ASSESSMENT OF THE BURIAL, THERMAL AND HYDROCARBON GENERATION HISTORY
USING AFTA® AND VITRINITE REFLECTANCE
with maturity modelling provided
by Dr. Doug Waples
microcontinent covers an area of approximately 300,000 km2
within the western Indian Ocean, an area equivalent to the productive
North Sea or the Texas/Louisiana Gulf Coast province. Until the Late
Cretaceous, this microcontinent was sandwiched between northern Madagascar
and the west coast of India; that is, between two giant tarsand fields
and what became the Bombay High Offshore Oil Province.
In three of the
four exploration wells drilled in the Seychelles, possible source rocks
were encountered at several stratigraphic levels. Although relatively
few source-rock analyses have been performed in the region, there is
abundant evidence for the presence of effective source rocks. Some of
the organic-rich horizons show evidence of having generated and expelled
hydrocarbons. Minor hydrocarbon shows, plus gas sniffer and UV fluorescence
anomalies, beach-stranded tars geochemically correlated to specific
source rock horizons, and direct hydrocarbon indicators on seismic data
all confirm a history of active hydrocarbon generation in the area.
However, the present-day geothermal gradient and burial depth are insufficient
to account for the measured organic maturities. Therefore, some of the
key questions facing explorationists are:
- When were observed maturities
reached? When was generation?
- Is there evidence for
multiple periods of heating and cooling?
- What is the timing and
magnitude of each of these episodes?
geology of Seychelles evolved through three phases of rift/drift tectonics
that included multiple periods of uplift, erosion and associated volcanism.
The burial and thermal histories of the resultant sedimentary packages
are therefore quite complex, and a thorough understanding of the relationship
between time of generation and time of structuring is critical for a
proper assessment of prospectivity.
Project details and techniques
is used to identify, characterise and quantify the timing and magnitude
of (multiple) thermal episodes. VR data is also used to constrain the
magnitude of maximum paleotemperature. In combination, AFTA and VR are
powerful tools which provide much needed constraint for rigorous basin
models. Thermal history constraints provided by Geotrack will be employed
by Dr. Doug Waples, an international recognised leader in basin modelling,
to give a constrained basin model for the region and a framework within
which the prospectivity of this frontier region can be confidently appraised.
The study includes
samples from three offshore wells and three outcrop samples from Mahé.
Nine AFTA samples and 13 new VR samples from the Reith Bank-1 well,
together with 12 VR samples from the Owen Bank A-1 well are used to
determine the paleogeothermal gradients and amounts of eroded section.
Well data from Seagull Shoals-1 is interpreted in light of the new results
and included in the regional synthesis. Finally, the new thermal history
and basin modelling constraints are tied to and reconciled with seismic
lines which cross the region. This project aims to provide the most
detailed and comprehensive investigation of the thermal history that
has yet been attempted in the region.
- Identify, characterise
and quantify the main paleothermal episodes (including estimates of
maximum and peak paleotemperatures) with AFTA giving constraints on
- Calculate the paleogeothermal
gradients during each episode
- Investigate the cause(s)
of elevated paleotemperatures - e.g., burial prior to uplift and erosion,
fluid movement, igneous activity
- Estimate the amount
of section missing due to uplift and erosion
- Use the constrained
thermal history derived from AFTA and VR to understand the history
of source rock maturation and oil/gas generation
- Provide constrained
basin models using existing wells and pseudo-well data from various
depocentres within the Seychelles microcontinent
For further details please contact