Technology Study On Polymer Gel For Enhancing Water Flooding Efficiency In NB35-2 Oilfield

Since the offshore oilfield has the characteristics of high porosity, high permeability, more serious heterogeneity, high crude oil viscosity, high temperature and high salinity, it will not only take more time, but also the recovery ratio will decrease if carrying on the early stage water-injection development implemented ordinarily in the oilfield on land. In order to curtail the oilfield development cycle and enhance the whole development effect of oilfield, according to the geological characteristics, fluid property and the practical demand of offshore oilfield, the author took property filtration on polymer weak gel system, and evaluated the viscosity property, rheological property and viscoelasticity of polymer and Cr³⁺ polymer weak gel which were screened out. The results show that under condition of water quality of source well, Cr³⁺ can form gel system that has intra-molecular cross-linking structure property with polymer molecule, which has the characteristics of low viscosity and high flowing resistance. On this basis, making use of the experimental method of indoor physical simulation, study on technology and economic effect of Cr³⁺ polymer weak gel profile control and flooding in early stage in NB35-2 Oilfield is carried out. The results show that the polymer weak gel profile control and flooding in early stage can not only shorten the oilfield development time, save operating cost, but also has the higher recovery efficiency. Moreover, injection time, dosage and polymer concentration of Cr³⁺ polymer gel can influence the effect of profile control and flooding directly. The earlier the injection time, the more the dosage, the higher the polymer concentration, the higher the increasing degree of pressure, the better the effect of enlarging swept volume, the higher the decreasing degree of water cut, and the better the effect of increasing oil production. On the basis of indoor study, Cr³⁺ polymer gel profile control and flooding in early stage was carried out in NB35-2 Oilfield. The results of experimentation show that Cr³⁺ polymer gel can increase injection pressure drastically and improve fluid entry profile, which has better effect of oil increasing and water decreasing.