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XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela
1988198819881988----2008200820082008 20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO
TESTING THE SOURCE ROCK MODEL OF-MOD IN A MATURE PETROLEUM PROVINCE
M. Inthorn1, B. Badics2, M. Daszinnies1, O. Lauvrak2, U. Mann1, J.K. Nielsen1, C.Vandré2, and J. Zweigel1, 3
1SINTEF Petroleumsforskning AS, S. P. Andersens vei 15B, NO-7031, Trondheim, Norway, maik.inthorn@iku.sintef.no
2 StatoilHydro ASA, Research Centre, Postboks 7200, NO-5020, Bergen, Norway
3 now with: StatoilHydro ASA, Strandveien 4, 7501 Stjørdal, Norway
This modelling study investigates the source rock potential of Top Pliensbachian to Top
Hauterivian sediments of the Northern Carnarvon Basin offshore north-west Australia
(Figure 1) spanning the eastern Exmouth Sub-basin and the entire Barrow and Dampier
sub-basins (Figure 2). The study area was large (386 x 140 km) and the long modelled
time interval (67 Ma) covered a rather complex tectonic setting. The study was a test of the
capabilities of SINTEF’s Organic Facies Modelling software OF-Mod to predict source
rock quantity and quality away from well control. For this purpose, only half of the wells
with geochemical data were available to SINTEF during modelling, while the remaining
wells were held back by the client (StatoilHydro ASA) until the end of the project. The OF-
Mod model achieved a good fit with the majority of the geochemical data from the hidden
wells confirming the capabilities of the software.
The Carnarvon Basin is Australia’s leading production region for both liquid hydrocarbons
and gas (Baillie and Jacobson, 1997). The region provides an advantageous combination
of good quality, mature Mesozoic source rocks and reservoir rocks of excellent porosity
and permeability. The reservoirs are sealed effectively by several thick shale sequences.
The Carnarvon Basin is an elongate arcuated basin covering an area of 650 000 km2
along the coastline of north-western Australia with 115 000 km2 lying offshore (Baillie and
Jacobson, 1997).The offshore part of the Northern Carnarvon Basin is subdivided into four
major sub-basins (Figure 2). Aligned from SW to NE these are the Exmouth, Barrow,
Dampier and Beagle sub-basins. Although the Carnarvon Basin is a mature petroleum
exploration area, relatively little specific information on the source rocks in this area has
been published so far. The principal effective oil source rock of the Dampier, Barrow and
XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela
1988198819881988----2008200820082008 20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO
Exmouth sub-basins are syn-rift anoxic marine shales of the Dingo Claystone (Oxfordian
to Tithonian, Longley et al., 2002).
The good fit of the OF-Mod model with the majority of the geochemical data from the
hidden wells was achieved by combining the input data with the principle algorithms
accounted for in OF-Mod and general geological understanding based on literature
information. A 3D grid of 2.8 million cells with organic carbon content and quality were
calculated. Maps of source rock thickness, average organic carbon content and hydrogen
index were produced for the most important source rock intervals for later usage in
petroleum system models.
The geological setting with rift basins in a shallow water shelf environment, low distance to
the coastline, and several large river deltas within or in the vicinity of the study area leads
to a high content of terrigenous organic matter in the sediments (e.g. Bishop, 1999;
Longley et al., 2002). This was confirmed by geochemical interpretation of the available
well data and the modelling results. Accordingly, the dominant part of the modelled
Jurassic to Lower Cretaceous section only has poor or fair source rock potential in the
study area.
While the fit of the modelling results with the well data is generally very good for the Lower
Jurassic Athol Fm. and the Early Cretaceous section (Figure 1), the results for the Dingo
Claystone are more ambiguous. One main advantage of the OF-Mod software is that
several conceptual settings can be easily tested within short time. Three settings are
presented differing in the way deposition during the formation of the lower Dingo Claystone
(Oxfordian to Kimmeridgian) was handled. Setting 1, modelling a conservatively low
production of marine organic matter and a completely oxic water column, is the best-fit
model if the entire set of well data is considered. However, this setting results in
dominantly fair and only locally good source rock potential of the lower Dingo Claystone
sediments. In Setting 2 the productivity was increased, while in Setting 3 anoxia was
modelled below 110 m water depth during deposition of the Dingo Claystone. Settings 2
and 3 predict several hundred meters accumulated thickness of sediments with very good
and good source rock potential but overestimate the well data at some well positions. The
XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela
1988198819881988----2008200820082008 20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO
results indicate that anoxia may only have occurred temporally and in parts of the study
area, where the deepest parts of the rift-basins were protected from water exchange by
currents.
References
Australian-Government, (2006) Areas W06-13, W06-14 and W06-15 Barrow Sub-basin,
Carnarvon Basin Western Australia. Release of offshore petroleum
exploration areas Australia (Ed. by Department of Industry, Tourism and
Resources), pp. 33.
Baillie, P.W., Jacobson, E.P., (1997) Prospectivity and exploration history of the Barrow
Sub-basin, Western Australia. APPEA Journal, 37(1), 117-135.
Bishop, M.G., (1999) Total Petroleum Systems of the Northwest Shelf, Australia: The
Dingo-Mungaroo/Barrow and the Locker-Mungaroo/Barrow, Open-File Report
99-50-E (Ed. by U. S. Department of the Interior, U. S. Geological Survey),
pp. 49.
Longley, I.M., Büssenschütt, C., Clydsdale, L., Cubitt, C.J., Davis, R.C., Johnson, M.K.,
Marshall, N.M., Murray, A.P., Somerville, R., Spry, T.B., Thompson, N.B.,
(2002) The North West Shelf of Australia – a Woodside perspective. In: M.
Keep, S.J. Moss (Eds.), The Sedimentary Basins of Western Australia 3:
Proceedings of the Petroleum Exploration Society of Australia Symposium,
Perth, WA, 2002 (Ed. by M. Keep, S.J. Moss), pp. 27-88.
XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela
1988198819881988----2008200820082008 20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO
Figure 1. Regional stratigraphy of the Carnarvon Basin (modified after Australian-Government, 2006). Red box outlines time interval of particular interest.
XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela
1988198819881988----2008200820082008 20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO20 AÑOS DE ALAGO
Figure 2. Structural elements of the northern Carnarvon Basin (modified after Australian-Government, 2006).