Petroleum Geology of Baltimore Canyon Trough

Abstract

Abstract Exploration activity to date on the U.S. Atlantic Continental Shelf includes 3 oil and gas lease sales and the drilling of 5 deep strati-graphic test wells and 26 wildcat wells. Wildcat drilling in the Baltimore Canyon trough has been concentrated in the vicinity of the Great Stone dome and along the shelf edge. The Great Stone dome, a large domal structure inferred to be associated with an Early Cretaceous mafic intrusion, appeared to be one of the largest and most promising single structures on the shelf on the basis of the interpretation of seismic data. Six wells have been drilled on the structure, but no shows of oil or gas have been reported. Results of wildcat drilling along the outer edge of the Continental Shelf have been more encouraging. Significant shows of natural gas have been reported from 3 out of 14 completed wildcat wells. The combined initial flow rates were about 2 million m3 per day (68.5 million ft3 per day) from Upper Jurassic sandstone beds at depths of about 4,000 m. An additional test, at one of these wells, flowed 48.4° gravity oil at the rate of 100 m3 per day (630 barrels per day) from a thin bed of Lower Cretaceous sandstone. A commercial size field, however, has not been established. In the Baltimore Canyon trough, analysis indicates that shelf sediments have a relatively low potential for the generation of liquid hydrocarbons, but indications are favorable that natural gas could have been generated below a depth of 3,000 m. However, sandstone porosities deteriorate below 3,000 m, and at these depths, the Jurassic sandstone beds may lack lateral continuity. Tracts to be leased in upcoming sales will extend out to water depths of 2,500 m. In the deep-water area beneath the Continental Slope, the interpretation of seismic data suggests that the shelf prograded seaward during Jurassic time. Consequently, Jurassic shelf facies containing potential reservoir rock may interfinger with slope facies that could contain source rock capable of having generated liquid petroleum. In spite of the huge investments of money that will be required for deep-water exploration, the possible presence, under the slope, of complex extensional-fault patterns, reef complexes, and salt diapirs will probably encourage interest in upcoming sales.