Drilling fluid for the super-deep Well Mashen-1

Well Mashen-1 is a key vertical well deployed in northeastern Sichuan by SINOPEC for preliminary exploration. Boasting of a TD of 8 418 m, it is the deepest land well drilled in Asia. The fourth and fifth spud-in intervals were drilled at depth of 6 225.4 ~8 418 m with bottom-hole temperature up to 175 ℃. Accordingly, these intervals have problems related to high-temperature pollution, sidewall instability in mud shale, acidic pollution and sand-carrying. Generally speaking, properties of conventional drilling fluid may not satisfy demands for routine operation. With consideration of these technical challenges, optimized materials and formula were deployed to develop KCl polyamine sulfonated drilling fluid system and temperature -resistant polysulfonate drilling fluid system. Test results indicate that KCl polyamine sulfonated drilling fluid has outstanding inhibition capabilities and can endure temperature up to 200 ℃. In addition, highly matured processing technologies for drilling fluids in super deep well have been developed. Field application results show that the well diameter has been enlarged by approximately 3.1% during the fourth spud-in and 5.1% in the fifth spud-in. Since these technologies can effectively cope with the challenges in drilling fluid for super deep wells, they can be promoted for more extensive application.