CO₂ Flooding Experiment Research Of Low Permeability Oil Reservoir In The Ordos Basin

With the oilfield development entered the middle and later period,the condition of petroleum exploitation is more and more severe,especially in the low?ultra-low?permeability reservoir,how to enhance oil recovery has been the focal point of attention.CO₂ flooding for enhancing oil recovery technology is considered to be an economic and efficient enhancing oil recovery technology,and which meets the world broad demands of energy conservation and emissions reduction,protecting the environment.The Ordos Basin has rich low?ultra-low?permeability oil and gas resources,but the surface is drought,and natural environment is fragile,therefore adopt CO₂ flooding?the water saving/no water flooding technology?has incomparable advantages.The Ordos Basin is the basin which carries out CO₂ flooding later than other basins in China,recognition and application of CO₂ flooding in the area is not enough comprehensive and systematic.The paper taked the Chang6 of M area of A oilfield of the Ordos Basin as the research area,and used the indoor experiment as the main research means,and conducted a series of CO₂ flooding relevant laboratory experiments,the systemic understanding of CO₂ flooding for enhancing oil recovery technology of the research area had been acquired,and which has important guiding significance to the field application and promotion of low permeability reservoir of the Ordos Basin for CO₂ flooding.By displacement experiments,combining with electron microscope and the measurement of surface tension and contact angle measurement and the measurement of density and viscosity measurement and infrared spectrum analysis method,the CO₂flooding mechanism and quantification intuitive understanding of affecting factors of oil displacement effect in the research area.Using unsteady-state oil displacement experiments to study seepage flow characteristics of the oil/water,oil/gas two phase.By CO₂-crude oil system phase behavior experiment,the CO₂-crude oil system PVT parameters had been gotten.The minimum miscible pressure of CO₂-crude oil in the research area had been gotten respectively by using thin tube method and the interfacial tension disappear method,and the empirical formula method to predict the minimum miscible pressure of CO₂-crude oil had been discussed,then,influence factors of minimum miscible pressure of CO₂-crude oil and reduction method of minimum miscible pressure of CO₂-crude oil had been researched by oil displacement experiments under different condition.By CO₂ plugging experiments and oil displacement experiments,the rule of CO₂ escaping in the porous medium had been revealed,and the expanding sweep volume technology had been formed.Using numerical simulation method,the optimization design of CO₂ flooding development program had been carried out,and the CO₂ flooding development program of the research area had been put forward.The main conclusion can been drawn as follows:?1?Reducing the oil-water interfacial tension,changing the composition of crude oil,which play negative role?Restricts the CO₂ flooding efficiency?in the CO₂flooding of the research area.Reservoir heterogeneity influence CO₂ flooding effect seriously,the greater the heterogeneity,the worse the flooding effect of continuous CO₂ drive.?2?WAG can inhibit gaschannelingeffectively,and which can delay the gaschanneling time and improve the oil displacement effect of heterogeneous reservoir.The WAG parameters under the condition of indoor experiment:gas injection speed is 50 ml/min?the ground under the standard conditions?,slug size is 0.1 PV,gas water ratio is 1:1,injection time is water cut 90%.?3?CO₂ flooding is more advantageous to enhance oil recovery in the research area,and the recovery is more than 10%higher than water flooding.The water flooding of the research area reservoir exists insurmountable contradictions:dimensionless oil production index falls sharply and the dimensionless liquid production index has alittlechange.?4?With C₂ and C₄ mole fraction increasing,the CO₂-crude oil minimum miscible pressure reduced,and the higher the light hydrocarbon component content in the injected gas,which will benefit for becoming miscible.Carring out the implementation plan of"lauryl polyoxyethylene poly propylene ether oxygen slug+C₂ gaseous hydrocarbon",can reduce CO₂-crude oil minimum miscible pressure significantly.?5?The most influencing factor of gaschanneling is heterogeneity,and reducing reservoir heterogeneity is the key to improve the effect of CO₂ flooding.Targeting for escaping in fracture and high permeability zone of matrix,"Gel system+Ethylenediamine"two-stage sealing channeling system had been developed,and cooperating with water alternating injection pattern,which can play sealing channeling system and injection pattern together,and get the best effect.?6?Recommended development program of CO₂ flooding in the research area:gas injection speed 10t/d,flowingbottomholepressure of producingwell 3.5MPa,continuous gas injection for 5 years,then transfer WAG11 for 10 years.The largest bottom hole flowing pressure of gas well is 27MPa,and the minimum bottom-hole flowing pressure of production well is 3.5MPa,and limit of gas-oil ratio of production well is 1200m³/m³.