The Riser and Flowline Monitoring (RFM) project deployed one of the most comprehensive subsea structural monitoring systems to date on a Tahiti infield (production) Steel Catenary Riser (SCR) and associated flowline. State-of-the-art motion and strain measurement devices are optimally placed along the SCR to continuously measure and store real-time full scale riser response. In addition, RFM project is the first to implement monitoring devices on a flowline to measure the flowline buckling, a phenomenon that is predicted during repeated start up/shut down. The project goals are two-fold:1. Understand fundamental hydrodynamic behavior of SCRs and flowlines, specifically, floater motion induced response of catenary risers, Vortex Induced Vibration of catenary risers, riser behavior at the pull tube exit region, riser-soil interaction at the touchdown region, flowline buckling, flowline axial walking, and flow assurance characteristics of infield flowlines. The information generated will be used in future riser designs.2. The information will be used to validate Tahiti riser and flowline system robustness and conduct "health checks" on the fatigue critical risers and flowlines, particularly after significant environmental or operational events. This paper describes the monitoring system configuration, the technology deployed, and the installation methods.
Steel catenary risers (SCRs) in deepwater environment exhibit complex dynamic dynamic response governed by various factors such as environmental conditions, vessel motions, soil-structure interaction and material degradation. Uncertainties in the SCR design exist in the design data, analysis methodologies, fabrication, and hence a conservative approach has been adopted to overcome these shortfalls. Recent advances in monitoring systems installed on SCRs provide operator the assurance of the integrity of the SCRs in service, verify the SCR design, and enhance basic understanding of the SCR response. This paper outlines a strategy for monitoring the SCRs to characterize the response due to vessel motions, vortex induced vibrations (VIV), and soil-structure interaction. A detailed example of real-time SCR monitoring system with optimized array of motion and strain measurements is presented. The methodology for sensor selection and optimization is based on linear regression analysis. The measured data processing methods include shape matching the response amplitudes with correlating response frequencies. The principles and methods of measured data interpretation to capture global response shape due to wave and vessel motions induced and VIV are presented. The pipe-soil interaction such as soil stiffness, suction, softening and trenching effects characterized using the strain measurements in the touch down zone are presented. In addition, the methods to calibrate the individual vertical, lateral and axial models for pipe-soil interaction are presented.
The Riser and Flowline Monitoring (RFM) project deployed one of the most comprehensive subsea structural monitoring systems to date on a Tahiti infield (production) Steel Catenary Riser (SCR) and associated flowline. State-of-the-art motion and strain measurement devices are optimally placed along the SCR to continuously measure and store real-time full scale riser response. In addition, RFM project is the first to implement monitoring devices on a flowline to measure the flowline buckling, a phenomenon that is predicted during repeated start up/shut down. The project goals are two-fold:1. Understand fundamental hydrodynamic behavior of SCRs and flowlines, specifically, floater motion induced response of catenary risers, Vortex Induced Vibration of catenary risers, riser behavior at the pull tube exit region, riser-soil interaction at the touchdown region, flowline buckling, flowline axial walking, and flow assurance characteristics of infield flowlines. The information generated will be used in future riser designs.2. The information will be used to validate Tahiti riser and flowline system robustness and conduct "health checks" on the fatigue critical risers and flowlines, particularly after significant environmental or operational events. This paper describes the monitoring system configuration, the technology deployed, and the installation methods.
This paper will describe the first use of a retrofit non-intrusive pressure measurement system to monitor effects of remediating a hydrate blockage in a deep-water flowline jumper. The system was developed in response to a requirement to monitor pressure on the jumper in order to aid in gas hydrate remediation and to monitor the effects of the remediation processes to clear the blockage. An ROV-deployed non-intrusive hoop strain monitoring system (subC-pts*) was designed for clamping to the flowline, which had unknown internal pressure distribution, in order to report hoop strain changes, therefore derive the internal pipe pressure during intervention and remediation. In addition to the requirement for permanent storage of data, Schlumberger’s design included a high intensity LED mounted in the wall of unit, indicating the value of hoop strain on the subC-pts. Four self-contained systems were supplied. Each stand-alone sensor comprised an optical interrogation system, battery pack, data storage and real-time LED. The subsea optoelectronics were contained in a pressure-sealed housing secured to a composite structure containing fiber-optic strain sensors. The housing was removable from the sensor unit, for maintenance purposes, and was connected to the composite structure by an optical jumper cable. The systems were ROV-deployed onto a 30m length of jumper, at depths greater than 1000m. The measurement of hoop strain using highly linear strain sensors, and the deduction of pressure variation is examined. Focus is given to the novel aspects of the technology, and to areas where further improvements can be made, particularly with a view to developing alternative potential problem solving applications.
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