Method and device for pressure regulation of a well

Abstract

A method for the pressure regulation of a well ( 1 ) extending into a well formation ( 2 ) and being drilled from a drilling vessel at sea, the well ( 1 ) including a blowout preventer ( 10 ) on the seabed ( 12 ) and a riser ( 14 ) extending from the blowout preventer ( 10 ) up to the vessel, and the return path ( 8, 14, 20 ) of a drilling fluid ( 24 ) being provided with a rotatable surface seal ( 22 ) sealingly surrounding a drill string ( 4 ), the rotatable surface seal ( 22 ) being arranged to seal against a pressure difference between the surroundings and the return path ( 8, 14, 20 ), and there being arranged, at the rotating surface seal ( 22 ), a closable drilling-fluid outlet ( 28 ), the method including: arranging a pump inlet ( 32 ) from the return path ( 8, 14, 20 ) under water; connecting a pump ( 30 ) to the return path ( 8, 14, 20 ), the pump ( 30 ) being connected to a pressure pipe ( 34 ) discharging on the vessel; monitoring the drilling-fluid pressure; and controlling the pumping rate through the pump ( 30 ) to maintain a substantially constant drilling-fluid pressure at the well formation ( 2 ), both when drilling fluid ( 24 ) is flowing and when it has been stopped.

1 . A method for the pressure regulation of a well ( 1 ) extending into a well formation ( 2 ) and being drilled from a drilling vessel at sea, the well ( 1 ) including a blowout preventer ( 10 ) on the seabed ( 12 ) and a riser ( 14 ) extending from the blowout preventer ( 10 ) up to the vessel, and the return path ( 8 ,  14 ,  20 ) of a drilling fluid ( 24 ) being provided with a rotatable surface seal ( 22 ) sealingly surrounding a drill string ( 4 ), the rotatable surface seal ( 22 ) being arranged to seal against a pressure difference between the surroundings and the return path ( 8 ,  14 ,  20 ), and there being arranged, at the rotating surface seal ( 22 ), a closable drilling-fluid outlet ( 28 ), characterized in that the method includes:
 arranging a pump inlet ( 32 ) from the return path ( 8 ,  14 ,  20 ) under water;   connecting a pump ( 30 ) to the return path ( 8 ,  14 ,  20 ), the pump ( 30 ) being connected to a pressure pipe ( 34 ) discharging on the vessel;   monitoring the drilling-fluid pressure; and   controlling the pumping rate through the pump ( 30 ) to maintain a substantially constant drilling-fluid pressure at the well formation ( 2 ) both when drilling fluid ( 24 ) is flowing and when it has been stopped.   
     
     
         2 . The method in accordance with  claim 1 , characterized in that the closable drilling-fluid outlet ( 28 ) is opened. 
     
     
         3 . The method in accordance with  claim 1 , characterized in that the closable drilling-fluid outlet ( 28 ) is closed, whereby overpressure or underpressure may be established in the return path ( 8 ,  14 ,  20 ) relative to the surroundings. 
     
     
         4 . The method in accordance with  claim 1 , characterized in that at least a portion of the return path ( 8 ,  14 ,  20 ) that is above the pump inlet ( 32 ) is filled with a second fluid ( 38 ) which has a different specific weight in relation to the drilling fluid ( 24 ). 
     
     
         5 . The method in accordance with  claim 4 , characterized in that the pumping rate through the pump ( 30 ) is controlled to keep an interface ( 40 ) between the drilling fluid ( 24 ) and the second fluid ( 38 ) at an approximately constant height level. 
     
     
         6 . A pressure-regulation device for a well ( 1 ) extending into a well formation ( 2 ) and being drilled from a vessel at sea, the well ( 1 ) including a blowout preventer ( 10 ) on the seabed ( 12 ) and a riser ( 14 ) extending from the blowout preventer ( 10 ) up to the vessel, and the return path ( 8 ,  14 ,  20 ) of the drilling fluid being provided with a rotating surface seal ( 22 ) sealingly surrounding a drill string ( 4 ), the rotating surface seal ( 22 ) being arranged to seal against a pressure difference between the surroundings and the return path ( 8 ,  14 ,  20 ), and there being arranged a closable drilling-fluid outlet ( 28 ) at the rotating surface seal ( 22 ), characterized in that a pump inlet ( 32 ) from the return path ( 8 ,  14 ,  20 ) is arranged under water and a pump is connected to the return path ( 8 ,  14 ,  20 ), the pump ( 30 ) being connected to a pressure pipe ( 34 ) which discharges on the vessel, the pumping rate being adjustable to maintain a substantially constant drilling-fluid pressure at the well formation ( 2 ), both when drilling fluid ( 24 ) is flowing and when it has been stopped. 
     
     
         7 . The pressure-regulation device in accordance with  claim 6 , characterized in that at least a portion of the return pipe ( 8 ,  14 ,  20 ) that is above the pump inlet ( 32 ) is filled with a second fluid ( 38 ) which has a different specific weight in relation to the drilling fluid ( 24 ). 
     
     
         8 . The pressure-regulation device in accordance with  claim 7 , characterized in that the pumping rate is controllable to keep an interface ( 40 ) between the drilling fluid ( 24 ) and the second fluid ( 38 ) at an approximately constant height level.