Ben J. Rostron¹, Chris Holmden²
(1) University of Alberta, Edmonton, AB
(2) University of Saskatchewan, Saskatoon, SK

Abstract: Fingerprinting formation-waters using stable isotopes: applications for exploration and production

Recent prolific hydrocarbon discoveries in southeast Saskatchewan, have renewed hydrocarbon exploration interest in deep strata of the Williston Basin. Hydrogen, oxygen, and strontium isotope compositions of formation waters have been obtained from drill stem tests and produced waters in Saskatchewan, North Dakota, and Montana. Producing zones ranging in age from Devonian to Cambrian have been sampled.

Results show that each major aquifer has a unique isotopic fingerprint. The Birdbear and Duperow aquifers exhibit the highest D (-17 per mil) and ¹⁸O (7.9 per mil) values known from the Williston Basin. They are substantially more D and ¹⁸O enriched than formation waters from other aquifers in the basin. Below the Prairie Evaporite aquitard, the deeper aquifers in the Williston Basin yielded lower D and ¹⁸O values than the Birdbear and Duperow aquifers, but higher strontium isotopic compositions.

These new data, in conjunction with data from the literature, show that Williston Basin formation waters vary substantially in isotopic composition between aquifers in stratigraphic section and within the same aquifer regionally. These large isotopic variations reveal the enormous potential of H, O, and Sr isotopes in Williston Basin formation waters to trace petroleum migration pathways and to fingerprint sources of contaminant water encountered during drilling/testing and production of hydrocarbons.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana