Verlag des Forschungszentrums Jülich
JUEL-3592
An integrated organic geochemistry - basin modelling approach was applied to
reconstruct the burial and thermal history, oil generation and migration in the
Songliao Basin. Basin modelling was conducted along the constructed regional
profile using the two dimensional modelling programme PETROMOD™ as well as the
one-dimensional modelling programme PDI-PC both developed by IES Jülich, Germany.
Organic geochemical data were integrated into the basin model, and provided
valuable constraints on the simulated results.
Organic maturity parameters are widely used as calibration data for simulation of
burial and thermal histories of sedimentary basins. A review of the related case
studies shows that facies and lithology influence the organic maturity parameters.
However, the degree of the these influences differs from parameter to parameter,
from lithofacies to lithofacies, and from basin to basin. A detailed investigation
on maturity parameter variability with lithofacies in the Upper Cretaceous
lacustrine deltaic sequence of the western Songliao Basin provided a preliminary
evaluation of the applicability of different maturity parameters in the basin.
23 samples of black shale, grey siltstone, fine grained sandstone and limestone
were collected from the lacustrine deltaic sequence. These different lithofacies
are characterized by a different bulk geochemistry. The organic rich shales
contain Type I kerogen of mostly algal origin, whereas the organiclean sandstones
and limestones contain mostly Type III/IV kerogen of terrestrial origin. Molecular
geochemistry indicates that the extracted bitumen is generated from the algal rich
shale. Within the studied sequence (from 1380 m to 1720 m depth), vitrinite
reflectance values range from 0.60% to 0.82% and show an overall trend of increase
with depth. No systematic variation of vitrinite reflectance with lithofacies in
this sequence has been found. Tmax values from Rock Eval pyrolysis for this suite
of samples, however, show a large variation with lithology and organic carbon
richness. Among the molecular maturity parameters, MPI 1 shows the least variation
between the adjacent lithofacies. The theoretical vitrinite reflectance (Rc)
calculated from the MPI 1 values is consistent with the measured reflectances (Ro),
suggesting that MPI 1 can also be used as valid maturity indicator for lacustrine
sediments in this case, in which organic matter is predominated by Type I kerogen
of algal origin. In contrast, the biomarker maturity parameters in the sequences
of different lithofacies cannot be use as maturity indicators.
Oil generation and accumulation in the Songliao Basin were largely attributed to
the two organic matter-rich successions of lacustrine origin: the Qingshankou
Formation and the lower member of the Nenjiang Formation. These two sheet drape
style organic matter rich successions were deposited due to the large scale lake
transgressions during the basin subsidence. A set of core samples of lacustrine
mudstones and shales from the two successions at depth ranging from 450 to
2200 m were measured by means of regular screening methods, open system pyrolysis,
gas chromatography, and gas chromatography mass spectrometry. The organic matter
in the lacustrine source rocks is dominated by alginite and bacterially reworked
terrestrial plant material. Vitrinite and inertinite make up low proportions of
the organic material. The examined samples have TOC contents from 1.5% to 7%.
Hydrogen Index values are up to 860 mg HC/g TOC. The Oxygen Index values are
remarkably low, and mostly between 3 and 28 mg CO2/g TOC, representing typical
Type I kerogen. Open system pyrolysis measurements of three samples selected from
the Qingshankou Formation revealed extremely narrow activation energy distributions
peaking at 55 and 58 kcal/mol. The variation in principle activation energy
distribution is most likely related to the facies variation of the source rocks.
Hydrocarbon biomarkers in the lacustrine source rocks are characterized by
pentacyclic terpanes dominated by the C30 hopane, the presence of gammacerane
with gamm/(gamm + hopane) ratio ranging from 0.15 to 0.40, presence of 4-methylsteranes,
and very low amounts of the diasteranes. Pronounced changes in
the biomarker distribution with increasing thermal maturity enable to establish
a correlation between Tmax or Ro and different maturity ratios based on pentacyclic
terpanes. Oils extracted from six reservoir sandstones of the underlying Quantou
Formation exhibit similar biomarker characteristics with those of the rock
extracts of the Qingshankou Formation, in particular the lower member of the
formation. The correlation indicates that oils generated from the Qingshankou
Formation migrated downward into the underlying Quantou Formation.
The reconstructed burial histories show a close relationship with the tectonic
evolution of the basin. During the syn rift phase (154 Ma - 127 Ma), the rifting
process produced large relief within the graben horst systems. High burial rates
of up to 200 m per million years, were associated with formation of large scale
grabens, such as the East Central Depression, while the West Slope and the Central
Uplift were uplifted. During the post rift phase, the thermal subsidence of the
basin as a whole caused the basin wide deposition of the fluvial and lacustrine
sediments. The burial histories of the basin during this period were characterized
by an overall trend of decreasing burial rate. The late stage compression was
initiated in the area of the Southeast Uplift Zone at the end of Nenjiang time
(72.5 Ma) and continued during the Early Tertiary, forming a series of the anticline
syncline systems. The Southeast Uplift Zone represents the most intensive uplift
and erosion region of the Songliao Basin. In the anticlines, up to 700 m of the
Nenjiang Formation were eroded. In the synclines the erosional thickness is
estimated to vary from 300 to 400 m. The relatively large subsidence, however,
occurred in the West and East Central Depressions during the Sifantai and Mingshui
time, forming two large synclines. Between the two synclines the Daqing area
developed into a giant anticline. During the Early Tertiary the differential
uplift and erosion enhanced the structure relief between the synclines and
anticlines.
At present the Songliao Basin is situated in a relatively high thermal regime
as compared to its adjacent areas. Based on the thermodynamic evolution models
of extensional basin and on the analogy of the heat flow distributions of the
tectonically active Cenozoic rift systems, very high paleo heat flow ranging
from 80 to 110 m W/m2 is estimated for the period of the rifting phase
(154 Ma - 127 Ma). Using the measured vitrinite reflectance profiles as
calibration data, the simulation indicates that the heat flow in the Central
Depression during the Early Tertiary ranged from 76 to 78 m W/m2. The heat flow
in the Southeast Uplift is estimated between 76 and 78 m W/m2 at the end of the
Cretaceous, between 75 and 72 m W/m2 during the Early Tertiary. Assuming an
overall trend of decreasing heat flows from the Late Jurassic to present, this
study established a regional heat flow evolution model along the regional profile.
In this model, the West Slope of the basin is defined as a low thermal regime,
while the West Central Depression and the Central Uplift are regarded as high
thermal regimes. The Qingshankou Formation in the West and East Central Depressions
reached its maximum maturation during the Early Tertiary. The isoreflectance
lines transverse the anticline syncline system in the Central Depression reflects
post-orogenic or late syn-oroganic maturation, while the isoreflectance lines
broadly parallel with the folds in the Southeast Uplift Zone show preorogenic
maturation.
Kinetic parameters of petroleum generation for the lacustrine source formations
form a sensitive basis for the simulation of oil generation and migration in the
Songliao Basin. In this study, Both vitrinite reflectance and transformation
ratio data measured in the lower member of the Qingshankou Formation were used
to calibrate the kinetic parameters. Using the principle activation energy peaking
at 54 kcal/mol and a pre exponential factor of about 4.2 ·1027 m.y. -1, the
simulation obtained a relatively good match with the measured transformation
ratios. The relationship between the transformation and the maturity level is
determined by the kinetic parameters of kerogen decomposition. Simulation results
indicate that the source formations with maturity levels higher than 0.75% Ro
reached the oil generation windows, and that the Qingshankou Formation in the
West and East Central Depressions constituted the major oil formation zones in
the basin. The Early Tertiary is the major phase of generation, migration and
accumulation of oils from the Qingshankou Formation. In the West Central Depression,
the generated oils migrated upwards into the Yaojia Formation followed by the
updip migration into the Daqing Anticline and towards the local structural high
along the West Slope. In contrast, the oil migration in the East Central
Depression was dominated by the downward movement from the lower member of the
Qingshankou Formation followed by the updip migration towards the Caoyang
Anticline. The simulated oil accumulations are in a good agreement with discovered
oil fields in position, implying a potential application of the model for
prediction and evaluation of new exploration targets in the Songliao Basin.
Zhou, Yongheng
Reconstruction of burial and thermal history, oil generation and migration in the Songliao Basin, Northeastern Chima
129 S., 1998
The Songliao Basin in northeastern China is a large nonmarine petroliferous basin.
The sedimentary sequence in the basin is up to 10000 m thick and is predominated by
Cretaceous fluvial and lacustrine strata with interlayed volcanic and volcaniclastic
rocks. The constructed 270 km long profile across the Songliao Basin reveals a rift
architecture. The early grabenhorst systems were filled by volcanic and
volcaniclastic rocks and alluvial and lacustrine sediments of the Upper Jurassic
Huoshiling Formation and the Lower Cretaceous Shahezi and Yingchenzi Formations.
The graben-horst systems were covered by basin wide fluvial and lacustrine deposits
of the Lower Cretaceous Denlouku, the Quantou, the Upper Cretaceous Qingshankou,
the Yaojia, the Nenjiang, the Sifangtai and the Mingshui Formations. At the top
part of the sequences was truncated by a regional unconformity between the
Cretaceous and the Tertiary. Basin structure and basin fill indicate that the
Songliao Basin was formed by rifting during the Late Jurassic and Early
Cretaceous (154 Ma - 127 Ma), followed by thermal subsidence during the Cretaceous
and late stage compression. The late stage compression was initiated in the
southeastern part of the basin at the end of Nenjiang time (72.5 Ma). During the
Early Tertiary the compression reached its maximum.
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