Flexible risers have been one of the preferred riser solution for many floating production systems in shallow to deepwater in many regions of the world for their good dynamic behavior and their reliability. The flexible pipe is composed of several plastic and steel layers. The weight of the riser is carried by a large number of steel wires (called tensile armours) that are essential to the integrity of the pipe. It is therefore important to be able to ensure the integrity of those armour wires and to detect a possible failure early enough to intervene in time, inspect the riser and if needed plan to re-terminate or partially replace it.To answer to this operational and safety issue, Technip and Schlumberger Subsea Surveillance (SSS) have a joint effort to develop a new technology allowing to detect failure or conditions likely to lead to failure of tensile armour wires. This new monitoring technology is based on a clamped composite structure with embedded optical fiber using among others Fiber Optics Bragg Gratings technologies (FBG). The developed device allows capturing armour failure monitoring the permanent deformation (torsion and elongation) results from an unbalanced equilibrium of the tensile armour layers. These crossed informations increase reliability of integrity assurance.The paper will present the essentials of the behaviour of the armour wires in a flexible riser, and the resulting requirements that need to be taken into account for the development of a system monitoring their possible breakage. The selected technologies and their optimization are presented as well as the way they are integrated in the riser system. The pipe and monitoring equipment prototypes are presented.

Flexible risers have been one of the preferred riser solution for many floating production systems in shallow to deepwater in many regions of the world for their good dynamic behavior and their reliability. The flexible pipe is composed of several plastic and steel layers. The weight of the riser is carried by a large number of steel wires (called tensile armours) that are essential to the integrity of the pipe. It is therefore important to be able to ensure the integrity of those armour wires and to detect a possible failure early enough to intervene in time, inspect the riser and if needed plan to re-terminate or partially replace it. To answer to this operational and safety issue, Technip and Schlumberger Subsea Surveillance (SSS) have a joint effort to develop a new technology allowing to detect failure or conditions likely to lead to failure of tensile armour wires. This new monitoring technology is based on a clamped composite structure with embedded optical fiber using among others Fiber Optics Bragg Gratings technologies (FBG). The developed device allows capturing armour failure monitoring the permanent deformation (torsion and elongation) results from an unbalanced equilibrium of the tensile armour layers. These crossed informations increase reliability of integrity assurance. The paper will present the essentials of the behaviour of the armour wires in a flexible riser, and the resulting requirements that need to be taken into account for the development of a system monitoring their possible breakage. The selected technologies and their optimization are presented as well as the way they are integrated in the riser system. The pipe and monitoring equipment prototypes are presented. Introduction Continuous integrity surveillance of flexible risers is an emerging technology that aims at maximizing the safe service life against degradation in hostile operating environments. Continuous surveillance measures are designed to detect the earliest signs of degradation of integrity so that mitigating actions can be implemented well in advance for maintaining the safe operation of the riser system. Some failures of flexible pipe armour wires in particular cases, offshore, over the past years, has caused a growing interest in Integrity Surveillance of tensile armors in flexible risers, Anderson (2007), Marinho (2008). The damage usually occurs in the upper sections of the riser between the wave zone and the topsides hang-off. The external sheath of a flexible riser has a higher risk of damage in this zone, potentially resulting in corrosion or corrosion-fatigue of the tensile armor, which could eventually lead to a failure of tensile armor wires. A flexible riser is highly redundant against failure in the tensile mode thanks to the a large number of tensile armour wires (no less than 40 and up to 240). Early detection of breakage of some wires due to material degradation could thus prevent failure of the riser. Current integrity practice may not detect a damage location for several months or years due to the infrequency and uncertainties of general visual inspections and riser annulus tests. External access to a flexible riser within a platform conductor tube is very restricted and prevents general inspection for integrity assessment. Technip and Schlumberger Subsea Surveillance (SSS) are collaborating to develop new technologies for monitoring failure of tensile armor wires. The surveillance systems provides advance warning that allows resources to be allocated for confirmation of damage and implementation of mitigation measures. Both integrated and retrofit surveillance system are being developed. The technology described in this paper is based on a retrofit clamp that monitors axial elongation and torsional twist of a flexible riser. The paper reviews the project background and the progress to-date of the ongoing development.

Fatigue is one of the key governing conditions in the design of rigid risers, in particular those in ultra-deep water. One effective way of improving fatigue is to adopt a lazy wave configuration, rather than a simple catenary. Steel Lazy Wave Risers (SLWR) have been successfully used offshore Brazil (Hoffman et al. 2010, Oliveira et al. 2017) and in the Gulf of Mexico (Beattie et al. 2013), and have been considered for the North Sea (Felista et al. 2015) and offshore Australia (Vijayaraghavan et al. 2015). Yet, it is probably the most computational-intensive aspect of it. Fatigue analyses require a very large number of load cases to be run, on complex, non-linear models. Methods for simplifying aspects of the analysis are highly desirable, but they must be weighed to provide the required safety levels whilst not introducing uneconomical, overconservative assumptions. The top first weld is a crucial hotspot, in particular for production SLWRs (Senra et al. 2011). These typically adopt flexible joints (FJ) at the connection to the vessel/platform, and linearization of the FJ stiffness is one of these key simplifications that bring significant value in reducing analysis cost. This paper describes a method for estimating the characteristic angle used for the linearization, which results in significant stiffness reduction in contrast with the usual, simpler method. Non-linear FJ stiffness curves are usually available, and they provide stiffness associated to the FJ absolute angle. The FJ stiffness significantly reduces with the angle of rotation. The conventional method adopts the stiffness corresponding to the most likely riser angle – absolute value measured from the static configuration. Conversely, the proposed methodology for estimating the most likely change in angle. As the angles often turn up in alternate angles, the proposed method results in much higher characteristic angle, and hence much lower FJ stiffness. The outcome is significantly less conservative designs, whilst still meeting the same required safety margins.

Despite the abrupt fall in crude oil prices since 2014, operators continue to explore for, and develop, oil and gas resources in some of the most challenging offshore environments. Exploration and development drilling is currently ongoing or planned in locations such as West of Shetland, offshore Eastern Canada, along Ireland’s Atlantic margin, in the South Atlantic Ocean and offshore South Africa. All these locations are characterized by the challenges of deepwater, powerful ocean currents and high seas. With the lower oil price environment, carrying out drilling operations at these locations both safely and economically requires the adoption of new digital technologies and associated processes that maximize efficiency and reduce the cost of well programs. A significant aspect of this relates to planning and execution of operations involving the marine drilling riser, which can be a major contributor to non-productive time in deepwater and harsh environment locations. This paper describes a holistic approach to addressing this challenge, which covers every phase of riser operations for the drilling program, from pre-operations global riser analysis through to post-operations assessment. The paper focuses on the technology that enables this holistic solution, with emphasis on the state-of-the-art riser management technology that is deployed on the drilling vessel. This uses an advanced finite element model of the riser, BOP stack, wellhead, conductor, casing and soil interaction as well as a detailed model of the riser tensioning system. The same model is used in both the pre-operations global drilling riser analysis phase and the operational drilling phase to ensure consistency. Incorporation of the model provides the capability to perform forecast analysis on-board the rig, allowing offshore personnel to simulate a range of operations hours and days in advance using forecast metocean conditions, thereby assessing the feasibility of critical well construction operations before they commence. Capabilities for real-time monitoring of ongoing operations, fusing sensor data with the riser model, are also described. These provide calculation of live watch circles and operating envelopes for connected-mode operations, in addition to tracking of riser joint, wellhead, conductor and casing fatigue from both wave and VIV excitation. Additionally, calibration of soil models — often a critical input to wellhead fatigue analyses — can be performed. Application of the technology is illustrated by means of a case study describing deployment on a record-breaking well in a harsh environment location. This demonstrated significant cost savings while simultaneously increasing safety and improving integrity assurance.

With the extension of the offshore drilling operations to water depths of 10,000 ft and beyond, the technical challenges involved also increased considerably. In this context, the management of the riser integrity through the application of computational simulations is capital to a safe and successful operation — particularly in harsh environments. One of the main challenges associated with keeping the system under safe limits is the recoil behavior in case of a disconnection from the well. The risk that an emergency disconnect procedure can take place during the campaign is imminent, either due to failure of the dynamic positioning system or due to extreme weather in such environments. Recent work [1] in the field of drilling riser dynamic analysis has shown that the recoil behavior of the riser after a disconnection from the bottom can be one of the main drivers of the level of top tension applied. Tension fluctuations can be very large as the vessel heaves, especially in ultra-deep waters where the average level of top tension is already very high. In order to be successful, a safe disconnection must ensure that the applied top tension is sufficient for the Lower Marine Riser Package (LMRP) to lift over the Blow-Out Preventer (BOP) with no risk of interference between the two. This tension should also not exceed a range in which the riser will not buckle due to its own recoil, that the telescopic joint will not collapse and transfer undesirable loads onto the drilling rig or that the tensioning lines will not compress. A good representation of such behavior in computational simulations is therefore very relevant to planning of the drilling campaign. A case study is presented herein, in which a recoil analysis was performed for a water depth of 11,483ft (3,500m). Numerical simulations using a finite element based methodology are applied for solving the transient problem of the riser disconnection in the time domain using a regular wave approach. A detailed hydro-pneumatic tensioning system model is incorporated to properly capture the effect of the anti-recoil valve closure and tension variations relevant during the disconnection. A reduction of conservativism is applied for the regular wave approach, where the maximum vessel heave likely to happen in every 50 waves is applied instead of the usual maximum in 1000 waves approach. ISO/TR 13624-2 [4] states that using the most probable maximum heave in 1000 waves is considered very conservative, as the event of the disconnection takes place in a very short period of time. The challenges inherent to such an extreme site are presented and conclusions are drawn on the influence of the overall level of top tension in the recoil behavior.