The San Jorge Gulf Basin is located in the central portion of Patagonia, Argentina. It has more than 100 years of oil exploration and development. This contribution aims to show the first results of evaluating unconventional reservoirs of the Pozo Anticline Aguada Bandera Formation (PAAB Fm.) in Cerro Piedra oilfield, Santa Cruz province. During the middle Jurassic to Early Cretaceous, an extensional period led to the initial opening of the San Jorge Gulf Basin generating a series of deep isolated basins, called informally "Neocomian depocenters". These were filled first with sedimentary volcanic complex and equivalents after that lacustrine and deltaic sediments in the eastern sector of the San Jorge Gulf Basin while marine and mixed lacustrine environments prevailed in the western region. The Neocomian cycle started with the filling of these halfgrabens with shaly conglomerates and shales of the PAAB Fm. and equivalents that constitute the late synrift sequence. During the sag stage, these depocenters were filled up with sandstones of the Cerro Guadal Formation. In the study area, the shale rock has type I/II kerogen. The total organic Carbon (TOC) varies between 2 and 4%, with organic rich sections that can be around 200 to more than 1000 meters thick. The maturity ranges from oil to gas depending on the position and depth of grabens. An exploratory well was drill in the oil window, and hydraulic stimulated during completion in PAAB Fm. shales at 2400 meters below sea level. From the DFIT data, an overpressure of 30% was verified and the fracture gradient was 0.87 psi/ft. The post-frac test showed 43° API oil and became the first sample of PAAB Fm. in source fluid in the basin. These encouraging results reinforce the potential of this lacustrine shale to continue the exploration as shale resource system, which was previously envisaged on its excellent geochemical characteristics, adequate thickness and its more than 2000 km2 areal extension.
The Golfo San Jorge Basin (GSJB) is located in central Patagonia between latitudes 44° and 47°S, covering a surface of approximately 180,000 km2. This intracratonic basin is mostly extensional and extends roughly in an east-west direction from the Andean Belt to the Atlantic Ocean. It is bordered to the north by the Cañadon Asfalto Basin and to the south by the Deseado region. The basin is divided into five different regions according to the present structural style. The North Flank, South Flank, and Basin Center are characterized by normal faults with E-W strike, where each region is dominated by dipping directions basinward (Figure 1) (Figari et al., 1999; Sylwan et al., 2011). The San Bernardo Fold Belt (SBFB) and Western Flank are identified by positive tectonic inversion features. The former characterized by the domain of contractional structures N-S oriented and the latter by structures with NW-SE strikes with a lower degree of inversion (Fitzgerald et al., 1990; Figari et al., 1996, 1999; Sylwan et al., 2011). The study area, Cerro Piedra Cerro Cuadrado oilfield, is in the boundary between SBFB and the Western Flank.