No abstract

No abstract

No abstract

The displacement efficiency of welan gum on enhanced heavy oil recovery has been investigated by comparing that of xanthan gum which is commonly used for polymer flooding, and it is found that the displacement efficiency of biopolymer welan gum is higher (>7.0 % at the normal permeability) than that of xanthan gum. In‐depth rheological investigations show that both storage modulus and loss modulus of welan gum solution are higher than those of xanthan gum solutions at the same concentration, temperature and salinity. The higher displacement efficiency for enhanced heavy oil recovery by welan gum is mainly caused by its stronger ability to form aggregates. Although the molecular weight of welan gum is lower than that of xanthan gum, the aggregates of welan gum molecules help to improve the sweep efficiency. It is proposed that welan gum improves oil recovery by drawing and dragging on the residual oils which is derived from the interlinked network structures formed by the adjacent double helices in the arrangement of the zipper model. The intermolecular structures formed by zipper model are stable in high temperature and high salinity condition. Copyright © 2014 John Wiley & Sons, Ltd.

Microbial exopolysaccharides secreted by microorganisms during metabolic processes have been widely used in biotechnology because of their environmentally friendly and renewable nature. This study evaluates the potential of a novel microbial exopolysaccharide, diutan gum, which is produced by Sphingomonas species, for enhanced heavy oil recovery at high temperature and high salinity. In addition, two conventional polymers [xanthan gum and partially hydrolyzed polyacrylamide (HPAM)] used in oil exploitation are compared under the same conditions. It is found that the steady apparent viscosity and dynamic modulus of aqueous diutan gum solutions are not sensitive to the temperature and virtually independent of the salinity, while those of xanthan gum and HPAM significantly decrease at high temperature and high salinity. The retention values of the apparent viscosity and the dynamic modulus of diutan gum at 90 °C and 244 121 mg•L −1 salinity are greater than 90%. The gellike structure of diutan gum is dependent on the shear rate rather than the shear time and the aging time. The thermal stability and salt tolerance of diutan gum are mainly attributed to the stability of the gel-like molecular structure, which is greatly related to the double helix. Flow tests in sandpacks demonstrate the excellent mobility control capacity of diutan gum in porous media, and the permeability reduction of porous media is attributed to the adsorption and interception of diutan gum at high temperature and high salinity. Sandpack flooding experiments confirm that the heavy oil recovery efficiency of diutan gum is raised by 20.9% OOIP and is higher than that of either xanthan gum (9.3%) or HPAM (5.4%) at 90 °C and 244 121 mg•L −1 salinity. It is believed that diutan gum will be a promising oil recovery agent for enhanced oil recovery in high-temperature and high-salinity reservoirs.

www.rsc.org/ packing for P2 during spin-coating. Further improved performances were obtained by introducing two thiophene units into the polymer backbone to give P3, due to closer π−π stacking, in-plane π−stacking alignment in thin film and a higher HOMO energy level. Therefore, optimized device performance was realized through subtle modification of the polymer structure, including both main chain and side chain, which provides an insight into structure-property relationships for high-mobility polymer semiconductors.

How to further sweep residual oil from unswept areas is crucial to enhance oil recovery after polymer flooding, which is widely used.

The fractures and kerogen, which generally exist in the shale, are significant to the CO2 huff-n-puff in the shale reservoir. It is important to study the effects of fractures and kerogen on oil recovery during CO2 huff-n-puff operations in the fracture–matrix system. In this study, a modified CO2 huff-n-puff experiment method is developed to estimate the recovery factors and the CO2 injectivity in the fractured organic-rich shales and tight sandstones. The effects of rock properties, injection pressure, and injection time on the recovery factors and CO2 usage efficiency in shales and sandstones are discussed, respectively. The results show that although the CO2 injectivity in the shale is higher than that in the sandstone with the same porosity; besides, the recovery factors of two shale samples are much lower than that of two sandstone samples. This demonstrates that compared with the tight sandstone, more cycles are needed for the shale to reach a higher recovery factor. Furthermore, there are optimal injection pressures (close to the minimum miscible pressure) and CO2 injection volumes for CO2 huff-n-puff in the shale. Since the optimal CO2 injection volume in the shale is higher than that in the sandstone, more injection time is needed to enhance the oil recovery in the shale. There is a reference sense for CO2 huff-n-puff in the fractured shale oil reservoir for enhanced oil recovery (EOR) purposes.