Salinity Transport and Fluid Flow Modeling in the Alberta Basin, Canada

I. Gupta and A. Wilson
University of South Carolina

In the Alberta Basin, Canada, a strong disparity exists between geochemical and hydrogeologic estimates of the residence times of brines which translates to significant uncertainties in transport rates for hydrocarbon migration, ore formation, diagenesis and sequestration of carbon dioxide. Geochemical evidence suggests that brines in this basin have been preserved at depths for hundreds of millions of years with little to no halite dissolution, whereas hydrogeologic models suggest that these brines should have been flushed out of the basin within 2 million years of the uplift of the Rockies.

This project goes beyond previous hydrogeologic models of fluid and heat flow by adding variable-density solute transport and uses the 2D finite element FORTRAN code, COMPACT that originally only accounted for sediment compaction in tectonically evolving basins. In this study, COMPACT has been modified to add erosional capabilities with associated sediment decompaction, and dissolution of evaporites. Brine migration and groundwater age are simulated over the last 100 million years, along a 700 Km, east-west cross-section of the basin, using salinity, and Br/Cl ratios as geochemical constraints.

Our results suggest that contrary to geochemical interpretations, halite dissolution has significantly contributed to the salinity distribution in the basin. Formation waters in this basin are not simple end members of a seawater evaporation model, but bear signatures of original residual brines, halite dissolution, freshwater infiltration and mixtures of the above in various proportions. Waters in the younger formations are young and mixed, but older waters exist in the deeper western parts of the basin.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas