Experimental Study On Inhibiting Edge Or Bottom Water Invasion Of N₂/CO₂/Gas Mixture Huff And Puff

Fault-block reservoirs with edge or bottom water have the characteristics of fracture system development,reservoir type and oil-water system complexity,which can cause the water invasion during production.Water invasion can lead to early water breakthrough,fast water cut rise and reduced oil production.Gas injection huff and puff is an effective water cut control and oil increment technology which has the characteristics of small injection volume,not affected by the inter-well connectivity and minor gas channeling.For the problem of the water invasion of fault-block reservoirs with edge or bottom water,experimental study on inhibiting the water invasion of gas injection huff and puff is conducted.Through designing the 3D physical model,laboratory experiment methods are used to investigate the process of the horizontal well CO₂/N₂/N₂ foam huff and puff in the bottom water reservoir,and the effect on water cut control and oil increment is compared and evaluated.Based on the experimental results,the mechanism of water cut control and oil increment is analyzed.The experiments of CO₂/N₂/gas mixture huff and puff on inhibiting the water invasion are conducted by building the one-dimensional edge water model.By changing the injection volume and injection ratio,the effect on water cut control and oil increment is evaluated,and the adaptability of reservoir conditions and injection parameter optimization are investigated.The changes in temperature and pressure conditions during CO₂/N₂/gas mixture huff and puff are simulated by PVT-sim Nova numerical simulation software.The possibility of asphaltene deposition caused by gas injection is analyzed and the deposition pressure with different injection ratio of various gas injection is compared.The results show that the horizontal well CO₂/N₂/N₂ foam huff and puff in the bottom water reservoir has certain effect on water cut control and oil increment.However,the existence of fractures has a greater impact on water cut control and oil increment.Blocking fractures with high-strength starch gel can further improve the effect of CO₂/N₂/N₂ foam huff and puff.For the pure CO₂ huff and puff,the main mechanisms for oil increment are extraction,viscosity reduction and escape with oil droplets.For the pure N₂ huff and puff,the expansion of N₂ is the main driving force for the crude oil displacement.For the gas mixture huff and puff,when CO₂ and N₂ are injected at a ratio of 7:3,the synergistic effect of CO₂ slug and N₂ slug is best.Gas injection huff and puff has a good adaptability to permeability on water cut control and oil increment.The mobility control ability of CO₂/N₂/gas mixture is limited,and the permeability ratio should not be too large.Gas injection huff and puff technology is not only suitable for heavy oil reservoirs,but also for thin oil reservoirs.In the application of gas injection huff and puff,high injection pressure should be maintained,preferably above 15 MPa.The injection timing is preferably driven to the water cut of 60%by water flooding.The possibility of asphaltene deposition caused by gas injection is related to the composition of crude oil.When the content of heavy components in crude oil is high,CO₂ injection will cause asphaltene deposition,and as the CO₂ injection volume increases,the pressure range of asphaltene deposition decreases,and asphaltenes are more likely to deposit.Compared with CO₂ injection,asphaltene deposition is more difficult to occur with N₂ injection.For the gas mixture injection,when the injection ratio of CO₂ and N₂ reaches 1:1,the asphaltene deposition is most prone to occur.The experimental results can provide data support and reference for the application of gas injection huff and puff technology.