Offshore Applications of Underbalanced Drilling Technology -Well Control Considerations When Applied to Overbalanced Drilling

摘要

Written and presented to be in keeping with the theme of thern2003 Offshore Technology Conference, ENVISION –rnENABLE – ENACT, this paper speaks to a broad applicationrnto more conventional offshore drilling of the tools andrntechnology one normally associates with underbalancedrndrilling (UBD). The specialized tools developed primarily forrnthe safe practice of UBD are first and foremost wellborernpressure management tools and when applied to morernconventional overbalanced drilling in marine environmentsrnhave significant positive Health, Safety, and Environmentalrn(HSE) implications, may lower overall spread sheet costs, andrnin some cases, render “economically undrillable wells”rnviable prospects.rnUnderbalanced drilling and conventional well control arernsimilar technologies. That is, the well is shut in againstrnpressure in the wellbore and the well is circulated throughrna choke.rnMost of the challenges (barriers to economically drillablernwells and a litany of drilling related issues) facing thernshallower and deeper water wells have well controlrnimplications, either directly or indirectly. Managed PressurernDrilling (MPD) is the term given when the use of UBDrntechnology and its specialized equipment is deployed for thernpurpose of overcoming a number of drilling related barriers orrnproblems commonly encountered when drilling overbalanced.rnAdditionally, MPD facilitates Low Head (near-balanced) andrnbalanced drilling. An important point presented in this paperrnillustrates that offshore practice of MPD has the potential tornenhance well control in the process with an enhanced ability tornavoid underground blowouts and may add an additionalrnbarrier (in well control terms) for HSE benefit.rnEnvision – Visualize the barriers to economicallyrndrillable wells and the litany of drilling related issues facingrnshallow water drilling from rigs with surface BOP’s, in deeprnwater from floating rigs with subsea BOP stacks, and thernpractice of slim riser deepwater drilling with surface BOP’s.rnAll of these challenges either directly or indirectly have thernpotential to have a detrimental impact on well control, somernmore so than others.rnEnable – Specialized tools developed for UBD, whenrnused onshore and offshore, enable full time “well control”, asrnin underbalanced drilling the well is “live” while drillingrnahead. Often UBD tools are used to overcome drilling andrnformation damage issues when drilling more conventionally,rnand the industry has found that doing so has enabled arnsignificantly better well control track record compared tornwells drilled without the benefit of any of the tools developedrnfor the safe practice of UBD.rnEnact – UBD equipment has been applied to manyrntens of thousands of onshore wells over the past 30 years.rnOffshore from rigs with surface BOP stacks, over a hundredrnhave been drilled underbalanced or nearer balanced than couldrnhave been safely practiced otherwise. One well has beenrndrilled underbalanced in deep water from a floating rig with arnsubsea BOP. As offshore hydrocarbon resources deplete andrnthe need to drill in deeper water grows, more wells will berndrilled underbalanced in the future, as that will be the onlyrntechnology available to do so.rnEnact - The greatest potential for UBD tools andrntechnology applications in marine environments will, in thernnear term at least, be for overcoming a number of commonrnproblems facing more conventional offshore drilling methodsrnand as enabling equipment for new drilling technologies suchrnas dual gradient deepwater drilling, deepwater drilling with arnslim riser and a surface BOP, and as a well control alternativernto the current industry standard Pump & Dump method whenrndrilling top holes riserless.rnThis paper discusses the specialized equipment developed forrnUBD with a focus on offshore applications where the intent isrnnot to achieve a true state of underbalance at any point in thernwell’s drilling program.