Study On Steam Flooding After Multi-Thermal Fluid Stimulation In Mid-Deep Heavy Oil Reservoirs

Multi-thermal fluid stimulation is a potential technology for the development of mid-deep heavy oil reservoir.However,after multiple cycles of multi-thermal fluid stimulation,the gas stored in reservoir increased,and the formation fluid distribution became complicated.Gas channeling contradiction was becoming more and more serious,which seriously restricts the efficient development of oil reservoir.Research on the succession technology after multiple cycles of multi-thermal fluid stimulation is crucial.In this paper,the distribution law of fluid,temperature and pressure after multiple cycles of multiple thermal fluid stimulation is studied by numerical simulation for B oilfield in Bohai Bay.Through the PVT tests of heavy oil and N₂/CO₂ system and numerical simulation,the gas occurrence state in reservoir after multiple cycles of multiple thermal fluid stimulation was studied.Through numerical simulation,the effects of cold production,steam stimulation,steam flooding,intermittent steam flooding+single well stimulation and intermittent steam flooding+multi-well stimulation after multiple hot fluid stimulation were evaluated,and the best development method suitable for the oilfield was selected.The research results show that the formation gas saturation is less than 30%,the maximum value is 29.5%and the average gas saturation is 2.75%after multiple cycles of multi-thermal fluid stimulation.The gas distribution is uniform,and the gas saturation is high in the low pressure area and high position of the reservoir.The average formation pressure in the B08 well area is about 5.19MPa(3.15?7.64MPa),which is suitable for steam flooding and steam stimulation.After multiple cycles of multiple thermal fluid stimulation,N₂ and CO₂ in the formation mainly occur in the low-pressure area with high recovery degree and the top of the reservoir.The content of N₂ in the oil phase is?6.7%,and that of N₂ in the gas phase is?85%(the content of CH₄ in N₂ and CO₂ rich areas is as low as about 4%).The molar fraction of CO₂ is?1%in the oil phase and the molar fraction of CO₂ is?12%in the gas phase.Compared with steam simulation,steam flooding,intermittent steam flooding+multi-well simulation,intermittent steam flooding+B03 well steam simulation is the best way to development B oilfield after multiple cycles of multi-thermal fluid stimulation,because it's more economical to operate and has a higher recovery rate.In the stage of intermittent steam drive+B03 well stimulation effect,the recovery percent is relatively high,in which the injection speed is 300t/d,and the injection period is 1.5 months,and the shutdown period is 0.5 months.During the shutdown of well B08,the B03 well performs steam stimulation,and steam injection intensity was15t/m,steam injection intensity increased by 15%?20%in a cycle,and the well was shut down for 3 days.The final recovery percent of the intermittent steam drive+B03well steam stimulation is 19.932%,and the cumulative oil-vapor ratio is 0.456.