Petroleum Systems of Deepwater Scotian Basin, Eastern Canada: Challenges for Finding Oil versus Gas Provinces

Abstract

Abstract The preliminary Petroleum System Risk Assessment (PSRA) has predicted the presence of viable petroleum systems with possible gas- or light oil-saturated deepwater fans and other reservoirs of economic significance within various sectors of the Scotian Slope, Eastern Canada. Four factors have controlled the variations within the individual Petroleum Systems: heat flow and basement fractures; turbidite flow and source rock anoxicity; timing of fluid flow movement within the defined trap; and survival of hydrocarbons within traps. Gas-condensate is considered the major hydrocarbon component within various sectors of the Scotian Slope. The prognosis implies the presence of six petroleum provinces within the Scotian Slope that may contain 15 to 43 Tcf of gas and 1.7 to 4.7 BB of crude oil (mostly of light oil and condensate) based on probabilistic resource assessment. Introduction The Scotian Basin is one of the major Mesozoic-Cenozoic sediment depocenters of Eastern Canada that lies in offshore Nova Scotia extending from the Laurentian Channel in the northeast and the Georges Bank in the southwest near Canada- US (Maine) border. Since the late 1960's, a total of 180 exploration and development wells have been drilled in the Scotian Basin, almost all on the shallow shelf. Previous wells were mostly drilled surrounding the Sable Island area resulting in twenty-three significant hydrocarbon (mostly gas and condensates) discoveries (Ref. 1). Since 1995, renewed interest in gas exploration within North America and global deepwater exploration successes have led most major oil and gas companies to obtain exploration licenses in both the Scotian Shelf and Slope (Fig. 1). Fig.1. Map of Nova Scotia offshore regions showing distribution of exploration licenses (permission from Nova Scotia department of Energy)(AVAILABLE IN FULL PAPER) Implication of Petroleum System Risk Assessment A Petroleum System Risk Assessment (PSRA) has recently been introduced in the deepwater portion (Scotian Slope) of the Scotian Basin, Eastern Canada (Fig. 2; Refs. 2-3). This type of 'Risk Assessment' that leads to a 'Proven Success' is dependent on the complete appraisal of three modular components associated with Petroleum System Analysis (Refs. 3 and 4):Geological and Geophysical (2D/3D seismic analysis and configuration of play types);Synthesis of geochemical and petrophysical data interpretation and comprehensive 2D/3D petroleum system modeling (hydrocarbon generation, expulsion, and migration of fluid flow through porous media); and Comparing seepage analysis, seismic wipeout and petroleum system modeling (hydrocarbon survival within target reservoirs). Accordingly, PSRA will vastly improve predictions of 'oil' and 'gas' saturation versus no saturation and the probable volume of expelled hydrocarbons within selected play types. This concept was primarily developed for the Scotian Slope because of associated high risk factors inherent in this virtually unexplored region: unknown distribution of hydrocarbon source and reservoir rocks within various sectors of the Scotian Slope in relation to salt movement and growth faults and possible timing of oil/gas flow within source-carrier bed-reservoir conditions.