Riser Life Cycle Monitoring System Undergoes Initial Research Phase
Roy Long, SPE, National Energy Technology Laboratory, US Department of Energy
The National Energy Technology Laboratory (NETL) of the US Department of Energy (DOE) supports a wide range of research and development (R&D) projects to develop technology for enhancing deepwater capabilities and improving safety and protection of the environment.
Much of this work has taken place under the auspices of the Research Partnership to Secure Energy for America, a nonprofit agency funded by NETL, which initiates and manages R&D through industry and academic consortia that supply funding in kind with the provision of resources and materials. Among the recently completed deepwater projects is Phase I of an assessment and design of a riser life cycle management system (RLMS).
The project was conducted by a team at GE Global Research under the direction of principal investigator Judith Guzzo. The two-phase project is aimed at developing an integrated, reliable, and commercially viable solution for a real-time, telemetry-based marine RLMS.
The RLMS is an integrated system of hardware and software tools composed of sensors located on select riser joints, wireless subsea communication between the vessel and select instrumented risers, and software for data collection, processing, riser fatigue analysis, visualization, and alerts for enhanced operational decision making. Although the initial focus is on drilling risers, this technology may be transferrable to production risers.
The initial results of Phase I, which focus on the RLMS technical solution design, development, and risk retirement, are summarized. Initial end-user requirements for an integrated structural riser monitoring system design were obtained using information collected from drilling contractors, an offshore classification society, and experts on riser engineering and manufacturing.
Using the Six Sigma method, this input was translated into preliminary user requirements for an RLMS system and functional design specifications for select subsystems using a quality function deployment (QFD) tool.
Summary of Project
The key RLMS subsystems are radio frequency identification (RFID), subsea sensors, acoustic communication, vibration and fatigue analysis, topside software, and architecture. Operational considerations such as the installation and maintenance of the RLMS system are also considered.
Following industry input analyses, a Pareto diagram of prioritized system requirements for an RLMS system (Fig. 1) highlights the key attributes of a successful system design that will be accepted by the industry (e.g., an easy, tetherless installation that does not interfere with existing riser operations).
As a part of Phase II, a rigorous cost/benefit analysis will be conducted to quantitatively assess whether the potential system users, public and private enterprises, and government agencies would experience a net benefit from the proposed RLMS solution. A systematic estimation will be made of all benefits and costs in comparison with alternative options.
Subsystems’ Technical Design Elements
Based on the initial industry input and identification of initial system design requirements, the following enabling technical design elements for the RLMS solution are required.
- RFID for automating marine riser identification and enabling of topside riser analytics, examination of riser pedigree, and condition-based maintenance (CBM)
- Subsea sensing and communication for marine riser monitoring and near real-time tetherless data transmission and for enabling CBM
- Vibration and fatigue analysis for topside “surface” alerts during drilling operations and for estimated riser life prediction
- Topside software for data acquisition, RLMS analytics, and intuitive user interface Fig. 2 illustrates these design elements, highlighting the functionality of the subsea sensing and acoustic platform and the underwater and surface analytics. Detailed design elements, risk assessment, and the next steps in Phase I for each subsystem are described in subsequent sections of the article.
A QFD tool was used to translate the information in the Pareto diagram (Fig. 1) into subsystem product design specifications, and the specifications were rated for acceptability by the industry.
Failure Modes and Effects Analysis
The team performed a risk analysis in six key categories: (1) RFID, (2) subsea sensor package, (3) subsea acoustic communication, (4) vibration and lifting analytics, (5) topside data acquisition and software, and (6) system installation and maintenance.
The team rated each risk by severity, probability, and detectability, with the following definitions:
Sev = Severity of consequences if failure mode activates
Prob = Probability of occurrence of failure mode
Detect = Detectability of activation of failure mode
From the 66 risks identified, three emerged as high probability and high severity, and 14 emerged as medium or high probability and medium or high severity. Risk mitigation plans were assigned to each potential failure mode.
System Component Design
A key component design also incorporates industry commentary, including the design of the RFID and subsea platform components.
RFID Initial Design Criteria
The following initial design criteria are used in addressing industry comments.
- RFID reader will be handheld and dockable.
- RFID reader battery life will last for an entire drilling campaign (3 to 6 months).
- RFID reader will be ruggedized and water resistant.
- RFID tags will attach to the riser without requiring modifications.
- RFID tags will withstand 5,200 psi pressure and 32°F to 34°F temperatures.
- RFID tags will be passive (no battery).
- RFID tags will read from 2 ft away.
- RFID tag placement will not interfere with riser operations.
- Riser sections will be scanned during staging before going to the spider.
Initial Design Criteria of Subsea Platform
The primary customer expectations in the preliminary discussions define the initial design criteria for the subsea platform, including
- An integrated acoustic telemetry allowing real-time or near real-time condition monitoring and alerts
- A modular platform integrating commercial off-the-shelf motion sensors (accelerometer+gyro), interfaces for additional sensor data acquisition, processing capability for customized edge computation and analytics, wireless communication, storage for data backup in the absence of wireless, battery, and marinized pressure vessel/casing
- “Plug-and-go” and battery power capabilities, eliminating the requirement of auxiliary cabling, and minimally affecting existing operations
- An open operating system (OS) environment on the microprocessor, allowing customized software application development for interfacing with additional sensors, performing signal processing, and edge analytics
These criteria have led to a modular subsea platform design that is meant to provide a “plug-and-go” system for easy installation and minimal impact on existing operations.
The platform incorporates the following components:
- Acoustic modem and transducer.
The subsea platform will integrate an acoustic modem with a transducer attached, thereby enabling underwater wireless communication to the topside of a drilling vessel. The subsea platform uses the acoustics to transmit data to the topside data center, as well as for platform management and control when needed.
- Battery. A rechargeable lithium ion battery will be used to power the subsea platform and eliminate the use of auxiliary cabling. A detailed and scalable battery model is being developed to estimate and optimize the battery life of the subsea platform. Various aspects of the RLMS system specifications have been factored into the model, such as the sensor data sampling interval, sampling duration, and sampling rate, as well as the selection of the acoustic transmission power level and the transmission rate. Depending on the choice of the system specifications and the intended battery life, the battery model will output the estimated battery size/capacity.
- Sensors and sensor interfaces. Each subsea platform will consist of two motion sensors: a triaxial accelerometer and a triaxial gyroscope (angular rate sensor). Together with the vibration and fatigue algorithms, it is expected that loads and stresses at different sections of the risers and related fatigue levels will be calculated using the motion sensor data. The subsea platform will also have additional sensor interfaces, such as serial/RS232 connections,
I2C/SPI digital interfaces, analog-to-digital conversion input/output, that are open to end users for connecting existing field sensors to provide real-time visibility for topside control.
- Microprocessor. A single board computer will serve as the “edge intelligence” of the subsea platform and will control the acquisition of the sensor data, perform signal processing and/or algorithms on the collected data as needed, and manage the acoustic communication protocol, data backup/storage, and power. The open OS of the microprocessor will provide spaces for users to develop customized software applications, e.g., a user-specific analysis of the sensor data.
System Functionality Testing
Following a laboratory testing, additional steps in the development of the subsea platform will include
- Testing the rig by attaching the subsea platform to a full-scale riser joint to (1) test the sensor signal integrity under controlled axial tension and bending loads, and (2) evaluate the installation mechanism of the subsea platform
- Enhancing the software functionality and capability, and defining the strategy and architecture for customized application development
- Building the transfer function for modeling the platform battery life related to the various system parameters
- Working with the Woods Hole Oceanographic Institution to benefit from its experience in underwater acoustic communication systems and vessel marinization (e.g., in 12,000-ft depths) and defining the system marinization approach for a customized, pressurized enclosure for field testing
- Defining the strategy and planning for a system installation in a riser deployment operation
Once fully developed, the RLMS system will provide continuous updates on key parameters related to the “health” of the riser string. These data will assist the rig operator with decision-making processes that affect drilling operations.
The top-level parameters that will be continuously updated are
- Maximum level of fatigue damage in the riser assembly
- Average and maximum rates of fatigue damage during the past day, week, and month
- Planned and recommended time till the next inspection
- Remaining useful life based on accumulating fatigue predictions vs. design specifications
- Estimated time history of the axial force on the wellhead
The continuous availability of these key parameter data will offer the rig operator an enhanced picture of the effects of the current drilling operations on riser life metrics and will assist in decision-making processes related to performance-based inspection and maintenance of the riser.