--> Abstract: Regional Hydrochemistry Of Cambrian To Devonian Aquifers In The Williston Basin, Canada-Usa, by B. J. Rostron and A. A. Benn; #90928 (1999).

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ROSTRON, BEN J.1 and ADAM A. BENN2
1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB
2Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK

Abstract: Regional Hydrochemistry of Cambrian to Devonian Aquifers in the Williston Basin, Canada-USA

Petroleum accumulations in the Williston Basin are influenced by fluid flow and hydrochemistry. However the flow system in the basin remains poorly understood because it has not been examined using a truly "regional" approach. This lack of understanding, combined with the current renewed interest in deep exploration solicits further evaluation of the hydrogeology and hydrochemistry of this basin.

A basin-wide digital database of formation water chemistries has been compiled from several sources in Canada and the USA. Data from Cambrian through Devonian strata were divided into seven hydrostratigraphic units based on stratigraphic associations, hydraulic properties, and previous studies.

Maps of total dissolved solids (TDS), major ions, and ion ratios have identified three distinct water "types" in the basin, those being: 1) CaSO4 type water with low TDS (<30,000 mg/L) associated with recharge conditions, 2) NaCl type water with moderately high TDS (100,000 to 200,000 mg/L), and 3) NaCaCl type waters with high TDS in the deep basin (>300,000 mg/L).

Results show: 1) differences in water chemistry across the basin suggest there are distinct hydraulic flow regimes present, 2) variations in water chemistry play a significant role in hydrodynamics in the basin, and 3) groundwater evolution in the basin is controlled by a complicated set of factors. Hydrocarbon exploration and production operations in the Williston Basin could benefit from this new picture of the regional hydrochemistry of the basin.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas