Novel MPD Technology Applied in Ultradeep Waters in the Caribbean

Abstract

Ultra deep water presents the most challenging conditions during drilling operations. When weak carbonates increase the likelihood of fracturing a formation, the challenge increases further still. High hydrostatic pressures, due to the long riser as well as the narrow gap between pore and fracture pressures, add to the complexity. Performing successful cementing operations is equally challenging. This paper describes the drilling of a well at approximately 2200m in the eastern GoM. The formations were carbonates with potential for high-to-total losses. The rig was a new Sixth Generation DPMODU. To manage the BHP and avoid or reduce losses, the rig had been equipped with a new type of MPD system. This is a pumped riser system, with the pump mounted approximately 400m below the bell nipple. The pump reduces the riser level in a precisely controlled manner to manipulate the BHP as required. Due to a very weak 20"shoe the 17 ½" section had a drilling window of only 0,3ppg. The MPD system was used to drill the section with nearly constant BHP, compensating for the ECD by managing the hydrostatic column level while drilling, and bringing the level back up for connections. No losses were seen. The same applies for cementing of the 13 3/8 casing. The main focus in this paper will be the 8,5"section where this MPD system again was necessary due to potential for severe losses. The section was drilled with riser level actively managed to control the BHP. On connections riser level was increased to account for the loss of annular friction, thus always keeping the BHP under control. It soon became evident that this formation could not have been drilled conventionally as weak zones were penetrated at the start of the section. Loss pressure was 8,4 ppg. Drilling with returns was still required in order to get the required geological information from the well, which was achieved. As drilling proceeded a normal-pressured zone was encountered. This paper will describe the planning and drilling operation of the mentioned ultra-deepwater well with focus on the very challenging 8,5" section