Drilling fluids for shale fields: Case studies and lessons learnt

In recent years, Shale gas has been the fastest-growing energy source in the world. In USA, shale gas now contributes to more than 60 % of natural gas supply. In China, annual shale gas production climbed to 800 Bcf (billion cubic feet) in 2021. However, drilling in shale has been a major challenge since the dawn of petroleum industry due to the reactive clay minerals.This paper surveys the field cases of drilling fluids in major shale plays. OBM (oil based mud), formulated with diesel and low fraction of water phase, provides effective shale stability, excellent lubricity, and high rate of penetration (ROP). As a result, more than 70 % of shale gas wells have been drilled with OBM with very few reported cases of wellbore instability. WBM (water-based mud) is made of water and necessary chemical additives. WBM is less costly and more environment-friendly than OBM, however some shale wells drilled with WBM reported severe instability issues. Nevertheless, recent innovations in WBM lead to successes in drilling major shale plays. WBM has great potential in shale drilling and deserves more research and improvements.