Investigation on influence of temperature and pressure on fatigue damage of subsea wellhead in deepwater drilling

Abstract

The fatigue damage of subsea wellhead has become one of the important issues in deepwater oil and gas industry. Current research on the fatigue damage evaluation of the subsea wellhead is based on the recommended practices (DNVGL-RP-0142, 2015; DNVGL-RP-E104, 2018), where the influence of the temperature and pressure is ignored. This paper presents the fatigue damage of the subsea wellhead under the condition that the temperature and pressure is considered. Firstly, the analysis model of the temperature and pressure is established. Then, the influence of the temperature and pressure are considered in the local response analysis based on the recommended practices. In addition, the interaction between the conductor and soil is evaluated by the Goodman element model and the P-y model in the local response analysis. Finally, the accumulated fatigue damage of the subsea wellhead is obtained according to the S–N curve recommended by DNVGL (DNVGL-RP-C203 (2016)). On this basis, the influence of the temperature, pressure, top of cement (TOC), contact surface model on the fatigue damage of the subsea wellhead is discussed in detail. Analysis results show that both the temperature and pressure have effect on the fatigue damage of the subsea wellhead. The ranking of the influence strength is temperature and pressure (TP), pressure (P) and temperature(T). The fatigue damage of the subsea wellhead would be underestimated if the temperature or pressure is neglected. This study has guiding significance for fatigue damage evaluation of the subsea wellhead and safe operation of deepwater drilling.