A PDE MODEL FOR ESTIMATING THE LIFE TIME OF A RISER

摘要

Subsea intervention operations may expose wellheads to very high structural loads. Traditionally, structural fatigue was not regarded as a challenge for wellheads, and design codes did not include verification with respect to structural loads. However, development in mathematical modeling and numerical techniques as well as monitoring systems have revealed that semi-submersible rigs with marine riser systems and BOP (Blowout Preventer) can cause quite significant loads on permanently installed equipment. Being able to describe a risers movement under the action of external forces is important in order to calculate the effects on the wellhead. This may be used to predict the expected remaining lifetime of the system. In this article, the existing literature on numerical modeling of a riser system is discussed. Different mathematical models of a riser system were approximated numerically by a finite element method. The models are compared and their correctness is discussed. The error bounds for the finite element solutions are derived. Boundary conditions are further developed to improve realism and ensure compliance with existing standards and guidelines. The sensitivity of such changes are assessed and discussed. A discussion cm how to use the numerical simulated data to train a machine learning algorithm to estimate well loading is presented and key parameters affecting the cyclic wellhead loads are identified.