Study And Application On Nitrogen Foam Flooding In Mobei Low Permeability Reservoir

The characteristics of the reservoir-J1S21 in Xinjiang Mobei oilfield well-area-2 are low to medium porosity(The average is 13.57%),low to extra-low permeability(The average is 3.19mD).The reservoir has been in production decline stage at present which means the development contradictions become increasingly severe,such as serious water-breakthrough phenomenon caused by vertical heterogeneity,high water-cut(some well groups are above 90%),high ratio of well-shutdown,poor exploitation efficiency.The water-flooding recovery is only 12.8%so far,therefore,the field application of EOR measures appears to be extremely urgent.Due to the advantages of profile-control and oil-displacement simultaneously and less damage to the reservoir,nitrogen foam flooding can be an applicable and effective method in terms of water-control and oil-enhancement field application in this reservoir.The related study on nitrogen foam flooding was carried out based on the reservoir characteristics.The results are as follows:(1)Foam formulation selection and evaluation on its reservoir adaptability were carried out.The formulation applied to injection water was FA-2 0.2wt%+FA-3 0.4wt%+FS-30.05wt%,foam volume was 720mL,half foam life period was 128min;The formulation applied to formation water was FA-2 0.1wt%+FA-3 0.5wt%+FS-3 0.03wt%-0.05wt%(or FS-4),foam volume was 600mL,half foam life period was 95min,meanwhile,it had the good high-temperature resistance,salt resistance,time stability and oil sensitivity.(2)Foam equivalent-mobility injection parameter optimization was carried out.Under the condition of three kinds of permeability contrast(set value:3,6,9)built by paralleling high and low permeability cores,for the purpose of the optimal profile adjustment effect,the gas-liquid ratio were 2:1,1:1,1:1;injection rate were 0.6mL/min,0.8mL/min,0.6mL/min;slug size were 0.2PV,0.3PV,0.3PV;injection pattern was simultaneous injection,respectively.The profile adjustment effect of foam on heterogeneous porous media was observed through the visualization model.(3)Foam displacement efficiency evaluation was carried out.The profile adjustment effect of foam could be better when the difference of residual oil saturation between high and low permeability cores became more prominent.The oil recovery was increased by 20.33%,25.48%,12.81%respectively in the three parallel core combinations as a result of injecting foam after water-flooding,the extent of oil-enhancement showed the first upward and then downward trend with the increase of permeability contrast.(4)The construction schemes aiming at the typical well groups were designed and applied.The good application effect was achieved successfully in the field pilot test:the average oil production per-day increased by 8.4t/d,the average water-cut per-well decreased by 26.3%.The study based on the reservoir-J1s21 in well-area-2 in this thesis can make some sense to the research and application of EOR technologies in Mobei low permeability oil reservoir.