陕北志丹三角洲长6油层组高分辨率层序分析与等时对比

以高分辨率层序地层学理论体系为指导思想,通过基准面旋回结构和叠加样式的沉积动力学分析,采用多级次基准面旋回划分方案,本文详细地讨论了陕北志丹三角洲上三叠统延长组长 6油层组高分辨率层序地层学特征,从该油层组中识别出四种具不同成因、产状特征、发育规模和识别标志的基准面旋回界面;以界面的成因和级别为依据,将长 6油层组划分为超短期、短期、中期和长期四个级次的旋回层序,其中超短期、短期旋回层序可细分为向上“变深”非对称型、向上变浅非对称型、对称型三种基本层序类型和更多的亚类型,在三角洲的不同沉积相带具有不同结构和叠加样式的分布模式。而中期、长期旋回层序以发育具完整湖进-湖退旋回的对称型结构为主,区域分布较稳定;根据多级次旋回层序划分结果,运用旋回等时对比法则对各级次旋回层序进行等时对比和建立不同时间尺度的时间-地层格架,讨论了不同时间尺度的层序地层格架在油气勘探开发各阶段的研究意义。

Analysis and Isochronostratigraphic Correlation of High-Resolution Sequence Stratigraphy for Chang-6 Oil Reservoir Set in Zhidan Delta, Northern Ordos Basin

On the basis of sedimentary comprehensive study of core and well logging, taking the high-resolution sequence stratigraphy theory from Cross T A. As an instruction through the technique of sedimentary dynamic analysis of sequence structure and stacking pattern of base-level cycle and using the classification system of six-grade division scheme of base-level cycle, the authors discuss in detail the high-resolution sequence stratigraphic characteristics of Chang-6 Oil Reservoir Set, Upper Triassic in Zhidan Delta developed in Northern Ordos Basin. In the study mentioned above, four grades and genetic types of base-level cycle interface can be recognized from the formation, which is of different occurrence characteristics, developmental scales and discriminating markers. Depending on the genetic characteristics of base-level cycle interface, the formation may be divided into four order cycle sequences supershort-term,short-term,middle-term and long-term cycle sequences. Among these sequences, the cycle sequences of supershort-term and short-tem may be ubdivided further into three basic types of sequence structure, including up-deepening non-symmetry, up-shallowening non-symmetry and symmetry from up-deepening to up-shallowienng, and into seven subtypes of low or high accommodation and non-complete or nearly complete symmetry. These basic sequence types and subtypes are of various stacking and distribution patterns in differentfacies belts of Zhidan Delta. The middle-term and long-term cycle sequences are usually of symmetric structures which develop complete depositional sequence of lacustrine transgressive-regressive cycle and distribute stably in the different facies belts of the delta. According to the high-resolution isochronostratigrahpic correlation of the turnround boundaries of the multi-order base-level cycles of Chang-6 Oil Reservoir Set, the chronostrata unit frameworks in different time scale can be built, which have different application significance in each stage of hydrocarbon exploration and development.