Review of Nova Scotia's Deepwater Drilling and Its Effect on the 2002 Resource Assessment

Abstract The Scotian Slope is 850km long with an area of 80,000km2 and has been tested by only ten wells clustered into two narrow areas. Four deep water wells drilled between 1982 and 1986 were Shubenacadie, Shelburne, Evangeline and Tantallon. These wells were dry and abandoned. Between 2002 and 2004 industry drilled six deepwater wells on the Scotian Slope resulting in one gas discovery (Annapolis), one gas show (Newburn), and four dry wells (Balvenie, Crimson, Weymouth and Torbrook). The Scotian Basin is a passive margin with proven petroleum systems and past production from the Cohasset-Panuke oil fields, ongoing gas production from the Sable Project and probable future production from Deep Panuke gas field. This activity is all on the shallow Scotian Shelf. Around 2000, the exploration focus shifted to the deepwater Scotian Slope because of the impressive hydrocarbon discoveries and high success rates in the deepwater of other circum-Atlantic basins such as the Gulf of Mexico, offshore Brazil and West Africa, and recently Northwest Africa (Mauritania). In 2002 the CNSOPB completed a deepwater resource assessment prior to results from the recent six wells. The assessment consisted of 12 geostatistical computation runs to capture the diversity of play areas and play types. The recent drilling results affect three of those twelve runs by altering input parameters addressing the presence and quality of reservoir. Gas in Annapolis and Newburn proves that an active petroleum system is working. Annapolis found 27m of generally thin gas-bearing sands and Newburn encountered several thin (2-3m) gas-bearing sands. Furthermore, many of the gas-bearing sands were encountered unexpectedly below 5000m with average porosities from 14-19% which expands the zone of prospectivity. In 2006 the CNSOPB revised the 2002 assessment. The impact of the deepwater well results on the undiscovered gas and oil potential was found to be minimal. The comparison is shown in Table 1, with gas potential reduced only by several Tcf and oil potential by fractions of billions of barrels. Table 1. - Assessment Results(Available in full paper) Introduction The deepwater slope offshore Nova Scotia extends from the shelf break at 200m of water to almost 4000m. The slope area under study is defined by the seaward limit of the Argo salt and industry seismic coverage generally within the 3000 to 4000m range. A highly exaggerated three-dimensional perspective of the offshore bathymetry, with the original four slope wells, is shown in Figure 1. Fig. 1 - Pre 1987 Deep Water Wells This area was the subject of the CNSOPB's 2002 report; "Offshore Hydrocarbon Potential Deepwater Slope" (Kidston, A.G., Brown D.E., Smith B.M., and Altheim, B., 2002). This study included a basin analysis and numerical assessment of the hydrocarbon potential for gas and oil. Since that report, six new deepwater wells were drilled between 2002 and 2004. This paper examines these well results and their impact on the 2002 assessment numbers. In order to fully understand thea ssessment process used in this paper, the original report should be consulted. In addition to the evaluation of the recent six wells, four wells drilled in the mid-1980's are also examined.

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