| At present,during the development process of low permeability oilfields in China,there are some difficulties as following,difficult water injection,high water flooded degree,low utilization efficiency of water injection,low formation pressure of oil well,the decline of liquid production and oil production.As the gas-oil ratio is very unfavorable flow when gas injection,and prone to gas channeling,leading to a large part of the available reserves not being mined.Therefore,there is urgently need to adopt effective measures to improve the development effect of the block,to enhance oil recovery.CO2 foam flooding,as a kind of foam flooding,can greatly improve the apparent viscosity of injected fluid,expand the sweep volume,and the foam also has the advantages of low density,small damage to the formation,selective plugging ability for oil and water in the process of oil displacement.When the residual oil saturation is low,the sealing ability of foam is strong and the flow rate is low;when the residual oil saturation is high,the stability and sealing performance of foam is poor,the foam system can improve and enhance oil recovery effectively.In this paper,H block of Jilin oilfield is chosen as the test area,which block is a typical multi-reservoir heterogeneity low permeability sandstone oilfield.Based on full investigation of CO2-foam flooding mechanism,the three kinds of CO2 foam formula system were developed and optimized for the reservoir of H block:1)CO2+0.4wt%FP388 + 0.1wt%WP125;2)CO2+0.4wt%FP246 + 0.1wt%WP125;3)C02+0.4wt%FP275 + 0.1wt%WP125.The characteristics of the foam system in stability,foaming,injectable and permeability range and other performance were evaluated in laboratory.The results showed that,three kinds of foaming agents all have good foaming performance and stability,and that of FP388 is the best,and three kinds of foam system are all in the permeability range of injection.In order to ensure the foam system can fully foam in formation,the visual PVT cell of high temperature and high pressure which product model is 240/1000FV produced by the French ST company is used to study the phase characteristics of the determined CO2 formula system,to measure the parameters of volume,density,viscosity etc.of the foam system along with the change of pressure,to analyze the connection between the change of these parameters and the foam phase.The experimental results showed that,the stability of three kinds of foam system reduced with the increase of temperature,improved with the increases of pressure;three kinds of foam formula system still can form stable foam under high temperature and high pressure,but different systems have different critical pressure of forming stable foam;there is some relationship between foam density and phase state,and according to this relationship,we can determine whether to form stable foam by monitoring the density of the ground.The laboratory oil displacement experiments were carried on the CO2-foam system,by which the dynamic displacement effects of three CO2-foam systems were determined and compared in the core.The experimental results showed that,the same permeability of low permeability cores after water flooding,three kinds of foam system all can enhance oil recovery by more than 20%,all have better ability to enhance oil recovery.Finally combining with CO2 injection and foam flooding processes at home and abroad,a set of CO2-foam flooding field injection process and related tools were designed. |
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