Petroleum Geology of the Upper Jurassic and Lower Cretaceous, Baltimore Canyon Trough, Western North Atlantic Ocean (1)

Abstract

Numerous hydrocarbon shows, including a noncommercial gas and gas-condensate accumulation, occur in the Baltimore Canyon Trough within sandstone units deposited in prograding coastal-plain and transitional-marine environments located updip of an Oxfordian/Kimmeridgian carbonate shelf edge. The coastal-plain and transitional-marine facies are overlain by a fine-grained deltaic complex dominated by delta-plain shales which collectively form a regionally extensive top seal unit. This deltaic complex prograded into a back-reef lagoon during aggradation of lower Kimmeridgian through Berriasian shelf-margin carbonates. Wells drilled seaward of the continental shelf edge (>1500 m water depth) tested large structural/stratigraphic closures along the downdip termination of the Upper Jurassic/Lower Cretaceous carbonate shelf edge but encountered no significant hydrocarbon shows. Reservoir rocks in these wells consist of (1) oolite grainstone, which was deposited within a shoal-water complex located at the Aptian shelf edge, and (2) coral-stromatoporoid grainstone and boundstone, which formed an aggraded shelf-margin complex located at the late Kimmeridgian through Berriasian shelf edge. Structural closures having reservoir and top seals are present in both updip and downdip trends. Hydrocarbon shows in wells along the shelf interior trend indicate the presence of mature source beds, at least locally. The absence of hydrocarbon shows in downdip carbonate reservoirs and around the Schlee Dome, however, suggests charge/migration mechanisms within the fetch areas of these objectives have failed. Failure of charge can be due to (1) absence of mature source rocks, (2) absence of migration pathways from source rocks to reservoirs, and/or (3) absence of top seals at the time of hydrocarbon migration. Continued development of play concepts in the Baltimore Canyon Trough, therefore, requires identification and mapping of potential source-rock intervals and construction of hydr carbon expulsion models to time hydrocarbon generation relative to trap formation.