Retrofittable External Hoop Strain Sensors to Monitor Changes in Internal Pressure, During Hydrate Blockage Remediation, in a Deep-Water Flowline

Abstract

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.