Minimum Structure for Well Appraisal in Marginal Fields at 35m Water Depth without Jacket & Mudline Suspension System

ABSTRACT This paper proposes a minimum structure for drilling two appraisal wells. Conductors will be driven into seabed by a crane vessel or drilling-rig crane through a pre-installed lightweight guide-frame placed on seabed. After driving the conductors to required depth, the frame is raised and joined to the conductors at appropriate elevation by bolted and grouted connections. Six tie members connected between the frame and seabed by specially-designed small mat foundations will ensure stability of the structure against environmental loads. A small deck will be installed on the top of conductors to provide space for essential equipment required for prolonged well testing after departure of drilling rig. The platform will be accessed by small boats through a boat landing and ladder. In case of positive drilling outcome, a riser and flexible pipeline will be added to connect with the nearest subsea tie-in point. A detailed structural design of the minimum facility is performed to withstand omnidirectional environmental loads due to 10.0m high wave along with associated wind and current loads. Susceptibility of the structure against dynamic effect of wave loads is also investigated. Demonstration of structural adequacy against wave-induced fatigue loads and reserve strength against extreme environmental loads show the robustness of the minimum structure to perform against design environmental loads.

An Efficient Solution to Mudmat Design for Jacket Structures in Soft Seabed Soil

Conventional jacket structures are normally equipped with mat foundations for support during offshore installation when the jacket sits on the seabed before piling. An efficient mudmat design is required to support the jacket since the weight of the mudmat contributes about 20% to the overall structural weight. It is challenging to analyze and to find an exact solution when calculating the bearing capacity of the soil beneath the mudmat because the seabed conditions vary from hard to very soft soil: this is especially true for a relatively slender jacket on very soft soil. The paper presents an efficient method for conducting such design.

Finite element analyses of a buckling-restrained pile

<p>In existing building renovation projects, the strength of the structure is often limited by the capacity of existing foundations. Foundation strengthening typically consists of expanding existing footings and/or adding piles to supplement load-carrying capacity. These traditional methods are generally not feasible for the retrofit of mat foundations where increasing the mat footprint is unlikely to reduce bearing pressure considerably and adding piles outside the mat will change the distribution of internal stresses and may affect the long-term differential settlement behaviour of the structure.</p><p>This paper presents finite element analyses that were performed as part of the development of a new approach to retrofitting mat foundations which consists of enlarging the footprint of the existing mat and adding piles that include an innovative axial capacity-limiting mechanism. The maximum resistance provided by these piles to the existing foundation can be tuned to not exceed the maximum connection capacity that can be achieved at the interface between the existing mat and the new mat extension. The proposed design is unique in that the pile axial load is limited even under significant potential settlements experienced by the rest of the building foundation.</p>

Experimental Study on the Distribution of Wave-Induced Excess Pore Pressure in a Sandy Seabed around a Mat Foundation

Mat foundations are widely used in jack-up offshore platforms to support and transfer loads. Regarding mat foundations working on the seabed, the excess wave-induced pore pressure is critical to seabed stability, which may finally cause structural failure. Therefore, it is important to investigate the distribution of the excess pore pressure in the seabed around the mat foundation. In this study, experiments were performed to study the excess pore pressure distribution around a mat foundation in scale considering the true load state by recording wave profiles and pore pressures inside a sandy seabed. To guarantee the reliability of experiments, a numerical study was conducted and compared with the experimental results. Experimental results indicate that with the existence of the mat foundation, the excess pore pressure is higher at the region, the range of which is the width of the model mat (Wm) before the structure. The maximum pore pressure appears at 0.55 Wm in front of the center of the mat foundation. In addition, the current significantly increases the range of high pore pressure area and the amplitude of the excess pore pressure. As the mat orientation changes, the position of the maximum pore pressure changes from the front to the edge of the mat.

Control of Early-Age Cracking in Watertight Concrete Structures

Considering the importance of leaking cracks in terms of serviceability and durability of watertight concrete structures, emphasis is placed on thermal movements and their effect on foundation slabs and walls. Both members are usually restrained to some degree externally and/or internally. The results indicate that restrained thermal stresses are the primary cause of early-age cracks in concrete members. This paper offers a discussion of mitigation strategies to prevent the formation and propagation of early-age separating cracks. A FEM-based analysis was used to determine the development of stresses in walls on mat foundations in relation to the crack risk assessment.