Load Monitoring at the Touchdown Point of the First Steel Catenary Riser Installed in a Deepwater Moored Semisubmersible Platform

Abstract

Abstract A 10-inch Steel Catenary Riser (SCR) was installed in the Petrobras XVIII semi-submersible production platform, moored in 910 meters water depth in the Marlim field, Campos Basin, offshore Brasil. This is the first SCR ever installed on a floating moored platform. In order to evaluate and verify the methodologies and to calibrate the numerical models used in the riser, mooring system, and platform design, it was necessary to establish a monitoring program for all the relevant parameters (environmental, platform positions and motions, riser loads and stresses at the top and at the touch down point (TDP), and vortex induced vibrations). The TDP monitoring system consists of several strain-gage collars in pipe sections close to the TDP, subsea strain conditioning, control and data storage electronics, and an acoustic telemetry data transmission system. Mobilising this complex system required several innovative solutions. The paper describes the monitoring system developed to measure tension and moments at the Touch Down Point (TDP) region of an SCR, its installation and operational aspects, and its performance to this date. Introduction As part of its continuing effort to develop hydrocarbons in deep water responsibly and cost effectively, Petrobras initiated a project to assess the feasibility of using Steel Catenary Risers (SCR) on moored, floating production platforms in deep water. Numerical analyses to predict the stress history in the touch down region of the SCR sometimes presented different results depending on the numerical model used. Accordingly, Petrobras considered it essential to obtain full-scale data from a prototypical 10 inch SCR installed in the PXVIII, a semisubmersible FPSO moored in 910 meters of water. The experiment was outlined by the Petrobras R&D Center's Exploitation Projects Division. Its Subsea Engineering Group prepared Technical Specifications for the Environmental, Platform Positions and Motions, Top Loads, TDP Loads and Vortex Induced Vibrations Monitoring Systems and its processing, and is conducting this monitoring project. The measurement of the stresses in the touch down point of an SCR in deep water had never been done before and presented several difficulties. This paper describes the development of a monitoring system to do that.