The Successful Application of MPD Technology in Drilling Ultra Deep and Ultra-high Pressure Saltwater Formation to Mitigate Drilling Hazards: A Case Study in Tarim Basin

The ultra-high pressure saltwater formation coupled with high permeability sand intercalation makes the ultra-deep salt and gypsum formation (6670–7700 m TVD) drilling of the 9–1/2ʺ hole section particularly challenging in the piedmont area in Tarim Basin. Drilling strategy is usually oriented to the use of high density OBM with densities normally ranging between 2.32 and 2.60 g/cm3. High density mud causes losses and sticking events. To overcome the challenges mentioned, the application of MPD technology with the constant liquid volume during the drilling of the 9–1/2ʺ hole section enables utilizing the balance between formation pressure and downhole pressure. The technology involves keeping constant circulation fluid volume during drilling, and pipe connection under shut-in, shut-in during trip and keeping fluid in wellbore constant by squeezing in and releasing liquid, so as to keep pressure in wellbore balanced. This paper summarizes the key points of field implementation and related calculation method of the constant liquid volume MPD technology. Comparing with conventional drilling methods, the constant liquid volume MPD technology can enhance drilling efficiency and mitigate drilling hazards such as losses and differential sticking. As a result 325 m of salt and gypsum formation were drilled in only 29 days while field average is around 97 days. The successful application of MPD technology will provide a new approach for safe drilling of ultra-high pressure saltwater and narrow density window formation.