Sediment provenance and facies characteristics of the Lower Cretaceous Qingshuihe Formation in the hinterland of Junggar Basin (NW China) and its exploration implications

Origin of Mesozoic Biodegraded Crude Oils from the Eastern Chepaizi Uplift (Junggar Basin) Constrained by the Biomarker Recovery Method

“…However, it seems that even the greatest paleotemperature and formation pressure that the Mesozoic interval experienced were lower than the above-mentioned fluid traps and trapping pressures according to the investigated geological evolution of burial–thermal–pressure histories. , This abnormal phenomenon was similar to the cases in the Carboniferous and Neogene petroleum reservoirs in the eastern Chepaizi Uplift. ,, Thus, many literature studies reported that the paleofluid with high temperature and high pressure was involved in deep hydrothermal fluid activities and charged the study area so quickly that the paleofluid was trapped in calcite and quartz veins before the temperature decreased to the formation temperature. − Referencing the petroleum generation history, ,,, the sealing process of the Hongche Fault Zone, ,, and the charging history of neighboring petroleum reservoirs in the Chepaizi and Chunfeng oilfields, ,, the charging timeframe can be tentatively identified. From the Late Triassic-Early Jurassic, previous reconstruction burial and thermal history showed that the Permian source interval reached the threshold of hydrocarbon generation and entered into the peak oil window in the Middle and Late Jurassic. ,,, From the Late Jurassic-Late Cretaceous, the Hongche Fault Zone experienced strike-slip, dipping, and tension movements, ,,− thus possibly formed a petroleum accumulation of early period ( Th : 52.9–73.4 and 71.7–80.9 °C) in the Mesozoic interval, which was subjected to biodegradation or loss because of its shallow depth and poor preservation. Also, this view is confirmed by the history of crude oil filling in the Chepaizi and Chunfeng oilfields in the neighboring areas. , For higher temperature fluids (120.0–130.0 °C), many literature studies reported that it should be the adjustment accumulation. ,,, From the Neogene, the structure of the Chepaizi Uplift gradually began to tilt northward, , with the hydrocarbon supply intensity of Permian source rocks being very low and the re-extension of the Hongche Fault Zone, ,, which inferred the adjustment of heavy oils previously formed in the Chepaizi area or the Hongche Fault Zone.…”

“…This study also carried out paleogeomorphology restoration in the eastern Chepaizi Uplift (Figure ). It has been widely recognized that paleogeomorphology can control the filling process of the basin and the spatial configuration of the sedimentary system and then play a leading role in the formation and distribution of oil reservoirs. ,, As shown in Figure , the Cretaceous in the eastern Chepaizi Uplift is developed on the gentle slope belt inclined from NW to SE, and the terrain in the slope belt is undulating, showing the geomorphological characteristics of the valley and beam. The paleo oil was filled in wells P72 and P68, respectively, and migrated from the Shawan Sag along two valleys to the study area.…”

“…The Junggar Basin is a typical large-scale superimposed hydrocarbon-bearing sedimentary basin in NW China that is bounded to the SE by the Bogda and Boro Horo Mountains, to the NW by the Zhayier and Hala’alat Mountains, and to the NE by the Kelameili and Altay Mountains (Figure a). ,, The eastern Chepaizi Uplift is located in the NW of the Junggar Basin, which is mainly surrounded by two hydrocarbon-producing centers, that is, the Sikeshu Sag in the south and the Shawan Sag in the east. Also, it is adjacent to the Hongche Fault Zone in the east, the Zhonggai Uplift and the Dabasong Uplift in the NE, and the Zhayier Mountains in the NW (Figure b,c).…”