Subsea Business: Fiscal Allocation, a New Endeavour for a Better Wet Gas and Multiphase Measurement
Authors: Pinguet Bruno , Vaagen Nils , Smith Michael 
Published: May 2016

1) Abstract

In subsea business, the use of wet gas or multiphase flowmeter is becoming a standard for the deep and ultradeep field development. The business growth has been outstanding over the last few years and will continue. In the meantime, the tieback of these fields to hosting platform or onshore facility has increased drastically, in Australia it is few hundredth kilometres. In such conditions there are more and more satellite fields hooked to the main pipeline subsea. This leads to issues with custody transfer and fiscal allocation. Already production are transferred between countries under this scheme, tax, royalties, regulations need to be fully taken into acocunt and understood wihtout using anymore fiscal metering at surface.

Under these schemes of development, the criticality on the measurement is not only high accuracy flow rates with one meter per well but also on how to guarantee the performance over the years knowing that the production of each phase is changing versus the well ageing. Therefore, a versatile solution is compulsory where no physical access can be done easily and where the use of Subsea Sampling is unfortunately limited yet, showing a lack of understanding on the fluid behavior criticality about the flow assurance too.

What can be done to ensure and audit the meters? API Chapter 20.3, NPD (Norway), DECC (UK), ISO TC 193 have been already met some recommendation. One meter is complying with this recommendation and then field experience and results versus fiscal metering will be presented. This paper will show the challenges in Brazil, North Sea and Australia. The real economical value of a subsea meter will be briefly highlighted in this paper. How can it impact the production by being the eye of the oil operator during the production phase? Cost of installing meter or replacing meter versus the gain will be shown in few cases. this paper is addressing also the use of multiphase flow meter beyond the classical metering flow rate performance and focus on the benefits of brought for a subsea flow assurance and reservoir management and the cost effectiveness of a subsea deployement versus a surface one.

2) Introduction

In the petroleum industry, allocation refers to practices of breaking down measures of quantities of extracted hydrocarbons across various contributing sources. Allocation aids the attribution of ownerships of hydrocarbons as each contributing element to a commingled flow, i.e. where produced fluids from multiple wells and/or producing zones are combined before flowing to a surface facility, which in deep water is typically a floating production, storage and offloading (FPSO) unit. Commingled flow is becoming increasingly common in the growing number of deep-water developments, where subsea production facilities combine flow before joining riser systems that transport hydrocarbons to the surface. Such systems often include tiebacks to other oil or gas fields operated by different company partnerships.

Allocation of produced hydrocarbons has major fiscal consequences for a variety of involved parties. It directly affects the revenue and tax liabilities of oil and gas operators and is the subject of increasingly stringent guidelines and regulations from industry bodies and government authorities. Manufacturers of equipment and suppliers of services to the oil and gas industry are challenged to meet the requirements of these guidelines and regulations, and have developed new technologies and processes to enable more accurate measurement of hydrocarbon production on a well-by-well basis.