Micropore Structure And Remaining Oil Distribution Characteristics Of Clastic Reservoir Based On Digital Core

At present,Daqing Lamadian Oilfield has entered the late stage of extra high water cut.The remaining oil resources are rich and the degree of exploitation is low,which is the focus of future development.However,after the reservoir enters the ultra-high water cut stage,there are problems such as the complex structure of reservoir microscopic pore structure and the unclear understanding of microscopic residual oil distribution.Therefore,it is of great significance to further study the pore structure and microscopic residual oil distribution characteristics and reveal the microscopic residual oil distribution law for the development of residual oil.This paper takes Gaotaizi clastic reservoir in the second area of northwest Labei,Daqing Oilfield as an example.The pore structure characteristics of the reservoir were studied by mercury intrusion data,and the classification standard of the reservoir microscopic pore structure was established.The pore structure of the clastic reservoir was classified into I,II and III types.The core samples with different pore structures were selected,and the pore structures of different types of samples were characterized by CT scanning technology,which verified the reliability of pore structure classification.The physical simulation experiment of water flooding was carried out,and the remaining oil occurrence form and distribution mode of different types of pore structure samples were characterized by CT scanning technology.The visual quantitative analysis of remaining oil was realized.It is considered that the microscopic remaining oil after water flooding in clastic reservoir can be divided into five types : large-scale connected,network,thin film,porous and isolated.The distribution characteristics of fluid in the pore throat before and after displacement were clarified,and it was considered that the oil phase in the pre-displacement stage mainly existed in the pores with large-scale connectivity,and the remaining oil types after water flooding were mainly network and porous.During the displacement process,the large-scale connectivity oil phase gradually transformed into network and porous remaining oil.It is found that the isolated residual oil increases with the decrease of permeability,and the thin film residual oil decreases with the decrease of permeability.The microscopic residual oil was quantitatively characterized,and the parameters characterizing microscopic residual oil were analyzed.It is found that,in general,with the reservoir physical properties becoming better and worse,the remaining oil distribution becomes more complex,and the remaining oil shows the characteristics of increasing block number,surface area,decreasing oil droplet radius,and poor oil displacement efficiency.