An Experimental Study On High-hydrolysis-polymer Solution's Displacement Performances

In the process of displacement of oil by polymer solution, the viscosity and viscoelasticity of polymer solution are vital to displacement efficiency. Low TDS fresh water is generally used to prepare polymer solution to ensure polymer displacement effect. The consumption of fresh water in oil field has increased dramatically as the extension of polymer- displacement industrialization. Meanwhile extremely large amount of produced water has to be drained away, directly resulting in water resource waste and serious environmental pollution. To resolve this problem, LaMaDian Oil Field embarks on the study of using produced water in polymer–displacement process to realize recycle application of produced water.Polymer solution's viscosity and viscoelasticity are vital in the process of displacement. The main mechanism is to enhance oil recovery by improving water oil mobility ratio and expanding volumetric sweep. The more conspicuous effects could be obtained with a better polymer's viscoelastisity. The hydrolysis range of high-hydrolysis-polymer available is 30-50%. As the hydrolysis degree rising, the total amount of carboxyl group is increasing and the viscosity is getting much higher as well. In order to lower injection cost, a series of experiments in which test high-hydrolysis-polymer solution's stability, viscosity, using conditions and displacement effects are conducted.Lab tests show: microbes and reducing substances in produced water are major factors to influence polymer solution's viscosity. Although the TDS of produced water is relatively high (4000mg /L or so), the polymer solution mixed with it can still maintain a higher viscosity. At the same time, this kind of polymer solution has a desirable property to match the reservoir, and demonstrate a better ability to maintain its viscosity in simulative reservoir; a lot of tests prove that the method of exposure-to-oxygen is a economical and logical way to treat microbes and reducing substances existing in produced water; combining studies of viscoelasticity and displacement ability of polymer solution preparing in fresh water and produced water respectively with the latest mix and injection process, an injection method is determined finally that preparing super- high molecule weight polymer solution in fresh water and diluting it with produced water after exposure-to–oxygen treatment. Four fifth fresh water could be replaced with produced water by using this way. Good results have been achieved in field experiments conducted in 5# and 6# injection station, locating in west northern block of LaMaDian Oil Field. Comparing to ordinary polymer solution, high-hydrolysis-polymer solution has relatively higher viscosity and desirable stability. It could achieve the same displacement effects when reducing polymer powder consumption by 10% by means of using high-hydrolysis-polymer with a hydrolysis degree of 40% to mix with ordinary polymer or injecting small volumes of the two sorts of polymers alternately.