Study On CO₂ Flooding For EOR In Ultra Low Permeability Reservoir Of Longhupao Oilfield

In recent years,with high-quality reservoir exploration and development into the high water cut — especially high water cut period,production decreased year by year,the low permeability reservoir has become the focus of oil and gas production in our country.But because of poor physical properties,low porosity,low permeability,low natural energy and other factors resulting in low permeability reservoir,low permeability reservoir present high injection pressure,poor water absorbing capacity,slow effective in oil well,fast production decline and other characteristics,how to achieve economical and efficient development in ultra low permeability reservoir is the most important problem to be solved for yield replacement.This paper takes Daqing Longhupao oilfield Gaotaizi reservoir as the main research object,through theoretical analysis,laboratory experiment and numerical simulation,the feasibility of CO₂ flooding in ultra-low permeability reservoir is analyzed.By comparing and demonstrating a variety of theoretical prediction methods of minimum miscible pressure,determination of crude oil and CO₂ test by slim tube test method of minimum miscibility pressure is 20.3MPa.And,by carried out water flooding,CO₂ miscible phase displacement and non miscible flooding lab experiment,we found the breakthrough of gas recovery and ultimate recovery,gas oil ratio and injection capacity and CO₂ flooding injection pressure positive correlation.When gas breakthrough,gas/oil ratio increased,furthermore,the increase of the positive change with the pressure.Experimental results of water flooding and gas flooding show that the yield of miscible displacement is higher than that of water flooding,water flooding recovery was higher than that of non miscible flooding,core gas injection capacity is much higher than the water injection capacity,The ratio is greater than 16.318.Displacement pressure displacement fluid volume curve shows that the starting pressure gradient of water flooding is 2.9 times of the CO₂ flooding,CO₂ flooding could reduce formation pressure,and CO₂ flooding improves the relative permeability obviously.The relative permeability of gas phase is significantly lower than water phase.meanwhile,the rising rate of gas permeability is slow.Combining Longhupao oilfield Gaotaizi reservoir test well area geological characteristics,current well network condition and development data base data to build petrel phased geological model.Based on the results of laboratory test results and CO₂ injection method,well pattern deployment,injection production pressure,injection production method and other numerical simulation,The analysis results show that the Longhupao oilfield with CO₂ Gaotaizi reservoir drive development potential and implementation conditions.Expected recovery rate is greater than 30%,20 percentage points higher than that of water flooding.Through the comparison of different kinds of well pattern,determine the method of anti nine point method for enhanced oil recovery.Gas injection pressure is greater than 30 MPa,reasonable flow pressure range is 1³MPa.Final recovery rate of CO₂ flooding is 33.07%,increases yield obviously.