Surface Geochemical Evaluation of Offshore Brazilian Marginal Basins

Geochemical Solutions International, Inc. (GSI)

Oil and gas seeps are of great significance to modern offshore petroleum exploration. Foremost, they indicate the presence of generative hydrocarbon source rocks, without which there can be no accumulations. Sediment cores retrieved using a ship-based piston core device can be analyzed in the laboratory to detect hydrocarbons derived from seeping oil and gas. 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 such as Trinidad and Colombia. In deep water where exploration costs are high and few wells have been drilled, the occurrence and nature of hydrocarbon seeps is one of the few available means for assessing prospective areas.

Piston coring has several advantages over other surface geochemical techniques. In addition to being one of the most cost-effective approaches, sediments record an integrated seep signal over time and typically yield sufficient hydrocarbon material to perform conventional geochemical analyses used to identify oil properties, thermal maturity and source rock type. This information is integral to proper play concepts necessary for a successful exploration program.

Heat flow measurements serve critical purposes in oil exploration and production. The measured background or equilibrium heat flow, and measured sediment thermal conductivity provide strict constraints to geochemical models that determine regional scale maturation of basins with respect to oil and gas. In addition, area-wide heat flow surveys provide significant geological information on fluid flow from faults, lineaments, and around structures. Heat flow measurements in conjunction with seismic and sea floor geochemical studies provide a mechanism to assess fault and structural seals and contribute to a better understanding of regional hydrodynamics and hydrocarbon occurrence.

 

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