US 12,247,478 B2
Management of subsea wellhead stresses
Rune Woie, Tananger (NO); and Harald Nevoey, Tananger (NO)
Assigned to CONOCOPHILLIPS COMPANY, Houston, TX (US)
Filed by CONOCOPHILLIPS COMPANY, Houston, TX (US)
Filed on Mar. 11, 2021, as Appl. No. 17/198,819.
Claims priority of provisional application 62/988,165, filed on Mar. 11, 2020.
Prior Publication US 2021/0285317 A1, Sep. 16, 2021
Int. Cl. E21B 47/007 (2012.01); E21B 33/035 (2006.01); E21B 47/12 (2012.01); G01B 7/16 (2006.01); G01L 1/00 (2006.01)
CPC E21B 47/007 (2020.05) [E21B 33/035 (2013.01); E21B 47/12 (2013.01); E21B 2200/20 (2020.05); G01B 7/16 (2013.01); G01L 1/00 (2013.01)] 16 Claims
OG exemplary drawing
 
1. A computer implemented method for determining accumulated fatigue in subsea wellhead assembly installed in a subsea template while drilling with a mobile drilling unit and marine riser connected to the wellhead assembly, the method comprising:
providing a subsea template having at least two template slots;
providing a subsea wellhead assembly comprising a wellhead and associated tubing, the associated tubing including a conductor housing mounted to one of said template slots, a conductor mounted to said conductor housing and a surface casing, wherein said conductor housing is of larger diameter than said conductor and wherein said conductor housing is supported in said template slot by means of co-operating shoulder formations on said template slot and said conductor housing, and wherein said conductor is welded to said conductor housing;
mounting between 10 and 20 strain gauges on the conductor at a location immediately below said conductor housing and mounting between 10 and 20 strain gauges on the surface casing at a location immediately below the wellhead, said locations of strain gauges on the conductor and surface casing being locations where normally the highest and most critical loads arise from lateral loads on the riser connected to the wellhead assembly, said strain gauges being evenly spaced around the circumference of the conductor and surface casing respectively, wherein the strain gauges are of a type capable of measuring 1 micro-strain at 10 Hz or better;
by means of said strain gauges, measuring deformation of each of the conductor and surface casing;
gathering strain data from the strain gauges over a period of time;
using the gathered strain data, by means of a suitably programmed computer modelling stresses on the wellhead assembly, determining the number and magnitude of stress cycles of the wellhead assembly over the period of time, and calculating accumulated fatigue damage in the worst direction; and
adjusting operating envelopes for the mobile drilling unit and riser tension to ensure design limits are not exceeded and conducting operations with said adjusted operating envelopes.