Novel Environmentally Friendly Lubricants for Drilling Fluids Applied in Shale Formation

One of the biggest difficulties with water-based drilling fluids for shale horizontal wells is its relatively high friction, especially for long horizontal wells. Improving the lubricating ability of drilling fluids is very important for expanding the extension range of horizontal wells in unconventional oil and gas wells. In this work, three kinds of lubricants, graphene oxide (GO), choline chloride/glycerol deep eutectic solvent (Gly-DES), and GO/Gly-DES, were synthesized to investigate their ability to improve the lubricity of water-based drilling fluids. These synthesized lubricants were all environmentally friendly. The tribological test and the filter cake adhesion coefficient test were used to compare the lubricity of these fluids. On the other hand, the traditional commercial lubricant solid graphite (HY-202) was taken as the reference sample. The results indicated that GO and Gly-DES can exert a more obvious lubricating effect at much lower concentrations compared to the reference sample. GO (0.25 wt %) can reduce the adhesion coefficient of filter cake by 93.33% and the friction coefficient of drilling fluid by 48.47%. The complex of GO and Gly-DES can further increase the reduction rate of adhesion coefficient and friction coefficient. Whether it was in reducing the adhesion coefficient of the filter cake or the friction coefficient of the drilling fluids, the combined lubrication effect of GO and Gly-DES was significantly better than using GO or Gly-DES alone. GO and Gly-DES decreased the coefficient of friction due to their good ability in producing a strong protective film on the contacting surfaces of the metal and filter cake. GO and Gly-DES can slightly reduce the filtration volume of drilling fluids and are suitable for shale water-based drilling fluids.