Ever since Shell introduced underbalanced drilling (UBD) in the offshore environment in 1997, Shell has been looking at ways to reduce the footprint for the equipment required for underbalanced operations. Much of this work involved reducing the size of the separator (volume) and modularising the UBD kit by stacking and containerising. As UBD takes a foothold in low-cost operating areas, Shell has actively looked at ways to not only reduce the footprint but also the unit operating cost driven mainly by the need for experienced expatriate personnel to man the equipment. Recent introduction of new or improved tools and equipment combined with growing recognition that the primary value driver for the application underbalanced drilling is dynamic reservoir characterization, creates a window of opportunity to move this initiative forward.

This paper presents the conceptual framework to replace large, manpower intensive surface equipment with a combination of down-hole and surface tools and equipment having the same functionality but improved efficiency, which enable a reduced footprint.

It illustrates how the functionality of the 4-phase separator can be replaced by combining inline phase separation, a gas buster and down-hole multiphase metering. Furthermore it describes how massive surface snubbing systems are being replaced with down-hole isolation systems and proposes replacing current intrusive and high maintenance BHA equipment with low-cost rotary steerable systems, non-intrusive MWD systems and the development of non-return valves (NRVs) that are compatible with through bore solutions to optimise data gathering while drilling. The paper postulates that every piece of equipment is driven by a functional need, has an impact on efficiency and therefore cost and may offer opportunity for enabling add-ons if the underbalanced drilling process is viewed from a different perspective.

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