The Study of Nanosurfactant EOR in Carbonates by Advanced NMR Technique

Abstract

Abstract The application of conventional surfactant-based enhanced oil recovery (EOR) suffers from either the adsorption of the surfactant on the rock near the wellbore or from diffusion into small water-filled pores. An approach to mitigate the loss of surfactant and enhance deliverability to the oil phase is achieved by formulating the surfactant molecules into nano-sized particles, which are referred to as NanoSurfactant (NS) in this study. An essential step to unleash the potential of NS in EOR is the accurate understanding of its performance under conditions reasonably close to actual conditions. In the current study, crude oil, synthetic brine, and petroleum sulfonate based NS were used. Eight limestone core plugs with a permeability range of about 125 millidarcies (mD) to 1282 mD were utilized in this study. Coreflooding was conducted under the near-reservoir condition. Advanced low-field nuclear magnetic resonance (NMR) techniques have been used to quantify the oil saturations by both secondary water injection and tertiary NS injection. The NMR techniques have also been used to assess the mechanisms underlying oil mobilization in carbonate core plugs. The protons in brine and NS solution were substituted with proton (H1) NMR invisible deuterium to enhance the contrast between oil and brine. The core samples were selected to investigate the effect of the NS soaking condition (soaking versus non-soaking), the NS injection rate, and the remaining oil saturation on the observed oil mobilization, respectively. All core plugs were initially saturated with oil and water, waterflooded, injected with NS (with and without soaking), followed by chase waterflooding. NMR measurements were conducted after each flooding stage. The results of the current study demonstrate that the investigated NS has a great potential for EOR applications in carbonate reservoirs, and that soaking NS before chase waterflooding enhances its efficiency. Significant oil mobilization was observed when soaking was applied before chase waterflooding. The oil mobilization was much lower without soaking of NS for the cores with low quality and less oil wetting tendency. The analysis indicated that NS flooding can produce both of the trapped oil and oil adsorbed to the rock surfaces.