Through Flowline Communication System Based On Pressure Waves: Validation Tests
Authors: Rosa Alberto Dana , Mattei Lucilla 
Published: October 2008

This paper describes the main results of an experimental activity carried out to demonstrate the feasibility of a communication system based on pressure waves traveling through the fluid contained in flowlines. Moreover, the tests were aimed at validating a theoretical model regarding pressure wave attenuation in single phase and multiphase flows.

The results of a series of tests carried out during the experimental phase boosted confidence in the possibility of communicating at distances greater than 10 km with acceptable signal attenuations even when the fluid was two-phase liquid/gas and the flow pattern was intermittent or bubble dispersed flow.

INTRODUCTION

The Deep Water Autonomous Multiwell Production System-DAMPS is a research project which began in February 1990 and was completed in August 1992. The project developed the design of a guidelineless and diverless subsea production system, based on a six slot drilling/production template, with lattice protection structure (Fig. 1), production modules and dedicated tools for their re-entry/removal and maintenance are deployed by a dedicated installation vehicle (Fig.2). Each module is equipped with electro-hydraulic connectors performing both process and electrical matings.

The system does not use umbilicals. Control requirements have been complied by an autonomous system in which communication relies on an acoustic link. The electric power is generated locally by a turbo generator (gas turbine) running on gas coming from the reservoir. Tests carried out on a full scale prototype, equipped with pressure compensated lubrication and turbine to alternator magnetic coupling, have demonstrated the technical feasibility of this system.

On the other hand, the technology for the subsea hydraulic power unit and the relevant hydraulic closed loop has been derived from the Subsea Well Autonomous Control System-SWACS, operating since 1987 on Agip's Luna field, in the Jonian Sea.

AUTONOMOUS SUBSEA SYSTEMS: DATA ACQUISITION AND CONTROL

The development of satellite and marginal fields demands subsea production systems characterized by an ever increasing level of automation and reliability. When the subsea system is more than 10+15 km away from its surface facility, rendering the subsea system highly autonomous and avoiding the use of any umbilical, it becomes a cost effective solution.

Generally speaking, a system for the exploitation of subsea fields can be broken down into three main subsystems:the subsea production system, embodying production trees, manifold and template (if any),the surface facility, either a floating structure, like a semi submersible or a tanker, or a fixed structure,the link between the aforesaid quoted subsystems, made up of production flowline, umbilicals and injection lines(if any).

In conventional control and data acquisition systems (Fig.3), the control centre generates the electrical and hydraulic power to feed the subsea installation, carries out the processing and storage of data coming from the subsea system, and sends commands to actuate valves and to start automatized procedures. The subsea installation monitors critical parameters, like well pressure and temperature, valve status etc., and executes commands received from the surface control centre.