Search

In order to improve the vertical and lateral load bearing capacity of the drilling conductor, composite design of bucket foundation and drilling conductor was studied. The bearing behavior of composite conductor subjected to lateral and longitudinal external loads was investigated. In this paper, the finite element analysis was conducted by two methods, load loading and displacement loading. The bearing capacity and influencing factors of composite conductor were studied with consideration of contact surface models of composite structures and surrounding soil. The results show that the vertical bearing capacity increase with the depth increasement of the bucket foundation under the combined bearing effect of the bucket foundation and the conductor. Meanwhile, the depth of the embedded point of the composite conductor increases with the bending moment when subjected to lateral loads. When the bending moment is constant on the structure top, the lateral displacement of the structure increases with the increase of the vertical force, and the depth of the embedded point increases with the increase of the vertical force. The results also show that the change of the bending moment at the top of the composite conductor is more significant than that on the lateral displacement. The composite foundation can effectively reduce the displacement of the deepwater conductor and improve the lateral and vertical load bearing capacity of the structure. And also the research results can provide theoretical reference for further development and optimization of the deepwater composite conductor structure.

With gap elements modeling the gap contact condition between jacket platforms guided supports and the conductor pipe, the deflections of the conductor pipe induced by the motions of Jackup in cantilever mode, and offsets of the jacket platforms under operating conditions are investigated. The limiting relative excursions between the jacket out of phase or in phase with the jackup and the distributions of the moment are quantified by the strength and stability analysis of the conductor systems. The results show to avoid an overload for given conductor strength and dimensions, the maximum relative displacement between jackup and jacket platform with guide offsets is about 75.0cm.

There is ice in the Gulf of Mexico, and this type of ice called gas hydrates burns when ignited. Gas hydrates form slowly within the soil mass when the gas seeping up from offshore oil reservoirs mixes with water under high pressures (>500 m of water) and low temperatures (a few degrees Celsius). The oil travels from the well to the platform through a conductor pipe. The oil and therefore the conductor are very hot and melt the existing hydrates that are within the depth of the foundation piles. The melting process generates a large amount of gas that can endanger the stability of the foundation. The rate at which the temperature rises around the hot conductor in the hydrate rich soil is studied using the finite-element method (FEM). A detailed thermodynamic analysis is performed. It includes a laboratory experiment to help validate FEM, a study of the mesh size, the thermodynamic analysis results, a study of the conductor size, and of the latent heat influence. The results can be used to evaluate the temperature rise around a hot pipe buried in soil and therefore the propagation of the hydrate melting front around the conductor and toward the piles.

ABSTRACT Conductor pipe or drive pipe, including platform conductors, Jackup-supported conductors and free-standing conductors, is an area that can offer significant cost savings. This paper contains a comprehensive discussion of various facets of conductor pipe including structural design, as well as fabrication and installation considerations. The API LRFD interaction equations for combined axial and bending loadings are revised to include the effects of infernal and external Conductor loads. This approach will result in a more rational and cost effective conductor pipe design. Other structural design considerations are discussed including selection of environmental criteria, vortex shedding, fatigue, SCFS, S-N curves, slenderness ratio limitations and deepwater applications. An equation for conductor penetration is presented which is based on loss of circulation of drilling fluids. Recommendations are also made concerning fabrication and installation issues including Iifting, driveability, welding, inspection, mechanical connectors and practical considerations. Finally a recommendation is made on drive shoe bevel shapes based on field studies of actual installations. INTRODUCTION In an offshore well, conductor pipe, also known as drive pipe is the external pipe which provides structural support for the internal well tubing and casing strings. The objective of conductor pipe design is to provide the most economical structural member that will safely support the well during all phases of its life, including installation, drilling and production. Each phase may have different structural requirements that govern its design. The selection of the structural member can have significant cost ramifications not only in weight savings on an individual conductor, but also in the weight of a drilling/production platform. The difference in conductor sizes, i.e., between 30" and 26" diameters, could heavily influence the jacket design by increasing or decreasing environmental loadings. DEFINITIONS There are several different offshore applications for conductor pipe with each having specific requirements for its design. These applications are best categorized by three basic types: platform conductor, jackup-supported conductor (marine riser) and free-standing conductor (self-supporting caisson). They are defined for the purposes of this paper as follows:Platform ConductorA platform conductor is installed through the guides of an existing platform. Lateral support is provided to the conductor by guides at the platform's horizontal elevations. They typically have diameters of 26"-30" with uniform wall thicknesses ranging from ½" - 1" or more. Typical loading and moment diagrams are shown in Figure 1.Jackup-Supported Conductor A jackup-supported conductor, or marine riser, is a temporary conductor used only during drilling operations (usually about three to four months) which is installed by a jackup drilling rig. The conductor in this case has lateral support provided by multiple cables at the drilling rig. The cables should be taut to insure no deflections of the conductor are allowed at the rig. Internal strings are supported by a mudline suspension system and are usually not grouted to the surface. Upon completion of drilling operations the conductor is either cut off slightly above the mudline to allow for future operations or plugged and abandoned (P&A).

A drilling system is described for geotechnical exploration and soil sampling in the seabed, modelled after the concept of the marine riser pipe. The system derives its stability from a "tensioning weight," in the form of a cylindrical concrete block at the bottom, which keeps the conductor pipe in tension at all times. The axial tension from the tensioning weight and the self-weight of the conductor pipe substantially reduce the bending effects in the conductor pipe resulting from current and wave forces, as well as from the drift of the drilling vessel. The lateral reaction required to keep the pipe in place at the sea floor is provided by a concrete footblock. The bottom end of the conductor pipe slides into the footblock, which has a doughnut-shaped cross section that allows for the vertical movement or heave of the drilling vessel. The Hermitian equation is used to solve for the secondary effects due to the deformation of the flexible conductor under wave or current forces and the self-weight of the conductor pipe. The system has been used successfully on the Grand Banks in 122 m of water. Keywords: geotechnical exploration, sampling, deep water drilling, marine riser analogy, tensioning weight.

Summary Subsea wellheads can be subjected to extreme external loads when a drilling or production riser remains connected during storm or vessel drive-off conditions. In addition, vortex shedding from high currents and wave action on drilling and production risers can subject the wellhead to high-cycle fatigue loads. These extreme external and high-cycle fatigue loads can cause failure of the wellhead system when a fully cemented annulus between the 30-in. [76-cm] structural conductor pipe and 20-in. [51-cm] surface casing is not achieved. This effect of cement shortfall is most damaging when the cement level is just below the wellhead-body/conductor-housing region. Purposefully setting the cement level far below the mudline can be a cost-effective solution to the unintentional cement-shortfall problem.