The Research Of Microscopic Percolation Mechanism In L Reef Limestone Reservoir

The reef limestone is one kind of biogenetic originated carbonate reservoir,mostly developed in marine sedimentary environment,the study on filtration theory in limestone reef reservoirs is rarely reported.The research object of this paper is the largest scale reef reservoir in China,which has large reserves but low recovery.Because of the complexity of the reservoir geology and sufficient natural energy,the water content of the adjustment wells rose rapidly to above 90%when it just have been put into production.Therefore,the research of microscopic percolation mechanism are the most imperative problems to be solved,of which the oil and water movement is complex,the remaining oil distribution is complex and the EOR methods are not clear.Based on the basic geological characteristics of reservoirs,this paper studies the micro seepage mechanism by using various experimental methods,reservoir engineering and seepage mechanics theory and cluster analysis method,The main achievements of this thesis are listed as following:(1)By thin section analysis,SEM,high pressure mercury injection and nuclear magnetic resonance method,this paper studied the microscopic pore structure and microscopic pore fluid characteristics of reef limestone reservoir in L oilfield.The result shows that the microscopic pore structure types of reef limestone reservoir in L oilfield are complex.Four types of the fractures and solution cavities are presented,including relative tight type,fracture network type,fractured-vuggy type,and pore cave type.By cluster analysis method,the oil well production performance can be divided into three types,each type has a certain relationship with the classification of pore structure.The types of reservoir,physical properties and permeability and pore structure are the important factors influencing the production performance of oil wells.(2)Based on the four types of reservoirs and their classification criteria,the characteristics of oil-water seepage of various reservoirs were analyzed by using micro-water flooding experiment.The result shows that the relative permeability of water phase in residual oil saturation is very low.The theoretical model of microscopic water flooding shows that fluid viscosity,reservoir wettability,boundary layer thickness and dominant seepage channel are the main causes of this phenomenon.(3)Controlling the flow of water along the dominant seepage channel and reducing the viscosity of crude oil is the main direction of future oil production.