Monitoring of Polymer Injectivity and Mobility Control Performance in Carbonates Using Coreflood Integrated with Computed Tomography (CT)

Abstract

Abstract Oil production enhancement from mature fields through polymer injection has gained elevated interest due to the improved mobility and conformance controls. The suitability of polymer with harsh reservoir condition and its insitu performance dictate the success of polymer-augmented waterflooding. This motivates thorough evaluation of polymer to build optimum injection strategy for the targeted reservoir. This study aims to evaluate the impact of polymer and chase water injections in high salinity carbonate rock using single-phase coreflood experiments coupled with real-time saturation monitoring. A sulfonated polymer, acrylamido tertiary-butyl sulfonate (ATBS), was utilized and polymer solutions at different concentrations were prepared in 20 wt% brine. Coreflooding integrated with computed tomography (CT) scanning was used to generate 3D images during polymer flooding in carbonate outcrop (95.2 mD) at 70°C. Polymer injection was also evaluated in a tapered injection scheme in which polymer slug concentration was stepwise reduced. Polymer injectivity, retention, flow patterns, and inaccessible pore volume (IPV) were analyzed using pressure drop, average saturation, and CT images in real time. The results showed that the selected polymer has favorable injectivity behavior with acceptable injectivity losses (0.5-0.85) at all tested concentrations and injection rates. Polymer injection at higher concentration provided higher resistance factor, lower injectivity, and higher injectivity reduction. In-situ saturation monitoring showed polymer breakthrough before 0.8 PV with an IPV of 20%. The brine post-flush exhibited 74.1% decrease in polymer saturation after 1 PV and 99% of the polymer was recovered after 10 PVs of brine injection. For polymer augmented waterflooding with a concentration tapering mode, the IPV was reduced to 26.8%. Moreover, the chase water after tapered polymer injection showed 4.5 times high flow resistance compared to that of pre-flush brine. The chase water injection for about 1 PV reduced the retained polymer to 20% due to the increased flow resistance. This study assessed polymer injectivity and retention behavior for mobility control performance in carbonate under moderate temperature and salinity conditions. The findings of this work would guide future studies on the optimization of polymer-augmented waterflooding by using different injection schemes to improve the efficiency of mobility control process in carbonates, which would further aid in designing successful field projects.