Un nuevo sistema petrolero en el Flanco Norte de la Cuenca San Jorge: revaloración de áreas marginales y exploratorias

BELLOSI E., H. VILLAR Y G. LAFFITTE

Mar del Plata

Congreso; 5° Congreso de Exploración y Desarrrollo de Hidrocarburos; 2002

Instituto Argentino del Petroleo

A NEW PETROLEUM SYSTEM IN THE NORTH FLANK OF THE SAN JORGE BASIN:REAPPRAISAL OF MARGINAL AND EXPLORATION AREASThe Pozo D-129 Formation has been historically considered the unique source unit in the eastern, most prolific, region of the San Jorge Basin. The hydrocarbon generative beds bearing lipid-rich, oil-prone, unstructured kerogen were formed in a large lacustrine system (Lower Cretaceous). Towards the basin margins, its generation potential decreases considerably due to low-quality organic facies associated to limited thickness and depth. The evaluation of geologic and geophysical information of exploration wells of the Colhue-Huapi Area (North Flank) indicated the potential existence of a second hydrocarbon source, where D-129 has no effective generation capability. This hypothesis found support on geochemical analysesof rocks and oils that pointed to hydrocarbon generation from a Neocomiano (Las Heras Group) source, charging the reservoirs of the Chubut Group. The Neocomian lacustrine deposits of the Pozo Anticlinal Aguada Bandera-1 Fm. are concentrated in restricted depocenters (grabens and hemigrabens) formed during the late rift stage of the basin. The source facies, identified in the LV-2 (Las Vacas) and RChN x-1 (Río Chico Norte) wells, have good organic contents, moderate pyrolysis yields and mixed amorphous/structuredorganic matter. Their characteristics are comparable to those typically recognized in the Western Flank of the basin, where this unit is a proved oil source. The comparison of an oil recovered from the Mina del Carmen reservoir at the Ea.LE.x-101 (Estancia La Escondida) well with oils of a neighbor field showed significant geochemical differences, indicating distinct origins. In particular, a Neocomiano source has been attributed to the Ea.LE.x-101 oil. The inferred generation of Neocomiano hydrocarbons in marginal sectors of the basin raises the exploratory potential of these areas.