The deep-sea ground contains a huge amount of energy and mineral resources, for example, oil, gas, and minerals. Various infrastructures such as floating structures, seabed structures, and foundations have been developed to exploit these resources. The seabed structures and foundations can be mainly classified into three types: subsea production structures, offshore pipelines, and anchors. This study reviewed the development, installation, and operation of these infrastructures, including their structures, design, installation, marine environment loads, and applications. On this basis, the research gaps and further research directions were explored through this literature review. First, different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations. Second, the subsea production structures, including subsea manifolds and their foundations, were reviewed and discussed. Third, the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers, were analyzed and reviewed. Finally, the installation and bearing capacity of deep-sea subsea anchors and seabed trench influence on the anchor were reviewed. Through the review, it was found that marine environment conditions are the key inputs for any offshore structure design. The fabrication, installation, and operation of infrastructures should carefully consider the marine loads and geological conditions. Different structures have their own mechanical problems. The fatigue and stability of pipelines mainly depend on the soil-structure interaction. Anchor selection should consider soil types and possible trench formation. These focuses and research gaps can provide a helpful guide on further research, installation, and operation of deep-sea structures and foundations. This paper reviewed the development, installation, and operation of these infrastructures, including their structures, design, installation, marine environment loads, and applications. The research gaps and further research directions are explored through this literature review. First, different floating structures were briefly analyzed and reviewed. Second, the subsea production structures, including subsea manifolds and their foundations, were reviewed and discussed. Third, the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers, were analyzed and reviewed. Finally, the installation and bearing capacity of deep-sea subsea anchors and seabed trench influence on the anchor capacity were reviewed. image center dot Provide a brief introduction about seabed structures and foundations related to deep-sea resource development. center dot Introduce subsea production structures, including subsea manifolds and their foundations (mudmats, suction piles), from a design perspective. center dot Analyze the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers. center dot Introduce the installation and bearing capacity of anchors in deep-sea, and summarize seabed trench influence on anchor capacity.

This paper presents a fully coupled solution in the time-domain, using the finite-differences method to the system of equations that model the dynamic behavior of the riser, blow-out preventer (BOP), and casing strings, when connected for well drilling/completion-the model is suitable to evaluate wellhead fatigue, even when the amplitude of oscillation and accelerations of the BOP are high. Sensibility analysis is used to show the effect of changing the Riser Top Tension to the resulting maximum values of wellhead bending moment and casing stress ranges. For the case where the rig is oscillating around a fixed position and there is no current, using a regular wave, the results show that there are some wave periods for which an increase in the Riser Top Tension reduces the maximum wellhead bending moment and the max casing stress range, therefore increasing fatigue life of the casing and wellhead. The effects of varying the weight of the BOP and soil parameters and the effect of the phase difference between the wave and first-order vessel motion are analyzed. The proposed solution can also be used to perform riser and casing analysis during drift-off/drive-off.

Prediction of the fatigue life of steel catenary risers (SCR) in the touchdown zone is a challenging engineering design aspect of these popular elements. It is publically accepted that the gradual trench formation underneath the SCR due to cyclic oscillations may affect the fatigue life of the riser. However, due to the complex nature of the several mechanisms involving three different domains of the riser, seabed soil, and seawater, there is still no strong agreement on the beneficial or detrimental effects of the trench on the riser fatigue. Seabed soil stiffness and trench geometry play crucial roles in the accumulation of fatigue damage in the touchdown zone. There are several studies about the effect of seabed soil stiffness on fatigue. However, recent studies have proven the significance of trench geometry and identified the touchdown point oscillation amplitude as a key factor. In this study, a boundary layer solution was adapted to obtain the dynamic curvature oscillation of the riser in the touchdown zone on different areas of seabed trenches with a range of seabed stiffness. The proposed analytical model was validated against advanced finite element analysis using a commercial software. A range of seabed stiffness was examined, and the corresponding fatigue responses were compared. It was observed that in the elastic seabed, the effect of soil stiffness is attributed to the curvature oscillation amplitude and to the minimum local dynamic curvature that SCR can take in the touchdown zone. The proposed analytical model was found to be a simple and reliable tool for riser configuration studies with trench effects, particularly at the early stages of riser engineering design practice.