Study On Enhanced Oil Recovery Effect And Parameter Optimization Of CO₂ Synergistic Huff And Puff In Shale Reservoir

Due to the complex pore structure and strong heterogeneity,shale oil reservoirs are difficult to be effectively developed in practical situations.CO₂ single well huff and puff and gas flooding technology can expand and increase energy,reduce crude oil viscosity and extract light hydrocarbons,etc.,and synergistic huff and puff can effectively inhibit gas channeling and increase the average formation pressure through the linkage between multiple wells.There is huge potential in terms of recovery.This thesis compares the applicability of gas flooding and huff and puff in shale oil reservoirs through experiments,establishes a single-well numerical simulation model,studies and analyzes the practical effect of the mine and optimizes the parameters.Through the establishment of the synergistic huff and puff well group model,the influence of number of wells,production modes,and gas injection distribution on the synergistic effect is analyzed,which provides an effective solution for mine application.The results of indoor physical experiments on CO₂ displacement and huff and puff showed that under the condition of low permeability（such as 0.057 m D,0.0016 m D）,the CO₂ huff and puff has better applicability,and the two are exploited in the early stage of development.There is not much difference in the effect.With the extension of development time,the huff and puff effect gradually dominates due to the higher sweep volume and the effect of fully replenishing energy,and the recovery factor is eventually higher than the gas flooding recovery factor.A typical horizontal well numerical simulation model is established,and the results verify that gas channeling and short injection time are the main reasons for the poor stimulation effect of the single-well CO₂huff and puff pilot test.The simulation curve shows that the gas injected effectively is only 25%of the total gas injection,and the average pressure of the formation under the current injection time can only increase by about 4 MPa,which is far from the effect of effectively restoring the formation pressure.Parameter optimization shows that the injection volume is 4000 t and the injection rate is 40000 m³/d,which has the best recovery effect,and the oil change rate of the first two rounds is higher than 0.6.Based on the geological model,a numerical simulation model of collaborative huff and puff in shale reservoir considering the influence of fracture gas channeling is established to analyze the influence of different development methods and parameter changes on the ultimate recovery factor.Multi well huff and puff can effectively increase the CO₂ sweep volume and inhibit gas channeling,and has a higher gas utilization rate,which is higher conducive to the CCUS project.Synchronous synergistic huff and puff has the multiple effects of supplementing formation energy,inhibiting gas channeling and expanding gas sweep volume,and the stimulation effect is the best.Due to diffusion effects,more production can be achieved when more gas is injected into the intermediate well.