Study On The CO₂ Injection Experiment And Material Balance Of TSD Low Permeability Reservoir

After water flooding and polymer flooding,Gas injection flooding is another important way to enhance oil recovery.As a kind of effective EOR methods,Gas injection flooding is widely applied in oilfields all over the world.Among them,the CO₂ injection flooding technology has dual advantages in greenhouse gas emissions and enhancing oil displacement efficiency.It also got the attention of petroleum technical personnels and has great potential and development prospects.On the late period of water flooding,the TSD oil field has the characteristics of high Water Content and faster production decline,and need to explore and study the adaptation of CO₂ flooding technology in this field.This study mainly adopts the indoor physical simulation.Firstly,gas injection expansion experiment of CO₂ and hydrocarbon gas was used to evaluate the influence of oil properties by gas injection.Secondly,long core experiment was carried out to evalute the feasibility of CO₂ injection flooding.Finally,a material balance equation which considered effect of the dissolution of CO₂ in brine would be established.Through this study,we get the following conclusions and understandings:1)The study of gas injection expansion experiment and asphaltene deposition experiment Shows that:Injected gas could make the volume of crude oil expand,increase the volume factor and gas-oil ratio,and decrease the viscosity of oil.CO₂ has better effects of expanding volume and decreasing viscosity than the hydrocarbon gas.Both of them would not cause asphaltene deposition.2)The result of slim tube experiment shows that:The minimum miscible pressure of CO₂ injection is 25.54 MPa.The MMP of hydrocarbon gas injection is 41.34 MPa.Therefore,when the gas injection pressure is 32 MPa,CO₂ injection flooding is miscible flooding,but hydrocarbon gas injection flooding is immiscible flooding.3)Long core experiment of different gas injection methods shows that:WAG injection is more efficient on displacing oil than continuous gas injection.CO₂-water alternating injection has a better displacement effect than continuous CO₂ injection.Hydrocarbon gas-water injection also has a similar regular.4)Long core experiment of different WAG parameters shows that:A smaller slug volume has a better displacement efficiency.There is a best effective displacement results when the slug volume ratio of gas and water is 1:1.The displacement effect of 0.05HCPV slug volume of gas and water is better than effect of 0.11 ICPV.And the 0.15 HCPV slug volume of gas and water has the worst displacement efficiency.When the slug volume ratio of gas and water is 1:1,the displacement efficiency of CO₂-water alternating injection reaches the highest value which a little more than displacement effects of slug volume ratio 1:2 and 2:1 of CO₂ and water.5)The study of Material balance equation shows that:Empirical formula of transition zone volume got by slim tube simulation experiment could correctly reflect the regular of the transition zone volume and is also suitable for other CO₂ injection displacement reservoirs.The material balance equation for CO₂ injection displacement reservoirs could correctly evaluate effects of CO₂ dissolution caused by the early water injection.It also has a good precision for calculation of reserves and production prediction.This material balance equation could provide theoretical basis for analysis on CO₂ injection displacement reservoirs.