Exploration Insights March 2020 | Page 32

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Pseudo 1
Quseir
A-1X
Quseir
Pseudo 2 B-1X Pseudo 3
Pseudo 4
Shagara
Mobile Salt
Kareem-Zeit
1D MODELING: CALIBRATION WELLS AND PSEUDO WELLS
Shagara
Rudeis
0.8 Ro Early Oil
1.35 Ro Main Oil/Late Oil
2.0 Ro
Gas
an
rd
Wa
The first stage of any modeling project is the calibration well. A combination of the key controlling
inputs listed above is sought that provides a good fit to the data available in the well, the structural
history of the basin, and known observations on any petroleum systems present (e.g. age of effective
traps). Close collaboration among regional specialists, structural geologists, and modelers is vital.
Mobile Salt
Kareem-Zeit
0.6 Ro
Many thermal histories in passive margin settings are fortunately relatively simple. However, more
complex thermal histories do occur. A complex heat flow history, involving several short periods of very
high heat flow related to mantle/volcanic activity, was necessary to honor the various types of data
from the calibration well shown in Figure 1.
Basal heat flow increases with proximity to rift axis
Legend
Oligocene
Data control for modeling
Late Pliocene–Pleistocene Late Cretaceous–Eocene Depth control
Early Pliocene Paleozoic–Early Cretaceous Lithological control
Middle–Late Miocene Exhumed Mantle Present-day heat flow data
Early Miocene Basement Geothermal gradient data
© 2020 Halliburton
Figure 2> Location of two calibration and four pseudo well models on a play cross-section in the Red Sea. Results are illustrated
by the 0.6, 0.8, 1.35, and 2.0 Ro lines, which depict how the depth to the oil and gas windows changes along the transect, due to
variations in (thermally conductive) salt thickness, overburden, and heat flow. For further details of this model, see Stanton et al.,
(2019) and the February 2020 issue of the Exploration Insights magazine.
2D MODELING: SECTIONS
2D modeling is more time consuming than 1D modeling. A
cross-section is constructed, and lithology polygons are assigned
properties that honor expected lateral facies changes. The line of
section needs to intersect, or be close to, 1D calibration wells and
representative kitchen locations.
Figure 1> Modeled temperature history of a well in a gas-bearing structure in Algeria. The region is currently experiencing a high
heat flow of around 100mW/m 2 related to a mantle plume. Ro (vitrinite reflectance) and apatite and zircon fission track data (Logan
and Duddy, 1998) suggest that the region experienced spikes of even greater heat flow in the past, represented by the rise of the
red and yellow isotherms. If such data were integrated into the model, the resulting thermal history and any subsequent modeling
results would have been wrong.
2D modeling enables lateral movements of heat and fluids to be
evaluated, and should be considered in complex regions, such as
salt basins (Figure 3), where heat transfer may be focused laterally
into, then up, salt diapirs. Pressure predictions are also possible, as
is 2D modeling of oil and gas migration.
“1D modeling is relatively
simple and quick, often
enabling ten or more
1D pseudo wells to be
created in the time it
would take to construct a
2D model.”
Once the initial 1D model has been calibrated, a series of pseudo wells can be created elsewhere in the
basin, as in the example shown in Figure 2. Depth-controlled or converted seismic data are the main
methods of obtaining these columns. The calibrated thermal history is projected to these locations of
interest, which are not data-controlled. A prediction of temperature, and thus maturity, through time is
made at the predicted source level. Petroleum systems charts can readily be produced for each model.
1D modeling is relatively simple and quick, often enabling ten or more 1D pseudo wells to be created
in the time it would take to construct a 2D model. It is also easy and quick to run sensitivities to test
the impact of varying inputs, such as changing the kerogen type or varying heat flow history. The main
limitation of 1D modeling is that it is difficult to extrapolate predictions any significant distance away
from the pseudo well location, and the possible effects of lateral heat or fluid flows cannot be modeled.
Figure 3> A 2D model produced over a section in a Mexican salt basin. Note how the modeled oil window is lower below the region
of thick, thermally conductive salt on the left-hand side of the section. For further details of this model, take a look at the article on
this modeling project in the May 2019 issue of the Exploration Insights magazine.
These may be derived from examination of regional cross-sections, and can be adjusted to fit the
vitrinite reflectance profiles in the control well.
North-east
South-west
The timing and amount of erosion on unconformities
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