Mixed-Gas Hydrate Onset and Cage Occupancy Calculator

Compare sI and sII hydrate onset for a methane-rich gas using guest fugacities, supplied water activity and explicit Langmuir cage occupancies.

Results

Calculate to view linked results. Default values are examples, not recommended operating inputs.

Learn, compare and practice

Worked explanations, controlled studies and printable exercises connected to this calculation.

Hydrate onset versus wax appearance in a flow assurance model

Calculation sequence

Supply a fixed methane-rich guest gas (methane at least 0.8), absolute pressure and water activity relative to pure liquid water at the same temperature and pressure. Fractions sum exactly to one; an inhibitor weight percentage is not a water activity. Present components are at least 0.001. Pure methane is also accepted for the independent limiting case.
At every trial temperature require stable single-phase guest gas, evaluate PR fugacity and compare both cage structures. Return only a bracketed root with chemical-potential residual below 1e-8 RT. A structure whose onset is below freezing is reported through the model boundary rather than assigned an invented temperature. The selected hydration number follows both cavity populations and their empty sites, not a fixed water-to-gas ratio.
Interpret temperature minus onset as an equilibrium temperature difference. Negative values favor the selected hydrate relative to the specified gas and liquid-water reference. They do not predict blockage, hydrate mass, formation rate, a safe inhibitor dose or how much water is available. A positive computed difference is not an engineering safety margin.
Calculations remain local in a dedicated WebAssembly worker. The existing self-hosted scientific engine is about 33 MB raw on first use; the envelope additionally loads the pinned CoolProp engine and eccentric flow loads a 178 KB FEM package. Nothing is downloaded until calculation. No composition, heat history or measurements are sent to a calculation server. Save retains canonical input values; file backup can be shared with colleagues, while CSV/PDF retain samples, assumptions and sources. Browser storage alone can be lost.

Worked check

For the illustrative 0.90/0.05/0.02/0.02/0.01 CH4/C2/C3/CO2/N2 gas, 5 MPa(a) and aw=1, the selected sII onset is about 287.264214 K with hydration number 6.367966. At 290 K the equilibrium temperature difference is +2.735786 K. These are model results, not laboratory observations.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

273.15-303.15 K, 3-10 MPa(a), water activity 0.8-1; fixed CH4-rich gas only. Condensation, failed gas stability and unbracketed onset fail explicitly.
Water activity is supplied, not derived from salinity, glycols, methanol, dissolved gas or reactive aqueous chemistry. The PR gas and empirical hydrate parameter combination needs measured validation for a particular feed.
No ice competition, sH, hydrate quantity, kinetics, multiple simultaneous hydrate phases, condensate or joint VLLS equilibrium. This is a bounded onset screen, not the full NeqSim process simulator.

Implemented equations

Competitive Langmuir occupancy

Y_{ic}=\frac{C_{ic}f_i}{1+\sum_j C_{jc}f_j}

Water chemical-potential onset

\begin{aligned}0&=\Delta(T,p)-\ln a_w\\&\quad-\sum_c\nu_c\ln(1+\sum_i C_{ic}f_i)\end{aligned}

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: 2026-10-22. This does not claim independent expert review.

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