Abstract
The efficacy of surfactant flooding as a Chemical Enhanced Oil Recovery (EOR) method depends on the amount of the surfactant loss in the porous medium. Adding alkali to surfactant-polymer (SP) floods lowers surfactant adsorption/retention, but alkali has several key challenges that prevent operators from adopting it as the universal chemical EOR technique. Sodium polyacrylate has been successfully used as a sacrificial agent to reduce surfactant adsorption in static and dynamic adsorption tests. In this study, we evaluated the effect of sodium polyacrylate in Berea sandstone in the presence/absence of petroleum crude oil and compared dynamic adsorption/retention values with and without NaPA. Prior to corefloods, ultra-low interfacial tension surfactant formulations were identified using microemulsion phase behavior experiments for two different crude oils. Corefloods were conducted at corresponding optimum salinity of the surfactant formulations with a negative salinity gradient towards polymer drive. Surfactant concentration in effluent was measured by a high-performance-liquid-chromatography method (HPLC), and the adsorption/retention values were calculated by material balance. In our experiments, surfactant adsorption during single-phase corefloods (in the absence of crude oil) in Berea sandstone cores was found to be around 0.17-0.23 mg/g-rock;; addition of a 0.5~(-1).0 wt % sodium polyacrylate decreased surfactant adsorption to 0.10 mg/g-rock. Surfactant retention in SP oil recovery corefloods in Berea sandstone cores without and with NaPA was found to be 0.20 mg/g-rock and 0.11 mg/g-rock, respectively.
NSTL