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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