November/December 2011 71 Summary Since the announcement made in April 2008 concerning the shale- gas potential of the southern Québec lowlands, 30 new wells have been drilled in the area. The calcareous and organic-rich Middle Ordovician Utica shale is the main target of this recent explora- tion effort. Current knowledge of the area’s geology has led opera- tors to subdivide the shale-gas potential into different play types. To date, most operations have been performed in approximately one-third of the shale basin in the medium-to-deep thermogenic shale-gas play (1000 to 2000 m), located in the central part of the Saint Lawrence lowlands. With original-gas-in-place (OGIP) esti- mates ranging from 120 to 160 Bcf per section, the deep play is considered to be promising. Current efforts focus on determining the highest gas-prone unit within the Utica. The remaining two- thirds of the shale basin has not been largely tested yet, but the po- tential remains promising. On the basis of exploration work carried out over the past 5 years in southern Québec, four other play types have been described: (1) shallow-to-medium-depth thermogenic shale gas, (2) overthrusted shale gas, (3) biogenic shale gas, and (4) Intra-Appalachians sub- basin shale gas. They are less explored than the deep-shale play, but also present interesting potential. This paper describes the previously mentioned plays using basin geology, shale mineralogy, organic-matter type, gas geochemistry, structural style, and infrastructure access. The characteristics of the previously described plays are reviewed from geological, geochem- ical, structural, and production perspectives. Results of evaluations using the concept of flow units, and volumes of OGIP calculated by various organizations, are compared with a recent evaluation using the petroleum resources management system (PRMS). It is concluded that there is promising hydrocarbon potential in the Saint Lawrence lowlands of Québec that continues to stimulate operators to pursue the exploration and development of these plays. Introduction Fig. 1 shows the location of the study area, Utica shale, Québec, Canada, relative to other shale basins in North America, particu- larly the Marcellus and Barnett shales in the United States. Fig. 2 shows the stratigraphic column of the study area. The presence of natural gas in Ordovician shales of Québec’s St. Lawrence low- lands basin has been known for more than a century. A few jobs during the last few decades have shown a certain potential for gas but without achieving any commercial production. It is only in re- cent years, mainly because of relatively higher natural-gas prices in Québec (approximately CDN 1 higher than in the rest of Canada) and access to new drilling and hydraulic-fracturing technologies, that the true potential of Utica gas shales has been demonstrated. Several different scientific and technical studies were needed to evaluate this resource. Results published during the past 3 years, and the new work presented in this paper, tend to show that the Utica shale compares favourably with other North American de- posits (e.g., the Barnett and Eagleford shales located in Texas). The gas quality, the ability to hydraulically fracture the shale, its geographic location, and the economic environment in Québec are all factors that encourage development of this resource. The gas-in-place accumulation in the Utica shale is gigantic (multiple Tcf). Effective methods of production are being investi- gated directly in the Utica shale and by careful examination of ana- logues in other regions, particularly in the United States. Although all shale basins are different, the premises to assess them are essen- tially the same and include a clear understanding of •฀Basin฀geology •฀Shale฀mineralogy •฀Organic-matter฀type •฀Gas฀geochemistry •฀Structural฀style •฀Reservoir฀parameters •฀Pilot฀wells,฀resources,฀and฀reserves •฀Infrastructure Five shale-gas plays in southern Québec (Fig. 3) have been studied on the basis of previously described parameters: 1. Medium-to-deep thermogenic shale gas. 2. Shallow-to-medium-depth thermogenic shale gas. 3. Deep shale and overthrusted shale gas. 4. Biogenic shale gas. 5. Intra-Appalachians subbasin shale gas. The most-studied shale-gas play in the St. Lawrence lowlands at this time is the medium-to-deep thermogenic shale. The play is now in a transition stage between exploration and drilling of pilot wells. Although the project’s development seems slower compared with other basins, work is progressing satisfactorily and positive results have been obtained over the last year. Basin Geology of the Québec Lower Paleozoic Shale-Gas Play Fig. 4 shows a schematic cross section of key geologic elements in southern Québec, which are explained in the next subsections. Calcareous and Organic-Rich Middle Ordovician Utica Shale. The Utica group belongs to the Saint Lawrence lowlands geological province, a sedimentary basin formed during the Early Paleozoic time. Sedimentation starts at the Lower Cambrian time and contin- ues until Devonian time. The Grenville province, in the eastern part of the Laurentia continental shelf, is the basement of the basin. At present day, Silurian and Devonian rocks have been eroded in the basin. The calcareous and organic-rich Utica shales are Ordovician marine shales deposited on top of the massive Trenton limestone sequence. The shales were deposited during the Taconic orogeny, the result of the collision between the Laurentia shelf and a volca- nic arc. At that time (455 to 445 megaannum), a closed sea, rich in organic matter, was forming at the equatorial latitudes, starting the regression of the Early Paleozoic Iapetus ocean. The Utica shales are time and lithological equivalent to Ontario’s Collingwood and Blue Mountain shales, and also to eastern Québec’s offshore MacAsty shales in the Gulf of St. Lawrence. A typical description Natural-Gas Potential in the St. Lawrence Lowlands of Québec: A Case Study J.-Y. Lavoie, J.-S. Marcil, P.K. Dorrins, and J. Lavoie, Junex Incorporated, and R. Aguilera, Schulich School of Engineering, University of Calgary Copyright © 2011 Society of Petroleum Engineers. This paper was accepted for presenta- tion at the Canadian Unconventional Resources and International Petroleum Conference held in Calgary, 19–21 October 2010, and revised for publication. Original manuscript received for review 17 August 2010. Revised paper received for review 26 March 2011. Paper peer approved 28 June 2011 as SPE paper 137593.