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Baiyun Sag has become the primary focus of deepwater exploration in the Pearl River Mouth Basin. However, its complex and high-variate geothermal characteristics have severely constrained further oil and gas exploration and resource evaluation. In this study, the present-day geothermal field and tectono-thermal evolution histories of Baiyun Sag were systematically studied based on measured rock thermal conductivity and heat generation data, borehole temperatures, low-temperature thermochronometer analyses, and geodynamic methodologies. The thermal conductivity of 251 core samples ranges from 1.131 to 4.478 W/(m·K), with an average of 2.258 W/(m·K), while the heat generation rate of 106 samples ranges from 0.868 to 1.735 μW/m³, averaging 1.499 μW/m³. The thermal conductivity in Baiyun Sag exhibits a gradual decrease from the Wenchang Formation to the Hanjiang Formation, whereas the heat generation rate decreases with depth. The present-day heat flow in Baiyun Sag ranges from 66.6 to 139.1 mW/m2, with an average of 89.7 ± 14.7 mW/m2, showing a gradual increasing trend from northwest to southeast. Formation temperature at depths of 1–5 km increases proportionally with depth. Thermal inversion, as inferred from low-temperature thermochronological data of six basement samples, reveals distinct temperature paths for each tectonic unit in Baiyun Sag. These paths are primarily linked to regional tectonic uplift-subsidence and basement heat flow variation. Geodynamic simulations further indicate two extensional events in Baiyun Sag during the Eocene and Middle Miocene, leading to a rapid increase in basement heat flow. This study systematically elucidates the present-day geothermal field characteristics and tectono-thermal evolution history of Baiyun Sag, bearing significant implications for regional tectonic evolution and future deepwater oil and gas explorations.

The element geochemical characteristics and diagenetic alteration products of tuffaceous components in sandstone reservoirs of Paleogene Wenchang Formation in typical subsags of the Huizhou-Lufeng area of the Zhu I Depression, Pearl River Mouth Basin, were identified through microscopic analysis and quantitative analysis of main and trace elements. The impacts of dissolution of different tuffaceous components on physical properties of reservoirs were discussed through quantitative characterization of reservoir physical properties. The results show that there are mainly four types of tuffaceous components in the study area, which are acidic, intermediate, basic and alkaline tuffaceous components. The acidic tuffaceous components evolved in a process of strong alteration and weak dissolution of alteration products, with a large amount of kaolinite precipitated during alteration to disenable the improvement of porosity and permeability. The intermediate and alkaline tuffaceous components evolved in a process of strong dissolution of tuffaceous components and strong alteration of residual tuffaceous components; the dissolution of tuffaceous components created intergranular pores, but the alteration products such as autogenic quartz, apatite and illite deteriorated the pore structure; ultimately, the dissolution of tuffaceous components resulted in the increase of porosity but no increase of permeability of the reservoir. The basic tuffaceous components dominantly evolved in a process of dissolution of tuffaceous components to strong dissolution of alteration products; both tuffaceous components between particles and laumontite generated from alteration can be strongly dissolved to create pores; thus, the dissolution of tuffaceous components can significantly increase the physical properties of the reservoir.

The Baiyun East area is one of the two favorable reservoir-forming areas in the Baiyun Sag in the Pearl River Mouth Basin. At present, exploration is facing the stage of turning to the deep strata of the Paleogene. In recent years, drilling has found that the sandstone in the deep gentle slope zone becomes less abundant, which contradicts the development model of extensional half-graben reservoirs. Based on the comprehensive interpretation of deep reprocessing 3-D seismic data and drilling data, a full 3-D structural analysis of the Paleogene and subbasement detachment surface in the Baiyun East area is carried out. The basin evolution stages are reclassified according to the dynamic mechanism. The tectonic sequence has been modified from a passive rift cycle to three cycles of passive rift-active rift-passive rift.The tectonic episode is subdivided into six curtains from three stage cycles: fault episode-fault depression conversion episode-depression episode is subdivided into rift two subepisodes-fold two subepisodes-rift shrinking episode-drift episode, and the subdivision scheme better reflects the law of strata deformation.A new model of compression-extension deformation of the Paleogene basin has been established in the eastern Baiyun area. In the development process of the extensional structure, the new model coordinates the Paleogene structure-sedimentary response of the eastern Baiyun area. This model enriches the evolutionary model of the South China Sea Basin and provides support for the exploration of new deep areas in the Baiyun Sag.

Abstract: The Huizhou Movement refers to the Middle Eocene tectonic transition from the early to the late Wenchang Rifting stage (about 43 Ma ago) in the Pearl River Mouth Basin. Based on seismic reflection, drilling, logging and geological data, fault characteristic analysis, denudation thickness recovery, magmatism statistics, regional tectonic dynamics comparison and other methods are used to reveal the characteristics, properties and dynamic mechanism of the Huizhou Movement. The Huizhou Movement mainly shows the North-South transition of rifting and the migration along the faults, basement uplift, magmatic diapir and stratigraphic denudation. It is believed that the Huizhou Movement is a comprehensive reflection of plate interaction and lithospheric thinning process in the Pearl River Mouth Basin, which is closely related to the transition of lithosphere from initial rifting to rapid thinning, the India-Eurasia hard collision and the change of subduction direction of the Pacific plate. The Huizhou Movement has significant influence and control on the Paleogene hydrocarbon-generating sags and the development of hydrocarbon source rocks, sedimentary system and deep high-quality reservoir, hydrocarbon migration and accumulation in the Pearl River Mouth Basin.

The Paleogene geological framework and evolution process in the central anticline zone in the Lufeng 13 sag in Pearl River Mouth Basin is well analyzed through seismic data and drilling data, and control of tectonic evolution on hydrocarbon accumulation is also discussed. The results show that the central anticline zone in the Lufeng 13 sag develops the upper deformation layer and lower deformation layer. The “arched graben system” is developed in the upper deformation layer, and the magmatic diapir structure and flowing deformation of plastic strata is developed in the lower deformation layer. The evolution process of the central anticline zone can be divided into four stages, i.e. fault block uplifting stage, prototype stage, strengthening stage and finalization stage. The geological framework and tectonic evolution of the central anticline zone control Paleogene hydrocarbon accumulation. The Paleogene two-layer geological framework is favorable for development of structural traps and composite traps; the paleostructure highs are the direction of hydrocarbon migration, and the gravitational gliding faults are the main carrier bed for vertical hydrocarbon migration; the tectonic uplift is a key factor for reservoir diagenesis improvement and preservation of primary pores, and also controls distribution of high-quality reservoirs. Keywords: Geological framework, Upper and lower deformation layers, Gravitational gliding faults, Hydrocarbon migration and accumulation, Carrier bed, The central anticline zone, Lufeng sag

Shelf sand ridge is a significant type of reservoir in the continental marginal basin, and it has drawn so much attention from sedimentologists and petroleum geologists. We were able to investigate the morphology, distribution, and sedimentary structures of shelf sand ridges systematically in this study based on the integration of high-resolution 3D seismic data, well logging, and cores. These shelf sand ridges are an asymmetrical mound-like structure in profiles, and they developed on an ancient uplift in the forced regression system tract and are onlapped by the overlying strata. In the plane, shelf sand ridges present as linear-shaped, which is different from the classical radial pattern; not to mention, they are separated into two parts by low amplitude tidal muddy channels. Corrugated bedding, tidal bedding, and scouring features are distinguished in cores of shelf sand ridges together with the coarsening up in lithology. All of these sedimentary characteristics indicate that shelf sand ridges deposited in the Pearl River Mouth Basin are reconstructed by the tidal and coastal current.