Genesis And Spatial Distribution Model Of Calcareous Interlayer Of Toutunhe Formation In Shinan Area,Junggar Basin

Calcareous interlayer are widely developed in Jurassic in the hinterland of Junggar Basin.As an ineffective layer in reservoir,they can not only reduce the effective thickness of reservoir,but also increase the heterogeneity of reservoir.From the point of view of secondary and tertiary recovery,calcareous interlayer plays a great role in the process of oil recovery.Interlayer will have a specific impact on the distribution of remaining oil and control effect,mainly by its shape,distribution scale,reservoir location and thickness and other factors.The study of Toutunhe formation in Shinan4wellblock has important practical and theoretical significance,and can provide endorsement for the development and exploration of subsequent oilfields.Based on the data of cores,thin sections,casting thin sections,scanning electron microscopy,X-ray diffraction and conventional logs,the characteristics of calcareous interlayers in Toutunhe Formation of Jurassic in Shinan 4 wellblock,the genesis mechanism of interlayers,logging influence characteristics and distribution scale of interlayers are discussed in depth.The results show that the main lithologies of calcareous interlayers inin the study area are gray,grayish-white calcareous?medium?fine-grained lithic sandstone,?fine?medium-grained lithic sandstone and unequal-grained lithic sandstone,with medium structural maturity and low component maturity.Calcareous cements are mainly iron calcite,followed by calcite.Based on formation dip logging data and conventional logging data,thin calcareous interlayers can be accurately identified.On this basis,logging identification criteria for calcareous interlayers inin the study area are established.The source of calcareous cements and acid water are studied.It is considered that the formation of calcareous interlayer inis caused by diagenesis.During diagenesis,Ca²⁺ions produced by feldspar dissolution in clastic grains are combined with a large mount ofreleased from thermal evolution of organic matter to form calcium carbonate precipitation,thus forming dense calcareous intercalation.Calcareous interlayers usually develop vertically in two parts:first,the characteristics of"bottom calcium"and"top calcium"in the development of mudstone and sandstone contact surface;second,the characteristics of"top calcium"in the development of thick sandstone layer anywhere.The plane distribution of calcareous interlayers is controlled by faults and sedimentary facies zones.The thickness of well calcareous interbeds near faults is larger.The sedimentary facies zones are mainly developed in underwater distributary channels and estuary bars in the front of delta.