The prospectivity of Peru’s offshore basins has been evaluated by a USTDA funded study conducted by Gaffney Cline & Associates for Perupetro. In contrast to most convergent margins, the coastal basins of the northern continental margin of Peru have been highly productive, producing more than 1.8 billion barrels of oil. This productivity is fundamentally related to the anomalous nature of the continental shelf and upper slope, which are underlain by Precambrian and Paleozoic continental crystalline rocks rather than accreted oceanic rocks. Paleozoic and Cretaceous sediments overlie the crystalline rocks. During the Cenozoic, several extensional basins formed and subsequently were inverted as a result of reactivation of basement faults.

Unlike offshore basins farther south, the northernmost Tumbes- Progreso basin is a large pull-apart basin. The basin has produced oil and gas from the Neogene section; however, a thicker Eocene section remains essentially untested. BPZ Energy is currently proceeding with the development of Corvna and Pietra Redonda gas fields. Good source rocks are present within the basin. Exploration risks are presented by the complex structure produced by extensional faulting and local inversion, and also by reservoir uncertainties.

The bulk of coastal production has been from the Talara Basin, where numerous Paleogene, Cretaceous and Paleozoic reservoir intervals have been established. Exploration risks relate to reservoir quality and reservoir segmentation caused by multiple sets of extensional faults. Recently, Petro-Tech Peruana made a discovery at the south end of the basin in fractured Paleozoics.

Farther south, the Trujillo Basin has been tested by only four exploratory wells, while the offshore portions of the Sechura, Salaverry and Pisco Basins remain undrilled. Oil seeps and maturation modeling suggest the presence of mature Cretaceous source rocks in all three basins and early mature Eocene source rocks in the Trujillo basin. Anticlinal and fault traps are widespread in these basins as a result of multiple periods of Cenozoic extension and compression. Analysis indicates that two of the four Trujillo wildcat wells were drilled off-structure with respect to deep targets, while the other two tested the basement arch between the Trujillo and Salaverry basins. Reconstructions indicate traps along this arch formed only in the late Miocene. Although this timing diminishes the prospectivity of the arch, it allows charging of traps in the Salaverry basin with hydrocarbons migrating from the Trujillo basin during the late Eocene to early Miocene.

Targets in the Trujillo Basin include turbidite sands. This study has resulted in a better

Unnumbered Figure. Peru Basins.

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Unnumbered Figure. Depth-converted seismic profile from offshore Peru traversing the Trujillo basin (SP 1400-2400), the Trujillo-Salaverry arch (SP 2600-2800) and the northern part of the Salaverry basin (SP 3000-4200). The profile shows a pop-up structure to the northeast of an extensional basin.

Unnumbered Figure. Structure map of the Middle Eocene, inferred from its seismic-stratigraphic signature to be carbonate-prone. The structure map shows the areal extent of a pop-up structure to the northeast of an extensional basin. Spacing between adjacent dip profiles is approximately 20 km so only the largest features show up on this regional grid.

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understanding of the paleogeography that controlled the distribution of these sands. Cretaceous sandstones in the Trujillo and Salaverry Basins and probable Eocene carbonates in the Salaverry and Pisco Basins may also be prospective. Fractured Paleozoic strata are objectives in the Sechura Basin and perhaps in the other basins as well.

Unnumbered Figure. Isopach map from the top of the Middle Eocene to the top of the Paleozoic basement metamorphics, encompassing the basal Tertiary, Paleocene and Cretaceous sections which include coarse siliciclastics (conglomerate and sand) in the Lobos 1X well. The Cretaceous section may include a Muero Fm (equivalent) source interval known to be present to the north in the Talara basin. The Cretaceous section is mature for oil in the subbasin roughly defined by the 2,500 m isopach contour, based on thermal maturation modeling.

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