Changmin Zhang

Lake-margin successions preserve interactions between terrestrial sediment supply and lacustrine deposition. We examined the Toutunhe–Qingshuihe succession at the Anjihai section in the western sector of the southern Junggar Basin using outcrop logs, lithofacies descriptions, sedimentary structures, and assemblage relationships. Eighteen lithofacies were organized into eighteen lithofacies assemblages (A–R), interpreted as depositional microfacies and grouped into four depositional facies: lacustrine (FA1), fluvial channel–floodplain (FA2), alluvial-fan (FA3), and shallow-water delta (FA4). Depositional systems constitute the highest level and comprise the stacking of depositional facies. The succession records Toutunhe shallow-water delta–lacustrine deposition (FA4–FA1), Qigu fluvial channel–floodplain deposition (FA2), Kalaza alluvial-fan–lacustrine deposition (FA3–FA1), and Qingshuihe lacustrine deposition (FA1). Repeated sandy–gravelly beds and their association with lacustrine fines support a possible gravelly beach-bar interpretation for parts of the Kalaza Formation. A fan-delta–beach-bar model is proposed for the Anjihai section. The documented facies changes provide a record of depositional evolution for comparison with regional models.

Based on core observations, well‐log data, and 3D seismic attributes, this study integrates lithofacies analysis, log‐facies interpretation, and seismic‐facies delineation to investigate the sedimentary characteristics and depositional architecture of the Enping formation in the Lufeng X Oilfield, Pearl River Mouth Basin. The Enping formation is interpreted as a shallow‐water braided delta system composed of distributary channels and interdistributary bays on the delta plain and underwater distributary channels, mouth bars, and interdistributary bays on the delta front. From the delta plain to the delta front, single‐channel sand bodies evolve from vertically erosional stacking to lateral channel‐stacking and isolated patterns, accompanied by decreasing channel scale, increasing channel number, and reduced connectivity. Seismic attribute calibration indicates that RMS amplitude responds positively to sand‐prone intervals, whereas RGB spectral decomposition attributes help delineate facies boundaries. On this basis, the spatial distribution and evolutionary pattern of the Enping formation sedimentary system are reconstructed, and a shallow‐water braided‐delta depositional model with a dominant sediment source from the northeast is proposed. The results provide a geological basis for reservoir prediction and remaining‐oil evaluation in the Paleogene interval of the Lufeng X Oilfield.

Digitate shallow-water deltas are commonly found in modern lakes and bays, as well as within cratonic petroliferous basins. They develop one or multiple sinuous finger-like sands (i.e., bar fingers), including high-R_SI (sinuosity ratio of distributary channel and bar finger ≥1) and low-R_SI (R_SI < 1) types. Bar fingers consist of four types of subenvironments, that is, distributary channels, point bars, mouth bars, and levees. However, the internal architecture within the above subenvironments is still unclear. This paper documents the internal architecture of a digitate delta based on the integration of shallow-core and ground-penetrating radar data from the Ganjiang Delta, China, coupled with Delft3D simulations. Our results show that multiple convex-up muddy-silty accretion beds are developed in mouth bars, which top lap the side of the distributary channels or point bars and down lap the bottom of the mouth bar. The accretion beds have low dip angles (10°) compared with those in the supplying river. This dip angle exhibits a negative relationship with downstream distance and a positive exponential relationship with lateral migration distance. Silty drapes become dense along the migration direction of the distributary channel. The levee develops multiple horizontal muddy accretion beds. The high-R_SI bar finger develops a large number (>3) of accretion beds in mouth bars with high dip angles, and a large number of accretion beds in thick levees, compared with the low-R_SI bar finger. The results of this paper provide insights into the prediction and development of cratonic digitate shallow-water delta reservoirs.

Abundant hydrocarbon resources were discovered in the Xiazijie fan-delta in the Triassic Baikouquan Formation in Mahu sag, Junggar Basin. However, the maximum depositional age of Baikouquan Formation and provenance of this fan-delta are still unclear, which would be unfavourable for further hydrocarbon exploration. In this study, we used detrital zircon U-Pb dating and composition statistics of conglomerate clast and sandstone grain from Baikouquan Formation to constrain the maximum depositional age and provenance of the Xiazijie fan-delta. The results showed that (1) the conglomerate clast compositions of Xiazijie fan-delta mainly consisted of tuff and intermediate-felsic magmatic rocks, and sandstone samples could be classified as litharenite type with the lithic fragments were almost entirely volcanic lithic fragments; (2) the average Qt:F:L values of sandstone samples (M152-S1 and M152-S2) were 26:7:67 and 21:8:71, respectively, and they plotted in the magmatic arc domain in the Qt-F-L ternary diagram, indicating the tectonic setting of source area of Xiazijie fan-delta was magmatic arc; (3) M152-S1 yielded U-Pb ages ranging from 417 Ma to 253 Ma, with a dominant age peak at 313 Ma and two secondary age peaks at 411 Ma and 268 Ma, respectively, while M152-S2 yielded U-Pb ages ranging from 467 Ma to 256 Ma, with a dominant age peak at 307 Ma and two secondary date peaks at 405 Ma and 262 Ma; (4) the mean age of youngest two zircon grains of M152-S1 was 254.8 ± 4.7 Ma, while that of M152-S2 was 257.6 ± 3.8 Ma, suggesting the Baikouquan Formation might be deposited after the Changhsingian to Olenekian; (5) the magmatic rock ages of central West Junggar were distributed mostly between 450–260 Ma, with a dominant age peak at 307 Ma. The ages distribution between magmatic rock of central WJ and detrital zircons of M152-S1 and M152-S2 were similar, indicating the central WJ domain should be the major source area of the Xiazijie fan-delta; (6) the magmatic rock of Hakedun–Hongguleleng area in the Central WJ was characterized by a peak age at 305 Ma, which was consistent with the peak ages of M152-S1 and M152-S2, indicating the Hakedun-Hongguleleng area was likely to be their major source area; and (7) one minor peak age at 411 Ma and another at 405 Ma were obtained from M152-S1 and M152-S2, respectively, and a zircon grain with Middle Ordovician age at 467 Ma was obtained from M152-S2, indicating Late Silurian–Early Devonian Chagankule pluton in the Saier Mountain and Ordovician Honggleleng ophiolite mélange in the Sharburt mountain were the minor source areas. This research has significant implications for stratigraphic correlation in Junggar Basin and hydrocarbon exploration in the Xiazijie fan-delta conglomerate reservoir.

The Upper Urho Formation on the northwest margin of the Junggar Basin is a key formation for oil and gas exploration. Based on the core observation, combined with the analysis of cast thin section, scanning electron microscope, energy dispersive spectrum, X-ray diffraction, fluid inclusion, and porosity-permeability test, the petrological characteristics, physical properties, diagenesis types, and their effects on the physical properties of the glutenite reservoir of Upper Urho Formation were studied systematically. The results show that the lithology of reservoir of the Upper Urho Formation in Zhongguai Salient is mainly conglomerate with a small amount of sandstone. The permeability of conglomerate is generally higher than that of sandstone, and the physical properties of granule conglomerate and fine pebble conglomerate are relatively better. The reservoir experienced complicated diagenesis, mainly including compaction, cementation, and dissolution, also including filler shrink seam and metasomatism. At present, the reservoir of Upper Urho Formation in Zhongguai Salient is mainly at the middle diagenetic stage A period and partly at the middle diagenetic stage B period. The original porosity lost by compaction is the largest, which is the fundamental reason for low porosity and low permeability of reservoir. The influence of cementation on reservoir physical properties has two sides. On the one hand, the development of cementation is the main reason for low porosity and low permeability of reservoir. On the other hand, the early cementation resists compaction to a certain extent and provides a material basis for the later dissolution. The reservoir of Upper Urho Formation in Zhongguai Salient is deeply buried and has experienced strong compaction and cementation, and the reservoir properties are poor, but the secondary pore space formed by dissolution improves the reservoir properties to some extent. The study concluded that the dense glutenite reservoirs of the Upper Urho Formation can develop relatively high-quality reservoirs on a local scale, which is of guiding significance for the exploration of the Upper Urho Formation.

Since Miall’s architectural element analysis (AEA) was introduced to China in 1986, the method has been widely applied to studying the heterogeneity of oil and gas reservoirs in China. The development history, research field, research progress, and potential limitations of AEA in China have been reviewed based on 601 Chinese documents retrieved from the China National Knowledge Infrastructure (CNKI) database and some English documents retrieved from various databases. The development of sedimentary AEA in China experienced four stages: (1) the conceptual and introduction stage (1985–1995), (2) the test and trial stage (1995–2005), (3) the popularization and application stage (2005–2015), and (4) the innovative stage (2015 to present). The research field covers all reservoir types of continental petroliferous basins in China. Papers published on AEA were distributed in the fields of (1) alluvial fan reservoirs, (2) braided channel reservoirs, (3) meandering channel reservoirs, (4) fan delta reservoirs, (5) braided river delta reservoirs, (6) shallow-water delta reservoirs, (7) large-scale delta reservoirs, (8) beach and bar reservoirs, and (9) lacustrine deepwater gravity flow reservoirs. Among all these fields, the architecture of alluvial fans, braided channels, meandering channels, braided river delta, and fan delta reservoirs was mainly researched. AEAs in China have made outstanding innovations in hierarchical sedimentary boundary surface classification, depositional architectural models, and quantitative reservoir architectural modeling. Combining the hierarchical AEA with geostatistical modeling, big data, and artificial intelligence technology and comprehensively using geology, geophysics, and production information to realize the hierarchical integrated reservoir architectural characterization are the development directions of the AEA in China and around the world.