Complex Petroleum Systems Developed by Subduction Process Offshore Talara Basin, Northwest Perú

Zúñiga-Rivero, Fernando, Hugh Hay-Roe, BPZ & Associates, Inc., Houston, TX; Linda Jenkins, Picayune, MS; and Allen Lowrie, Picayune, MS

Abstract

Study of 2-D marine seismic data, acquired in 1993 along the Peruvian coast, and particularly in the Talara basin, has led to a new geologic model involving five essential components:

1. Subduction of both continental and oceanic sediments along the Peru Trench
2. Incorporation of rich organic material of three different origins:
• From the east: continental derived, mass-wasted debris and turbidites descending across the slope
• From the west: subducted, deep ocean sediments
• From above: organic matter precipitated from the surficial Humboldt Current.
3. Duration of this previously unexamined petroleum system during the past 100 million years.
4. Upward migration of thermally mature, buoyant hydrocarbon fluids (first as petroleum, later as natural gas) through shattered sediments and along normal faults cutting the slope margin.
5. Entrapment of rising hydrocarbons in normal fault blocks and fluviodeltaic stratigraphic traps.

Unique oceanographic-geologic conditions (probably effective since mid-Cretaceous) associated with the "El Niño" phenomenon periodically create a massive organic die-off, as well as normal organic settling-out from the nutrient-rich Humboldt Current. Shallow cores indicate total organic carbon (TOC) ranging from 0.5% to 2.0%. Hydrocarbon generation could take place shortly after incorporation into the subduction zone. Subsidence and burial of Tertiary, Mesozoic, and Paleozoic sediments would also provide hydrocarbon sources, whether along the paleo-shelf or the paleo-slope.

The presence of three separate hydrocarbon-generating systems adds to the prospectiveness of the Peruvian continental margin. The logical area to commence exploration would be westward of the prolific and well-explored onshore and shallow offshore sectors of the Talara basin.