Recent advances in offshore geotechnics for deep water oil and gas developments

Abstract

The paper presents an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water. Typically the seabed in deep water comprises soft, lightly overconsolidated, fine grained sediments, which must support a variety of infrastructure placed on the seabed or anchored to it. A particular challenge is often the mobility of the infrastructure either during installation or during operation, and the consequent disturbance and healing of the seabed soil, leading to changes in seabed topography and strength. Novel aspects of geotechnical engineering for offshore facilities in these conditions are reviewed, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seabed; and submarine slides and their impact on infrastructure. Example results from sophisticated physical and numerical modelling are presented.

On the instability of offshore foundations: theory and mechanism

“…The failure envelope is a boundary to identify whether the foundation is safe under a certain combination of loads. The key advantages of the failure envelope approach over the conventional bearing capacity theory are explicit consideration of the independent loading components and a graphical interpretation of the factor of safety associated with different load paths [6].…”

“…the anchor plate is approximately normal to the mooring line. This process is known as "keying", which usually causes the loss of the embedment depth (typical in the range of 0.5-1.5 fluke width) [6]. As the seabed sediment, e.g.…”

“…Historically, each type of the aforementioned offshore foundations was designed and constructed to endure certain hydrodynamics (waves, currents, tides), potential submarine geo-hazards and soil conditions of the seabed, e.g., soft clays, stiff sands, carbonate sediments and layered soils [6]. It has been well recognized that the more rapidly an industry or engineering technology is developing, the wider would be the gap between engineering practices (represented in design guidelines) and theory advances.…”

A new partition model for the optimization of subsea cluster manifolds based on the new definition of layout cost

“…If the number of well slots is greater, the size and weight of the cluster manifold may become much bigger and heavier. 5,6 With the scarcity of deepwater resources and exorbitant daily rents, it may induce the greater challenges for the installation of subsea cluster manifolds. Hence, subsea cluster manifolds with the less number of well slots are considered generally in engineering, such as four slots, six slots or eight slots.…”

Experimental Study of Installation of Concrete Suction Caisson in Clay

“…Depending on the usage, a suction caisson has also been named as suction anchor, suction pile or bucket foundation. Suction caissons have been successfully employed in recent years in many projects including mooring anchors (Andersen and Jostad, 1999;Andresen et al, 2011;Randolph et al, 2011;Wang et al, 1975), beak water or sea walls (Chu et al, 2012;, offshore platforms (Zhang et al, 2007;Zhang and Ding, 2011) and foundation for wind turbine in deep waters (Byrne et al, 2002;Gavin et al, 2011;Houlsby and Byrne, 2000;Houlsby et al, 2005).…”