Research On Methods Of Improving Polymer Flooding Effeciecy In Sub-layers Reservoir Of Daqing Oil Field

This article analyzed geologic characteristic of sub-layers reservoir in Daqing Oil Field, and in the view of the prevalent problem of polymer flooding used of sub-layers in Daqing oil field, made some researches as bellow:1.Research on viscoelasticity of polymer solution with various molecular weights sheared by molecular weight regulator and which with same molecular weight (unsheared) was carried out , in the view of the different medium and pressure injected technique of polymer flooding used of sub-layers in Daqing oil field. It concludes that: The viscosity of polymer solution sheared or unsheared fits power law mode, consistency index increase with the increasing of molecular weight; while the power law index decrease with the increasing of molecular weight; the first normal stress different of polymer solution sheared does not change greatly with the increasing of shear rate, the first normal stress different of which with the low molecular weight is lower, nearly with no change. Through testing the residual resistance factor of polymer solution sheared and unsheared, results show that: Polymer solution with the same molecular weight, the residual resistance factor of unsheared is higher than that of which sheared; the residual resistance factor increase with the increasing of the molecular weight.2. Research on adaptiveness of core with different permeability and different molecular weights of polymer solution carried by doing flooding experiment of polymer solution which molecular weight is 600×10⁴,800×10⁴,1200×10⁴ and 1600×10⁴, which are sheared when flow through the molecular weight regulator, as well as which with the same molecular weight but unsheared on the core, the results show that: The recovery rate of polymer flooding unsheared is higher than which sheared with the same molecular weight, no matter the molecular weight is higher or not; the recovery rate of polymer flooding sheared with higher molecular weight is higher than the unsheared but with the lower molecular weight; the maximum injection pressure of polymer flooding unsheared is higher than which sheared with the same molecular weight, no matter the molecular weight is higher or not; when multi-zone produce, recovery rate of different medium injection is higher than commingled injection, and the maximum injection pressure is lower; for the core with the permeability from 200×10^-3μm² to 300×10^-3μm², polymer solution with medium molecular weight which was sheared is best for displacement, but for the core with the permeability 100×10^-3μm²,which with the low molecular weight is the best.3. Fetched the injection pressure formula of polymer flood by using production formular of five-spot flood system,analysed the factors which impact on injection pressure of polymer, and on the basis of it, researched on the methods of decreasing polymer flooding injection pressure of sub-layers reservoir, the results show that: Injecting SAA, decreasing well spacing , dropping injection rate, fracturing bond gravel, injecting polymer periodically and so on are workable for decreasing polymer flooding injection pressure of sub-layers reservoir; injection pressure could be decreased greatly and recovery rate could be also increased by injecting SAA and polymer alternatively; injection pressure could be decreased by injecting polymer periodically, the more period, the better effect, it doesn't have much effect on homogeneous core while it could improve recovery rate of inhomogeneous core.4. Heterogeneity of the sub-layers is serious, polymer and water flooding exist in the same unit for polymer injection, the coexistence make polymer flooding potential difficult to play. In this paper, take polymer flooding sub-layers of western North Block for example, research recovery feature of water and polymer displacement at the same time with different combination of injection parameters use numerical simulation method. Study results showed that: relation of the various types of oil and water wells statistics in water- polymer contact zone show that there are two mainly types of connection, first zone connection is oil well third infill- water well third infill-oil well polymer flooding-water well polymer flooding, second is water well third infill- oil well third infill-oil well polymer flooding-water well polymer flooding. When coexistence of water and polymer displacement, border should be sealed by two oil wells, connection of water and polymer contact zone is water well third infill- oil well third infill-oil well polymer flooding-water well polymer flooding. For first zone, it should be developed with high water injecting force,the best rate is 1:2 of polymer and water injection force;for second zone,it should be developed with high polymer flooding force,the best rate is 3:1 of polymer and water injection force.For the first zone, when the ratio of force between polymer and water is 1:2,the reasonable pressures of polymer and water zone are 11.7Mpa and 11.25Mpa, and For the second zone, when the ratio of force between polymer and water is 3:1,the reasonable pressures of polymer and water zone are 10.95Mpa and 10.42Mpa.