Hydrate and scale deposition in pipelines
The aim of the project has been to improve existing models for formation and deposition of gas hydrates, for simulation of salts in aqueous solution, and for salt deposition. A secondary purpose has been to make the developed models applicable to the oil industry through implementation in Calsep's commercial software for simulation of oil and gas phase behavior.
Deposition of solids at the inner side of offshore pipelines is a frequent problem in the oil industry. Among the solids which may contribute to this process are scale and gas hydrates. Scale consists esentially of salts which are dissolved in the formation water at reservoir conditions but during transport precipitate in the pipeline. Gas hydrates consist of water and light gases and have a consistence similar to that of snow or ice. Formation of hydrates can be avoided by addition of hydrate inhibitors like methanol and glycol. The salts dissolved in the formation water also act as hydrate inhibitors and contribute to lower the melting point of the hydrates. In relation to pipeline transport hydrates and salts are therefore closely related. The project will be started by development of a model for prediction of the conditions at which salts may precipitate from formation water. It is desirable that the same model is suited to predict the inhibitor effect of the salts dissolved in the water. This model will be combined with a hydrate growth model previously developed by Calsep. A study of the deposition mechanisms for hydrates and salts will follow. The effect of kinetic hydrate inhibitors will be considered in this phase of the project. The developed models will be coupled with a wax deposition program developed in parallel in a different EFP-project. The final product will thus consist of a program package for simulation of wax as wellas scale and hydrates
At the start of the project Calsep already had reliable models for simulation of formation of hydrates of types I and II, while a simulation model for the 3rd type of hydrates (type H) has been developed as a part of the project. Hydrates of type H cannot form from natural gas as is the case with hydrates of types I and II, but type H hydrates may form from mixtures as for example oil mixtures containing heavier hydrocarbons. In collaboration with Norsk Hydro's research department in Porsgrunn, a simulation model for hydrate deposition in pipelines during shutdown and start-up has been developed Norsk Hydro has expressed an interest in continuing this part of the project in 2001. A model has been developed for precipitation of salt - also called scale - from formation water. This model handles precipitation of BaSO4, CaSO4, SrSO4, CaCO3, FeS and FeCO3. The scale potential dependes on the acidity (pH) of the formation water and on the concentration of esay soluble salts like NaCl and KCl, and the developed model takes both these effects into account. Finally a new model has been developed for simulation of the solubility of natural gas in formation water. Souch model is useful when designing degassers, i.e. separators for removing dissolved hydrocarbons from formation water. The model for structure H hydrates, the scale model and the solubility of gas in salt water have all been implemented in Calsep's commercial simulator, PVTsim being used by more than 100 companies in the oil and gas industry all over the world. The aim of the project has been fulfilled
Key figures
Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Well Flow Dynamics AS | ||
| Statoil A/S |
Contact
Gl. Lungtoftevej 7
DK-2800 Lyngby, Denmark
Schou Pedersen, Karen (dir.), 45876646, info@calsep.com
Øvr. Partnere: Well Flow Dynamics AS; Statoil
