Through tubing rotary managed pressure drilling

Abstract

Managed pressure drilling (MPD) has been known to the industry for a few years. MPD with the ability of coping with risky down-hole pressure situations has gained a great deal of attention. Compared to MPD, the drilling method designated ‘’through tubing drilling’’ (TTD) is considerably younger. StatoilHydro, as one of the TTD pioneers, has drilled TTD wells in its North Sea assets, of which the majority have been the ‘’through tubing rotary drilling’’ (TTRD) wells. The aim of initiating this technology was to access small and by-passed oil pools in mature assets in a cost effective manner, since TTRD rules out the need of pulling the well completion. From StatoilHydro’s experience we see that TTRD is one of the complex drilling methods. Drilling by this technique has seen a number of challenges and drilling problems. In fact, the majority of these problems are linked to system and down-hole pressure environments, and thus to drilling hydraulics. Pressure induced drilling problems can be solved by application of MPD. The idea in this study is that the simultaneous application of TTRD and MPD will enable us to mitigate problems relating to pressure conditions and drill cost effective TTRD. Therefore, this thesis was initiated to study the hydraulics of ‘’through tubing rotary managed pressure drilling’’ (TTRMPD). In this study two specially looked at MPD methods: back pressure and continuous circulation system allow for the reduction of the static mud weight in order to manage circulating mud weight and stay within available drilling window. This study looks into hydraulics of the TTRMPD operation in terms of equivalent circulating density (ECD), hole-cleaning, extended reach ability. In the TTRD, ECD management is particularly challenging due to narrow annular clearance. This master thesis focuses on the feasibility of combining MPD and TTRD to improve the ECD management in TTRD. We will look into the effects that the reducing mud weight may have on drilling parameters.