Formation And Tectonic Evolution Of Central Paleouplift Of Ordos Basin And Its Relationship To Gas Accumulation

The Central Paleouplift plays a central role in the formation and tectonic evolution of Ordos Basin, and it is closely related to gas accumulation in the basin. The Central Paleouplift constructions are suitable for hydrocarbon migration and accumulation. This study conducted a multiple disciplinary approach and provides supportive and detailed data for exploration of oil and gas formed during Palaeozoic eon.This study investigated the formation and tectonic evolution of Central Paleouplift in different sedimentary periods, evolution of important tectonic boundaries, geological constraints of tectonic setting, formation mechanism of Central Paleouplift, and their contributions to the basic conditions for oil and gas accumulation. Based on the theory of basin analysis, stratigraphy, petroleum geology, geophysics approaches of this region and the connection among North China Plate, Qin-Qi Trough, He-Lan Aulacogen and Central Paleouplift the Formation and tectonic evolution of Central Paleouplift are clarified such as it is indicated that the background of Mesoproterozoic and Neoproterozoic of Ordos Basin is extensional setting. The whole set of caprocks of Mesoproterozoic and Neoproterozoic basin cannot be observed, but several separated basins and bock can be identified. Besides, Jinning movement happened at the end of Neoproterozoic shows substantial differences at south and western margin of Ordos Basin. The caprock of platform in Ordos Basin as a whole was gradually formed from Cambrian. It implies that Central Paleouplift was nonexistent during Mesoproterozoic and Neoproterozoic, and the Central Paleouplift was formed from the late Cambrian. Its formation was featudred by the Majiagou formation, with the lack of Well Zhentan2- Zhentan1-Ningtan1-Ling1 which experienced long term extrusion and rising stage. Consequently, the distribution of North China Sea, Qi Lian Sea and Qin Ling Sea was influenced by the existence of Central Paleouplift, Yi Meng uplift, San Men Xia uplift. In addition, although Central Paleouplift existed during Benxi age of Carboniferous and Shanxi age of Permian, its structure and setting implies difference in comparison with Majiagou formation. As the Central Paleouplift was nonexistent during the Late Permian, the uplift with relevance to fore deep of foreland basin did not exist. Within the Central Paleouplift, the geological structure of Ordovician top was changed with the evolution of tectonic sequences. The developing stages of Ordovician top surface were characterized by slope, low-angle uplift and depression from Shanxi to Yanan periods. Ordovician top surface failed into a structural pattern of uplift in the east and depression in the west part of Ordos Basin in last stage of early Cretaceous. The Central Paleouplift described by Ordovician top surface was merely present during late Cambrian to last stage of Shihezi. Discussion on characteristics of Xiangshan Group, tectonic setting in Northern Qi-Lian mountains in Cambrian-Ordovician, granites of Caledonian in the north QinLing mountains and the south margin of Ordos Basin, suture zone of Qin-Qi mountains, of Shang-Dan mountains. Evidence could be provided to show tectonic setting of Central Paleouplift. The Central Paleouplift was formed at an extensional setting and developed during the transpressional stage. L-Shaped Paleouplift therefore was formed under compression environment produced by Qi-Lian Trough extension from west to east during the early Caledonian, and in the mean time, the Qin-Ling Trough extension from south to north directions during the late Caledonian.Its relation to gas accumulation in Ordos Basin is also suggested such as Formation and tectonic evolution of Central Paleouplift mainly controlled the development of sedimentary condition, depression for the generation of hydrocarbon, conditions for accumulation, formations of caprock and traps, immigration and storage of oil-gas.