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Potential Cretaceous Shale Plays in Talara and Sechura Basins, Northwest Peru


The growing importance of U.S. shale gas resources is reflected in the worldwide extension of unconventional shale plays market. This fact has motivated its exploration and exploitation in South America. In Peru, industry reports have suggested that Cretaceous source rocks of Talara and Sechura Basins may be an important future resource of shale plays. For this reason, a unified biostratigraphic review of more than 40 wells was performed using micropaleontological zonations with key data from unpublished reports in order to update the Campanian and Early Maastrichtian stratigraphy from Talara and Sechura Basins, adjusting the assigned age of these units considered as source rocks. The integrated stratigraphic analysis recognized two depositional sequences of widespread distribution in the study area. Cerro La Mesa Sequence (Middle? to Upper Campanian) is comprised of Cerro La Mesa Fm.: lower (LST) and upper member (TST-HST). Redondo Sequence (Upper Campanian-Lower Maastrichtian) is comprised of Sandino Mb. (LST-TST), Tablones Fm. (TST), Redondo Fm. (TST-HST) and Montegrande Fm. (HST). TST units of the proposed sequences are consistent with maximum transgression events recognized in Northern Peru and Ecuador. The next step was an integrated geological-geochemical assessment for Cerro La Mesa (dark brown, dark gray and black shales and limestones) and Redondo formations (dark brown to gray shales) in order to identify their exploratory potential as shale plays. High average TOC: 2.08 wt % (n = 44), kerogen type II/III, OM predominantly marine, Ro values within the oil window (0.6% < Ro < 1.0%), thickness of 110′–1000′, actual drilled depth between 2400 and 10200 feet, and the heavy oil recovered in the well RC1–2XD (46 Bbls, 12.5° API); suggest that Cerro La Mesa Fm. has appropriate conditions for potential shale oil play. On the other hand, regular average TOC: 0.85% (n = 36), kerógeno type III/IV, OM that varies regionally from marine to terrestrial, Ro values within the oil window (0.6% < Ro < 1.0%) and gas window (Ro > 1.0%), thickness of 100′–1100′, actual drilled depth between 2350 and 12350 feet, and records of gas shows in the well CO1–1X; suggest that Redondo Fm. has appropriate conditions for potential shale oil-gas play. This study shows a new possibility for the investment and extraction of potential resources of unconventional hydrocarbon in the near future; and thereby increases the hydrocarbon production in Peru.