The Silurian Sayabec Formation reservoir potential in the Lower St. Lawrence River area, Québec, Canada Stéphanie Larmagnat1, Alexandre Aubiès-Trouilh2, Michel Malo1, Jasmin Raymond1 1INRS - Centre Eau Terre Environnement, 490, rue de la Couronne, Québec (Québec), Canada, G1K 9A9, 2 Ressources & Énergie SQUATEX Inc., 7055, boul. Taschereau, bureau 500, Brossard (Québec), Canada, J4Z 1A7

Context Fine-scale stratigraphy of the Sayabec Formation (Massé No. 2 well) Reservoir analogs Squatex has recently demonstrated interest for developing In the Massé structure area, the average thickness of the Sayabec Fm is 300 meters. The succession is mainly carbonate interbedded with silty and/or argillaceous The Sayabec Fm facies can be considered as analogous of the oil and gas potential of the Lower St. Lawrence River layers or variable thickness. The interval revealed four levels of reservoir quality (Figure 2). hydrothermal dolomite reservoir facies of the Albion-Scipio area. The company drilled over 6000 meters of stratigraphic and Stony Point fields in the Trenton–Black River Fms wells over the past 10 years. Several of them revealed oil or 1517,0 1587,3 1653,0 1719,0 1784,8 (Ordovician, Michigan basin, USA; Figures 5 and 6) or the gas shows associated with naturally fractured zones, notably Ladyfern gas field (Devonian, Slave Point Reservoir, British within the carbonate Silurian Sayabec Formation (Fm). This Columbia; Boreen and Colquhoun, 2001; Smith, 2006). research project intended to assess the reservoir quality of sedimentary facies from this later lithostratigraphic unit in a 1530,2 1596,1 1661,9 1728,0 1000 µm 1793,4 prospective play, the Massé structure. Here we documented primary depositional facies and established a fine-scale stratigraphic framework.

The Massé structure 1539,0 1605,0 1670,8 1736,0 1801,2 1000 µm The Massé structure belongs to the northern part of the Bioclastic Connecticut Valley-Gaspé synclinorium. In this area, the Coarse grained grainstone Taconian unconformity separates the Cambro-Ordovician bioclastic packstone with strata (to the north) and the Siluro-Devonian sucession (to 1547,7 1613,8 1679,5 1745,3 Pentamerus rich Bioturbated siltstone/mudrock the south; Malo and Bourque, 1993; Bourque et al., 1995). layers The Massé structure is limited by two normal faults and its Laminated/bioturbated mudrock/siltstone sedimentary sequence was preserved with little amount of deformation and only local brecciation and/or fracturing Bioclastic wackestone with 1556,6 1622,6 1688,4 1753,8 bioturbation Figure 5 : Left - Albion-Scipio HTD reservoir facies (from occurrences. Boundstone Thornton and Grammer, 2011). Right - Fractured and vugs Peloidal packstone 68°30'W 68°W 67°30'W (bryozoan showing interconnected porosity within the Sayabec Fm thickets) Bioclastic wackestone to carbonate facies. Price ! Mont-Joli Saint-Noël packstone ! ! Sayabec ! 1565,2 Bioclastic 1631,5 1697,0 1762,8 Ü Bioclastic packstone with large Val-Brillant Luceville Sainte-Angèle-de-Mérici ! packstone with ! ! bioclast Pointe-au-Père ! large bioclasts

Saint-Anaclet 48°30'N Bryozoan boundstones 48°30'N ! Rimouski ! ! La Rédemption 1574,1 1640,2 1705,8 1771,5 Coarse grained packstone with Saint-Gabriel ! crinoids Saint-Léon-le-Grand ! Sainte-Blandine Bioclastic grainstone !

Saint-Zénon-du-Lac-Humqui 48°20'N Breccia

48°20'N ! Saint-Narcisse-de-Rimouski 1648,7 1714,7 1780,3 ! 1582,9 Sample

Affleurements visités Naturally fractured interval

Traverses 100 µm Kilomètres Chemin de Portage 48°10'N

48°10'N Figure 2 : Detailed stratigraphic log of the Sayabec Fm within Massé No.2 well. Reservoir quality intervals (red arrows) are associated with variable porosity types 0 5 10 15 20 68°30'W 68°W 67°30'W (intergranular, intragranular, moldic and vuggy). Permeability is potentially high due to the presence of naturally fractured intervals (green arrows). Figure 6 : Left - Albion-Scipio burrowed reservoir facies with Figure 1 : Location map of the study area illustrating the 252 variable size porosity at the cm-scale (from Thornton and outcrop locations and cross-sections visited. Lateral variation - Massé No. 1 Lateral variation - HTD outcrop Grammer, 2011). Right - Similar fine-grained burrowed facies Massé no.1 has a distinctive 40 m thick with matrix locally replaced by microdolomite in the Sayabec Methods At Saint-Cleophas the Sayabec Fm is exposed in Fm. interval of hydrothermal dolomite (HTD; a quarry on the southern flank of the Lac Ÿ Mapping the Sayabec Fm in the Massé structure area Figure 3) where highly connected porosity is Matapedia Syncline (Figure 4). The 20 m thick Future works (Figure 1); common. Pores are associated with fractures, brecciated dolostone section consists of To improve our understanding of the Sayabec Fm reservoir Ÿ Sedimentologic, stratigraphic and structural analysis at dissolved bioclasts and vugs. Size of voids replacive and pore-filling saddle dolomite of potential, future works will focus on: the outcrop scale; Ÿ ranges from millimetric to pluricentimetric hydrothermal origin (Lavoie and Chi, 2001; geochemistry analyses of fractures-filling mineral phases; Ÿ Core logging of Massé No.1, Massé No.2 and Portage Ÿ and shape varies from circular/pseudo circular Lavoie and Morin, 2004). wireline log re-interpretations with new refined wells (approx. 2 000 meters); to lenticular. stratigraphic framework; Ÿ Ÿ Petrography of 54 thin sections from cores; Figure 3 : Fractured and vug-bearing acquisition of new seismic lines in the Massé structure; Ÿ Figure 4 : Highly porous dolostone from Integration of wireline logs, seismic interpretations and intervals within Massé No.1 well. Width of Ÿ building a 3D geological model of the Sayabec Fm core logging into a 3D database. the Sayabec Fm at the Saint-Cleophas the picture is approx. 30 mm. quarry. integrating all subsurface data available. Ackowledgements References Financial support of the project was provided by both Mitacs and Bourque, P.A., Brisebois, D., and Malo, M., 1995. Gaspé belt, In : Geology of the Appalachian-Caledonian Orogen in Canada and Greenland. H. Lavoie, D., and Morin, C. (2004). Hydrothermal dolomitization in the Lower Silurian Sayabec Formation in northern Gaspé-Matapédia Ressources and Energie Squatex Inc. through a Mitacs Acceleration Williams (ed). Geological Society of America, Geology of North America, v.F-1, p. 316-351. (Québec): Constraint on timing of porosity and regional significance for hydrocarbon reservoirs. Bulletin of Canadian Petroleum Geology, 52(3), postdoctoral fellowship (IT06251). We are gratefull to K. Bedard and Boreen, T., and Colquhoun, K. (2001). Ladyfern, NEBC: major gas discovery in the Devonian Slave Point Formation. 256-269. F.A. Comeau (INRS-ETE) for their technical support throughout the Davies, G. R., and Smith Jr, L. B. (2006). Structurally controlled hydrothermal dolomite reservoir facies: An overview. AAPG bulletin, 90(11), 1641- Malo, M., and Bourque, P. A. (1993). Timing of the deformation events from Late Ordovician to Mid-Devonian in the Gaspé Peninsula. project. 1690. Geological Society of America Special Papers, 275, 101-122. Lavoie, D., and Chi, G. (2001). The Lower Silurian Sayabec Formation in northern Gaspé: carbonate diagenesis and reservoir potential. Bulletin of Thornton, J. E., and Grammer, G. M. (2011). Prediction of Petrophysical Properties of Trenton-Black River (Ordovician) Reservoirs by Canadian Petroleum Geology, 49(2), 282-298. Comparing Pore Architecture and Permeability to Sonic Velocity. ESAAPG abstract, AAPG Search and Discovery, 90142.