VMGSim: Rigorous Upstream and Midstream Process Simulation for Oil & Gas Facilities
VMGSim, developed by Virtual Materials Group (VMG), is a high-fidelity process simulator purpose-built for upstream and midstream oil and gas applications. Unlike general-purpose simulators that treat hydrocarbon systems as an afterthought, VMGSim was architected from the ground up around the thermodynamic complexity of reservoir fluids, natural gas processing, and LNG production. This article examines VMGSim's core capabilities, its equation-of-state (EOS) framework, and practical workflows for facility engineers.
Thermodynamic Engine: Beyond Standard Cubic EOS
The foundation of any process simulator is its thermodynamic package. VMGSim ships with the VMG Thermo library, which extends classical cubic equations of state (Peng-Robinson, Soave-Redlich-Kwong) with proprietary mixing rules and binary interaction parameter (BIP) regression tools optimized for C1–C10+ hydrocarbon systems.
Key differentiators include:
- Generalized Cubic Plus Association (CPA): Handles polar components such as methanol, glycols (MEG, TEG), and water in equilibrium with hydrocarbons — critical for hydrate inhibition and dehydration unit design.
- PC-SAFT: Perturbed-Chain Statistical Associating Fluid Theory for heavy oil, bitumen, and wax appearance temperature (WAT) prediction.
- Multiflash Integration: VMGSim can call the Multiflash kernel for specialized calculations including hydrate equilibrium, wax deposition, and asphaltene onset pressure.
For a gas processing facility, selecting the correct EOS is not academic — a 2% error in dew-point prediction translates directly to off-spec LPG product or compressor liquid carryover. VMGSim's Fluid Characterization Wizard accepts PVT lab reports (CCE, CVD, separator tests) and automatically regresses EOS parameters to match measured data, reducing characterization time from days to hours.
Steady-State Simulation: Gas Processing Trains
VMGSim's unit operation library covers the full upstream/midstream scope:
Turboexpander-Based NGL Recovery
The Turboexpander unit in VMGSim models isentropic expansion with mechanical efficiency curves, enabling rigorous simulation of the expander-compressor pair used in cryogenic NGL extraction. Engineers can specify:
- Inlet conditions (pressure, temperature, composition)
- Isentropic efficiency vs. flow curve (from OEM data)
- Recycle compressor polytropic head and efficiency
The simulator automatically calculates the dew-point margin at the cold separator, NGL recovery rates (C2+, C3+), and residue gas heating value — all in a single converged flowsheet.
Amine Gas Treating
VMGSim includes a Rate-Based Absorber/Stripper model for amine treating (MEA, DEA, MDEA, piperazine blends). Unlike equilibrium-stage models, the rate-based approach accounts for:
- Mass transfer resistance in both vapor and liquid films
- Reaction kinetics for CO₂ and H₂S absorption
- Column hydraulics (structured packing, trays)
This is particularly valuable for selective H₂S removal with MDEA, where equilibrium models systematically over-predict CO₂ co-absorption and undersize the regenerator.
Glycol Dehydration
The TEG Contactor model in VMGSim uses the CPA EOS to rigorously predict water dew-point depression as a function of TEG circulation rate, lean TEG concentration, and contactor pressure. The model outputs BTEX emissions from the regenerator — a regulatory requirement in many jurisdictions — without requiring a separate emissions calculation tool.
Dynamic Simulation and Surge Analysis
VMGSim's Dynamic Module extends steady-state flowsheets to time-domain simulation. A common application is compressor surge analysis:
- Define the compressor map (head vs. flow at multiple speeds)
- Specify the anti-surge control valve (ASV) with its Cv characteristic
- Simulate a sudden load rejection or inlet pressure drop
- Observe whether the ASV opens fast enough to prevent surge
The dynamic module uses implicit integration (Gear's method) with automatic step-size control, making it stable for stiff systems such as high-pressure separators with fast pressure dynamics. Results include time traces of flow, pressure, temperature, and valve position — directly exportable to control system vendors for DCS tuning.
Workflow Integration: Python API and Excel Link
VMGSim exposes a COM automation interface accessible from Python via the win32com library:
import win32com.client
sim = win32com.client.Dispatch("VMGSim.Application")
sim.OpenCase("NGL_Plant.vmp")
flowsheet = sim.ActiveDocument.Flowsheet
# Adjust feed composition
feed = flowsheet.MaterialStreams("Feed Gas")
feed.SetComposition({"Methane": 0.85, "Ethane": 0.08, "Propane": 0.04, "CO2": 0.02, "N2": 0.01})
sim.ActiveDocument.Solve()
# Read NGL product rate
ngl = flowsheet.MaterialStreams("NGL Product")
print(f"NGL rate: {ngl.MolarFlow:.2f} kmol/h")This enables parametric studies — sweeping feed gas composition across seasonal variations or reservoir decline scenarios — without manual GUI interaction. Results feed directly into economic models or production forecasting tools.
Practical Considerations for Facility Engineers
Convergence: VMGSim uses a sequential-modular solver with Wegstein and Broyden acceleration for recycle loops. For tight recycle systems (e.g., refrigeration loops), enabling the simultaneous convergence option reduces iteration count by 40–60% compared to pure sequential solving.
Validation: Always validate the thermodynamic package against plant data before using the model for design decisions. VMGSim's Data Reconciliation tool adjusts measured flow and composition data to satisfy mass and energy balances, providing a consistent baseline for model tuning.
Licensing: VMGSim is commercially licensed with node-locked and floating options. Academic licenses are available through VMG's university program.
Conclusion
VMGSim occupies a well-defined niche: rigorous, thermodynamically consistent simulation of upstream and midstream hydrocarbon facilities where standard simulators fall short. Its CPA and PC-SAFT thermodynamics, rate-based treating models, and integrated dynamic module make it a preferred tool for LNG, NGL recovery, and gas treating design. For engineers working at the intersection of reservoir fluids and process equipment, VMGSim provides the fidelity needed to make confident design and operational decisions.
Further Reading: