Organic-rich, marine shale Valanginian to Early Aptian Lower to Middle members of Palermo Aike Formation are the main source rock in Austral Basin, Argentina, with an average thickness of 250 meters and six vertically stacked transgressive-regressive cycles. TOC values range from 0.5 to 2.5%, kerogen type II to III and HI from 150 to 300 mg HC/g TOC. About 6.5 billion boe was recovered from Cretaceous to Lower Tertiary conventional reservoirs in the last 50 years.

At present time, the beginning of the oil window in a regional NW-SE framework start at 2,100 meters depth in the eastern flank of fore-deep basin (10,000 sq km), wet gas window is reached at 3,500 meters (5,000 sq km), and dry gas window at 4,300 meters, in the fore-deep and foothill to the west (10,500 sq km). This unit outcrops in the Andean Ranges.

More than 100 wireline logs, 6,000 sq km 3-D seismic and 20,000 km 2-D seismic were used to build the sequence stratigraphic framework, to calibrate the sonic and resistivity curves (Passey method), mapping key seismic stratigraphic surfaces and seismic attributes. Selected cores and cuttings samples were used for analytical research, including litofacies, SEM for pore types and networks, geochemistry for source rock potential, paleoenvironmental indicators and mineralogical composition.

Abundance of hydrocarbon shows were detected while drilling this interval. The C1- C5+ ratio calculation was integrated with wireline logs and mud-log data. Pore pressure analyses show intervals with abnormally high pressures due to hydrocarbon generation.

A complex fault system is affecting Palermo Aike formation. It is composed by

  1. N-S to NE-SW strike-slip trends resulting of the deeper hemi-graben bounding normal fault reactivation in the Danian times and

  2. normal faults forming a polygonal network.

The polygonal faults system is closely spaced (1–2 sq km), and faults mapping is possible only with 3-D seismic data. The polygonal faults suggest a compaction-related mechanism restricted to low-permeability facies in the transition between the fore-deep and the fore-bulge. Combination of both systems may enhance shale's productivity.

Integration of available subsurface in Santa Cruz province and outcrop data allowed to identify potential sweet spot or core areas. Non economic production was performed from this play, for that reason a probabilistic assessment of prospective resources was made comparing with analogous producing basins in the world. Unrisked resources from the unconventional Lower Cretaceous Shale Play are about 1.0 billion barrels of oil and 85 TCF of gas.

URTeC 1579591

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