Multi-mode pumped riser arrangement and methods

Abstract

A riser system in the form of a pumped riser, i.e. a riser having an outlet from the riser at a depth below the surface of a body of water, where the outlet is coupled to a return pump to return fluid from the riser to the surface, and various operational methods to facilitate greater versatility when performing hydrocarbon drilling related operations. A sealing element to seal an annulus of the riser, and a by-pass around the sealing element. Various methods make it possible to switch between open mode and closed mode, and vice versa, monitoring leakage across the sealing element, as well as performing other operations exploiting the advantages of the two different modes.

1 . A method of controlling pressure in a riser extending from a bottom of a body of water, the method comprising:
 providing a sealing element at a sealing position in the riser;   providing a first return outlet from the riser to a return pump below the sealing position;   providing a second return outlet from the riser between the first outlet and the sealing position;   pumping drilling fluid downward into a drill string extending along the riser and returning the drilling fluid upward through an annulus formed by the drill string and the riser;   selectively opening or closing the sealing element, or a sealing element bypass, to manage pressure in the riser;   operating the return pump to maintain a fluid level in the riser above the first return outlet; and   allowing fluid to flow out of the second return outlet when the fluid level in the riser reaches the level of the second return outlet.   
     
     
         2 . The method according to  claim 1 , wherein the sealing element is a rotary sealing device (RSD). 
     
     
         3 . The method according to  claim 1 , further comprising monitoring the pressure below the sealing element using a pressure sensor. 
     
     
         4 . The method according to  claim 1 , wherein the return pump is operated to reduce the pressure below the sealing element. 
     
     
         5 . The method according to  claim 1 , further comprising using a choke to add pressure to the return line. 
     
     
         6 . The method according to  claim 1 , wherein the fluid level in the riser is maintained below a slip joint. 
     
     
         7 . The method according to  claim 1 , further comprising using a level sensor to monitor the fluid level above the sealing element. 
     
     
         8 . The method according to  claim 1 , wherein the sealing element is selectively opened or closed to switch between open and closed modes. 
     
     
         9 . The method according to  claim 1 , further comprising using a by-pass line to allow fluid flow around the sealing element. 
     
     
         10 . The method according to  claim 1 , wherein the return pump is isolated by closing isolation valves. 
     
     
         11 . The method of  claim 1 , wherein a pump by-pass line is opened to allow fluid to bypass the return pump. 
     
     
         12 . The method according to  claim 1 , further comprising using a branch line to connect the second return outlet to a return line. 
     
     
         13 . The method according to  claim 1 , wherein the sealing element is adjusted to control leakage rate across it. 
     
     
         14 . The method according to  claim 1 , further comprising using a fill line to adjust the fluid level above the sealing element. 
     
     
         15 . The method according to  claim 1 , wherein the return pump is operated to control a pressure differential across the sealing element. 
     
     
         16 . The method according to  claim 1 , further comprising using a pressure sensor to monitor the pressure in the riser above the sealing element. 
     
     
         17 . The method according to  claim 1 , wherein the sealing element is a non-rotating annular seal. 
     
     
         18 . The method according to  claim 1 , further comprising using a flow meter to monitor the flow rate through the return pump. 
     
     
         19 . The method according to  claim 1 , wherein the return pump is operated to maintain a fluid level at a predetermined height above the first return outlet. 
     
     
         20 . The method according to  claim 1 , further comprising using a pressure sensor to monitor the pressure in the return line.