Drilling with a gas cap over the Natih formation in Oman often results in excessive flat time. Using the current dynamic fill equipment to deal with kick and loss scenarios leads to extensive nonproductive time on the rig. Managed pressure drilling (MPD) is a well-established drilling technology, and diverse variants exist to suit different requirements. All those variants use the rotating control device (RCD) as a common piece of equipment, but their procedures are different. The pressurized mud-cap drilling (PMCD) technique in the Natih formation replaces the need for traditional dynamic filling technology. The PMCD application enhances the drilling and completion processes by reducing flat time when total downhole losses are experienced. This paper elaborates on PMCD as a proven drilling technique in total loss scenarios when drilling with it for the first time in the Natih formation in Oman. It describes the PMCD process, the associated equipment, and the results of the inaugural application in the Qalah field.

Underbalanced drilling technology is widely used to minimize formation damage in the reservoir section and enhance productivity. It involves drilling with a fluid whose hydrostatic pressure is lower than that of the formation being drilled. As a consequence of this lower hydrostatic there is a continuous flow of hydrocarbons to surface which is handled by separation equipment and exported thru pipelines where they exist or burned at the flare if no transportation infrastructure is located near rig-site. The injection of nitrogen into drill-pipe to lighten the hydrostatic pressure of the drilling fluid introduces significant challenges with regards to corrosion mitigation planning. A very well developed corrosion mitigation plan often exists for single phase drilling fluid but the introduction of a gaseous phase leads to changes that need to be incorporated to prevent against excessive corrosion. Problems and complications due to corrosion issues were hindering an underbalance drilling operation's progress. This paper examines how, optimizing the corrosion control techniques leads to improved drilling performance in subsequent bit runs. The willingness by the operator to tweak and improve the chemical concentrations and learn and apply those lessons learned immediately in the field pays immediate dividends.