Exploration Opportunities

Compared with other circum-Atlantic producing offshore basins such as the North Sea, Gulf of Mexico, Brazil and West Africa, the Scotian Basin is largely unexplored. There are only 127 exploration wells, with the majority concentrated in the productive Sable Subbasin where most wells targeted the rollover anticline play. While this play has been successful, with five fields currently under production, exploration drilling has made it clear that issues such as fault seal, reservoir prediction and the timing of hydrocarbon charge are not fully understood. Nevertheless, a large number of undrilled prospects remain in the Sable Subbasin, in addition to a number of existing oil and gas discoveries that remain undeveloped. The proximity of existing and planned production and transportation infrastructure to many of these prospects and undeveloped discoveries should improve their exploration and development attractiveness. Likewise, a large number of undrilled prospects exist in other basins on the margin that, with the Play Fairway Study (OETR, 2011), have only begun to be evaluated utilizing modern knowledge of petroleum systems and play concepts.

Several of the ExxonMobil Sable Offshore Energy Project (SOEP) fields - Alma and North Triumph - are considered shelf margin deltas of the Lower Cretaceous Missisauga Formation (Cummings and Arnott, 2005; Cummings et al., 2006). They have high in-place gas reserves (>500 Bcf) in excellent quality sandstone reservoirs with high flow rates, are located in shallow water, and at shallow drill depths (~3000 m) (CNSOPB, 2000). These complexes were not deliberately targeted during earlier exploration phases and there remain a number of undrilled structures near these fields. Detailed seismic and lithological studies should help refine the distribution and evolution of shelf margin deltas in the Sable Delta complex, and may reveal additional prospective areas. Based on evidence from seismic profiles, an extension of this shelf margin delta play could exist within younger Logan Canyon equivalent strata now located on the present-day upper slope (particularly along the eastern parts of the margin).

Given the abundance of coarse clastics on the outer shelf, it was expected that potential coarse grain, deep water depositional facies existed in the deeper parts of the Scotian Slope. Deepwater wells such as Annapolis G-24 (2001) and Newburn H-23 (2002) encountered reservoirs and gas confirming an active petroleum system exists on the slope. However, the paleogeography of turbidite systems was poorly defined at the time these wells were drilled and consequently the distribution of turbidite reservoirs was not well understood. Re-evaluation of well data and detailed 2D and 3D seismic mapping of progradational sequences and linkages to canyon systems has revealed depositional fairways that are interpreted to have facilitated deposition of coarser grain turbidites in the salt-dominated region of the Scotian Slope (CNSOPB 2008, 2011, 2012; Deptuck, 2011; OETR, 2011). While some play types have been tested by existing deepwater wells, most have been through a single well, and many other deep water plays have yet to be tested. For example, numerous Jurassic through Tertiary minibasins exist along the 850 km length of the Scotian Margin with excellent potential for traps in sandy slope aprons or the fill of submarine canyons. Turtle structures, salt diapir flanks and crests, sub-canopy traps and fold-and-thrust belts associated with down-slope shortening, remain largely untested (Kidston et al. 2002, 2007; CNSOPB 2008, 2011, 2012; Deptuck, 2011; OETR, 2011).

The development of 1.0 Tcf gas (mean OGIP) Deep Panuke field in the Late Jurassic Abenaki carbonate bank margin also holds great promise for future discoveries. Slightly sour dry gas (0.2% / 2000 ppm) is concentrated in a combined structural and stratigraphic trap within dolomitized, leached and fractured reef margin and reef foreslope facies with highly vuggy to cavernous porosity (Weissenberger et al., 2006). Only a handful of wells have tested this play that extends along the edge of the Scotian Shelf for about 650 km to the United States border, and continues to Florida. A similar succession exists along the edge of the Northwest African margin that remains virtually unexplored. Related plays include lowstand by-pass sands (e.g. turbidites), dolomitized oolitic shoals, reef talus / debris aprons, and backreef patch reefs and shoals (Kidston et al., 2005). Several of these plays have been tested adjacent to the Deep Panuke field confirming the play concepts and in several cases with gas shows.

Stratigraphic plays in the Sable Subbasin have yet to be tested. For example, the large A-B Sand reservoir in the Thebaud field is thought to pinch-out far to the northwest of the field adjacent to the Jurassic carbonate bank margin near the Deep Panuke field. These Early Cretaceous fluvial-marine / strandplain sands of the Missisauga Formation have good reservoir characteristics, are over-pressured and produce at high flow rates (CNSOPB, 2000). Similar plays may exist elsewhere in this subbasin within known producing Jurassic and Cretaceous intervals.

Several subbasins in the Scotian margin have not been explored for over 30 years. These areas – Abenaki and Huron Subbasins - were targeted during the initial exploration cycle to test simpler and easily defined play concepts such as drape over basement structures and salt diapirs. Rollover anticlines were tested during the second cycle in the 1980s. Acquisition of new seismic data coupled with new ideas and play concepts will improve understanding and prospectivity of long-overlooked depocentres like the Orpheus, Mohican and Naskapi Grabens, and the Fundy, Sydney and Maritimes Basins. New knowledge and data should illuminate new plays and better define older ones including subsalt plays, salt related structures, anticlinal features, basement fault structures and stratigraphic traps.

References

Canada-Nova Scotia Offshore Petroleum Board, 2012
Call For Bids NS12-1 Parcels.
http://www.callforbids.cnsopb.ns.ca/2012/01/

Canada-Nova Scotia Offshore Petroleum Board, 2011
Call For Bids NS11-1 Parcels.
http://www.callforbids.cnsopb.ns.ca/2011/01/index.html

Canada-Nova Scotia Offshore Petroleum Board, 2008
Call For Bids NS08-2 Parcels.
http://www.callforbids.cnsopb.ns.ca/2008/02/index.html

Canada-Nova Scotia Offshore Petroleum Board, 2000
Technical Summaries of Scotian Shelf Significant and Commercial Discoveries.
Canada-Nova Scotia Offshore Petroleum Board, Halifax, 257p.
http://www.cnsopb.ns.ca/sites/default/files/pdfs/Technical%20summaries%20of%20Scotian%20Slope.pdf

Cummings, D.C. and Arnott, R.W.C., 2005
Growth-faulted shelf-margin deltas: a new (but old) play type, offshore Nova Scotia.
Bulletin of Canadian Petroleum Geology, vol.53, no.3, p.211-236.

Cummings, D.C., Hart, B.S. and Arnott, R.W.C., 2006
Sedimentology and stratigraphy of a thick, areally extensive fluvial-marine transition, Missisauga Formation, offshore Nova Scotia and its correlation with shelf margin and slope strata.
Bulletin of Canadian Petroleum Geology, vol.54, no.2, p.152-174.

Deptuck, M.E., 2011
Proximal to distal postrift structural provinces on the western Scotian Margin, offshore Eastern Canada: Geological context and parcel prospectivity for Call-for-Bids NS11-1.
Canada-Nova Scotia Offshore Petroleum Board, Geoscience Open File Report (GOFR) 2011-001MF, 42p.
http://www.cnsopb.ns.ca/sites/default/files/pdfs/gofr__2011_001mf.pdf

Kidston, A.G., Brown, D.E., Smith B.M. and Altheim, B., 2005
The Upper Jurassic Abenaki Formation Offshore Nova Scotia: A Seismic and Geologic Perspective.
Canada-Nova Scotia Offshore Petroleum Board, Halifax, 165p.
http://www.cnsopb.ns.ca/sites/default/files/pdfs/Abenaki_report_06_2005.pdf

Kidston, A.G., Brown, D.E., Smith B.M. and Altheim, B., 2002
Hydrocarbon Potential of the Deep-Water Scotian Slope.
Canada-Nova Scotia Offshore Petroleum Board, Halifax, 111p.
http://www.cnsopb.ns.ca/sites/default/files/pdfs/Hydrocarbon_Potential_Scotian_Slope.pdf

Kidston, A.G., Smith, B., Brown, D.E., Makrides, C. and Altheim, B., 2007
Nova Scotia Deep Water Offshore Post-Drill Analysis – 1982-2004.
Canada-Nova Scotia Offshore Petroleum Board, Halifax, Nova Scotia, 181p.
http://www.cnsopb.ns.ca/sites/default/files/pdfs/Deep_Water_Post_Drill_Analysis_2007.pdf  

Offshore Energy Technical Research Association (OETRA), 2011.
Play Fairway Analysis Atlas - Offshore Nova Scotia.
Nova Scotia Department of Energy Report, NSDOE Records Storage File No. 88-11-0004-01, 347p.
http://www.offshoreenergyresearch.ca/OETR/OETRPlayFairwayProgramMainPage/tabid/402/Default.aspx

Weissenberger, J.A.W., Wierzbicki, R.A. and Harland, N.J.,  2006.
Carbonate Sequence Stratigraphy and Petroleum Geology of the Jurassic Deep Panuke Field, Offshore Nova Scotia, Canada.
In: P.M. Harris and L.J. Weber (Eds.), Giant Hydrocarbon Reservoirs of the World: From Rocks to Reservoir Characterization and Modeling. American Association of Petroleum Geologists, Memoir 88, p.395-431.