OLGA Multiphase Flow Assurance

ModelScript provides first-class, polyglot support for OLGA (High-Fidelity Dynamic Multiphase Flow Simulation). Engineers can author, simulate, lint, formally verify, and co-simulate multiphase production flowlines, deepwater catenary risers, and slug catchers directly within ModelScript's unified digital thread.

Supported File Formats

Format	Extension	Description
OLGA XML GUI Project	`.opi`, `.xml`	Complete graphical network model defining wells, pipes, chokes, separator terminals, and operational controllers.
Legacy Keyword Deck	`.key`, `.genkey`	Standard industrial keyword decks specifying flowpath geometry, branch connections, boundary conditions, and valve schedules.
PVT Flash Tables	`.tab`	Compositional and black-oil tabular fluid files for bilinear interpolation of fluid densities, gas-liquid ratios, and viscosities.
Simulation Trends	`.tpl`	High-frequency time-series trend files containing arbitrary multi-axis channel catalogs ( $P$ , $T$ , $α_{L}$ , $Q_{L}$ , $U_{G}$ , etc.).
Spatial Profiles	`.ppl`	Spatial profile snapshots along pipeline coordinate $X$ with multi-variable channels, flow regime decoding, and time scrubbing.

3-Tier Execution Architecture

ModelScript implements a 3-tier operational execution framework, accommodating headless cloud workflows, system-level co-simulation, and ground-truth industrial verification:

Rendering diagram...

1. Tier 1: Native In-WASM Drift-Flux Solver

Zero Intermediate Allocations: Lowers directly into ModelScript's DAEBuilder linear memory arena.
Transient Hydrodynamics: Solves staggered-grid mass, momentum, and energy balances coupled with Zuber-Findlay drift-flux gas-liquid slip.
Mechanistic Physics:
- Taitel-Dukler (1976) & Barnea (1987) Flow Regime Map: Exact geometric wetted perimeters ( $S_{i}, S_{G}, S_{L}$ ) and Andritsos-Hanratty wave friction enhancement.
- Pal & Rhodes (1989) Emulsion Inversion: Captures apparent viscosity peaks during water breakthrough ( $W C_{inv} \approx 42 %$ ).
- Lagrangian Slug Tracker: Propagates discrete moving slug bodies, resolving slug length distributions ( $L_{s, mean}, L_{s, 95}$ ) and riser-base severe cyclic slugging.
- Dynamic Pipeline Scraper Pig (OlgaPig): Solves pig motion ODEs ( $M d v / d t = Δ P \cdot A - F_{friction} - M g \sin θ$ ) and liquid slug sweep volume accumulation.

2. Tier 2: FMI 2.0/3.0 & SSP Co-Simulation

Exposes standard FMI input and output ports via OlgaCoSimParticipant in @modelscript/exchange:

Input Ports: choke.opening, wellhead.mass_rate, separator.pressure, ambient.temperature.
Output Ports: inlet.pressure, arrival.temperature, arrival.liquid_holdup, arrival.liquid_rate, slug.surge_volume, hydrate.subcooling, maop.margin, slug.mean_length, slug.frequency, pig.position.

3. Tier 3: Industrial OLGA Engine Orchestration

Automates invocation of local Schlumberger OLGA executable engines (olga.exe / olga-cli), dynamically ingesting binary .tpl trajectories into ModelScript's data structures for verification.

Command Line Interface (`msx olga`)

ModelScript CLI provides headless subcommands for flowline engineering:

bash

# Run 1D transient simulation and export trajectory to CSV
msx olga simulate subsea_tieback.opi --duration=3600 --out=trajectory.csv

# Pre-flight flow assurance diagnostic check
msx olga lint deepwater_riser.key

# Verify formal flow assurance limits (MAOP, Hydrate Margin, Slug Catcher Capacity)
msx olga verify flowline.genkey --maop=250 --margin=3.0 --capacity=150.0

# Generate standalone SVG bathymetry elevation profile
msx olga diagram subsea_tieback.opi --view=profile --out=bathymetry.svg

# Convert legacy keyword deck to modern XML or SysML v2 operating procedures
msx olga convert input.key --to=opi --out=project.opi
msx olga convert input.opi --to=sysml2 --out=procedures.sysml

Flow Assurance Verification & Lint Rules

ModelScript includes automated pre-flight linter diagnostics and limit verifications:

13 rules8 error5 warning Run with msx olga lint

Code	Rule	Severity	Message
`M7001`	`cfl-condition-violation`	error	Simulation timestep maxDt (`<maxDt>` s) violates convective/acoustic CFL stability limit (`<value>` s).
`M7002`	`invalid-pipe-dimensions`	error	Pipe section '`<sectionId>`' has invalid geometry: `<reason>`.
`M7003`	`missing-boundary-condition`	error	Flowpath '`<flowpath>`' has no defined `<missing>` boundary condition.
`M7004`	`steep-elevation-warning`	warning	Pipe section '`<sectionId>`' has steep inclination (`<value>`\xB0), risking hydrodynamic slugging.
`M7005`	`fully-closed-choke-hazard`	error	Choke valve '`<chokeName>`' is fully closed (opening = 0) with no active bypass route.
`M7006`	`severe-slugging-hazard`	warning	Severe slugging geometry detected on flowpath '`<flowpath>`' (seabed dip to steep riser).
`M7007`	`pig-stuck-hazard`	error	Pig '`<pigName>`' required differential pressure (`<value>` bar) exceeds maximum available (`<value>` bar).
`M7008`	`pvt-table-missing-or-invalid`	error	PVT fluid table validation error: `<detail>`.
`M7009`	`wax-deposition-risk`	warning	Fluid temperature (`<value>`\xB0C) on flowpath '`<flowpath>`' drops below Wax Appearance Temperature (`<value>`\xB0C).
`M7010`	`sand-erosion-or-dropout-hazard`	warning	Sand transport issue on section '`<sectionId>`': `<reason>`.
`M7011`	`sour-service-metallurgy-violation`	error	H2S partial pressure (`<value>` bar) on flowpath '`<flowpath>`' violates NACE MR0175 material limit (`<value>` bar).
`M7012`	`asphaltene-precipitation-hazard`	warning	Operating pressure (`<value>` bar) on flowpath '`<flowpath>`' enters Asphaltene Onset Pressure envelope (`<value>` bar).
`M7013`	`heatexchanger-parameter-violation`	error	Heat exchanger '`<hxName>`' parameter violation: `<detail>`.

Generated from languages/olga/src/errors.ts. All languages →

Dual-View SVG Visualization

ModelScript renders dual-view vector diagrams for every OLGA network:

Topological P&ID Schematic: Wells, manifolds, choke valves, flowpath pipes, and topside slug catchers.
Pipeline Elevation Bathymetry $Z (X)$ :
- High-contrast seabed-to-platform elevation profile.
- In-situ liquid holdup ( $α_{L}$ ) segment color heatmaps.
- Active discrete slug bubbles highlighted along the flowline path.
- Real-time scraper pig marker displaying traveling velocity and differential drive pressure.
- Hydrate subcooling margin callout ( $T_{fluid} - T_{hyd}$ ).

SysML v2 Operating Procedure Integration

OLGA models can be formally projected into SysML v2 packages (@modelscript/olga $\to$ SysML v2):

sysml

package Subsea_Tieback_System {
    import ScalarValues::*;

    part def FlowlineAssembly {
        attribute totalLength: Length = 4450.0 [m];
        attribute maopRating: Pressure = 250.0 [bar];
    }

    state def SubseaFlowlineOperatingProcedure {
        entry; then SteadyProduction;

        state SteadyProduction {
            doc /* Continuous production at nominal design rates */
        }
        accept ESD_Trip_Signal then EmergencyShutIn;
        accept Turndown_Command then LowTurndown;

        state EmergencyShutIn {
            doc /* Choke closed; cooldown clock active */
        }
        accept Depressurize_Command when wallTemperature > 18.0 [degC] then ControlledBlowdown;
        accept Cooldown_Timeout when shutInDurationHours >= 8.0 [hr] then ChemicalInhibitionFlushing;

        state ControlledBlowdown;
        state ChemicalInhibitionFlushing;
    }
}

State Checkpointing & Zero-Discontinuity Warm Restart

Long-duration or multi-stage pipeline flow assurance operations can be snapshot to disk and resumed with zero trajectory discontinuity:

bash

# Snapshot simulation state at completion
msx olga simulate subsea_tieback.opi --duration=3600 --checkpoint-out=t3600.rst

# Resume simulation from t=3600s
msx olga simulate subsea_tieback.opi --duration=7200 --restart=t3600.rst --out=second_stage.csv

The .rst snapshot encapsulates complete distributed states across the spatial grid:

Cell pressure $P$ , temperature $T$ , phase holdups ( $α_{L}, α_{G}$ ), and velocities ( $u_{L}, u_{G}$ )
Active Lagrangian slug states (tail/front positions, slug lengths, propagation velocities)
Scraper pig position, speed, and accumulated swept liquid volume
Machinery operating states and closed-loop controller integral accumulators

Autonomous Field History Matching & Parameter Calibration

Calibrate flowline simulation models to match production SCADA telemetry and test separator observations using bounded Nelder-Mead simplex optimization:

bash

msx olga tune subsea_tieback.opi field_telemetry.csv \
  --tune=roughness,choke-cd,heat-transfer \
  --max-evals=150 \
  --out=calibrated_model.opi \
  --report=tuning_report.md

The optimizer automatically estimates:

Effective pipe hydraulic roughness ( $ϵ$ )
Overall ambient heat transfer coefficient ( $U_{ambient}$ )
Choke discharge coefficients ( $C_{d}$ )
Well productivity index (PI) / reservoir inflow rates

Outputs comprehensive statistical goodness-of-fit metrics ( $R^{2}$ , RMSE in bar and Kelvin) and ready-to-run calibrated .opi / .genkey models.

Native In-WASM Cubic Equation of State (PR78 & SRK)

ModelScript includes a native WebAssembly cubic equation of state solver executing directly in linear memory with zero intermediate AST wrapper overhead.

Governing Thermodynamic Formulations

The general two-parameter cubic EOS takes the form:

P = \frac{R T}{v - b} - \frac{a (T)}{v^{2} + u b v + w b^{2}}

EOS Model	$u$	$w$	$Ω_{a}$	$Ω_{b}$	Temperature Correction $α (T_{r}, ω)$
Peng-Robinson (1978)	$2$	$- 1$	$0.45724$	$0.07780$	${[1 + m (1 - \sqrt{T_{r}})]}^{2}$ , with $m = 0.37464 + 1.54226 ω - 0.26992 ω^{2}$
Soave-Redlich-Kwong (SRK)	$1$	$0$	$0.42748$	$0.08664$	${[1 + m (1 - \sqrt{T_{r}})]}^{2}$ , with $m = 0.480 + 1.574 ω - 0.176 ω^{2}$

Van der Waals Mixing Rules with Binary Interaction ( $k_{i j}$ )

For multicomponent reservoir and hydrocarbon fluids:

a = \sum_{i = 1}^{N} \sum_{j = 1}^{N} z_{i} z_{j} \sqrt{a_{i} a_{j}} (1 - k_{i j}), b = \sum_{i = 1}^{N} z_{i} b_{i}

Rachford-Rice Vapor-Liquid Equilibrium (VLE) Flash

Isothermal-isobaric flash equilibrium is determined by solving the objective function for vapor fraction $β = V / F$ :

\sum_{i = 1}^{N} \frac{z_{i} (K_{i} - 1)}{1 + β (K_{i} - 1)} = 0, where K_{i} = \frac{y_{i}}{x_{i}} = \frac{ϕ_{i}^{L}}{ϕ_{i}^{V}}

Accelerated by successive substitution initialized via Wilson's heuristic $K$ -value correlations and accelerated by Cardano analytical cubic root solving.

Dense Fluid Transport Properties

Lohrenz-Bray-Clark (LBC) Viscosity: Computes high-pressure gas and liquid dynamic viscosities from reduced mixture densities $ρ_{r} = ρ / ρ_{c}$ : $[(μ - μ_{0}) ξ + 10^{- 4}]^{1 / 4} = a_{0} + a_{1} ρ_{r} + a_{2} ρ_{r}^{2} + a_{3} ρ_{r}^{3} + a_{4} ρ_{r}^{4}$
Macleod-Sugden Parachor Surface Tension: Evaluates gas-liquid interfacial tension $σ$ from parachors $P_{i}$ : $σ = {[\sum_{i = 1}^{N} P_{i} (x_{i} \frac{ρ_{L}}{M_{L}} - y_{i} \frac{ρ_{G}}{M_{G}})]}^{4}$

Command Line EOS Flash & Grid Synthesis

bash

# Evaluate multi-component P-T flash and trace saturation envelope
msx olga flash --comp="C1:0.75,C2:0.10,C3:0.08,nC4:0.04,C7:0.03" \
  --p=55.0 --t=295.15 --model=pr --envelope --out=flash_summary.csv

# Synthesize a 2D tabular PVT file (.tab) for 1D drift-flux simulation
msx olga flash --comp="C1:0.80,C2:0.10,C3:0.06,C7:0.04" \
  --model=srk --out=reservoir_fluid.tab

Active Topside Anti-Slug Closed-Loop Feedback Control

Topside choke throttling stabilizes severe cyclic slugging in deepwater catenary risers by dynamically manipulating backpressure using high-frequency subsea pressure transmitter measurements.

Rendering diagram...

Mathematical Architecture

Subsea PT Feedback Error: $e (t) = P_{sp} - P_{inlet} (t)$
Washout High-Pass Filter: Isolates oscillatory slug resonance from slow reservoir depletion: $τ_{w} \frac{d e_{f}}{d t} + e_{f} = τ_{w} \frac{d e}{d t}$
Gain-Scheduled PI Control: Compensates for non-linear choke valve flow characteristics: $K_{p} (Z) = K_{p 0} \cdot [1 + γ (1 - Z)]$ $Z (t) = Z_{baseline} + K_{p} (Z) [e_{f} (t) + \frac{1}{τ_{i}} \int_{0}^{t} e_{f} (τ) d τ]$
Physical Actuator Slew-Rate Constraints: Clamps valve motion rate to realistic hydraulic actuator speeds: $| \frac{d Z}{d t} | \leq R_{max} (e.g. 5 % / s)$
Slug Catcher Surge Override: Emergency high-liquid override closes choke if topside separator approaches liquid carryover capacity ( $V_{surge} > 0.8 V_{cap}$ ).

CLI Anti-Slug Simulation

bash

msx olga simulate subsea_catenary_riser.opi \
  --duration=3600 \
  --anti-slug \
  --slug-setpoint=52.0 \
  --slug-kp=1.5e-6 \
  --slug-ti=30.0 \
  --slug-washout=20.0 \
  --slug-choke=0.50 \
  --out=stabilized_trajectory.csv

Coupled Multi-Branch Gathering Network Transient Solver

Simultaneously models converging multi-well subsea gathering manifolds, shared export lines, and platform separators with dynamic acoustic relaxation:

Rendering diagram...

Governing Manifold Dynamic Balances

Dynamic Junction Mass Continuity: $V_{J} \frac{d (ρ_{L} α_{L})_{J}}{d t} = \sum_{in} {\dot{m}}_{L, in} - \sum_{out} {\dot{m}}_{L, out}$ $V_{J} \frac{d (ρ_{G} α_{G})_{J}}{d t} = \sum_{in} {\dot{m}}_{G, in} - \sum_{out} {\dot{m}}_{G, out}$
Mixture Thermal Energy Accumulation: $\frac{d (m u)_{J}}{d t} = \sum_{in} ({\dot{m}}_{in} h_{in}) - \sum_{out} ({\dot{m}}_{out} h_{J})$
Acoustic Pressure Relaxation: $\frac{d P_{J}}{d t} = \frac{c_{m}^{2}}{V_{J}} (\sum {\dot{m}}_{in} - \sum {\dot{m}}_{out})$

Well Trip & Flowline Shut-In Redistribution

bash

# Simulate 2-well gathering network with emergency Well 1 trip at t=20s
msx olga network gathering_manifold.opi \
  --duration=120 \
  --dt=0.5 \
  --junction-vol=8.0 \
  --trip="WELL_1:20" \
  --out=network_transient.csv

Flow Assurance CI/CD Safety Gate & 3D Bathymetry Survey

Automated Pull Request Safety Gate (`msx olga gate`)

Integrates flow assurance validation directly into automated GitHub Actions / GitLab CI pipelines:

bash

msx olga gate subsea_tieback.opi \
  --max-surge=85.0 \
  --min-hydrate-margin=3.0 \
  --max-wax="2mm" \
  --max-corrosion="0.1mm/yr" \
  --out-report=audit_gate_report.md

Generates a markdown audit report detailing compliance matrices and exits with non-zero status upon constraint violations.

3D Seabed Bathymetry Survey Ingestion (`msx olga survey`)

Ingests ROV/multibeam sonar seabed bathymetry CSV survey logs ( $E a s t i n g, N o r t h i n g, D e p t h$ ) and computes 3D pipeline curvature, span lengths, and dogleg severity:

bash

msx olga survey bathymetry_survey.csv \
  --diameter=0.254 \
  --roughness=4.5e-5 \
  --out=flowline_model.opi

Comprehensive CLI Subcommand Reference Matrix

Subcommand	Purpose	Key Arguments	Generated Artifacts
`simulate`	1D transient drift-flux simulation	`--duration`, `--dt`, `--restart`, `--checkpoint-out`, `--anti-slug`	Trajectory CSV/JSON, `.rst` state snapshots
`flash`	Native Cubic EOS (PR78/SRK) flash	`--comp`, `--p`, `--t`, `--model`, `--envelope`, `--out`	Terminal state summary, CSV, `.tab` 2D grid
`network`	Coupled multi-branch gathering solver	`--duration`, `--dt`, `--junction-vol`, `--trip`, `--out`	Composite multi-branch trajectory CSV
`gate`	Automated CI/CD safety gate audit	`--max-surge`, `--min-hydrate-margin`, `--max-wax`, `--max-corrosion`	Markdown compliance report, CI exit codes
`survey`	3D seabed bathymetry survey ingestion	`<survey.csv>`, `--diameter`, `--roughness`, `--out`	Geometrically resolved `.opi` / `.genkey`
`tune`	History matching parameter calibration	`<model>`, `<telemetry.csv>`, `--tune`, `--max-evals`	Calibrated model `.opi`, Markdown fit report
`lint`	Pre-flight flow assurance diagnostics	`<model>`, `--severity`	Diagnostic listings (`M7001`–`M7008`)
`verify`	Formal design limit verification	`--maop`, `--margin`, `--capacity`, `--min-vel`	Verification summary, constraint headroom
`diagram`	Vector SVG visualization	`--view=profile\|schematic\|pvt\|wellbore\|slug\|bathy`	Standalone publication-ready SVG files
`convert`	Model format translation	`--to=genkey\|opi\|sysml2`, `--out`	Translated model files, SysML v2 packages
`trend`	Ingest high-frequency `.tpl` trend files	`<file.tpl>`, `--channels`	Channel catalogs, time-series metrics
`profile`	Ingest spatial `.ppl` snapshot profiles	`<file.ppl>`, `--out`	Elevation SVG snapshots, holdup heatmaps
`cosim`	Multi-rate FMI/SSP co-simulation	`<subsea.opi>`, `<topside.opi>`, `--macro-step`	Synchronized boundary trajectory CSV
`fmu`	Standalone FMI 2.0/3.0 FMU packaging	`<model>`, `--fmi-version=2.0\|3.0\|both`, `--out`	Portable binary `.fmu` zip archive

OLGA Multiphase Flow Assurance ​

Supported File Formats ​

3-Tier Execution Architecture ​

1. Tier 1: Native In-WASM Drift-Flux Solver ​

2. Tier 2: FMI 2.0/3.0 & SSP Co-Simulation ​

3. Tier 3: Industrial OLGA Engine Orchestration ​

Command Line Interface (msx olga) ​

Flow Assurance Verification & Lint Rules ​

Dual-View SVG Visualization ​

SysML v2 Operating Procedure Integration ​

State Checkpointing & Zero-Discontinuity Warm Restart ​

Autonomous Field History Matching & Parameter Calibration ​

Native In-WASM Cubic Equation of State (PR78 & SRK) ​

Governing Thermodynamic Formulations ​

Van der Waals Mixing Rules with Binary Interaction (kij) ​

Rachford-Rice Vapor-Liquid Equilibrium (VLE) Flash ​

Dense Fluid Transport Properties ​

Command Line EOS Flash & Grid Synthesis ​

Active Topside Anti-Slug Closed-Loop Feedback Control ​

Mathematical Architecture ​

CLI Anti-Slug Simulation ​

Coupled Multi-Branch Gathering Network Transient Solver ​

Governing Manifold Dynamic Balances ​

Well Trip & Flowline Shut-In Redistribution ​

Flow Assurance CI/CD Safety Gate & 3D Bathymetry Survey ​

Automated Pull Request Safety Gate (msx olga gate) ​

3D Seabed Bathymetry Survey Ingestion (msx olga survey) ​

Comprehensive CLI Subcommand Reference Matrix ​

OLGA Multiphase Flow Assurance

Supported File Formats

3-Tier Execution Architecture

1. Tier 1: Native In-WASM Drift-Flux Solver

2. Tier 2: FMI 2.0/3.0 & SSP Co-Simulation

3. Tier 3: Industrial OLGA Engine Orchestration

Command Line Interface (`msx olga`)

Flow Assurance Verification & Lint Rules

Dual-View SVG Visualization

SysML v2 Operating Procedure Integration

State Checkpointing & Zero-Discontinuity Warm Restart

Autonomous Field History Matching & Parameter Calibration

Native In-WASM Cubic Equation of State (PR78 & SRK)

Governing Thermodynamic Formulations

Van der Waals Mixing Rules with Binary Interaction ( $k_{i j}$ )

Rachford-Rice Vapor-Liquid Equilibrium (VLE) Flash

Dense Fluid Transport Properties

Command Line EOS Flash & Grid Synthesis

Active Topside Anti-Slug Closed-Loop Feedback Control

Mathematical Architecture

CLI Anti-Slug Simulation

Coupled Multi-Branch Gathering Network Transient Solver

Governing Manifold Dynamic Balances

Well Trip & Flowline Shut-In Redistribution

Flow Assurance CI/CD Safety Gate & 3D Bathymetry Survey

Automated Pull Request Safety Gate (`msx olga gate`)

3D Seabed Bathymetry Survey Ingestion (`msx olga survey`)

Comprehensive CLI Subcommand Reference Matrix