A Unique Software Tool for Estimating Subsea Measurement System Uncertainty
Authors: Kelner Eric 
Published: April 2012

Abstract
Flow rate measurement uncertainty analysis is a key methodology for addressingproduction allocation, reservoir performance optimization, operationalquestions, and regulatory issues. Until now, no unique collection of procedureshas been available to estimate the total system uncertainty associated withmultiphase flow meters, well test separator systems, and the pipelinesconnecting them, especially for commingled flow configurations. A tool to dothis would assist industry stakeholders in understanding the uncertaintyassociated with fiscal allocation of production, reservoir management, andforecasting processing facility operations.
With this need in mind, and the support of several offshore operators and DOEthrough the RPSEA program, the team developed a software tool with auser-friendly interface for predicting total network uncertainties for systemswith subsea multiphase flow meters (MPFMs). The tool accounts for meteroperating conditions, in-situ pressure - volume - temperature (PVT) properties, system configurations, and flowline/riser effects. It is anticipated that thistool will be attractive to all industry stakeholders, in order to moreequitably allocate production and optimize reservoir performance. Thebackground of the tool's development, an overview of use cases, and lessonslearned from the effort will be presented.

Introduction
Flow rate measurement uncertainty analysis is a key methodology for addressingproduction allocation, reservoir performance optimization, operational issues, and regulatory requirements. Unfortunately, no unique collection of proceduresis currently available for predicting the total system uncertainty associatedwith multiphase flow meters (both subsea and topside), well test separatorsystems, and the pipelines connecting them, especially for commingled flowconfigurations. This lack of tools for understanding and predicting uncertaintycauses significant problems for all parties involved, especially for fiscalallocation of production, with reservoir management, and with forecasts foroperation of process facilities.
A software tool with a user-friendly interface for predicting total networkuncertainties for systems with subsea multiphase flow meters (MPFMs) wasdeveloped as part of RPSEA 07121-1301. The tool accounts for meter operatingconditions, in-situ PVT properties, system configurations and flowline/risereffects. It is anticipated that this tool will find use among vendors, oilindustry operating companies and regulatory agencies, in order to moreequitably allocate production and optimize reservoir performance.

Motivation
Accurate flow rate measurement has become a critical issue for the oilindustry, especially for offshore and subsea developments. Multiphase flowmeasurements are traditionally made using a well test separator andsingle-phase metering system topside. In recent years, multiphase flow metermeasurements topside and subsea have been accepted for well tests, when themeters are operated within meter specifications and near calibrated conditions. However, no reliable uncertainty models that couple multiphase flow in flowlines with the separator and meter uncertainty under flowing conditions existeduntil now.