Wei Wang

The Late Eocene Huizhou-A sandy conglomeratic system in the Pearl River Mouth Basin presents a highly heterogeneous reservoir system shaped by intense synsedimentary fault activity and variable depositional processes. Utilizing 3D seismic interpretation, well log analysis, and core calibration, this study reconstructs the tectono-sedimentary evolution, facies distribution, and diagenetic modifications controlling reservoir quality. Results show that the best reservoir quality is not confined to proximal fan-delta coarse-grained deposits near steep boundary faults, but occurs mainly in fan-delta front and braided-river-delta deposits, especially braided- and turbidite-channel microfacies. These reservoirs benefit from better sorting, favorable grain size, and higher textural maturity, whereas proximal clastic-flow deposits are poorer due to heterogeneity, poor sorting, and compaction. Reservoir quality is also depth-dependent: upper Enping reservoirs are mainly controlled by maturity, while lower Enping reservoirs are more influenced by grain size. Semi-quantitative analysis identifies the 7–11 km transport-distance zone as the optimal fairway for vertically stacked high-quality reservoirs. This approach not only guides exploration and development in the Huizhou Sag but also offers a transferable predictive model for similar steep slope lacustrine rift basins with comparable tectono-sedimentary settings worldwide.

Liaozhong Sag is an important hydrocarbon-bearing area in the Bohai Bay Basin. During the deposition of the Shahejie Formation, the provenance system within and outside the basin is complex with variable lithologies, leading to remarkable reservoir heterogeneity and obscure provenance effects on reservoir development. Based on detrital zircon U-Pb dating and petrological analysis, the eastern and western provenance systems of the Shahejie Formation are interpreted. The results indicate that the detrital zircons in the western Liaozhong Sag are predominately Archean and Cretaceous in age, with the material composition of sandy conglomerates closely matching that of the buried-hill drilled in the Liaoxi Low Uplift indicating an intrabasinal uplift as the primary source. In the eastern Liaozhong Sag, a tri-peak distribution of Archean, Proterozoic, and Cretaceous detrital zircons suggests that the Liaodong Uplift is not fully formed during this period. Instead, Archean and Proterozoic metamorphic rocks from outside the basin are the major sources, with occasional contributions from Mesozoic volcanic rock on the slope. Based on the provenance analysis and microscopic observation, we develop that in the west, sediments around the intrabasinal uplift are periodically exposed, leached, and intensely dissolved, leading to the formation of high-quality reservoirs with tightly calcareous cemented sandstone interbeds. In the east, two models of high-quality reservoirs and diagenetic evolution are established. One is characterized by shallow burial depth, volcanic provenance, minimal compaction, and extensive dissolution; and the other is characterized by greater burial depth, metamorphic provenance, and fracture development within conglomerate gravels.

The Paleogene sandstone reservoir of Huizhou Sag is an important target for deep exploration in the Pearl River Mouth Basin, South China Sea. Because of the intense volcanic activity, it had a significant impact on the development of reservoirs, making it hard to predict. The diagenetic process of volcanogenic sediment and their influence of the reservoir have been studied by petrographic analysis, X-ray diffraction and scanning electron microscopy (SEM). Four types of volcanogenic sediment were identified: volcanic dust (<0.05 mm), volcanic rock fragments, crystal fragments (quartz and feldspar) and vitric fragments. The strong tectonic and volcanic activity of the Wenchang Formation resulted in a high content of volcanic materials, which led to significant reservoir compaction. The main sedimentary facies types are fan delta facies and lacustrine facies; the thick lacustrine mudstone can be used as high-quality source rock. After the source rock of the Wenchang Formation matured and discharged acids, feldspar and rock fragments dissolved to form dissolution pores, which effectively increases the porosity of the reservoir, but the argillaceous matrix and clay minerals produced by the volcanic dust alteration would reduce the permeability of the reservoir. With the weaker tectonic activity of the Enping Formation, the sedimentary facies changed into braided river delta, resulting in the greater componential maturity of the reservoir. Due to the relatively small impact of acidic fluids on the reservoir, the pore types of the reservoir are mainly primary pores with good physical properties.

The sedimentary facies, architecture, and depositional mechanism of deltaic systems have been one of the global research hotspots in recent decades; however, the detailed distribution, sedimentary evolution, source rock potential, and major control factors of the coal-bearing shallow-water delta are still unclear. A typical shallow-water braided delta with coal-bearing source rocks developed in the Middle–Late Triassic Mungaroo Formation of the North Carnarvon Basin, which can be a good study area for an analysis of coal-bearing source rocks. In this study, the sedimentary facies, distribution and evolution, and coal-bearing source rock features of the Triassic strata were analyzed based on the integrated study of wireline logs, drilled cores, thin sections, seismic facies and attributes, and geochemical data. A range of shallow-water delta sedimentary facies was identified, including the proximal delta plain channel/interdistributary bay, distal delta plain channel/interdistributary bay, and the delta front. The coal-bearing shallow-water delta system of the Middle–Late Triassic Mungaroo Formation was characterized by the largest scale delta system with relatively broad proximal and distal delta plains and relatively narrow delta front subfacies. The scale of the delta system showed a trend of increasing from the Early Triassic Locker Shale to the Middle–Late Triassic Mungaroo Formation and then decreasing to the Late Triassic Brigadier Formation. The distal delta plain subfacies of the Mungaroo Formation should have the highest potential coal-bearing source rock, and the proximal delta plain also can be a favorable target for source rock evaluation. The major control factors of the coal-bearing source rocks of the Mungaroo shallow-water delta mainly included the Triassic megamonsoon climate, the topographic features, eustatic changes, and provenance supply. The proximal and distal delta plains of the shallow-water delta system with thin coal seams, carbonaceous mudstone, and dark mudstone lithologies’ association could be a favorable source rock exploration facies for the next stage of natural gas field exploration.

The discovery of the BZ19-6 large-scale condensate gas field illustrates the great potential of the sandy conglomerate reservoirs in the Bohai Bay Basin. However, the stratigraphic correlation of the sandy conglomerate sequence in northern Huanghekou Sag remains a challenge due to the lack of syn-depositional volcanic layers and biostratigraphic constraints. The challenge limits understanding the regional strata distribution and further exploration deployment. In this study, we conducted in situ U-Pb dating of vein calcite and detrital zircons of the sandy conglomerate samples from borehole BZ26-A. The vein calcite age and the youngest age of detrital zircons provide the upper and lower bounds of the depositional age, respectively. We also correlated the samples with those from well-understood strata through a comparison of XRD mineral components. The absolute age of 47.0 Ma of the vein calcite and the youngest detrital zircon age of 103.5 Ma suggest the sedimentary sequence is supposed to be referred to as the Kongdian Formation (65–50.5 Ma). The XRD data and petrological analysis suggest that the lithostratigraphy of the Kongdian Formation in Huanghekou Sag could be divided into at least three members, with Member 3 consisting of red sediment deposited in a hot and dry climate; Member 2 and Member 1 deposited as fan delta with major parent rock of Mesozoic volcanic rocks and Precambrian meta-granitoid, respectively. Member 1 shows significant potential for energy exploration due to high brittle mineral components and fracture development.

The Late Mississippian was a critical time interval in Laurentia's history, marking the transition from carbonate deposition on a stable platform, during the Early to Middle Mississippian, to extensive clastic deposition in the Pennsylvanian to Permian associated with the Laurentia‐Gondwana collision. In the U.S. midcontinent, Chesterian incised valley fill (IVF) systems that developed within a carbonate‐dominated platform provide new insights on the patterns and drivers of continental‐scale sediment dispersal during this transitional period. Here we report 1,037 new concordant detrital zircon U‐Pb ages from nine samples of Uppper Mississippian sandstone collected from cores in southwestern Kansas and from outcrops in northwestern Arkansas. The sandstones are characterized by major age clusters corresponding to the Grenville (900–1,300 Ma) and Taconic‐Acadian (350–500 Ma) orogenies and minor older age groups, suggesting derivation from the Appalachian region. A compilation of published detrital zircon ages from Early Paleozoic sandstones as well as from temporally equivalent units across North America, including from the Appalachian Foreland Basin, Illinois Basin, Arkoma Shelf, Ozark Dome, Black Warrior Basin, and Grand Canyon, suggests Chesterian sandstone age distributions are distinct from those of older sandstones and are consistent with a change to a dominantly Appalachian age signature that was roughly synchronous across the continent. Together, the new and compiled ages support development of a generally E‐W transcontinental sediment dispersal system in the Late Mississippian that was likely controlled by orogenesis on the eastern Laurentian margin, while local variations in the age signatures appear to be controlled by N‐S drainage networks, influenced by glacioeustatic fluctuations and local structures.

Researchers have long suspected a source‐to‐sink link between the Yangtze Block (and/or North China Block) and Eocene‐Miocene passive margin strata in Taiwan, and various models have been proposed to explain similarities in provenance and the presence of Archean grains. The East China Sea Shelf Basin, whose evolution has been neglected in most models, resides between potential mainland China source regions and the sediment sink in Taiwan, and occupies the corridor through which sediment would have been transported. Here we present 378 new concordant detrital zircon U–Pb ages from the Oligocene Huagang formation in the Xihu Sag, eastern East China Sea Shelf Basin. We also present a compilation of published detrital zircon data from major rivers across mainland China to evaluate potential sediment source regions. Detrital zircons in the Huagang formation range in age from 33 ± 0.4 to 2842 ± 43 Ma, with major clusters at 100–300 and 1,600–2,200 Ma and small early‐middle Paleozoic, Neoproterozoic, and Paleoproterozoic to Archean peaks. Visual and statistical comparison of age distributions suggest close relationships between the Min River and Eocene–Oligocene samples from western Taiwan and between the Oligocene Huagang formation and Miocene strata in western Taiwan. Combined with the tectonic and depositional evolution of the region, these observations suggest that Eocene–Oligocene sediments in Taiwan were mainly sourced from the Min River or similar drainage in the Cathaysia Block. However, the similarities between the Huagang formation and Miocene strata are best explained by reworking of the Oligocene sediment in the Xihu Sag and transportation to western Taiwain during Miocene tectonic inversion of the East China Sea Shelf Basin.