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Exploration History

Hydrocarbon exploration offshore Nova Scotia began in 1959 and has seen three distinct cycles of activity since that time. A total of 204 wells have been drilled with 127 of these being exploration wells (Figure - Historical Assessments ). Twenty-three significant oil and gas discoveries are confirmed with additional wells encountering numerous oil and gas shows. Total 2D and 3D seismic data acquired to date is 400,954 km and 29,512 km2 respectively.

Exploration Cycle 1

The initial exploration cycle commenced with the awarding of exploration licences to Mobil Oil Canada for the Sable Island region on the shallow water Scotian Shelf in 1959. Subsequent magnetic and gravity surveys lead to the drilling of the first well on Sable Island in 1967 that confirmed the existence of a thick Tertiary- Mesozoic stratigraphic succession (Sable Delta) and had both gas and oil shows. Further licences were awarded to industry and the seismic coverage expanded to cover most of the margin. Between 1967 and 1978, 71 wells were drilled of which 57 were wildcats, and over 140,000 km of 2D seismic profiles were acquired. A number of play concepts were tested, focusing on easily imaged salt structures using the successful Gulf of Mexico analogues, as well as drape over basement features and the carbonate bank margin. Of the 28 wells drilled in the salt structure play, three significant oil and gas discoveries were made: Onondaga (Shell, 1969 - gas), Primrose (1972, Shell - oil & gas), and West Sable (Mobil, 1971 - oil & gas).

In 1972, Mobil tested a new play concept involving rollover anticlines associated with down-to-the-basin listric faults in the Sable Subbasin, thus-far the most prolific depocentre in the basin. The Thebaud P-84 well made a major gas discovery in the fluvial-deltaic sandstones of the Early Cretaceous Missisauga and Late Jurassic Mic Mac formations, and also encountered significant overpressure gas pay in the deeper section of the well. The next year, another new play concept was tested, with the Mobil Cohasset D-42 well discovering light oil in a subtle drape structure overlying the Jurassic age Abenaki formation carbonate bank margin. At the end of this exploration cycle, additional exploration of the rollover anticline play resulted in significant gas discoveries at Citnalta and Intrepid.

Exploration Cycle 2

The second phase of exploration, 1979-1989, was sparked by the major gas discovery in 1979 at Venture by Mobil and Petro-Canada just east of Sable Island. This was a continuation of the rollover anticline play with the Venture D-23 well encountering multiple Cretaceous and Jurassic sandstone reservoirs with very high flow rates (e.g., 22.6 MMcf/d, 278 Bbls/d condensate). The Venture well discovered in a single well about the same total amount of gas that had been found to date in the Sable Subbasin.

Throughout the 1980s, Mobil, its partners and other companies delineated existing discoveries, drilled deeper to new gas-charged overpressured reservoirs (e.g., Venture, Thebaud), and drilled other anticlinal structures. New significant gas discoveries were made at South Venture, West Venture, Olympia, West Olympia, Arcadia and South Sable (Mobil), Glenelg, Alma, North Triumph, Uniacke, Eagle (Shell), Banquereau (Petro-Canada) and Chebucto (Husky-Bow Valley). Shell's light oil find in Early Cretaceous sands within a shallow drape structure at Panuke and Penobscot confirmed on-trend extensions of the earlier Mobil Cohasset discovery. Three deep water wells were drilled to test possible Tertiary and Cretaceous turbidite fan plays but were unsuccessful. At the end of this second cycle (that was ended due to the precipitous fall in oil and gas prices), 54 wells were drilled with 15 significant discoveries confirmed, and a number of wells having significant shows.

Exploration Cycle 3

The third exploration cycle was a two-prong campaign with drilling on the shallow Scotian Shelf and deep water Scotian Slope. The former was initiated by the announcements to develop the light oil discoveries at Cohasset and Panuke in late 1989 by LASMO (Cohasset-Panuke Project), and six gas fields in the Sable Island area in 1996 by Mobil, Shell and partners (Sable Offshore Energy Project). Several exploration wells were drilled by LASMO to test related and nearby structures, with more light oil found at Balmoral in 1991.

In 1999, PanCanadian (now EnCana), the new operator of the Cohasset-Panuke Project, drilled beneath Panuke and made an impressive discovery of slightly sour gas in dolomitized and leached limestones of the Late Jurassic Abenaki reef margin. Delineation drilling confirmed about 39.6 E9M3 (1.4 Tcf) gas in place and the field is scheduled for production in 2010. Additional wells were drilled to test backreef oolitic shoal, forereef talus/debris apron and by-pass sand plays. Some shows were present and play concepts confirmed, but no additional significant discoveries were made.

At the same time, Mobil (now ExxonMobil) and partners initiated an extensive exploration program to test large rollover anticlinal structures in the vicinity of their Sable Project. Although several of the wells discovered good gas pay in a number of the fluvial deltaic sands of the Missisauga and Mic Mac formations, none were deemed to be commercial, as were the results from delineation drilling of earlier discoveries at Onondaga and Glenelg. Other explorers such as Canadian Superior unsuccessfully tested the Abenaki play at Marquis, though they discovered gas at Mariner.

In 1998, large tracts of the deep water Scotian Slope were acquired by industry and following acquisition of large volumes of regional 2D and prospect-centric 3D seismic data, six wells were drilled between 2002 and 2004. The focus of four of the wells was directed towards large anticlinal features related to salt withdrawal. Initial results were encouraging, with Marathon discovering 30 m of net gas pay in its Annapolis G-24 well, and Chevron encountering sands and shows at multiple levels in its Newburn well. Additional drilling by Marathon (Crimson) and Imperial (Balvenie) was disappointing in not encountering any charged deep water sands. Crimson, however, did encounter a 12 m turbidite sand with questionable thin gas pay (Kidston et al., 2007). EnCana drilled an interpreted Tertiary fan on the western portion of the Scotian Slope at Torbrook that in hindsight was determined to be a slump feature. They also drilled a large anticlinal subsalt feature at Weymouth that failed to find any good reservoir sands. Since late 2004, no exploration wells have been drilled in the shallow and deep water regions of the Scotian Basin.

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