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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.

Experience with modern ultra-deepwater capable drilling vessels and their associated marine riser tensioner systems has led to increased concerns over tensioner load variations in extreme environments. Modern drilling riser tensioners are complex hydro-pneumatic systems whereby the tension applied at the slip-ring can vary significantly with tensioner stroke in response to vessel heave. The aforementioned tensioner load variations that occur with modern tensioner systems can have a significant effect on the loads transferred to the wellhead and conductor/casing. This can lead to fatigue concerns at critical locations. The connectors along the conductor and surface casing can be highly susceptible to fatigue if they are located in regions of high bending loads below the mudline. This paper will give a detailed overview of recent technology advancements that have been incorporated into the latest version of an industry-standard tool for global analysis of drilling risers [1] and that allow these concerns to be addressed. It will focus on two main areas where significant enhancements have been made in tensioner and wellhead & casing modelling. (Note that the version of the software incorporating these capabilities will be made commercially available during 2014.) The advanced tensioner modelling capability consists of a detailed tensioner model that includes individual hydraulic and pneumatic components of the tensioner system that are fully integrated with a non-linear 3D structural finite element model. This tensioner model is capable of fully capturing all transient behaviour and load variations of real world tensioner systems. This paper will describe in detail this unique modelling capability and its application, including riser recoil analysis. Additionally, accurate modelling of the wellhead, conductor/casing and the surrounding soil structure is crucial in order to accurately predict bending loads experienced in this region. This includes modelling individual wellhead sections (high pressure housing, low pressure housing and tapered sections) and multi-pipe structures for conductor/casing sections (including cement layers). The advanced soil modelling includes the capability to specify different soil types at different depths. This paper will describe in detail these advanced modelling capabilities. The detailed tensioner modelling capability represents a highly advanced technical and innovative development and is fundamental to providing a realistic recoil analysis capability. The advanced wellhead and casing modelling allows for accurate prediction of the stresses experienced in this critical region and accurate determination of the fatigue lives of these components. This paper will demonstrate how all of these advanced modelling capabilities can be used to accurately model deepwater drilling risers and provide increased confidence in conducting drilling operations in the harshest of environments.

With exploration and development of hydrocarbon resources moving into ever deeper waters, there is significantly increased demand for drilling vessels capable of drilling in water depths of up to 10,000 ft and beyond. One of the main challenges associated with drilling in these water depths is control of the recoil behavior of the drilling riser after an emergency disconnect. This is required from time to time in the event of loss of the vessel’s station-keeping capability, either in extreme weather or through a failure of the dynamic positioning system. In these scenarios, the riser must be quickly disconnected below the Lower Marine Riser Package (LMRP) to avoid damage to the riser or well structure. Once disconnected, the LMRP should lift sufficiently clear of the Blow-Out Preventer (BOP) to avoid subsequent contact between the LMRP and the BOP, while at the same time the upward movement of the riser must be arrested in time to prevent collapse of the telescopic joint (which could cause impact loads on the drillfloor) or compression in the tensioning lines. These conflicting requirements become more severe in deepwater, where the ratio between the wet weight and inertia of the riser is reduced. This highlights the requirement for an accurate recoil analysis capability in order to determine the optimum riser stack-up and operability limits for deepwater operations. This paper describes the development of a disconnect and recoil analysis software tool that for the first time has been integrated with a 3D finite element (FE) structural model of the drilling riser system. The tool incorporates a detailed model of the riser tensioning system, including the ability to model the behavior of each tensioning cylinder independently and the ability to model the behavior of the anti-recoil control system. The tool also incorporates an advanced fluid flow model, implemented by means of a finite volume numerical model, that models the flow of drilling mud out of the riser immediately after disconnect. The details of the tensioner system and fluid flow models are discussed, along with the approach taken to integrate these into the existing FE structural analysis code. A number of case studies are presented to illustrate the application of the tool to deepwater riser recoil analysis and to examine the effect of key parameters (including vessel offset) on the recoil behavior of the riser system.Copyright © 2009 by ASME

With drilling and exploration occurring in ever deeper waters and harsh environmental conditions, the ability to properly plan critical operations such as deployment and retrieval of the drilling riser becomes increasingly important. Particularly in deepwater high current environments, deployment and retrieval operations can be limited by the length of time it takes to deploy or retrieve the riser and the danger of the riser joints binding in the diverter housing. These limitations can have significant impact on both operations and riser integrity. Drilling contractors have devised a number of means of conducting operations in high current environments in order to increase operational up-time and mitigate the risks involved. One approach is drift-running, where the drilling rig is positioned upstream of the well at the start of the deployment operation and the rig is allowed to drift in a controlled manner to the well as the riser is deployed. This procedure effectively reduces the current loading on the riser, thereby allowing the riser to be deployed without risk of binding in the diverter housing. This paper describes an on-board simulation tool designed for use on dynamically-positioned (DP) drilling rigs that can be used to plan deployment/retrieval and drift-running operations. The tool is a development of an on-board drift-off simulator that has been in operation on-board the latest generation of DP drillships for some time. The simulator uses a fully-coupled 3D finite element (FE) model of the riser system, thereby allowing accurate determination of the riser response to current loading. The simulator computes the angle of the riser in the diverter housing throughout the deployment/retrieval process. Additionally, the simulator can compute the optimum drift speed of the vessel to minimise the riser angle. Based on the results of these simulations, the on-board tool can determine the feasibility of deploying or retrieving the riser and can compute the required vessel track for carrying out drift-running operations. The tool allows on-board personnel to plan these operations using either prevailing or forecast metocean conditions. The key features of the on-board simulator are discussed, with particular emphasis on the procedure used to compute the drift-running track for the drilling rig during riser deployment. The benefits of the system in planning deployment/retrieval operations are illustrated by means of a number of case-studies.Copyright © 2007 by ASME

With development occurring in increasingly challenging environmental conditions, including Arctic locations, the potential benefits of riser monitoring for completion/workover operations with open sea completion risers are becoming more apparent. This is particularly the case when monitoring is combined with an on-board numerical riser model that can provide real-time operational guidance to rig personnel. The use of a Riser Management System (RMS) with these capabilities presents opportunities for significant cost savings from a maximized operational window and enhanced safety and riser integrity. This paper describes an RMS that has been supplied for a completion/workover riser application in the Barents Sea. The RMS comprises riser-mounted strain gauge instrumentation connected via data acquisition hardware to a topside PC. Data is also acquired from other vessel systems, e.g. Environmental Monitoring System (EMS), Drilling Control System (DCS) and Workover Control System (WOCS). The RMS incorporates an advanced finite element (FE) numerical model of the riser system, which coupled with the measured riser response data is used to predict the operating envelope for the vessel under the prevailing metocean conditions in pseudo-real time. This capability represents a key feature of the RMS and is used to provide operational guidance to rig personnel. The RMS also includes a riser joint tracking feature that automatically records the measured fatigue damage for the instrumented riser joints and the fatigue damage predicted by the riser numerical model for the non-instrumented riser joints. The paper describes the key features of the RMS, with particular emphasis on the procedure used to determine the riser response from a limited number of riser strain measurements using the FE numerical model of the riser. Experience with deployment of the system and its use in practice is described and some of the key benefits are highlighted.Copyright © 2006 by ASME

With the move to the development of remote, deepwater fields, increasing use is being made of floating production, storage and offloading (FPSO) facilities from which oil is intermittently offloaded to a shuttle tanker via offloading lines and an anchor leg mooring buoy. The response of the individual components of these systems is significantly influenced by hydrodynamic and mechanical coupling between adjacent components, precluding the use of traditional analysis techniques such as displacement RAOs derived from tank model tests or diffraction/radiation analyses of the independent components. Consequently, the reliable and accurate design of these complex systems requires an analysis tool capable of determining the fully coupled response of each of the individual components of the system. A recently-developed time domain coupled analysis tool has been extended to incorporate a frequency domain coupled analysis capability. This tool combines radiation/diffraction theory with a non-linear finite element (FE) structural analysis technique used for the analysis of slender offshore structures. This paper describes the application of frequency domain analysis to the coupled FE/floating structure problem, with particular consideration given to the linearisation of viscous drag loads on floating structures and the treatment of low-frequency second-order loads in the frequency domain. Results from frequency domain and time domain coupled analyses of a typical West of Africa type offloading system are compared, highlighting areas of application where frequency domain coupled analysis can offer significant benefits when used in conjunction with time domain analysis. Based on this, recommendations are made for the appropriate use of frequency and time domain coupled analysis for this type of system.Copyright © 2005 by ASME

Abstract The design of dry tree spar risers with top tension provided only by passive buoyancy differs in significant respects from the design of other top tensioned risers, such as TLP risers. Critical differences are the provision of tension using buoyancy cans, the position and type of can (integral or nonintegral) and the interfaces or contact areas between the risers and hull guide supports. Predicting riser response to environmental loads and vessel motions requires the accurate modeling of the riser configuration, lateral hull guides and moonpool hydrodynamics. This paper presents a comparison between recent full-scale offshore measurements of risers on the Chevron Genesis spar platform with response predictions made using an enhanced riser analysis software tool (DeepRiser) capable of modeling the mechanics of spar riser behavior. Comparisons made between the measurements and the results from the analysis software show reasonable agreement, and highlight major areas of response sensitivity. Important lessons from this work relate to the significance of hull motion on the riser response and the sensitivity of response to the width of the gap between air cans and hull guides. Introduction The use of spar platforms like Neptune and Genesis as facilities for deep water hydrocarbon production poses special challenges for the design of riser systems. The Genesis classic spar hull form and riser system, located in 2,600ft water depth in Green Canyon 205, are illustrated in Figures 1 and 2. The riser moonpool and seabed layout is presented in Figure 3. Unlike tension-leg platform risers, the spar production and export risers used to date have been tensioned only by passive buoyancy. The buoyancy support system has consisted either of a group of air cans which sleeve the riser, with the riser being suspended from the top of the sleeved section, as with those on Neptune, or of air cans integral with the wall of the riser, such as those on Genesis. While the moonpool of the spar affords a protected environment for the risers, the structure and geometry are such that contact between the risers and the hull are an essential consideration in the riser design. Early spar designs like eptune and Genesis have hull guides at several elevations to provide lateral support to the risers. These hull guides have clearances of one inch or more on the diameter, initially considered necessary to prevent the binding of the risers in the guides as the spar displaces horizontally and pitches. As the platform moves relative to the risers, these gaps will open and close, resulting in a highly non-linear problem of riser response. The intermittent contact problem is further complicated by the friction between the riser and the guides. This intermittent contact challenges the validity of the use of tools that assume the riser to be either in contact with hull guides or laterally unsupported. Recent experience with such designs has emphasized the need for design tools that accurately model this intermittent contact behavior. Recent software advances have produced an analysis tool capable of modeling the complex hull-riser interaction.