Unstable Well Test Interpretation Technology For CO₂ Flooding In Low Permeability Reservoirs

In recent years,CO₂ flooding technology in low permeability reservoir has been developing rapidly.However,the existing CO₂ flooding well test technology is complicated,and the CO₂ flooding well test technology is needed in the low permeability reservoir.Based on the numerical simulation method,the influencing factors of pressure recovery are analyzed from three aspects:reservoir characteristics,fluid characteristics and development process parameters.The main factors of pressure response characteristics are obtained.In the"composite reservoir model"Based on the"profile equalization method",the mathematic model of CO₂ flooding test in low permeability reservoir considering the start pressure gradient is established.The semi-analytical solution of bottom hole pressure is given by Laplace transform and other mathematical methods.The experimental results show that the pressure response of the experimental wells is controlled by the experimental data of the experimental wells,and the stress response of the test wells is analyzed and the well test interpretation is carried out.The study has achieved four aspects of achievement and awareness:?1?Vertical heterogeneity,segregation development,diffusion,dissolution and skin coefficient?within reasonable range?have little effect on CO₂ well test pressure response;The influence of horizontal permeability and permeability anisotropy on the pressure response of CO₂ flooding wells is the same as that of water flooding;The reservoir width,the original gas-to-oil ratio,and the original water saturation mainly affect the CO₂ flooding pressure-pressure derivative curve.?2?CO₂ pressure-pressure derivatives reflect the characteristics of composite reservoirs at different formation pressures.In the non-miscible flooding,the well section is long and the pressure-pressure derivative curve is low.When the miscible flooding is carried out,the well is not obvious and the pressure-pressure derivative curve is high.?3?The early pressure curve of the pressure-pressure derivative in the pressure recovery stage is the straight line of slope 1/2,which reflects the characteristics of the composite reservoir.After the water vapor is injected,the pressure recovery stage The linear flow characteristics of the curve are not prominent,showing the characteristics of the composite reservoir,and the method of profile equalization is established for the CO₂-crude oil-water three-phase system.?4?The pressure response of single well instability is similar to that of conventional waterflooding.In the process of pressure recovery and landing,the variation of tail curve is less than that of composite reservoir due to the existence of pressure gradient.