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SUMMARY:High pressure solubility of sulfate minerals in high density and l
 ow density water - Sébastien Facq
DTSTART:20151023T100000Z
DTEND:20151023T110000Z
UID:TALK62003@talks.cam.ac.uk
CONTACT:Vicky Rennie
DESCRIPTION:A significant problem occurring during oil and gas production 
 is the precipitation and deposition of inorganic scales in the near wellbo
 re area\, and the formation of ‘fouling layers’ on the surfaces of pip
 ework and equipment. This affects the safe and reliable operation of equip
 ment which must be repaired or replaced at a high cost. The ability to acc
 urately predict what minerals will precipitate as scale\, and where\, info
 rms the strategy developed to prevent or mitigate the risk. Modeling of sc
 ale formation at pressure above 1000 bar and temperatures up to 200°C (HP
 HT) is not well understood and so a significant margin of uncertainty must
  be adopted in engineering choices–potentially adding unnecessary cost o
 r complexity. To make scale prediction robust at HPHT conditions the therm
 odynamic basis of the models used must be extended\; new empirical data ar
 e required describing the speciation and solubility of carbonate and sulfa
 te minerals in equilibrium with fluids at deep well (HPHT) conditions. \nM
 ineral solubility and fluid speciation can be measured in situ by coupling
  a diamond anvil cell (DAC) with Raman spectroscopy. This non–invasive a
 nd non–destructive optical technique enables in situ characterization of
  molecular composition and structure of a material. Coupled with a DAC\, t
 his technique provides precise information on the nature and the content o
 f chemical species released in the fluid during dissolution of minerals at
  HPHT conditions. In this study\, we present studies of the stability of s
 ulfate ions up to 4 GPa during equilibration of a natural single crystal o
 f CaSO4 in equilibrium with brine solutions. CaSO4 solubility was deduced 
 from Raman intensities of symmetric stretching mode of sulfate ions and ca
 libration curves obtained from aqueous solutions of known concentration. D
 uring compression\, atypical changes in intensity and frequency shifts of 
 the symmetric stretching mode of sulfate ions were observed between 0.2 an
 d 0.5 GPa and explained by the presence under those conditions of a liquid
 –liquid phase in the fluid from low density water to a high density wate
 r phase. Similar behaviour was also detected for carbonate ions during com
 pression of Na2CO3 aqueous solutions of different concentrations at ambien
 t temperature. Finally\, using appropriate equations of state for aqueous 
 fluids\, Grüneisen parameters have also been calculated for the two liqui
 d phases of H2O.  \n
LOCATION:Department of Earth Sciences - Harker II
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