Study Of Sweep Characteristics For Waterflooding Reservoir

Water flooding is a widely used reservoir development mode.In the case of reservoir characteristics and development mode unchanged,oil displacement efficiency is constant.Recovery efficiency is defined as the product of sweep efficiency and oil displacement efficiency.When sweep efficiency is very high,keeping water flooding will be difficult to improve oil recovery greatly.During the field development practice,reservoir plane and vertical sweep efficiency is extremely high at the extra high water cut stage.However,keeping water flooding can still increase recovery efficiency greatly,which contradict the traditional understanding.Therefore,it is necessary to make a study on the sweep characteristics of water flooding reservoir and establish a new evaluation methods for sweep.A new evaluation method for sweep characteristics is proposed,and the concepts of pore sweep degree and porous media displacement efficiency are defined.On this basis,sweep characteristics are studied from pore scale,well group scale and reservoir scale.Firstly,water flooding process within single pore and porous units are simulated using pseudo potential model.Then sweep characteristics are analyzed under different wettability and displacement pressure gradient.Subsequently,some numerical conceptual models of well group are established,and its sweep characteristics are studied under injection production difference,permeability heterogeneity in plane and vertical,and compared with the traditional method.Finally,the numerical simulation model of an actual reservoir is selected,and its sweep characteristics are analyzed under the condition of fault and imperfect flooding pattern.Studies have found that when porous unit have strong hydrophilicity,injected water can enter the small pore and throat,and pore sweep degree is high.Conversely,when porous unit have strong lipophilicity,injected water enter the pore along the central part,and pore sweep degree is relatively low.Pore sweep degree increase gradually with the increase of displacement pressure gradient and injection pore volume.In fact,well group and reservoir are composed of numerous porous units.Pore sweep degree is affected by different conditions of well group and reservoir,which makes them present different sweep characteristics.