Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Survivability Study of Marine Drilling Conductor Considering Soil Disturbance
Minghe Zhang1, Jin Yang1, Yuanming Wang1, Yisu Zhou2, Lei Li1, Yuxiang Yang1
1. College of Safety and Ocean Engineering, China University of Petroleum (Beijing)
2. College of Petroleum Engineering, China University of Petroleum (Beijing)
Beijing, China

is regarded as a hinge and the connection between conductor and soil isregarded as fixed support. The disturbance of soil below the mudlinecaused by marine environmental loads is ignored, which will lead to theentry of seawater into the gap between drilling conductor and soil andreduce the vertical bearing capacity near the mudline.

ABSTRACT
Large lateral displacement and bending moment of marine drilling
conductor are produced under loads such as wave, current, and ice,
which seriously threaten the safety of offshore operations and wellhead
stability. Due to soil disturbance, the bearing capacity of the drilling
conductor under the mudline is reduced, and the installation depth may
not meet the requirements of wellhead bearing capacity. In this paper, astatic analysis model for the survivability of drilling conductor
considering soil disturbance is proposed, and an ideal elastoplastic p-y
curve model is used to define the properties of soil layers under themudline and guide the installation depth and bearing capacity design ofmarine drilling conductor.

Except for the lateral loads, drilling conductors are exposed to axial
compression loads, which will increase the depth of the plastic hinge
and the lateral displacement near the mudline; consequently, thedrilling conductor will show a greater response to lateral loads.
Therefore, the offshore oil and gas drilling conductor is different fromthe pile under pure lateral loads (Wang, LZ et al. 2020) and the drillingriser under tensile axial loads (Mao, LJ et al. 2019; Tian, DQ et al.
2020).
The complicated and changeable environment like wind, wave, current,
and ice must be considered during offshore drilling and the extended
testing for marginal oilfields. (Ramesh, R et al. 2017). Therefore, thelong pile failure mechanism is more likely to occur in the offshore
drilling conductor. A more than 100 tons of wellhead load is provided
by the vertical friction force between drilling conductor and soil.
Unlike the deep-water surface conductor, there are tens of meters ofdrilling conductors between wellhead and mudline, which leads tomore sensitivity to the environmental load, especially for the ice(Baerheim, M et al. 2008).

KEY WORDS: Marine drilling conductor; Ice load; Survivability; py curve; Soil disturbance.

INTRODUCTION
Vertical pile foundations are widely used in offshore oil and gas
structures such as jack-ups, surface conductors in deep-water, andmarine drilling conductors in the neritic region (Jeanjean, P. 2002;
Akers, T.J., 2008). For a typical drilling conductor, the upper portion issurrounded by water and air; therefore, drilling conductors areconsidered as partially embedded piles structures. The overall length ofdrilling conductors can be divided into two segments: unsupported
length defined as the length of the conductors above the mudline, andembedment length defined as the length of the conductors below themudline.

Based on the above, the survivability of marine drilling conductors
considering soil disturbance should be researched comprehensively,
and the soil disturbance rules of vertical depth and horizontal range
should be summarized to guide the design and installation of marine
drilling conductors.

The offshore drilling conductor is subjected to primarily lateral loads
from the surrounding marine environment, like wave, current, wind,and harsh ice in winter (Carter, JP 1992; El Naggar, H and Novak, M1995). The offshore drilling conductors will undergo great horizontal
displacement under those lateral loads; thus, the drilling conductor may
develop a plastic hinge along its embedment length below the mudline(El Naggar, H 2018). In a traditional mechanical analysis of drilling
conductors, the connection between the wellhead and upper conductor

MECHANICAL MODEL
The typical marine drilling conductor system is depicted in Fig. 1, andthe basic components from top to bottom are jack-up platform,
wellhead, tensioner, drilling conductors, and surrounding soil undermudline. A marine drilling conductor is a large size pile installed fromthe jack-up to the shallow soil. It is the key structure connecting the629