Experimental Research On CO₂ Injection Mode Optimization And Oil Displacement Improvement Under Well Pattern Conditions In Low Permeability And Ultra-low Permeability Reservoirs

There are some key problems such as poor CO₂ displacement effect and serious gas channeling phenomenon in low permeability and ultra-low permeability reservoirs,the parameter optimization study of CO₂ flooding injection and expanding sweep volume to improve CO₂ displacement effect was conducted.The effects of CO₂flooding on different permeability and heterogeneity of low permeability and ultra-low permeability cores were evaluated by physical simulation.Natural outcrops and artificial heterogeneous cores are selected,and the CO₂ injection method including water-gas alternating?WAG?,injection speed,injection parameters and injection volume and the adaptation study of water-gas alternating methods are studied.In order to reduce the CO₂ mobility ratio and improve the CO₂ flooding effect,a new thickener LSS is proposed.The stability system of the thickener and carbon dioxide was evaluated for temperature resistance,pressure resistance,shear rheology and oil displacement effect.The experiment based on the Chang 6 reservoir was conducted by the radial flow model under the anti-five-point well network.Combined with water flooding,continuous gas flooding,WAG flooding,thickener/CO₂ system flooding,subsequent gas flooding and subsequent water flooding.The CO₂ injection mode and oil displacement effect under ultra-low permeability reservoir conditions were comprehensively evaluated.Experimental results show that for the low permeability and ultra-low gas-water displacement mobility control effect is obvious,which can significantly delay the CO₂ escape,and the permeability is lower,gas channeling is later.For heterogeneous cores that the permeability ratio is 5?5/1?,10?10/1?and 50?50/1?,the permeability ratio is smaller,the gas-water ratio is higher,and the enhanced recovery is better.When the permeability ratio reached 10?10/1?,the gas channeling was obviously advanced,especially when the permeability ratio was greater than 50?50/1?,the gas-water slug could not start the remaining oil in the low-permeability matrix.Indoor experiments have shown that for low and ultra-low permeability in heterogeneous reservoirs,WAG can significantly reduce CO₂ mobility within the limits of adaptation,delay CO₂ escape time,start the remaining oil in the matrix and enhance the recovery of remaining oil.At the same time,the new thickener and carbon dioxide can form an experimental system with good stability,when the concentration of the thickener is 1.0%,the viscosity of CO₂ can be increased by about 20 times,which has obvious effect on reducing CO₂ mobility.And when the core permeability ratio is less than 10?10/1?,the thickener-carbon dioxide system can increase the recovery by more than 12%.Under the three-dimensional physical anti-five-point well pattern model,the WAG and thickener/CO₂ systems can reduce CO₂ mobility,delay gas time,improve oil displacement and increase oil recovery by 14.87%.Combined with indoor dynamic and static evaluation,the optimal experimental results of CO₂injection method can provide theoretical guidance and reference for the implementation of oilfield mine scheme and improvement of CO₂ flooding effect.