Sedimentary System Of Passive Rift Basin In Sudan And Comparative Study Of Active Rift Basin In Bohai Bay

Although the area of rift basin accounts for only5%of the world, its oil and gas reserves account for16%of world reserves, a huge amount of resources."Rift" was proposed when Gregory studied the East African Graben in1894, which had obvious landscape features with a deep central valley, normal faults roughly parallel to both sides, or a combination of shear slip normal faults. The formation of this unique environment in the sediment, heaps up thickly, often up to several kilometers, and is also an important region gathering oil and gas. As a result, the study of rift basin system is of great significance.The rift basin is divided into two types according to mechanism:Active rift and passive rift, which are the two extreme modes of rift basin. These extreme modes are embodied in the depositional of reservoirs. Active rift basins originated from the apophysis of mantle heat flow or the plate subduction have the development sequence of volcanic activity followed by rift activity. The sedimentation of reservoir rocks is monocycle. Passive rift basins originated from the weakening of lithosphere intensity which is caused by extensional stress. The development sequence is rift activity followed by volcanic activity. The sedimentation of reservoir rocks is multi-cycle.Bohai Bay Basin of East China, the East African rift system, the Gulf of Suez rift basin are the highly studied active rift basins. Nearly half a century, the genetic mechanism, evolution model, basin filling, combination of reservoir, extensional tectonics and the both controls to the formation and the distribution of oil and gas reservoirs of these rift basin have been extensively researched. Especially the researches in eastern China rift system, has been formed rift basin gas accumulation theory about continental rift basins with Chinese characteristics. Passive rift basin is of the lower level, this study on the passive rift basin is Sudan Muglad basin, which is China National Petroleum Corporation’s exploration projects abroad.Rift basins in Sudan are the passive rifts which are formed and controlled by the Central African Strike--slip Zone triggered by the opening of Atlantic Ocean in Late Mesozoic. The three rifting sequences of Lower Cretaceous, Upper Cretaceous, and Paleogene are superimposed vertically, ranging from passive rift in Early Cretaceous to active rift in Paleogene. The sub-basins typically have a half graben geometry characterized by steep planar boundary faults and a low extensional factor. Trace volcanic activities and continuous tectonic subsidence result in a complete sedimentary cycle during Early Cretaceous and a set of excellent source rocks. The sediment system and the formation and distribution of oil and gas reservoirs and other features of Sudan rift basin are significant different from Bohai Bay Basin, eastern China.The project, on the basis of exploration results, aims to summarize the formation and characteristics of depositional system of the passive rift basin of Sudan, to form a passive rift basin system model to guide exploration and strategies techniques for passive rift basin to provide oil and gas exploration experience for these blocks and other similar basins.The study also based on previous studies to explore classification between the active and passive rift basins, clarify the factors affecting rift basin deposition system. On the basis of experimental analysis and investigation of modern deposition system we use the research ideas of "Historical Comparison ", combining with the method of "Sedimentary Comparison" to study the difference between the active and passive rift basin sedimentary system.The deposition of the modern Gulf of Suez, for example, with the research of typical active rift basin, Bohai Bay Basin and the typical passive rift basin of the Sudan Muglad basin, to systematically summarize rift basin system’s affecting factors and the process depositional characteristics, especially in the different water depth, slope and size factors and the different stages of the depositional system.Development of the rift basin system characteristics, directly controlled by the basin’s tectonic movement patterns. Rift basins of different ways of splintering, of different times, so the filling is also different.The mainly different sedimentary of the rift basin active and passive rift basin is the filling features are different. The nature of the fault, catchment systems, tectonic units (transformation zone, structural slope break) of active rift basins and passive rift basin have obvious differences, and these differences led to differences in depositional system. For example, the active rift basin with steep slopes, shovel-like, Block pedestal-like, plate-like and stepped-like, more developed offshore submarine fan deposits, while the main ramp zone, narrow and steep-type, developed fan deltament. Thus different tectonic units or structures controlled the distribution patterns of the specific depositional systems tracts and the sand bodies in the basin.We evaluate the classification between the active and passive rift basin, clarify the main factors affecting rift basin depositional system, and response of sedimentation to structural evolution, and then summary and figure out the differences of sedimentary environment and depositional systems between passive and active rift basin.Based on the full application of the rift basin resources at home and abroad, we established the passive rift basin’s new sedimentary systems models in different periods, of great significance to the future exploration and development of the development of sedimentary systems for large oil and gas fields, as well as providing guidance to enrich and develop the rift basin petroleum geology theory.