Mid-riser pump system provides advantages of MPD while keeping a statically balanced wellbore. As offshore drilling progresses into deeper water and highly fractured and depleted formations, the drilling window between pore and fracture margins continues to become narrower and less predictable. Under such conditions, maintaining a wellbore pressure that is high enough to prevent an influx and maintain well-bore stability while remaining low enough to prevent lost circulation, differential sticking and permit kick tolerance can be a significant challenge.
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