Mechanism Research On Nitrogen Assisted Steam Stimulation For Mid-deep Heavy Oil Reservoirs

Surface steam injection is the most common enhanced oil recovery(EOR)technology used in heavy oil production.Nevertheless,limits exist due to heat loss for deep reservoirs.In the process of steam injection,adding a certain amount of nitrogen,which can reduce heat loss,maintain formation pressure and expand steam chamber,can effectively improve the development efficiency of steam injection.In this paper,high-temperature-pressure PVT measurements,sand pack flooding experiments and huff and puff experiments have been operated for heavy oil of the target reservoir in Bohai Oilfield,observing effect of nitrogen on property of heavy oil and displacement efficiency of nitrogen assisted steam stimulation.And injection parameters have been optimized by numerical simulation.On this basis,mechanism of nitrogen assisted steam stimulation to enhance heavy oil recovery has been analyzed in detail.At last,the development effect of nitrogen assisted steam stimulation for mid-deep heavy oil reservoirs has been evaluated through field test results.Experimental simulation,numerical simulation and field test all show that nitrogen assisted steam stimulation can improve development effect significantly.Compared with steam stimulation,cumulative oil of nitrogen assisted steam stimulation can be increased with 30% every cycle.The key of using nitrogen assisted steam stimulation is steam injection volume and gas-water ratio optimization,and while optimizing steam injection volume and gas-water ratio,properties of heavy oil,reservoir depth,formation pressure and oil viscosity should be taken into account.For the target reservoir,the optimal steam injection volume is 10m3/m and the optimal gas-water ratio is 50.Through mechanism research on nitrogen assisted steam stimulation and optimization of injection parameters,hoping to provide a feasible development method and theoretical support for mid-deep heavy oil reservoirs development.