OTC: New approaches hold promise for overcoming drilling barriers

May 6, 2003
Offshore drillers must move away from conventional overbalanced drilling to drilling with tools normally associated with underbalanced drilling, according to presentations at this year's Offshore Technology Conference in Houston.

Guntis Moritis
Production Editor

HOUSTON, May 5 -- Offshore drillers must move away from conventional overbalanced drilling to drilling with tools normally associated with underbalanced drilling, according to presentations at this year's Offshore Technology Conference in Houston.

Don Hannegan, Weatherford International Ltd., said these tools may make "economically undrillable wells viable prospects."
He said managed pressure drilling (MPD) can overcome some drilling-related barriers commonly encountered in conventional drilling with an overbalanced mud column.

Hannegan said that offshore underbalanced drilling has been limited, although the industry has drilled with underbalanced equipment tens of thousands of onshore wells over the past 30 years. He estimated that wells drilled underbalanced or near balanced with offshore rigs with surface blowout preventer (BOP) stacks total just over 100, while only 1 well has been drilled underbalanced in deep water from a floating rig with subsea BOPs.

He also said that more than one third of the world's known hydrocarbon resources are not economic to drill with conventional drilling tools and technology. In water deeper than 4,000 ft, this threshold may be as high as 70%, he added.

Hannegan said that MPD ". . .is key to several emerging new deepwater technologies—such as several variations of dual-gradient, slim-riser deepwater drilling with a surface BOP—and may be key to a more-effective technology to riserless drilling the top holes when initiating a deep-sea location with a less-expensive (second or third generation) floating rig."

He added that "MPD facilitates nearer-balanced and balanced drilling with essentially the same technology and equipment used to control a well being drilling underbalanced where there is an expected and sometimes coaxed (prompted) influx of hydrocarbons. The intent of MPD is not to achieve a true state of underbalanced, but (it) applies some of the specialized equipment to enable better wellbore pressure management and control."

Hannegan said, "MPD offers significant benefits, as it relates to using underbalanced technology to overcome a litany of challenges facing conventional overbalanced drilling, and one does not have to achieve a true state of underbalance to enjoy most of the potential value."

Microflux control
Helio Santos, Impact Engineering Solutions, discussed microflux control as an approach that combines the best features of underbalanced drilling, standard drilling, and near-balanced drilling. In this approach, the driller keeps fluid influx or loss to a minimum by monitoring continuously predicted and expected mud returns.

He said, "Direct determination of both the pore and fracture pressure curves while drilling allows the well to be drilled to the limit in a safe manner. Casing strings can be reduced, as well as time to combat kicks and mud loss problems."

Santos added, "The method is especially suitable for challenging wells, with narrow margin between the pore and fracture pressure curves, which often leads to risky kick and loss situations."
He said that implementation of the method requires only the addition of a limited amount of equipment and control software.