Geological Survey of Denmark and Greenland Bulletin 13, 2007
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Review of Survey activities 2006, 17-20 |
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Intense investigations of deep aquifers in Jylland, western
Denmark, during the last seven years have resulted in de -
tailed mapping of Miocene sand-rich deposits laid down in
fluvial channels, delta lobes, shoreface and spit complexes
(Fig. 1; Rasmussen 2004). Detailed sedimentological and paly -
no logical studies of outcrops and cores, and interpretation of
high-resolution seismic data, have resulted in a well-founded
sequence-stratigraphic and lithostratigraphic scheme (Fig. 1)
suitable for prediction of the distribution of sand.
Denmark, during the last seven years have resulted in de -
tailed mapping of Miocene sand-rich deposits laid down in
fluvial channels, delta lobes, shoreface and spit complexes
(Fig. 1; Rasmussen 2004). Detailed sedimentological and paly -
no logical studies of outcrops and cores, and interpretation of
high-resolution seismic data, have resulted in a well-founded
sequence-stratigraphic and lithostratigraphic scheme (Fig. 1)
suitable for prediction of the distribution of sand.
The Miocene succession onshore Denmark is divided into
three sand-rich deltaic units: the Ribe and Bastrup sands and
the Odderup Formation (Fig. 2). Prodeltaic clayey deposits
of the Vejle Fjord and Arnum Formations interfinger with
the sand-rich deposits. Most of the middle and upper Mio -
cene in Denmark is composed of clayey sediments referred to
the Hodde and Gram Formations (Fig. 2).
the Odderup Formation (Fig. 2). Prodeltaic clayey deposits
of the Vejle Fjord and Arnum Formations interfinger with
the sand-rich deposits. Most of the middle and upper Mio -
cene in Denmark is composed of clayey sediments referred to
the Hodde and Gram Formations (Fig. 2).
This paper presents examples of seismic reflection patterns
that have proved to correlate with sand-rich deposits from
lower Miocene deltaic deposits and that could be applied in
future exploration for aquifers and as analogues for oil- and
gas-bearing sands in wave-dominated deltas.
lower Miocene deltaic deposits and that could be applied in
future exploration for aquifers and as analogues for oil- and
gas-bearing sands in wave-dominated deltas.
Geology
During the Early Miocene, the eastern North Sea Basin was
filled by siliciclastic sediments sourced from the Fenno
filled by siliciclastic sediments sourced from the Fenno
-
scandian Shield. The sediment supply was high due to tec-
tonic uplift of the Fennoscandian Shield (Ziegler 1990;
Rasmussen 2004). The North Sea was located in the high-
lati tude belt of westerly winds, which resulted in a long fetch,
and the tidal range is interpreted to be micro- to meso-tidal.
Regressions and transgressions during the Early Miocene
were strongly controlled by eustatic sea-level changes (Friis et
al. 1998; Rasmussen 2004; Rasmussen & Dybkjær 2005).
tonic uplift of the Fennoscandian Shield (Ziegler 1990;
Rasmussen 2004). The North Sea was located in the high-
lati tude belt of westerly winds, which resulted in a long fetch,
and the tidal range is interpreted to be micro- to meso-tidal.
Regressions and transgressions during the Early Miocene
were strongly controlled by eustatic sea-level changes (Friis et
al. 1998; Rasmussen 2004; Rasmussen & Dybkjær 2005).
During the early Miocene, two phases of shoreline progra-
dation occurred. Sand deposited adjacent to the delta mouth
or in association with topographic highs was immediately
redistributed and deposited either as spit complexes or as bar-
rier islands in the down-drift areas of delta lobes. These sand-
rich successions are commonly around 20 m thick; however,
delta lobes prograding into topographic lows, i.e. deep water,
are characterised by up to 70 m thick successions of clean
sand. The delta front sediments were deposited either as
or in association with topographic highs was immediately
redistributed and deposited either as spit complexes or as bar-
rier islands in the down-drift areas of delta lobes. These sand-
rich successions are commonly around 20 m thick; however,
delta lobes prograding into topographic lows, i.e. deep water,
are characterised by up to 70 m thick successions of clean
sand. The delta front sediments were deposited either as
mass-flow sediments or current-derived deposits. During sea-
level fall, incision of the delta plain took place. These incised
valleys were successively filled with thick, sand-rich fluvial
deposits during the succeeding sea-level rise.
level fall, incision of the delta plain took place. These incised
valleys were successively filled with thick, sand-rich fluvial
deposits during the succeeding sea-level rise.
Prediction of reservoir sand in Miocene deltaic deposits
in Denmark based on high-resolution seismic data
in Denmark based on high-resolution seismic data
Erik S. Rasmussen, Thomas Vangkilde-Pedersen and Peter Scharling
© GEUS, 2007.
Geological Survey of Denmark and Greenland Bulletin
13, 17-20. Available at:
www.geus.dk/publications/bull
Fig. 1. Map of Jylland showing distribution of Lower Miocene environ-
ments (from Rasmussen 2004). Insert map shows position of seismic
sections and boreholes used in this study.
Seismic data acquisition
Mapping of aquifers in Denmark has previously been domi-
nated by electric and electromagnetic methods, as the high
nated by electric and electromagnetic methods, as the high
cost of conventional, shallow, onshore reflection seismic sur-
veys was a factor that limited its use. Recently, however, the
technique of landstreamer high-resolution seismic data has
provided considerable savings of manpower and increased
productivity compared to using traditionally planted geo-
phones and cable lay-outs. The mapping of deeper units is
also possible now. The landstreamer technique also facilitates
short geophone spacing and differential spacing of geo-
phones along the spread without increasing time- or man-
power consumption.
veys was a factor that limited its use. Recently, however, the
technique of landstreamer high-resolution seismic data has
provided considerable savings of manpower and increased
productivity compared to using traditionally planted geo-
phones and cable lay-outs. The mapping of deeper units is
also possible now. The landstreamer technique also facilitates
short geophone spacing and differential spacing of geo-
phones along the spread without increasing time- or man-
power consumption.
The use of landstreamers for acquisition of shallow seismic
data has increased throughout the world in recent years. The
landstreamers are commonly used together with relatively
weak sources such as a pipegun or sledgehammer (e.g. van der
Veen & Green 1998; van der Veen et al. 2001) resulting in a
relatively limited penetration depth (typically a few hundred
metres). Since the year 2000, more than 1000 km of high-
resolution seismic data have been acquired to map deep
aquifers in Denmark. The acquisition setup used has
included high-frequency seismic vibrators (3.5 T and 6.5 T)
as the energy source. Under normal conditions the land-
streamer setup has provided very high data quality with
reflections from c. 20-50 m down to more than 1 km with a
vertical resolution of 5-10 m. The coverage, especially in the
central and western parts of Jylland, provides unique oppor-
tunities for interpretation and correlation.
landstreamers are commonly used together with relatively
weak sources such as a pipegun or sledgehammer (e.g. van der
Veen & Green 1998; van der Veen et al. 2001) resulting in a
relatively limited penetration depth (typically a few hundred
metres). Since the year 2000, more than 1000 km of high-
resolution seismic data have been acquired to map deep
aquifers in Denmark. The acquisition setup used has
included high-frequency seismic vibrators (3.5 T and 6.5 T)
as the energy source. Under normal conditions the land-
streamer setup has provided very high data quality with
reflections from c. 20-50 m down to more than 1 km with a
vertical resolution of 5-10 m. The coverage, especially in the
central and western parts of Jylland, provides unique oppor-
tunities for interpretation and correlation.
The design of the seismic landstreamers has developed
from a 150 m, 60-channel streamer with 2.5 m spacing used
18
Fig. 2. Lithostratigraphy of the Danish Miocene sediments (modified
from Rasmussen 2004).
Fig. 3. Seismic section with boreholes from the Billund area illustrating two prograding deltaic sand-rich units (Billund sand and Bastrup sand). The
grain size of the penetrated succession is indicated by different colours. Note that the parallel clinoformal seismic reflection pattern (arrows) always
correlates with sand. Seismic data courtesy of COWI A/S and Rambøll A/S.
in 2000 to the current 200-220 m streamers with 96-102
channels and differential geophone spacings of 1.25, 2.5 and
5 m (Vangkilde-Pedersen et al. 2003, 2006). The differential
geo phone spacing along the streamers, with the shortest spac-
ing close to the vibrator, has greatly improved the quality and
reso lution of the near-surface data. In the same period, both
the vibrator sweeps and processing of the data have also been
optimised. During the first couple of years a simple standard
processing sequence was applied to the data, but in recent years
the processing sequence has been significantly improved.
channels and differential geophone spacings of 1.25, 2.5 and
5 m (Vangkilde-Pedersen et al. 2003, 2006). The differential
geo phone spacing along the streamers, with the shortest spac-
ing close to the vibrator, has greatly improved the quality and
reso lution of the near-surface data. In the same period, both
the vibrator sweeps and processing of the data have also been
optimised. During the first couple of years a simple standard
processing sequence was applied to the data, but in recent years
the processing sequence has been significantly improved.
Examples of Lower Miocene reservoir sand
Delta front sand.
Thick delta front sands occur in association
with progradation into deep water that is normally associated
with structurally confined areas. Delta lobes deposited dur-
ing a relative sea-level fall are especially sand-rich. These
deposits are characterised by a parallel clinoform reflection
pattern (Figs 3, 4) in which the dip of the clinoforms range
from 7° to 10°. The thickness of sand associated with this
reflection pattern has never been recorded as less than 20 m
and thicknesses of up to 50 m have been found at Billund
(Fig. 3); the thickness may be more than 70 m within the
Brande lobe, north of Billund. The grain size is commonly
medium to coarse sand, but gravel may occur in connection
with mass-flow deposits on the delta front or in association
with channels and shoreface deposits in the upper part of the
delta. Delta sand laid down during a sea-level fall is particu-
larly clean and homogenous.
with progradation into deep water that is normally associated
with structurally confined areas. Delta lobes deposited dur-
ing a relative sea-level fall are especially sand-rich. These
deposits are characterised by a parallel clinoform reflection
pattern (Figs 3, 4) in which the dip of the clinoforms range
from 7° to 10°. The thickness of sand associated with this
reflection pattern has never been recorded as less than 20 m
and thicknesses of up to 50 m have been found at Billund
(Fig. 3); the thickness may be more than 70 m within the
Brande lobe, north of Billund. The grain size is commonly
medium to coarse sand, but gravel may occur in connection
with mass-flow deposits on the delta front or in association
with channels and shoreface deposits in the upper part of the
delta. Delta sand laid down during a sea-level fall is particu-
larly clean and homogenous.
Fluvial point-bar sand.
Delta deposits of the Lower
Miocene Bastrup sand are often capped by fluvial sediments
that have been protected during the succeeding transgression.
The fluvial channels are expressed by a concave-up structure
that have been protected during the succeeding transgression.
The fluvial channels are expressed by a concave-up structure
filled with a shingled seismic reflection pattern probably rep-
resenting point-bar deposits (Fig. 5). From seismic and bore-
hole data, the point-bar deposits comprise up to 20 m thick,
fining-upwards successions composed of coarse- to fine-
grained sand that are commonly capped by coal.
resenting point-bar deposits (Fig. 5). From seismic and bore-
hole data, the point-bar deposits comprise up to 20 m thick,
fining-upwards successions composed of coarse- to fine-
grained sand that are commonly capped by coal.
Incised valley sand.
Well-defined, large, concave-upward
erosional surfaces are found especially in the proximal parts
of the deltas. The infills of these features on the seismic lines
are often characterised by a transparent seismic reflection pat-
tern (Fig. 6). From outcrop and borehole data the valleys are
known to be filled typically by coarse-grained sand and gravel
that were deposited in braided river systems. The thickness and
lateral distribution of the fill vary within the delta complexes.
of the deltas. The infills of these features on the seismic lines
are often characterised by a transparent seismic reflection pat-
tern (Fig. 6). From outcrop and borehole data the valleys are
known to be filled typically by coarse-grained sand and gravel
that were deposited in braided river systems. The thickness and
lateral distribution of the fill vary within the delta complexes.
Future perspectives
The application of seismic data in the search for aquifers in
Denmark by recognition of different seismic reflection pat-
Denmark by recognition of different seismic reflection pat-
19
Fig. 4. Seismic section from Sønder Omme. Note the close relationship between the parallel clinoformal reflection pattern and the sand as indicated
by the arrows. Note especially the lower delta where only the toe of the delta front has been penetrated by the Stakroge borehole. Seismic data cour-
tesy of Rambøll A/S. See Fig. 3 for legend.
Fig. 5. Seismic section showing shingled, seismic reflection pattern
(arrow) within a channel structure. Similar structures have been found
on 3D seismic data from Canada (Posamentier 2005) and represent late -
ral accretion of a point bar. Seismic data courtesy of COWI A/S.
20
terns and morphological features, e.g. the geometry of clino-
forms, has proved to be useful in the prediction of sand-rich
sediments in Miocene deposits. Sand-rich sediments in front
of a delta complex are normally associated with clinoform
reflection patterns. A shingled seismic reflection pattern
within channels characterises sand-rich, point-bar deposits.
Distinct erosional features, with a transparent reflection pat-
tern, capping delta foresets commonly indicate fluvial sand-
rich sediments. A detailed mapping of the Miocene delta
complexes and the construction of a three-dimensional
model of delta lobes will be essential for developing future
hydrogeological models.
forms, has proved to be useful in the prediction of sand-rich
sediments in Miocene deposits. Sand-rich sediments in front
of a delta complex are normally associated with clinoform
reflection patterns. A shingled seismic reflection pattern
within channels characterises sand-rich, point-bar deposits.
Distinct erosional features, with a transparent reflection pat-
tern, capping delta foresets commonly indicate fluvial sand-
rich sediments. A detailed mapping of the Miocene delta
complexes and the construction of a three-dimensional
model of delta lobes will be essential for developing future
hydrogeological models.
Furthermore, the connection between the observed seis-
mic facies and sand-rich environments may also be applied as
a tool for prediction of Jurassic hydrocarbon reservoir sands
in the North Sea area.
a tool for prediction of Jurassic hydrocarbon reservoir sands
in the North Sea area.
Acknowledgements
The Carlsberg Foundation and the counties of Vejle, Ringkøbing and
Ribe are thanked for financial support of the study of the Miocene suc-
cession in Denmark.
Ribe are thanked for financial support of the study of the Miocene suc-
cession in Denmark.
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Authors' address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail:
esr@geus.dk
Fig. 6. Seismic section showing 2 km wide and 20 m deep erosional features on top of clinoforms interpreted as a fluvial valley fill. These features are
often filled with coarse-grained sand or gravel deposits. Seismic data courtesy of COWI A/S.
