Performance of Preformed Particle Gel in Supercritical CO2

Conformance problems plagued gas flooding, which can result in poor sweep efficiency and high gas oil ratio (GOR). As remediation of gas bypassing and channeling, Preformed Particle Gels (PPGs) have attracted increasing interest. Albeit PPGs were extensively studied, their actual performance in gaseous or supercritical conditions has not been reported. In this work, we deployed high-pressure vessel (HPV) to investigate the real-time performance in supercritical CO2 (scCO2) where various pressures and constant temperatures were loaded. The PPG volume was monitored and quantified through this visual instrument. Moreover, comprehensive comparisons upon particle size distribution (PSD), swelling capacity, and rheology properties were established between CO2 exposed and virgin particles. Furthermore, the differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were implemented to elucidate the scCO2 effects in respects of polymer transition and gel microstructure. It was manifest that the PPGs underwent significant dehydration in the presence of scCO2. The gel-pack shrank to 85% in volume while dewatered 66.4% in weight. The dehydration was found more pronounced at higher pressures. The particles size diminished from 5.2 to 3.7 mm whereas their swelling capacity and rheology properties were not strongly impaired. In DSC measurements, the glass transition temperature (Tg) deteriorated, denoting the plasticizing effect of scCO2 may induce a redistribution on the polymer chain. Namely, the polymer chain became more flexible and less stiff, which lead the PPGs prone to shrinking in scCO2. The SEM images illustrated a minute change in the microstructure. In conclusion, the plasticizing effect, pressure effect and pH effect played pivotal roles to account for the performance of PPGs, especially severe dehydration in scCO2. This work first reported the real-time performance of PPG in scCO2 while examined its applicability for CO2-EOR. The experimental results can facilitate the designing of PPG treatment for CO2 conformance control.