Qingjie Liu

Low Salinity Waterflooding in Low Permeability Sandstone: Coreflood Experiments and Interpretation by Thermodynamics and Simulation

In recent years, ions tuning water flooding (ITWF) has been a promising technique to recover oil in sandstone reservoirs. In view of research results for the last decade, it is acknowledged that substantial oil recovery beyond conventional waterflooding from sandstone is wettability alteration. However, the major contributor to wettability alteration is still uncertain. Therefore, this paper investigates this major mechanism and shows how it is due to involved in the process of IOR. Rock and oil surface chemistry were tested to explain the influence of zeta potential on the disjoining pressure. Coreflood experiments with permeability less than 1mD were performed with two different brines. Moreover, the impact of different wettabilities ranging from strong waterto slight water -wet on ITWF recovery was investigated with combination of thermodynamic theory and corefloods experiments. Relative permeability curves were obtained by history matching the corefloods experiments for both oil-wet and water-wet cores with consideration of salinity effect. Thermodynamics of wettability by ion tuning waterflooding was analyzed to characterize the surface forces between the surfaces of oil/water and water/rock. Zeta potential results showed that decreasing divalent cations and salinity makes the electrical charges at both oil/brine and brine/rock interfaces become strongly negative, which results in elevation of the repulsive forces between oil and rock, and as a result the rock turns more water-wet, which was confirmed by thermodynamics characterization. Coreflooding experiments showed that a high potential in oil-wet reservoirs can be achieved by ion tuning waterflooding due to the double layer expansion. The relative permeability curves obtained by history matching showed that ITW improves oil recovery by accelerating oil production (relative perm changes) and reducing residual oil saturation in oil-wet rock but not in water-wet rock. Thermodynamics of wettability analysis indicated that the mechanism of ion tuning waterflooding can be interpreted by disjoining pressure calculation. These findings can help in composition design of ion tuning water to maintain higher potential to recover oil in oil field.

Effect of PEO molecular weight on the miscibility and dynamics in epoxy/PEO blends

Abstract.In this work, the effect of poly(ethylene oxide) (PEO) molecular weight in blends of epoxy (ER) and PEO on the miscibility, inter-chain weak interactions and local dynamics were systematically investigated by multi-frequency temperature modulation DSC and solid-state NMR techniques. We found that the molecular weight (Mw) of PEO was a crucial factor in controlling the miscibility, chain dynamics and hydrogen bonding interactions between PEO and ER. A critical PEO molecular weight (Mcrit) around 4.5k was found. PEO was well miscible with ER when the molecular weight was below Mcrit, where the chain motion of PEO was restricted due to strong inter-chain hydrogen bonding interactions. However, for the blends with high molecular weight PEO (Mw > Mcrit), the miscibility between PEO and ER was poor, and most of PEO chains were considerably mobile. Finally, polarization inversion spin exchange at magic angle (PISEMA) solid-state NMR experiment further revealed the different mobility of the PEO in ER/PEO blends with different molecular weight of PEO at molecular level. Based on the DSC and NMR results, a tentative model was proposed to illustrate the miscibility in ER/PEO blends.Graphical abstract