Unveiling the Changes in the Molecular Groups of Tight Sandstones in Response to an Electric Field.

The electric field method proved in the lab and oil fields is an effective and fast way to significantly improve oil recovery, which can be applied to greatly realize the urgent-need requirements for energy, especially in tight sandstones. Generally, the changed molecular groups treated with an electric field modulate the wettability of reservoirs, affecting the final oil recovery. Herein, the investigation of the impact of the electric field on the molecular groups of reservoirs is imperative and meaningful. In this paper, tight sandstones were placed into a particular instrument and subjected to various strengths of the electric field. Nine treated powders and one untreated powder of tight sandstones were processed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) experiments. FTIR results show that the electric field decreases aromatic groups, C-O groups, COOH groups, and aliphatic groups, whereas it increases C=C groups, C=O groups, and OH groups. Interestingly, the changes in C-O groups, C=O groups, COOH groups, and OH groups are all the competitive results of production and consumption during the treatment process. With regard to C-O groups and COOH groups, the consumption has an advantage over the production on the content of functional groups, and the situations for C==O groups and OH groups exhibit a contrary trend. The fitted result of XPS proves the fact that the electric field improves C=O groups, OH groups, and COOR groups, whereas it reduces C-O groups, supporting that the molecular groups can be mutually transformed during the electric field treatment. The obtained knowledge is beneficial to the study of electric field-related technologies on the molecular groups of reservoirs.