Key Reservoir Engineering Technologies for Industrial Application of Polymer Flooding and Their Application Effect

In Daqing Oilfield, the industrial application of polymer flooding began in 1995. The peak annual oil production by polymer flooding remained above 10 million tons for 14 years. With the expanding industrial application, the targets of polymer flooding gradually transit from the reservoirs with good properties to those with poor properties. Such poor reservoir properties may deteriorate development effect of polymer flooding. Thus, it is necessary to find key reservoir engineering technologies in line with industrial application of polymer flooding to ensure an efficient development performance.

This paper establishes a mathematical model of oil displacement mechanism for polymer flooding. With the support of the mathematical model, the fluid flow patterns and polymer flooding effects in several projects of industrial applications of polymer flooding are analyzed comprehensively, and the key reservoir engineering technologies for industrial application of polymer flooding are proposed.

The theoretical research results show that, only a small quantity of oil is scattered in reservoirs after long-term water flooding, polymer flooding can enrich and aggregate scattered remaining oil. A polymer with higher molecular weight and concentration is more capable to improve oil displacement efficiency. The analysis of polymer flooding data (incl. energy spectral logging, sealed coring well, well injection profile surveillance and produced fluid salinity) reveals that polymer flooding is capable of oil enrichment and aggregation to improve displacement efficiency and also conformance control to greatly increase the swept volume to enhance oil recovery. The analysis on field development data of polymer flooding suggests that, in order to efficiently develop the sandstone reservoirs with multiple pay zones and strong heterogeneity, polymer solution should enable equilibrium displacement and simultaneous response of all pay zones. Accordingly, a method for matching polymer molecular weight with reservoir properties is established to ensure polymer solutions with different molecular weight are injected into reservoirs with different permeabilities. Moreover, the key reservoir engineering technologies for industrial application of polymer flooding are formed, including target reservoir configuration, scenario design, and follow up control.

With the application of above-mentioned technologies in Daqing Oilfield, the incremental recovery factor in 23 projects with polymer flooding in Class II reservoirs is more than 14%OOIP on average, suggesting an equivalent development performance to the Class I reservoirs that also registered a enhanced recovery by 14%OOIP through polymer flooding. Obviously, the presented key reservoir engineering technologies for industrial application of polymer flooding have provided important support for the efficient development of Daqing Oilfield.