Fatigue Monitoring Of Coiled Tubing In Downline Deployments

Abstract

Methods for real-time coiled tubing fatigue monitoring can establish a remaining operational life of a coiled tubing strand. Standard or low-cycle plastic fatigue in bending is measured each time the coiled tubing strand is deployed through a guide arch. Also, smaller, but higher frequency loads, e.g., high cycle loads imparted to the coiled tubing strand due to interaction with an oceanic environment, are also measured. A plurality of weight detectors may be coupled to a support frame below the guide for monitoring the high-cycle loads. The remaining operational life of the coiled tubing strand may be calculated based on both the plastic strains using a low-cycle fatigue analysis and the elastic strains using a high-cycle fatigue analysis. An operator may retire a coiled tubing strand prior to failure based on the calculated remaining operational life.

What is claimed is: 
     
         1 . A method of evaluating a coiled tubing strand, the method comprising:
 deploying the coiled tubing strand from a reel positioned on a surface reference location;   receiving the coiled tubing strand with a guide arch positioned on the surface reference location and conveying the coiled tubing strand below the surface reference location;   measuring one or more characteristic values indicative of a weight of the coiled tubing strand carried by the guide arch with at least one weight detector disposed between the guide arch and the surface reference location, thereby generating one or more weight measurement signals;   receiving the one or more weight measurement signals with a data acquisition system communicably coupled to the at least one weight detector;   processing the one or more weight measurement signals with the data acquisition system to estimate an elastic strain imparted to the coiled tubing strand; and   generating an output signal with the data acquisition system indicative of real-time bending fatigue of the coiled tubing strand based on the elastic strain estimated from the one or more weight measurement signals.   
     
     
         2 . The method according to  claim 1 , wherein measuring the one or more characteristic values further comprises measuring the characteristic values with a plurality of weight detectors disposed at distinct fixed locations with respect to a surface reference location. 
     
     
         3 . The method according to  claim 2 , wherein processing the one or more weight measurement signals further comprises determining a directionality of the elastic strain imparted to the coiled tubing strand with weight measurement signals received from the plurality of weight detectors. 
     
     
         4 . The method according to  claim 1 , further comprising measuring a real-time elastic strain assumed by the coiled tubing strand with one or more bend sensors, thereby generating one or more bend sensor signals. 
     
     
         5 . The method according to  claim 4 , wherein generating the output signal further comprises generating the output signal based on both the one or more weight measurement signals and the elastic strain measured by the one or more bend sensors. 
     
     
         6 . The method according to  claim 1 , wherein the surface reference location comprises a deck of an offshore vessel, and wherein the method further comprises detecting heave and movement of the offshore vessel and allowing for motion effects of the offshore vessel in at least one of the weight measurement signals, an accelerometer signal and a reference sensor signal received with the data acquisition system. 
     
     
         7 . The method according to  claim 6 , wherein the heave and movement of the offshore vessel are detected with the at least one weight detector. 
     
     
         8 . The method according to  claim 1 , further comprising estimating a remaining operational life of the coiled tubing strand and removing the coiled tubing strand from operation if the remaining operational life of the coiled tubing strand is below a predetermined threshold. 
     
     
         9 . A coiled tubing deployment system, comprising:
 a reel positioned on a surface reference location and coiled tubing strand wound on the reel;   a guide arch positioned on the surface reference location to receive the coiled tubing from the reel and to direct the coiled tubing strand into a deployed location;   at least one weight detector positioned between the guide arch and the surface reference location, the at least one weight detector operable to measure one or more characteristic values indicative of a surface weight of the coiled tubing strand and operable to generate one or more weight measurement signals; and   a data acquisition system communicably coupled to the at least one weight detector to receive and process the one or more weight measurement signals to determine an elastic strain imparted to the coiled tubing strand, the data acquisition system further operable to generate an output signal indicative of real-time bending fatigue of the coiled tubing strand based on the elastic strain determined from the one or more weight measurement signals.   
     
     
         10 . The system according to  claim 9 , wherein the at least one weight detector comprises a plurality of weight detectors disposed at distinct fixed locations with respect to the surface reference location. 
     
     
         11 . The system according to  claim 10 , further comprising an injector coupled between the guide arch and surface reference location, wherein the plurality of weight detectors are disposed in array beneath the injector. 
     
     
         12 . The system according to  claim 9 , further comprising at least one bend sensor operable to measure a strain in the coiled tubing strand and to generate a bend sensor signal indicative of the elastic strain imparted to the coiled tubing strand. 
     
     
         13 . The system according of  claim 12 , wherein the data acquisition system is operable to determine a real-time bending fatigue of the coiled tubing strand based on both a plastic strain calculated at least in part based on the geometries of the reel and guide arch and the elastic strain determined by the data acquisition system based on at least one of the at least one weight measurement signal and the strain measured by the at least one bend sensor. 
     
     
         14 . The system according to  claim 9 , wherein the surface reference location comprises the deck of an offshore vessel and wherein the deployed location comprises a body of water on to which the offshore vessel is deployed, and wherein the system further comprises a wellhead disposed within the body of water, and wherein the coiled tubing strand extends directly through the body of water between the wellhead and the offshore vessel without a riser. 
     
     
         15 . A method of evaluating a remaining operational life of a coiled tubing strand, the method comprising:
 deploying the coiled tubing strand from a reel positioned on a surface reference location;   measuring at least one characteristic value indicative of a surface weight of the coiled tubing strand with at least one weight detector;   determining an elastic strain imparted to the coiled tubing strand based on the surface weight of the coiled tubing strand; and   estimating the remaining operational life of the coiled tubing strand based on the elastic strain imparted to the coiled tubing strand.   
     
     
         16 . The method according to  claim 15 , further comprising measuring the at least one characteristic value at a plurality of fixed locations on the surface reference location with the at least one weight detector. 
     
     
         17 . The method according to  claim 16 , further comprising injecting the coiled tubing strand into a body of water with an injector disposed on an offshore vessel, and wherein the plurality of fixed locations are disposed between the injector and a deck of the offshore vessel. 
     
     
         18 . The method according to  claim 15 , further comprising determining a plastic strain imparted to the coiled tubing strand, and wherein estimating the remaining operational life of the coiled tubing strand further comprises estimating the remaining operational life of the coiled tubing strand based on both the plastic strain and the elastic strain imparted to the coiled tubing strand. 
     
     
         19 . The method according to  claim 17 , further comprising measuring an elastic strain imparted to the coiled tubing strand, and wherein estimating the remaining operational life of the coiled tubing strand further comprises estimating the remaining operational life of the coiled tubing strand based on both the elastic strain measured and the elastic strain determined based on the surface weight of the coiled tubing strand. 
     
     
         20 . The method according to  claim 19 , wherein measuring the elastic strain imparted to the coiled tubing strand includes measuring a stain on the coiled tubing strand with at least one bend sensor disposed on a tubing guide extending below a deck of the offshore vessel.