flotools 1.4.2 added support for calculating hydrate curves based on three different methods:
| Method | Inputs | Outputs |
|---|---|---|
| Sloan | Gas specific gravity & pressure | Hydrate formation temperature |
| Motiee | Gas specific gravity & pressure | Hydrate formation temperature |
| Bahadori and Vuthaluru | Gas composition & temperature | Hydrate formation pressure |
Sloan
The Sloan correlation calculates hydrate formation temperature by the following equation:
where the 
terms are functions of gas specific gravity.
Motiee
The Motiee correlation calculates hydrate formation temperature by the following equation:
where 
is gas specific gravity and A, B, C, D, E, and F are constants.
Bahadori and Vuthuluru
The Bahadori and Vuthuluru correlation calculates hydrate formation pressure given gas temperature and composition by the following equation:
The terms a, b, c, and d are functions of the molecular weight of hydrate-forming components in the gas, as calculated from the gas composition.
Calculating gas molecular weight from gas composition
When a composition is entered, the gas specific gravity is calculated from the molecular weight of hydrate-forming components by the following formula
Where 
is the mole percent of hydrate-forming component c in the gas. flotools will automatically normalize all mole fractions entered into the hydrate tool by dividing each individual mole fraction by the sum total of all mole fractions.
The hydrate-forming components and their molecular weights are defined as:
| Component | Molecular Weight |
|---|---|
| Nitrogen | 28.014 |
| Carbon Dioxide | 44.010 |
| Hydrogen Sulfide | 34.000 |
| Methane | 16.043 |
| Ethane | 30.070 |
| Propane | 44.097 |
| i-Butane | 58.124 |
| n-Butane | 58.124 |
The molecular weight of air is defined as 28.964.
Hydrate Temperature Suppression
Hydrate temperature suppression is calculated using the Heriot-Watt correlation, given by:
However, because the dissociation pressure term 
is not typically known, flotools omits the entire 
term from the calculation, resulting in:
where the 
terms are constants that are unique to the specific inhibitor component causing the temperature suppression.
Further Reference
Feel free to email us at support@evoleap.com with any further questions.
These papers contain more information about each of the specific correlations:
- Sloan ED. Clathrate Hydrates of Natural Gas. 3rd ed. New York: Marcel Dekker Inc.; 2008.
- Motiee M. Estimate possibility of hydrates, Hydrocarbon Processing, July 1991. p. 98.
- Bahadori A., Vuthaluru H B. A novel correlation for estimation of hydrate forming conditions of natural gases, Journal of Natural Gas Chemistry; 2009, 18, 453-457.
- Østergaard KK., Masoudi R., Tohidi B., Danesh A., Todd, A.C. A General Correlation for Predicting the Suppression of Hydrate Dissociation Temperature in the Presence of Thermodynamic Inhibitors, Journal of Petroleum Science and Engineering; 2005, 48, 70-80.