Experimental Study On Nitrogen Foam Flooding In High Temperature And High Salt Reservoirs

Due to general chemical flooding is subject to the temperature and salinity, nitrogen foam flooding characterized by nitrogen flooding and foam displacement is relatively suitable for developing reservoirs with high-temperature, high-salinity and high-heterogeneity. The thesis investigated the foaming agents with high-temperature and high-salinity tolerance, and the generation, stability, mobility controlling and oil displacement in the porous media by laboratory displacement experiments under the conditions of one reservoir in Tahe oilfield (temperature is 106??117?, the total mineralization is more than 22×104mg/L and the hardness is more than 1.2 × 104mg/L).Foam volume was 420ml and half-life time was 158s of 0.2%NZ after aged in the simulated injection water (the total mineralization is 22×104mg/L) at 120?? The long-term stability in the injected brine was highly improved by adding 50mg/L bactericide PA and 100mg/L deoxidant TA, which was abbreviate to 0.2%NA. By adding a surfactant SA with ultralow interfacial tension, NAS (short for 0.16%NA+0.4%SA) had the ability to decrease the interfacial tension of oil and water to 0.5mN/m and good foam properties, and low static adsorbance. Foam volume was 400ml and half-life time was decreased by 18% of NAS after five times adsorbance with fresh oil sands.By monitoring the differential pressure of nitrogen foam in the porous media, the results indicated that the bubble extinction was mainly showed in the middle and tail of sand pack when the dimension flow was small, and the bubble extinction was weakened in the middle and tail of sand pack and foam stability was enhanced when the dimension flow was big. The generation and stability of foam was bad in the oil-bearing sand pack, and they were improved as the decreasing of oil saturation.By monitoring the mobility reduction factor (MRF) of nitrogen foam in the porous media, the results indicated that, the MRF of foam was enhanced when oil saturation decreased or the reservoir pressure increased or the permeability contrast increased to some extent or formation sloped downward. For the MRF of foam in heterogeneous core, the added layer was good for the low permeability contrast but bad for high the low permeability.The results of nitrogen foam flooding in homogeneity core indicated that, the pure nitrogen foam slug (0.5 PV) was injected at the gas-liquid ratio of 2:1 after the water cut was added up to 95%, which led to a decline of water cut (lowered into 58%) and an increase of enhanced oil recovery (EOR) (up to 34.39%). The effect of water cut decreasing and EOR increasing was improved when the injected volume increased or the permeability increased. The results of nitrogen foam flooding in heterogeneous double-core indicated that, the increase of permeability contrast or mean permeability was conducive to the effect of water cut decreasing and EOR increasing. For the water cut decreasing and EOR increasing of foam, the added layer was good for the low permeability contrast but bad for high the low permeability. The results of nitrogen foam flooding in heterogeneous sand model indicated that, nitrogen foam performed excellent in the vertical heterogeneity, and could displace well in high-permeability layer and increase the swept volume in the top of model or in other low-permeability zones due to the obvious gravity segregation of foam in the sand model with vertical and horizontal heterogeneity.The research achievements of thesis can be extended in the other similar reservoirs with high-temperature, high-salinity and high-heterogeneity, which helps to improve the potential of the oil production even more and increase the economic benefit of oilfield.