On the Use of Online Monitored Key Parameters From Pipe Lay Operations

For pipe lay operations parameters like heading and position of the lay vessel, lay-back and information about feeding of joints are usually collected and stored by the contractor. Many lay vessels are also equipped with a MRU unit for measurements of dynamic vessel motions, and in some cases the current profile is also monitored. This is especially the case for pipes with low bending stiffness and low ratio between weight and drag diameter (i.e. small pipe diameter) where current is important for the configuration of the pipe catenary. Together with the seabed these parameters constitutes the boundary conditions for a nonlinear time domain analysis of the lay operation. Such an analysis approach will have a wide range of application areas, from online monitoring to realistic back-calculation of a lay operation. During recent year’s work with the Ormen Lange field (see Figure 1) Marintek has developed a new generation of 3D pipeline analysis tools. Ormen Lange is the largest natural gas field on the Norwegian continental shelf. The field is situated 120 km northwest of Kristiansund. The seabed depths in the reservoir area vary between 800–1100m, and the terrain is very rough due to remnants from the Storegga slide. In the period 2006–2007 two 30" import lines, two MEG lines, and two umbilicals were installed at the Ormen Lange field. In the present paper monitored data collected during the installation of the 30" pipelines are used to back-calculate the lay operation. The agreement between observed and calculated lay parameters are reported and discussed.

Numerical Simulation and Practical Sand Silting in Waterways of Langya Bay

Dongjiakou Harbor is located at the Langya Bay in the city of Qingdao, Shandong Province. It is a multi-functional harbor of heavy passing capacity under planning in China. The sediment distribution and dispersion in the waterways and harbor basin water areas is of great importance to the construction and operation of the harbor. This article is based on the measurement of waves and currents as well as sediment suspension characteristics on site, and using numerical methods to predict the dispersion and deposition rules in this area. A combined wave-current-sediment model of COHERENS-SED is created through the combination of hydrodynamic model COHERENS and wave model SWAN as well as a sedimentation model SED developed by the authors. Inside COHERENS-SED, SWAN is regarded as a subroutine and it gets time and space varying current velocity and surface elevation from COHERENS. COHERENS gets time and space varying wave relevant parameters calculated by SWAN. Wave-enhanced bottom stress, wave dependent surface drag coefficient and radiation stress are introduced to COHERENS. Then a fully coupled hydrodynamic–sediment model COHERENS-SED accounting for interaction between the waves and currents is obtained and adopted to simulate these hydrodynamic conditions and the sedimentation processes in Langya Bay area. The open boundary of waves and currents is obtained through nesting from running a wider model which includes the Bohai Sea and the North Yellow Sea with coarser solution and contains coastal regions of Shandong Peninsula which includes the whole area of Langya Bay. Generally, the values of time series of current velocities, current directions and water levels as well as sediment concentrations have good agreements with observation data. The study shows the currents in the waterways and harbor basin water areas are relatively weak due to the narrow water width at the port mouth and the current directions parallel to the wharf directions. Also, sediment dispersion scales and strength are predicted according to the computation. The study also estimates the average sediment deposition amount and seabed erosion in this area. Besides, significant wave height and wave period obtained by COHERENS-SWAN shows that simulation result with wave-current interaction is better agreed with the measurement than the case without current.

A Parametric Study for the Design of Steel Catenary Riser System in Deepwater Harsh Environments

In recent years, offshore reservoirs have been developed in deeper and deeper water environments, where floating production, storage and offloading (FPSO), semi-submersibles, spars and TLPs are considered to be the most economically viable platforms. Steel catenary risers (SCRs) are being considered for these production units in deepwater development such as Northern North Sea. A variety of uncertainties are associated with material behaviour, environmental loading, hydromechanics modelling, structural modelling, and fatigue / corrosion / wear characteristics, especially around hang-off and touch down areas. SCRs used in conjunction with a semi-submersible or a FPSO in deepwater harsh environments present significant design challenges. The large vertical motions at the FPSO or semi induce severe riser response, which results in difficulty meeting strength and fatigue criteria at the hang-off and touch down point locations. To improve the understanding of SCR behaviour and increase the confidence in the design of such systems in deepwater harsh environments, a parametric study was carried out in this paper to deal with the factors that mainly influence the loading condition and fatigue life of the riser. Two cases, one steel catenary riser connected to a semi-submersible and one steel catenary riser connected to a FPSO, were studied and compared. And weight-optimized configurations were applied for both risers. Riflex combined with DeepC was the primary analysis tool used for the long-term response of the nonlinear structure SCR’s simulations, which is high computer time consuming. Hence, the parameters affecting the efficiency and accuracy of the simulations have also been studied during the analysis process.

Modal Analysis of the Ice-Structure Interaction Problem

In this paper the authors build upon the single degree of freedom ice-structure interaction model initially proposed by Matlock, et al. (1969, 1971). The model created by Matlock, et al. (1969, 1971), assumed that the primary response of the structure would be in its fundamental mode of vibration. Modal analysis is used in this study, in which the response of each mode is superposed to find the complete modal response of the entire length of a pier subject to incremental ice loading. In Matlock, et al., the physical system is a bottom supported pier modeled as a cantilever beam. Realistic conditions such as ice accumulation on the pier modeled as a point mass and uncertainties in the ice characteristics are introduced in order to provide a stochastic response. The impact of number of modes in modeling is studied as well as dynamics due to fluctuations of ice impact height as a result of typical tidal fluctuations. A Poincare´ based analysis following on the research of Karr, et al. (1992) is employed to identify and periodic behavior of the system response. The intention of this work is to provide a foundation for future work coupling multiple piers and connecting structure for a comprehensive ice-wind-structural dynamics model.

Efficient Finite Element for Evaluation of Strain Concentrations in Concrete Coated Pipelines

MARINTEK has developed software for detailed analysis of pipelines during installation and operation. As part of the software development a new coating finite element was developed in cooperation with StatoilHydro enabling efficient analysis of field joint strain concentrations of long concrete coated pipeline sections. The element was formulated based on sandwich beam theory and application of the Principle of Potential Energy. Large deformations and non-linear geometry effects were handled by a Co-rotated “ghost” reference description where elimination of rigid body motion was taken care of by referring to relative displacements in the strain energy term. The non-linearity related to shear interaction and concrete material behaviour was handled by applying non-linear springs and a purpose made concrete material model. The paper describes the theoretical formulation and numerical studies carried out to verify the model. The numerical study included comparison between model and full-scale tests as well as between model and other commercial software. At last a 3000 m long pipeline was analysed to demonstrate the strain concentration behaviour of a concrete coated pipeline exposed to high temperature snaking on the seabed.

Development of High Steel Grade Seamless X100 Weldable

The technological evolution in the offshore sector points out a trend towards an increasing use of high strength steels (grade 80ksi and higher), for both pipelines and risers. Pipeline specifications for deepwater offshore fields demand developments in design criteria (i.e. limit state design), welding, installation, and laying technologies. As long as the market goes deeper in offshore exploration and production, the market trend is to use heavier pipes in steel grade X65/X70 and some technological limits from several fronts are faced and more attractive becomes for the market to have a lighter high strength 100ksi seamless steel grade. The joint industrial program (JIP), termed “Seamless 100 ksi weldable” launched by Tenaris in order to address the complex design issues of high strength Q&T seamless pipes for ultra deep water applications has been finalized. The 100ksi steel grade has been achieved in two wall thickness 16 mm and 25 mm. The main results from both phase I devoted to the development and production of seamless pipes with minimum 100ksi and phase II devoted to evaluate the high strength seamless pipe weldability will be addressed in this paper. Main microstructural features promoting the best strength-toughness results obtained from phase I and the results from phase II, where the heat affected zone (HAZ) characterization made using stringent qualifying configuration such as API RP2Z and the promising results after qualifying the girth welds simulating a typical offshore operation and the Engineering Critical Assessment for installation will be addressed. The results from this development are of interest of all oil & gas companies who are facing as an output from the design project analysis the need to have high strength seamless pipes.

Reduced Model Device of Solutions to Control Thermal Buckling Effects in HP-HT Subsea Pipelines

Nowadays, the safe operation of HP-HT subsea pipelines resting on seabed must take into account the thermal buckling phenomenon. The transport of oil with high pressure and temperature can cause uncontrolled thermal buckling in subsea pipelines. The failure risk must be carefully evaluated to design the pipeline with safety. Nowadays to control the thermal buckling the use of man made triggers is seen like the best solution for cost and safety of subsea pipelines. Some projects employ man-made triggers to control the thermal buckling in the last years around the world. In this article is presented the system and methodology used to test some solutions in a reduced scale model. Different geometric setups along the model line were tested. Solutions like sleepers, dual sleepers and buoyancy were tested and the geometric and structural behavior monitored. The reduced model has 195 m length, and was developed in the IPT Towing Tank, representing a pipeline section of almost 6 km long. Strains, temperature, pressure and displacements were measured in several sections of the model. Additionally, an imaging technique for the model geometry retrieval was developed. This paper presents the experimental setup developed to investigate the performance of man-made triggers solutions for HP-HT subsea pipelines.

Estimation of Ice Load on a Ship Hull Based on Strain Measurements

The increased activity related to the oil and gas industry in polar waters implies that proper operation of ships such areas also will be in focus. The loading on a particular ship hull depends strongly on the route selection and vessel speed. Lack of information about the actual ice condition and the corresponding loads acting on the hull is identified to be among the most critical factors when operating in Arctic waters. This implies that there is a challenging interaction between strength-related design rules and schemes for operation of ships in arctic regions. In particular, the possibility of monitoring ice-induced stresses in order to provide assistance in relation to ship manoevering becomes highly relevant. The present paper is concerned with estimation of ice loads acting on the hull of the coast guard vessel KV Svalbard based on strains that were measured during the winter of 2007 as part of a project headed by DNV. Application of a finite element model of the bow structure is also applied in order to correlate the loading with the measured strains. The influence of ice thickness and vessel speed on the measured strain levels is also investigated.

Dynamics of Boat Seine Fishing Using a Net Geometry Simulator

Boat seine fishing is used to catch mainly demersal species; it has many benefits such as reduced energy and labor costs, and low damage to the sea bottom if it is controlled. This fishing technique has complex motion between the seine boat and the supple net over large operating areas; therefore, the dynamics of its operating processes during fishing are unknown. To investigate the dynamics of boat seine fishing in detail, we calculated its dynamics during a fishing operation using a net geometry simulation system that we developed. Two experimental surveys were carried out in January 2007 at Hokkaido, Japan. Latitude, longitude, and depth were measured in 10 places, from casting the anchor buoy to picking up the seine net. Depth sensors were installed at the top and bottom of the seine net mouth to record a time series of net shape during fishing. Using our net geometry simulator, we simulated net shape and the dynamics of boat seine fishing based on ship position and net depth. Very close agreement was observed between the experimental and simulated depths of the top and bottom of the net mouth during fishing. Three-dimensional visualization of the simulation results showed the capture processes of this fishing technique in a large scale operation. This study shows that our method is valid for modeling fishing operations to better implement smart fishing.

Evaluation of Key Hydraulic Tensioner Performance Parameters for Ultra Deep Water Applications

Hydraulic tensioners are widely used to provide tension and stiffness to vertical risers on spar and tension leg platform floating production facilities. Their performance directly affects dynamic response of the risers and the global motions of the floating system. The coupling effect of the tensioners, risers and vessel becomes increasingly important as the water depth increases into the ultra deep. This paper evaluates key performance parameters of long-stroke high-tension hydraulic tensioners for ultra deepwater application. It derives the fundamental equations and evaluates key performance parameters and their impact on the riser and vessel responses. This paper also proposes data measurement locations and methods to collect field data for calibrating these key performance parameters for future hydraulic tensioner design. The key tensioner performance parameters are the gas constant and the cylinder friction. In addition for a typical spar riser configuration, the keel joint friction also plays an important role in the overall riser performance. Their importance increases as water depth increases to 8,000 feet and beyond due to the nature of the coupling effect, long stroke and high tension requirements. Gathering of full scale-test data for these parameters has been costly. With several 7000 to 8000 feet risers and tensioners to be installed in the next few years, a method of collecting field data and its analysis for calibrating against the current assumptions of these parameters is proposed.