Diagenetic Differential Evolution And Controlling Factors Of Turbidite Reservoir In Shahejie Formation Of Niuzhuang Sag

The turbidite reservoir of Shahejie formation in Niuzhuang subsag is low permeability reservoir with strong Heterogeneity,great difference in physical properties and complicated genesis.In order to deepen the understanding of turbidite reservoir evolution in Niuzhuang subsag and guide the subsequent exploration,this paper studies the types and sequences of diagenesis of the turbidite sandbodies in the third member of Shahejie formation in Niuzhuang subsag,the differential diagenetic evolution of turbidite sandbodies in different fluid environments is analyzed,and the effect of differential diagenetic evolution on reservoir performance is analyzed based on the inversion results of porosity in the period of oil and gas injection in the study area,the controlling factors of reservoir physical properties in the study area are discussed.The results show that:(1)The main reservoir in Niuzhuang subsag is medium-high porosity and low permeability reservoir,which has good physical properties and average porosity of 17% during the period of oil-gas injection,belonging to a high quality reservoir;(2)The reservoir in the study area experienced compaction/early pyrite cementation/early calcite cementation ? feldspar dissolution/quartz enlargement/authigenic kaolinite precipitation ?(hydrocarbon charging)? dolomite cementation/a little quartz dissolution ? late ferro-dolomite cementation/quartz micro-dissolution diagenetic sequence,the diagenetic fluid undergoes a transformation process of “weak alkalescence-acidity-alkalinity”;(3)The temporal and spatial evolution model of fluids in Niuzhuang Subsag is established:About 30 ma ago,acidic fluid moved in the West,diffused to the whole Niuzhuang subsag at 26 ma,alkaline fluid began to appear in the West at 10 ma,and alkaline fluid spread to the East at 4 ma ago;(4)Diagenesis controls the physical properties of turbidite fan sand reservoirs in Niuzhuang subsag,in which compaction is the dominant factor for pore reduction,cementation is affected by the evolution of diagenetic fluid,and the degree of pore reduction varies in different fluid environments,dissolution can improve reservoir physical properties to a certain extent,and overpressure has a greater contribution to pore preservation;(5)The difference of diagenesis between the East and the west of Niuzhuang subsag results in the difference of physical properties between the East and the West.The strong compaction and cementation in the West leads to the loss of porosity,while the weak compaction and less cementation in the east lead to better physical properties.