Fatigue Strength Evaluation of Drill Pipe for Challenging Scientific Drilling Operations

During drilling operations, the scientific drilling vessel Chikyu encounters vortex-induced vibration (VIV) of the riser during riser drilling as well as that of the drill pipe during riserless drilling. The characteristics of the VIV of the drill pipe will differ from those of the riser because the drill pipe rotates during operations. Therefore, investigating the characteristics of the VIV during drill pipe rotation is important. In this paper, the results of model experiments that show the characteristics of the VIV of a rotating drill pipe and drill pipe whirl are described. The authors conducted model experiments on the VIV response of a rotating cylinder in a water tank to observe the motion of the rotating cylinder. The results confirmed that rotating affects the characteristics of the VIV. When the rotating frequency of the drill pipe was low, the VIV resonated with the rotation; as the rotating frequency increased, the frequency of the VIV decreased. In addition, a self-excited whirl motion was also observed during the experiments. This “drill pipe whirl,” which rotated in the direction opposite to the rotation of the drill pipe at a low frequency, was larger in amplitude than the VIV. The results demonstrate that rotation of the drill pipe affects the characteristics of the VIV and generates the whirl motion.

Download Full-text

Fatigue Evaluation of Drill Pipes for Scientific Drilling Program by Applying Non-Stop Driller Concept

Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology ◽

10.1115/omae2019-95896 ◽

2019 ◽

Cited By ~ 1

Author(s):

Tomoya Inoue ◽

Masahiko Fujikubo ◽

Kenji Nakano ◽

Noriaki Sakurai

Keyword(s):

Time Series ◽

Fatigue Strength ◽

Nankai Trough ◽

Drilling Fluid ◽

Drill Pipe ◽

Ship Motions ◽

Bending Stress ◽

Deep Drilling ◽

Scientific Drilling ◽

Drilling Equipment

Abstract The scientific drilling vessel Chikyu is performing Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a challenging deep drilling activity, for scientific purpose. We faced difficulty to drill deep during past NanTroSEIZE operations due to unstable sediments and insufficient cutting removal. Non-Stop Driller concept is, therefore, applied for the operation of NanTroSEIZE scheduled to start Oct. 2018 to enable continuous circulation of drilling fluid circulation. The Non-Stop Driller concept requires an additional, specially-designed sub called an “NSD sub” with a ball valve for drilling fluid inlet. Generally, the fatigue strength of a drill pipe is a critical factor governing the performance of challenging deep drilling. This study, therefore, focused on the fatigue failure of the NSD sub due to the bending stress caused by interference with risers including flex joints, ship structure, or drilling equipment resulting from ship motions. The bending stress leads to cyclic stress caused by rotation of the drill pipe. This is especially the case at the Nankai Trough where ocean currents are very strong reaching or sometimes exceeding 4 knots, a high bending stress is assumed to be exerted on the NSD sub. Full-scale fatigue tests of the NSD sub were first conducted to acquire the actual fatigue curve. Further, the bending stress distribution of a drill pipe, which refers to the locus of the bending stress during the drilling operation, was analyzed by considering interference of the drill string with the structure, drilling equipment, and risers that are deformed by the ocean current. Time-series ship motions is prepared using the response amplitude operators of the Chikyu for the sea states at Nankai Trough area, and then time-series stress response is obtained by considering the operational conditions such as rate of penetration and rotational velocity of drill pipe. The numbers of occurrence of each stress amplitude can be counted from the time-series stress response. Consequently, the cumulative damage ratio is calculated for evaluating the fatigue of the NSD sub. The results confirmed that the cumulative fatigue is within a safe range. This study focused on the evaluation of the fatigue strength of the specially designed NSD sub for the challenging scientific drilling operation at Nankai Trough, a harsh environment because of the presence of strong ocean currents. This paper presents the overview of NanTroSEIZE including the Non-Stop Driller concept, and the results of fatigue evaluations.

Download Full-text

Drill String Strength Evaluation for Deep Earthquake Zone Drilling

Volume 1: Offshore Technology ◽

10.1115/omae2012-83965 ◽

2012 ◽

Cited By ~ 5

Author(s):

Tomoya Inoue ◽

Masanori Kyo ◽

Koji Sakura ◽

Toshihiko Fukui

Keyword(s):

Nankai Trough ◽

Drill Pipe ◽

High Strength ◽

Seismogenic Zone ◽

Deep Drilling ◽

Deep Earthquake ◽

Strength Evaluation ◽

Scientific Drilling ◽

Drill Pipes ◽

Earthquake Zone

The scientific drilling vessel Chikyu was designed to have the deep drilling capability to reach the deep earthquake zone. To realize such deep drilling, a drill pipe with higher than ever strength and reliability is of necessity. A strength evaluation of such high strength drill pipe is also necessary. Around Japan, the earthquake zones are widely located under the seabed in deep water. For example, the Nankai Trough located beneath the ocean off the southwest coast of Japan is one of the most active earthquake zones where large-scale earthquakes have occurred repeatedly throughout history. Thus, the Chikyu has started the first scientific drilling at the Nankai Trough as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). NanTroSEIZE targets the megasplay fault zone at 3500 m below the seafloor and finally 6000m deep drilling into the seismogenic zone and across the plate interface into the subducting crust at water depths of around 2500m. In addition, a huge earthquake zone is expected to be located about 1000m below the seafloor at water depths of around 7000m. For this drilling task, the riserless drilling technique should be applied. To realize such deep drilling with both riser and riserless techniques, a S150 drill pipe was developed during the construction phase and has been used in the past scientific drillings of the Chikyu. For deeper drillings in the future and drilling operations in harsh environments, we are developing superior high strength drill pipes, S155 and S160, possessing high reliability including corrosion resistance to achieve high toughness and reduction of stress concentration. An evaluation of the maximum possible stress was conducted. In the maximum strength evaluation, we considered dynamic stress and bending stress due to the current and the vessel inclination. This paper describes the development of superior high strength drill pipes and the strength evaluation of such drill pipes for deep earthquake zone drilling.

Download Full-text