level circles, the high-resolution sequence (stratigraphic) correlation framework of the depression can be established. Based on the analysis of sequence boundary and microfacies sequence, the mid-term stratigraphic base-level circles can be divided into three types of different structure (deepening upward nonsymmetric, shallowing upward nonsymmetric and (symmetric) mid-term stratigraphic base-level cyclic sequences). It is suggested that the mid-term (stratigraphic) base-level circles bear a close relation to source-reservoir-cap rock assemblage. The braided river channel sandbodies developed in the early stage of the uprising periods of the mid-term stratigraphic base-level circles. The channel bar sandbodies developed in the middle stage of the uprising periods of the mid-term stratigraphic base-level circles. The channel-mouth bar and distal bar sandbodies developed in the middle-late stage of the subsiding periods of the mid-term stratigraphic base-level circles. And the (subaqueous) distributary channel sandbodies developed in the late stage of the subsiding periods of the mid-term stratigraphic base-level circles.