Natural manifestations of hydrocarbons

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Natural manifestations of hydrocarbons
How does oil form?
Oil originates from the decomposition of organic matter through the action of living microorganisms (bacteria) under
anaerobic conditions (without oxygen) which, over geological periods (millions of years), lead to the formation of
"kerogen".
Hydrocarbon and kerogen accumulation formation diagram.
Subsequently, due to the continuous growth of organic sediments, there is a natural rise in temperature that reaches
approx. 150°C. The temperature rise in the parent rock causes the progressive "rupture" of the molecular bonds,
transforming the kerogen into simpler compounds: hydrocarbons. Depending on the temperature, the kerogen can be
transformed into liquid hydrocarbons (at lower temperatures) or gaseous hydrocarbons (at higher temperatures). At this
point, since the hydrocarbons have a lower density than water, once generated, they migrate upward through the pores
in the rocks. When they encounter impermeable rock layers, the reservoir or "oil trap", the hydrocarbons are blocked and
accumulate.
What are surface oil manifestations?
Migration of the oil in the vertical direction has often resulted in the formation of surface oil manifestations. If during the
ascent, in fact, the hydrocarbons meet only porous rocks, cracks and water connections, they may seep to the surface. A
prerequisite for a manifestation to occur is that the quantity of hydrocarbons present can be identified directly on the
ground and not by means of particular chemical analyses.
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A: Manifestation at the edge of the basin. B and C: inside the basin in correspondence with the faults. D: in contact with a
salt dome. E: igneous intrusion. F: erosion phenomenon. G: discrepancy. Examples of surface oil manifestations. The
arrow indicates the direction of migration and seepage of the hydrocarbons, while the deep accumulation in the rockreservoir is marked in black (source: http://www.treccani.it/enciclopedia/petrolio/).
Surface oil manifestations are divided into active, or live, and fossil, or dead, manifestations. The former are gaseous and
liquid are and remain active due to a continuous supply of hydrocarbons (such as in the case of Tramutola). The latter
are solid and are the product of migrations that occurred in the past.
The natural seeps of Tramutola
The natural seeps of hydrocarbons at the Tramutola site are liquid and naphthalene manifestations. They consist of a
drippage of oil due to its ascent from shallow levels (the oilfield is at a depth of approx. 300-400 metres) along fractures
in the rock. The oil is associated with water and natural gas (primarily methane, carbon dioxide and hydrogen sulphide).
The manifestations essentially consist of more or less oxidised dark or blackish, very viscous or even doughy oils that do
not evaporate.
Natural hydrocarbon manifestation – Tramutola. Photo: Dario Colucci.
These spontaneous manifestations were, and still are, evident mainly in a small valley which hosts a tributary stream of
the Rio Cavolo, the Torrente Fossatello, situated east of the village of Tramutola. They are therefore situated inside
marly-arenaceous siliciclastic soils (historically called "Eocene flysch auct."), in the vicinity of the (tectonic) contact
between the same and the Mesozoic carbonate reliefs that form the hill of the West bank of the stream.
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Natural hydrocarbon manifestation – Tramutola. Photo: Dario Colucci.
The hydrocarbons and the sulphur water mingle with the clean water of the stream until they enter the main stream of the
Rio Cavolo, in turn a tributary of the Agri River, which contributes to replenishing the "Pietra del Pertusillo" reservoir.
Tramutola: historical notes of legends and written proof
Val d’Agri has been known since ancient times for its surface manifestations of hydrocarbons. According to certain local
stories, it appears that in Tramutola such manifestations were known for some time: it seems that the local population
had a certain familiarity with a blackish substance with a peculiar smell and that seeped to the surface near the Rio
Cavolo forming oily stains. This information, however, is not present in the documents of the time, not even in the reports
produced by the Benedictine monks, present in the area from the mid-12th century. Only in the nineteenth century do we
find the first written mention of the columns of fire spontaneously spurting from the Apennine mountains, a sign of the
presence of small reserves of methane gas underground, or of the natural emission of hydrocarbons from the ground of
the region, also following the disastrous earthquake of 1857 with epicentre in Val d'Agri.
The earthquake and the first written proof
There are, in the documents of the time, mentions of columns of gas seen spurting out near Salandra a month before
and a few days after the earthquake of 1857. Historians and scholars such as Racioppi and Del Giudice speak of
changes in the land before and after the earthquake, of the smell of bitumen and sulphur before and after the event and
luminous globes and columns, or in any case lights, seen near Viggiano, but also in the proximity of other towns, of
changes in springs and wells. In the French weekly L’Illustration: Journal Universel, published from 1843 to 1944,
various prints related to the earthquake of 1857 were published at the time of the quake. In one of these prints, reference
is made to sulphur springs created after the earthquake.
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Prints taken from the magazine L'Illustration: Journal Universel and depicting the sulphur springs
created with the earthquake of 16 December 1857 in Val d’Agri. Source: Casa Museo Moliterno – Domenico Aiello.
No mention, however, was made of the seeps in Tramutola, not even by the Irish geophysicist Robert Mallet during his
study and exploration journey caused by the earthquake of 1857. Only in 1860 was a first reference to the seeps in
Tramutola made ("the asphalt of Marsico and Tramutola in Basilicata») by the geographer, historian and politician Amato
Amati. In 1878 and 1879, a study of Basilicata was then published in which there was a description of the oil
manifestations in the region and in Val d'Agri, without, however, exploring the case of Tramutola specifically but only
mentioning the presence of hydrocarbons. In the early twentieth century, the presence of seepage was well known and
documented, also in 1908 based on the observations made between 1888 and 1892. A sample of the fuel had in any
case already been presented at the Paris Universal Exposition in 1878 (even though, in the official exhibition catalogue,
reference was only made to samples from Rivazzano, in the province of Pavia). At the end of the nineteenth century,
however, the phenomenon had certainly been observed and studied, so much so that in 1902 there was talk of mining
engineers, both Italian and foreign, who verified the presence of an oilfield in the Valle del Cavolo.
The studies of the early twentieth century
The first scientific study entirely dedicated to Tramutola dates back to 1902. That year, an engineer called Crema, at the
request of the Inspectorate of the Royal Corps of Mines, conducted a number of studies in order to carry out a general
exploration of the oil manifestations in certain areas of Tramutola. Thus a "small source of water mixed with oil [...]
emitted in small quantities but continuously" was observed, while other manifestations of lesser importance were found
at the mouth of the river Cavolo. In 1909 the City Council passed a resolution for drilling assays to be carried out in the
Tramutola oil field. In 1912, the company Petroli d'Italia concluded a license agreement for the exploration and
exploitation of deposits that might be found under the municipality with eighty-seven owners in Tramutola. Drilling began
in 1920, reaching a depth of 144 metres. Drilling was then suspended in order to work to regulate the flow of water found,
while in 1922 the excavation was abandoned with the intent to resume it in another area. Starting from the second half of
the 1920s, aided by the autarchic and expansionist ambitions of the fascist regime, oil exploration in the Tramutola area
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experienced a new lease of life. Subsequently, Mr. Crema carried out surveys, ensuring that the hydrocarbons tracks in
Basilicata were not only focused on the area of Tramutola but also on the area of Cersosimo. Subsequently, there were
various events related to creating regulations governing oil exploration, also from the economic-financial point of view,
and only in 1931 was further analysis in this regard possible. The geologist Guido Bonarelli was the first to foresee the oil
potential of the region. Bonarelli identified, in the lower valley of the Rio Cavolo, six types of visible oil manifestations with
gassing hydrocarbons and "semi-light oil, rich in lubricants and with an aromatic smell".
In 1933, Agip carried out research in the area, identifying the presence of hydrocarbons, resulting in drilling and the
creation of 47 wells between 1936 and 1943. After 1945-46, however, the activities were gradually dismantled. Only in
1957, Naples University Professor Antonio Lazzari carried out a new study of Tramutola, indicating the importance of
carrying out research in the area between Valle del Cavolo and Valle La Monica. Agip carried out a new survey and a
new excavation West of Tramutola, without, however, following the indications of Lazzari, but it all ended with renouncing
the Tramutola license since the well proved sterile. Following these events, oil prospecting and activities in Basilicata
were put aside. Only as a result of exploration of the deep traps in the early 1980's was the value of the Val d'Agri subsoil
demonstrated.
Coexistence of the ecosystem and oil: the Tramutola case today
The peculiarity of the seepage phenomenon and the naturalness of the Tramutola site still today arouse great interest in
both the observer who visits these places and in the scientific community. The latter is particularly interested in studying
the adaptation phenomena, in order to understand which processes are put in place by organisms to survive the
presence of hydrocarbons. Natural seeps of hydrocarbons may in fact be considered a living laboratory to study how
natural processes affect the fate of hydrocarbons and how living organisms are able to survive in the presence of these
substances.
Frog spotted near the Tramutola seeps. Photo: Dario Colucci.
Bacteria, plants and animals, in an environment chronically characterised by the presence of hydrocarbons, do not
passively suffer the effects of an environmental transformation but put in place a series of expedients that tend to rebuild
a new balance. In this way, an unusual habitat for plants and animals is created. There are frequent sightings of frogs
around the seeps and pioneer plants of the Equisetum
smallest form of life that exists.
species, but special attention should be paid to bacteria, the
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Specimen of Equisetum growing in the seeps of Tramutola. This plant has
very ancient origins and fossil remains have been found in rocks dating
back to approx. 350 million years ago. Photo: Dario Colucci.
Such information could be the background for implementing
bioremediation studies which are experiencing a growing interest among
sector experts, but also among public administrators that need to find
sustainable and economic systems with low environmental impact for the
remediation of contaminated sites.
Studies on the natural seeps of Tramutola tend, however, to assess above
all the impact they can have on the environment. In detail, in 2009-2010
Metapontum Agrobios, within the scope of the Study to evaluate the
impact of mining activities in Val d’Agri financed by the Basilicata Region,
examined samples of water mixed with oil coming from the sulphur spring
of Sulphur Water II (Tramutola), far from significant human activities.
These analyses showed that the amount of hydrocarbons decreases with
increasing distance from the source, a sign of scarce mobility of the
contaminant. To date, however, no intensive monitoring has yet been
carried out to evaluate, according to parameters such as continuity over
time and changing climatic conditions, the quantity of hydrocarbons
emitted by the manifestations, their degree of biodegradation and
adaptation of the indigenous plant and animal species to the presence of
these hydrocarbons.
By Eleonora Ippolito, Elisabetta Fortunato, Francesca Scannone, Dario Colucci
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