Synthesis and Evaluation of Two Gas-Wetting Alteration Agents for a Shale Reservoir

It is well-known that shale gas production is affected by the wettability of the reservoir. In this work, two gas-wetting alteration agents were synthesized and characterized by 1H NMR and FTIR. To evaluate the effect of the gas-wetting alteration agents on the shale wettability, the contact angle for droplets on the shale surface was detected, and the results showed that the contact angles of water and n-hexadecane increased from 36° and 0° to 119° and 88° after treatment with sodium [N-propyl-N-(perfluorooctanoyl)amino]acetate (SCF-102), while the contact angles increased to 122° and 110°, respectively, after treatment with sodium [N-[[N-(perfluorooctanoyl)amino]ethyl]amino]propionate (SCF-113). The surface free energy rapidly decreased from the primeval 72 to 10.3 and 6.8 mN/m at equal concentration. These values agreed with the results of spontaneous imbibition, the capillary tube rise test, and the fluid flow test. Additionally, the analysis with energy dispersive spectroscopy and scanning electron microscopy revealed that the fluorine-containing adsorption layer was formed and the roughness of the shale surface was significantly increased. This indicated that the gas-wetting surface can be achieved by using the gas-wetting alteration agents. The above results confirmed that the wettability of the shale surface is altered from the original water-wetting or oil-wetting to gas-wetting. Furthermore, the thermal analysis exhibited that the two gas-wetting alteration agents have good thermal stability under 165 and 216 °C, respectively. It demonstrated that they have greater potential to be applied to high-temperature reservoirs.