The Origin And Integrated Prediction Of The Special Reservoir In Bayindulan Sag,Erlian Basin

A set of special reservoir develops within Aershan Formation of Bayindulan Sag,Erlian Basin.By using core,thin sections observation and X ray diffraction analysis,we do general study on the lithological characteristics of this special rock type and based on those,the lithological classification has been done.The result shows that the dolomitic rocks reservoir of Aershan Formation can be divided into three types in lithology: dolomitic sandstone,dolomitic mudstone,calcareous sandstone and conglomerate.Through core and cast thin section observation,physical property analysis and high pressure mercury injection analysis on special rocks,especially the physical property characteristics and pore types of dolomitic rock reservoir.The porosity range of dolomitic mudstone is 4.4%~36.4%,with an average of 16.01%,the permeability range is 0.01 mD ~26.3mD,with an average of 1.92 mD.Overall,the data shows that dolomitic mudstone is a "high porosity and low permeability" reservoir.The porosity range of dolomitic sandstone is 1.1%~33.7%,with an average of 16.07%,the permeability range is 0.01 mD ~5163mD,with an average of 79.72 mD.Overall,the data shows dolomitic sandstone is a "high porosity and medium permeability " reservoir.Dissolution pores and cracks mainly developed in dolomitic mudstone,intergranular porosity are also well-developed;Inter-partical dissolution pores and intra-granular dissolution pores are mainly developed in dolomitic sandstone,calcareous sandstone and conglomerate.This paper studies the main types and orders of diagenesis in special rocks by using thin sections observation and thermometry of fluid inclusions.The result shows that replacement and dissolution are the main diagenesis types that developed in dolomitic mudstone and the order of whose diagenesis is: formation of dolomite and ankerite?organic acid generation?dolomite dissolution.The main diagenesis types developing in dolomitic sandstone includes dissolution,cementation and replacement,and the main order of whose diagenesis is: slight compaction?quartz dissolution?quartz secondary overgrowth ? cementation of dolomite and ankerite ? organic acid generation ?dissolution of dolomite,ankerite and feldspar.The main diagenesis types and the main order of whose diagenesis in calcareous sandstone and conglomerate are similar to dolomitic sandstone.By using carbon and oxygen isotope analysis as well as microelement analysis,we studied the geochemical characteristics of dolomitic rock.The values of ?18O range from-18.4‰ to-3.6‰ with an average of-10.9 ‰,while the values of ?13C range from 0.4‰ to 8.7‰ with an average of 4.6‰,The contents of element Sr and the values of Sr/Ba are relatively high while the values of V/Ni are relatively low.By analyzing all the index of geochemical,we get the conclusion that the dolomitic rock within Aershan Formation of Bayindulan Sag formed in the enclosed alkaline environment with high temperature and high salinity.On the basis of integrated analysis of petrological features and geochemical characteristics of the special reservoir,this paper analyzes the genetic mechanism of special rock and establish the genetic model of dolomitic mudstone,dolomitic sandstone,calcareous sandstone and conglomerate.Abundant intermediate-basic volcanic rocks formed before and in Early Cretaceous provide special rock with important material basisMg2+ and Ca2+.Dolomitic mudstone formed in the process of dolomite and ankerite replaced CaCO3,which formed in the sedimentary phase.Dolomitic sandstone,calcareous sandstone and conglomerate formed as the result of that carbonate minerals precipitate out of intergranular pore water.The special reservoir in Bayindulan Sag is mainly affected by volcanic process,geological fault,sedimentary faces and developing areas and there are four favorable areas in study area.