The Performance Evaluation Of Nitrogen Foam System In Low Permeability Reservoir After Water Flooding

Foam performance under the condition of high pressure was researched in this paper. The experiments were from two views of micro and macro. First, differential interference microscope was used to study the interaction mechanism between oil and foam and analyze the influence factors of three-phase foam stability. Next, the foaming ability, oil resistance and salt resistance of foam systems under condition of high temperature and high pressure were studied to screen two good systems which were used to conduct core flooding experiments. Evaluate the oil displacement efficiency and percolation capacity to research the enhanced recovery efficiency of foam. This paper is mainly composed of five parts as described below.Firstly, differential interference microscope was used to observe the interfacial structure of three-phase foam. From micro process, it was found that dissolved oil will make bubbles fracture fast while emulsified oil and bubbles can form pseudoemulsion film, which stability determines the oil resistance stability of foam.Secondly, foam performance of different gas was studied by MRM-RI ROSS-Miles to select the best gas which can produce the optimal foam. It was shown that both under the condition of no oil and 30% oil N2 foam performance is best. The N2 was chosen to perform subsequent experiments. Then foam performance evaluation device was used to evaluate the foaming ability, oil resistance and salt resistance of foam systems under condition of high pressure. Four systems were measured and the result is Ⅱ and Ⅳ foam system are better than Ⅰ and Ⅲ foam system under the condition of 45℃, 10 MPa, so two optimized systems were selected to conduct core flooding experiments.Finally, foam performance measurement device was used to research the oil displacement efficiency and percolation capacity of Ⅱ and Ⅳ foam system. The experimental data point out that the improve oil recovery degree and profile control ability is strong and the best injected foam slug size is 0.4PV. Compared the two systems we can find that Ⅱ foam property is more excellent than Ⅳ foam system. Then two parallel tube core model displacement experiment was selected to estimate the property of Ⅱ foam system. Permeability contrast is 10:1 and the high permeability core is 600×10-3μm2 to simulate fracture. The flow distribution ratio, oil recovery and pressure curve show that foam can effectively block high permeability layer and improve oil recovery significantly.