An Innovative Multiphase Sampling Solution at the Well Site to Improve Multiphase Flow Measurements and Phase Behavior Characterization
Authors: Hollaender Florian , Pinguet Bruno G. , Zhang Jing Jing , Bastos Vlamir , Delvaux Emmanuel 
Published: February 2016

Representative reservoir fluid sampling and characterization has become increasingly important over the years. With exploration, appraisal and development activities moving into marginal fields and more challenging environments, accurate fluid characterization becomes more critical. This can be said for the formation tester, DST and multiphase sampling and fluid characterization environments with the most challenging area in recent years arguably being the multiphase environment. Multiphase flow meters have been accepted for several years now by the industry. Their use in permanent or well testing applications has been growing rapidly. In many cases, multiphase flow meters have replaced the separator for flow rate evaluation, but some fundamental needs from operators were not addressed properly, such as the ability to collect representative samples for phase-behavior characterization. Moreover, metering accuracies has been questionable in many cases (at very high GVF or in wet gas conditions, high pressure or /and high temperature).

This paper focuses on the Multiphase Active Sampling Device Service (MASS), a fluid sampling and analysis service that can be provided with the Vx* multiphase metering technology with the objective of collecting representative samples, isolating and analyzing each fluid phase, and providing data from the analysis as input to the Vx* acquisition software data to obtain more accurate flow rates.

The collection of phase representative samples also opens the opportunity for a full recombination PVT study to be performed using the improved recombination ratio at line conditions from the multiphase flow meter. This dedicated multiphase fluid sampling and analysis system, combined with Vx technology provides a comprehensive and accurate set of fluid properties for improved flow-rate measurement accuracy compared to conventional systems.

Overview

Multiphase flow meters (MFM) have been accepted now by the oil industry (Ref. [11], [12], [26], [28]). All MFM as other devices (Coriolis, Ultrasonic, Separators…) by construction are measuring flow rates at line conditions and therefore the use of PVT data to convert the flow rates at standard conditions is necessary (Ref. [3]). Currently, this is not addressed properly by most multiphase suppliers. Schlumberger has been a leader to bring this into the picture via the synergy of several divisions within Schlumberger being each expert in knowledge of phase behavior and sampling techniques. A generic software solution to address the needs of our customers has been proposed from Heavy Oil to Condensate (Ref. [2], [3], [28]).

The way to handle this need is very simple and until now only two approaches were possible:using published correlations to estimate oil, water and gas properties. This simple approach leads to acceptable metrological results up to 1500 psia. The upper limit can be extended to 5000 psia with great care (Ref [2], [3], [6]).1using experimental and modelled data from an Equation of State (EOS) software package using data from a PVT report. This requires a competent phase behaviour specialist to generate and control the generated fluid data (Ref [2], [3]).

A MFM could be located anywhere from the well head flowing temperature and pressure up to separator conditions or lower. Figure 1 illustrates this.

As said previously, MFM's request PVT information for conversion, this is unavoidable, and has been similarly required to obtain flow rates at standard conditions with a separator or any other devices. Figure 2 illustrates a generic flow path from line to standard conditions for any MFM and any fluid types (i.e. from Heavy Oil to Gas Condensate).