Tubarão Martelo Field Riser System: Shallow Water Challenging

Currently the oil and gas industry is focusing on challenging deep water projects, particularly in Campos Basin located coast off Brazil. However, there are a lot of prolific reservoirs located in shallow water, which need to be developed and they are located in area very far from the coast, where there aren’t pipelines facilities to export oil production, in this case is necessary to use a floating production unit able to storage produced oil, such as a FPSO. So, the riser system configuration should be able to absorb FPSO’s dynamic response due to wave load and avoid damage at touch down zone, in this case is recommended to use compliant riser configuration, such as Lazy Wave, Tethered Wave or Lazy S. In addition to, the proposed FPSO for Tubarão Martelo development is a type VLCC (Very Large Crude Carrier) using external turret moored system, which cause large vertical motion at riser connection and it presents large static offset. Also are expected to install 26 risers and umbilicals hanging off on the turret, this large number of risers and umbilicals has driven the main concerns to clashing and clearance requirement since Lazy-S configuration was adopted. In this paper, some numerical model details and recommendations will be presented, which became a feasible challenging risers system in shallow water. For instance, to solve clashing problem it is strictly recommended for modeling MWA (Mid Water Arch) gutter and bend stiffener at top I-tube interface, this recommendation doesn’t matter in deep water, but for shallow water problem is very important. Also is important to use ballast modules in order to solve clashing problems.

Integrity Assurance of an Oil Transportation Pipeline in a Transformed Design Environment

A large Oil and Gas pipeline gathering system is commonly used to transport processed oil and gas from an offshore platform to an onshore receiving facility. High reliability and integrity for continuous operation of these systems is crucial to ensure constant supply of hydrocarbon to the onshore processing facility and eventually to market. When such a system is exposed to a series of complex environmental loadings, it is often difficult to predict the response path, in-situ condition and therefore the system’s ability to withstand subsequent future loading scenarios. In order to continue to operate the pipeline after a significant environmental event, an overall approach needs to be developed to — (a) Understand the system loading and the associated integrity, (b) Develop a series of criteria staging the sequence of actions following an event that will verify the pipeline integrity and (c) Ensure that the integrity management solution is simple and easy to understand so that it can be implemented consistently. For a complex loading scenario, one of the main challenges is the ability to predict the controlling parameter(s) that drives the global integrity of these systems. In such scenarios, the presence of numerous parameters makes the technical modeling and prediction tasks arduous. To address such scenarios, first and foremost, it is crucial to understand the baseline environment data and other associated critical design input elements. If the “design environmental baseline” has transformed (due to large events e.g. storms etc.) from its original condition; it modifies the dynamics of the system. To address this problem, a thorough modeling and assessment of the in-situ condition is essential. Further, a robust calibration method is required to predict the future response path and therefore expected pipeline condition. The study further compares the planned integrity management solutions to the field data to validate the efficiency of the predicted scenarios. By the inclusion of real field-data feedback to the modeling method, balanced integrity solutions can be achieved and the ability to quantify the risks is made more practical and actionable.

Multidisciplinary Optimization Design for Section Layout of Complex Umbilical Cables Based on Intelligent Algorithm

Umbilical which links the top floater and the subsea devices provides control functions through electrical cables and hydraulic remote transmission. They are treated as the “lifeline” of the subsea production system for offshore oil and gas exploitation. During operation, umbilical needs to undertake self-weight and periodical load due to the ocean environment. Meanwhile, the heat during power transmission in electric cable is released to the umbilical body, which influences the mechanical properties and optical transmission in the cable. However, there are a number of components and many kinds of sectional arrangement for the umbilical. So the sectional design with multiple components needs to be solved as a multidisciplinary optimization problem. From the mechanical point of view, the umbilical structure should be designed with more compacted and symmetric layout to obtain even probability of resistance to loads and reduce structural stress to improve its fatigue performance. Concerning thermal effect, these units should be arranged to dissipate the heat easily to avoid the influence on the functional and structural components. In this paper, compactedness, symmetry and temperature distribution are quantified through introducing corresponding indices. Then multidisciplinary optimization framework is established. Particle Swarm Optimization (PSO) intelligent algorithm is adopted to carry out the optimization to obtain the optimal solution, which is far superior to the initial design. The optimization design strategy is proved to be effective and efficient by some numerical examples, which provides reference for design of umbilical cables.

Tensioned Step Riser Configuration for Ultra-Deep Application

This paper presents and compares the results of a research study for an ultra-deep water field development. A total of three riser configurations were modeled with the commonly used commercial software, and both extreme and fatigue analysis were performed. The advantage of tensioned step riser configuration, a patented and innovative riser configuration specially designed for ultra-deep water application, is demonstrated over other traditional configurations such as free-hanging configuration and double-hump lazy wave configuration. The analysis results indicated that the proposed tensioned step riser configuration has largely favorable features in extreme and fatigue performance for deep water application. The tensioned step riser configuration should be treated as a strong candidate for ultra-deep water flexible developments under substantially harsh environmental loading with worse vessel responses.

Comparative Review of the Established UHB Assessment Methods for Offshore Pipelines

Out of straightness upheaval buckling (OOS UHB) assessment considers the pipeline design and operational parameters, post-lay survey data and the properties of back-fill and rock in order to determine load and resistance factors that are applied. The factors allow for the natural variation of all parameters and are ultimately used to determine the download requirements along the route of a pipeline that is susceptible to UHB. Two methods are most commonly used in OOS UHB assessments. The structural reliability analysis (SRA) method is the most established and explicitly considers the variation of parameters in a Monte-Carlo simulation, enabling load and resistance factors to be calculated with a defined reliability level. A more recently developed methodology is documented in DNV-RP-F110 and provides a unified approach to the calculation of safety factors. The approach was calibrated using structural reliability based methods, undertaken with target reliability levels that are compliant with DNV-OS-F101. This paper presents a review of two key components of OOS UHB assessments. These components are the accuracy of post-lay survey data and the load resistance factor calculation method. These components are reviewed in the context of SRA and DNV-RP-F110 based assessments for a range of pipeline sizes, and ranges of soil and operational parameters. This enables characterisation of the differences between the two methodologies for ranges of design parameters that represent the majority of in-field flowlines that are installed in the United kingdom Continental Shelf (UKCS). SRA and DNV-RP-F110 derived load and resistance factors are compared and the effect of survey data smoothing upon rock-dump requirements is also discussed.

Flexible Spools Solution for Hybrid Risers Base for Green Fields Developments

Rigid spools are commonly used at the riser base of hybrid riser systems such as STTRs (Single Top Tensioned Risers) or BHORs (Bundle Hybrid Offset Risers) for the deep water oil fields. Rigid spools design is critical and governed by numerous operating constraints such as dynamic loadings (due to motion of the vertical riser, Vortex Induced Vibration, slugging, etc.), soil properties and soil/spools/structures interaction. Recent surveys on existing brown fields have highlighted unexpected issues on existing rigid spools. To solve these issues, an innovative flexible spool solution has been developed, combining unbonded flexible pipe structures in a “steep wave” configuration to accommodate the riser motions and FLET (Flowline End Termination) excursions avoiding soil deterioration and preventing unexpected spool behavior which could ultimately jeopardize its integrity. A steep wave configuration solution can be introduced with distributed buoyancy over the flexible spools length. This design allows a direct connection between the riser base assembly and the flowline termination, solving the embedment issue and easing accommodation of the hybrid riser motions. This paper describes the recent issues with rigid spools design and describes the solutions developed with flexible spool configurations to provide a more reliable riser base spools system for green fields.

Prediction and Qualification of Radial Birdcage and Lateral Buckling of Flexible Pipes in Deepwater Applications

Increasing oil exploitation in deepwater regions is driving the R&D of flexible pipes which are subjected to high external pressure loads from the hydrostatic head during their installation and operation. One of the challenges of flexible pipe design for such applications is to overcome the local buckling failure modes of tensile armor layers due to the combination of high external pressure, compressive loads and pipe curvature. This paper presents the latest progress in local buckling behavior prediction theory and the qualification process of flexible pipes. First, the mechanisms of two types of buckling behaviors, radial birdcage buckling and lateral buckling, are described. For each failure mode, the analytical buckling prediction theory is presented and the driving parameters are discussed. As part of the qualification process, the ability to resist radial birdcage and lateral buckling must be demonstrated. Suitable test protocols are required to represent the installation and operation conditions for the intended applications by deep immersion performance (DIP) tests. Several flexible pipes were designed based on radial birdcage and lateral buckling prediction theory, and pipe samples were manufactured using industrial production facilities for DIP tests. The results clearly show that flexible pipes following current design guidelines are suitable for deepwater applications. An alternative in-air rig was developed to simulate the DIP tests in a controlled laboratory environment to further validate the model prediction as a continuous development.

Effects of Underwater Explosion on Pipeline Integrity

Unexploded charges e.g. mines, bombs, torpedoes, etc... are rarely identified at a very early stage of reconnaissance surveys for pipeline route corridors. These ordnances are found during detailed pre-engineering or pre-lay surveys and, sometimes and not surprisingly, during the ordinary surveys performed on the pipeline in service. UXOs represent a hazard for the pipeline as well as for the assets and people involved in the construction phase. An appropriate mitigation plan in areas potentially affected is generally performed, including ordnance removal or mined-area clearance. Large diameter long offshore trunk lines crossing different territorial waters are often exposed to this kind of hazard. As such, pipeline construction and operation call for advanced numerical modelling as unique/valuable tool for providing a quantitative measure of the UXOs related risks. In recent projects the understanding of the underwater explosion process and prediction of damages associated to specific weapon-target engagement are based on the outcome of engineering tools based on finite element modelling. The continuing development of multi-purpose and multi-physics finite element analyses codes facilitates their application, providing sharp and detailed insight into the complex subject of underwater explosive effect and the coupled response of nearby structures. The scope of the structural integrity assessment is to define the minimum distance to be guaranteed between the pipeline and unexploded ordnance to avoid any risk of pipeline damage, as a function of the quantity of explosive. The engineering task of the integrity assessment includes the definition of the relevant conditions for the pipeline whether buried or free spanning, the analysis of the interaction between the gas bubble and shock pressure waves and the cylindrical shape of the pipeline, both as a shell that collapse under a pressure wave and a pipe length that moves laterally and develops bending. The objective is to evaluate the minimum allowable distance of the ordnance from the pipeline, as a function of the explosive quantity and type. In this paper, a series of real cases is presented in order to provide the most relevant parameters characterizing the integrity assessment under the applied load scenario from propagating shock waves. The propagation in water of shock pressure waves induced by the underwater explosion of a spherical charge is performed using finite element modelling, after model verification and validation with respect to the analytical and experimental formulations available in open literature. The outcome from finite element modelling is compared with findings from a simplified model based on modal analysis of the pipe shell – inward bulging and collapse of the pipe section and of the pipe beam – lateral displacement of the impacted stretch and bending at the crest of the buckle.

Thermal Effects on the Anchoring of Flexible Pipe Tensile Armors

In the design of flexible pipes, predict the anchoring behavior on end fittings is always challenging. In this sense, Prysmian Surflex has developed a finite element model, which should help the end fitting design as well the prediction of the structural behavior and the acceptable maximum loads. The current model considers that the contact between armor-resin is purely cohesive and has been suitable for the design of end fittings [1] and [2]. But tests and new studies [3] and [4] indicate that only cohesive assumption would not be the best approach. Experimental data from prototype tests also show that the current model would not predict acceptable results for loads higher than those used in previous projects. This document will describe a study developed considering the friction and thermal contraction, instead of the cohesive phenomenon in the anchoring behavior analysis. Small scale tests were conducted in order to understand the anchoring relation between the resin and the wire used in the tensile armor. For this purpose, a special test device was developed to simulate an enclosure system. A parametric study was also performed to identify the cooling temperatures, coefficients of friction and contact properties parameters taken from small scale tests. The finite element model considers the thermal effects during exothermic curing. Using the new parameters obtained, a second model was developed. This model consists of only one real shaped bended wire inside an end fitting cavity. To validate the model, samples were tested on laboratory according anchoring design. The results of this round of tests were studied and corroborate the argument that use friction and thermal effects is better than use only the cohesive condition.