Predictive Software
Hydrate/aqueous and hydrocarbon PVTX thermodynamic modelling at Hydrafact dates back over 25 years. Numerous industry/government sponsored R&D projects undertaken by the Heriot-Watt Hydrate and Reservoir Fluids research groups over the years have led to the generation of a vast, largely unpublished in-house hydrate and hydrocarbon equilibria database which has been used to tune and validate our predictive software.
The well known commercial version of our hydrate and fluid phase equilibrium predictive model, Heriot-Watt Hydrate (HWHYD), is currently used by a large number of major oil, gas and service companies. Comparative assessment of model predictions with those of other commercial hydrate programs by industrial clients have repeatedly demonstrated the superior versatility and reliability of the HWHYD model for simulating various production scenarios.
The HWHYD model can perform a wide range of hydrate and VLE predictive calculations for multicomponent, multiphase aqueous and hydrocarbon systems. Examples are given below.
Phase Equilibria Calculations Involving Hydrates
The following calculations involving gas hydrates can be performed with HWHYD:
- Hydrate (H) phase boundaries for systems containing liquid water (L1), ice (I), vapour, and liquid hydrocarbons (L2)
- H+L1+V (gas systems)
- H+L1+L2+V (gas and liquid hydrocarbons)
- I+L1+V (gas and ice)
- H+V (low water content gases)
- Liquid water, vapour, hydrate PT flash compositional calculations (H+L1+V and H+L1+L2+V options)
Hydrate calculations can include sH in addition to the two most common hydrate structures, sI and sII.
General Phase Equilibria Calculations
The following phase equilibria calculations can be performed with HWHYD:
- Hydrocarbon bubble point and dew point PT calculations for systems with and without water present
- Liquid hydrocarbon, water and gas PT flash compositional calculations (L1+L2, L1+V, L2+V, L1+L2+V options)
- Fugacity calculations
Other Phase Equilibrium Calculations
In addition, Hydrafact HWHYD can be used to predict:
- Water freezing (ice melting) point depression in the presence of electrolytes and/or organic inhibitors
- Salt and gas solubility in the aqueous phase
Modelling Approach
Two modelling approaches are typically used in the model, these are:
- Standard EoS (Typically the VPT EoS)
- New Cubic Plus Association (CPA)
In the standard EoS method, the Valderrama-Patel-Teja Equation of State (VPT EoS, Valderrama, 1990) with non-density dependent mixing rules (NDD) is used in modelling fluid phases. This combination has proved to be a strong tool for modelling systems with polar as well as non-polar components. Other equations of state can be used, including the SRK, PR and VDW EoS. Classical mixing rules are also available for calculations.
In the latest commercial version (2.1 CPA), a new approach has been introduced for modelling fluid phase equilibria in systems containing components which can form hydrogen bonds (e.g. water, methanol, ethanol, MEG) and hydrocarbon mixtures using a robust general-purpose implementation of the CPA (Cubic Plus Association) model (Kontogeorgis, 2006a,b; Haghighi, 2008a,b).
For both approaches, the hydrate phase is modelled by the solid solution theory of van der Waals and Platteeuw (1959). The Kihara (Kihara, 1953) model for spherical molecules is applied in order to calculate of the potential function for compounds forming the hydrate phases. A general multi-phase flash routine based on that of Cole and Goodwin (1991) allows calculation of the hydrate fraction/composition at specified temperature, pressure, and system composition.
Electrolytes are modelled by an improved Aasberg-Petersen (Aasberg-Petersen et al., 1991, Tohidi et al, 1995) gas solubility model, developed at the Centre for Gas Hydrate Research. The model can be used over a wide range of temperature and salt concentration, and is capable of handling mixed electrolyte solutions.
HWHYD Components
Components included in the Hydrafact HWHYD program are given in the table below.
Included are the most common structure-I, structure-II and structure-H hydrate formers (including water soluble hydrate formers), normal alkanes up to C20, chemical inhibitors, water, and salts.
In addition to existing components, it is possible to include other components (e.g. heavy fraction pseudo components) if one of the following combinations is specified:
- Critical constants, molecular weight and acentric factor
- Molecular weight and specific gravity
- Molecular weight only
Hydrafact HWHYD main Windows interface
Example prediction output for H+L+V calculation
Hydrate and Phase Equilibrium Database Add-On
The Hydrafact HWHYD hydrate and phase equilibrium database is an essential reference tool for engineers and academics involved in gas hydrate and VLE/SLE prediction.
The database allows quick and easy access to data from over 1,500 in-house and literature publications, including:
- Pure compound properties
- Gas hydrate data (PVT, enthalpies...)
- VLE, VLLE, LLE, solubilities
- Salt solubilities
- Freezing (ice melting) and boiling points of aqueous solutions
The user can search for data on single or multicomponent systems by CAS number, molecular formula or name. Data can be exported to a text (.txt) file or directly into Microsoft Excel with the option to choose output units (e.g.,°C, K, MPa, psia...).
HWHYD can be purchased with the database integrated. The licensing cost of the database is significantly reduced if purchased as part of the HWHYD model package.
Demo Versions
Demo versions of both the HWHYD and Database applications are available for download on the demo downloads page.
Purchase and Licensing Information
Licences may be obtained for commercial and/or academic use of HWHYD (2.1). Three licensing options are available:
- One-off purchase, unlimited usage with 1 year technical support and upgrades
- 1 year licence including technical support and upgrades, with the option for subsequent yearly renewal
- Options 1 or 2 with the hydrate and phase equilibrium database integrated into the software
The Hydrate and Phase Equilibrium database is available as a stand-alone application, with a similar licensing options as for HWHYD above (options 1 and 2).
Discounted rates are available for educational/academic use. Please contact us for details.
All enquires should be directed to:
Sid Chadha
Business Manager
Hydrafact Limited
Institute of Petroleum Engineering
Heriot-Watt University
Edinburgh EH14 4AS
UK
Tel: +44 131 451 3672 / 3798
Fax: +44 131 451 3127
E-mail: sid.chadha@hydrafact.com
References
Aasberg-Petersen, K., Stenby, E., and Fredenslund, A. (1991) Prediction of high-pressure gas solubilities in aqueous mixtures of electrolytes. Industrial & Engineering Chemistry Research, 30, 2180-2185.
Haghighi, H., and Chapoy, A., and Tohidi, B. (2008a) Freezing point depression of electrolyte solutions: experimental measurements and modeling using the CPA equation of State. Submitted to: Industrial and Engineering Chemistry Research (2008).
Haghighi, H., Chapoy, A., and Tohidi, B. (2008b) Experimental data and modeling methane and water phase equilibria in the presence of single and mixed electrolyte solutions using the CPA equation of state. Submitted to: Geochimica et Cosmochimica Acta.
Kihara, T. (1953) Virial coefficient and models of molecules in gases. Reviews of Modern Physics, 25, 831-843.
Kontogeorgis, G. M., Michelsen, M. L., Folas, G. K., Derawi, S., von Solms, N., and Stenby, E. H. (2006a) Ten years with the CPA (Cubic-Plus-Association) Equation of State. Part 1. Pure compounds and self-associating systems. Journal of Industrial and Engineering Chemistry Research, 45, 485-4868.
Kontogeorgis, G. M., Michelsen, M. L., Folas, G. K., Derawi, S., von Solms, N., and Stenby, E. H. (2006b) Ten years with the CPA (Cubic-Plus-Association) equation of state. Part 2. Cross-associating and multicomponent systems. Journal of Industrial and Engineering Chemistry Research, 45, 4869-4878.
Parrish, W. R., and Prausnitz, J. M. (1972) Dissociation pressure of gas hydrates formed by gas mixtures. Industrial and Engineering Chemistry Proc. Des. Dev., 11, 26-35.
Tohidi, B., A. Danesh and A. C. Todd (1995). "Modelling Single and Mixed Electrolyte-Solutions and Its Applications to Gas Hydrates." Chemical Engineering Research & Design 73(A4): 464-472.
Valderrama, J. O. (1990) A generalized Patel-Teja Equation of State for polar and nonpolar fluids and their mixtures. Journal of Chemical Engineering of Japan, 23, 87-91.
Van der Waals, J. H., and Platteeuw, J. C. (1959) Clathrate solutions. Advances in Chemical Physics, 2, 1-57.
Hydrocarbon Hydrate formers |
Non-hydrocarbon hydrate formers |
Non-hydrate formers |
Organic Inhibitors |
Salts |
methane |
carbon dioxide |
n-pentane
|
Methanol |
NaCl
|
*Offer some degree of inhibition, but can also form hydrates under certain conditions.
