| In July 2012,CO2 flooding test was carried out in the small well spacing test zone of the black 79 block in Daqingzi oilfield.With the continuous advancement of small-hole distance CO2 test,due to the heterogeneity of reservoirs,development contradictions such as unbalanced flat displacement and poor longitudinal suction profile have gradually emerged.Continuous injection of gas has resulted in the gradual formation of oil wells and injection wells.Gas channel and high production gas wells gradually increased,affecting the yield in the test area.The water-gas alternately displacing technology named WAG(Water-Alternating-Gas)currently used can improve the injection and production profile to a certain extent,and expand the volume of coverage.However,due to the complexity of the pore structure for the ultra-low permeability reservoirs,there is an urgent need to carry out research on control of gas logging and enhanced oil recovery to more effectively improve the CO2 flood development effect.CO2 foam drive is a kind of control technology for gas channeling with wide application prospects.Based on the geological characteristics of the reservoir in Block Hei79 and the current status of CO2 flooding,this paper carried out a large number of CO2 foam flooding experiments and obtained the following results:(1)Using the high-temperature and high-pressure foam performance test system(temperature resistance 150?,pressure resistance 30MPa),the formula of CO2 foam control system suitable for Block Hei79 was selected:XP-1(0.2%)+ XP-2(0.1%)+WP-1(0.05%).At 96? and 24MPa,the maximum foaming volume of the foam system was 648mL,the half-life was 89min,and the comprehensive coefficient was 57672minˇmL.The evaluation results of foam system performance show that the system has good temperature resistance,salt resistance,oil resistance and stability.(2)Conducted a comprehensive performance study of the rheology and microstructure characterization of foam systems.The experimental results show that the CO2 foam system is a pseudoplastic fluid with non-Newtonian properties and good viscoelasticity;by observing the foam microstructure of the foam system,After that a foam stabilizer WP-1 is added to the compounding system XP-1 and XP-2,the cross-linking effect deepened;at the same time,it was found that the foam in the compound foam system under high pressure remained more and stable,and the foam molecules showed a more compact planar network structure.(3)Conducted research on the performance impact of foam systems under dynamic pressure.The experimental results show that with the increase of pressure,the foaming and stabilizing properties of the CO2 foam system are all significantly improved,and the half-life of the CO2 foam system is increased from the initial 7 min to 101 min.At the same time,as the pressure increases,the dynamic resistance factor of the natural core gradually increases,that is,the resistance factor increases from 2.7(normal pressure)to 10.2(25MPa).Therefore,the theory of static foam stability think that the higher the pressure,the foam is more stable,and the ability to control the air bubble is stronger;(4)Conducted CO2 foam core flow experiments.The experimental results show that the CO2 foam has the strongest sealing ability when the optimal gas-liquid ratio is 2:1;when the CO2 gas and the foam liquid slug are injected,the resistance factor using the multiple injection methods of small slugs is larger and it can generated better plugging effect;SO,optimal injection rate of CO2 gas and foam slug is 1 mL/min;(5)Conducted a CO2 foam control gas trap effect evaluation study(visual microscopic displacement model).Before and after the injection of foam,the quartz sand in the upper and lower parts of the visualization model turned white,and more crude oil was displaced at the outlet end.Therefore,it can be concluded that the CO2 foam can better control the gas flow,expand the sweep volume,and increase the oil displacement efficiency.The research results of this paper provide reference for the field application of CO2 foam flooding to enhance oil recovery technology in block Hei79 of DaqingZi Oilfield. |
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