Pore-scale investigation of residual oil displacement in surfactant–polymer flooding using nuclear magnetic resonance experiments

Abstract

Research on the Gangxi III area in the Dagang Oilfield shows that there was still a significant amount of oil remaining in oil reservoirs after many years of polymer flooding. This is a potential target for enhanced oil recovery (EOR). Surfactant-polymer (SP) flooding is an effective chemical EOR method for mobilizing residual oil and improving displacement efficiency macroscopically, but the microscopic oil displacement efficiency in pores of different sizes is unclear. Nuclear magnetic resonance (NMR) is an efficient method for quantifying oil saturation in the rock matrix and analyzing pore structures. In this paper, the threshold values of different pore sizes were established from the relationship between mercury injection curves and NMR T 2 spectrums. The distribution and migration of residual oil in different flooding processes was evaluated by quantitatively analyzing the change of the relaxation time. The oil displaced from pores of different sizes after the water flood, polymer flood, and the SP flood was calculated, respectively. Experimental results indicate that (1) the residual oil in medium pores contributed the most to the incremental oil recovery for the SP flood, ranging from 40 % to 49 %, and small pores usually contributed \30 %; (2) the residual oil after the SP flood was mainly distributed in small and medium pores; the residual oil in medium pores accounted for 47.3 %-54.7 %, while that trapped in small pores was 25.7 %-42.5 %. The residual oil in small and medium pores was the main target for EOR after the SP flood in oilfields.

Cationic/Nonionic Mixed Surfactants as Enhanced Oil Recovery Fluids: Influence of Mixed Micellization and Polymer Association on Interfacial, Rheological, and Rock-Wetting Characteristics

“…In EOR processes, surfactant fluids recover residual oil molecules by interfacial tension (IFT) reduction. − Previous studies reported that the IFT between oil and displacing fluid must decrease to ultralow magnitudes for displacement of in situ oil from pore spaces (otherwise trapped by capillary forces) of hydrocarbon-bearing reservoir rocks. , Surfactant monomers are adsorbed onto the oil/aqueous interfaces, with the hydrophobic tail groups orienting toward the oil phase and hydrophilic heads pointing toward the aqueous phase. This results in micelle/aggregate formation, which is an important transport conduit for crude oil movement. , Mixed surfactant fluids improve the oil micellization ability of constituent surfactants by forming mixed micelles in dynamic flow systems. − Incorporation of ionic + nonionic surfactants into aqueous fluids reduce the repulsive interactions among charged polar head groups and favors improved adsorption efficiencies, which in turn is responsible for improved oil extraction.…”

Oil Recovery Performance by Surfactant Flooding: A Perspective on Multiscale Evaluation Methods

“…Liu et al 184 utilized a low-frequency NMR spectrometer (Reccore-04) to quantify the distribution of oil in rock samples from the Dagang oil field in China after waterflooding, polymer injection, and SP injection. The tests aimed to evaluate the performance of different surfactant/polymer formulations for EOR applications and revealed the contribution of every pore system (i.e., small, medium, and large) to the oil recovery.…”

Nuclear Magnetic Resonance Measurement of Oil and Water Distributions in Spontaneous Imbibition Process in Tight Oil Reservoirs

“…Combining C and T 2 spectrum, the pore-radius distribution, shown in Figure 3, is obtained. The relationship between T 2 , pore radius, and pore type is shown in Table 3 following the methods of Lai et al [36] and Liu et al [42].…”