Study On Thermal Recovery Mechanism Of Thermal Nitrogen Assisted Steam

In view of the situation that the heat loss along the wellbore is large,the formation energy decreases rapidly,the huff and puff cycle decreases rapidly,the water cut is high and the recovery rate is low in the late stage of heavy oil multi-cycle steam stimulation,the improved technology is nitrogen-assisted steam thermal recovery technology,which can reduce steam heat loss,reduce steam consumption,reduce water cut in oil wells,slow down bottom water coning,and maintain formation pressure and raise oil recovery.High oil recovery,but the effect of increasing oil is limited.Therefore,this paper analyses the feasibility and production mechanism of hot nitrogen assisted steam thermal recovery technology,and optimizes the proportion of hot nitrogen injection,which provides a theoretical basis for the test and popularization of this technology in oilfields.Firstly,this paper studies the flow law of steam-hot nitrogen mixture in wellbore,and studies the variation law of wellbore parameters when the mixture flows in wellbore with different temperature,flow rate and dryness of wellbore steam.Then,the experimental study of condensation heat transfer of steam-hot nitrogen on vertical plate surface was carried out.The condensation heat transfer experiments of pure steam,steam-hot nitrogen at different temperatures and steam-hot nitrogen at different proportions were carried out on vertical plate,and the effects of injection temperature of hot nitrogen and different proportions of hot nitrogen on condensation heat transfer of water vapor were studied.Finally,the experimental study on heat transfer of hot nitrogen assisted steam is carried out.The experiments of steam drive,nitrogen assisted steam drive and hot nitrogen assisted steam drive are carried out through sand filling simulation device with heat insulation effect.The temperature,recovery and water cut along the process are compared and analyzed.The results show that increasing the temperature of hot nitrogen gas can increase the dryness of bottom hole steam.When the temperature of hot nitrogen gas rises from 20 to 400 ℃,the dryness of bottom hole steam increases by 0.1.The condensation heat transfer of pure steam occurs Beaded condensation process because the liquid can not wet the wall,which has a high condensation heat transfer coefficient.The existence of hot nitrogen will greatly affect the condensation heat transfer effect of steam.Under the same conditions,the condensation form of steam-hot nitrogen mixture is film condensation.Increasing the temperature of hot nitrogen can increase the inlet temperature of mixed gases,thus increasing the mainstream temperature of gases and decreasing the condensation heat transfer coefficient.With the increase of the ratio of injected hot nitrogen,less and less water condenses in unit time,so the condensation rate of steam decreases and the heat transfer coefficient decreases.In the process of steam and hot nitrogen co-injection,hot nitrogen can enhance the heat transfer of steam,and with the increase of hot nitrogen injection,the recovery rate increases,but when the hot nitrogen injection rate increases to a certain extent,the recovery rate decreases.When steam and hot nitrogen are injected together,there exists an optimum heating nitrogen ratio,and the optimum heating nitrogen ratio should be about 30.