Abstract

For the past century, eastern Gaspé 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 Gaspé 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.

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