One of the perceived blockers for Underbalanced Drilling (UBD) operations globally is the necessity for flaring gas in most operations. As the world becomes more aware of the impact of CO2 emissions, oil and gas producers are implementing flaring reduction targets or, in some cases, flaring bans as a key component in their corporate strategies. Project teams make often argue that due to flaring requirements, UBD is not aligned with corporate directives and is is not environmentally acceptable. Thus the technology is eliminated as a considered option when finalizing field development plans. As the UBD industry has matured, use of UBD to increase production and reserve recovery from wells, which has resulted in a reduction of the number of wells needed to develop a field. Reservoir characterization from UBD has been used to better target wells in the reservoir, reducing the chances for "junk wells" with poor or no production. UBD is also used as an enabler to slim down wells with reduced steel requirements and to drill faster with reduced rig emissions. This paper will evaluate the trade off of increased CO2 emissions from UBD flaring against reduced CO2 emissions from fewer required wells, reduced steel requirements and reduced rig time. Case studies of several Shell UBD projects will be presented to determine the "CO2 cost neutral point" and if the projects reduced or increased global CO2 emissions. Conditions under which UBD may be justified to reduce project CO2 emissions will be determined and discussed.

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