Dedolomitization in Na-Ca-Cl brines from 100/sup 0/ to 200/sup 0/C at 300 bars
Dedolomitization experiments were run at 300 bars for 7 to 8 weeks at 100/sup 0/, 150/sup 0/, and 200/sup 0/C in chloride brines containing 2 m (molal) Na, 0.5 m Ca, and 0.02 m Sr. The ordered dolomite dissolved and low-Mg calcite back precipitated as a replacement and/or rim cement of equant spar calcite crystals 10 to 50 ..mu..m in diameter. Between 100/sup 0/ and 200/sup 0/C the mode of calcite formation changed from direct precipitation into void space produced by dissolving dolomite to pseudomorphic replacement of dolomite. The dedolomitization textures formed in these experiments are similar to those found in the rock record. Solution compositions were monitored as a function of experimental time and imply that calcite-dolomite equilibrium was approached at 100/sup 0/C and reached at 150/sup 0/ and 200/sup 0/C. The final aqueous molality ratios of Ca:Mg were 14.2, 23.5, and 35.4, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C. The respective activity ratios, computed using Pitzer's model, were 14.3, 23.6, and 37.0, representing estimated constants for the dissolution of dolomite. The estimated standard state enthalpy of reaction is 3.6 kcal between 150/sup 0/ and 200/sup 0/C. The empirical Sr distribution coefficient for the precipitated calcite was determined from micro-probe analyses of the calcite and solution data. The average coefficient values increased with increasing temperature, being 0.027, 0.048, and 0.063, respectively, at 100/sup 0/, 150/sup 0/, and 200/sup 0/C.
- Research Organization:
- Univ. of New Orleans, LA (USA)
- OSTI ID:
- 7188784
- Journal Information:
- Geochim. Cosmochim. Acta; (United States), Vol. 51:4
- Country of Publication:
- United States
- Language:
- English
Similar Records
Intracrystalline porosity - a newly discovered pore type in dolostone reservoirs and implications for dedolomitization and pseudospiculites
Middle Jurassic great oolite of southern England, facies development and regional significance of dedolomitization during basin evolution
Related Subjects
BRINES
CHEMICAL COMPOSITION
GEOCHEMISTRY
DOLOMITE
ACTIVATION ENERGY
DISSOLUTION
ENTHALPY
CALCITE
CALCIUM COMPOUNDS
CHLORIDES
CRYSTALLIZATION
EQUILIBRIUM
MINERALIZATION
PRECIPITATION
SODIUM COMPOUNDS
STRONTIUM COMPOUNDS
TEMPERATURE EFFECTS
THERMODYNAMICS
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
CHLORINE COMPOUNDS
ENERGY
HALIDES
HALOGEN COMPOUNDS
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
SEPARATION PROCESSES
THERMODYNAMIC PROPERTIES
580400* - Geochemistry- (-1989)