Study And Application Of CO₂ Flooding Gas Channeling In Low Permeability Reservoirs

Low-permeability reservoirs have the characteristics of low permeability,strong heterogeneity,and complex reservoir physical properties.It is difficult to achieve the ideal oil recovery effect using conventional reservoir water injection development methods.CO₂ flooding is a very important improve oil recovery method in low-permeability reservoirs.However,gas channeling will result in the poor performance of CO₂ flooding in low-permeability reservoirs.The XL10 fault block is a complex low-permeability reservoir.The G43 block is the worst developed.The reservoir has high temperature and pressure,high crude oil viscosity,high oil-water viscosity ratio,strong reservoir heterogeneity,and poor water injection development effects.Because such outstanding problems,it is urgent to study the technical solution of gas flooding to increase oil recovery.Therefore,studying the law of CO₂ flooding and gas channeling in this block and optimizing the gas injection plan are of great significance to keep the production.Firstly,this paper summarized the physical properties and fluid characteristics of the XL10fault block.Then,numerical simulation methods are used to establish a mechanism model to study the influence of different well patterns,permeabilities,reservoir heterogeneity and viscosity on the gas channeling and dynamic characteristics of production.Gas channeling identification methods and gas channeling prevention and control methods has been established.Guide with the actual block simulation model,the CO₂ flooding pilot area is optimized to carry out gas injection program optimization research,and a gas injection enhanced oil recovery program for the XL10 fault block is proposed to provide technical countermeasures for keeping the production of the XL10 fault block.Through this research and analysis,the thesis has mainly obtained the following conclusions:1.It is clear that the XL10 fault block is a low-permeability heavy oil reservoir with problems such as strong reservoir heterogeneity and poor water injection development effects.CO₂ has mechanisms such as viscosity reduction,interfacial tension reduction,acidification and plugging removal,which clarifies the technical countermeasures for CO₂ flooding to increase oil recovery.2.According to the physical properties of the reservoir fluid in the XL10 fault block,numerical simulation software Eclipse is used to divide the components,and a slim tube model is established.The minimum miscible pressure in the XL10 fault block is determined to be 37 MPa,which is higher than the original pressure of the reservoir.Therefore,CO₂ flooding cannot be achieved.Miscible.3.According to the mechanism model in order to study the influence of reservoir permeability,reservoir heterogeneity,and crude oil viscosity on gas channeling,we found that:(1)The higher the permeability,the earlier the gas channeling time of vertical well pattern,while the horizontal well and the combined well pattern show a later channeling time;(2)The heterogeneity of the reservoir has less influence on the gas channeling for the three well pattern types.The positive rhythm reservoir is more conducive to gas injection,and it is not easy to occur compared to the reverse rhythm which gas channeling or gas channeling time is later;(3)High viscosity of crude oil has more obvious effect of oil viscosity reduction after gas injection;(4)The identification method of the ratio curve of cumulative gas production to daily gas production can identify gas channeling,and has the characteristics of obvious stage division and strong regularity.The actual production can be combined with this method to assist in the identification of gas channeling.4.The CO₂ flooding method that uses gas and water alternately to control the gas channeling of the actual block and maintain the reservoir pressure is proposed.The simulation results show that:(1)Constant liquid production has a higher recovery rate and oil exchange rate than constant pressure production.The preferred production method is fixed-liquid production,and the preferred CO₂ gas injection rate is 0.3 HCPV,which is about 104,100 tons;(2)The CO₂ gas injection rate mainly affects the daily gas production and gas-liquid ratio,and the preferred gas injection rate is0.03 HCPV/a;(3)Preferred alternate interval time is 6 months and the injection slug size is 0.03HCPV,the result shows when water-to-air ratio is 1:1 has higher oil recovery;(4)In the G43 block gas-water alternate program,the gas-oil ratio and cumulative gas production ratio did not show that gas channeling occurs.