Recent survey highlights frontier
exploration potential offshore Argentina
The Argentine basin covers an unexplored area of more than 450,000 sq km (173,746 sq mi) on the outer shelf, slope, and basin floor offshore Argentina. In order to support renewed exploration activity and growing interest in offshore explora- tion, Spectrum is currently acquiring a 35,000-km ( 21,748-
mi) multi-client 2D survey offshore Argentina. The new acquisition
program will provide high quality imaging necessary to understand
both tectonic architecture and prospectivity in the Argentine basin,
using a 12,000-m ( 39,370-ft) streamer and dense fold geometry. Final
deliverables will include both broadband PSTM and PSDM, with the
first tranche of data expected to be available in 4Q 2017.
As the first data was relayed via satellite to the company’s operations center in Houston, Spectrum’s President of NSA, Richie Miller,
said: “The new data is amazing even in brute stack, allowing early
participants to begin their analysis of this area in real time.” This is
the first dense regional grid of modern, long-offset, broadband seismic
data on this margin. This data will enable explorationists to search
for oil in a number of plays, complemented by regional studies on
conjugate margins of the southern Atlantic.
On the northern par t of Argentina’s shelf, the Salado and Colorado
basins form part of a series of pre-Atlantic (Karoo equivalent) rift
grabens running east-west. These grabens were infilled during and fol-
lowing the formation of the Atlantic Rift, and acted as funnels for major
Cretaceous and Tertiary sediment input into the Argentine basin. On
existing legacy data, Cretaceous clastic deltaics are observed prograd-
ing over Triassic and Jurassic syn-rift basins at the shelf margin, then
down slope over Early Cretaceous syn-rift geometries which grade into
seaward dipping reflector rich transitional crust and oceanic crust in
the east. The slope sediments of this passive margin acted as conduits
transporting clastics to the basin floor, inevitably depositing extensive
sands as basin floor fans
(BFF). In common with
other passive margins
these have often been in-
terpreted on two-way time
sections, which indicate
the sandy channels provide an up-dip leak point to the BFF. It is
unusual, though widely sought after for exploration purposes, for
these channels to have depositional by-pass zones within them or
between the channel and the BFF. In the absence of these by-pass
zones, such plays have been downgraded due to the risk on up-dip
seal. However when imaged in depth (either as depth converted data
or PSDM), the BFF of the southern Atlantic are observed to be dip-
ping up in a seaward direction, where they pinch out yielding lower
risk stratigraphic traps of immense size.
Such plays at the Early Cretaceous level have been discovered on
modern 2D PSDM seismic data acquired east of Uruguay’s Punta Del
Este basin in the Oriental Del Plata basin, but are as-yet unexplored.
The recent Raya well in Uruguay did not go deep enough to test
these BFF systems, but there is considerable exploration potential
along the Atlantic margin. Additionally, the evaluation of this margin
indicates that a regionally-extensive rich oil source rock of post-rift
Aptian age will be present in both the Oriental Del Plata and the
adjacent Argentine basins.
Initial basin modelling of this margin indicates that Karoo-Jurassic
syn-rift source rocks on the Argentine shelf margin, where geothermal
gradients are high, are oil generative. Progressively lower geothermal
gradients over lower slope, transition and oceanic crust allow both
syn-rift and post-rift sources to be oil generative despite burial under
significant sedimentary packages.
Pre-rift and syn-rift
The Salado basin is a narrow symmetrical basin with up to 7 km
( 4 mi) of continental syn-rift, basal sag and marine sediment fill.
This basin is a conjugate to the Orange basin in South
Africa. Plate reconstructions suggest that prior to Atlantic
rifting a series of Karoo rift basins, aligned in a northeast-
southwest orientation, extended from the Somali Obbia
basin, through the Selous basin of Tanzania, and southwest
Karyna Rodriguez • Mike Saunders
Laurie Geiger • Neil Hodgson
Spectrum Geo Ltd.
Spectrum’s multi-client 2D seismic
acquisition offshore Argentina.
(All images courtesy Spectrum
Basins offshore Argentina with
seismic acquisition area highlighted
by the red polygon and an inset map
showing the Salado, Colorado, and
Argentine basins’ orientations.