A new study designed to investigate the
timing, magnitude and extent of paleo-thermal effects, and to provide
an independent assessment of maturity levels, using AFTA®
Analysis of ~30 new AFTA®
(apatite fission track analysis) samples from 13-15 wells will be the
basis for evaluating variation in thermal, tectonic and maturation histories
throughout the Carnarvon Basin. Using the latest AFTA® and
THR (thermal history reconstruction) technologies, this regional
study (the first of its kind for this area), will delineate the timing
and extent of paleo-thermal effects in each study well, plus provide
an independent test of maturity levels in Mesozoic source rocks. Integration
of the new AFTA results with existing VR and FAMM data will arm explorationists
with an independently-generated thermal and maturation history framework,
which can later be used to constrain more detailed basin models, and
thus help identify which play-types are best targeted in different parts
of the Carnarvon Basin.
A proposal to industry
This proposal to industry outlines the
aims and objectives of a research study which will be undertaken in
the northern Carnarvon Basin by Geotrack International Pty Ltd. Attachment
A provides some background detail about the techniques that will be
applied in this study. More details can be obtained by contacting Paul
Green (61 3 9380 1077). Attachment B contains the application form,
which should be returned by committed parties, prior to the 31st January
Proven oil and gas fields throughout
the Barrow and Dampier Sub-Basins of the greater Carnarvon Basin are
based on numerous and diverse play-types, located in a complex structural
setting. Principle reservoir rocks vary in age from Triassic in the
Gorgon Gas Field, Late Jurassic in the Mutineer Oil Field, and Early
Cretaceous in the Barrow Oil Field. The challenge presented to explorationists
by such a broad range of possible drilling targets is further complicated
by widely recognised suppression of Ro data. This problem mainly affects
measurements in Jurassic and Cretaceous sediments, and stems largely
from difficulties in identifying vitrinite in fine grain marine sediments.
Uncertainties surrounding maturity levels currently make it difficult
to accurately assess magnitudes of maximum paleotemperatures and burial
depths in the Carnarvon Basin.
The tectonic evolution of the Carnarvon
Basin is also complex, and has produced a broad array of structural
traps, for which the "timing" of emplacement is a crucial
element needing to be defined in each petroleum system. Both sub-basins
are bound to the north-west by the Rankin Trend (a series of en-echelon
horsts and grabens), and to the south-east by the Peedamullah and Lambert
Shelves. Within the sub-basins, anticlinal trends occur at Barrow Island,
the Mermaid nose, the Madeleine and Legendre Trends, and the De Gray
nose. All of these structures are associated with unconformities of
varying age and extent (both temporal and spatial), and so the timing
of uplift and erosion, and amounts of section removed need to be accurately
assessed for entry into constrained basin models.
Aims and objectives:
Application of Apatite Fission Track
Analysis (AFTA®) to delineate the timing and extent of
paleo-thermal effects in 13-15 wells (see figure above and provisional
well list below).
Comparison of AFTA-derived maximum
paleotemperatures with VR (vitrinite reflectance) and FAMM (fluorescence
alteration of multiple macerals) data, to independently assess true
maturation levels of Triassic to Cretaceous units throughout the
Provision of constrained thermal
history reconstructions for each study well, plus an interpreted
overview of thermal history styles throughout the northern Carnarvon
Comments on the variation of maturation
and burial/uplift histories within the Carnarvon Basin.
Detailed work program:
- Process 2-3 AFTA® samples from each of
13-15 wells. Sampling will concentrate on pre-Triassic to Cretaceous
aged sediments in: De Grey-1, Goodwyn-1, Wandoo-1, Arabella-1, Candace-1,
Barrow-1, North Gorgon-1, Vlaming Head-1, Fennel-1, Echo Bluff-1,
Onslow-1, Loggerhead-1, West Muiron-3, Resolution-1 and Cape Range-1.
(This list is provisional and changes may be made in response to suggestions
from subscribing companies. Geotrack would also welcome company contributions
of VR and FAMM data to this study.)
- Derive "timing of onset of cooling" and
"maximum paleotemperature" constraints for each AFTA sample
using the latest in-house Geotrack software, which incorporates measured
Cl contents of each apatite grain analysed, as well as fission track
age and length data. Where multiple thermal events have affected well
sites, obtain subsequent "peak paleotemperatures" from the
- Convert VR data to estimates of maximum paleotemperature.
Compare these with the AFTA results to assess the degree and extent
of suppression affecting the VR data in each well.
- Construct maximum paleotemperature profiles for each
well, using AFTA and selected-reliable VR results, and hence comment
on possible mechanisms of heating and cooling in each well. Provided
that paleotemperature profiles are linear, provide formal estimates
of paleogeothermal gradients and removed section (with associated
95% confidence limits).
- Reconstruct thermal, burial and maturation histories
for each of the study wells.
- Provide a synthesis of results, and an overview of
the paleo-thermal events recognised throughout the study area based
on the AFTA results and selected-reliable VR.
to the study is $12,000 per company.
Price includes a full report containing
the thermal history interpretations of each AFTA® sample,
THR (thermal history reconstruction) for each well,
paleogeothermal gradient and section removed analysis (where applicable),
plus full presentation of the AFTA, VR and geological data.
Study commitment date: Notification
that your company will be subscribing to this Research Study must be
received by Geotrack on, or before the 31st January 2000.
(Please use the attached application
form - Attachment B.)
Delivery date: May
report will be available on a non-exclusive basis. Results will be held
confidentially by Geotrack International Pty Ltd for 2 years after the
completion of the study.
Attachment A: Technical background
Apatite Fission Track Analysis
AFTA is based on analysis of radiation
damage trails ("fission tracks") within the crystal lattice
of detrital apatite grains, which are a common constituent of most sandstones.
The continuous production of new fission tracks through time, coupled
to the reduction in track length as a function of temperature and time,
provides the basis of the technique. Thermal history information is
extracted from the AFTA data by modelling measured AFTA parameters through
a variety of possible thermal history scenarios, varying the magnitude
and timing of the maximum paleotemperature so as to define the range
of values which give predictions consistent with the measured data.
A "multi-compositional" kinetic model is employed, which makes
full quantitative allowance for the effect of chlorine content on annealing
rates of fission tracks in apatite. This model is calibrated using a
combination of laboratory and geological data from a variety of sedimentary
basins around the world.
Thermal History Reconstruction
THR involves using AFTA®
and VR to identify, characterise and quantify the major episodes of
heating and cooling which have affected a well section. Specifically,
AFTA is used to determine the timing and magnitude of maximum paleotemperatures
in individual samples. VR data are also used to provide independent
estimates of maximum paleotemperatures, the timing of which is interpreted
on the basis of the information provided by AFTA. The variation of paleotemperature
with depth is then used to constrain paleogeothermal gradients, and
to characterise the mechanisms of heating and cooling.
Linear paleotemperature profiles with
paleogeothermal gradients close to the present-day geothermal gradient
provide strong evidence that heating was caused by greater depth of
burial with no significant increase in basal heat flow, implying in
turn that cooling was due to uplift and erosion. Paleogeothermal gradients
significantly higher than the present-day geothermal gradient suggest
that heating was due, at least in part, to increased basal heat flow,
while a component of deeper burial may also be important. Paleogeothermal
gradients significantly lower than the present-day geothermal gradient
suggest that a simple conductive model is inappropriate, and more complex
mechanisms must be sought for the observed heating. Highly non-linear
profiles can sometimes be suggestive of lateral input of heat at a relatively
shallow level in the well, perhaps due to hot fluids, or igneous intrusions.
Where appropriate, extrapolation of
paleogeothermal gradients to assumed paleo-surface temperatures allows
estimation of amounts of section removed by uplift and erosion.
for enquiries contact us