Assessing Alkali-Polymer Interactions for EOR: Observations from Laboratory Evaluations and Field Application in Austria

Abstract

Abstract We investigate into optimizing alkali-polymer (AP) flooding in brownfields, focusing on the critical initiation of fluid-fluid and rock-fluid interactions for enhanced oil recovery. A detailed screening of the AP cocktail is vital for cost efficiency and for maximising the efficacy of the chemical slug. Our research outlines industry-standard laboratory methods to screen chemicals for AP pilots and field implementation, using the example of an AP pilot in Austria. The key to our screening process is fluid characterisation, enabling the selection of chemical concentrations suitable for the targeted interactions. Crucial to the fluid-fluid interaction assessment is the stability of produced emulsion, interfacial tension (IFT) measurements, and comprehensive fluid rheology analysis. For probing rock-fluid interactions, we employed both single-phase and two-phase core floods, which are fundamental for understanding the dynamics within the heterogeneous reservoir. Core floods were conducted using low permeability (perm) and high perm core plugs to capture the breadth of reservoir conditions. This approach allowed for a detailed evaluation of displacement efficiency and potential injectivity limitations. In a novel extension of our study, we simulated the in-situ ageing of the AP slug, considering its increased anionicity. This involved conducting two-phase core floods with aged chemicals, providing unique insights into the temporal evolution of chemical efficacy and interaction. Our findings revealed a specific alkali concentration of 7,500 ppm as optimal for the AP slug—the interaction between the alkali-polymer and high Total Acid Number (TAN) dead oil produced emulsions. A noteworthy observation was the micro-instability of these emulsions, evidenced by changes in viscosity and volume over time. Regarding injectivity, single-phase core floods indicated that the vendor-B AP slug (PolymerB) outperformed the vendor-A AP slug (PolymerA), although challenges in mechanical stability were observed. Interestingly, the additional recovery factors (RF) were higher for PolymerA-based AP slugs than PolymerB-based APs from high perm core plugs. A similar trend for the additional RF for low perm plugs was observed. Furthermore, a consistent trend in additional oil recovery was observed for both aged and un-aged chemical slugs through high perm core plugs. This led to the conclusion that in-situ ageing of the AP slug could be a viable strategy for reducing costs (low concentrations) while enhancing injectivity. Overall, we provided valuable insights into the in-situ stability of the AP slug derived from fluid-fluid optimisation and rock-fluid interactions. It also underscores the significance of in-situ stability as it directly impacts injectivity and sweep efficiency in porous media. The findings presented are crucial for refining the screening criteria for the pilot project. Moreover, ensuring a more effective and economically enhanced brownfield oil recovery process.