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The AAPG/Datapages Combined Publications Database
CSPG Bulletin
Abstract
Microstructural Analysis and Geochemical Vein Characterization of the Salinic Event and Acadian Orogeny: Evaluation of the Hydrocarbon Reservoir Potential in Eastern Gaspe
ABSTRACT
For the past century, eastern Gaspe Peninsula has generated an interest in oil and gas exploration. This paper examines the fractured reservoir play in the Upper Ordovician to Lower Silurian limestones of the White Head Formation. The White Head Formation is strategically important for play concepts in eastern Gaspe because of its stratigraphic position, overlying potential source rocks of Cambrian and Ordovician age, and underlying Silurian and Devonian rocks that host oil seeps. Combined microstructural and petrographic evidence, as well as isotope geochemistry, helped in proposing a genetic link between fracture sets and the Salinic event and Acadian Orogeny. The proposed tectonic model involves three distinct events beginning with shallow to moderate burial, followed by fracturing and uplift as a result of normal faulting during the Salinic disturbance, and deeper burial, fracturing, folding and strike-slip faulting during the Acadian Orogeny. Fractures that developed within the White Head limestones during the Salinic event and the Acadian Orogeny contributed to enhance porosity and permeability to some extent at different stages during the entire tectonic history of the rocks. The presence of liquid hydrocarbon inclusions in Salinic veins and methane inclusions in the Acadian veins indicates that hydrocarbon-rich fluids migrated through the fracture network. The Salinic fracture network could therefore have provided a pathway for expulsion of liquid hydrocarbons from source rocks before they became overmature.
RESUME
Au cours du dernier siecle, l'Est de la Gaspesie a suscite l'interet pour l'exploration de l'huile et du gaz. Cet article evalue le potentiel en reservoirs fractures dans les calcaires ordoviciens superieurs a siluriens inferieurs de la Formation de White Head. Cette derniere est strategiquement importante pour cette demarche d'evaluation a cause de sa position stratigraphique au-dessus de roches cambriennes et ordoviciennes potentiellement roches-meres, et en-dessous de roches siluriennes et devoniennes dans lesquelles on a repertorie des sources d'huile. Une combinaison d'evidences venant de l'analyse microstructurale et petrographique et de la geochimie isotopique conduit a proposer l'existence d'un lien genetique entre des ensembles de fractures, la pulsation salinique et l'orogenie acadienne. Le modele tectonique propose implique trois evenements distincts: d'abord un enfouissement peu profond a intermediaire, suivi par de la fracturation et du soulevement relies a du faillage normal durant la pulsation salinique, puis finalement un enfouissement plus profond, de la fracturation, du plissement et du faillage de decrochement durant l'orogenie acadienne. Des fractures se sont developpees dans les calcaires de White Head pendant l'evenement salinique; l'orogenie acadienne a par la suite contribue a ameliorer dans une certaine mesure la porosite et la permeabilite a differents stades pendant toute l'histoire tectonique de la formation. La presence d'inclusions d'hydrocarbures liquides dans des veines saliniques et d'inclusions de methane dans des veines acadiennes indique que des fluides riches en hydrocarbures ont migre a travers le reseau de fractures. Le reseau de fractures salinique a pu consequemment presenter une voie d'expulsion des hydrocarbures liquides de la roche-mere, avant qu'ils ne deviennent trop matures.
Traduit par les auteurs.
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