The Control Factors on Hydrocarbon Accumulation of Jurassic in Alashan Fault Block
The differential structure process found in Alashan fault block results in no well-developed source rocks in Bayinhaote basin;the source rock in Chaoshui basin reaches mature stage,but seldom well-developed source rocks occur due to multiple small sub-sags formed by synsedimentary faulting activity.Hence,it is hard to shape commercial medium-and small-scaled oil and gas fields.In Yabulai basin,huge thick and good source beds are developed,but because of sedimentary center migration and structural denudation,which leads to non-mature condition in fine source rock segment,it is also unable to form commercial fields.Moreover,in Chaoshui and Yabulai basins,owing to their absence of developed source rocks beyond Jurassic,commercial fields won't be found in the future.The study results indi cate that the major factors controlling scale and shape of Jurassic coal-bearing reservoirs are the suitable structural superimposing conditions,matured and a certain quantity or quality of effective source beds as well as multi-complete sets of cyclic quasi-sequence group with lake level variations.