Problem:
Recent poor exploration results in the Møre and
The aim of the project
is to address two main uncertainties in the exploration process:
-
The absence
of clay mineralogical input to a "rock properties" model for the
Upper Cretaceous (shale rock properties in particular), enhancing seismic
attribute evaluation
-
Methodologies
to predict sand-presence in a distal/basinal setting
Furthermore, clay
diagenesis data will reveal differences in the accumulated local heatflow,
which may be crucial for the understanding of the hydrocarbon generation
history.
A last but not less
important aim of this consortium would be to establish/ develop/ maintain a
viable, high-quality “shale rock properties” and clay mineralogical expertise
in
Project background
Sediment composition
The sediments in
relatively deep marine basins are composed of the three main components:
Deposition in the
Similar to what has
been observed in the North Sea Tertiary (cf., Thyberg et al., 2000), one
expects to see regional changes in clay mineralogy reflecting structural and/or
paleoclimatic changes at the basin margin. The most distal fine (silt and clay)
fraction still contains information and has a physical character that is
related to its source area, plus additional characteristics related to the basinal
physico-chemical and depositional conditions (e.g., carbonate content, presence
of biogenic or pyroclastic silica, etc.). In addition, subtle clay
mineralogical changes will also correspond to progradational or
retrogradational depositional trends. Thus, grain size and clay mineral content
(i.e. illite /kaolinite ratio) and the shale facies may give indication of the
distance to the clastic source and provide some indications of source area and
the prediction of turbidite sand deposits.
Volcanic sediments are
normally characterized by high smectite contents. It may contain glass
(hyaloclastites) and basic rock fragments that will be altered to smectite and
Diagenesis may induce
phase changes in the fine fraction (e.g., clay mineralogical diagenesis,
Opal/CT, etc.) that determine present-day “rock physical” properties such as
porosity, density and
velocity (acoustic impedance). Consequently, all these mineralogical changes
will affect “rock physical” properties, and will be visible in seismic. These
changes will potentially affect the “visibility” of potential sandstones hidden
in the rock physical background and/or create ambiguous responses.
Clay diagenesis is
temperature dependant. The illitization of smectite, which normally occurs at
2-3 km burial depth (80-100°C), may occur at much shallower depths due to
high geothermal gradients. Similarly the reaction between kaolinite and
K-feldspar to form illite, which normally occurs at 3.5-4 km depth (130°C), would also
occur at much shallower depths. Thus lateral changes in geothermal gradients,
particularly during the early Tertiary, could cause diagenetic reactions to
occur at variable depths. The effect in
terms of density and velocity increase of these clay mineral reactions may be
more pronounced at shallower depth because the mechanical compaction then is
less advanced.
The diagenesis of the
sandstones should be studied to provide a basis for prediction of reservoir
quality. Evidence of dissolution of feldspar and mica and precipitation of
kaolinite may provide evidence for the presence or absence of meteoric water
flushing which may be limited to a rather proximal facies.
The carbonate content
may also strongly influence the log and seismic response.
Carbonate may be
present as distinct carbonate layers and as carbonate cements in sandstones and
mudstones. The source of the carbonate will be dominantly biogenic. The
carbonate content will be related to the carbonate productivity, clastic
sedimentation rate and the rate of carbonate dissolution in the water and on
the sea floor. It will be interesting to determine the stratigraphically
relevant fossils and also the bulk composition of the pelagic carbonates and
the initial aragonite /calcite ratio.
Sequence Stratigraphy
Biostratigraphical
signals may partly correspond to observed mineralogical changes. These signals
are analysed by both micropaleontology (siliceous microplankton, planktonic vs.
benthonic foraminifera, benthic foraminifera biofacies) as well as palynology
(terrestrial vs. marine input, dinocyst biofacies, reworking). Therefore,
integration of clay mineralogical and biostratigraphical trends may reveal
distal "sand-signals" which may aid to explain trends observed in
regional seismic mapping.
The amount of biogenic silica will be expressed by the
number of radiolaria, and (if present) diatoms and sponge spicules, per weight
unit of sediment. It will be looked for signals of diagenenetic dissolution.
Pyrite steinkerne of radiolaria and diatoms will be quantitatively registered.
High planctonic productivity is commonly connected to transgressive events.
Therefore, we expect increased influx of biogenec silica at flooding surfaces
(intervals), which can be defined by a sequence stratigraphic approach.
Benthic foraminiferal facies reflects environmental changes
in the sea floor waters and the
substrate. To interpret bottom conditions a combination of several
facies parameters will be used: diversity, dominance, wall material groups and
morphogroups. Deep water turbidite deposition is usually associated with
assemblages strongly dominated by simple agglutinated foraminiferal faunas of
low diversity. Their composition is potentially affected by the degree of
turbidite activity.
Regional water mass changes can be monitored by the
quantitative occurrence of planktonic foraminifera and radiolaria. The
distribution of these groups is strongly influenced by the communication
between the depositional area and open oceanic waters. The plankton/benthos
ratio of foraminifera is commonly employed in this connection, and will be used
also by this project. The position of the local CCD is a critical factor for
occurrence of planktonic foraminifera.
During the past few
years, B.Dale (
The environmental and
stratigraphic interpretations from the micropaleontology as well as palynology
data will be compared with a sedimentological synthesis based on mineralogy and
geochemistry. These results will again be compared with geophysical data from
this area.
This will be a fully
integrated interdisciplinary study of the Upper Cretaceous of the
In summary, the product
of the activities of this consortium will be:
-
An
extensive dataset consisting of detailed mineralogical analyses and physical
measurements of regularly spaced silt and clay samples from the Upper Cretaceous
of as many as possible of the existing deepwater wells. This product may be
used as input to each companies’ in-house calibration process (integration with
electric log interpretation, log acoustic properties, etc.).
-
A
calibration of log response as a function of clay mineralogy and other
lithological variables.
-
A
statistical evaluation of existing digital biostratigraphic datasets.
-
Finally, a
(sequence?) stratigraphical and mineralogical model, monitoring and explaining
the spatial (lateral and vertical) distribution of shale (and sand)
mineralogical and rock properties in the Deepwater area, which helps to explain
observed and/or modelled features seen in the seismic data.
In order to be
successful, the consortium should be given access to as much as possible of the
existing/remaining in-situ sample material (sidewall core, core sample).
Project structure
The proposed project
will thus consist of the following parts parts:
Establish a distal,
high-resolution physico-chemical model
Methodology
-
Characterise
shale and silt lithological properties, i.e.:
o
Bulk clay
mineralogy (XRD) and detailed analyses of clay fraction.
o
(the
product of Provenance, Paleoclimate, Transport, Deposition and Diagenesis)
o
Major and
Trace element distribution (XRF)
o
Thin
sections of in-situ samples and a choice of ditch cuttings material (e.g., to
reveal the presence of (pyroclastic?) microcrystalline silica)
-
(If
possible: Establish physical properties of in-situ shale and silt material
(sidewall core and core samples
o
Density
o
Acoustic
properties)
-
Characterise
biogenic components:
o
Biogenic
silica (i.e., the quantitative abundance in the residue, or the relative
abundance of siliceous radiolaria and diatoms)
o
Seafloor
substrate changes, monitored by Benthic Foraminiferal biofacies
o
Regional
water mass events, monitored by e.g., Dinocyst biofacies
-
Distal sand
indicators:
o
Mineralogical
(e.g., Al2O3/SiO2 ratio)
o
Biogenic
(e.g., Palynofacies: Terrestrial vs. Marine, Reworking)
-
Sets of
preferably wet ditch cuttings
samples, available sidewall core and core samples of all released deepwater
wells (Ormen Lange 6305/1-1 T2, Helland-Hansen 6505/10-1, Gjallar Ridge
6704/12-1, Vema Dome 6706/11-1 and Nyk High 6707/10-1). Relatively dense
sampling (ca. 1/20m) for clay mineralogy (XRD).
-
Possible
inclusion of non-released wells (Havsule 6404/11-1, Solsikke 6403/10-1)
-
Aavilable
quantitative biostratigraphic datasets + additional quantitative analyses (both
palynology and micropaleontology).
Sampling
of wet cuttings and possibly also side-wall cores at regular intervals (ie.20m
distance). This could amount
to more than 500 samples. Sampling of cored intervals of sandstones and also
mudstones were they are included in some cores.
Denser sampling over
some intervals with lithological (mineralogical) contrasts as expressed on well-logs
and by marked seismic reflectors. The purpose is to calibrate the log response
with the lithology (mineralogy).
The project will start
by analysing the Helland-Hansen well (6505/10-1), and the results from this
well will be used to plan the remaining analytical programme.
All the samples
(probably 6-700) will be analysed by XRD,
XRF analyses on powder
for the major and trace elements will the carried out on at least two wells.
Selected samples will be analysed by SEM using element mapping and
cathodoluminescence.
Strict quality
requirements are an important measure to maintain consistency between data-sets
generated, in particular for mineralogical characterisation. The consortium
participants should therefore agree upon rigorous quality requirements for clay
mineralogical analyses
-
The project
will mainly be performed at the Geological Institute,
-
Knut Bjørlykke , Jens Jahren and J.P Nystuen will be involved in
the mineralogical and sedimentological analyses. J.I.Faleide and J.P.Nystuen in
the seismic interpreations.
-
J.Nagy and
B.Dale will be responsible for the micorpaleontolical and the palynological
analyses.
Work plan
The project will start
shortly after the budget is finalized probably before the end of 2003.
I year - Sampling of cuttings and cores
from the well listed above in co-operation
with
the oil companies.
Petrographic,
mineralogical and geochemical analyses.
We plan to complete at
least 50% of the analytical programme the first year.
The results and preliminary
interpretations will be made available to the
partners shortly after they are produced.
II
year - Completion of the
analytical programme.
Presentation of the final results
III
year Preparation of the
final report and publications. This will mainly involve the
PhD
student and his supervisors.
Costs (tentative, see budget below)
- Total costs, ca. 4.000.000 NOK / 6 companies:
-
2004:
250.000,- per company; Total 1.5 MNoK
-
2005:
250.000,- per company; Total 1.5 MNoK
-
2006:
100.000,- per company; Total 1.0 MNoK
Budget (Tentative)
PhD stipend for 3 years
total inclusive overhead 1600
000 NOK
Temporary technical
assistance inclusive overhead 150 000
Laboratory analyses
Department of Geology
Technical
assistance for sample preparation etc. 50 000
XRD analyses,
approximately 700 samples 400 000
XRF analyses, approximately 500 samples 200 000
Thin sections and
optical petrographic analyses, 100 samples 150 000
SEM analyses approximately 100 samples 100 000
Experimental compaction
of mud from core samples
in cooperation with NGI 100 000
Travels and running
costs for PhD student 100 000
Travels for sampling
and presentation of results for the
Research Group at UIO 150 000
Log data and seismic
data from PetroBank 250 000
Paleoecological
analyses inclusive overhead
(B.Dale) 300 000
Micropaleontological
analyses inclusive overhead (J.Nagy) 300 000
Total expenses 3800
000 NOK
300 000
Details from
paleonological projects (B.Dale):
330 hrs A.L. Dale @ Kr
800/h = Kr 264 000
(includes 24% moms plus overhead/consumables GeoResearch)
Kr 20 000
computer/software – B. Dale UiO
10 000 consumables “ “
“
6 000 travel (2X2 Oslo/Stavanger)