Petroleum Systems of Deep-Water Basins - Gulf Coast Section SEPM

Complex Petroleum Systems Developed
by Subduction Process, Offshore Talara Basin,
Northwest Peru
Fernando Zúñiga-Rivero
Hugh Hay-Roe
BPZ & Associates, Inc.
11999 Katy Freeway, Suite 560
Houston, Texas 77079
(e-mail: bpz@bpzenergy.com)
Linda Jenkins
10 McCarty Island Road
Picayune, Mississippi 39466
(e-mail: libertybelle55@hotmail.com)
Allen Lowrie
238 FZ Goss Road
Picayune, Mississippi 39466-9458
(e-mail: alowrie@webtv.com)
Abstract
Study of 2-D marine seismic data of 1993 vintage along the Peruvian coast has led to the idea that subduction of
marine sediments beneath a continental plate may be a potentially important mechanism for petroleum generation.
The concept can be embodied in a new geologic model involving five essential factors:
1. Subduction of both continental and oceanic sediments along the Peru Trench.
2. Incorporation into the subducted material of rich organic material from two different sources:
3. From the west: subducted deep-ocean sediments.
4. From above: organic matter precipitated from the surficial Humboldt Current.
5. Probable duration of this previously unexamined mechanism during the past 100 million years.
6. Upward migration of the thermally mature, buoyant hydrocarbon fluids (first as liquid petroleum, later as natural
gas) through the shattered sediments and along normal faults cutting the slope margin.
7. Entrapment of rising hydrocarbons in anticlinal closures, normal fault-blocks and fluviodeltaic stratigraphic traps.
Hydrocarbon formation must have benefited from unique oceanographic-geologic conditions associated with the
“El Niño” phenomenon, and probably effective for the past 20-25 Ma. El Niño periodically generates a massive erosion
of the coastal plain, which provides reservoir-grade sediments to the continental slope. Normal organic output
from the nutrient-rich Humboldt Current is a primary factor in the creation of source rocks; the other source is subducted
deep-sea sediments. Shallow cores taken during Leg 112 of DSDP (Yeats et al, 1976) indicate total organic
carbon (TOC) ranging from 0.5% to 2.0%. Hydrocarbon generation could take place after incorporation into the subduction
zone. Subsidence and burial of Tertiary, Mesozoic, and Paleozoic sediments would also provide hydrocarbon
sources, whether derived from the paleo-shelf or the paleo-slope. The presence of two separate hydrocarbon-generating
systems would enhance the prospectiveness of the Peruvian continental margin. The logical place to commence
exploration is westward from the prolific and long-developed onshore and shallow offshore sectors of the Talara
Basin.
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