PRECIPITATION KINETICS OF CALCIUM CARBONATE IN CONCENTRATED SODIUM CHLORIDE SOLUTIONS (CARBONATE, TEXAS, LOUISIANA, BRINES)

The current research was initiated to develop potential solutions to the problem of CaCO(,3) scale formation during the recovery of natural gas from geopressured aquifers. A very large natural gas resource has been identified in the extensive geopressured reservoirs along the Texas-Louisiana gulf coasts. These waters coexist under abnormally high pressures with natural gas and carbon dioxide. The reported compositions of these brines vary widely, but they are basically NaCl with many minor and trace components (anticipated TDS are in the range of 20,000 to 250,000 ppm). The brines are saturated with calcite and quartz. Flashing of CO(,2) during natural gas recovery causes the brine pH to increase, leading to supersaturation for CaCO(,3). Chemical inhibition techniques have been proven effective for prevention of scale formation in processing equipment and injection wells. Recently, interest has developed in a seeded crystallization technique to remove scale components from the brine without causing scale on equipment surfaces. Although as yet unproven, this technique may improve the economic viability of this natural gas resource.; The primary objective of the current research was to investigate the seeded crystallization kinetics of CaCO(,3) in NaCl brines. It was also endeavored to develop a usable approach for the analysis of brine equilibria and precipitation kinetics. A series of batch precipitation experiments were performed in the laboratory to measure the rate of CaCO(,3) precipitation from NaCl brines. These experiments covered NaCl concentrations from 0 to about 3 m (0 to about 175,000 ppm TDS) and temperature from about 20(DEGREES)C to 55(DEGREES)C. A general rate equation for CaCO(,3) precipitation kinetics has been verified for low ionic strength waters. This rate equation was based upon the activities of the precipitating ions rather than concentration, as done conventionally. Thus, the problem was reduced to one of predicting aqueous activities. Two approaches are currently available for prediction of aqueous activity coefficients in concentrated electrolytes. One approach is based upon an extension of hydration theory. The second approach is based upon an extended ion-interaction model. Each approach for activity coefficients was applied to the experimental data. Equilibria and activity data for CO(,2) was described by using solubility data from the literature that covered a broad range of temperature and salinity. A computer based data analysis program was developed, incorporating the above, to analyze the experimental crystal growth data. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI...