Polymer Qualification for Low Permeability Reservoirs in Austria: Liquid vs.Powder

Liquid polymer emulsions, a promising alternative to powder polymers, can minimize facility footprintand initial CAPEX. This study evaluates their use in a low permeability, small-sized reservoir in Austria,typically used in high permeability reservoirs. It aims to assess the performance and economic feasibility ofliquid versus powder polymers, identifying potential benefits and limitations of liquid polymer emulsionsin pilot projects. Rheological measurements were conducted to estimate product consumption neededto achieve the target viscosity of chemical slugs under reservoir conditions. The primary focus forqualifying liquid and powder polymers was on rock-fluid interaction, with an emphasis on injectivity in lowpermeability core plugs (60 and 300 mD), considering reservoir heterogeneity. Single-phase core floodswere performed at injector wellbore conditions. Additionally, two-phase core floods were conducted atdeeper reservoir conditions for selected polymers to compare injectivity and assess additional oil recovery.Two liquid and four powder polymers from two vendors were tested. Fluid-fluid interactions were evaluatedfor emulsion polymers due to the small concentration of surfactants in liquid polymers.
Interfacial tension measurements and phase behavior tests concluded that liquid polymers from bothvendors are non-reactive with reservoir's crude oil. However, injectivity challenges were observed for liquidpolymers from both vendors, indicating that liquid polymers are not suitable for low permeability reservoirs.A critical observation was the continuous increase in injection pressure after the brine flood. Testedpowder polymers did not show injectivity issues, suggesting that the emulsion phase in liquid polymerspotentially causes filtration or adsorption. Evaluations of powder polymers focused on the resistancefactor, residual resistance factor, mechanical degradation, and conditions near the wellbore and deep inthe reservoir. This screening process selected one product from each vendor. The powder polymer fromvendorA showed higher injection pressure but required a lower concentration to achieve the target viscositynear wellbore conditions. Supplementary two-phase core floods performed at in-situ conditions concludedthat both powder polymer products performed similarly in terms of injection pressure and additional oilrecovery. Further cost analysis of all available options revealed similar economic results for liquid polymeremulsions and powder polymers. However, limitations for traditional powder polymers include higherintitial CAPEX, the availability of surface facilities and a comparatively larger physical footprint. Ourcomparative study provides valuable insight that the currently available commercial liquid polymers arenot suitable for low permeability reservoirs, making powder polymers the only viable option. Furthermore, communication with vendors has highlighted the need to develop new liquid polymers specifically forsmall-scale, low permeability onshore reservoirs. Liquid polymers would have a beneficial impact on initial CAPEX investments for surface facilities, but the total costs are 50 % higher after 10-year project lifespan.