Research On Separate Zone Injection Technique Of Polymer Flooding

It is indicated that polymer flooding can enhance oil recovery above 10% on the basis of water flooding in Daqing Oil Field. The annual yield of polymer flooding has measured up to 11.10 million ton in 2008 at Daqing Oil Field,occupy 1/4 of total yield,continuously exceed 10 million ton for seven years,played an important part in high production and stable yields for Daqing Oil Field.Affected by depositional environment of Daqing Oil Field,inhomogeneity of oil layer is serious,the difference between high and low permeability zone is large. Under vague injection,the contradiction of invalid cycle seriously in high permeability zone and usage level lowly in low permeability zone is existence. In order to enhance resource utilization ratio,improve develop effect,we should achieve separate zone injection.It is to say that we should ensure the injected fluid drive uniformevenly in the method of piston by confine injection of high permeability zone and enhance injection of low permeability zone. But polymer solution is viscoelasticity and non-Newtonian fluid,routine water drive separate injection technology is about forming orifice pressure difference and controlling influx through decreasing open area,so the problem of high viscosity loss factor(40～70%)and the affection on displacement effectiveness is existence.At the basic of in-depth research,the technological research of separate zone injection in polymer flooding is launched. At the moment,two core technologies are formed aiming at the feature of different oil zone,which are the technology of concentric separate zone injection in polymer flooding and the technology of dual injection in polymer flooding. The technology of concentric separate zone injection in polymer flooding is fit forⅠoil zone whose single zone injection amount is large,can achieve 2~3 layers separate injection of polymer. The technology of dual injection in polymer flooding is fit forⅡ,Ⅲoil zone whose interlamination contradictory is more larger,can achieve multilayer dual injection of polymer. Through achieving the adjustment of layering molecular weight, the problem of low permeability zone blocking up which is caused by the poor adaptability of the low permeability zone to the middle,high molecular weight polymer is alleviated.The technology of concentric separate zone injection in polymer flooding: In order to control the injection pressure, the concentric injection distribution device use the streamline ring step-down groove, which satisfied 20-150m3 /d diurnal injection, the maximum choke pressure difference can reached to 3.0MPa, the maximum visco-loss rate to the polymer solution less than 4.0%.The technology has used in 757 wells by the end of 2008,the daily crude output increased 2t/d, water content decreased 1.4%of a single well in Connected oil well, oil production accumulativel increased 9.6×10~5 tons.The technology of dual injection in polymer flooding: The dual control of layered molecular weight and layered injection volume, so that the matching relations of the polymer molecular weight and the reservoir permeability become rational. Molecular weight regulator use the mechanical degradation to control the polymer molecular weight. Under the the scope of 50m3/d, polymer molecular weight can be reduced by 20% -50%.,the maximum choke pressure difference can reach to 1.5MPa. Identified the matching relations of the polymer molecular weight and the reservoir permeability by oil flooding experiments, and found the calculation model of the choke pressure difference and the visco-loss. Pressure regulator to control pressure reached 3.5MPa, single-layer flow control less than 70m3/d, viscosity degradation rate less than 8%.The technology has used in 114 wells by the end of 2008. After dual injection, compared with the normal separated polymer injection well, The use ratio of thickness increased from 85.9% to 94.9%. The decrease range of water content in dual injection well is 7% higher than response well in all region. Compared with general polymer injection well, water content decreased 14.5%, the daily crude output increased 3.5t, oil production accumulativel increased 2.6×10~5 tons.