Study On Heat Transfer And Enhance Heavy Oil Recovery Of Wellbore With Multiple Thermal Fluids Injection

The demand for crude oil in the world is increasing.With the exploitation of oil,the conventional oil resources are constantly exhausted,and the heavy oil resources on land and sea are gradually attracting people's attention.Therefore,enhance heavy oil recovery technology has become a hot research topic at home and abroad.The thermal recovery technology of multiple thermal fluids huff and puff is a new breakthrough in the exploitation of heavy oil in the sea,which can significantly improve the recovery of heavy oil,but the related research is still very insufficient.For further studying the heat transfer of well and mechanism of enhance heavy oil recovery of multiple thermal fluids,the flow and heat transfer of well injected with multiple thermal fluids are discussed,and the hot water-gas-chemical compound oil recovery technology are studied and developed in this paper.Firstly,the component of high temperature and high pressure multiple thermal fluids gas is simplified as an ideal gas in the previous flow and heat transfer model of multiple thermal fluids in injection wellbore.Based on the actual gas state equation,the actual gas mixing rule and the transient thermal conductivity function considering the influence of the wellbore thermal property,the model of the flow and heat transfer of well injected with the multiple thermal fluids in different flow conditions is established.This new model can more accurately analyze the variation of various parameters of multiple thermal fluids in wellbore.This model is used to analyze the flow and heat transfer process of multiple thermal fluids injected in the land wellbore,compared with the results of the ideal gas model.At the same time,the steam injection in well is compared with the multiple thermal fluids injection,and heat transfer in wellbore and reservoir heating of two kinds of media are compared in detail.The results show that there is a certain difference between the calculated results of the actual gas model and the results of the ideal gas model.It is proved that the actual gas state equation has a certain influence on the flow and heat transfer process of the multiple thermal fluids in wellbore.The flow and heat transfer model of multiple thermal fluids established in this paper is more applicable.It is not only applicable for multiple thermal fluids injected in wellbore under low pressure but also under high pressure.It can accurately analyze the flow and heat transfer of multiple thermal fluids injected in wellbore.Through the comparison with the flow and heat transfer process of wellbore with steam injection,it is found that the drop of pressure and temperature of multiple thermal fluids in the wellbore is faster compared with steam injection under the same injection temperature and injection rate.The temperature of multiple thermal fluids at the bottom of the well is lower,the temperature difference between the formation and the oil layer is smaller,and the wellbore heat loss is less,but the heating range of the oil layer is small.To achieve the same heating effect as steam,it is necessary to increase the injection rate and injection temperature of multiple thermal fluids.The structure of the offshore thermal recovery well is different from the land well structure,and the heat transfer mechanism of well in the ocean is more complex than that in the rock.It is very important to accurately predict temperature distribution and the heat loss of the ocean thermal recovery well for the evaluation and design of the thermal recovery well.At the same time,two-phase flow temperature model of the multiple thermal fluids based on the Total law and the ideal gas mixing rule is not suitable for the analysis of the hot water with multiple fluids in the wellbore.Based on the above model,this paper establishes the flow and heat transfer model of multiple thermal fluids adapted to the offshore wellbore structure and analyzes the heat loss of the multiple thermal fluids injection in the offshore thermal recovery well.The comparison with the measured data from Bohai oilfield shows that the average relative error of the pressure is about 0.7%and the mean absolute error of the temperature is about 1.4 C.The results show that the model has a high accuracy for predicting temperature and pressure distribution of ocean well injected with multiple thermal fluids.Through the analysis of heat loss ofdeep water well injected with multiple thermal fluids,it is found that the heat loss in the environment is less than 9%,and the loss of heat in the ocean accounts for more than 50%of the total heat loss.The influence of injection rate,injection temperature and wellbore heat insulation on heat loss of well is great.For the hot water with multiple fluids,the proportion of hot water has a great influence on the heat loss of the deep water well,and the injection pressure,injection time and the ambient temperature have little effect on the heat loss.For the steam with multiple fluids,the heat loss of wellbore is influenced by injection pressure,but the steam dryness and steam ratio have little influence on heat loss.The effect of the thermal recovery of heavy oil depends not only on the flow and heat transfer in the wellbore of the thermal fluid,but also mainly depends on the oil displacement process of the thermal fluid in reservoir.In this paper,the characteristics of combined with hot water-gas-chemical additives flooding are studied in this paper.Hot water flooding is one of the most common thermal recovery methods to enhance the recovery of heavy oil.However,due to the low enthalpy value of hot water and the existence of water channeling,the effect of hot water on enhancing the recovery of heavy oil is very limited.CO₂,N2,Air and flue gas have the positive impact on the recovery of heavy oil,which can be used to enhance the recovery of heavy oil,so it can be combined with hot water and chemical additives to make up the shortage of hot water flooding and further enhance the recovery of heavy oil.In this paper,firstly the influence of nitrogen,carbon dioxide,flue gas and Air co-injected with hot water for heavy oil recovery is analyzed.The experimental results show that different gases,including CO₂,N2,Air and flue gas co-injected with hot water can significantly enhance the recovery of heavy oil.Compared with other injected fluids,the hot water-CO₂-chemical additive flooding has the highest efficiency for heavy oil recovery.The combination of hot water,gas and chemical additives can form foam flooding to significantly enhance the recovery of heavy oil.For nitrogen,increasing the nitrogen injection rate would reduce the oil recovery of hot water-N2-chemical additives flooding.For hot water-N2/Air-chemical additives,with the injection temperature of hot water increasing,the recovery ratio could the firstly increase and then decrease,existing the best injection temperature of hot water.For Air,without oxidation reaction with crude oil,the effect of Air on hot water-Air-chemical additives is limited.Only when the injection rate of Air is increased to a certain extent,the recovery ratio of oil can be significantly increased.Meanwhile,the injection temperature of hot water has little effect on the hot water-Air-chemical additives process.Based on the comparison and analysis of the effect of different gas and hot water-chemical additives on the recovery of heavy oil,this paper proposes hot water-CO₂-chemical additive flooding technology for enhance heavy oil recovery.Then,the hot water-CO₂-chemical flooding,the heat transfer process of reservoir and the sequestration of CO₂ are studied.Compared with CO₂,cold water,hot water,cold water alternately-CO₂ and hot water alternately-CO₂,the hot water-CO₂-chemical additive is the best injection fluid with the best final oil recovery ratio.In the state of CO₂ as an immiscible drive,CO₂ does not enhance the oil recovery after the hot water flooding and the cold flooding.Most of the CO₂ can be sealed in reservoir in the process of the CO₂ flooding and hot water-CO₂-chemical additive flooding,of which the CO₂ storage efficiency is 85.60%in the CO₂ flooding and the CO₂ storage efficiency in the hot water-CO₂-chemical additive flooding is 80.61%.The CO₂ Joule Thompson cooling effect does not occur during hot water-CO₂-chemical additive flooding,and the CO₂ has little effect on the heat transfer between the hot water and reservoir.Increasing the injection rate of hot water can significantly increase the oil recovery of the hot water-CO₂-chemical additive flooding.With the increase of injection temperature of hot water,although the heat transfer and heating effect between the hot water and the reservoir is strengthened,the recovery ratio is increased first and then decreases,so there is one the best injection temperature of hot water existed.With the increase of reservoir pressure,the recovery of heavy oil is increasing,but the reservoir pressure has little effect on the heat transfer of the reservoir.The reservoir permeability and the viscosity of the crude oil have a great influence on the reservoir recovery,but they have little effect on the heat transfer of the reservoir in the process of the hot water-CO₂-chemical additive compound flooding.