The Jura – Molasse system: Hydrocarbon system and exploration

by Simon Freitag (329303)

Abstract

The Molasse Basin stretches from Switzerland to Germany and ends in the east of

Austria. Its main lithostratigraphic units, which were formed from Middle Oligocene to

Upper Miocene, are underlain by a Mesozoic basement. The first major phase for

hydrocarbon (HC) generation began at the end of the Jurassic. Another one was

initiated in Oligocene-Miocene times. The main driving mechanism for migration and

accumulation of the hydrocarbons is the excess pressure, resulting from the Alpine

orogeny in the south of the basin. Fold- and fault-structures of the Unfolded and

especially Folded Molasse formed good traps for an accumulation of hydrocarbons

mainly in Germany. However, vertical fault zones may lead to a pressure drain-off

and thus to a prevention of migrations and aggregation of hydrocarbons. In

combination with the missing Lower Marine Molasse, these aspects may be reasons

for the scarce occurrence of hydrocarbons in the Swiss part of the Molasse Basin, in

contrast to the German and Austrian parts. There, all of the HC generating source

rocks and reservoir rocks are existent. Furthermore, a general southwest dipping

direction leads to the migration of oil and gas from Swiss parts to German areas

where they accumulate. That is why the history of oil and gas exploration in Germany

and Austria was successful in comparison to Switzerland, although the search started

in all three countries at about the same time. At the moment, there are still two oil

fields being exploited in Germany while in Austria, this number is much bigger for

both oil and gas fields. In Switzerland, there has only been drilled one moderately

successful well in its history. But since 2005, the search activity has picked up again.

In Germany and Austria, the focus will mainly be on storage of gas in exploited HC

fields.

1

Content

Introduction ............................................................................................................................................ 1

Geological Setting................................................................................................................................. 1

Evolution of the Swiss Molasse Basin (SMB) .................................................................................. 2

Hydrocarbon Systems .......................................................................................................................... 4

Permo-Carboniferous – Triassic-Jurassic-Neogene ................................................................... 4

Posidonia Shale – Cretaceous-Neogene ...................................................................................... 5

Migration and accumulation of hydrocarbons .................................................................................. 7

Exploration history ................................................................................................................................ 9

Outlook for future explorations ......................................................................................................... 11

Conclusion ........................................................................................................................................... 11

References .......................................................................................................................................... 13

Introduction

The search for hydrocarbons in the Molasse Basin (MB), which is located to the north

of the Alps, reaches back to the early 20th century. However, some areas of the MB

are, compared to others, enriched with oil and gas including regions in Austria and

South Germany. Switzerland by contrast, was moderately successful in the search

for hydrocarbons only once in its exploration history. This may be ascribed to the

Alpine orogeny, which by tectonic weight-loading led to a slight dipping of the rock

layers to the south. The result of this process was the migration of the hydrocarbons

to the north by northeast. Even so, there is still some potential for yet undiscovered

hydrocarbon reservoirs in these three countries left. This paper deals with the four

main hydrocarbon systems in the Jura and especially the Molasse Basin in the Alpine

foreland. Furthermore, a short overview on the history of the hydrocarbon exploration

of Switzerland, South Germany and Austria will be given as well as an outlook for

future exploration projects in these countries.

Geological Setting

The Molasse Basin is located to the north of the Alps (Fig. 1). Its lateral expansion

reaches about 700 km and stretches from France across Switzerland and Germany

to Austria. In the Bavarian foreland, it reaches its maximum width of 130 km thus

decreasing to both sides to 20 km in the most western part at Lake Geneva and to 10

km to the eastern part of the MB (Ford, 2004; Ibele, 2011). There, it forms a

connection to the Vienna Basin and the Pannonian Basin further east. The Molasse

2

sediments, which are deposited on top of a Mesozoic basement, reach a thickness of

up to 6 km (Ford, 2004). The western part of the Molasse Basin is situated in

between the Jura Mountains in the north and the Prèalps or Swiss Alps to the south

of Switzerland. In the southwest, it is confined by Lake Geneva, whereas by Lake

Constance and the Rhine in the northeast. The middle part of the MB is located in

South Germany. It is confined to the area between the Danube in the North and the

Northern Calcareous Alps in the south. In the westerly part of the Molasse Basin,

mainly in East Bavaria and Upper Austria, it is bordered by the Bohemian Massif to

the north. Further to the west, the Molasse Basin merges to the Vienna Basin. In the

south, it ends at the Alpine system. For a more detailed insight into the tectonics and

evolution of the Molasse Basin, have a look at the paper “The Molasse Basin:

tectonics, sea level and basin dynamics” of Eva Görke.

The Jura Mountains are located in the north-western part of Switzerland at the border

to France. They have a length of about 370 km and a width of some 75 km. Along the

western and northern border of this fold-and-thrust belt, the Bresse Depression and

the Upper Rhine Graben are situated (Becker, 2000). This mountain range was

formed by the so-called “Fernschub-mechanism” during the Alpine orogeny and its

formation began in the Cenozoic Era (Sommaruga, 1997). A more detailed review on

the evolution and geometry of the Jura Mountains and the Fernschub mechanics is

given by Tabea Kleineberg (“Evolution and geometry of the Jura Mountains:

Fernschub mechanics”).

Figure 1: Molasse Basin location and generalised distribution map of the reservoirs in Germany and

Austria (Véron, 2005).

Evolution of the Molasse Basin

The Molasse Basin is a result of the Alpine orogeny. The subduction of the European

plate by the African plate started in the late Mesozoic. The collision of the two

continents and several microcontinents in-between occurred during the Cenozoic

(Lower Tertiary, 66 – 23 Ma) and is still continuing (Ziegler, 1999). In this process,

the weight of the orogenic wedge increased dramatically thus forcing the lithosphere

3

to bend downward, which resulted in the formation of a deep marine foredeep. This

basin then was filled up with the so-called “Molasse” sediments. The basement of this

foreland basin is dipping slightly to southeast (1° to 3°) (Sommaruga, 1997).

The stratigraphy of the MB can be subdivided into the basement rocks, which consist

of Palaeozoic and older rocks with Mesozoic rocks above, and the Molasse

sediments (Fig. 2).

The crystalline, metamorphic basement was formed by the collision of the two

continents Gondwana and Laurasia, also called the Variscan orogeny. During the

latest stage of this orogeny, crustal thinning along normal faults and strike-slip faults

formed several basins (Bachmann, 1987).

The Mesozoic sediments are provided by Triassic to Cretaceous limestones and

sandstones. These were deposited in an epicontinental sea that dried out

occasionally. The Triassic can be subdivided into the “Buntsandstein”, consisting of

conglomerates and sandstones, the “Muschelkalk”, characterized by marine

sandstones, marls and dolomites as well as evaporates, and the “Keuper”, which also

contains evaporates and dolomites, but additionally lignites. During the Jurassic,

predominantly limestones and marls were deposited (Liassic, Dogger and Malm)

(Bachmann, 1987). Some of these layers form very important source rocks.

Cretaceous sediments were deposited in shallow waters, forming calcareous marls or

limestones (Bachmann, 1987), which are good reservoir rocks

today (Véron, 2005).

The Tertiary, which represents the late stage of Alpine orogeny and the evolution of

the Northern Alpine Foreland Basin (NAFB), can be subdivided into four

lithostratigraphic groups. These are:

Lower Marine Molasse (LMM): 35 to 30 Ma

Lower Freshwater Molasse (LFM): 30 to 20 Ma

Upper Marine Molasse (UMM): 20 to 16,5 Ma

Upper Freshwater Molasse (UFM): 16,5 to 5 Ma

Some of these sedimentary rocks provide fairly good gas generators, reservoir rocks

as well as seal layers (Véron, 2005).

During the last stage of the alpine orogeny, the Jura Mountains in the northwest of

the Swiss Molasse Basin were created after the Serravalian (Burkhard, M. &

Sommaruga, A., 1998). Because sediments of Miocene age are involved in this

folding, the formation had to happen during the Miocene and Pliocene. As already

mentioned, the Triassic evaporite pillows acted as sliding surface for the overlain

sediments, which were thrusted towards the northwest and thus forming the folded

Jura Mountains, mainly exposing Jurassic sediments. This process is called

“Fernschub”-mechanics and involved also small parts of the north-western Swiss

Molasse Basin.1

1 (http://de.wikipedia.org/wiki/Jura_(Gebirge), 2013)

4

Figure 2: Geological profile of the Swiss Molasse Basin (Schegg, 1999, modified by author).

Hydrocarbon Systems

The term “hydrocarbon system” represents a concept, which comprises all processes

from the generation of hydrocarbons to their entrapment and accumulation in

reservoir rocks. These processes are also dependent on the age and distribution of

source and reservoir rocks, as well as the timing of hydrocarbon migration and

trapping (Ziegler, 1999).

In the geological history of the Molasse Basin, two main hydrocarbon generation

phases can be assigned. The first one took place in the Permo-Carboniferous

sediments, which are situated in Variscan orogeny related graben-structures, during

Late Jurassic times (Véron, 2005). The second one happened in the internal parts of

the MB close to the Alpine front during Oligocene-Miocene times. Two other

hydrocarbon systems are of secondary importance (Véron, 2005). Figure 3 shows a

summary of the main hydrocarbon systems in the Swiss Molasse Basin, but can

basically be accounted for the total Molasse Basin.

Permo-Carboniferous – Triassic-Jurassic-Neogene

Besides the already mentioned “Autunia” shale (total thickness 32 m), which was

deposited during the Lower Permian (“Rotliegend”), Upper Carboniferous coal seams

and bituminous shales may also be accounted to potential source rocks. These

bituminous sedimentary rocks are confined to narrow rift graben, formed during the

Variscan orogeny. The Maturity of this oil and gas zone increases from northwest to

southeast towards the Alpine front. This is due to increasing experienced pressure

and temperature resulting from the overlain thrust belt (Schegg, 1999).

As the hydrocarbons rose due to overpressure zones in the frontal part of the orogen,

they got trapped in antithetic, tilted fault blocks of the Unfolded Molasse area and

thrust sheets or subthrust fault blocks in the Folded Molasse region, mainly in the

German Western Molasse area, which were formed during Oligocene to Mid Miocene

times (Véron, 2005). The part of the Molasse Basin that got incorporated in alpine

deformation is addressed to as “Folded Molasse” area, whereas the more distal part

of the MB is called “Folded Molasse” area, because it was passively involved in the

deformational tectonics ( (Ibele, 2011). Its formation happened in the time from Late

Eocene to Late Miocene (Véron, 2005). The just mentioned overpressure zones and

the slight dipping to the southeast of the Mesozoic basement additionally forced the

hydrocarbons of the Permo-Carboniferous to migrate upwards and lateral to the

5

north-eastern, where they accumulate in Jurassic, Triassic and Neogene reservoirs in

the German Molasse Basin (Schegg, 1999). Further mechanism for migration will be

discussed in the following passage.

Potential reservoir rocks in the Molasse Basin are mainly Triassic sediments,

lacustrine (“Stuben”), littoral – deltaic (“Rhaetian”) and nearshore shallow marine

chert sandstones of the “Keuper” as well as dolomites (“Trigonodus”) of the

“Muschelkalk” in particular (Schegg, 1999; Véron, 2005; Chevalier, G., Diamond,

L.W. & Leu, W., 2010). The marine-brackish “Chattian Baustein Beds” of Neogene

(LMM) age form a further reservoir rock in the western part of the MB (Véron, 2005).

Potential reservoir rocks above the mentioned ones are Lower/Middle sandstones

and Upper Jurassic carbonates (Schegg, 1999; Chevalier, G., Diamond, L.W. & Leu,

W., 2010; Véron, 2005). All of these reservoir rocks are mainly sealed by

Intraformational shales. In addition, evaporites partly seal Triassic reservoirs and

Lower Tertiary and Upper Jurassic reservoirs are sealed by shales and marls of the

Early Tertiary (Véron, 2005).

The Posidonia Shale – Cretaceous-Neogene

In the Lower Jurassic (Toarcian), the Posidonia Shale was deposited in the “Jura”

sea. This formation is built up of fine-grained sediments with several bituminous

limestones embedded in-between. It’s well known for the exceptional good

preservation of complete skeletons of fossil marine fish and reptiles.2 The name

results from the frequently occurring bivalve species “Posidonia bronni” of

the family “Posidoniidae”. These sediments were deposited on the sea floor in the

ancient Tethys Ocean under anoxic conditions.3 The “Opalinus” shale also may

provide a source rock of Middle Jurassic age although with a lower potential than the

Posidonia Shale (Schegg, 1999).

Similar to the Permo-Carboniferous source rocks, the oil and gas maturity of the

Posidonia Shale is relatively low in the distal parts of the SMB (northwest) and

increases towards the Alpine front (southeast). The reason therefore is that the

sediments reach higher depth and temperatures there thus conditions, which

promote hydrocarbon generation (Véron, 2005).

Lower densities than surrounding rocks and particularly excessive pressure force

these HC to rise. They eventually get trapped by antithetic, tilted fault blocks in the

Unfolded Molasse area, formed during Oligocene to Mid Miocene times, and by

subthrust fault blocks and especially thrust sheets in the Folded Molasse region of

mainly Lower Austria (“Waschberg Zone”), created during Late Eocene to Late

Miocene times (Véron, 2005).

As reservoirs rocks, Middle and Upper Jurassic carbonates and partly sandstones

play the most important role in this hydrocarbon system (Schegg, 1999). Concerning

the carbonates, these were deposited in a reefal environment during the Upper

Jurassic and are providing a fracture reservoir. The sandstones are represented by

Dogger-beta sandstones (Véron, 2005).

2 (http://en.wikipedia.org/wiki/Posidonia_Shale, 2013)

3 (http://de.wikipedia.org/wiki/Posidonienschiefer_(Jura), 2013)

6

The Lattorfian Fish Shale – Cretaceous-Neogene

The Oligocene (“Sannoisian” stage) marine fish shale “Lattorfian Fish Shale” is

accounted to the primary source rocks for oil of the Molasse Basin (Véron, 2005).

Again, traps of the Unfolded and Folded Molasse in the “Waschberg Zone” of Lower

Austria are responsible for the accumulation of oil. Petroleum arrives from deeper

parts of the basin after migrating upwards along pathways with updip direction. The

reasons for its migration are again the overpressure in zones close to the alpine front

as well as buoyancy (Véron, 2005).

The reservoir rocks range from the Upper Austria’s Dogger sandstones and

carbonates and the Cenomanian sandstone to Upper Eocene sandstones and

Oligocene carbonates and sandstones (Véron, 2005). Sandstones of the Cretaceous

(“Cenomanian”) provide one of the main reservoir rocks for hydrocarbon deposits of

the Austrian Molasse. These are for example the Voitsdorf and Schwanenstadt fields

(Véron, 2005).

Most of these reservoirs are sealed by intraformational shales. However, the

sandstones of the Dogger reservoirs are additionally caulked by Upper Jurassic

carbonates. Lower Tertiary shales may have the same effect on the Campanian

reservoir (Cretaceous) (Véron, 2005).

All in all, the hydrocarbon deposits which are sourced by the Lattorfian Fish Shale are

restricted to the areas of the Austrian and German Eastern Molasse as well as to

parts of the German Western Molasse (Véron, 2005).

The Oligocene – Oligocene-Lower Miocene

The source rock that generates the hydrocarbons, mainly gas, of Oligocene age is

the sandstone of the Rupelian (LMM) (Leu, W. & Oester, H., 2012). The sandstones

of Rupelian, Chattian, Aquitanian and Burdigalian age (LFM and UMM) provide

reservoir rocks (Véron, 2005). Sandstones of the Lower Marine Molasse were

deposited in marine-brackish (“Baustein”) and deltaic channels (“Chattian and

Aquitan”) environments as well as turbidits (from west to east). Latter sediment series

is called the “Puchkirchen Formation” and this hydrocarbon field was the first

commercial oil field discovered in the Austrian Molasse Basin (Véron, 2005). The

sandstones of the Upper Marine Molasse comprise the basal, transgressive marine

Gendorf Sandstone of the Burdigalian in the Bavarian part of the MB. The Hall

Formation is situated in the area of Upper Austria (Véron, 2005). Although there are

hardly any reservoirs existent in the Freshwater series (Lower and Upper), some of

the transition zones like the brackish freshwater environment provide a number of

hydrocarbon fields. One of these zones is called the “Oncophora Beds” and they

occur in Lower and Upper Austria. This formation stores several fields, e.g. the

Wildendurnbach, Roseldorf and Alt Prerau fields. They show very high porosity and

permeability values: 13 to 33.8% and up to 3000 mD (average is 30 mD) (Véron,

2005).

7

Trap formation took place from Oligocene to Middle Miocene and is characterized by

antithetic fault blocks and stratigraphic traps (sealed off bodies of channel sands). In

addition, intraformational Oligocene and Miocene shales seal the reservoir

rocks (Véron, 2005).

The hydrocarbons, which are produced in or close to the reservoir rocks, the gas

migrates due to the same reasons as it is the case for the other petroleum systems,

with respective retardation. The process of gas generation is still

ongoing (Véron, 2005).

All of the Tertiary and Mesozoic reservoirs in the Molasse Basin are ultimately sealed

by the Oligocene fish shale formation (Véron, 2005). Furthermore, because of the

deep wells that were drilled over the last hundred years, it is well known nowadays

that the quality of the reservoir rocks in the Swiss Molasse Basin is fairly bad due to

low porosity and permeability. Reasons therefore are given by de Haller et al. (2011).

These are mainly the overcompaction of the sediments related to the late uplift and

erosion as well as strong and complex diagenetic alterations and cemen-

tations (De Haller, 2011).

Migration and accumulation of hydrocarbons

For a comprehensive understanding of a hydrocarbon system in the Molasse Basin,

it’s important to know, where all the potential source and reservoir rocks are located,

as well as how these are interconnected and why the hydrocarbons migrate in the

first place. These questions should be answered in the following.

A connection of the mother rock with the reservoir rock is either given and controlled

by the basin-fill geometry or by fault systems (Schegg, 1999). Latter may also work

as pressure releasing structures leading to a prevention of oil and gas migration, but

this aspect will be discussed later in this passage. The basin-fill geometry of the

Swiss Molasse Basin is characterized by a succession of alternating highly

permeable dolomites, limestones, sandstones and low permeability shales, marls and

evaporites (Fig. 4) (Schegg, 1999).

The main driving mechanism constitutes the excess pressure evolution. Very high

pressure gets built up in the frontal part of the alpine orogeny, namely the Subalpine

Molasse. The degree of pressure depends on the overlying weight, which is made up

of the sedimentary and tectonic load (Schegg, 1999). This overpressure zones are

probably the reason for driving deep fluids updip into the foreland (Schegg, 1999).

Nevertheless, the excessive pressure is not the only factor the behaviour of

hydrocarbons in this dynamic system depends on. It also hangs on the depth and

type of source rocks, the chronology of generation and squeezing out of HC in

relation to the structural development of the Swiss Molasse Basin and the

8

Figure 3: Generalized petroleum system chart for the Swiss Molasse Basin with key source rocks, generation/expulsion history, reservoir units, seals and tectonic history. This classic diagram does only present the conventional hydrocarbon systems and not unconventional resource plays (modified from Greber et al. 2004) (Leu, W. & Oester, H., 2012).

hydrogeological conditions. Latter factor comprises lateral and vertical lithological

changes such as permeability and porosity of the Molasse sediments as well as

faults (Schegg, 1999).

Referring to just mentioned faults as influencing factor, their development and

properties are highly complex. Dependencies are on lithology, deformation

mechanisms and stress conditions at different depths to name some important of

them. As already mentioned, faults can act as pressure releasing and migration

pathway. When this happens for example at the front of the Subalpine Molasse, a

scenario by Schegg et al. (1999) indicates that the oil of the Posidonia Shale wouldn’t

migrate upwards into the reservoir rocks thus an absence of HC in the Middle and

Upper Jurassic carbonates. However, faults may be sealed again either by

cataclastic rocks or by processes which close these pathways, such as pressure

solution, compaction or cementation (Schegg, 1999).

9

Figure 4: Modelled present-day permeability (mD) (Schegg, 1999; modified by author).

Exploration history

Switzerland

The exploration history of hydrocarbons in Switzerland is several hundred years old.

Since 1714, large asphalt deposits have been mined in the Val de Travers, a valley in

the Swiss Jura Mountains. There, Cretaceous limestones got impregnated by

hydrocarbons already before the folding of the Jura Mountains. This process included

thrust-related uplift, deformation and at the same time erosion of the MB which

stopped the HC generation. Until today, it is not known which source rocks were

responsible for their production (Schegg, 1999).

The history of subsurface hydrocarbon exploration in Switzerland started hundred

years ago and since then, only 37 deep wells have been drilled. At the beginning, it

was mainly looked for conventional reservoirs in the Tertiary to Palaeozoic section of

the Swiss Molasse Basin. But with time, the focus shifted to oil/gas in the Mesozoic

and to gas in reservoir rocks of Permo-Carboniferous age

(Leu, W. & Oester, H., 2012).

In the first decades until 1950, only small ventures of independent petroleum

companies drilled for oil. The decisions, where to locate the wells, were made based

on areas, where oil seeped out of the soil, surface geology and sometimes on hints

of geomantic specialists. Although seismic data of this area already existed since

1954, it was used economically as hydrocarbon search tool only after 1960 (Leu, W.

& Oester, H., 2012).

In the time after 1956, over 27 deep wells were drilled by the Swisspetrol Group. This

group is a federation of over ten local Swiss companies and two major foreign

petroleum companies; these were the BEB-Shell-Exxon and ELF

Aquitaine (Lahusen, P.H. & Wyss, R., 1995). Only one of these 27 deep wells was

> 100 mD

10 – 100

1 – 10

0,1 – 1

0,01 – 0,1

0,001 – 0,1

distance

depth

(km)

NW SE permeability

0

2

4

6

LMM

LFM

CB

PC

TM – L

TU

JL

JM

JU

CL

OMM

10 20 30 40

10

moderately successful (Entlebuch-1), which commercially produced gas in the time

between 1985 and 1996 (Gisler, 2011).

When the Swisspetrol Group was dissolved in 1993, only the SEAB (Schweizerische

Erdöl AG) in eastern Switzerland and the Petrosvibri SA in Vevey remained and kept

on searching for hydrocarbon. During 1995 to 2005, only one well was drilled called

the Weiach-2 (Leu, W. & Oester, H., 2012).

Austria

The hydrocarbon exploration and production in Austria began about 100 years ago.

Just like it was the case in Switzerland, the focus was on simple HC targets at that

time. Except of two moderately successful wells, Neusiedl 1 and Zistersdorf-

Gaiselberg, no major HC discoveries were made until 1950. In this year, the giant

Matzen field in the Vienna Basin was detected due to the usage of single-fold and

six-fold 2 seismic (Hamilton, 2000). In this area, hydrocarbons are stored in over 20

different reservoir rocks.4

In Austria, the Vienna Basin is by far the biggest hydrocarbon producer. Until 1999,

108,5 MM tonnes/oil and 72,1 Bm³ gas in total have been produced in Austria, most

of it in the Vienna Basin (Hamilton, 2000). Since the beginning of the exploration

history in Austria, 4400 wells have been drilled, 900 thereof in the Austrian Molasse

Basin (Hamilton, 2000).

Germany

The first proven oil finding was made at the Tegernsee in the 15th century. In 1904, a

first well was drilled which encountered oil in a depth of 500 m. After that, ten further

exploration wells were conducted. However, these wells are already watered-down

again since 1912. During the time of the World War II, no search for hydrocarbons or

exploration was run. Right after this period, the search for oil picked up again and HC

were exploited since 1954. Until today, around 60 wells have been drilled which have

pumped up about 6,9 Million tonnes/oil and 18,2 Mrd. m³/gas from this time to 2000.

Most of them are located in an area southeast of Munich close to the border of

Austria.5

Nevertheless, only a very small part of the hydrocarbons exploited in Germany are

situated in the German Molasse Basin. Most of the hydrocarbons - namely 94% - in

Germany are exploited in Lower Saxony and Schleswig-Holstein. However, three oil

fields are still located in the German North Alpine Foreland Basin. These are Aitingen

(Bavaria), Hebertshausen (Baden-Wuerttemberg) and Schwabmünchen (Bavaria).

4 (http://www.wabweb.net/history/oel/noe.htm, 2011)

5 (http://de.wikipedia.org/wiki/Erdölförderung_in_Deutschland#Alpenvorland)

11

The First and biggest one was found in 1976 and is still producing. The oil field

Heberthausen is exploited since 1982 and the last one since 1968.6

Outlook for future explorations

Since 2005, the rate of hydrocarbon exploration wells in Switzerland increases again.

Today, more than two third of the SMB and the Jura Mountains are reserved by in

total eighteen exploration permits (Leu, W. & Oester, H., 2012).

Seven joint venture exploration companies, that own these permits, concentrate on

four different types of hydrocarbon exploration techniques. Two companies focus on

the extraction of conventional shallow oil and gas from the Mesozoic-Palaeozoic

sections of the Jura Fold belt and the northern rim of the Molasse Basin. Another one

tries to get shallow heavy oil out of Tertiary sediments in the Geneva area. Three

further companies drill for deep conventional and unconventional tight gas in the

southern part of the MB. One of them was successful lately, because the Noville-1

well (3500 m TVD) encountered a tight gas accumulation in Palaeozoic clastic rocks.

The last exploration company normally wants to explore unconventional shale gas in

the Jurassic section of the SMB. However, this process can’t keep going at the

moment due to an exploration ban in Canton Fribourg and a hydraulic fracturing

moratorium in the Canton Vaud (Leu, W. & Oester, H., 2012).

In the near future, two further exploration wells are planned. Although the exploration

of shale gas is still banned at the moment, Oester & Leu (2012) assume that this

form of hydrocarbon could play a major role in the transition to a renewable energy

supply of Switzerland. A first estimation of the potential recoverable shale gas in the

Aalenia-Toarcian results in ~50-100 Mrd. m3. The annual gas consumption of

Switzerland accounts for 3,5 Mrd. m3. Further studies have to be conducted to show

that an usage of this unconventional resource is profitable and that it has no negative

impact on the environment, (Leu, W. & Oester, H., 2012).

In Austria, the focus is more on the storage of gas in already exploited HC fields in

the near future. Nevertheless, there are still some smaller hydrocarbon fields

available in areas, where exploration is already processed.7

Conclusion

The migration of hydrocarbons in the Molasse Basin is mainly controlled by the

basin-fill geometry, which comprises a succession of highly permeable sedimentary

layers and low-permeable shales and marls, as well as fault zones. Due to a tectonic

weight-loading created by the alpine orogeny located to the south of the MB, its rock

layers also dip this direction. This results in the upwards-migration of generated

hydrocarbons to the north to north-east. The main driving mechanism for the

movement of hydrocarbons is the excessive pressure evolution in the alpine

6 (http://de.wikipedia.org/wiki/Erdölförderung_in_Deutschland#Alpenvorland)

7 (http://www.wabweb.net/history/oel/noe.htm, 2011)

12

forefront, which is also created by the tectonic weight-loading of the Alps. However,

major fault zones may act as migration pathways for hydrocarbons. Besides the

dipping of the layers to the south, this might be another reason for missing

hydrocarbons in Switzerland. That is the case when in the past generated oil or gas

may have left the petroleum system through these fault zones before it could have

been trapped in overlying reservoirs. However, fault-sealing processes like cataclasic

rocks or pressure solution could have stopped the escape of the hydrocarbons.

Taking the stated aspects into account, it may be explained, why there are hardly any

hydrocarbons found in Switzerland, but in Germany there are. Most important

hydrocarbon systems in the Molasse Basin are the Posidonia Shale – Cretaceous-

Neogene system with the Posidonia Shale as main source rock, and the Lattorfian

Fish Shale – Cretaceous-Neogene system with the Lattorfian Fish Shale as oil

generating rock. Even so, there are several smaller ones in the MB, too. Although,

the Jura-Mountains form good trapping structures, they contain hardly any

hydrocarbons. This may be accounted to thrust-related uplifting, deformation and at

the same time erosion of the MB, which stopped the generation and accumulation of

hydrocarbons in this area. Most of the HC reservoirs can be found in the Austrian

part of the Molasse Basin, with the Matzen field representing the biggest one. There,

the oil is stored in more than 20 different reservoir rocks. Despite most of the HC

fields already being discovered, there are still some yet undiscovered economical

fields thought to be existent in all of these three countries. However, the focus will be

more on the storage of gas in already exploited HC fields and possibly on the

exploration of shale gas than of petroleum in the near future.

13

References

(2013, July 14). Retrieved August 19, 2013, from http://en.wikipedia.org/wiki/Posidonia_Shale:

http://en.wikipedia.org/wiki/Posidonia_Shale

(2013, July 23). Retrieved August 19, 2013, from

http://de.wikipedia.org/wiki/Posidonienschiefer_(Jura):

http://de.wikipedia.org/wiki/Posidonienschiefer_(Jura)

Bachmann, G. M. (1987). Evolution of the Molasse Basin (Germany, Switzerland).

Tectonophysics 137 , pp. 77-92.

Beck C., D. E. (1998). Horizontal shortening control of Middle Miocene marine siliciclastic

accumulation (Upper Marine Molass) in the southern termination of the Savoy Molasse Basin

(northwestern Alps-southern Jura). Geological Society Special Publications 134 , pp. 263-278.

Bieg, U. N. (2007). North Alpine foreland basin (Upper Marine Molasse) of southwest Germany:

sedimentology, stratigraphy an palaeontology. Geo.Alp, Vol. 4 , pp. 149-158.

Butler, R. W. (1991). Hydrocarbon maturation, migration and tectonic loading in the Western Alpine

foreland thrust belt. Geological Society, London, Special Publication 59 , pp. 227-244.

Chevalier, G., Diamond, L.W. & Leu, W. (2010). Potential for deep geological sequestration of CO2 in

Switzerland: a first appraisal. Swiss J. geosci., 103 , pp. 427-455.

De Haller, A. T. (2011). Fluid flow through the sedimentary cover in norther Switzerland recorded by

calcite-celetite veins (Oftringe borehole, Olten). Swiss Journal of Geosciences 104 , pp. 493-506.

Eynatten, v. H. (2003). Petrography and chemistry of sandstones from the Swiss Molasse Basin: an

archive of the Oligocene to Miocene evolution of the Central Alps. Sedimentology 50 , pp. 703-724.

Ford, M. L. (2004). Foreland basin evolution around the western Alpine Arc. Geological Society,

London, Special Publications 221 , pp. 39-63.

Gisler, M. (2011). Erdöl in der Schweiz - Eine kleine Kulturgeschichte. Zürich: Verein für

wirtschaftshistorische Studien.

http://de.wikipedia.org/wiki/Jura_(Gebirge). (2013, August 13). Retrieved August 20, 2013, from

http://de.wikipedia.org/wiki/Jura_(Gebirge)

Ibele, T. (2011). Tectonics of the Western Swiss Molasse Basin during Cenozoic times . Fribourg.

Kempf, O. M. (1999). Depositional and structural evolution of a foreland basin margin in a

magnetostratigraphic framework: the eastern Swiss Molasse Basin. International Journal of Earth

Sciences 88 , pp. 253-275.

Lahusen, P.H. & Wyss, R. (1995, December). Erdöl- und Erdgasexploration in der Schweiz: Ein

Rückblick. Bull.schweiz.Ver.Petroleum-Geol.u.-Ing., Vol. 62, Nr. 141 , pp. 43-72.

14

Leu, W. & Oester, H. (2012, September 12). SPE Swiss Section Fieldtrip 2012 - Mont Terri Project

(shale research laboratory) & Hydrocarbon Potential of Western Switzerland. Retrieved August 16,

2013, from http://higherlogicdownload.s3.amazonaws.com/SPE/a6c2d780-4741-4804-b4e0-

010e4812ddc0/UploadedImages/2012/Field%20trip%202012_xs.pdf

Schegg, R. C. (1999). Migration and accumulation of hydrocarbons in the Swiss Molasse Basin:

implications of a 2D basin modeling study. Marine and Petroleum Geology 16 , pp. 511-531.

Schlunegger, F. M. (2001). Climate, exposed source-rock lithologies, crustal uplift and surface

erosion: a theoretical analysis calibrated with data from the Alps/North Alpine Foreland Basin

system. International Journal of Earth Sciences 90 , pp. 484-499.

Sommaruga, A. (1997). Geology of the Central Jura and the Molasse Basin: new insight into an

evaporite-based foreland fold and thrust belt. Neuchâtel: Société neuchâteloise des Sciences

natureltes.

Véron, J. (2005, July). The Alpine Molasse Basin - Review of Petroleum Geology and Remaining

Potential. Bulletin for Applied Geology, Vol. 10/1 , pp. 75-86.

Ziegler, P. R. (1999). Petroleum system of Alpine-Mediterranean foldbelts and basins. Geological

Society, London, Special Publications 156 , pp. 517-540.

Zweigel, J. (1998). Reservoir analogue modelling of sandy tidal sediments, Upper Marine Molasse,

SW Germany, Alpine foreland basin. Geological Society Special Publications 134 , pp. 325-337.