ARG-1 exploration sour and high CO2 gas well was drilled vertically in South Sumatra, Indonesia, with a total depth (TD) of around 5000 ft-MD. The operation has been facing many challenges in drilling and completion phase; one of them is the occurrence of massive fluid losses in fractured limestone formation. Pressurized mud cap drilling (PMCD) technique is the possible solution to complete this well without sacrifice drilling fluids in enormous volume and minimize non-productive time (NPT). PMCD is one of managed pressure drilling (MPD) techniques applied in situations when drilling without return to the surface and with a full annular fluid column which is maintained above the formation. The key of successful PMCD technique is the rotating circulating device (RCD) which is used to close the annulus. Furthermore, sacrificial fluid is injected through drill string and light annular fluid is pumped down from the annulus to maintain borehole fill and prevent annular gas migration. Limestone formation was drilled with 6 in slim hole which is a contingency plan. In addition, the premature set of 7 in casing was to cover the gas zone which is located above the limestone formation. Total loss circulation occurred when drilling through upper limestone formation. Conventional combat loss techniques i.e. spot loss circulation material, gunk plug, and cement plug were used to cure the loss but none of them give significant result. It took approximately 2 months for combat loss with such common technique. In consequence, PMCD technique was decided to apply in this situation and it only required 4 days to drill until TD and ready to run 4-1/2 in casing. By successfully utilizing the PMCD technique, the company was able drastically to reduce the NPT and reach the TD successfully. This paper presents a case study of the drilling operation in ARG-1 exploration well that had massive loss circulation while using common combat loss techniques were unable to reach TD. Furthermore, it explains how drilling in PMCD mode allowed operation in ARG-1 to reach the TD after total loss of circulation was experienced and how the completion assembly was run and cemented in PMCD mode.

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