Field Tests on VASPS Separation and Pumping System
Authors: Benetti Massimo , Villa Marco 
Published: October 2008

VASPS (Vertical Annular Separation and Pumping System) is an innovative concept for two phase subsea separation and pumping system to be installed within a 30" conductor in a dummy well by conventional drilling and completion technology and equipment. The system is conceived for the exploitation of subsea fields either as subsea separation or as separation and pumping system. Depending on the specific field development, VASPS can produce an enhancement of the well production and an extension of the field life. VASPS can also find application on surface facilities giving an answer to typical problems such us deck space limitations, area classification, dimension, vessel motions. The present paper illustrates the main activities performed and the results achieved in the VASPS development in which a prototype was tested in Agip's Trecate Field in Italy. Field data confirm the viability of the concept both as gas-liquid separator, reaching a separation efficiency higher than 99.5% with inlet liquid flowrate up to 12,000 bpd, and as pumping system. Field tests on various types of level sensors indicate that VASPS level can be measured with commercial components such radar sensors. The VASPS concept and most of the test results on VASPS separator have been presented in previous paper 3.4.5. This paper mainly concerns with the discussion on the VASPS Application and the presentation of the results of the tests on the VASPS Pumping System and level sensors.

Introduction

In the recent years the development of marginal fields represents one of the most challenging issues in offshore technology. Several offshore areas have now turn mature and large discoveries are becoming unlikely. In these areas the typical offshore scenarios is characterized by an extensive pipeline and flowline network, a high degree of integration and offshore platforms located in the proximity of new developments. New projects mainly involve the exploitation of marginal reservoirs which in many cases are tied-back to existing facilities (Fig. 1), which usually are located within a distance of 10-20 km. Because of the limited amount of reserves in place, the efforts are focused to minimize the development costs, anticipate the production and increase the amount of recoverable reserves. In these cases the application of VASPS would benefit the overall development. VASPS produces a reduction on the wellhead flowing pressure, thus increasing the production rate and extending the field life. Furthermore, because of the, quite high efficiency of the VASPS pumping system the power involved is less than any other multiphase boosting systems, thus minimizing the platform modifications and reducing the problems associated with the power transmission. In some cases the field might also have a spare flowline capacity that can be reused, thus further reducing the development cost.

In other offshore areas the technological challenge is the development of deepwater subsea fields with facilities located in shallower waters (Fig. 2). In these cases the production profile of the subsea field is significantly influenced by the back pressure of the wells which in turn is governed by the liquid column in the risers and flowlines.