Published 1995 as part of Memoir 62
Copyright © 1995 The American Association of Petroleum Geologists.   All Rights Reserved.

The Oriente basin of Ecuador has produced a substantial amount of oil over the past 20 years. Nearly 3 billion bbl of oil have been recovered from the principal reservoirs in the Cretaceous Napo and Hollin formations. Subtle north-south structures, commonly associated with Andean-related faulting, have trapped much of the recoverable hydrocarbons in the thicker sandstones deposited within the Hollin and Napo reservoirs. East to west thinning of these reservoir units also contributes to the formation of stratigraphic traps. Both the Hollin and Napo formations comprise successions of eastward-sourced fluvial and deltaic sedimentary deposits that prograded westward into shoreline and marine shelf parasequences. The Albian Hollin reservoir interval consists of a dominant alluvial plain sandstone sequence (Main Hollin sandstone) that occupies much of the Oriente basin. In the western Oriente, the uppermost Hollin section grades vertically into open marine strata with isolated tidal- and storm-influenced sandstone bodies. The overlying Napo stratigraphy also consists of sand-rich fluvial and deltaic deposits in the eastern Oriente and abruptly changes to marine shales and limestones and lowstand valley-fill sandstones in the western part of the basin. Extensive structural and stratigraphic trap potential remains within the Napo and Hollin strata in the Oriente basin. High-resolution geophysical techniques and detailed geologic reservoir characterization facilitate successful exploitation of these remaining reserves.