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The AAPG/Datapages Combined Publications Database

Wyoming Geological Association

Abstract


Wyoming Gas Resources and Technology; 52nd Field Conference Guidebook, 2001
Pages 107-121

Sr Isotopic Identification of Coal and Sandstone Aquifers and Monitoring of Aquifer Interactions in an Area of Active Coalbed-Methane Production, Powder River Basin, Wyoming

C. D. Frost, J. E. Viergets, B. N. Pearson, E. L. Heffern, R. M. Lyman, K. M. Ogle

Abstract

The Powder River Basin provides a third of the nation's supply of coal, and it also hosts a significant coalbed-methane resource. Coalbed-methane production involves withdrawal of groundwater in order to depressurize coal seams and desorb methane. It is important to understand the degree of hydraulic connection between coal seams and adjacent aquifers, particularly because aquifer leakage can make it difficult to adequately depressurize coal and recover gas. In this study we evaluate the Sr isotopic ratio of groundwater as a potential fingerprint of waters from coal and silicate aquifers and a monitor of aquifer interactions. Our results show that groundwaters at shallow depths close to the recharge zone do not have distinct Sr isotopic ratios. However, waters from coal and sandstone aquifers located more than approximately 5 km from the recharge area do have distinctive Sr isotopic compositions. Moreover, we are able to demonstrate that the Sr isotopic ratio is useful in identifying wells that contain mixed waters, whether due to well construction or to incomplete aquifer isolation. Continued, periodic measurement of the Sr isotopic ratio in groundwaters of the Powder River Basin should be helpful in monitoring changes in groundwater hydrology related to coalbed-methane activity.


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