The Southwestern Northwest Territories has an elevated geothermal gradient, which has resulted in recent interest in the area for research of its geothermal energy potential. Geological data characterizing the reservoir properties of target rocks for geothermal energy development are scarce. The Liard Geothermal Reservoir research program has the main objective to fill this knowledge gap and gather baseline geological data of the prospective reservoir rocks in the southwestern NWT. The target reservoir rock for this study is the regionally extensive limestone of the Nahanni Formation and its locally dolomitized Manetoe facies. To fulfill this objective, the Northwest Territories Geological Survey (NTGS) and the Department of Infrastructure – Energy Division (INF-Energy) initiated a collaborative research program in 2019.

In phase one of the study, well cores stored at the Core and Sample Repository, Geological Survey of Canada (GSC) in Calgary, Alberta were examined and sampled. Eight wells were selected based on their location and availability of cored Nahanni Formation and Manetoe facies strata, and sampling intervals were defined and approved by OROGO for SR 2019-003. Cores were photographed and described by NTGS. Samples for analysis were collected by AGAT Laboratories (Calgary, AB) under supervision of the Core and Sample Repository, GSC, Calgary. The samples were analysed for porosity and permeability, mineralogy, and pore space characterization.

Phase two of the study comprised field work and field sampling in the summer of 2021 and targeted the same facies that were sampled from core in phase one. A total of 72 samples were collected from a broad region of the southwestern NWT, including locales west of Fort Simpson from Cli Lake toward the south and west of Nahanni Butte.  

This presentation details the results of phase one of the study. The obtained results indicate that reservoir quality is limited through most of the strata, which comprise fine-grained and well-cemented limestone and crystalline dolomite (in the order of 0.01-0.1 mD and <<1 % porosity). Reservoir quality is, however, moderate locally through the stratigraphy, where dolomitization increased vuggy pore space (1 to ~40 mD and 1-7 % porosity). Field observations support the observation of a patchy facies fabric. Additionally, the discontinuous nature of the Manetoe facies was noted in the field; in the southern part of the study area it is thick, well developed and laterally continuous, however toward the north it becomes increasingly discontinuous and only affects the limestone of the Nahanni Formation in discrete, several m to Dm wide lenses. Currently the samples from phase two of the project are being analysed at AGAT Laboratories.