The story of petroleum exploration in the Sydney Basin is best understood in the context of regional historical exploration and specifically for this NS17-1 Call for Bids in the encompassing latest Devonian to Early Permian Maritimes Basin of which the Sydney Basin is its large eastern extension. Though intermittent, petroleum exploration in Atlantic Canada Carboniferous age basins has been ongoing for almost 150 years with two fields discovered in New Brunswick. However, the much larger offshore extensions of the basins are far less explored.
It is important to note that except for four wells, the remaining 209 and almost all 2D seismic in offshore regions under Nova Scotia jurisdiction are located in Tertiary-Mesozoic basins. Of these four wells in Late Paleozoic basins, three are in the Sydney and one in the Magdalen. Within the latter that underlays the south half of the Gulf of St. Lawrence, a total of nine wells were drilled between 1943 and 1983 to test mostly salt-related structural traps. Approximately 30,000 km of 2D seismic data was acquired since the mid-1940s to early 1980s. Of the wells, there is one significant gas discovery. The Hudson’s Bay-Fina East Point E-49 well (1970; re-entered for testing in 1974) is located in shallow waters under Prince Edward Island jurisdiction. It tested 5.3 MMcf/d gas over a 12 m thick interval within a fluvial sandstone of Stephanian age. Of additional note is the Hillsborough No. 1 well drilled in 1943-44 by Island Development Company - a subsidiary of Socony-Vacuum that later became Mobil. It was the first offshore well drilled in the British Commonwealth and tested drape of Mississippian and Pennsylvanian sediments over a deep salt swell offshore Prince Edward Island.
As of 2017, 209 wells were drilled offshore Nova Scotia with 129 exploration and the remainder either delineation or development wells. Over 401,000 km of 2D and approximately 49,000 km² of 3D seismic data has been acquired offshore Nova Scotia since 1960. This exploration lead to twenty-three significant and eight commercial hydrocarbon discoveries with additional wells encountering numerous oil and gas shows in Cretaceous and Jurassic sediments. Three commercial developments evolved from these discoveries: Cohasset-Panuke (1992-1999; oil), Sable (1999 – present; gas & condensate), and Deep Panuke (2013 – present; gas). There are no significant discoveries in Nova Scotia’s offshore Carboniferous basins.
Onshore Exploration – New Brunswick
Carboniferous (Mississippian-Pennsylvanian) strata of the Maritimes Basin blanket a significant portion of the Atlantic provinces of Eastern Canada both on- and offshore (Figures 2.1 and 2.2). They provide significant contributions to their economies through the extraction coal, gypsum, salt, potash, limestone, base metals (Pb-Zn-Ba-Cu-Cs), and, petroleum.
Some of the earliest conventional exploration for petroleum in North America began in 1859 in southeastern New Brunswick. Wells drilled near surface seeps in the Moncton Subbasin tested earliest Mississippian oil-prone continental lacustrine sediments of the Horton Group, with a number drilled over the next four decades. Based on this knowledge, drilling of structural configurations in southeastern New Brunswick occurred over the early 1900s. In 1909, the Stoney Creek oil and gas field was discovered near Hillsborough, New Brunswick at the eastern end of the Moncton Subbasin. It is a combined structural / stratigraphic trap of Early Mississippian lacustrine shoreline sandstones and oil shales. Production of oil and gas followed and up into the 1950s with over 150 wells drilled in and around the field, and a number of modern exploration / delineation wells completed over the 1980-2010 period.
In the early 2000s, Contact Exploration re-entered and cleaned up over 40 historic wells and drilled two additional ones in 2006. Production reinitiated in 2007 and the field is currently under production by Orlen Upstream Canada Ltd. producing 37 API paraffinic oil and minor sweet gas. Average field production in 2015 was about 35 Bbls/d, with cumulative oil production from 1909 to the present approximately 980,000 barrels. In 2000, Corridor Resources Inc. discovered natural gas while drilling a water-disposal well for the Potash Corporation’s mine near Sussex, New Brunswick (also in the Moncton Subbasin). The gas was trapped in the same tight lacustrine shoreline sandstones and organic-rich lacustrine shales as those at Stoney Creek field about 60 km northeast. The McCully gas field has been in production since 2003 with average daily gas production for 2016 of 5.8 MMscf/d.
The source and reservoir rocks for the New Brunswick fields is the Frederick Brook Member of the Albert Formation (Horton Group). In the Sussex area, this organic-rich lacustrine shale has an estimated maximum thickness of 1100 metres and covers an area of almost 500 km2. This unit is recognised as a high-ranking resource play with an estimated in-place gas resource of 67.3 Tcf. (Note: The above statistical information was sourced from the Government of New Brunswick and Corridor Resources websites, (Accessed June 2017)).
Onshore Exploration – Nova Scotia
In Nova Scotia, initial drilling for petroleum occurred on Cape Breton Island with the first recorded well in 1869 (Bell, 1958). Exploration was concentrated in the Lake Ainslie area on western side of the island where surface seeps were known for centuries. It was soon determined the reservoir-source combination was the same Carboniferous age as those successfully explored in New Brunswick, and intermittent exploration and drilling was undertaken throughout Nova Scotia during the 1900s to 1940s. Although hydrocarbon shows were documented, no commercial discoveries were made.
Following Bell’s detailed assessment of Nova Scotia’s petroleum potential (Bell, 1958), and perhaps influenced by it, a new period of exploration was initiated by major industry companies such as Imperial Oil, Pacific Petroleum, and Murphy Oil. This period is considered the first era of ‘modern’ exploration utilizing surface geological mapping, seismic, gravity and magnetic surveys. Eleven wells were drilled between 1958 and 1968 with nine in the Lake Ainslie area of western Cape Breton Island, and one on the mainland near Antigonish, all targeting early Carboniferous plays. Several wells at Lake Ainslie had oil shows in Early Mississippian Horton Group siliciclastics though none deemed commercial (McMahon et al., 1986).
The remaining well was the Murphy et al. Birch Grove No. 1 well (1968). It was the first to be drilled in the Sydney Basin in which coal mining existed since the late 1700s with known presence of associated coal bed methane gas. Between 1963 and 1965, Pacific Petroleum Limited acquired 53 km of seismic data and with surface mapping defined a large anticlinal feature. The well was drilled in 1968 with no hydrocarbons encountered, and while additional seismic profiles were acquired several years later, no further drilling was done. The Birch Grove well, and the basin’s four others noted below are described in detail with petrophysical analyses in Section 3: Well Summaries.
During the 1970s, a large number of serendipitous petroleum shows were present in many mineral exploration boreholes (see McMahon et al., 1986). This was a period of intense exploration for Mississippian carbonate-hosted base metal (Pb-Zn) and potash deposits in the basal part of the Windsor Group in Carboniferous subbasins throughout Nova Scotia and New Brunswick.
Along the north shore of the Bras d’Or Lake in Central Cape Breton Island, Amax Exploration Inc. drilled 36 bore holes between 1975-1978 to assess the Jubilee Pb-Zn deposit. All had varying degrees of liquid petroleum shows (oil, pyro-bitumen and tar) present in cavities, vugs and fractures within limestones and anhydrites (McMahon et al., 1986). In 1978 Chevron Standard explored for similar deposits 10 km northeast at Malagawatch, and one of six boreholes it drilled had oil shows. A seventh borehole – Chevron Bras d’Or No.3A-78 – was drilled specifically to assess this accidental discovery and had flow to the surface of 40° API oil (McMahon et al., 1986). Further drilling for potash there in 1978-1981 had varying degrees of oil shows in all eleven boreholes. This discovery encouraged Chevron to initiate an exploration program in Cape Breton, though with the collapse of oil prices in the early 1980s no further activity occurred.
Offshore Exploration – Sydney Basin
Industry interest in the offshore part of the Sydney Basin began in the late 1960s during Nova Scotia’s first offshore exploration cycle beginning in 1959. Three distinct cycles of exploration activity have occurred in the Nova Scotia offshore since then with the fourth focusing on the deep-water slope starting in 2013.
In the Sydney Basin, the first reconnaissance seismic lines were shot by Texaco Canada in 1969, and then more focused seismic, gravity and magnetic surveys acquired by Murphy Oil Company Limited (1970, 1971) and Texaco (1972-1973) on the Nova Scotia and Newfoundland side of the basin respectively. Murphy had earlier obtained exploration rights for several parcels on the Nova Scotia side of the basin. Prospects were defined through mapping with the largest a long, narrow NE-SW trending anticlinal high being fault bounded on its long sides with simple closure on the ends. The trap was defined as drape over a presumed deep basement ridge. Postulated reservoir targets were early Mississippian Windsor Group porous shallow marine carbonates, and underlying Horton Group fluvial-lacustrine siliciclastics.
The North Sydney P-05 well (1974) was drilled to a depth of 1660.8 m and encountered gas-bearing coals and sands of the Pennsylvanian Morien Group. The targeted Mississippian succession was not penetrated and none of the gas zones tested. In 1976, following reassessment of the seismic data, and encouraged by discovery and flow testing of gas by Hudson’s Bay Oil & Gas at its East Point E-49 well in the Magdalen Basin to the west, Murphy’s partner Shell Canada drilled the North Sydney F-24 well. It was located 5.6 km southwest of P-05 slightly off the crest of the North Sydney feature, and designed to flow test the sandstone F-24 pay zones to determine potential deliverability. P-05 found gas throughout the Morien Group section though log analysis revealed the sands had low porosity and gas was likely sourced from coaly intervals. Nevertheless, two sands, in F-24, were tested that included acidizing and fracking but no gas flowed to surface.
In the late 1970s, Petro-Canada acquired a large exploration licence in the northwestern part of the Sydney Basin extending from Nova Scotia to Newfoundland and up to and including the Cabot Strait. The company acquired a large seismic, magnetic and gravity dataset over its licenses in 1981 and 1983, with the latter including a grid over the North Sydney structure. The operator defined a prospect opposite St. Paul Island located in the Cabot Strait that Murphy originally outlined in 1971. The prospect was a northeast-southwest trending narrow elongate closure bounded on the southeast by a rhombic-shaped structural high. The stratigraphic successions showed steep dips to the north and closure on transverse and normal fault seals. Postulated reservoir zones were within all Carboniferous intervals. The Petro-Canada et al. St. Paul P-91 well was drilled in 1984 to a depth of 2883 m and did not find any evidence of hydrocarbons nor sufficient reservoirs, with the Pennsylvanian succession eroded away.
In 1997, the CNSOPB's NS97-1 Call for Bids included five parcels in the Sydney Basin. Hunt Oil Company of Canada was the successful bidder and in 1998 awarded two Exploration Licences (ELs) in the western side of the basin - EL 2364 and EL 2365. Exploration was delayed for a period of time due to environmental and associated licencing issues, with the acquisition of a 2D seismic dataset in 2005. Following assessment of geophysical and geological data, Hunt decided to let its ELs expire and the lands reverted to Crown.
Though not petroleum-related, a recent onshore well has generated geoscience information useful towards understanding the offshore Sydney Basin. Carbon Capture & Storage Nova Scotia – a government-industry-academic consortium – is responsible for research on the potential for onshore CO2 sequestration and storage. In their initial project phase they assessed the potential of different age geological units throughout the province having sufficient reservoir and seal characteristics. The onshore Sydney Basin near the city of Sydney was determined the best candidate as a thick succession of Carboniferous sediments underlay the region, and a CO2-generating coal-fired power facility is located at nearly Point Aconi. The second project phase required the drilling of a test well to evaluate viability of the rocks. The Early Mississippian Horton Group was determined to be the best potential storage reservoir and overlying Windsor Group carbonates and evaporites as a seal. In 2014, the Carbon Capture & Storage Nova Scotia (CCSNS) No. 1 well was drilled about 6 km east of the Birch Grove No. 1 well (1968). It penetrated 1372 m of Pennsylvanian fluvial sediments followed by 154 m of presumed basement rocks of possibly late Neoproterozoic age. The expected Horton-Windsor rocks were not present and the well terminated at a total depth of 1527 m.
The most recent period of offshore exploration in the Sydney Basin took place on the northeastern half of the basin in waters under Newfoundland jurisdiction. The Canada-Newfoundland and Labrador Offshore Petroleum Board (C-NLOPB) Call for Bids NL06-2 offered three large parcels for industry consideration (Enachsecu, 2006a, 2006b), and in 2008 Husky Canada was the successful work commitment bidder for the southernmost Parcel 1. There were no historic wells and only limited vintage seismic data in and surrounding their new Exploration Licence - EL 1115. In 2010, Husky completed a large 2D regional seismic survey over and adjacent to their licences that extended across the inter-provincial offshore boundary into Nova Scotia jurisdiction. After assessing the basins’ potential, Husky allowed the parcels to reverted back to the Crown. Currently, there are no exploration licences within the Sydney basin in either jurisdiction.