Three Dimensional Physical Model Experiment And Parameter Optimization Of CO₂ Huff And Puff In Heavy Oil Reservoir

The heavy oil resource is very rich in our country,thermal recovery technology is often used to develop it currently.However,the thermal recovery technology is suitable for reservoir which is shallow.It will suffer large heat loss and receive poor economic benefits when used in deep reservoir,resulting in heavy oil in deep reservoir not being effectively developed.The CO2 huff and puff technology can reduce the viscosity of crude oil and improve the flow capacity of the formation fluid in deep heavy oil formation,which is a new skill in developing deep heavy oil and have a good perspective.Study on the method of combination of the literature research,laboratory experiment and numerical simulation,reveals the characteristic of the phase state of CO2 heavy oil system characteristic,CO2 injection in heavy oil flow mechanism,stimulation mechanism to optimize the CO2 injection parameters,providing theoretical and practical basis to formulate reasonable development project.The main achievements of this thesis are as follows:(1)The experimental study on the fluid state of the original formation indicates that the content of C9 in the degassed crude oil is only 0.88%,and there is no light hydrocarbon content below C9,which shows a typical characteristic of heavy oil.(2)The experimental result shows that with the increase of CO2 injection,the saturation pressure of crude oil system increases,the density of crude oil decreases.The coefficient of expansion of crude oil increases.The viscosity of crude oil decreases but the decline is gradually reduced.(3)The P-T diagram of CO2 injection system in heavy oil shows that:with the increase of gas injection rate,the critical point of it shifts to the upper left gradually and the lighter the system becomes.The expansion and viscosity reducing ability of CO2 to crude oil enhances with temperature increasing when the temperature range of formation is below 245?.(4)Under the condition of the same viscosity,the equilibrium time of the degassed crude is greater than that of the crude oil containing gas.The diffusion coefficient of CO2 of the degassed crude is less than that of the crude oil containing gas,showing that the properties of the crude oil will affect the diffusion rate.The higher the heavy hydrocarbon content is and the less the diffusion coefficient of CO2 is,the longer the equilibrium time of system is.(5)The results of the CO2 huff and puff three-dimensional physical experimental model result shows that,with the increase of steam stimulation cycles,the total amount of oil increases and the net oil amount is reduced while viscosity of the production oil increases.CO2 has an extraction effect on the light content in crude oil.(6)The results of numerical simulation of heavy oil CO2 huff and puff mechanism demonstrates that the mechanism of CO2 huff and puff is mainly reducing oil viscosity and expanding oil volume as well as reducing the interfacial tension.The diffusion of CO2 in the formation is mainly concentrated in the region of 6cm radium around wells.With the increase of steam stimulation cycles,the increase of the range that the CO2 sweeps is less and less.(7)119 wells CO2 injection huff and puff parameter optimization shows that the optimal injection amount is 500t and the gas injection rate is 500 m3/d.The soaking time is 20 and the production rate after soaking liquid is 6m3/d.(8)It forecasts that there will be 214.59 t of increased oil with the optimal parameter combination than depletion drive one year later and 449.21 t of increased oil than depletion drive when two years later.It also forecasts that there will be 80.92 t increased oil with the optimal parameter combination than the injection production parameters on the field after one year and 168.62t increased oil after two years.