Quantitative Description Of Gas Channeling Channels In CO₂ Immiscible Flooding In Low Permeability Reservoirs

At present,CO₂oil drive is one of the main technologies to improve the recovery of low permeability reservoir.However,gas channeling is the main problem restricting the effective development of CO₂drive low permeability reservoir.Therefore,it is urgent to establish a characterization model for the quantitative description of gas channeling channels..According to the characteristics of the gas channel,Firstly,according to the production dynamic characteristics,the gas channeling in the study area is systematically analyzed.According to the permeability difference between diversion channel and matrix,three types of gas channeling are divided:high permeability and high conductivity,low permeability and high conductivity,high permeability and low conductivity.The analysis shows that the greater the permeability difference between matrix and diversion channel,the stronger the degree of gas channeling.Then,based on the black oil model,the effects of starting pressure gradient,stress sensitivity and CO₂viscosity reduction on gas channeling are comprehensively considered.the mathematical characterization model of gas channeling of CO₂oil displacement is established,The channeling channels between different types of injection-production wells are described,and the CO₂flooding of typical well groups in the study area is simulated.The analysis shows that the greater the permeability difference between injection and production wells,the smaller the breakthrough angle of gas channeling,the smaller the gas channeling area,and the greater the gas-oil ratio.When the permeability difference is 2-4 times,the gap of gas-oil ratio can reach 40-50 times.Finally,the injection-production index is optimized.The results show that when the permeability difference is less than 20 times,the gas injection rate under water-gas alternating flooding is 0.4PV/d,and the water-gas ratio is 1:1.For the high conductivity channel in the reservoir,the permeability differential limit that needs to be blocked is preferably 20 times.The method can be used to quantitatively characterize the gas channeling channel of CO2 non-miscible flooding in low permeability reservoirs,which provides guidance for the formulation of gas channeling prevention and control schemes for CO2 flooding reservoirs.