| On the basis of previous research results,the petrological characteristics,reservoir space types,reservoir pore permeability characteristics,diagenesis types,dolomitization genesis,diagenetic sequence and pore evolution of reservoirs are studied in Dachigan-Gaofengchang Drilling Sites by means of thin section identification,cathodoluminescence analysis,fluid inclusion analysis,in situ laser trace element analysis and 87Sr/86Sr isotope analysis.In addition,The drilling coring of Dachigan-Gaofeng profile and the outcrop of The Feixianguan Formation in Lichuan Gongjiayakou are compared with each other.The main achievements are as follows:(1)Oolitic beach of The Feixianguan Formation in Dachigan-Gaofengchang structure and Gongjiayakou reservoirs are mainly developed in The Third Section of Feixianguan and The Second Section of Feixianguan;The main rock types in the study area are micrite limestone,granular limestone,granular limestone and granular limestone,grain dolomite and(residual)granular dolomite.Reservoir space types are mainly intergranular pore,intergranular pore,intragranular pore and casting pore.Through the analysis of porosity and permeability,this paper considers that the physical properties of The Feixianguan Formation reservoir in Gongjiayakou are better.(2)The main diagenesis types of The Feixianguan Formation in Dachi dry-peak field are mud crystallization,compaction and pressure dissolution,cementation and filling,dissolution(including hydrothermal dissolution),dolomitization and so on.The selective dissolution of atmospheric freshwater during the syngenetic to quasi-syngenetic period forms the casting hole,which is an important dissolution in the area.The dissolution during burial period related to hydrocarbon generation has formed a large number of intergranular pores,and some intragranular dissolution pore.However,the filling effect is also obvious,which is the main reason for the tight reservoir of The Feixianguan Formation in Dachigan-Gaofeng field.(3)Sedimentary background,petrofabric and geochemical analysis show that dolomitization of The Feixianguan Formation has great influence on reservoir.There are mainly two dolomitization modes,i.e.the percolation-reflux dolomitization mode from syngenetic to quasi-syngenetic period and the dolomitization mode during shallow burial period.The dolomitization of Feixianguan Formation reservoir in Dachigan-Gaofeng field of open platform facies belt is mainly belong to the latter one.The early percolation-reflux dolomitization of The Feixianguan Formation reservoir in Gongjiayakou of platform margin facies zone is more obvious,and the dolomitization is obviously stronger,and dissolution in diagenesis stage is more developed.Therefore,more pore is retained.This is main controlling factor for the better development of The Feixianguan Formation reservoir in Gongjiayakou.(4)This paper clarifies the relationship between diagenesis,pore evolution and hydrocarbon filling stages.In the diagenetic stage of the seabed and continents,the early atmospheric freshwater calcite cementation,syngenetic dissolution and osmotic reflux dolomitization occurred,which reduced the primary intergranular pore and formed intergranular pore and early casting die pore.The osmotic reflux dolomitization was more intense in The Feixianguan Formation at Gongjiayakou.Compaction and pressure dissolution during shallow burial period are one of the main reasons for the decrease of porosity,but the shallow burial dolomitization during this period can improve the pore development to a certain extent.During the middle burial period,liquid hydrocarbons began to form.The dissolution of organic acid fluids formed a large number of intergranular,intragranular and intergranular dissolution pores,but almost all of them were filled with calcite,dolomite,fluorite and other minerals in the deep burial period.Gaseous hydrocarbons began to form in the deep burial stage and reached the peak in the uplift burial stage.The burial dissolution in the uplift burial stage was also filled by the latest calcite.(5)Based on the characteristics of sedimentary facies,energy storage coefficient,dissolution development degree and dolomite distribution,the reservoir of The Feixianguan Formation in Dachigan-Gaofengchang structure is comprehensively evaluated.It is considered that favorable reservoir development areas are mainly distributed in the East and northeast of Dachigan-Gaofeng field,It is considered that the favorable reservoir development areas are mainly distributed in the East and northeast of Dachigan-Gaofeng field,with well Fengl5 to Chi50,well Chi61 to well Chi037-2 to well-Chi10 and well Chi19 to well-Chi2 as typical areas.Oolitic beach thickness,atmospheric freshwater dissolution and burial period dissolution are strong in these structures,and the content of dolomite and asphalt is high,which is a favorable reservoir development area. |
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