Successful Implementation of the PMCD Technology for Drilling and Completing the Well in Incompatible Conditions at Severo – Danilovskoe Oil & Gas Field

This paper discusses the successful implementation of PMCD (Pressurized Mud Cap Drilling) technology at Severo – Danilovskoe oil and gas field (SDO) located in the Irkutsk region. The abnormally high-pressure reservoir B1 and the abnormally low-pressure reservoir B5 are the target layers in this field. Wells drilling at SDO is accompanied with simultaneous mud losses and inflows conditions, especially if the strata B1 is being penetrated. Pumping lost circulation materials (LCM) and cement plugs do not solve lost circulation complications which subsequently lead to oil and gas inflows. As a result, most of such wells are getting abandoned. It was assumed that complications in this formation occurs due to the narrow safe pressures’ operating window (ECD window), therefore, the managed pressure drilling technology (MPD) was initially used as a solution to this problem. However, after the penetration of the abnormally high formation pressure B1 horizon with a pore pressure gradient of 1.86 g/cm3 it was found that there is no operating window. In this regard, there were simultaneous mud losses and oil and gas inflows during the circulation. The well was gradually replaced by oil and gas, regardless of the applied surface back pressure value in the MPD system. The mixing of the mud and reservoir fluid was accompanied by catastrophic contamination. As a result, the drilling mud became non - flowing plugging both the mud cleaning system and the gas separator. On the other hand, the plugging of the B1 formation with LCM did not bring any positive results. Bullheading the well followed by drilling with applied surface back pressure and partial mud losses gave only a temporary result and required a large amount of resources. An implementation of PMCD technology instead of MPD has been proposed as an alternative solution to the problem. This technology made it possible to drill the well to the designed depth (2904 - 3010 m interval). For tripping operations, as well as the subsequent running of the production liner it was necessary to develop an integrated plan for well killing and completion in extreme instability conditions. As a result of various killing techniques application, it became possible to achieve the stability of the well for 1 hour. Oil and gas inflows inevitably occurred when the 1 hour lasted. Based on these conditions, the tripping and well completion process was adapted, which in the end made it possible to successfully complete the well, run the liner and activate the hanger in the abnormally high-pressure reservoir.