Reservoir Characteristics And Environmental Evolution Of Cambrian-Ordovician Carbonate In Nanpu Sag And Surrounding Area Of Bohaiwan Basin

The petroleum exploration of Nanpu sag and surrounding area of Bohaiwan basin is dominated by Tertiary,it begins to extend to Paleozoic carbonates since 10 years ago.However,the sedimentary environment evolution and reservoir distribution of Cambrian-Ordovician carbonate are still unknown,it becomes the main factor to suppress the Paleozoic petroleum exploration.Combined several research methods such as outcrop description,core and rock thin section observation,geochemical analysis,geophysical well logging,to conduct a comprehensive research for the sedimentary environment evolution and reservoir distribution of CambrianOrdovician carbonate,and provide an useful clue for Paleozoic petroleum exploration and the sedimentary research of Paleozoic.In order to divide sequence stratigraphic and recognize the sequence boundary of different level in Cambrian-Ordovician,research,such as outcrop studying,sampling conodont,carbon and oxygen isotope and log sequence analysis,are carried out on the basis of sedimentology,petrology,carbonate reservoir,hydrocarbon accumulation of buried hill,sequence stratigraphy,cyclic stratigraphy,etc.Twelve third-order sequence have been recognized in Cambrian and Ordovician in Nanpu sag and surrounding area of Bohaiwan basin.Sequence stratigraphic framework has been established as a clue for underground stratigraphic correlation and reservoir prediction.The depositional trend of Cambrian-Ordovician in Nanpu sag based on sequence stratigraphic setting has been studied.Eight kinds of sedimentary models has been set up for Cambrian-Ordovician in North China.Regard the end of the depositional time of Zhangxia formation as the dividing line,the Middle and Lower Cambrian is ramp platform to shelf environment,the Upper Cambrian to Ordovician is a rimmed platform.The sedimentary environment from Funjunshan to Maozhuang formation and Xuzhuang formation to Ordovician develop an open to restricted sedimentary cycle,respectively,and shelf margin slope deposition has been founded in regional area in Cambrian.Combined with the relevant evidence,the main controlling factor of sedimentary environment evolution has been summarized: terrigenous material input and carbonate aggradation control the platform type and the platform evolution in Cambrian-Ordovician,global sea-level change control the development and evolution of third order sequence in Cambrian-Ordovician,the development of deep-water sediment is the main sedimentary response of contemporaneous tension fault.Basing the result of oil production test and the analysis of reservoir differences,two broad categories of five sets favorable reservoir had been divided in Cambrian-Ordovician Carbonate in Nanpu Sag and Surrounding Area of Bohaiwan basin: weathering crust reservoir in buried hill and dolomite reservoir.Summarizing the controlling factor and distribution characteristics of different reservoir types and shows that weathering crust reservoir in buried hill is controlled by lithology,karstification,paleogeomorphic forms and fault structure.However,dolomite reservoir is mainly controlled by penecontemporaneous dolomitization,fresh water leaching process,dissolution,and supplementary control by burial diagenesis and hydrothermal dissolution.