Percolation Mechanism Of CO₂ Flooding In WS Low Permeability Glutenite Reservoir

WS low permeability glutenite reservoir has poor waterflooding development effect due to its low water injection utilization rate,high comprehensive water cut and serious water flooding channeling.In view of these problems in water flooding development of this reservoir,it is necessary to study the mechanism of CO2 seepage in low permeability glutenite reservoir.A large number of studies also show that CO2 is a good oil displacement agent with unique physical and chemical properties such as solubilization and viscosity reduction.Therefore,this paper studies the mechanism of CO2 injection seepage,and provides basic data for the screening and scheme design of pilot test blocks of CO2 flooding for oil field companies.Based on a large number of investigations on reservoir characteristics,development characteristics,two-phase percolation characteristics and carbon dioxide displacement mechanism of low permeability glutenite reservoirs,the microscopic visualized percolation mechanism,PVT phase state,gas injection expansion and long core displacement of low permeability glutenite reservoirs are studied in this paper.The experiments and numerical simulations of low permeability glutenite reservoirs are carried out by means of scanning electron microscopy,X-ray-CT scanning,nuclear magnetic resonance,mercury injection,water flooding,CO2 miscible flooding and CO2 miscible flooding.The percolation mechanism of CO2 injection in permeable glutenite reservoir is studied.Through a large number of experiments and numerical simulation studies,the following conclusions and understandings are obtained:(1)Microporous pore structure experiments were carried out to study the reservoir characteristics of glutenite reservoirs.It is known that the pore types of glutenite rocks in the study area mainly include intergranular pore and intergranular dissolution pore,and there are locally gravel fissures and micro-fissures,and a small amount of residual intergranular pore can be seen.The physical properties of rocks after CO2 displacement are better than those before CO2 displacement.(2)Experiments on microscopic visualization seepage mechanism of water flooding,CO2 immiscible flooding and miscible flooding were carried out.The comparative analysis shows that the efficiency of water flooding is much lower than that of CO2 immiscible flooding,and the effect of CO2 immiscible flooding is not as good as that of CO2 miscible flooding.(3)Experiments on phase characteristics of CO2 injection have been carried out.It is known that the main properties of crude oil in the target block include smaller dissolved gas volume,lower bubble point pressure,smaller volume coefficient,smaller average gas dissolution coefficient,better compatibility between CO2 injection and crude oil,and that the reservoir belongs to typical unsaturated conventional black oil reservoir.In addition,the minimum miscible pressure of the reservoir is 33.51 MPa,while the formation pressure is 28.2 MPa,so CO2 injection in the reservoir is near miscible production.(4)Carried out single-tube high temperature and high pressure long core displacement experiment and numerical simulation experiment to study the seepage mechanism of CO2 injection.It can be known that the oil-gas two-phase zone is larger than the oil-water two-phase zone,and the residual oil saturation of CO2 displacement is lower than that of water displacement,and the displacement effect is better than that of water displacement.Gas injection parameters need to be further optimized.Through a large number of experiments,the seepage mechanism of CO2 flooding in low permeability glutenite reservoir is clarified,which provides technical support for the establishment of WS reservoir development plan.