VASPS Pre-subsea Phase Development: High Viscosity Field Tests and Outlook for Subsea Prototype
Authors: do Vale O.R. , Ribeiro G.S. , do Benetti M. , do Villa M. 
Published: October 2008

VASPS (Vertical Annular Separation and Pumping System) is an innovative concept for two-phase subsea separation and pumping system. This paper reports the latest efforts being taken in the development of such technology prior to the installation of the first subsea prototype, presenting a summary of the results of high viscosity tests onshore in the Atalaia Test Site, Brazil. It also provides an outlook of the final phase of the VASPS project, where a subsea VASPS unit will be installed at the Marimba field, Campos Basin, offshore Brazil.

Introduction

Several papers1–3 discussing the potential of subsea boosting technologies for oil production from deepwater fields have been published in recent years. Assayag et al.1 present a comprehensive review of the subject, outlining its advances, trends and challenges. Among these technologies, subsea separation has been considered one of the most promising alternatives2,4 VASPS (Vertical Annular Separation and Pumping System) is an innovative concept for two-phase subsea separation and pumping system, which allows a high capacity integrated separation and pumping equipment to be installed within a 30" conductor in a dummy well. This compact configuration is obtained by the use of internals which, without moving parts, induce helical flow path within the unit, thus generating centrifugal forces which enhance the gas-liquid separation (Fig. 1). The installation and maintenance of the unit are conceived to be accomplished using conventional subsea dri1ling and completion technology and equipment. VASPS technology is being developed in a phased approach addressing the various issues in a hierarchical manner Benneti & Villa4. Ref. 4 also describes the previous phase of the VASPS project development, in which a large scale surface prototype was tested in ENI-Agip's Multiphase Test Loop at Trecate, in Italy. Those tests confirmed the viability of the concept over a wide range of test conditions, with liquid viscosity ranging from 1–6 cPo The following step was to evaluate the gas-liquid separation performance with higher viscosity oils. These tests, part of the so caned "VASPS PreSubsea Phase", included testing of improved separator geometry and of associated technology, such as level sensors and control systems. Tests with high viscosity oils were performed at the Petrobras' Test Site for Multiphase Equipment at Atalaia, Brazil, using four different oils, with viscosities ranging from 5-65 cPo The results achieved validated both the separation process and the VASPS design models for such conditions. In particular, models' forecasted separation performances were compatible with those experimentally obtained. This paper also provides an outlook of the final phase of VASPS project's developments where a subsea VASPS unit will be installed in the Marimba field, Campos Basin, offshore Brazil.

Tests of VASPS as a Separator in Atalaia

After successfully testing a VASPS prototype as a separator for gas and low viscosity oils at ENI-Agip's Trecate Test Site, the whole assembly was brought to the Atalaia Test Site, in Northeastern Brazil, in order to have its performance evaluated when using higher viscosity oils. It is important to stress that this prototype was not specifically designed to the conditions of the Atalaia tests.