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TitleDefining the natural fracture network in a shale gas play and its cover succession: the case of the Utica Shale in eastern Canada
AuthorLadevèze, P; Séjourné, S; Rivard, CORCID logo; Lavoie, DORCID logo; Lefebvre, R; Rouleau, A
SourceJournal of Structural Geology vol. 108, 2017 p. 157-170, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170287
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf; html
Lat/Long WENS -71.9500 -71.7000 46.6833 46.5000
Subjectshydrogeology; fossil fuels; structural geology; environmental geology; tectonics; petroleum resources; hydrocarbons; gas; reservoir rocks; groundwater resources; aquifers; fluid flow; fluid migration; bedrock geology; lithology; sedimentary rocks; shales; siltstones; structural features; fractures; folds; anticlines; synclines; faults; bedding planes; observation wells; gas wells; well logging; modelling; structural controls; tectonic history; basement geology; rock mechanics; Utica Shale; St. Lawrence Platform; Logan's Line; Aston Fault; Lecelrcville Anticline; Jacques-Cartier River Fault; Chambly-Fortierville Syncline; Queenston Group; Lorraine Group; Pontgravé Formation; Nicolet Formation; Sainte-Rosalie Group; Lotbinière Formation; Les Fonds Formation; Utica Shale; Trenton Group; Black River Group; Chazy Group; Beekmantown Group; Potsdam group; Grenville Orogen; environmental assessment; Phanerozoic; Paleozoic; Ordovician; Cambrian
Illustrationslocation maps; geoscientific sketch maps; stratigraphic columns; geochronological charts; stereonet projections; cross-sections; tables; photographs; sketches; bar graphs; plots; variation diagrams; frequency distribution diagrams; well logs; 3-D models
ProgramEnvironmental Geoscience Shale Gas - groundwater
Released2017 12 14
AbstractIn the St. Lawrence sedimentary platform (eastern Canada), very little data are available between shallow fresh water aquifers and deep geological hydrocarbon reservoir units (here referred to as the intermediate zone). Characterization of this intermediate zone is crucial, as the latter controls aquifer vulnerability to operations carried out at depth. In this paper, the natural fracture networks in shallow aquifers and in the Utica shale gas reservoir are documented in an attempt to indirectly characterize the intermediate zone. This study used structural data from outcrops, shallow observation well logs and deep shale gas well logs to propose a conceptual model of the natural fracture network. Shallow and deep fractures were categorized into three sets of steeply-dipping fractures and into a set of bedding-parallel fractures. Some lithological and structural controls on fracture distribution were identified. The regional geologic history and similarities between the shallow and deep fracture datasets allowed the extrapolation of the fracture network characterization to the intermediate zone. This study thus highlights the benefits of using both datasets simultaneously, while they are generally interpreted separately. Recommendations are also proposed for future environmental assessment studies in which the existence of preferential flow pathways and potential upward fluid migration toward shallow aquifers need to be identified.
Summary(Plain Language Summary, not published)
In the St. Lawrence Lowlands (southern Québec), very little data is available in the intermediate zone between the shallow aquifers (<100m) and the deep shale gas reservoir (>1000-1500m). However, this zone controls the aquifer vulnerability to oil and gas operations. This paper presents the characterization of the natural fracture network of the shallow aquifers and deep gas reservoir. Fracture observations were made from outcrops, using borehole geophysics in shallow observation wells and from electrical imagery (FMI, Formation MicroImager) in industrial deep wells. Based on these results, it was demonstrated that extrapolation can be made to the intermediate zone. A conceptual model of the fracture network was defined and recommendations were made for future environmental assessment studies in which the potential for upward fluid migration toward shallow aquifers needs to be identified.

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