National Oilwell Varco Norway As

Geir K Skaugen

Åge Kyllingstad

Karl Erik Thoresen

A method for drilling a borehole includes selecting a lower pressure limit and an upper pressure limit for a drilling fluid at a drilling location in the borehole. In addition, the method includes activating a pump to circulate the drilling fluid down a drill string and up an annulus disposed about the drill string. Further, the method includes operating the pump to maintain the drilling fluid at the drilling location at a pressure between the upper and the lower pressure limits. Still further, the method includes deactivating the pump to stop circulating the drilling fluid up the annulus. The method also includes sealing the drilling fluid in the annulus at a selected time after deactivating the pump and maintaining the pressure of the drilling fluid at the drilling location between the lower and the upper pressure limits.

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Stavanger, Norway

Geir K Skaugen