Enhanced Oil Recovery Performance and Solution Properties of Hydrophobic Associative Xanthan Gum

Abstract

Xanthan gum (XG) is one of the widely used biopolymers in oilfield development. It has low cost and will not pollute the environment. However, its limited temperature and salt tolerance restricts its application in high temperature and high salt reservoirs. An environmentally friendly hydrophobic associative polymer was prepared by grafting long-chain alkyl groups onto xanthan gum through an etherification reaction for enhanced oil recovery (EOR). The hydrophobically modified xanthan gum (MXG) was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Due to the hydrophobic association, MXG had excellent thickening, rheological properties, antiaging, temperature, and salt resistance properties. In the 30 g/L NaCl solutions, the viscosity of MXG (335 mPa s) was about 3 times that of XG (115.3 mPa s) at 65 °C. Whether in a high-salt solution (20 g/L NaCl) or reservoir injection water (mineralization of water is 7542 mg/L), modified xanthan gum can show good antiaging properties. The polymer flooding experiments showed that EOR of MXG is 25%, 7% higher than that of XG. The macroscopic mechanism of MXG flooding was studied. In summary, MXG has a wide range of applications in EOR.

Viscosity and Structure Characterization of the 1-Bromohexadecane-Modified Welan Gum in the Saline Solution

“…The appearance of the new bands indicated that welan gum was successfully modified using 1-bromohexadecane. The elongated bands associated with C–H and C–O–C bonds were also observed in 1-bromooctadecane-modified xanthan gum, compared with the xanthan gum precursor …”

“…The FTIR analysis (Figure a) showed a considerable difference in the bands among HWG, welan gum, and guar gum. The intensity of the bands associated with the C–H bond, appearing at 1416 cm –1 , substantially increased in HWG, compared to welan gum. , The increased intensity of the bands observed at 1416 cm –1 for HWG likely appeared because of the asymmetric configuration between the methyl groups connected to the long alkyl chain of HWG and original methyl groups present in the main HWG chain . The absorption band of C–H appearing at 2904 cm –1 also elongated for HWG, compared with that for the welan gum.…”

“…The presence of salt ions led to an increase in the polarity of the aqueous environment, which promoted the association between hydrophilic and hydrophobic groups. The enhanced intermolecular interaction results in the formation of the HWG network structure that supports its high viscosity under high-saline and high-temperature conditions. ,,, Additionally, increased temperature is conducive to the interaction between hydrophobic and hydrophilic groups and, thus, hydrophobic association enhances. ,, …”

“…43,44 The increased intensity of the bands observed at 1416 cm −1 for HWG likely appeared because of the asymmetric configuration between the methyl groups connected to the long alkyl chain of HWG and original methyl groups present in the main HWG chain. 63 The absorption band of C−H appearing at 2904 cm −1 also elongated for HWG, compared with that for the welan gum. The band appearing at 1169 cm −1 , which was assigned to the C−O−C bond originating from the glycosidic bond and the newly formed ether bond of welan gum, also elongated.…”

“…The elongated bands associated with C−H and C−O−C bonds were also observed in 1-bromooctadecane-modified xanthan gum, compared with the xanthan gum precursor. 63 The XRD results (Figure 5b) showed that a broad diffraction band appeared at the 2θ = 19°for HWG, welan gum, and guar gum because they all exhibited the amorphous morphology. 64 Similarly, the broad diffraction band was observed at the 2θ = 19°for amorphous HWG.…”