Measurement and Prediction of Salt Solubility in the Presence of Hydrate Organic Inhibitors
- Rahim Masoudi (National Iranian Oil Co.) | Bahman Tohidi (Heriot-Watt University) | Ali Danesh (Heriot-Watt University) | Adrian C. Todd (Heriot-Watt University) | Jinhai Yang (Heriot-Watt University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- May 2006
- Document Type
- Journal Paper
- 182 - 187
- 2006. Society of Petroleum Engineers
- 1.6 Drilling Operations, 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene, 1.8 Formation Damage, 4.3.4 Scale, 4.3.1 Hydrates, 4.2.4 Risers, 5.9.1 Gas Hydrates, 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 3.2.6 Produced Water Management, 5.2 Reservoir Fluid Dynamics, 4.2 Pipelines, Flowlines and Risers, 2.1.7 Deepwater Completions Design, 5.2.2 Fluid Modeling, Equations of State, 4.1.2 Separation and Treating, 4.3 Flow Assurance
- 0 in the last 30 days
- 693 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Organic inhibitors (e.g. methanol, ethanol, ethylene glycol, and triethylene glycol) are generally used to reduce the risk of gas hydrate formation in drilling and production operations. The addition of organic inhibitors has a significant adverse effect on the solubility of salts, increasing the risk of salt deposition. A better understanding of salting-out problems is necessary for effective design and implementation of flow assurance strategies in such complex systems.
In this paper, we present an experimental investigation on the effect of methanol, ethanol, and ethylene glycol on the solubility of several salts, including halite, sylvite, and antarcticite. The results show that ethylene glycol has a much lesser adverse impact on salt deposition than methanol and ethanol. The details of an experimental setup used for measuring salt solubility and salting out are described. The setup could also provide valuable information on the effectiveness of various inhibitors used for preventing salt deposition in the presence or absence of gas hydrate organic inhibitors.
In addition, a novel predictive numerical approach is proposed to model salt formation in brine solutions with or without hydrate organic inhibitors. The model is based on the equality of the fugacity of salt in the solid phase and aqueous phase, which are calculated by an equation of state. The validity of the new developed model is demonstrated over a wide temperature range (i.e., -20 to 125°C), salt concentration up to saturation point, and hydrate inhibitor concentration up to 50 mass%.
Flow assurance is an essential aspect of safe and economical production of hydrocarbons over the lifetime of a field. Gas hydrate and scale control are two of the key aspects of flow assurance.
Gas hydrates, or clathrates, are icelike crystalline compounds consisting of low molecular diameter gases inside cavities formed by water molecules, which can form at certain pressure and relatively low temperature conditions. Gas hydrate formation is particularly troublesome for offshore drilling and production because of low seabed temperature, high residence time, and high operating pressure. Hydrates can block pipelines and subsea transfer lines and, in the event of a gas kick during drilling, form in the wellbore, risers, blowout preventers (BOPs), and choke lines (Barker and Gomez 1989). Common practice for preventing gas hydrate formation involves the injection of a large quantity of thermodynamic inhibitors (e.g., methanol, ethanol, ethylene glycol, or triethylene glycol). However, the addition of organic inhibitors may adversely affect salt solubility in the associated brine solutions, which often contain high concentrations of dissolved minerals, leading to potential salt precipitation, commonly termed "salting out?? (Kan et al. 2002; Matthews et al. 2002). The deposition of salt may result in flow restriction due to salt-plug formation, as well as hydrate formation (as a result of neglecting the effect of salt deposition on reducing the overall hydrate prevention characteristics of the system).
In the open literature, there is a little information on the solubility of mineral salts in hydrate organic inhibitor/water/salt solutions, which is only applicable to the studied systems and limited range of temperature and pressure (Kan et al. 2002; Tomson et al. 2003; Masoudi et al. 2004a; Pinho and Macedo 1996), and no accepted methodology for correlating the effects of hydrate organic inhibitors on scale formation/inhibition. Therefore, a better experimental and theoretical understanding of the salt formation as a function of both electrolyte and organic inhibitor concentrations in the presence or absence of scale inhibitors over a wide range of temperature and concentration is crucial to the success of any flow assurance strategy.
The work in this communication is the result of a systematic experimental and modeling investigation on the effect of three hydrate organic inhibitors (i.e., methanol, ethanol, and ethylene glycol) on various mineral salt solubility (i.e., halite, sylvite, and antarcticite) over a wide range of temperature and concentration. The applied experimental setup and its capability in determining salt solubility data in the presence or absence of hydrate organic inhibitor are first described. The development of a new thermodynamic approach capable of predicting salt formation in electrolyte solutions with or without hydrate organic inhibitors is then detailed for the studied systems in this work.
|File Size||172 KB||Number of Pages||6|
Avlonitis, D., Danesh, A., and Todd, A.C. 1994. Prediction of VL and VLLEquilibria of Mixtures Containing Petroleum Reservoir Fluids and Methanol Witha Cubic EoS. Fluid Phase Equilibria 94:181-216.
Babinets, D.M. and Polishchuk, A.G. 1981. Device for solubilitydetermination of salts in mix-solvent. Zhurnal Fizicheskoi Khimii55(2):535-537.
Barker, J.W. and Gomez, R.K. 1989. Formation of Hydrates DuringDeepwater Drilling Operations. JPT 41(3):297-301; Trans., AIME, 287.SPE-16130-PA.
Breton, A.M. 1967. Postgraduate thesis in physical sciences. U. of Pau,France.
Chiavone-Filho, O. and Rasmussen, P. 1993. Solubilities of Salts in MixedSolvents. Journal of Chemical and Engineering Data 38:367-369.
CRC Hand Book of Chemistry and Physics. 1989. CRC Press Inc., Boca Raton,Florida.
Kan, A.T., Fu, G., Watson, M., and Tomson, M.B. 2002. Effect of Hydrate Inhibitors onOilfield Scale Formation and Inhibition. Paper SPE 74657 presented at theSPE Oilfield Scale Symposium, Aberdeen, 30-31 January.
Kihara, T. 1953. Virial Coefficient andModels of Molecules in Gases. Reviews of Modern Physics 25(4):831-843.
Kirk, J.W. and Dobbs, J.B. 2002. A Protocol to Inhibit the Formationof Natrium Chloride Salt Blocks. Paper SPE 74662 presented at the SPEOilfield Scale Symposium, Aberdeen, 30-31 January.
Masoudi, R., Tohidi, B., Anderson, R., Burgass, R.W., and Yang, J. 2004a. Experimental measurementand thermodynamic modelling of clathrate hydrate equilibria and salt solubilityin aqueous ethylene glycol and electrolyte solutions. Fluid PhaseEquilibria 219:157-163.
Masoudi, R., Tohidi, B., Danesh, A., and Todd, A.C. 2004b. A new approach inmodelling phase equilibria and gas solubility in electrolyte solutions and itsapplications to gas hydrates. Fluid Phase Equilibria 215:163-174.
Masoudi, R., Tohidi, B., Danesh, A., Todd, A.C., Anderson, R., Burgass,R.W., and Yang, J. 2005. Measurement and predictionof gas hydrate and hydrated salt deposition in aqueous ethylene glycol andelectrolyte solutions. Chemical Engineering Science 60(15):4213-4224.
Matthews, P.N., Subramanian, S., and Creek, J. 2002. High Impact, PoorlyUnderstood Issues with Hydrate in Flow Assurance. Proc., 4th InternationalConference on Gas Hydrates, Yokohama 19-23 May, 899-905.
Parrish, W.R. and Prausnitz, J.M. 1972. Dissociation pressure of gashydrates formed by gas mixtures. Industrial and Engineering Chemistry,Process Design and Development 11:26-35.
Pinho, S.P. and Macedo, E.A. 1996. Representation of saltsolubility in mixed solvents: A comparison of thermodynamic models, FluidPhase Equilibria 116:209-216.
Potter, R.W. and Clynne, M.A. 1978. Solubility of Highly Soluble Salts inAqueous Media Part 1, NaCl, KCl, CaCl2, Na2SO4, and K2SO4 solubilities to100?C. Journal ofResearch of theU.S. Geological Survey6(6):701-705.
Stephen, H. and Stephen, T. 1963. Solubilities of Inorganic andOrganicCompounds. Pergamon Press, Oxford. London.
Tomson, M.B., Kan, A.T., Fu, G., and Al-Thubaiti, M. 2003. Scale Formation and Prevention in thePresence of Hydrate Inhibitors. Paper SPE 80255 presented at the SPEInternational Symposium on Oilfield Chemistry, Houston, 5-7 February.
Washburn. 1926. International Critical Tables (ICT) of numerical data,physics, chemistry and technology Natl. Research Council.
Valderrama, J.O. 1990. A Generalized Patel-Teja Equation of State for Polarand Nonpolar Fluids and Their Mixtures. Journal of Chemical Engineering ofJapan 23(1):87-91.
Van der Waals, J.H. and Platteeuw, J.C. 1959. Clathrate Solutions. Advancesin Chemical Physics 2:1-57.