Alkali-Polymer EOR Flooding in Europe: Part I - Surface: Water Softening Field Tests in Presence of Back-Produced Polymer

Abstract

Abstract Maximized depletion of mature oil reservoirs is gaining substantial importance. One of the last measures to be considered in the late life of a suitable brownfield is likely to be alkaline-polymer-EOR. OMV is currently carrying out alkaline polymer flood projects in Austria and Romania. Since AP flooding introduces significantly increased complexity, it is vital to take maximum advantage of available expertise and to not pass up any opportunity to generate additional field-based data whenever possible. Field tests performed in the Matzen Field (Austria) were used to qualify an ion-exchange-based water softening process in saline produced water and in the presence of back-produced partially hydrolyzed polymer (HPAM). A stringent goal was set to reduce the divalent cation concentration in produced water to less than 5mg/l at the test location. Evaluations were thoroughly performed under a broad variety of operating conditions and water characteristics. A thorough analysis and evaluation was performed on the impacts of various concentrations of oil and polymer or altered viscosities, as well as modified operating conditions such as flux rates. Observations describe different mechanisms related to water salinity and polymer-induced viscosity, as well as the way in which they affect the efficiency of the process. The WAC ion exchanger unit was optimized and adjusted to ensure compliance with the targeted divalent cation concentration in the presence of more than 400ppm of back-produced HPAM and more than 23 g/l of TDS content. Under these conditions, optimum operating conditions and risk mitigation measures were identified in order to achieve the best unit availability and service time between regeneration cycles. Last of all, an economic outlook was created in terms of expected chemical consumption for ion exchanger operation in the presence of back-produced polymer. The outcomes of this field trial provided crucial insights into operational aspects, allowed significant risk reduction, and represented the basis for designing upscaled water softening systems which were implemented in alkaline polymer flood projects in OMV assets.