Piston Coring Survey
A seabed piston coring surface geochemical study to identify sites of oil and gas seeps in the offshore Espirito Santo Basin of Brazil has been conducted by GEOCHEMICAL SOLUTIONS INTERNATIONAL (GSI). It is the third of several surface geochemical projects developed by GSI that evaluate the hydrocarbon potential of deep-water Brazilian marginal basins. This approach has been employed successfully in various offshore petroliferous basins including the northern Gulf of Mexico, West Africa and in parts of Latin America. In the Espirito Santo Basin, 100 cores have been acquired in water depths ranging from 100 m up to 2,000 m.
Several attributes of the Espirito Santo Basin favor the use of piston coring for regional hydrocarbon charge risk-assessment and source evaluation: (1) The existence of prolific source rocks, (2) Ongoing oil and gas generation and migration, and (3) The widespread occurrence of salt diapirs and faults that can act as vertical conduits for hydrocarbons from the subsurface to the seafloor. Offshore basins with these characteristics are most likely to exhibit a surface expression of hydrocarbon accumulations.
All of the piston cores have been acquired within deepwater ANP blocks available for exploration. Core locations have been selected from seismic data and seafloor sidescan sonar mosaics provided by Petrobras. The cores have been collected on the MARITIMA vessel Ultratec II and geochemical analyses performed at the Center of Excellence in Geochemistry (CEGEQ) in Rio de Janeiro.
The results have been documented in an interpretative final report describing the presence/absence of petroleum hydrocarbons in piston cores and their geochemical characteristics. The report contains maps showing distributions of key geochemical properties, highlighting sites of geochemical anomalies integrated with high-resolution sub-bottom profile of 3.5 KHz. In addition, hydrocarbon seeps encountered have been correlated with known accumulations using geochemical data for selected Espirito Santo Basin oils.
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