OLGA 6.2 Release Note

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VERSION 6.2

OLGA 6.2 Release Notes Page i

TABLE OF CONTENTS: OLGA 6.2 Release Notes

Page

1. INTRODUCTION 3

2. OVERVIEW OF THE OLGA 6.2 RELEASE 4 2.1 Version numbers 4

3. HIGHLIGHTS FOR OLGA 6.2 5 3.1 OLGA 6 is complete for engineering use 5 3.2 Extended compatibility between functionality 5 3.3 Computational performance 5 3.4 Second order scheme for mass equations 5 3.5 Improved FEMTherm 6 3.6 Time series in HEATTRANSFER and AMBIENTDATA 6 3.7 New emulsion viscosity correlations, modified emulsion/dispersion properties and

new entrainment correlation 6 3.8 Surface treatment in gas/water flow 7 3.9 New Network Component PHASESPLITNODE 7

4. OTHER CHANGES AND BUG FIXES FOR OLGA 6.2 8 4.1 Numerics 8 4.2 Steady state solver 8 4.3 Compositional/Inhibitor tracking 8 4.4 Steam / Single Component 10 4.5 Restart 11 4.6 Converter 11 4.7 Drilling 11 4.8 Hydrate 11 4.9 Source 12 4.10 Well 12 4.11 Controller 12 4.12 Process equipment 13 4.13 General 14 4.14 Input / Output 16

5. MODEL CHANGES BETWEEN OLGA 5 AND OLGA 6 20 5.1 Oil-water predictions 20 5.2 Better model consistency in OLGA 6 20 5.3 The node model 21 5.4 Simulation of two phase cases 22 5.5 Controllers 22 5.6 Separator 23 5.7 Bundle, Annulus and FEMTherm 23

6. OTHER DIFFERENCES BETWEEN OLGA 5 AND OLGA 6 24 6.1 Integration 24 6.2 Wall 24 6.3 Keywords moved to FA models 24 6.4 Heat Exchanger 24 6.5 Source 24 6.6 Valve 25 6.7 Heattransfer 26

OLGA 6.2 Release Notes Page ii

6.8 InitialConditions 26 6.9 Output Variables 26 6.10 Restart 27 6.11 Hydratecheck 28 6.12 Pig 28 6.13 Drillingfluid 28 6.14 Position 28

7. FUNCTIONALITY IN OLGA 5 NOT AVAILABLE IN OLGA 6 28

8. CONVERTING CASES FROM PREVIOUS OLGA VERSIONS 30 8.1 Converting from OLGA 5 to OLGA 6 30 8.2 Converting from OLGA 6.1 to OLGA 6.2 30

9. LIMITATIONS 31 9.1 Limitations in the steady state preprocessor 31

OLGA 6.2 Release Notes Page 3

1. INTRODUCTION

These notes accompany the release of OLGA 6.2 from SPT Group. The notes describe changes in OLGA 6.2 relative to OLGA 6.1 and also the main model changes between OLGA 5 and OLGA 6. The document should be read by all users of the program. The complete program documentation consists of the OLGA Help, OLGA GUI User Manual, Tutorial, Installation Guide and these Release Notes. The changes listed below refer to the previous main release, OLGA 6.1. The program is available on PC‟s with Microsoft Windows operating systems (Windows XP, Windows Vista and Windows 7). Several versions of OLGA may be installed in parallel. Note that you may also run several versions of the engine from one version of the GUI - please refer to the Installation Guide to learn how to configure the GUI for several engines. The customer center provides useful information about frequently asked questions and known issues. The customer center is accessible from www.sptgroup.com. Please contact SPT Group if problems or missing functionality are encountered when using OLGA or any of the related tools included in the OLGA software package. E-mail: [email protected] Telephone: +47 6389 0400 Fax: +47 6484 4500 Address: SPT Group Norway AS, P.O. Box 113, N-2027 Kjeller

http://www.sptgroup.com/


2. OVERVIEW OF THE OLGA 6.2 RELEASE

The OLGA 6.2 is an upgrade of the OLGA 6.1 simulation engine. The following modules are now available; Slug Tracking, Inhibitor tracking (MeOH, EtOH and Tracer) and Hydrate Kinetics. The FEMTherm module has been improved. All OLGA 5 modules are available in OLGA 6 except for Matlab Toolbox and the server functionality. In addition some minor functionalities are not covered. This is described in Chapter 7. Differences in OLGA 5 and OLGA 6 are described in Chapter 6. The graphical user interface (GUI) for OLGA 6 is also used for OLGA 5. Controllers, Bundles and Separators are implemented differently in OLGA 6 compared to OLGA 5. This is reflected in the GUI, see The User Manual for GUI for more information.

2.1Version numbers

The following table lists the version numbers for all programs installed with OLGA 6.2.:

Program/Tool File name Version number

OLGA GUI OLGA GUI.exe 6.2.0.67232

OLGA simulator OLGA-6.2.exe 6.2.0.67289

Geometry Editor Geometry.exe 1.6.0

Multiphase Toolkit Multiphase Toolkit.exe 6.1.0.1

FEMTherm Viewer FEMThermViewer.exe 1.0.0.1

MudTable mudtable.exe 3.3.9

OLGA Viewer OlgaViewer.exe 1.0.0.1

Rocx engine Rocx.exe 2.0.0.0

Rocx GUI RocxGUI.exe 3.0.0.0


3. HIGHLIGHTS FOR OLGA 6.2

3.1 OLGA 6 is complete for engineering use

All OLGA 5 modules except for Matlab Toolbox and the server functionality are available in OLGA 6. The following modules are completed in OLGA 6.2 compared to OLGA 6.1

Slug Tracking

Inhibitor Tracking

Hydrate Kinetics

3.2 Extended compatibility between functionality

OLGA 6.2 provides extended compatibility between key functionality compared to OLGA 5. The figure below shows the main new combinations.

3.3 Computational performance

OLGA 6 is a threaded application, developed for multi core platforms, and may give significant performance boost when run on such systems. Most modules are parallelized, e.g. Compositional Tracking and Slug Tracking.

3.4 Second order scheme for mass equations

A second order scheme for mass equations is an option which is available for all functionality. It will give more accurate results in simulations where it is important to keep sharp fronts, e.g. for rate changes, slugging and injection of inhibitors.


3.5 Improved FEMTherm

This module has been extended with the following functionality:

Easy modeling of partially buried pipelines

Varying ambient conditions around the cross section

Capability to handle phase changing materials

Trend / profile plot of temperature in the cross section

New custom dialog for FEMTherm in GUI (OLGA-05369)

3.6 Time series in HEATTRANSFER and AMBIENTDATA

A new keyword, TIMESERIES, has been implemented. This keyword can be used to define the variation in time of e.g. ambient temperature. (OLGA-01883)

3.7 New emulsion viscosity correlations, modified emulsion/dispersion properties and new entrainment correlation

Viscosity correlations: Three new emulsion viscosity correlations have been implemented. These are Barnea & Mizrahi, Woelflin and Table based model. See the user manual on how to use these. The Multiphase Toolkit has been updated accordingly.

Emulsion/dispersion properties:

An intermediate dispersion range is introduced. Between a new lower critical water cut (FWLOW, default value 0.0) and the inversion point (given by INVERSIONWATERFRAC) the flow is assumed to be a water-in-oil dispersion flowing above a free water layer. The degree of mixing of water into oil is predicted by the standard OLGA model, but the maximum fraction of the total water stream that can be mixed into the oil is given by EMAX (default value 1.0): (Volume flow of water in oil)/(Total volume flow of water) ≤ EMAX. Both parameters should be defined under the WATEROPTIONS keyword. Entrainment correlation:

A new entrainment correlation has been implemented. The effects are:

Reduced under-prediction of water holdup

Inconsistencies between gas-oil and gas-water removed

Better agreement between steady state and dynamic results because backflow is removed

Small improvements in total holdups and pressure drops (OLGA5-02275, OLGA-5213)


3.8 Surface treatment in gas/water flow

In earlier OLGA models, regardless of whether or not there was oil in the pipe, the gas-oil surface tension and oil viscosity were used in determining the wave height (gas-liquid) and the entrainment rates. Using oil properties even if there is no oil, could cause wrong holdup and pressure drop for gas-water two-phase flow. This is now fixed by using water physical properties for calculating gas/water two-phase. (OLGA-05673)

3.9 New Network Component PHASESPLITNODE

The new network component, PHASESPLITNODE, replaces the OLGA 5 BRANCH key PHASE. The PHASESPLITNODE should be used when modeling finger type slug catchers, and is located under ProcessEquipment on CaseLevel together with SEPARATOR. PHASESPLITNODE has six different terminals GAS, OIL, WATER, LIQUID, DRYGAS and MIXTURE. A FlowPath connected to a DRYGAS terminal will only have gas as inflow etc. When the volume fraction of the connected phase(s) is sufficiently low (0.01), the FlowPath inflow will be as from a NODE. If all the connected terminals are of type MIXTURE, the PHASESPLITNODE is identical to an internal node. (OLGA-03785)


4. OTHER CHANGES AND BUG FIXES FOR OLGA 6.2

4.1 Numerics

Stability Improved numerical stability for pressure driven sources with near zero pressure drop. (OLGA-05878) Stability Improved numerical handling of large water holdup gradient. (OLGA-06264) Run time step again for choke velocities above critical

After running a time step the velocities at a valve boundary is compared with the critical velocities calculated by the valve model. If the boundary velocities are larger than the critical velocities, the time step is simulated again with a new linearization. the velocities are then limited to the critical velocities. (OLGA-03394)

4.2 Steady state solver

Improved steady state preprocessor for compressor recycle Running the steady state preprocessor with a compressor and open recycle loop should give correct temperatures. (OLGA-05050) Initial interpolation of TEMPERATURE changed Interpolation of temperature for steady state preprocessor changed for SINGLEOPTIONS to not go outside limits set in input. (OLGA-4995) Improved logic for determination of flow-regime in steady-state A bug in bubble-flow made it difficult for the flow to enter slug-regime for some cases with large amount of gas. This has been fixed, giving better correspondence between steady-state flow-regime and dynamic flow-regime (OLGA-06009) More visible warning if preprocessor does not converge In addition to giving a notice in the beginning of a simulation if the preprocessor does not converge, the message is now repeated at the very end of the simulation. (OLGA-05719) Pressure driven source It is now possible to run Steady State preprocessor for cases which include a pressure driven source which is closed. (OLGA-05081)

4.3 Compositional/Inhibitor tracking

Improved pressure dependence of Heavy Oil extension of CSP viscosity model An improved pressure dependence of Heavy Oil extension of CSP viscosity model have been included in the Compositional Tracking library. (OLGA-05836)


Fixed problem for compositional tracking cases with mostly inhibitor in a section using SIMPLETHREEPHASE flash option For a composition consisting of almost pure MeOH, the simplified three-phase flash option found that a flash could be skipped. A check was implemented ensuring that for total compositions with aqueous components present in more than 99 mol%, a normal simplified flash was carried out. (OLGA5-01585) Fixed problem for compositional tracking cases with mostly inhibitor in a section using FULLTHREEPHASE flash option Using the FULLTHREPHASE flash option with a compositions consisting of almost pure MeOH, compositional tracking library found that the flash could be skipped and moved onto mutual saturation of existing phases. This lead to an infinite loop inside the compositional tracking routines. This has now been fixed (OLGA5-02015) Fixed bug for the initialization of the composition in the compositional tracking library The initialization of the composition inside the compositional tracking library, found the composition to be only gas when there was oil and gas. This required that VOIDFRACTION wrongly needed to be set to 1. This has been fixed. (OLGA5-02236) Fixed problem for compositional tracking when only small amounts of gas and oil are present Compositional tracking simulations crashed when the amount of gas and oil was very small. This was fixed by interpreting it as only an aqueous phase. (OLGA5-02242) More robust full three-phase flash routines in the compositional tracking library Full three-phase flash in compositional tracking routines exited due to non-convergence in the full three-phase flash (IER=27). To make these more robust, the maximum number of iterations has been increased. (OLGA5-02248) Updated key descriptions MEG tracking changed to Inhibitor tracking, and source valve changed to Pressure driven source. (OLGA-5037)

Problems with high pressure in Compositional Tracking fixed Problems with property tuning made water density huge, influencing the static pressure to drop. The property tuning and property limitations from OLGA 5 are implemented in OLGA. (OLGA-5144) Error in plotted mass transfer (PSI) when OPTIONS COMPOSITIONAL=ON The plotted mass transfer (PSI) was twice the actual value when OPTIONS COMPOSITIONAL=ON was used. There was only a bug in the plotted PSI. The mass transfer in OLGA is not changed. (OLGA-05325) Entrainment/deposition calculation at boundary to pressure node


The entrainment/deposition models in OLGA 5 and OLGA 6 were different for pressure nodes. OLGA 6.2 now uses the upstream gas fraction as is done in OLGA 5. (OLGA-03373) Default values for inhibitor fraction The inhibitor fractions on the branch inlet and outlet, ININHIBFRACTION and OUTINHIBFRACTION, are given default values 0.0 under INITIALCONDITIONS. (OLGA-05329) Compositional molar volumes for SIMPLETHREEPHASE In some cases we may have used wrong compositional molar volumes for SIMPLETHREEPHASE, which may have effected OLGA simulations. This has now been fixed. (OLGA-05889) Improved handling of components that are introduced into a composition Previously OLGA had some problems handling components that were introduced into a composition, for instance MEG from a source that was turned on at some point. The treatment of such issues has been introduced giving a much more physical behaviour in these cases. (OLGA-05890) Fixed normalization for thermal properties for shadow phases OLGA uses so-called shadow phases to simulate properties of phases, which only exist in dynamic flow situations (not at thermodynamic equilibrium). To get the right thermal properties (H, S and Cp) of the shadow phases, the property routines must be called with normalized composition (mole fractions summing to 1.0). By mistake the thermal properties were calculated using a non-normalized shadow phase composition, which has now been corrected. (OLGA-06574) Phase option water and liquid are now also available for black oil The key PHASE=WATER/LIQUID for keyword SOURCE and NODE can now also be used in combination with the black oil option. In previous versions PHASE=WATER/LIQUID would automatically be converted to PHASE=OIL if the black oil option was used. A warning was reported to the output file regarding this conversion. (OLGA-4846)

4.4 Steam / Single Component

Corrected calculation of the thermal conductivity and viscosity in Single Component Module An error in calculating viscosity and thermal conductivity for SINGLECOMPONENT has been fixed. This error gave an overestimation the viscosity and conductivity of the gas phase, and an underestimation of the conductivity in the liquid phase. (OLGA5-02237) Initial interpolation of temperature changed for Single Component Interpolation of temperature for steady state preprocessor changed for Single Component to not go outside limits set in keyword SINGLEOPTIONS. (OLGA-4995). Fixed problem with drying for Steam


The mass of water vapor in the gas phase was used to test if there was evaporation. The correct test should use the mass of hydrocarbon in the gas phase. This error resulted in no evaporation if the gas phase was initialized with zero water vapor. (OLGA-5088)

4.5 Restart

Improved handling of default values for the RESTART keyword When using the default settings for WRITE under RESTART, the restart file is now properly written at the interval given. (OLGA-04872)

4.6 Converter

Input converter extensions The input converter now handles conversion of MODE and MODETIME for controllers. Connections are set up for EXTSIGNCONTROLLER, EXTSETPOINTCONTROLLER, MODECONTROLLER and ACTIVATECONTROLLER. (OLGA-06204) Improved input file controller conversion from OLGA5 to OLGA6 Calculate Table controller MINSIGNAL/MAXSIGNAL form Y-values in POINT variable. (OLGA-05611)

4.7 Drilling

STDFLOWRATE / GOR available for DRILLING It is now possible to specify STDFLOWRATE / GOR when DRILLING is ON. (OLGA-3831) Negative pressure in drilling simulations Negative pressure, and pressures above table limit, are now allowed in drilling simulations. Fluid properties are extrapolated. (OLGA-05613) Leak for inhibitor and drilling fluid The leak outlet mass fractions and temperature were wrong. The isenthalpic flash is corrected. (OLGA-05314) Source standard volume flow variables and mud QWSTSOUR, QGSTSOUR and QLSTSOUR now show correct values when drilling mud is injected. (OLGA-06104) Drillingfluid components DRILLINGFLUID components are now available also when inhibitor tracking (MEG/MEOH/ETOH) is on. (OLGA-05671)

4.8 Hydrate

Output variable SAREA


SAREA is now plotted with correct unti; area per volume. (OLGA-05543) Hydrate curves with single point is allowed OLGA does no longer crash when hydrate curves with one single point are used. (OLGA-4608) HYDRATECURVE available in Library The keyword HYDRATECURVE is now available only in Library. Earlier it was also available on Flowpath level. (OLGA-5149) COLUMNHEADER in hydrate files not required Use default values (TEMPERATURE C, PRESSURE Pa) when COLUMNHEADER not given. (OLGA-5186)

4.9 Source

Pressure driven source and leak flow equation changed. The subcritical choke flow equation used in pressure driven source and leak have been modified. The inflow momentum is set to zero. This is consistent with OLGA 5. (OLGA-04617)

4.10 Well

WAXFRACTION available in WELL WELL WAXFRACTION can now be specified. (OLGA-02920) New keys CGR and WGR in SOURCE, WELL and NODE Added CGR and WGR as input variables for SOURCE, WELL and NODE. (OLGA-4972) More variables as time series in WELL It is now possible to specify GORST, HOLES, RESEXT, EXPONENTN and INJECTIVITY as a time series in WELL. (OLGA-4922)

4.11Controller

Algebraic controller Controller type Algebraic is implemented as in OLGA 5.(OLGA-05353) Branch variables for controller in OLGA GUI Branch variables are added to controllers. (OLGA-04512 )

Time step is reduced before a manual controller setpoint change Too avoid overshooting the time where a setpoint change happens, the time step is reduced. (OLGA-04264) RANGECHECK and TIMESTEPCONTROL in controllers. Controller BIAS is limited to MINSIGNAL and MAXSIGNAL Added RANGECHECK key to the Manual controller. Added TIMSTEPCONTROL key to Manual, PID, ASC, Cascade, ESD and PSV controllers. The initial output


from the controllers, BIAS, is limited to MINSIGNAL and MAXSIGNAL. (OLGA-05229) SCALER and SWITCH controller Two new controllers are available as network components; SCALERCONTROLLER and SWITCHCONTROLLER. (OLGA-05237) New controller STDCONTROLLER The new controller STDCONTROLLER converts a volumetric volume flow at standard conditions to a mass flow. The controller replaces the OLGA 5 SETPOINTVARIABLE and CONTROLLER REFCONDITION=STD. The calculated mass flow is given in the output terminal (OUTSIG). The input converter will automatically generate a STDCONTROLLER when a *.inp case file is run with OLGA 6. (OLGA-02385)

Controller sub key SETPOINTMODE Controller sub key SETPOINTMODE in OLGA 6.1 is removed. Controller MODE as defined in OLGA 5 is implemented in OLGA 6.2. (OLGA-06178, OLGA-6189)) Improved OLGA 5 to OLGA 6 input file conversion Extended input converter to handle connection from a controller output (VARIABLE CONTR) to another controllers measured value. (OLGA-05470) Manual controller Rate of change for CONTROLLER type MANUAL related to MAX and MINSIGNAL rather than 0 and 1. (OLGA-05800) Controller type LinearCombination Controller type LinearCombination is replace by controller type Algebraic. OLGA 6.1 cases need modifications. (OLGA-06727)

4.12 Process equipment

Changed heat calculations for pump OLGA does a isentropic flash to calculate the heat added to the fluid. Now this is consistent with OLGA 5. Earlier OLGA 6 assumed incompressible liquid and ideal gas compression. (OLGA-4095) INITOILEVEL and INITWATERLEVEL in the network separator INITOILEVEL and INITWATERLEVEL were not used in the network separator. The initial levels in the separator are now calculated from the given INITOILEVEL and INITWATERLEVEL. (Also when the steady-state preprocessor is used.) Added four new keys to the separator: FEEDNAME, FEEDMASSFRACTION, FEEDMOLEFRACTION and FEEDVOLFRACTION. It is possible to use these keys to specify a composition when COMPOSITIONAL=ON/BLACKOIL. (OLGA-05226) Changed static pressure for the oil outlets in separator Static pressure in the oil outlets is calculated as "g * oil_density * (oil_level - water_level)". Modified water level due to dispersion of water in oil and oil in water.


Both the static pressures and the water level is now consistent with OLGA 5. (OLGA-5227) Liquid outlets in separator The oil outlets switch to node mode (not separating) when the oil holdup is less than 0.001. The water outlets switch to node mode (not separating) when the water holdup is less than 0.001. Before both the oil and water outlet switched to node mode when either the oil or water holdup was less than 0.001. (OLGA-05284) Compressor files and tab -separation The number of mass flow points and number of speed points given in a compressor file can now be tab-separated. This was not supported earlier. (OLGA-05502) Fixed error in calculation of valve throttling OLGA used the hydraulic diameter as pipe diameter, but used the actual pipe area to calculate the valve throttling. The valve opening therefore got to small, and simulations could crash. This is now fixed. (OLGA-5544) Improved stability for Recycle/Bypass with components Improved stability for Pump and Compressor Recycle/Bypass when running with components. (OLGA-04941) Compressor instability Improved compressor flow/pressure differentials at low velocities. Stability at low velocity is therefore improved. (OLGA-05571)

4.13 General

Phase changing materials in walls The effect of phase changes has been added to the materials used for walls in OLGA. This can be used to model phase change materials used as insulation in pipe walls. It includes changes in thermal conductivity, heat capacity and the effect of latent heat of fusion. In the MATERIAL keyword, a new TYPE=PCM has been introduced. Also five new keys have been added to be used with this functionality: PHCHMAX - Upper temperature limit for phase change region PHCHMIN - Lower temperature limit for phase change region CONDMULT - Conductivity multiplier below PHCHMIN HCAPMULT - Heat capacity multiplier below PHCHMIN FUSIONMULT - Heat capacity multiplier between PHCHMIN and PHCHMAX used to model latent heat of fusion. (OLGA-05248)


CORROSION available on Flowpath level CORROSION is now available in each FLOWPATH instead of at Case level. Old OLGA 6 cases must be updated manually. (OLGA-3551) Mixture velocity now available in GUI USTOT is an old output variable, but is now also available in the GUI. (OLGA-4307) TUNING split in TUNING and SLUGTUNING A new keyword, SLUGTUNING, is added for the global slug tuning parameters. The TUNING keyword is moved from Case level FA-models to FlowPath level FA-models. (OLGA-04372) Pressure effect in pipe contraction and expansion Added default pressure loss/recovery due to pipe contraction/expansion. (OLGA-04677) Bug fixed in order of GASLIFTTABLES The order of GASLIFTTABLES does no longer influence on the simulation results. (OLGA-4777) Change of the level gradient implementation from channel geometry to pipe geometry for both steady state and dynamic simulation An error in the hydrostatic pressure in three phase flow for the dynamic equations was discovered and fixed. This fix gives more consistent result between steady state and dynamic simulations. However, due to numerical problems in the OLGA scheme the new level gradient term may give more numerical instabilities for shut in simulations. (OLGA-05192) FLUID given with TYPE=COMPLEXFLUID and FULL=YES Added fluid data test when FLUID is given with TYPE=COMPLEXFLUID and FULL=YES. Test for power law (POWERLAW) and yield stress (BINGHAM) data. The simulation will abort if the required fluid data is missing. (OLGA-04958) Pressure drop calculations Improved pressure drop calculations for laminar flow at Reynolds number < 0.1 (OLGA-04982) Consistency between the steady state and dynamic solver

OLGA steady state assumes zero velocity at the boundary and consider the acceleration from zero velocity to the velocity at the first section. This is now also implemented for the dynamic solver. (OLGA-05702)

Water wall shear stress when no water is present Previously, the water wall shear stress was set equal to the oil wall shear stress if there was no water in a pipe. Now, the value is set equal to zero instead. (OLGA-05731)


Improved handling of user-termination of batch run Pressing Ctrl-C or closing the batch-run window results in OLGA terminating execution immediately in a controlled fashion. Plot and restart files will not be updated or written. Pressing Ctrl-break will force a display of currently elapsed simulation time, execution will proceed as if not interrupted. (OLGA-05832) Interpolation between laminar and turbulent friction factor

Earlier the friction factor has been set to the maximum of the laminar and turbulent friction factor. This could overpredict the pressure drop for e.g. one phase MEG where laminar flow can be present for relatively high Reynold's numbers. In TUNING there is a functionality to set the friction factor as a function of Re: Laminar for Re lower then RELOW, turbulent for higher than REHIGH, and interpolation between RELOW and REHIGH. The default values for RELOW and REHIGH have now been set to 2300 and 3000, respectively (before the default was -1, that is, that this functionality was not used). Both RELOW and REHIGH must be within 0 and 10000, and (REHIGH-RELOW) must be at least 100. (OLGA-06272)

4.14 Input / Output

Output and restart written when user terminates interactive simulation from GUI Force TREND/PROFILE/OUTPUT/RESTART write if a simulation is terminated by the user from the GUI. Functionality only available when the case is run (interactively) through the GUI. If the case is run in batch mode, no restart etc. will be written. (OLGA-04578) Standard conditions given in keyword PVT table file are now used STDPRESSURE and STDTEMPERATURE in the PVT table file (keyword format) are the standard pressure and temperature given in PVTsim when creating the file, while GOR, GLR, STDGASDENSITY, STDOILDENSITY, STDWATDENSITY and WC (the two latter only for 3 phase table files) are the properties at this standard condition. These values have not been used in previous OLGA versions, but are now used for input (e.g. GORST in WELL) and output (e.g. QGST - Gas volume flow at standard conditions). This will give more precise results in simulations where e.g. GORST in WELL is used and the table is coarse around the standard conditions (e.g. if the two lowest pressure is 0.1 and 10 bara) since the gas mass fraction is not linear with pressure for such low pressures. A new key STDLIQDENSITY will be introduced in the next PVTsim version. This gives the standard density of liquid water and hydrocarbons (HC) in the case where a two phase PVT file is generated from a composition with water. STDOILDENSITY is the density for HC only and thus does not contain the necessary information. If the keys are not present (removed manually since always written), linear interpolation between the pressure and temperature points will be used as before. Note that the given standard pressure and temperature will be used for both input and output instead of the default values of 1 atm and 15.56 C. (OLGA5-00772)


Shear strain rate output variables The output variables SHRHL and SHRWT have been implemented for shear strain rate of oil and water film respectively. (OLGA-05635) Wrong calculation of output variable MACH The calculation of the output variable MACH is corrected. (OLGA-4765) Plot variables no longer limited to 1.0e-20 Earlier, plot variables have been set equal 1.0e-20 if their absolute value has been less than 1.0e-20. Now the variables get the value 0.0. (OLGA-4805) LSEGMENT warning removed There will be no warning issued when the LSEGMENT sum does not add up to the pipe length (SCR-04812). Fixed the calculation of plot variables MWOIL and MWWAT MWOIL/MWWAT gave only half the expected result earlier, due to bug where the sum was divided by number of fields in the phase. (OLGA-4857) Added input check for WAXDEPOSITION OLGA will return an error message if WAXDEPOSITION=ON and COMPOSITIONAL is not OFF. (OLGA-4939) Error in plot variable HTK when HINNERMIN is used The value of HTK written to plot files was previously not limited by HINNERMIN. However, the value used in the calculations was limited by HINNERMIN. (OLGA-04947) Output from bundles written to standard plot files Temperature, ambient heat transfer coefficient and geometry are now available as variables to be plotted in tpl and ppl files. (OLGA-05269) Shear strain rate output variables The output variables SHRHL and SHRWT has been implemented for shear strain rate of oil and water film, respectively. (OLGA-05636) Case with both tabulated and keyword based fluid files is now supported Previously, when fluid files with tabulated format was read after fluid files of keyword based format, OLGA terminated. (OLGA-04919) Better error message A message with location info (FLOWPATH/PIPE/SECTION) is displayed when the simulation is aborted due to P/T outside table values. (OLGA-05870) GASCST, OILCST,WATCST and LIQCST added as output variables These would be the total volume of gas, oil/condensate, water and liquid, respectively, in a branch; converted to standard conditions while accounting for


any mass transfer between phases from actual to standard conditions. (OLGA-5267) New output variables PSIHL and PSIWT PSIHL and PSIWT give the mass transfer rate (kg/m3/s) of oil and water, respectively, from liquid to vapor. They are available for TREND, PROFILE and OUTPUT. (OLGA-05582) Mixing variable types in trend data If several trend variables of different types, e.g., LIQC and TM, are specified together under a TRENDDATA key, the simulation will abort and the following error message will be given: "INPUT ERROR in keyword TRENDDATA: Variable type mismatch. Plot variables (LIQC, TM) are not of the same type." (OLGA-04897) Hydratecheck warnings Warnings about the temperature or pressure being outside the "hydrate curve" square only if DEBUG=ON and only the first time it occurs. (OLGA-04898) Viscosity and wall shear stress at t=0 The viscosity and wall shear stress are now plotted for time = 0s. Previously, these have been plotted as 0 at t=0. (OLGA-05639) Improved error message When an output variable is requested for a position in a branch where it is not defined, a more descriptive error message is given. (OLGA-05285) Branch variables with specified positions If a branch variable, e.g., LIQC, is given together with a position, the position will be ignored and an info message is printed. (OLGA-05148) Error in plotting for closed boundaries after restart Plotting flow variables for closed boundaries gave nonzero values at restart time. Only a plotting problem. (OLGA-05624) More informative error message for section out of range error. When the case contain references to illegal sections, the error message will indicate which keyword is the problem. (OLGA-05805) Min/max/mean branch variable Added MAXTMBR, MINTMBR, MEANTMBR, MAXPTBR, MINPTBR, MEANPTBR as BRANCH variables (OLGA-04967) Variable TWS Variable TWS now available in Trend plot. (OLGA-05430) HEATEXCHANGER - sub key SECTIONBOUNDARY changed to SECTION Heatexchanger is now placed inside the section and not on the boundary as in OLGA 6.1. OLGA 6.1 cases must be updated manually. An error message will be given. (OLGA5-05480)


Key DTTIME added to PROFILE keyword Functionality for setting the profile plotting frequency as a function time has been added. (OLGA-06058) Changed names of outputvariables XTSOUR, XTWELL and XTLEAK changed to ZSOUR, ZWELL and ZLEAK CGGLK, CGGWEL and CGGSOU changed to CGGLEAK, CGGWELL and CGGSOUR. These output variables are now named the same in versions OLGA 5.3.4 and OLGA 6.2. ( OLGA-06372) MEG output variables renamed to INHIB All MEG output variables are now changed to INHIB (e.g. MEGMFR is now INHIBMFR). OLGA 5 case are converted. OLGA 6 case from previous versions will now get a warning for deprecated keys. (OLGA-06576)


5. MODEL CHANGES BETWEEN OLGA 5 AND OLGA 6

This chapter goes into some detail on the changes in OLGA 6 compared to OLGA 5. This chapter concentrates on changes in the underlying models of the simulation engine.

5.1 Oil-water predictions

Three momentum equations In OLGA 6 there are three momentum equations. One for the gas field, one for continuous hydrocarbon liquid field and one for continuous water field. The different fields may include dispersions (e.g. water and oil droplets in the gas field). In OLGA 5 there are only two momentum equations; one for the gas field and one for the liquid field with a steady state momentum balance for the slip between the liquid phases. The three momentum equations in OLGA 6 will give different result from OLGA 5 when the individual inertia terms of hydrocarbon liquid and water are important. We have seen this e.g. during heavy slugging in risers where OLGA 6 is leaving more water holdup in the riser than OLGA 5. This behavior is corresponding better with what is expected. Interfacial level gradient term between oil and water In OLGA 6 there is an interfacial level gradient term between oil and water. This ensures that even in a horizontal pipe the heavier fluid will flow to the bottom of the pipe in a shut-in situation. This is also seen to give somewhat more water content in gas condensate pipelines for low flow rates compared to OLGA 5.

5.2 Better model consistency in OLGA 6

The steady state preprocessor The steady state preprocessor in OLGA 6 includes the effect of interfacial level gradients, giving more consistent results between the preprocessor and running the dynamic simulation to steady state. For gas condensate in long pipelines one may now run the case with steady state preprocessor and get the same result as in the dynamic simulation. In OLGA 5 the level gradient between gas and liquid is only included in the dynamic simulation. The steady state preprocessor in OLGA 6 considers the pressure drop due to acceleration from zero velocity at the boundary to the velocity at the first section, while the steady state preprocessor in OLGA 5 does not. Both the dynamic solver in OLGA 5 and OLGA 6 consider acceleration from zero velocity at the boundary to the velocity at the first section.


5.3 The node model

The NODE model in OLGA 6 differs from OLGA 5. In OLGA 5 the NODE is represented by the first/last section in one of the outgoing/incoming branches, but in OLGA 6 the NODE is a separate self-contained network component whose basic role is to either act as a boundary condition to the flow network or couple together an arbitrary set of flowpaths, both merge and split. The pipes connected to a node receive the masses, temperature, and pressure of the node as the boundary conditions. For separators and phase split node, the masses to the pipe boundaries are adjusted according to which fluid a pipeline receives from the node. For the flow calculations at each of the pipe boundaries connected to the node, the pipe parameters, such as diameter, inclination, roughness, are the same as the internals to the pipe. The model for internal nodes (merge/split nodes) uses more or less the same physics and the numerical methods as the sections in the pipes. Pressure, temperature and masses are calculated. Interphasial mass transfer is included in the node, but entrainment/deposition of liquid droplets are ignored. Volume in node The current implementation of internal nodes require a finite volume in the node. If no volume is specified (or given as less than or equal to zero), a default volume is calculated by OLGA based on the sizes of incoming and outgoing sections:

iii ALDV ,100min3

1max

where i is taken over all incoming/outgoing sections. It should be noted that the node does not account for heat lost to the surroundings. Treatment of momentum No momentum is carried forward from one pipe to the other pipes through the node. That is, the axial velocity external to the pipe is assumed to be zero. For cases where the velocity is high, the acceleration from zero external velocity and the velocity inside the pipe may contribute considerably to the total pressure drop over the boundary section. No pressure drop is calculated for flow through the node volume in OLGA 6. In OLGA 5, the pressure drop is calculated for the pipe sections connected to the section used as the node volume (node section). If the pipe geometry or the flow in the pipe section and the node section differ, OLGA 6 will give different pressure drops over the node compared with OLGA 5.

5.3.1 Defining internal loop in OLGA 5


A closed loop in OLGA 5 require that you need to define one split node and one merge node in order for the network solver to find a solution. This is a mathematical assumption in the solver. This is only a definition of geometry and positive flow-direction, and has nothing to do with actual flow direction. If violating this in OLGA 5 you get an error saying that you have defined an internal loop. In OLGA 6 there is no such assumptions in the solver since the internal node is more general than merge / split nodes.

5.4 Simulation of two phase cases

It is not possible to select PHASE=TWO in OPTIONS since PHASE is always THREE in OLGA 6. It is advised to use two phase PVT tables to simulate two-phase cases. If it is necessary to use three-phase PVT tables, the user should set FLASHMODEL=HYDROCARBON in OPTIONS in order to prevent the water vapor mass fraction in the PVT tables to be taken into account in the calculations. The FLASHMODEL key substitutes the WATERFLASH key in OLGA 5.

5.5 Controllers

The controllers are signal network components in OLGA 6 and need to be coupled in the controller signal network. This mainly affects how the controllers are used in the GUI and is described in the OLGA GUI User Manual. The INTERLOCKHIGH and INTERLOCKLOW keys are missing on the selector controller in OLGA 6. The selector controller in OLGA 6 is more generic than in OLGA 5. OLGA 5 have SUBCONHIGH and SUBCONLOW while OLGA 6 have the input signal terminals SUBCON_1, ..., SUBCON_N. The OLGA 5 variables HIGHLIMITVARIABLE and LOWLIMITVARIABLE are replaced with MEASRD_1, …, MEASRD_N. SUBCON_1 can act as SUBCONHIGH for MEASRD_1 and SUBCONLOW for MEASRD_2 etc. OLGA 6 uses a TRANSMITTER to measure and transmit process variables from the pipeline into the controller signal network. A transmitter is positioned on the pipeline, and can measure any trend variable in that position. One transmitter can measure several variables. The process equipment (e.g. the separator) has output signal terminals, and don‟t require a transmitter. The OLGA 5 controller key SETOFVARIABLES is removed in OLGA 6. SETOFVARIABLES refers in OLGA 5 to the SETPOINTVARIABLE key. With the introduction of controller signal network and transmitters in OLGA 6 the SETPOINTVARIABLE and SETOFVARIABLES becomes redundant. A one special use of SETPOINTVARIABLE is to convert from mass flow to standard volumetric flow rate by setting REFCONDITION = STD in the definition of SETPOINTVARIABLE. The same can be achieved in OLGA 6.2 using a STDCONTROLLER to convert from mass flow to standard volumetric flow rate and connect the output of the STDCONTROLLER to the MEASRD terminal of the flow rate controller. A second “very” special use SETPOINTVARIABLE in OLGA 5 is to make a forward reference to an OLGA controller input variable on a main object/keyword defined further down on the input file. This use of SETPOINTVARIABLE is also redundant in OLGA 6.


The VARIABLEFUNCTION key is available in OLGA 5 controllers. The ALGEBRAICCONTROLLER is introduced in OLGA 6.2 and the VARIABLEFUNCTION key is available in this controller type. The VARIABLEFUNCTION key can thus be replaced by a controller of type ALGEBRAICCONTROLLER whose output is connected to the MEASRD signal. The TABLECONTROLLER uses the controller input signal to interpolate in a TABLE. The interpolated value is used as output signal from the controller. The TABLECONTROLLER replaces the LOOKUP function with controllers on TABLES in OLGA 5. If a CONTROLLER in OLGA 5 measures a flow variable from a SOURCE, WELL or LEAK, the absolute value of the flow variables will be used. This is not the case in OLGA 6. Ex. Control a negative "GTLEAK" with a PID controller by manipulating the LEAK flow area. OLGA 5: Controller set point must be positive and amplification must be negative. OLGA 6: Controller set point must be negative and amplification must be positive.

5.6 Separator

In OLGA 6 the separator is a fluid flow network component and is handled as a special node model. In OLGA 5 one could set up a single train separator by modifying the properties (keys) of the separator. The OLGA 6 separator is more generic and one needs to add flow paths to model the drain and drain valve. See the OLGA 6 GUI User Manual for further details on how to set up a separator in OLGA 6. The OLGA 6 Conversion guide explains how to convert OLGA 5 cases with separators to OLGA 6.

5.7 Bundle, Annulus and FEMTherm

The thermal capabilities of the Bundle, Annulus and FEMTherm modules are in OLGA 6 available through three network components: the FluidBundle, the Annulus and the SolidBundle. A SolidBundle is a bundle with FEMTherm calculations (conduction) and a FluidBundle is a convective bundle. The functionality follows OLGA 5, but the LINE and CROSSOVER is more advanced in OLGA 6. In OLGA 5 a LINE has constant material properties, and there is no computation of pressure drop or flow. In OLGA 6 the equivalent of a LINE is a flowpath with LINE=YES. For such flowpaths single phase flow is assumed, and pressure drop and flow is computed in addition to the temperature. The equivalence of CROSSOVER is a pressure node with PARAMETER LINE=CROSSOVER. Such nodes have two connection points, and a pressure boost has to be given for the pressure difference between the two.

OLGA 5 cases containing bundles can be imported into OLGA 6, but such cases will need more information from the user in order to be „Ready to simulate‟. This is due to the more accurate lines and crossover couplings in OLGA 6. See the OLGA 6 Conversion Guide for more details.


6. OTHER DIFFERENCES BETWEEN OLGA 5 AND OLGA 6

This chapter describes differences in process equipment, how to set up models and differences in keywords and keys.

6.1 Integration

MAXDT and MINDT has default values (1 and 0.001 respectively) in OLGA 6. They have no default values in OLGA 5. STARTTIME is a required key in OLGA 6 unless it is a restart case. If it is a restart case and STARTTIME is missing, the last restart time in the restart file will be used.

6.2 Wall

INNERDIAMETER in OLGA 6 must match pipe diameter where the wall is used. In OLGA 5 the pipe diameter can be different from inner diameter.

6.3 Keywords moved to FA models

FA models keywords are moved from Case level to Flow path level. The keys on these keywords are then only applied to the local flowpath. This applies to TUNING, CORROSION, HYDRATECHECK, HYDRATEKINETICS and WAXDEPOSITION. In order to apply the same data to all flowpaths, right-click the keyword and select "Duplicate to all" and use "Global instances" to view all instances of a keyword. SLUGTRACKING is available both on Case level and Flowpath level in OLGA 6. DTCONTROL is available on both Flowpath and Case level in OLGA 6. In OLGA 5 it is

only available on Case level.

6.4 Heat Exchanger

The OLGA 6 heat exchanger has two modes; SETPOINT and CONTROLLED. In SETPOINT mode the heat exchanger is similar to the OLGA 5 heat exchanger. By setting TYPE=CONTROLLED the connected controller signal will scale the given CAPACITY. I.e. the heating/cooling is regulated by the controller signal. A heat exchanger with TYPE=CONTROLLED does not require a controller to be connected as the default controller signal is zero. That is; no heating/cooling.

6.5 Source

In OLGA 6 a new key, SOURCETYPE, is used to distinguish between PRESSUREDRIVEN, MASS and TRACER sources.


The pressure driven sources in OLGA 5 are not included in the preprocessor while they are in OLGA 6. For a pressure driven source, OLGA 6 accounts for the gas compressibility for subcritical flow through the source valve, whereas OLGA 5 does not. This means that OLGA 6 gives the transition between critical and subcritical flow that is consistent with the compressibility of the fluid. The fluid compressibility is an important factor influencing subcritical flow when the pressure drop is close to the critical flow condition. A Tracer source is defined in the SOURCE keyword, whereas in OLGA 5 there is a separate TRACERSOURCE. The source of type TRACER cannot be controlled by a CONTROLLER in OLGA 6.

6.6Valve

The choke models in OLGA 5 and OLGA 6 are the same, but the implementation of the model is different. When OLGA 5 crosses from sub-critical to critical flow, the time step will be run again, fixating the flow at critical flow. The OLGA 6 choke model doesn‟t require the time step to be run again. The following modifications have been made to the choke model:

The pressure drop is not only linearized with regard to change in the total mass flowrate but also with regard to changes in the upstream pressure, downstream pressure and phase fractions. This modification should give better transient induced by pressure drop changes due to the upstream phase fractions change.

The linearized pressure drop coefficient to the total mass flowrate is not relaxed from previous time step to the current time step as in OLGA 5. This modification should give more timely response to changes in the valve opening and flowrate changes.

The pressure recovery after the choke is considered. This may result in smaller pressure drop through the choke compared with OLGA 5.

For the Henry-Fauske option, in the iterative procedure for finding the critical pressure throat pressure, the flashing term is calculated at the new throat pressure for a new iteration. In OLGA 5, the flashing terms from all previous iterations are summed up and averaged and then used for the next iteration. Averaging reduces the effects of flashing term on the critical flow for under-saturated liquid flow. The pressures in some of the iterations are above saturation pressure and in other steps of the iterations are below the saturation pressure. Averaging in such cases give lower value of the flashing term which in turn results in higher critical flowrate. The iteration method of OLGA 6 is more rigorous. OLGA 6 has default values for opening (1) and time (0), OLGA 5 has not. Further, it is not allowed to position a valve at the first section boundary in a flowpath next to a closed node in OLGA 6. OLGA 5 does not have this restriction.


6.7 Heattransfer

For interpolation of values with an IN/OUT key pair (e.g. IN/OUTTAMBIENT), one can supply either a single pipe by label or number (e.g. PIPE="PIPE-1", PIPE=1), or supply a continuous pipe range by number (e.g. PIPE=(1-3)). Interpolation is only possible for whole pipes (e.g. section cannot be specified for partial pipes). For SECTIONWISE interpolation (e.g. TAMBIENT), a (non-continuous) list of pipes can be given by either label or number as long as the given key value is a single number. OLGA 6 also allows pipewise interpolation of HAMBIENT with the use of two new keys: IN/OUTHAMBIENT.

6.8InitialConditions

In networks containing a split node, the conversion from OLGA 5 to OLGA 6 cannot fully cope with the mass flow initial conditions. In a pipe with N sections, one should give the mass flow at the N+1 section boundaries. However, due to the treatment of nodes in OLGA 5, the last section boundary in a pipe leading up to a split node is discarded, i.e., only N mass flow points needs to be specified. When loading and converting such a case into OLGA 6, the state will be "Ready to simulate", however when running the simulation a runtime error will occur: "INITIALCONDITIONS: Number of MASSFLOW points are not equal to number of section boundaries in FLOWPATH ..." This error message is due to the fact that the input converter does not recognize a branch leading up to a split node in order to, if required, add an extra mass flow point to get the N+1 initial conditions. The user therefore needs to add this number. In order to get an input file compatible with both OLGA 5 and OLGA 6, N+1 mass flow points should always be given. Adding mass flow for the last section boundary will not affect the OLGA 5 simulation since it will be ignored when running the simulation.

In OLGA 5, if more than one pipe is specified in the same initial condition statement, all the pipes have the same inlet and outlet pressure and interpolation is carried out for sections in each of the individual pipes using the distance relative to the inlet of each of the pipe. In OLGA 6, if more than one pipe is specified in the same initial condition statement, the interpolation is carried for each section using the distance of the section relative to the first pipe in the pipe list. The distance of the sections are calculated by summing the section length of pipes in the same sequence as in the pipe list.

6.9 Output Variables

Most OLGA 5 output variables are available in OLGA 6. The exceptions are listed in olga5_only.xls.


Some new variables are implemented in OLGA 6, they are listed in olga6_only.xls. The branch variables are not enabled for output to the .out-file in OLGA 6. There are some differences between OLGA 5 and OLGA 6 with respect to which variable groups which can be combined in one TRENDDATA or PROFILEDATA statement. PLOT The PLOT keyword is used the same way as in OLGA 5 except that OLGA 5 may have multiple PLOT keywords. OLGA 6 can only have one PLOT keyword and this causes problems in conversion of such cases. (please refer to the OLGA 6 Conversion Guide)

6.10 Restart

In OLGA 5 the restart file (.rsw) contains most of the data covered in the input file, making it possible to use a very short input file in the restart run. In OLGA 6 the input file needs to be fully specified in a restart run. The restart file format used in OLGA 5 is not compatible with the one used in OLGA 6, i.e. the restart files must be reproduced with OLGA 6 before they can be used in a restart run. However, OLGA 6 is restart compatible with earlier versions of OLGA 6. The key READFILE is new in OLGA 6 - please refer to the OLGA 6 User Manual for a description of how to use it. In a restart run OLGA 6 will verify that the restart file and the input file are compatible, meaning that only certain keywords and keys are allowed to change between the original and the restart run. In particular the following rules are enforced:

The collection of MATERIAL, WALL and PIPE keywords must be identical in the original and the restart run.

All NODEs must be identical, although boundary nodes are allowed to change type.

All connections must be unchanged.

The key COMPOSITIONAL in the OPTIONS keyword cannot change.

Other discrepancies that might be significant are reported as info messages when the restart case is started.


6.11 Hydratecheck

Some of the HYDRATECHECK keys have been moved to the new HYDRATECURVE keyword. This split has been made due to better separation of concepts and ease of use. HYDRATECURVE contain keys that describe a specific hydrate formation curve. HYDRATECHECK contain keys for setting up hydrate formation checking in a single flowpath based upon one or more HYDRATECURVEs. HYDRATECURVE is available in the Library and each one can be referenced by HYDRATECHECKs in different flowpaths.

6.12 Pig

PLUG and PIGTRACKING is merged into a single keyword PIG. The slug tracking method is used to track the pig and the fluids ahead and behind the pig. The liquid/gas slip ahead the pig is not modified by the pig, resulting in sharper change of liquid holdup around the pig.

6.13 Drillingfluid

The drilling fluid functionality is equivalent to the one in OLGA 5 except for one feature: With OLGA 6.2 MEG is tracked as well as the production fluid, the drilling fluids and the cuttings.

6.14 Position

ABSPOSITION can be specified (read only in OLGA 5 GUI)

7.FUNCTIONALITY IN OLGA 5 NOT AVAILABLE IN OLGA 6

Some of the functionality in OLGA 5 is not available in OLGA 6. The list below shows functionality that is planned not to implement in OLGA 6 at all.

Functionality Reason for not including in OLGA 6

Soil module This functionality is covered by FEMTherm.

SHUTIN This keyword is used in OLGA 5 to avoid numerical flow regime flipping during shutdown operations. This keyword is not required in OLGA 6.

DELETEPREVIOUS in PROFILE, TREND and OUTPUT

In OLGA 6 the input needs to be fully specified also for restart cases (see section 7.14), i.e. the DELETEPREVIOUS key is not needed anymore.

PLUG TYPE=LONG, HYDRATE and HEAVYSSH

PRINTINPUT Defines the input data which will be printed in the output file.

REROUTE The possibility now to model closed loops covers the origin


of this keyword.

WAXDEPOSITION The following keys are not implemented in OLGA6: WAXVISC_ONLY, USE_TABLE_EQ_WXVFR, CALC_SHEARRATE and SHEARRATE.

VALVE

In OLGA 5, the critical flow models FROZEN, HENRYFAUSKE, and SUBCRITICAL exist whereas in OLGA 6 only the first two models are available. When converting an OLGA 5 case using SUBCRITICAL to OLGA 6, the critical flow model is set to FROZEN.

The following functionality is not implemented in OLGA 6 but may be included in later versions depending on feedback from the users.

Keyword Key(s)

INTEGRATION CPULIMIT

OPTIONS AXIALHEAT

OPTIONS POSTPROCESSOR

GEOMETRY/PIPE EWSTART, NSSTART, TVDSTART in GEOMETRY and EWEND, NSEND, TVDEND in PIPE

DTCONTROL SOUND_CFL, GRADPRESSURE, CFLFACTOR, PREFACTOR

The following functionality will be included in future versions of OLGA 6.

Functionality not included in OLGA 6

Drilling - This functionality is primarily used for training simulators, it will be included in a future OLGA 6 version.

Tuning – Bundle tuning (BNDTUNING) is not implemented in OLGA 6.

Bit nozzles

SEPARATOR - To avoid that the water/oil levels get too low (become zero) in the water/oil-drainage lines of a separator when the valves on the oil and water linear are not controlled, OLGA 5 has functionality that limits the velocity when the liquid levels in the separator approaches zero. This functionality is not implemented in OLGA 6.

Functionality for handling source-source cases in steady state preprocessor is not implemented for network

Pig and Wax - The combination of WAX and pigging is not implemented in OLGA 6

Complex fluid – The slurry plug extension to the complex fluid model in OLGA 5 is not implemented in OLGA 6. The following keys are not implemented in the FLUID keyword in OLGA 6: PARTICLESETTLE, WATERCUT, MAXPARTCONC, HYDTEMP, MAXCONCK_G_EMUL

WAXDEPOSITION – The following keys are not implemented in OLGA6: WAXVISC_ONLY, USE_TABLE_EQ_WXVFR, CALC_SHEARRATE and SHEARRATE.


8. CONVERTING CASES FROM PREVIOUS OLGA VERSIONS

When you open old cases in the OLGA 6 GUI they will be converted to the OLGA 6 format. Most cases will be converted automatically, but some need additional manual steps to be „runable‟ in OLGA 6. This is mainly cases with bundles and separators. Please refer to the OLGA 6 Conversion Guide available from the start menu (Start menu All Programs SPT Group OLGA 6.2 Documentation). There is only minor automatically converting of cases from OLGA 6 to OLGA 5.

8.1 Converting from OLGA 5 to OLGA 6

8.1.1Pipes

Roughness may not be defined for all pipes on a flowpath in OLGA 5. This must be converted manually when converting from OLGA 5 to OLGA 6

8.1.2 Single train separator

OLGA 6 does not have the single train separator functionality; hence cases with single train separators will be converted to a case with multi train separator in OLGA 6. Often such cases will not converge in the steady state pre-processor, and therefore it is recommended to use initial conditions (OPTIONS STEADYSTATE=OFF) for such cases.

8.2 Converting from OLGA 6.1 to OLGA 6.2

The input structure in OLGA 6.1 and OLGA 6.2 is to most extent the same. However, there are a few exceptions listed below. Pig If loading an OLGA 6.1 case into OLGA 6.2 it may be necessary to delete the TRENDATA keyword and add it again in order to set the PIG label correctly in the section “Slug and pig”. LinearCombination Controller The LinearCombination controller which was implemented in OLGA 6.1 is now substituted by the ALGEBRAIC controller available in OLGA 5. There is no automatically converting of cases with LinearCombination controllers.

Keywords moved to flowpath level The CORROSION and TUNING keywords are moved from Case level to Flowpath level. When importing a case with CORROSION or TUNING from OLGA 6.1 into OLGA 6.2, the keywords must be defined again, manually.


9. LIMITATIONS

9.1 Limitations in the steady state preprocessor

The steady state preprocessor may not always converge to the correct solution. Below is a list of case-types where this may happen:

- Cases with separators - Cases with pipelines that include pumps and compressors - Cases that include pipelines with very low (~zero) flow rate (closed valves?) - Cases with a split into pipelines with very different outlet pressures - Cases with injection wells - The preprocessor is not robust with respect to large networks - The preprocessor is not robust with respect to negative sources in networks

It is recommended to use INITIALCONDITIONS and OPTIONS STEADYSTATE=OFF for cases which the preprocessor handles poorly.

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