Well Control Considerations – Offshore Applications of Underbalanced Drilling Technology

摘要

This paper focuses upon the well control aspects related tooffshore applications of the tools and technology normallyassociated with underbalanced drilling systems (UBS). Adiscussion of the history of underbalanced drilling and theevolution of the specialized equipment required to practice thetechnology with a well established and commendable wellcontrol track record will help one recognize the potentialbenefits of offshore application. Whether onshore or offshore,a key component of UBS is a rotating diverter control head(RCH). As a key tool, the development of RCH’s enabled thetechnology of onshore UBD and led the way towardsencouraging the development of numerous other pieces of theUBS “tool chest”. RCH’s are fulfilling the same enabling roleoffshore, including leading the way towards numerous nonunderbalanceddrilling uses. Offshore applications of the toolinclude “onshore models” atop surface blowout preventionstacks (BOP’s). Several “offshore variations” of the toolenable deepwater drilling (subsea BOP) with lightweightfluids, managed pressure drilling, dual gradient deepwaterdrilling, slim riser deepwater drilling with a surface BOP, andone subsea model facilitates controlling abnormally pressuredaquifers and/or achieving zero discharge when riserlessdrilling top hole sections when establishing a subsea wellhead.Barriers to achieving a true state of underbalance during anoffshore well’s drilling program include wellbore instability,dealing with produced hydrocarbons, and in some cases,regulatory restrictions. Offshore applications were the intent inusing UBS was to drill ahead under a true state ofunderbalance now total around 100 wells. All but one has beendrilled from rigs a surface BOP’s. In deeper waters fromfloating rigs with subsea BOP’s, the trend to drill underbalanced is expected to be more aggressive in the futuregiven the large percentage of all known deepwater resourcesbeing economically undrillable otherwise.In the nearer term, non-underbalanced drilling applicationsof the specialized equipment and technology associated withunderbalanced drilling is much less of a step-change andavoids the aforementioned barriers to true underbalanceddrilling offshore.Therefore this discussion places emphasis upon the nonunderbalanceddrilling applications of the specializedequipment associated with underbalanced drilling andillustrates the well control considerations.In the context of this paper, well control implicationsrelate to the potential for surface events as well asunderground blowouts.