Hybrid tensioning of riser string operating with energy storage device

Abstract

An enhanced riser control system may employ electrical tensioners coupled to a drilling riser by wires. The electrical tensioners may provide quick response to a tension controller to handle positioning of the drilling riser. The electrical tensioners of the enhanced riser control system may be combined with hydro-pneumatic tensioners in a riser hybrid tensioning system. A controller within the enhanced riser control system may be configured to distribute tension to electrical tensioners and to control electrical tensioners to adjust the length of the first and second wires. Energy from an electrical tensioner may be transferred to an energy storage system or to power dissipaters for dissipating the energy generated by the electrical tensioner. The energy transferred from an electrical tensioner may be energy that has been generated by the electrical tensioner.

What is claimed is: 
     
         1 . An apparatus, comprising:
 a drilling riser;   a vessel;   a first motion reference unit (MRU) coupled to the drilling riser, configured to measure one or more properties of the drilling riser;   a second MRU coupled to the vessel, configured to measure one or more properties of the vessel;   a plurality of wires coupled to the drilling riser;   a first and second electrical tensioner coupled to the drilling riser via a first and a second wire of the plurality of wires; and   a controller configured to perform steps comprising:
 distributing tension to the first and second electrical tensioners; 
 receiving the one or more properties of the drilling riser from the first MRU; 
 receiving the one or more properties of the vessel from the second MRU; 
 determining a tension based, at least in part, on the one or more properties of the drilling riser and the one or more properties of the vessel; and 
 controlling the first and second electrical tensioners to adjust a tension of the first and second wires based, at least in part, on the determined tension. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the controller comprises:
 a first proportional-integral-derivative (PID) controller; and   a second PID controller,   wherein determining the tension based, at least in part, on the one or more properties of the drilling riser and the one or more properties of the vessel comprises performing wire-line displacement control by the first PID controller and performing wire-line velocity control by the second PID controller.   
     
     
         3 . The apparatus of  claim 2 , wherein an output of the first PID controller is provided as an input to the second PID controller for performing wire-line velocity control. 
     
     
         4 . The apparatus of  claim 1 , wherein the one or more properties of the drilling riser comprise a vertical movement of the drilling riser, wherein the one or more properties of the vessel comprise a vertical movement of the vessel, wherein the controller is further configured to perform steps comprising:
 determining a difference between the vertical movement of the drilling riser and the vertical movement of the vessel;   detecting the difference exceeds a predetermined threshold; and   entering an anti-recoil mode when a difference exceeding the predetermined threshold is detected.   
     
     
         5 . The apparatus of  claim 1 , wherein the one or more properties of the riser comprise a horizontal position of the riser, wherein the one or more properties of the vessel comprise a horizontal position of the vessel, wherein the step of determining comprises determining the tension based, at least in part, on a comparison of the horizontal position of the riser with the horizontal position of the vessel, and wherein the step of controlling comprises controlling the first and second electrical tensioners, in a vortex-inducted vibration (VIV) mode, to adjust the tension of the first and second wires, based, at least in part, on the determined tension to reduce VIV of the riser. 
     
     
         6 . The apparatus of  claim 4 , wherein controlling the first and second electrical tensioners in the VIV mode comprises controlling the first and second electrical tensioners to stabilize a top of the drilling riser within a predetermined range of an original position of the top of the drilling riser. 
     
     
         7 . The apparatus of  claim 4 , wherein controlling the first and second electrical tensioners in the VIV mode comprises controlling the first and second electrical tensioners to apply dynamic tensions to the first and second wires in one or more vertical directions to prevent a VIV frequency of the drilling riser from entering a natural frequency range of the drilling riser. 
     
     
         8 . The apparatus of  claim 1 , wherein the controller is further configured to perform steps comprising:
 determining a relative position of a top of the drilling riser to a seabed based, at least in part, on the received one or more properties of the drilling riser;   determining a relative position of the vessel to the seabed based, at least in part, on the received one or more properties of the vessel,   wherein the step of determining a tension comprises determining a tension based, at least in part, on the determined relative position of the top of the drilling riser and the determined relative position of the vessel.   
     
     
         9 . The apparatus of  claim 1 , further comprising:
 a hydro-pneumatic tensioner coupled to the drilling riser via a third wire of the plurality of wires,   wherein the controller is further configured to distribute tension to the hydro-pneumatic tensioner, and   wherein the controller is further configured to control the hydro-pneumatic tensioner to adjust a tension of the third wire based, at least in part, on the determined tension.   
     
     
         10 . The apparatus of  claim 1 , wherein the controller is further configured to perform steps comprising:
 detecting second-order transient shockwaves in the received one or more properties of the drilling riser indicating a disconnect between the drilling riser and a blow-out preventer (BOP),   wherein the step of determining comprises determining the tension based, at least in part, on the detected second-order transient shockwaves, and   wherein the step of controlling comprises controlling the first and second electrical tensioners to adjust the tension of the first and second wires based, at least in part on the determined tension to counter riser recoil resulting from the disconnect between the drilling riser and the BOP.   
     
     
         11 . A method, comprising:
 receiving one or more properties of a drilling riser from a first motion reference unit (MRU) coupled to the drilling riser;   receiving one or more properties of a vessel from a second MRU coupled to the vessel;   determining tensions for each of a plurality of electrical tensioners based, at least in part, on the received one or more properties of the drilling riser and the received one or more properties of the vessel;   controlling the plurality of electrical tensioners based, at least in part, on the determined tensions.   
     
     
         12 . The method of  claim 11 , wherein the step of determining tensions comprises:
 performing wire-line displacement control by a first PID controller; and   performing wire-line velocity control by a second PID controller.   
     
     
         13 . The method of  claim 11 , wherein the step of determining tensions further comprises providing an output of the first PID controller as an input to the second PID controller for performing wire-line velocity control. 
     
     
         14 . The method of  claim 12 , wherein the one or more properties of the drilling riser comprise a vertical movement of the drilling riser, wherein the one or more properties of the vessel comprise a vertical movement of the vessel, the method further comprising:
 determining a difference between the vertical movement of the drilling riser and the vertical movement of the vessel;   detecting the difference exceeds a predetermined threshold; and   entering a controller of the plurality of electrical tensioners into an anti-recoil mode when a difference exceeding the predetermined threshold is detected.   
     
     
         15 . The method of  claim 12 , wherein the one or more properties of the riser comprise a horizontal position of the riser, wherein the one or more properties of the vessel comprise a horizontal position of the vessel, wherein the step of determining comprises determining the tension based, at least in part, on a comparison of the horizontal position of the riser with the horizontal position of the vessel, and wherein the step of controlling comprises controlling the plurality of electrical tensioners, in a vortex-inducted vibration (VIV) mode, to adjust the tension of the first and second wires, based, at least in part, on the determined tension to reduce VIV of the riser. 
     
     
         16 . The method of  claim 14 , wherein controlling the plurality of electrical tensioners in the VIV mode comprises controlling the plurality of electrical tensioners to stabilize a top of the drilling riser within a predetermined range of an original position of the riser. 
     
     
         17 . The method of  claim 14 , wherein controlling the plurality of electrical tensioners in the VIV mode comprises controlling the plurality electrical tensioners to apply dynamic tensions to the first and second wires in one or more vertical directions to prevent a VIV frequency of the riser from entering a natural frequency range of the riser. 
     
     
         18 . The method of  claim 12 , wherein the step of determining comprises determining a tension for a plurality of electrical tensioners based, at least in part, on the received one or more properties of the drilling riser and the received one or more properties of the vessel. 
     
     
         19 . The method of  claim 17 , further comprising:
 determining a relative position of a top of the drilling riser to a seabed based, at least in part, on the received one or more properties of the drilling riser;   determining a relative position of the vessel to the seabed based, at least in part, on the received one or more properties of the vessel,   wherein the step of determining the tension comprises determining the tension based, at least in part, on the determined relative position of the top of the drilling riser and the determined relative position of the vessel.   
     
     
         20 . The method of  claim 11 , further comprising:
 distributing tension to a hydro-pneumatic tensioner; and   controlling the hydro-pneumatic tensioner based, at least in part, on the determined tension.   
     
     
         21 . The method of  claim 11 , further comprising:
 detecting second-order transient shockwaves in the received one or more properties of the drilling riser indicating a disconnect between the drilling riser and a blow-out preventer (BOP),   wherein the step of determining comprises determining the tension based, at least in part, on the detected second-order transient shockwaves, and   wherein the step of controlling comprises controlling the plurality of electrical tensioners based, at least in part, on the determined tension to counter riser recoil resulting from the disconnect between the drilling riser and the blow-out preventer (BOP).