Experimental Study On Adaptability Of Gel Foam Assisted Gas Flooding In Fracture-vuggy Reservoir

The fracture-vuggy reservoir in Tahe Oilfield is difficult to develop,due to the complex reservoir structure,harsh reservoir conditions and serious formation heterogeneity of it.Water flooding is used in the early stage of reservoir development.During this stage,the production decreases rapidly and the water cut increases rapidly,which results in a low degree of oil recovery ratio.Gas flooding is easy to form the dominant flow channel of gas,which leads to premature gas channeling appears in production wells.The degree of enhanced oil recovery is limited.Foam can control the gas channeling and expand the gas sweep volume,so as to further improve the oil recovery.As the characteristics of high temperature resistance and high salt resistance of gel foam can meet the harsh reservoir conditions of Tahe Oilfield,the adaptability of gel foam in fracture-vuggy reservoir has been study in this thesis.Aiming at three typical reservoir types of fracture-vuggy reservoir in Tahe Oilfield,based on the understanding of karst background and actual geological data of Tahe oil field,three different physical models of fracture-vuggy structure are designed by the similarity criterion.Then one-dimensional simplified model of fracture-vuggy medium,two-dimensional visual connected fracture-vuggy model and three-dimensional macroscopic simulated fracture-vuggy model are made after that.The corresponding physical simulation experimental methods are established respectively.On the basis of perfecting the preparation method of gel foam and evaluating the stability of gel foam system,the physical simulation experiments of gel foam assisted nitrogen flooding in fracture-vuggy reservoir are carried out.The injection effect of gel foam in fracture-vuggy reservoir with high temperature and high salt is studied,the flow characteristics of fluid in gel foam assisted nitrogen flooding are analyzed,and the adaptability of gel foam in fracture-vuggy reservoir is clarified in this thesis.Starch gel foam system can withstand high temperature(120℃)and high salt(24×10~4 mg/L).This gel foam system has good oil resistance and viscoelasticity,which can meet the harsh reservoir conditions of fracture-cave reservoir in Tahe oilfield.It has a good effect of improving oil recovery under the condition of high temperature and high salt reservoir.Gel foam can control gas mobility and restrain viscous fingering.It has a good displacement effect on secondary fracture channel and high angle fracture,and can also stabilize displacement pressure and delay gas channeling time.Thus it can improve oil recovery in fracture-vuggy reservoirs with strong heterogeneity.The larger the amount of gel foam injection is,the better the effect of enhanced oil recovery is.Multiple period with small slug can better inhibit the formation of gas channeling channel than few period with large slug,and the oil displacement effect is better.Gel foam has a great displacement effect in three typical fracture-vuggy reservoir of Tahe Oilfield.