Study And Application On Flow Law Of Steam-Nitrogen Gas Foam System

Over year practice proves that steam injection is an effective method in heavy oil recovery. But it has also shown some weakness, such as steam gravity override, steam interporosity flow along high permeability formation, viscous fingering, which will lose a great deal of injecting steam, cut down volumetric sweep efficiency, decrease recovery ratio and decline single well production of gas injection cycle. Foam is a kind of non-Newtonian fluid, which possesses many fine characteristics such as low density, low filtration, high ability of sand carrying and circulating out, low damage to the reservoir bed, selectivity to high/low permeable bed and water/oil bed and so on. Therefore, it can decrease mobility of vapor phase, broaden swept volumes and enhance heavy oil recovery ratio used in thermal recovery with steam injection. Simultaneously, well expansion ability of nitrogen gas can not only save steam inject volume, but also increase elastic energy in oil displacement process.The relationship of density with temperature and pressure of nitrogen gas foam was studied by laboratory experiment (PVT), a density empirical formula of different gas/liquid mass ratio with temperature and pressure was regressed. And the effects of initial gas/liquid mass ratio, temperature and pressure on foam compressibility were analyzed.The laminar flow law and heat exchange character of power law fluid in circular tube and annular duct was studied by theory. The velocity, temperature distributions and Nusselt number Nuz in circular tube were obtained. And the effects of liquidity index n on foam velocity and temperature distribution were analyzed. The flow and heat transfer processes of high temperature foam conduit flow were simulated with numerical modeling. And friction coefficients and Nusselt numbers of different Reynolds numbers were calculated, a friction coefficient empirical formula and a Nusselt number empirical formula with Reynolds number were regressed.The control equations of steam, nitrogen foam, steam-nitrogen mix gas and steam- nitrogen gas foam in wellbore were established, and the flow laws were studied and contrasted with each other. Annular heat insulation effects of different methods were compared. And the effects of nitrogen gas injection volume and steam quality in well-head on steam-nitrogen mix gas and steam-nitrogen gas foam were analyzed. The range of nitrogen gas injection volume when the steam injection rate of flow is constant, which is met with optimum diversion effect, was defined.The foam diversion attribute was studied by theory and laboratory experiment. The diversion processes of nitrogen gas foam in individual layer and bilayer were simulated with foam diversion model based on gas phase trapping factor conception. And the modeling results agree well with in-situ test data, which confirmed the diverting and stimulating capabilities of steam-nitrogen gas foam in the heavy oil well. The actions of foam plugging and foam stimulating were manifested in-situ test, and the effects of surface foaming method is superior to the methods of subsurface foaming and accompanying nitrogen gas only.The results presented in this dissertation provide not only an important guidelines and academic value for the thorough investigation on thermal recovery with steam-nitrogen gas foam, but also have great reference values for injection parameters optimized design in engineering.