Shale gas usually distributes in dense porous media reservoirs, which is not easy to develop without external force. Hydraulic fracturing has been an effective technology utilized to improve the yield of shale gas. However, the performance of this method depends on large displacement and liquid volume, resulting in the blockage of the flowing channels in the reservoir and huge waste of water resources. Thus, it is particularly important to increase the rate of fracturing fluid return.
The contact angle test, owens two-liquids method and spontaneous imbibition were conducted to investigate the effect of gas-wetting alteration on the shale wettability and liquid flow. Moreover, the energy dispersive spectroscopy was used to analyze elemental changes on the shale surface.
The results showed that the contact angles of water and n-decane on the shale surface increased from 36o and 0o to 128o and 115o, respectively. The surface free energy rapidly reduced from primeval 71 mN/m to 5.6 mN/m after treated by 0.4 wt.% gas-wetting reversal agent. The results were further verified by spontaneous imbibition. The analysis of energy dispersive spectroscopy (EDS) indicated that the gas-wetting reversal agent could product adsorption layer on shale surface, which played an important role in super gas-wetting.
The wettability of shale surface could be reversed from liquid-wetting to super gas-wetting by the novel gas-wetting reversal agent with double-chain hydrophobic and olephobic structure, which could significantly enhance the flowback rate of the fracturing fluid due to super gas-wetting alteration.