Axial-lateral-torsional coupling nonlinear vibration of riserless drill-string considering both seawater and stratum parts

Riserless drilling has the obvious advantages of small platform load bearing and short well construction period because it discards the bulky conventional riser. However, because the drill-string is directly exposed to seawater, its dynamic behavior is extremely complex, which has an important impac...
Ausführliche Beschreibung

Riserless drilling has the obvious advantages of small platform load bearing and short well construction period because it discards the bulky conventional riser. However, because the drill-string is directly exposed to seawater, its dynamic behavior is extremely complex, which has an important impact on the safety and efficiency of drilling operations. Using the energy method and microelement method, an axial-lateral-torsional (ALT) coupling nonlinear vibration model of deepwater riserless drill-string considering both seawater and stratum sections is established. The model takes into account the platform heaving and slow drift motion, wind and ocean current, tidal current, wave load, wellbore contact, bit-rock interaction and seawater formation interaction. A bi-directional coupling scheme is proposed to obtain a good model solving efficiency. Using torsional vibration model results and field test data, the effectiveness of the model is presented in detail from the qualitative and quantitative aspects. The developed model and calculation program are used to analyze the dynamic behavior of a typical deep-water riserless drillings. The work in this paper can provide an effective analysis method and theoretical guidance for riserless drill-string design. Ausführliche Beschreibung