The Qiantang Sag, as one of the East China Sea Shelf Basin’s sags with thick residual Mesozoic strata, has long lacked comprehensive foundational sedimentary research, significantly impeding the understanding of the region’s resource potential and geological history. This study focuses on the Cretaceous strata of the Qiantang Sag, proposing a multi-phase sedimentary model for the Cretaceous Period. Through detailed analysis of the regional geological structure and sedimentary strata, this study unveils the complex sedimentary processes experienced by the Qiantang Sag during the Cretaceous. Utilizing drilling and core data combined with seismic geological interpretation, this study identifies that the western part of the Qiantang Sag predominantly developed alluvial fan and braided river deposits in an arid to semi-arid environment during the Cretaceous. Detrital zircon U-Pb dating analysis provides key information on the provenance areas and sedimentation ages, indicating that the Zhe-Min Uplift was the primary source region for the Qiantang Sag during the Cretaceous. Integrating vertical sedimentary sequences with provenance analysis, this study proposes sedimentary models and reconstructs the paleo-depositional evolution of the Qiantang Sag across different geological periods. During the Early Cretaceous Yushan Period, the region was influenced by intense volcanic activity, while also developing alluvial fan deposits in an arid environment. The Late Cretaceous Minjiang Period was characterized by semi-arid alluvial fan and braided river deposits. In contrast, the subsequent Shimentan Period saw the development of similar deposits, with the possible addition of seasonal lake deposits.

The Paleogene system of the Zhuyi Depression exhibits a pronounced mechanical compaction background. Despite this compaction, remarkable secondary porosity is observed in deep clastic rocks due to dissolution processes, with well-developed hydrocarbon reservoirs persisting in deeper strata. We conducted a comprehensive study utilising various analytical techniques to gain insights into the dissolution and transformation mechanisms of deep clastic rock reservoirs in the steep slope zone of the Lufeng Sag. The study encompassed the collection and analysis of the rock thin sections, XRD whole-rock mineralogy, and petrophysical properties from seven wells drilled into the Eocene. Our findings reveal that the nature of the parent rock, tuffaceous content, dominant sedimentary facies, and the thickness of individual sand bodies are crucial factors that influence the development of high-quality reservoirs under intense compaction conditions. Moreover, the sustained modification and efficient expulsion of organic–inorganic acidic fluids play a main role in forming secondary dissolution porosity zones within the En-4 Member of the LF X transition zone. Notably, it has been established that the front edge of the fan delta, the front of the thin layer, and the near margin of the thick layer of the braided river delta represent favorable zones for developing deep sweet-spot reservoirs. Furthermore, we have identified the LF X and LF Y areas as favourable exploration zones and established an Eocene petroleum-accumulation model. These insights will significantly aid in predicting high-quality dissolution reservoirs and facilitate deep oil and gas exploration efforts in the steep slope zone of the Zhuyi Depression.

The Myanmar region experienced the subduction of the Indian Ocean plate to the West Burma block and suffered from the land–land collision between the Indian continent and the West Burma block that occurred from the Late Cretaceous to the Cenozoic. Its tectonic evolution has been complex; thus, oil and gas exploration is difficult, and the overall degree of research has been low. Recent exploration has been hindered by a lack of knowledge on the evolution of the petroleum system. To address this, we conducted hydrocarbon generation and accumulation modeling using both the 2D MOVE and Petro-Mod software 2017 for a complex tectonic section in the Northern Central Myanmar Basin. The results show that the maturity threshold depth of the Cretaceous source rocks in the study area is shallow, and the underground depth of 1200 m to 1400 m has reached the hydrocarbon generation threshold, indicating the start of hydrocarbon generation. Since 48 Ma, the Ro of the source rocks has reached 0.7%, became mature quite early. The Late Cretaceous Paleocene and Eocene formation, located in the southeastern part of the study area, migrated and accumulated hydrocarbons towards the western arc zone in the Eocene and Miocene, respectively. It is worth noting that although the oil and gas potential of each layer in the island arc uplift zone is relatively low, which is conducive to the migration and accumulation of oil and gas generated by the source rocks of the depression towards the island arc zone, shallow areas with developed extensional faults should be avoided. This study is the first to conduct a preliminary assessment and prediction of oil and gas resources, which will provide exploration guidance and reference for the study area and its surrounding areas in the future.