Study On Equi-fluidity And Parallel-multi-slug Displacement After Polymer Flooding

Polymer flooding has been an important enhanced oil recovery method adopted at the later stage of oilfield development in China. However, due to the effect of reservoir heterogeneity, there is still about 40%-50% remaining oil kept in oil–bearing formation after polymer flooding, and subsequent chemical agent was found in the produced well too early, cross flow phenomenon was too serious, which decreases injection utilization and flooding efficiency. This paper according to serious reservoir heterogeneity after polymer flooding, and complex remaining oil distribution, develops equi-fluidity and parallel-multi-slug displacement method which aims at realization of synchronous displacement in reservoir heterogeneity. The EOR mechanism of equi-fluidity and parallel-multi-slug displacement is put forward, which contains local closure on high-permeation channel, multi synergism and so on. And the details of equi-fluidity and parallel-multi-slug displacement method are designed, which includes viscosity, slug injection volume, runs, total injection amount and so on, the empirical formulas has been given also.Chemical agents in equi-fluidity and parallel-multi-slug displacement are screened and evaluated. Varies kind of functional polymer's viscosity property has been researched, which shows that viscosity changes with standing time in different concentration polymer solutions. Modification carboxylate is screened to be the surfactant of equi-fluidity and parallel-multi-slug displacement. HY-2 foamer is screened based on foamer's foaming ability and stability, the applied concentration is 0.6%, comprehensive foaming ability is evaluated after 0.6% HY-2 and varies concentration functional polymer complex formulation. It is pointed that foam is more stable with the amount increase of the functional polymer.Oil displacement formula aimed at different permeability layers is designed by equi-fluidity and parallel-multi-slug displacement method, laboratory evaluation has been made on parallel homogeneous cores and heterogeneous core. The parallel homogeneous cores displacement experiment results shows that oil recovery enhanced 23.93% after polymer flooding, oil recovery in low permeability core enhanced to 83.59%. The heterogeneous core displacement experiment results shows that equi-fluidity and parallel-multi-slug displacement formula with enhanced foam made oil recovery enhanced at least 22% after polymer flooding, and the ultimate recovery reaches 84%. Compared with other EOR methods after polymer flooding, equi-fluidity and parallel-multi-slug displacement's effect is significant. It is a reliable approach to excavating potentials of remaining oil and increase oilfield production.