Volcanic Stratigraphic Sequence, Age and Comparison with Mountain Layer Type Profile of Bai 72 Well in Xinjiang Oilfield

Establishment of stratigraphic sequence and determination of age in the well is the key evidence for the delineation and comparison of rock stratigraphic units. This is of great significance to the exploration and development of oil and gas reservoirs. In response to the key problem that the main stratigraphy of the Baikouquan oilfield Bai 72 well, in Xinjiang, lacks a chronological basis and the rock assemblage of the formerly delineated Jiamuhe Formation and the original Jiamuhe Formation in the mountainous area is not comparable, we have reconducted core compilation and supporting sample analysis and testing, established the stratigraphic sequence in the well, obtained high−precision zircon U−Pb dating results, and combined with the logging data to establish the sequence and age of the 1 182～2 937 m well section of the Bai 72 well.The results show that:The well section is dominated by volcanic lava in the lower part and volcanic clastic rocks in the upper part, interspersed with multiple layers of land−derived clastic sedimentary thin layers during the interval of volcanic eruption. The well section can be divided into six lithologic sections using the thin layers of terrestrial clastic sediments as segmentation markers. The LA−ICP−MS zircon U−Pb age of (304.3±3.9) Ma and (306.6±5.1) Ma were obtained in the almond shaped basalt of the third rock section and the ambersite breccia lava of the fifth rock section, respectively, indicating that the stratigraphic age was Late Carboniferous. The rock assemblage, stratigraphy and age are generally comparable with the Hala’alate Formation section in the northern mountainous region of the Bai 72 well, so it is revised that the Permian Jiamuhe Formation belonged to the Late Carboniferous Hala’alate Formation, providing good example of a stratigraphic comparison between the well ("basin")−northern margin mountainous in the Baikouquan oilfield.