Run the OLGA transient multiphase flow simulator from Python: locate the installation, generate its PVT table and hydrate equilibrium curve from a NeqSim fluid, validate a genkey case with a rule check, launch the batch engine with the right flags, decode the engine exit code, and read .tpl trend and .ppl profile results. USE WHEN: a task must execute an OLGA case, batch or sweep OLGA runs, build a two- or three-phase OLGA PVT table or a HYDRATECURVE for HYDRATECHECK, diagnose an OLGA failure or licence error, or benchmark OLGA against the NeqSim pipeline models (TwoFluidPipe, PipeBeggsAndBrills) so that a multiphase flow result can be quoted with a known accuracy.
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Run the OLGA transient multiphase flow simulator from Python: locate the installation, generate its PVT table and hydrate equilibrium curve from a NeqSim fluid, validate a genkey case with a rule check, launch the batch engine with the right flags, decode the engine exit code, and read .tpl trend and .ppl profile results. USE WHEN: a task must execute an OLGA case, batch or sweep OLGA runs, build a two- or three-phase OLGA PVT table or a HYDRATECURVE for HYDRATECHECK, diagnose an OLGA failure or licence error, or benchmark OLGA against the NeqSim pipeline models (TwoFluidPipe, PipeBeggsAndBrills) so that a multiphase flow result can be quoted with a known accuracy.
last_verified
2026-08-15
requires
{"python_packages":[],"java_packages":[],"env":["OLGA_HOME or OLGA_ENGINE (optional; overrides installation discovery)","LM_LICENSE_FILE or SLBSLS_LICENSE_FILE (licence source)"],"network":["Reachable licence server if the licence is served rather than node-locked"]}
OLGA (SLB) is a transient one-dimensional three-phase pipe-flow simulator. It
is the industry reference for slug tracking, terrain slugging, shut-in and
restart, blowdown, liquid surge to a receiving facility, hydrate and wax
management, well clean-up and drilling hydraulics.
This skill is the execution and post-processing layer: how to find the
installed OLGA, validate a case cheaply, launch the batch engine correctly,
understand why it stopped, and read its results into Python. It does not teach
you how to build a flow-assurance model from nothing, and it never replaces a
qualified flow-assurance review.
OLGA is licensed commercial software. This skill assumes the user already has a
valid installation and licence; it only drives what is installed locally.
When to Use
A task must run an existing OLGA case and extract numbers from the results.
An OLGA case needs a PVT table or a hydrate equilibrium curve generated from a
NeqSim fluid, so that OLGA and NeqSim share one fluid and one hydrate boundary.
A parametric or sensitivity sweep must be run reproducibly rather than by hand
in the GUI.
An OLGA run failed and the exit code, log or licence state must be diagnosed.
OLGA results must be compared against NeqSim screening or pipeline models.
Do not use this skill to invent a case from scratch, to guess PVT tables, or
to interpret a transient result without a flow-assurance engineer in the loop.
Inputs
case: path to the .genkey / .key keyword file the batch engine reads. The
GUI .opi project is not an engine input — generate the genkey from it first.
pvt_file: the .tab PVT table referenced by FILES PVTFILE=, resolved
relative to the working directory. Generated from a NeqSim fluid (two- or
three-phase) so OLGA and NeqSim share one fluid.
hydrate_curve: optional hydrate equilibrium curve for HYDRATECHECK, also
generated from the same NeqSim fluid.
restart_file: optional .rsw snapshot for a restart (RESTART READFILE=ON).
parameters: mapping of {KEYWORD: {ATTRIBUTE: value}} overrides applied by
apply_parameters / set_parameter / write_variant for sweeps, e.g.
.
{"INTEGRATION": {"ENDTIME": "6 h"}}
out_dir: output directory for the run (-outDir); defaults to the case directory.
nthreads: thread count for parallel execution (-nthreads).
timeout: wall-clock limit in seconds after which the run is terminated.
olga_home / olga_engine: optional explicit installation or engine path;
otherwise OLGA_HOME / OLGA_ENGINE or installation discovery is used.
Licence environment: LM_LICENSE_FILE or SLBSLS_LICENSE_FILE, plus a
reachable licence server when the licence is served rather than node-locked.
Outputs
installations: OlgaInstallation records from find_olga_installations() —
version, root and batch-engine path for every OLGA found on the machine.
rule_check: OlgaRunResult from the -exitRC input-rule pass, with
succeeded and the engine stdout.
run_result: OlgaRunResult with case, out_dir, command, returncode,
category, code_name, description, duration_s, stdout, timed_out,
and outputs (the .out, .tpl, .ppl, .plt, .h5 files produced).
summary() returns a JSON-ready dict for results.json.
trend: TrendData from read_tpl — time vector, time_unit, and one
OlgaVariable per catalog entry with its own unit; final(name) gives the
end-of-run value.
profile: ProfileData from read_ppl — spatial profiles per variable and
time step, with positions(name) giving the matching abscissa in m.
branches: OlgaBranch geometry (x distance along the branch, y
elevation) read from the result header, needed to plot or orient a profile.
exit_code_decoding: describe_exit_code(code) → (category, name, description), resolved offline from the embedded EXIT_CODES table.
Engineering Method
OLGA solves the transient one-dimensional two-fluid (three-phase) conservation
equations along a discretized pipe network. This skill does not reimplement
that physics — it drives the licensed engine and decodes what it produced:
Discovery. Installations are located from OLGA_HOME / OLGA_ENGINE, then
from the standard install roots, and the newest version is used by default. The
OLGA-S point model (OLGAS_SLB_x64) is deliberately excluded: it is the
steady-state model other hosts link against, not the transient engine.
Cheap validation before expensive runs. Every case is first run with
-exitRC, which parses keywords, units and topology in seconds. It does not
open the PVT file and does not validate TRENDDATA / PROFILEDATA variable
names, so the result-file CATALOG is read back afterwards to confirm every
requested variable actually exists.
Execution. The engine is launched with the working directory set to the
case directory, so relative FILES PVTFILE= references resolve, with the case
file last on the command line as the engine requires.
Outcome classification. The process exit code is mapped through the table
transcribed from exit_code_lookup.exe into a category, name and first action —
separating input errors (17, 20–22), licence failures (26), PVT problems
(23/34) and numerical divergence (65–73), which need different responses.
Discretization.discretize_route turns a surveyed route into OLGA pipes
and sections using a target section length with graded first-section lengths, a
neighbour length-ratio limit, and refinement at local elevation minima where
terrain slugging accumulates liquid.
Result decoding..tpl and .ppl share one ASCII header, geometry block
and CATALOG; the data block is consumed as a single number stream using the
catalog counts (nsections + 1 values for a BOUNDARY: variable, nsections
for a SECTION: one). Units are taken per variable from the catalog, because
OLGA mixes systems in one file (PT in Pa, TM in °C).
The engine result is only as good as the case and its PVT table. This skill
gives a reproducible, decodable run — it is not a flow-assurance method and does
not replace a qualified flow-assurance review.
Installed Layout (Windows)
A standard installation looks like this — several versions can coexist:
C:\Program Files\Schlumberger\
├── Olga 2025.1.0\ <- the simulator
│ ├── OPGFramework.exe <- graphical front end
│ ├── opi.exe <- launcher associated with .opi case files
│ ├── OlgaExecutables\
│ │ ├── Olga-2025.1.0.exe <- the batch engine (what you run)
│ │ ├── OlgaOpc-2025.1.0.exe <- OPC server build
│ │ └── exit_code_lookup.exe <- decodes engine exit codes
│ ├── Data\OPG Files\ <- bundled sample-case library
│ ├── Tools\ (OLGAViewer, FluidDefTool, Multiflash, ProfileGenerator, Rocx, FEMThermViewer)
│ ├── Modules\RmoParameterStudy\ <- built-in parameter-study module (RMO)
│ └── Plugins\ (FEMTherm, O4W, PipelineEditor)
├── OLGA-S 2025.1.0\Win64\ <- OLGA-S steady-state point model (used by other hosts)
└── OLGA Namespace Explorer 7.3.x\
OLGA-S is not the transient simulator — it is the steady-state point model
that third-party process and nodal-analysis tools link against. The installer
exports its location as OLGAS_SLB_x64. Never point the batch runner at it.
User-level libraries live under %USERPROFILE%\Documents\Schlumberger\
(PipelineLibrary\*.pml, WellLibrary\*.dml); shared settings under
%ProgramData%\Schlumberger\OLGA.
File Types
Extension
Role
.opi
OLGA GUI project/case file — opened by the GUI, not by the engine
.genkey / .key
Keyword input file the batch engine actually reads
The case file must be last. The options that matter for automation:
Option
Effect
-exitRC
Run only the input rule checks, then exit. Use before every long run.
-exitID
Rule checks plus input-object initialization, then exit.
-nthreads N
Use N threads for parallel execution.
-outDir DIR
Write output files to DIR (default: the current directory).
-noout-notpl-noppl-noplt-noopc
Suppress the corresponding output.
-log FILE / -consoleLog
Write engine messages / console output to a log file.
-restorePolicy N
Override the case RESTOREPOLICY for a restart.
-keep
Keep intermediate files for debugging.
-version all
Print engine, rules-engine and flow-model build information.
-help
Print the full option list.
A successful run ends with **** NORMAL STOP IN EXECUTION **** in the .out
file and console, and exit code 0.
What -exitRC does not check. The rule check validates keywords, units and
topology — nothing else. Verified on OLGA 2025.1:
It never opens the PVT file, so a broken or missing .tab still passes.
It does not validate PROFILEDATA / TRENDDATA variable names at all. A
deliberately invented name passes with RuleCheck: OK, exit 0 and no
message, and is then silently dropped from the results. The only authority on
which variables exist is the CATALOG block of the .ppl / .tpl after a real
run — read it back and confirm every variable you asked for is there.
It does not check that the physics is posed sensibly.
Treat a passing rule check as "the file parses", never as "the case is right".
Run with the working directory set to the case directory. OLGA resolves
relative references such as FILES PVTFILE=(./fluid.tab) against the current
directory, not against the case file location. OlgaRunner.run does this for you.
Exit Codes
OLGA reports the outcome through the process exit code, grouped by category. The
full table is embedded in runner.EXIT_CODES (transcribed from
exit_code_lookup.exe list), so it can be decoded offline. The ones you will
actually meet:
Code
Name
Meaning and first action
0
OK
Normal stop.
17
CMDLINE_FAILED
Illegal command line — check flag spelling and that the case is last.
20
INIT_FAILED
Initialization failed — read the .out header.
21
RESTART_FAILED
Restart file missing or inconsistent with the case.
PVT table missing, unreachable, or outside its P/T range.
26
LICENSE_FAIL
Licence checkout failed — check LM_LICENSE_FILE and server reachability.
35–40
WAX_/PLUGIN_/ROCX_/SLUG_/TRACER_/PROCEQ_FAIL
The named submodel failed.
65–73
PT_*, TM_*, H_*
Pressure/temperature/enthalpy out of range or NaN — the solution diverged.
97–101
internal errors
Reproduce with -keep and escalate to the vendor.
Codes 65–73 mean the physics or numerics failed, not the input. Reduce MAXDT,
check for a closed boundary, an unphysical source, or a MASSFLOW boundary that
cannot be met, and re-run with a shorter INTEGRATION ENDTIME to isolate the time
of failure.
Result File Format
Both .tpl and .ppl are ASCII with the same header, then a CATALOG of
variables, then numbers:
'OLGA 2025.1.0.24773'
TIME PLOT (or PROFILE PLOT)
INPUT FILE / PVT FILES / DATE / PROJECT / TITLE / AUTHOR
NETWORK
<nbranches>
GEOMETRY ' (M) '
BRANCH
'<BRANCH NAME>'
<nsections> <- boundary points = nsections + 1
<x coordinates> <y coordinates>
CATALOG
<nvariables>
PT 'BOUNDARY:' 'BRANCH:' 'PIPELINE' '(PA)' 'Pressure'
TIME SERIES ' (S) '
<numbers>
In a .tpl, each data row is time then one scalar per catalog entry.
In a .ppl, each time step is the time value then one full profile per
catalog entry: nsections + 1 values for a BOUNDARY: variable and
nsections values for a SECTION: variable of that variable's branch.
Values wrap across lines freely, so parse the data block as one number stream and
consume it with the counts above — that is what read_tpl / read_ppl do.
The header also carries each branch's geometry: the distance along the branch and
the elevation at every section boundary. OlgaBranch.x / .y expose them, and
ProfileData.positions(name) returns the abscissa that matches a given profile
(boundaries for a BOUNDARY: variable, section centres for a SECTION: one).
Without it a profile is just a list of numbers — you cannot plot it, and you
cannot tell which end is the wellhead. Check the sign of branch.y rather than
assuming index 0 is the inlet.
Units are per variable, and they are not one consistent system. In the same
file OLGA reports PT in PA but TM in C. Always read OlgaVariable.unit
and convert from that; assuming SI throughout turns a 16.8 °C fluid into
−256 °C.
Python Usage Pattern
from olga_multiphase_simulator import (
OlgaRunner, find_olga_installations, read_ppl, read_tpl, write_variant,
)
# 1. Which OLGA versions are installed?
for installation in find_olga_installations():
print(installation.version, installation.engine)
# 2. Cheap input validation first (seconds, not hours).
runner = OlgaRunner(default_nthreads=4) # newest version by default
check = runner.rule_check("case.genkey")
assert check.succeeded, check.stdout[-2000:]
# 3. Run, then decode the outcome.
result = runner.run("case.genkey", timeout=3600)
print(result.summary()) # JSON-ready, for results.json
if not result.succeeded:
print(result.category, result.code_name, result.description)
# 4. Post-process.
trend = read_tpl(result.outputs["tpl"])
print(trend.time_unit, trend.names())
print(trend.final("PT"), trend.variables[0].unit)
profile = read_ppl(result.outputs["ppl"])
pressure = profile.profile("PT", time_index=-1, branch="PIPELINE")
distance = profile.positions("PT", branch="PIPELINE") # matching abscissa, m
Enable output on a case that has none. TRENDDATA / PROFILEDATA inside the
network components is not enough — without the global keywords OLGA writes no
.tpl / .ppl at all:
from olga_multiphase_simulator import apply_parameters, ensure_statement
text = Path("case.genkey").read_text()
text = apply_parameters(text, {"INTEGRATION": {"ENDTIME": "120 s"}})
for statement in ("TREND DTPLOT=20 s", "PROFILE DTPLOT=60 s"):
text = ensure_statement(text, statement, after_keyword="INTEGRATION")
Parametric sweep — write a variant next to the original so its relative .tab
references still resolve, then run each variant into its own output directory:
genkey.get_parameter / set_parameter edit exactly one value and leave every
other byte untouched, handle \-continuation lines, skip ! comments, and
support repeated keywords through occurrence=. ensure_statement adds a
missing global statement. None of them validate physics — always rule_check
the variant before running it.
The bundled sample library under Data/OPG Files is a good end-to-end test, but
most samples ship only as .opi GUI projects. Well/Well-CleanUp_T includes a
generated .key, so it is the one case that runs in batch without opening the
GUI first.
For large designed experiments, OLGA also ships its own parameter-study module
(Modules/RmoParameterStudy), which is the right tool when the study must be
reproduced inside the GUI.
Authoring a Case From Scratch
A hand-written genkey must use OLGA's network structure. A flat list of
NODE / BRANCH / PIPE statements is rejected with "No network components
found in the input file". The minimum viable single-line case is:
CASE AUTHOR="...", TITLE="..."
OPTIONS TEMPERATURE=WALL, COMPOSITIONAL=OFF, STEADYSTATE=ON
FILES PVTFILE="fluid.tab"
INTEGRATION ENDTIME=12 h, STARTTIME=0 s, MINDT=0.001 s, MAXDT=10 s, DTSTART=0.001 s
OUTPUT DTOUT=12 h
TREND DTPLOT=1800 s
PROFILE DTPLOT=1800 s
MATERIAL LABEL="STEEL", TYPE=SOLID, CAPACITY=500 J/kg-C, CONDUCTIVITY=45 W/m-C, DENSITY=7850 kg/m3
WALL LABEL="PIPEWALL", THICKNESS=(0.02) m, MATERIAL=("STEEL")
NETWORKCOMPONENT TYPE=FLOWPATH, TAG=FLOWPATH_1
PARAMETERS LABEL="EXPORTLINE"
BRANCH FLUID="NewFluid"
GEOMETRY LABEL="ROUTE", XSTART=0 m, YSTART=-307 m, ZSTART=0 m
PIPE LABEL=PIPE_01, ROUGHNESS=4.5e-05 m, DIAMETER=0.355 m, WALL="PIPEWALL", \
NSEGMENT=5, LSEGMENT=(738.45, 738.45, 738.45, 738.45, 738.45) m, \
XEND=3692.26 m, YEND=-294.8 m, ZEND=0 m
HEATTRANSFER LABEL="SEABED", PIPE=ALL, HOUTEROPTION=HGIVEN, \
HAMBIENT=3.2 W/m2-C, TAMBIENT=4 C, HMININNERWALL=10 W/m2-C
SOURCE LABEL="FEED", PIPE=PIPE_01, SECTION=1, TIME=0 s, \
MASSFLOW=101.1 kg/s, TEMPERATURE=40 C, GASFRACTION=1 -
INITIALCONDITIONS PRESSURE=70 bara, TEMPERATURE=40 C, VOIDFRACTION=1 -
OUTPUTDATA VARIABLE=(PT, TM, HOL, ID, USG, USL)
PROFILEDATA VARIABLE=(PT, TM, HOL, ID, USG, USL, ROG, ROHL)
TRENDDATA PIPE=PIPE_01, SECTION=5, VARIABLE=(PT, TM, HOL, USG, USL)
ENDNETWORKCOMPONENT
NETWORKCOMPONENT TYPE=NODE, TAG=NODE_INLET
PARAMETERS LABEL="INLET", TYPE=CLOSED, X=0 m, Y=-307 m, Z=0 m
ENDNETWORKCOMPONENT
NETWORKCOMPONENT TYPE=NODE, TAG=NODE_OUTLET
PARAMETERS LABEL="OUTLET", TYPE=PRESSURE, X=73845 m, Y=-300 m, Z=0 m, \
PRESSURE=70 bara, TEMPERATURE=4 C, GASFRACTION=1 -, FLUID="NewFluid"
ENDNETWORKCOMPONENT
CONNECTION TERMINALS = (NODE_INLET FLOWTERM_1, FLOWPATH_1 INLET)
CONNECTION TERMINALS = (NODE_OUTLET FLOWTERM_1, FLOWPATH_1 OUTLET)
ENDCASE
Rules learned the hard way (each one was a rules-engine rejection):
Keyword names are singular on WALL: THICKNESS=, MATERIAL= — not
THICKNESSES/MATERIALS. MATERIAL needs TYPE=SOLID and W/m-C.
SOURCE has no FLUID= key. The fluid comes from the BRANCH FLUID= label.
INTEGRATION has no NSLUG key in 2025.1.
Global statements (OPTIONS, FILES, INTEGRATION, OUTPUT, TREND,
PROFILE, MATERIAL, WALL) go before the network components;
CONNECTION statements go after them.
Iterate against -exitRC. The rules engine names the offending key and its
owner, e.g. 1019: Key not found. (FLUID for SOURCE EXPORTFEED in FLOWPATH EXPORTLINE). Treat it as the authority rather than guessing from documentation.
Posing the boundary conditions
OLGA cannot fix inlet pressure, inlet temperature and flow rate at the same
boundary the way a steady-state marching model such as PipeBeggsAndBrills can.
To reproduce a NeqSim case that specifies all three, use a SOURCE for mass flow
and temperature plus a TYPE=PRESSURE outlet node, then iterate the outlet
pressure until OLGA's computed inlet pressure matches the NeqSim specification.
A secant iteration converges in three or four runs. Do not compare an OLGA run
against a NeqSim run at a different pressure level: gas friction scales roughly
as G²/ρ, so the pressure level materially changes the answer.
The SOURCE phase split is an input, and it is easy to get wrong.GASFRACTION on a SOURCE is a mass fraction and it overrides the table
equilibrium. Writing GASFRACTION=1 feeds OLGA dry gas. If the compositional
model flashes two phases at the inlet, the two cases are then not comparable —
a rich gas at 200 bara / 40 °C can be 99.5 % gas by mole but only 97.4 % by mass,
so GASFRACTION=1 silently deletes 2.6 % of the mass as condensate. Always take
the gas mass fraction from a NeqSim flash at the source conditions:
fluid.setTemperature(313.15); fluid.setPressure(200.0)
ThermodynamicOperations(fluid).TPflash(); fluid.initProperties()
total = sum(fluid.getPhase(i).getNumberOfMolesInPhase()
* fluid.getPhase(i).getMolarMass()
for i in range(fluid.getNumberOfPhases()))
gas_mass_fraction = (fluid.getPhase(0).getNumberOfMolesInPhase()
* fluid.getPhase(0).getMolarMass()) / total
Resolve the gas phase by type (fluid.getPhaseOfType("gas")) rather than by
index whenever the fluid may contain water — a flash returns only the phases that
exist, so index 0 is not reliably the gas.
Three-phase sources: GASFRACTION and WATERFRACTION are on different bases.
This is the single most expensive input error in this skill. When a SOURCE
carries both keys:
WATERFRACTION is the aqueous mass fraction of the total stream;
GASFRACTION is the gas mass fraction of the hydrocarbon part only, i.e.
of what is left after the water is removed — not of the total.
Feeding the total-stream gas mass fraction alongside a WATERFRACTION runs
without any error or warning and produces a plausible-looking result. On a wet
gas line with 80.3 % water by mass, writing the total-basis 0.19147 next to
WATERFRACTION=0.80333 gave GAS 19.37 / OIL 81.79 kg/s where the fluid should
have delivered 98.49 / 2.67 — a 30× condensate error that still converged.
# masses from a NeqSim TPflash at the source conditions
w_water = m_aqueous / m_total # -> WATERFRACTION
w_gas_hc = m_gas / (m_gas + m_oil) # -> GASFRACTION (HC basis)
Always read the split back from the .out file before believing any
three-phase number. OLGA echoes what it actually injected in a
MASS SOURCE INFORMATION: block giving GAS / OIL / WATER in kg/s per source;
check those three numbers against the NeqSim flash to within a per cent. A run
that passed -exitRC and exited 0 proves nothing about the phase split.
Proving the two models see the same input
Before reporting any OLGA-versus-other-simulator comparison, verify each item
below with a number rather than by inspection of the input files:
Input
How to prove it
Composition
Same source file (hash it), and the PVT table reproduces a direct flash density at the inlet, mid-line and arrival states
Mass rate
SOURCE MASSFLOW equals the other model's mass rate, not just the same volumetric rate — a standard-volume rate depends on the molar mass
Inlet phase split
GASFRACTION equals the flashed gas mass fraction (of the hydrocarbons only when WATERFRACTION is also set)
Injected phase rates
The MASS SOURCE INFORMATION: block in the .out file matches the NeqSim flash in kg/s for gas, oil and water
Diameter and roughness
The set of DIAMETER= and ROUGHNESS= values in the genkey is a single value matching the other model
Length
Sum of pipe lengths equals the other model's total, including elevation
Pressure level
Inlet pressures agree after the outlet-pressure iteration
Ambient
TAMBIENT and the U-to-HAMBIENT mapping stated explicitly
A 0.01 % density agreement between the table and a direct flash is the check that
turns "same fluid file" into "same fluid".
Generating the PVT table from NeqSim
generator = jneqsim.thermodynamicoperations.propertygenerator \
.OLGApropertyTableGeneratorKeywordFormat(fluid)
generator.setFluidLabel("NewFluid") # must equal BRANCH FLUID=
generator.setPressureRange(5.0, 260.0, 41) # bara
generator.setTemperatureRange(233.15, 353.15, 31) # K
generator.run()
generator.writeOLGAinpFile("linnorm.tab")
OLGApropertyTableGeneratorKeywordFormat emits PHASE = TWO and works for any
fluid, with or without a water component.
OLGApropertyTableGeneratorWaterKeywordFormat emits PHASE = THREE and
requires a water component. It is the only water generator that works end
to end with the plain run() + writeOLGAinpFile() sequence;
OLGApropertyTableGeneratorWaterEven throws NullPointerException on
bubPLOG unless calcPhaseEnvelope() is called first, and its run() then
throws IsNaNException: molarVolumeAnalytical - compressibility factor is NaN.
setFluidLabel must match the genkey. The label written into the table has
to equal the BRANCH FLUID= (and outlet-node FLUID=) string, or OLGA cannot
bind the table to the flowpath.
For a PHASE = THREE table set OPTIONS COMPOSITIONAL=OFF. The water profile
variables are HOLWT (water holdup) and HOLHL (hydrocarbon-liquid holdup);
UHL and UWT are not valid PROFILEDATA names and are silently dropped with
a warning.
Cover the whole P/T range the line will visit, including Joule-Thomson cooling
at the arrival end; an out-of-table state gives exit 23/34 (or 68 TM_BELOW
when an iteration walks off the cold edge).
Requires NeqSim with the 2026-08 generator fixes. Older builds ignored the
filename argument (writing to a hardcoded path and swallowing the error),
wrote BUBBLEPRESSURES and BUBBLETEMPERATURES with different lengths, and
— the defect that made them unusable beyond a always-two-phase fluid — indexed
phases by array position (0 = gas, 1 = oil, 2 = water) assuming all three
existed. Because a flash returns only the phases that are present, every
single-phase grid node wrote zero for the absent phase and OLGA refused the
file with ERROR IN THE INPUT FILE: OIL DENSITY IS ZERO AT: PRES.=... AND TEMP.=.... Dry gas, dead oil and dense-phase CO₂ all failed to load, and a
two-phase fluid failed at any grid corner outside its envelope. Current builds
resolve phases by type, mark absent phases, and nearest-neighbour fill in
grid-index space; mass fractions (RS, RSW) are deliberately left at zero
where the phase is absent.
A generated table is only validated when OLGA has actually loaded it.-exitRC does not read the PVT file, so a rule check passing says nothing
about the table. The two-stage harness that works:
Scan the written file for NaN, Inf and zero density/viscosity columns.
Run a throwaway minimal case — one flowpath, a SOURCE, a TYPE=PRESSURE
outlet node, a few minutes of ENDTIME — against the table and require exit 0
plus NORMAL STOP IN EXECUTION.
Exercise the fluid types the study will actually meet: dry gas, gas condensate,
black oil, dead oil, CO₂-rich, three-phase, gas+water without oil, oil+water
without gas, and a fluid with no water component at all.
Designing the P/T grid
The grid is the model. OLGA interpolates it, so a state the grid does not bracket
is either an extrapolation or a hard stop (exit 23/34 FLUID_FAILED/PVT_FAIL,
or 65–73 when an iteration walks off an edge).
Bracket the whole excursion, not the design point. Include Joule-Thomson
cooling at the arrival end, the seabed temperature, and any blowdown or
shut-in the case will simulate. A line entering at 200 bara / 40 °C can arrive
at 60 bara / −11 °C at high rate.
Give the pressure axis headroom above the inlet. When the arrival boundary
is iterated to match a target inlet, intermediate iterates overshoot; a table
topping out at the design inlet aborts with PRESSURE ABOVE TABLE VALUES.
Use an asymmetric grid when testing a generator. A square nP × nT grid
hides transposed-index bugs.
A 41 × 31 grid over 5–260 bara and 233–353 K is a workable starting point for a
subsea gas export line.
Hydrate input to OLGA
OLGA does not compute hydrate thermodynamics. It interpolates a tabulated
equilibrium curve that the case supplies, or falls back to the Hammerschmidt
correlation — a crude inhibitor shift. If the NeqSim side of a study uses a
rigorous CPA hydrate model and OLGA is left on its own default, the two halves of
the study disagree about where the hydrate boundary is, and the disagreement is
invisible in both sets of output.
Export the curve from the same fluid that produced the PVT table
(neqsim.thermodynamicoperations.propertygenerator.OLGAhydrateCurveGenerator):
gen = jneqsim.thermodynamicoperations.propertygenerator \
.OLGAhydrateCurveGenerator(fluid) # fluid must contain water
gen.setCurveLabel("HYD")
gen.setPressureRange(10.0, 200.0, 21) # bara, linear spacing
gen.run()
gen.writeOLGAinpFile("hydrate_curve.inp")
print(gen.getHydrateCheckKeyword()) # line to paste into the flowpath
It works on a clone, so the caller's fluid keeps its state, and it drops
pressures where the hydrate flash does not converge rather than writing a zero —
a zero temperature would silently move the boundary instead of failing. Check
len(getCurvePressures()) against the number requested; a curve that lost points
has a chord across the gap.
The generated block goes at library level, before the first
NETWORKCOMPONENT, and the flowpath refers to it by label. Verified against the
OLGA 2025.1 rules engine (-exitRC → RuleCheck: OK):
The output variable is DTHYD, and its sign is the opposite of a margin.
It is a SECTION variable in C, described in the catalog as "Difference
between hydrate and section temperature", and it is T_hydrate(P) − T_fluid:
section
P, bara
TM, °C
curve T_hyd, °C
DTHYD, °C
meaning
inlet
200.1
40.0
24.9
−15.1
15.1 K of margin, safe
mid
161.6
22.6
23.5
+1.0
1.0 K inside the hydrate region
arrival
121.5
8.4
21.7
+13.4
13.4 K of subcooling, hydrate risk
So positive DTHYD is subcooling into the hydrate region and negative is the
safe margin — reading it as a margin inverts every conclusion. Those numbers
also reproduce a linear interpolation of the supplied curve to about 0.1 K, which
is the proof that OLGA is interpolating the exported curve and not modelling
hydrates itself.
Because the interpolation is linear, curve resolution is an accuracy choice, and
the error concentrates where the curve is steepest — the low-pressure end.
Measured against a 39-point reference for a wet gas over 10–200 bara:
curve points
max error over 10–200 bara
max error within a 120–200 bara band
4
4.11 K
–
6
2.55 K
0.05 K
10
1.31 K
–
20
0.48 K
0.01 K
30
0.17 K
–
A steady high-pressure line is nearly straight on this curve, so six points are
enough. A case that depressurises — blowdown, shut-in, restart, or a rate sweep
that walks the arrival down — spends its time in the steep part, where four
points cost 4 K of hydrate temperature. Span the pressures the case will actually
visit and use at least 20 points whenever the range extends below about
50 bara.
Two further rules:
Inhibited curves must be exported, not assumed. OLGA's Hammerschmidt
fallback is a correlation shift; a MEG or methanol curve from the NeqSim fluid
with the inhibitor present is the whole point of exporting.
State the curve on every hydrate result. The label, the pressure range, the
point count and the fluid it came from. A DTHYD number without them is not
reproducible.
Discretising the geometry
OLGA's batch engine does not discretise. It consumes a PIPE list that already
carries NSEGMENT and LSEGMENT. OLGA's own "discretize geometry" lives in the
Geometry editor and Tools/ProfileGenerator/ProfileGeneratorTool.exe, both of
which are GUI-only — the tool has no command line and simply opens a window if you
pass it arguments. So an automated workflow has to produce the section list itself.
Use discretize_route rather than hand-picking NSEGMENT:
from olga_multiphase_simulator.geometry import discretize_route
mesh = discretize_route(
kp, elevation, # route waypoints, m
target_section_length=500.0,
boundary_section_length=100.0, # grade toward inlet and outlet
max_adjacent_ratio=1.5, # limit the jump between neighbours
refine_low_points=True, # refine where liquid accumulates
)
print(mesh.summary())
genkey_pipes = mesh.to_genkey(diameter_m=0.355, roughness_m=4.5e-5,
wall_label="PIPEWALL")
summary() returns the numbers to record with the run: total_sections,
min_section_length_m, max_section_length_m and max_adjacent_ratio. The
ratio is enforced across pipe boundaries as well as inside a pipe, because a step
change in section length is a numerical error source, and pipe lengths follow the
route including elevation change, not the horizontal distance.
A uniform "N sections per leg" mesh is the usual shortcut and the usual mistake:
on a survey-derived route the legs are unequal, so a fixed count produces a
section-length jump at every leg boundary. Always report the mesh statistics, and
demonstrate grid independence by halving the target section length and confirming
the answer moves less than the accuracy being claimed.
Working With NeqSim
OLGA and NeqSim are complementary; use each for what it is good at.
Choose the NeqSim model against the liquid loading, not by habit. Beggs &
Brill is calibrated for no-slip liquid fractions down to about 0.01–0.02; below
that its two-phase friction multiplier is extrapolated and ΔP is over-predicted
by 30–60 % on a large-bore high-pressure gas line. Above that it is a reasonable
conservative bound. TwoFluidPipe is mechanistic and matches OLGA on ΔP for
gas-dominated flow, but its holdup runs 2–4× OLGA and its transient is not usable
for liquid-rich lines. The authority on which NeqSim model applies, and on its
current measured accuracy and open defects, is the neqsim-flow-assurance
skill — read it before quoting a NeqSim pipeline number.
Typical composition: NeqSim characterises the fluid and produces the hydrate and
wax envelopes, OLGA transports it transiently, and the OLGA arrival trends
(PT, TM, liquid rates) become the boundary condition for the NeqSim topside
model. Screen first with the community flow-regime and slug skills; escalate to
OLGA only when the transient actually matters.
When the two models disagree, audit the correlation term by term
A headline gap in ΔP or holdup is not evidence of a bug in either code, and it
is not evidence of a modelling limitation either — until the intermediate terms
have been compared. Do this before writing either conclusion:
Reimplement the steady-state correlation from the published equations in
a few dozen lines of Python, driven from the same flashed NeqSim fluid
object so composition and properties cannot differ.
Run the simulator on a short, single-increment pipe (1 m, one segment).
A long segment lets the pressure change within the increment shift the state
at which the correlation is evaluated; a 10% holdup deviation seen over a
100 m segment vanished entirely at 1 m.
Compare every intermediate, not just the answer: no-slip liquid fraction,
Froude number, the regime-boundary numbers, the horizontal holdup, the
velocity number, the inclination factor, the two-phase friction multiplier,
the no-slip friction factor, then ΔP.
Sweep the inclination as well as the horizontal case. Terms that only
appear in the inclination correction are invisible in a horizontal test, and
they are raised to powers as high as 3.8, so a small input error becomes a
large output error.
This procedure found four real defects in PipeBeggsAndBrills that a
horizontal end-to-end comparison had hidden: a pipe angle converted from
degrees to radians twice, a distributed-regime boundary tested against the
wrong limit, gravity counted twice in the liquid velocity number, and a
volume-corrected density mixed with an uncorrected one inside a single formula.
Two residual differences are expected and are not defects:
Beggs & Brill was calibrated on small-bore air/water loops, for no-slip liquid
fractions down to roughly 0.01–0.02. A large-bore high-pressure gas line
carrying a few mass per cent of condensate runs below that range, so the
two-phase friction multiplier is being extrapolated. On a 74 km 14-inch line
at a mean no-slip liquid fraction of 0.009 the multiplier reached 1.42, which
accounted for the entire difference against the transient two-fluid model:
removing it brought the correlation from 124 bar to 87 bar against OLGA's
78 bar and a single-phase Darcy check of 84 bar.
A mechanistic two-fluid code computes an interfacial friction close to
single-phase in this regime, because the condensate rides as a thin film
rather than loading the gas core.
Do not reach for the Payne et al. (1979) holdup correction to explain such a
gap without checking the numbers. The Beggs & Brill S factor is monotonically
increasing in y = λ_L / H_L² over this range, so reducing the holdup
raises the friction multiplier: 0.0795 gave 1.42, the Payne-corrected value
gave 1.51, and the two-fluid code's own holdup of 0.023 would give 2.43. The
defect is in the multiplier's applicability at low liquid loading, not in the
holdup value.
Always run an independent single-phase Darcy–Weisbach hand check at the same
pressure level as a third opinion; it tells you which of the two simulators the
discrepancy belongs to.
Use NeqSim's own two-fluid model as the fourth opinion
neqsim.process.equipment.pipeline.TwoFluidPipe is a mechanistic two-fluid
model — the same modelling class as OLGA — so it discriminates between "the
correlation is being extrapolated" and "NeqSim has a bug" without leaving
NeqSim. On the 74 km line above:
OLGA
TwoFluidPipe
Beggs & Brill
Darcy check
pressure drop, bar
78.5
81.2 (+3.4%)
125.0 (+59.2%)
77.7
arrival temperature, °C
8.4
6.8
−6.7
–
max liquid holdup
0.023
0.064
~0
–
Two mechanistic codes and a hand calculation agree; the correlation is the
outlier. That settled the question.
pipe = jneqsim.process.equipment.pipeline.TwoFluidPipe("line", inlet_stream)
pipe.setLength(length_m)
pipe.setDiameter(id_m)
pipe.setRoughness(4.5e-5)
pipe.setNumberOfSections(160) # ~450 m sections on a long line
pipe.setElevationProfile(elevations) # needs numberOfSections + 1 values
pipe.setIncludeEnergyEquation(True)
pipe.setHeatTransferCoefficient(3.0) # W/m2K
pipe.setSurfaceTemperature(4.0, "C")
pipe.run()
assert pipe.isSteadyStateConverged() # ALWAYS
assert pipe.getSteadyStateIterationsUsed() > 1 # ALWAYS
assert not pipe.isSteadyStatePressureFloorLimited() # ALWAYS
profile = pipe.getPressureProfile() # Pa
dp_bar = (profile[0] - profile[-1]) / 1e5
Three gates, not one — each catches a different silent failure:
isSteadyStateConverged(). The refinement loop is an under-relaxed
fixed-point sweep; out of iterations it returns the last iterate, which can be
an order of magnitude wrong. Raise the budget with
setSteadyStateMaxIterations(int) (default scales with the section count) or
setSteadyStateMaxWallClockTime(...) (default 300 s) and check
isSteadyStateWallClockLimited() before blaming the model.
getSteadyStateIterationsUsed() > 1. A profile reported after a single
sweep still carries the densities the sections were initialised with, and
understates the pressure drop of a gas line by roughly ten per cent. A real
solve on a 74 km line takes a few hundred sweeps.
isSteadyStatePressureFloorLimited(). Section pressures are clamped at a
1 bara floor, and that clamp is a fixed point of itself, so a line with no
deliverability would otherwise report success on a profile that does not exist.
When it is true, discard the profile and report a deliverability limit.
PipeBeggsAndBrills throws Outlet pressure is negative and OLGA aborts with
PRESSURE ABOVE TABLE VALUES on the same case — three independent confirmations
that the infeasibility is physical.
Further usage notes:
Demonstrate grid independence. A 74 km line gave 80.39 / 80.93 / 81.20 bar
at 80 / 160 / 320 sections. Budget for it: an honest solve costs roughly 16 s
at 160 sections and 48 s at 320, not the sub-second the model used to return
when it converged prematurely.
Profiles available: getPressureProfile() (Pa), getLiquidHoldupProfile(),
getGasVelocityProfile(), getLiquidVelocityProfile(),
getFlowRegimeProfile(). There is no getMixtureVelocityProfile(). The model
is correctly insensitive to the elevation datum, so absolute seabed depths may
be passed directly.
Arrival temperature agrees with OLGA to about 1.6 °C on this line (6.8 °C
against 8.4 °C). If you see a much warmer arrival temperature, you are on an
older NeqSim in which the Joule-Thomson term was silently dropped — check it
with an adiabatic run (setHeatTransferCoefficient(0)) against an isenthalpic
PH flash to the same outlet pressure, which is the exact reference.
Do not quote its holdup or inventory as a design number. Holdup runs 2–4×
OLGA (0.064 vs 0.023 dry; 0.119 vs 0.034 with 15 m³/hr free water), with a slip
ratio near 10 against OLGA's ~3. The phase bookkeeping is clean — gas, oil and
water sum to the liquid holdup exactly — so this is a slip-closure gap, not an
accounting error.
Its ΔP can be blind to the temperature field. Adding 10 MW of DEH raised
arrival temperature 22 K and left ΔP unchanged to five figures, where OLGA moved
+12.3 % and Beggs & Brill +23.4 %. Warmer gas at fixed mass rate is less dense
and ΔP ~ G²/ρ, so ΔP must rise — an unchanged ΔP is the signature of a
pressure march that is not seeing the updated densities. Treat ΔP from any case
whose temperature field changes as indicative until it moves in the right
direction.
The transient is not usable on liquid-rich lines, including severe slugging:
with every boundary held constant it leaves its own steady state, and the liquid
outlet flux collapses to zero because the phase momentum equations develop
sustained backflow. Gas-dominated lines are unaffected (0.00 bar null-test
drift). Use OLGA for liquid-rich transients.
Reference benchmark — what "good accuracy" looks like
Measured on a 73.8 km × ID 0.355 m wet-gas export line, matched fluid, rate,
phase split, roughness, U and ambient, with OLGA's arrival boundary
secant-iterated to a 200 bara inlet. Use it to sanity-check a new comparison:
a deviation far outside these bands means the inputs differ, not the models.
Case
OLGA ΔP, bar
TwoFluidPipe
PipeBeggsAndBrills
Darcy hand check
dry, 10 MSm³/d
78.51
81.20 (+3.4 %)
125.00 (+59 %)
77.72
dry, 4 MSm³/d
10.15
13.52 (+33 %)
13.59 (+34 %)
10.61
dry, 7 MSm³/d
33.60
40.23 (+20 %)
43.87 (+31 %)
34.45
+ 10 MW DEH
88.19
81.20 (ΔP blind)
154.19
–
+ 15 m³/hr free water
104.06
91.31 (−12 %)
143.94 (+38 %)
–
Compare the rate exponentn in ΔP ~ rate^n, not just the level at one
point: OLGA gives 2.14 / 2.38 / 3.12 across the sweep and Darcy 2.10 / 2.28 /
2.41. n must exceed 2 because the gas density falls along the line. A model
returning a flat n ≈ 2 reproduces one operating point while having the wrong
sensitivity — which a single-rate benchmark cannot detect.
Validation Checklist
The engine used is OlgaExecutables/Olga-<version>.exe, not an OLGA-S path.
The case was rule-checked (-exitRC) before the full run.
The working directory was the case directory, so relative .tab paths resolved.
Exit code is 0 and the .out file ends with NORMAL STOP IN EXECUTION.
The engine version and case file name are recorded with the results.
Result units were read from the catalog, not assumed.
Profiles were reported against positions(...), and the shallow end was
identified from OlgaBranch.y rather than assumed to be section 0.
Reported values are at output times that exist in the file, not interpolated silently.
The PVT table covers the full P/T range reached, and its density and
viscosity columns were spot-checked for NaNs before the run.
A generated PVT table was validated by an actual OLGA run, not by
-exitRC — the rule check never opens the table — and its fluid label
matches the BRANCH FLUID= string.
For a three-phase case, GASFRACTION was given on the hydrocarbon
basis and the MASS SOURCE INFORMATION: block in the .out file was read
back and reconciled against the NeqSim flash in kg/s.
Every requested PROFILEDATA / TRENDDATA variable was confirmed present
in the result CATALOG, because the rule check does not validate variable
names and silently drops unknown ones.
If hydrates matter, a HYDRATECURVE was exported from the same fluid as
the PVT table and referenced with HYDRATECHECK — OLGA was not left on its
Hammerschmidt fallback — and the curve spans the pressures the case
actually visits with enough points for its steep low-pressure end.
DTHYD was interpreted with the right sign: positive is inside the
hydrate region, negative is the safe margin.
The mesh came from discretize_route, its summary() was recorded, and
grid independence was demonstrated by halving the target section length.
When benchmarking against another model, every row of the input-equivalence
table was proved with a number: composition, mass rate, inlet phase split,
diameter, roughness, length, pressure level and ambient conditions.
Any headline disagreement was audited term by term against the published
correlation on a short single-increment segment, over a range of
inclinations, and cross-checked against a single-phase Darcy hand
calculation before being attributed to either code.
If a TwoFluidPipe result was used as a cross-check, all three gates
passed — isSteadyStateConverged() true, getSteadyStateIterationsUsed() > 1,
isSteadyStatePressureFloorLimited() false — and the answer was shown to be
grid-independent over at least two mesh refinements.
No TwoFluidPipe holdup, slip ratio or liquid inventory was quoted as a
design number (it runs 2–4× OLGA), and any ΔP from a case whose temperature
field changed was checked to move in the right direction.
The comparison covers more than one rate, and the rate exponent n in
dP ~ rate^n was compared as well as the level. A model that reproduces one
operating point can still have the wrong sensitivity.
A single-phase variant of the case was run first, so that friction and the
energy equation were validated before any two-phase closure was judged.
Any rate that failed to converge was shown to be a deliverability limit
(a large change in the arrival boundary barely moves the inlet) rather than
a solver problem.
A qualified flow-assurance engineer reviewed the interpretation.
Common Mistakes
Symptom
Cause
Fix
Exit 26 LICENSE_FAIL
Licence server unset or unreachable
Check LM_LICENSE_FILE; use license_environment() to see what is set
Exit 23/34 fluid failure
PVT .tab not found, or state outside the table
Run from the case directory; widen the table P/T range
Exit 17 CMDLINE_FAILED
Case file not last, or a mistyped flag
Build the command with OlgaRunner.build_command
No .tpl or .ppl produced
No global TREND / PROFILEDTPLOT keyword in the case
Add them with ensure_statement; TRENDDATA/PROFILEDATA alone is not enough
Temperatures come out near −256 °C
TM is already in C, but the code subtracted 273.15
Convert from OlgaVariable.unit; units differ per variable in one file
Profile plotted against index
The abscissa was never read
Use ProfileData.positions(name); it matches the profile length
"Wellhead" pressure looks like a downhole one
Section 0 is not always the top
Check OlgaBranch.y to find which end is shallow
Exit 65–73
Numerical divergence, not bad input
Reduce MAXDT, shorten ENDTIME to bracket the failure, check boundaries
Parser reports trailing values
The run was killed mid-write
Re-run to completion; a partial .ppl has an incomplete final time block
Editing the .opi has no effect
The engine reads the generated .genkey
Automate the .genkey; regenerate it from the GUI when the topology changes
Results changed after a version upgrade
Different flow-model build
Record -version all output alongside the results
No network components found in the input file
Flat NODE/BRANCH/PIPE list
Wrap them in NETWORKCOMPONENT ... ENDNETWORKCOMPONENT and add CONNECTION statements
1019: Key not found
Keyword name or owner is wrong for this OLGA version
Read the owner named in the message; fix and re-run -exitRC
BUBBLETEMPERATURES and BUBBLEPRESSURES need to have the same size
PVT table saturation arrays are not paired
Regenerate with a NeqSim build that writes equal-length paired arrays
NeqSim wrote no .tab and raised nothing
Older NeqSim ignored the filename argument and swallowed the write error
Verify the file exists after writeOLGAinpFile; upgrade NeqSim
OLGA and a steady-state model disagree on ΔP
Often a different pressure level, not a model difference
Match the inlet pressure by iterating the outlet boundary before comparing
OLGA carries far less liquid than the compositional model
SOURCE GASFRACTION=1 fed dry gas and overrode the table equilibrium
Set GASFRACTION to the flashed gas mass fraction
A three-phase run gives condensate an order of magnitude wrong, but converges and looks plausible
GASFRACTION was given on the total-stream basis while WATERFRACTION was also set. With water present, GASFRACTION is the gas mass fraction of the hydrocarbons only
Recompute as m_gas / (m_gas + m_oil), and reconcile the MASS SOURCE INFORMATION: GAS/OIL/WATER kg/s in the .out against the NeqSim flash before believing any number
ERROR IN THE INPUT FILE: OIL DENSITY IS ZERO AT: PRES.=... AND TEMP.=...
A NeqSim-generated table indexed phases by array position, so single-phase grid nodes wrote zero for the absent phase
Regenerate with a NeqSim build that resolves phases by type and fills absent-phase columns; dry gas, dead oil and dense-phase CO₂ all failed on the old generator
OLGA cannot bind a generated table to the flowpath
The table's fluid label does not equal the BRANCH FLUID= string
Call setFluidLabel(...) with the same label used in the genkey
A generated PVT table passed -exitRC and then failed the real run
-exitRC does not open the PVT file at all
Validate every generated table with a throwaway minimal run (source + pressure node) and require exit 0
A requested output variable is missing from the results
The rule check does not validate variable names — an unknown one passes silently and is dropped
Read the CATALOG block of the .ppl/.tpl back and confirm every variable is present. UHL and UWT are not valid names; the water and hydrocarbon-liquid holdups are HOLWT and HOLHL
OLGA and NeqSim disagree about where hydrates form
No HYDRATECURVE in the case, so OLGA used its Hammerschmidt fallback instead of the NeqSim hydrate model
Export the curve with OLGAhydrateCurveGenerator from the same fluid as the PVT table and reference it with HYDRATECHECK HYDRATECURVE="..."
A hydrate conclusion is exactly inverted
DTHYD is T_hydrate − T_fluid, so positive means inside the hydrate region, not safe margin
Re-read the sign; cross-check one section against the curve by hand
Hydrate margin is a few kelvin out at low pressure
OLGA interpolates the supplied curve linearly, and the curve is steepest below ~50 bara
Export at least 20 points when the case visits low pressure; 4 points over 10–200 bara costs 4.1 K
The hydrate curve has fewer points than requested
The generator drops pressures where the hydrate flash did not converge rather than writing a zero
Check the returned point count; a dropped point leaves a straight chord across the gap
Looking for a batch "discretize geometry" command
OLGA's discretiser is GUI-only
Build the section list with discretize_route
Section length jumps at every leg boundary
A fixed NSEGMENT per leg on unequal legs
Use a target section length and the neighbour-ratio limit
Steady-state holdup barely changes when the pipe is inclined
The correlation's inclination correction is being suppressed
Sweep the angle and compare against the published correction; a near-constant holdup means the term is broken, not small
A correlation audit shows a few per cent deviation that will not close
The reference was evaluated at the inlet but the simulator evaluated it after the pressure change across the increment
Shrink the test segment to ~1 m with one increment
Liquid-property terms disagree by ~20% for no visible reason
phase.getDensity() and phase.getDensity("kg/m3") differ when volume correction is on
Use the explicit-unit accessor everywhere; never mix the two in one formula
TwoFluidPipe ΔP is several times below a Darcy hand check on a long line
The steady-state loop ran out of iterations and returned the last iterate
TwoFluidPipe returns instantly, claims convergence, and understates ΔP by ~10 %
It converged after a single sweep, so the pressure march still carries the densities the sections were initialised with
Also assert getSteadyStateIterationsUsed() > 1. An honest solve on a 74 km line takes a few hundred sweeps and tens of seconds
TwoFluidPipe reports "converged" with the arrival pinned at exactly 1.000 bara
Every section hit the 1 bara pressure-floor clamp, which is a fixed point of itself, so the per-section change fell below tolerance
Check isSteadyStatePressureFloorLimited(); the line has no deliverability at that rate — report the limit rather than the profile
TwoFluidPipe ΔP does not move when heating or cooling is added
The pressure march is not seeing the updated densities
ΔP ~ G²/ρ must rise with temperature at fixed mass rate; an unchanged ΔP invalidates that case, not just the heating term
TwoFluidPipe liquid holdup pins near 0.85, or ΔP jumps for a tiny elevation change
Fixed in NeqSim: the initializer and the refinement loop integrated different discrete momentum balances, so terrain hydrostatics stopped telescoping
Rebuild against current NeqSim; both call sites now share marchPressure
TwoFluidPipe arrival temperature is far warmer than OLGA
Fixed in NeqSim: the Joule-Thomson term was gated behind the heat-transfer coefficient and zeroed by a 1<Cp/Cv<2 guard that a two-phase mixture never satisfies
Rebuild against current NeqSim; verify with an adiabatic run against an isenthalpic PH flash
The outlet-pressure secant runs away and OLGA exits 68 TM_BELOW
The requested rate is beyond the line's deliverability, so no arrival pressure reproduces the target inlet; the secant then drives the arrival down until Joule-Thomson cooling leaves the PVT table
Bound the secant to a physically sensible arrival pressure and report the deliverability limit instead. The tell is that a large step in the arrival boundary moves the inlet only slightly (8 bar out, 2 bar in)
Two models agree at one rate and are compared no further
A single operating point cannot separate a friction-model error from a hold-up error
Run a rate sweep and compare the exponentn in dP ~ rate^n, not just the level. For a real gas line n > 2, because the density falls as the pressure drops along the line
A steady-state model's hold-up is several times OLGA's but the pressure drops agree
On a near-horizontal, friction-dominated line the hold-up barely enters the pressure balance
Do not treat pressure-drop agreement as hold-up validation. Report the slip ratio u_g/u_l = ((1-lambda)/(1-H))*(H/lambda) alongside; wet-gas values around 3 are typical, 10 indicates a closure problem
A hold-up maximum looks alarming but the mean is fine
One terrain-trap section, not a global bias
Compare mean, median and p90, and re-run with terrain tracking off; if the median is unchanged the maximum is a single trap
SOURCE: The following keys must have equal list length
A transient SOURCE was given TIME=(0, t) but scalar TEMPERATURE/GASFRACTION
Every list-valued key on that SOURCE must have the same length as TIME; repeat the constant ones, e.g. TEMPERATURE=(40, 40) C
A two-phase benchmark disagrees and every closure is suspect at once
The comparison mixes friction, hold-up, slip and the energy equation
Build a single-phase version of the same case first (strip the heavy ends so the fluid stays one phase over the whole P/T window, and set SOURCE GASFRACTION=1). Any deviation is then friction or energy alone. Confirm the table really is single phase by checking that the OLGA HOL profile is ~1e-16
A steady-state model's deviation does not shrink with mesh refinement
It is a model or closure error, not truncation
Stop refining. Recompute the pressure drop from the model's OWN reported profile (pressure, temperature, velocity, with density from a flash at each section state). If that disagrees with what the model reports, the model's state and its pressure are mutually inconsistent
Need to know which property a marching solver actually used
Invert the reported step
rho_used = f * G^2 * dx / (2 D dP_i) for a single-phase gas line. A value that is constant along the pipe and equal to the inlet density means the properties were never fed back into the momentum balance
trend.series("PT") returns the wrong location
names() repeats a name once per TRENDDATA statement and series(name) takes the first match
Select on the full triple: scan trend.variables for (name, variable.pipe, variable.section) and index trend.values yourself
A severe-slugging comparison is reduced to one peak-to-peak number
A limit cycle is trajectory-sensitive; the instantaneous peak is not reproducible, and a run that damps out can still show a large peak from its start-up transient
Report the cycle period, the P10-P90 band and the number of cycles detected in the window alongside the peak-to-peak. A P10-P90 far below the peak-to-peak means the trace is flat with spikes, not cycling
A pipeline-riser case oscillates in OLGA but under-predicts the measured amplitude and period
The gas SOURCE sits at the flowline inlet, so the only compressible upstream volume is the flowline itself, while the facility had a gas supply or buffer volume upstream
Model the upstream volume explicitly before comparing against a facility measurement; without it the comparison is still valid between simulators, but not against the experiment
Limitations
Windows-oriented discovery; on Linux clusters set OLGA_ENGINE explicitly.
genkey editing is a targeted text rewrite, not a validating parser: it cannot
add keywords, change topology, or check units.
Only ASCII .tpl/.ppl are read; binary .plt and .h5 are not parsed here
(use OLGA Viewer or the vendor API).
Result units are reported as declared; no unit system is imposed.
No physics is interpreted, checked or corrected by this skill.
Results depend on the OLGA version and licensed modules; both must be reported.
References
OLGA user documentation shipped with the installation
(Documentation/OLGAHelp.chm, OLGAGUIHelp.chm, release notes).
Olga-<version>.exe -help and exit_code_lookup.exe list for the authoritative,
version-specific option and exit-code lists.
