Depositional evolution characteristics of the Triassic Baikouquan Formation in Xiazijie fan area of Mahu sag, Junggar Basin
Pan Jin1, Zhang Chang-Min1, Pang Lei2, Li Peng2, Zhu Rui1
1 School of Geosciences,Yangtze University,Wuhan 430100,China; 2 Research Institute of Exploration and Development,Xinjiang Oilfield Company,PetroChina,Xinjiang Karamay 834000,China
Abstract：Mahu sag is the largest oil and gas accumulation belt in the Junggar Basin, and the exploration target is focusing on the complex and highly heterogeneous coarse-grained deposits. To reveal the internal heterogeneity of coarse-grained deposits, we carried detail sedimentary and reservoir architecture analyses (e.g., configuration, size, direction and stacking patterns) by using seismic, core and well logging data from the study area. We have identified 12 lithofacies and 10 sedimentary microfacies that are composed of different combinations of lithofacies Based on the stacking patterns of sedimentary microfacies in vertical and lateral, we have identified 10 vertically stacked fan lobes. Each fan lobes is strongly affected by the depositional environment and has changed from stacked alluvial fans and fluvial fans to fan delta under the influence of overall rise of the lake level and the decreased supply sediment. A detail analysis of the sedimentary characteristics for each phase of fan lobes, including long axis, short axis, long axis and short axis ratio, thickness changes of inner and outer fan, slope gradient and grain size change, shows several progressive changes when fan move downstream: (1) the grain size has become smaller when moving downstream and is controlled by the slope gradient of fan. For example, sediment grain size has reduced significantly in a steep slope. (2) The numbers of channel and water discharge have decreased toward downstream. (3) The connectivity of sedimentary bodies in lateral and vertical has reduced. (4) The thickness of sandstone and conglomerate has become thinner, while the mudstone has become much thicker. The lacustrine deposits become more dominant. In summary, we have recognized six fan models for the Baikouquan Formation in Mahu sag, including alluvial fan, alluvial-fluvial fan, fluvial-terminal fan, fluvial delta-fan delta, fan delta and large fluvial fan.
Pan Jin,Zhang Chang-Min,Pang Lei et al. Depositional evolution characteristics of the Triassic Baikouquan Formation in Xiazijie fan area of Mahu sag, Junggar Basin[J]. JOPC, 2019, 21(6): 913-924.
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