OLGAS - reliability for multiphase flow
OLGAS is the steady state flow correlation based on OLGA ® - the industry standard for dynamic multiphase flow
OLGAS Using the OLGA ® model for steady state calculations OLGAS is a mechanistic point model that calculates pressure gradients, liquid hold-up and flow pattern at a specific section of pipe/tubing. OLGAS is available in both the 2- and 3-phase options. Being a reference model with superior predictive capabilities, OLGAS is the natural default flow model in all steady state applications.
The OLGAS code
The OLGAS program is a steady-state multiphase model for the calculation of pressure drop, local phase volume fractions and related information at a single point in a pipeline. The OLGAS point model is available as a FLEXlm protected dll, which may be dynamically linked to (e.g.) a steady-state pipeline/well flow simulator.
OLGAS is the superior mechanistic model that has been developed from laboratory and test data supplied by operating companies since the mid 80’s. OLGAS is continuously being developed in conjunction with the OLGA® dynamic simulator and the power in the development has never been stronger than today. OLGAS updates are typically released twice per year.
The OLGAS dll has three main interfaces defined: • 2 phase interface • 3 phase interface • 3 phase interface w/effective oil and water phase viscosity including water/oil dispersion effects There are also defined interfaces for license control, extended input and output: The OLGAS DLL is currently available on the Winnt, Win32 and Linux. Default programming languages available for interfacing is Fortran 77/90/95 and C/C++.
The correlation challenge Engineers are charged with the responsibility to find the appropriate multiphase correlation for systems - especially when: • Lack of appropriate data when a new well or pipeline is being designed. • “Industry Standard” correlations do not fit the available test data for some or all of my wells. • Different correlations are used to match similar wells. • The same correlation yield incomparable results in different application. OLGAS is developed to support the engineer in these situations. No other flow model is valid in a wider operation than OLGAS.
3 rd Party Availability Each 3rd-party supplier is afforded identical implementations of OLGAS to assure that the flow correlation results provided by one simulator will be comparable to those from another. Vendors typically offer bi-annual upgrades.
OLGAS vs Beggs & Brill 7.5” ID 1deg incl 0.70
OLGAS is available, with a product specific license, from a number of leading vendors of steady state simulators: • • • • • • • •
Aspentech - Hysys® Calsep – DepoWax® Honeywell - UniSim® Invensys - PIPEPHASE® Neotech - Wellflo® & Pipeflo® Petroleum Experts - Prosper® & GAP® Schlumberger - PIPESIM® family and others
PREDICTED LIQUID HOLDUP
MEASURED LIQUID HOLDUP
OVIP – a key driver in the OLGAS development
OVIP – with focus on wells
OVIP (OLGA® Verification an Improvement Project) is a multi-client joint industry research and development program for validation and improvement of OLGA®. Over the last decade a chain of OVIP projects have dramatically improved the performance of the point model OLGAS. The current OVIP program is supported by BP, Chevron, ENI, ExxonMobil, Petrobras, Statoil, Total and Shell.
Work on multiphase flow in vertical upward wells and risers shows that there are fundamental differences between the flow in small and large diameter pipes. In flow patterns occurring in vertical upward flow the relative importance of flow regimes is very different for small and large pipes. In the OVIP 2002-03 project, OLGA was modified to take this better into account. Also, a new correlation for entrainment in annular flow by Pan & Hanratty (2003) has been modified based on the unique high-pressure data from the SINTEF Multiphase Flow Laboratory. These enhancements have improved OLGAS predictions of pressure drop in vertical annular flow in wells and risers.
OVIP embodies by far the largest multiphase flow data collection ever assembled. Containing both experimental and field data, including gas/condenasate pipelines, lower GOR pipeline, well, and transient data, OVIP contributes to significant improvements in OLGA® and OLGAS.
Selected References • Nossen, J., Shea, R.H., and Rasmussen, J.: New developments in flow modelling and field data
Some of the recent improvements includes important phenomena in stratified flow: • Wall shear stress models • Droplet entrainment models • Gas entrainment in the liquid layer • Droplet deposition on the pipe wall
verification: Banff 2000. • Bendiksen, K., Malnes, D., Moe, R. & Nuland, S.: The Dynamic Two-Fluid Model OLGA: Theory and Application. SPE Production Engineering, May 1991, pp. 171-180 • Shea, R., Rasmussen, J., Hedne, P. and Malnes, D.: Holdup predictions for wetgas pipelines Experiments in the Well Loop at the Institute for Energy Technology (IFE)
compared. Oil & Gas Journal, May 19, 1997
SPT Group is the world leader in dynamic modelling for the oil and gas industry. Employing highly skilled professionals worldwide, SPT Group provides a combination of software and consulting services within multiphase flow and reservoir engineering. w ww.sptgroup.com
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