Lab Experimental Study On Adaptability Of Polymer Flooding In Xingbei Area

Daqing oil field has already entered tertiary oil production stage, and annual oil production by polymer flooding has been kept at 1000×10⁴t for 5 years, which accounts for 1/4 of the annual production of the oil field. Polymer flooding means adding water soluble macromolecule polymer into injected water to increase water phase viscosity and reduce water phase permeability and to enhance oil recovery. The polymer used in Daqing Oil Field is called Partially Hydrolyzed Polyacrylamide . Geological reserves of the major pay zones in Xingbei Oil Field mainly distribute in reservoirs where effective thickness is equal to or more than 2.0m, penetration is equal to or more than 200×l0^-3μm², which accounts for 35.5% of the total geology reserves.Polymer flooding has been popularized in 5 blocks since 2002, and fresh water used to compound and produced water to dilute macromolecule polymer system. The result has been affected by the unique injection scheme and response differences of single wells. In addition, reducing viscosity loss and increasing viscosity of the injected polymer solution are key factors to ensure polymer flooding results. This paper has studied the relationship between viscosity and concentration of polymer system which is compounded by fresh water and diluted by produced water; determined viscosity influencing factors such as, salinity, cation, dissolved oxygen, etc.; optimized types, concentration ranges of polymer; determined polymer injection scheme and rational injection parameters suitable for pay zones in Xingbei Oil Field by numerical simulation and physical simulation tests and evaluated viscosity increase, stability , emulsification and displacement efficiency of new type macromolecule oil displacement agent.1. Study on technology of fresh waster compounding and produced water dilutingDuring polymer injection, not only factors such as molecular weight, molecule configuration, hydrolysis degree of its own properties, but polymer-compounding solvent, salinity, water-containing ions and dissolved oxygen all influence polymer viscosity. Among them, viscosity of the linear polymer is less than the branch type and the cross-linked; As for polymer solution with the same molecular weight, viscosity rises with concentration ,the higher the molecular weight of the polymer is, the higher the viscosity is; For polymer with the same molecular weight and concentration, viscosity is higher when fresh water is used and existence of bivalent cations makes viscosity of polymer drop significantly. Screening of polymer with different molecular weight through lab experiment indicates that 25 million ultra high molecular weight polymer compounded by fresh water and diluted by produced water can dispel the viscosity reducing materials to get the viscosity the scheme required under the condition of concentration of 1100mg/L, and the oxygen content above 0.8mg/L. This injection scheme is cost effective and feasible because the produced water is reused and discharge is avoided. In addition, after injection into the underground, viscosity loss is lower and higher viscosity can be maintained.2. Adaptability of polymer injection scheme for major pay zones in Xingbei Oil FieldBetter injection parameters are determined by numerical simulations and lab core flooding experiments. They are: molecular weight 25 million, injection speed 1.0m/d, injected viscosity 65.0mPa·s, injected volume 0.8PV. This injection order of relative molecule quality of polymers,35 million - 25 million - 16 million,is better than other orders. Displacement result when adding a little DW-1 active agent is better than using polymer alone, which can improve recovery by 20% OOIP. Periodical polymer injection has little influence on recovery.3. Lab study on new Functional Macromolecule SurfactantFunctional Macromolecule Surfactant is a new kind of macromolecule material whose viscosity is higher by introducing functional monomers on the polymer molecule skeleton to make polymer molecules keep spreading configurations under relatively higher temperature and ion concentration; Because of having amphiphilic characteristics, it forms aggregates and even reticular structures among molecules in the solution and has higher viscosity and stronger oil dissolving ability, therefore it can achieve the goal of improving recovery. Now, there are two types of functional macromolecular surfactant used in oil fields, and they are flooding modification type and washing - flooding typeIn contrast with ordinary polymer, the Functional Molecular Surfactant compounded by produced water can increase viscosity more when its concentration exceeds 800mg/L, and it keeps higher viscosity when it is laid aside for a long time. Lab core experiments show that it has a better oil displacement result than the ordinary polymer. It is a kind of promising macromolecular material because it makes water-cut drop and oil increase when used in the field.Lab study on adaptability of polymer in pay zones in Xingbei Oil Field has provided the best support to use polymer rationally, enhance injection capability of the whole block, keep injection and production balance, improve displacement efficiency and achieve best economic benefits.