Thermal springs and balneology in the Peri-Adriatic area: geochemical status

and prospects

Riccardo Petrini, Pisa University

(with contributions by R. Cataldi and B. Della Vedova)

1

(Picha F.J. 2002)

(Del Gaudio et al., 2007)

Epicenters of seismic events of magnitude > 2.0, from 1975 to 2005, U.S. Geological Survey Earthquake Database

The Peri-Adriatic Region

2

Thermal Spas in Peri-Adriatic Region

COUNTRY Number of active SPAs

Water volume used in 2010 (m3/year, excluding pool uses)

Albania 5 140.000

Bosnia Herzegovina 20 1.290.000

Croatia 18 1.345.000

Greece > 23 (up to 50?) > 500.000

Italy 149 48.000.000

Montenegro 1 60.000

Slovenia 25 1.780.000

T O T A L > 260 > 53.115.000

Including pool uses, a flow of about 112x106 m3/year (3.55 m3/s) of thermal waters can be estimated to feed Spas of the Adriatic-Jonian Region

3

(1) Data taken from different sources, they likely contain large uncertainties.

(2) Proceedings World Geothermal Congress 2010

(*) Water volumes have been estimeted starting from the Annual Energy Use of each country.

For each spring we estimated the average mean annual energy (based on the average flow) for the effective

temperature intervals (Tin –Tout), using the Annual Energy Use (TJ/yr) = Ave. flow rate (kg/s) x [inlet temp. (°C) - outlet temp. (°C)] x 0.1319

(**) Figures largely underestimated

Country N. of

SPAs

Total

average

flow rate

(kg/s)

Annual Total

average water

used (106*m3)

T (°C) Average T

(°C)

Resource

potential

capacity

(MWt)

Total

geothermal

energy used

(TJ/yr)

Estimated number

of tourists (1) Source (2)

Slovenia 26 115* 3.6 23-63 33-38 25 311 751000 (2010) ?

WGC 2010

Croatia 18 96* 3.0 25-85 42-47 33 216 400000 (2010) ? WGC 2010

Bosnia and

Herzegovina 20 79* 2.5 21-76 39-44 13 100 192000 (2009) ? WGC 2010

Montenegro 1 ? ? ? ? ? ? WGC 2010

Albania 6 21 0.7 27-60 45-50 12 8 ? WGC 2010

Greece >60 >1500 ≈ 47 18-100 ? 39?** 238?** >100000 (2010) ? WGC 2010

Serbia 59 700-800 ? ≈ 23 29-96 45-50 40 647 ? WGC 2010

TOTAL > 191 > 2.561

≈ 79,8

162 1520 >1.443.000

Thermal Spas in Peri-Adriatic Region: Q,T, V, MW, TJ

4

5

Conceptual flow diagram for water and energy utilization in spa systems, excluding pools

Conceptual flow diagram for water and energy utilization of thermal pools associated to spa systems

Energy Potential of thermal springs and waters

Mass and energy balances are crucial for sustainable use of excess heat, up- and down-stream Spa uses, and are tools to develop the balneotherapy sector.

Geothermal reservoirs are often related to areas of active or recent magmatism, where heat is transferred from a magmatic source to the circulating fluids However, low-enthalpy waters in different tectonic settings, including aquifers in deep carbonate-rocks and metamorphic basements, are receiving much attention, in particular for bathing and swimming The Peri-Adriatic area has many favorable geothermal characteristics; however, long-term abstraction of resources should be carefully planned to avoid overexploitation

6

Thermal springs and waters in peri-Adriatic context

Water geochemistry: source aquifers for a sustainable exploitation policy

The major ions chemistry gives the basic information on water-type and processes

Piper diagram

cations Ca2+, Mg2+, Na+, K+ anions HCO3

-, Cl-, SO42-

7

Geothermal manifestations in the Peri-Adriatic Region belong to different hydrofacies, reflecting

different origin and nature of aquifers

They include: Thermal waters in Mesozoic carbonate-rock aquifers

Thermal waters in aquifers within the metamorphic basement

Thermal waters in porous media in sedimentary basins

Thermal waters of marine origin in coastal environments Each requires to enhance knowledge to reduce future quantitative and

qualitative threats 8

Bosnia

Hydrofacies: mostly of the Ca-HCO3 type

Some of the Ca-HCO3 waters are displaced

towards Na-Cl marine components

seawater

9

Croatia

Hydrofacies: waters range from the Ca-HCO3 to the Na-Cl, Ca-SO4 type

seawater The data suggest mixing processes

between the different water-types

limited ion-exchanges

10

Greece

seawater

Hydrofacies: the Na-Cl type dominate; highly variable composition, including the

Na-HCO3 type.

SO4 reduction

CaCO3 solution

CaCO3 deposition Ca-HCO3

type The data indicate that a

number of different processes are active in the

different environments, and that gases (in

particular CO2) have an active role in driving

equilibria

11

Macedonia

Hydrofacies: waters range from Ca-HCO3, Na-Cl and the Na-HCO3 type

12

Serbia

Most waters range from the Ca-HCO3 to the Na-HCO3 type

Ca-HCO3

type

13

Slovenia

Conservative mixing between Ca-HCO3 and Na-Cl waters are absent or negligible, indicating

non-interacting reservoirs. Possible processes of

freshwater intrusion are highlighted

seawater Ca-HCO3

type

Hydrofacies: mostly waters range from the Ca-HCO3 and Na-HCO3 type Na-Cl waters are

limited

fresh water intrusion?

14

Waters origin: oxygen and hydrogen stable isotopes

-90

-70

-50

-30

-10

10

-12 -10 -8 -6 -4 -2 0 2

dD

d18O

Serbia

Greece

Bosnia

Slovenia

Global Meteoric Water Line Central Mediterranean Water Line

Seawater source

Most water-types have a meteoric origin. Na-Cl waters have a marine origin. Modern or ancient seawater?

15

Strontium isotopes: the modern or ancient origin of the marine Na-Cl type waters

0.7065

0.7070

0.7075

0.7080

0.7085

0.7090

0.7095

0 100 200 300 400 500

87S

r /

86 S

r

Numerical Age, Ma

Mc Arthur et al, 2001, 2007

The 87Sr/86Sr ratio in seawater

changes through geological time,

allowing the “age” of the saline

reservoir to be inferred

16

The Na-HCO3 waters: extreme compositions through water-rock interaction

0.1

1

10

100

1000

10000

0.1 1 10 100 1000 10000 100000

HC

O3

(mg/

L)

Na (mg/L)

Bosnia

Croatia

Greece

Macedonia

Serbia

Slovenia

The waters from the Peri-Adriatic region show a Na vs. HCO3 scattered distribution, in some cases with high HCO3. Most waters from Greece are displaced towards low HCO3

17

Some of the Na HCO3 thermal waters likely reflect silicate weathering:

silicates have low solubilities (NaAlSi3O8: 6x10-7 mol/L) and low

dissolution rates

the Na-HCO3 signature reflects long residence times of waters in deep environments

These thermal reservoirs are of particular interest

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Temperature

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80

TD

S (

mg/L

)

Temperature (°C)

(Miosic et al., 2013)

Bosnia

the trends of increasing temperature with increasing salinity and chloride content

suggest, at least in some cases, the role of a high-thermal

component of marine origin

0

50

100

150

200

250

300

350

400

0 20 40 60 80

Cl (

mg

/L)

Temperature (°C)

19

0

10

20

30

40

50

60

70

0 20 40 60 80

SiO

2 (m

g/L

)

Temperature (°C)

(Milenic et al., 2012)

0

20

40

60

80

100

120

140

0 10 20 30 40

Ca (

mg

/L)

Temperatura (°C)

Serbia

Despite some scatter, the trend of increasing temperature with

increasing silica likely indicate the role of high-thermal components

related to silicate dissolution.

The pattern of decreasing calcium with increasing temperature could

reflect the saturation state of carbonates, yielding cement

precipitation

Temperature

20

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

SiO

2 (m

g/L

)

Temperature (°C)

(Lambrakis & Stamatis, 2008)

Greece

Also in this case, some of the waters likely reflect the role of

high-thermal, deep components related to silicate dissolution.

Trends of decreasing calcite and dolomite saturation states with

decreasing temperature are also observed, indicating the role of

CO2-mediate carbonate equilibria

Temperature

21

A variety of hydrofacies characterize the active geothermal manifestations used for thermal balneology in the Peri-Adriatic region

Waters have both a meteoric origin or maintain a marine signature, likely attributable to modern or to remnants of ancient seawater. Isotopic studies would help to clarify this point

Some of the waters are diagenetically modified by long-lasting interactions with the aquifer lithologies, suggesting high residence times and/or slow flowpaths. In particular, the interactions with low-solubility silicate minerals is likely responsible for the particular Na-HCO3 signature of the thermal, deeper reservoirs. These waters would deserve further studies.

For these waters, long-term abstraction should be carefully planned

In some cases, mixing of waters with different geochemical signature occurs

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Example of application of geochemical tools

The Monfalcone (Grado – Lignano) thermal waters in the coastal area of the Friuli Plain

(NE-Italy): a case history

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Monfalcone: natural springs (34-40 °C) Grado: Grado-1 well (1100 m depth; 43 °C) Lignano: SIL well (≈2000 m depth; 53 °C)

Sites of study

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Geological framework of the Trieste Gulf

Monfalcone

Lignano Grado

After Carulli (2011) J. Geodyn. 51, 156-165 Mesozoic-Cenozoic carbonate Units

Paleogene Terrigenous Units

Quaternary alluvial sediments

A

B

25

Multichannel seismic profile across the Trieste Gulf

Busetti et al 2010

Friuli Carbonate Platform

Eocene Flysch terrigenous sequence

Plio-Quaternary marine sediments

A B

Lignano Grado-1

Monfalcone

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Hydrochemistry

Monfalcone Grado-1

freshwater

Modern seawater

Wells in the FVG Low Plain

The Monfalcone, Grado-1 and Lignano deep waters have all the chemical signature like modern seawater

NOTE Some of the waters

from geothermal wells in the FGV

Low Plain are of the Na-HCO3 type

Lignano

27

0

2000

4000

6000

8000

10000

12000

0 5000 10000 15000 20000

Na

(mg

/L)

Cl (mg/L)

Monfalcone

Grado-1

Lignano

Modern seawater

Waters from the Lignano well are the most representative of the marine end-member Dilution processes are active at the Monfalcone springs and Grado-1 well to a lower extent

A marine component also contributes to waters from geothermal wells in the FVG Plain (crosses)

The marine signature

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-80

-70

-60

-50

-40

-30

-20

-10

0

10

-13 -11 -9 -7 -5 -3 -1 1

dD

d18O

Monfalcone

Grado-1

Lignano

Dilution processes and origin of non-marine component

Karst-type waters

The freshwater component might be represented by karst-type groundwaters

FVG Low Plain geothermal wells

29

0

500

1000

1500

2000

2500

3000

0 5000 10000 15000 20000

SO4 (

mg

/L)

Cl (mg/L)

Monfalcone

Grado-1

Lignano

Evolutionary patterns of the marine component

seawater

Sulfate depletion

Sulfate excess

Sulfate excess and mixing corrosion

3

2

4

2

322

3

2

4

2

342

4222

2222

222

2

HCOSOCaCaCOOSH

HCOSOCaCaCOSOH

SOHOSH

30

0

200

400

600

800

1000

1200

1400

1600

0 5000 10000 15000 20000

Ca

(mg

/L)

Cl (mg/L)

Monfalcone

Grado-1

Lignano

seawater

Calcium excess

Diagenetic reactions of seawater with the hosting carbonates

31

Monfalcone

Grado-1 Lignano

Alpi orientali Sulfur springs in Eastern Alps

Crustal gas-water interactions

Samples deviate from the composition of air saturated water towards the admixing

of crustal gases.

This has implication on the volume of the thermal

reservoir, since the original atmospheric signature has been replaced by crustal

components:

LOW WATER VOLUME OR DISCONTINUOUS WATER

BODIES (?)

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0,7077

0,7078

0,7079

0,7080

0,7081

0,7082

0,7083

0,7084

87Sr

/86Sr

lignano monfalcone Grado-1

Modern or ancient seawater?

Sr-isotope ratio of modern seawater 0.70918

A possible common marine source for Monfalcone, Grado-1 and Lignano

The thermal waters do not have the isotopic signature of present-day seawater !

33

0,7070

0,7075

0,7080

0,7085

0,7090

0,7095

0 20 40 60 80 100

87

Sr

/ 8

6 S

r

Numerical Age, Ma

reservoir

excessexcess

reservoir

excessmeasuredreservoir

Sr

SrSrSr

Sr

SrSrSrSrSr 868786878687 /1//

Deconvolving the diagenetic chemical changes and “age” of the thermal component

the marine reservoir would be represented by ancient seawaters “dated “ at Miocene

Sr isotopic changes in seawater through time

Monfalcone, Grado-1, Lignano

Mass-balance equation

34

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 10 20 30 40 50 60

EC (

uS/

cm)

T (°C)

Monfalcone

Grado-1

Lignano

Temperature

Karst waters

The thermal reservoir is best represented by the saline ancient seawater Cooling by dilution is observed; however the karst-type waters of superficial aquifers are

unsuitable as cold term

?

35

60 70

80

Modern seawater

°C Lignano Grado-1

Deconvolution of the diagenetic processes of ancient seawater in the deep carbonate reservoir to estimate

temperature of the geothermal component

36

65 °C is the T at about 2.0-2.5 km in carbonate

reservoir

Friuli thermal waters represent the ancient, diagenetically modified seawater of a low temperature geothermal system

Deep saline reservoir might represent remnants of seawater entrapped in Mesozoic carbonates during the late Oligocene–Miocene sea transgression

In some parts the deep thermal reservoir mixes and homogeneizes with colder kast(?)-type waters flowing in, through a deep and long-lasting circuit

Thermal reservoir might be composed by discrete aquifers, or might not be widely extended

Hydrothermal diagenesis including dolomite cementation might change the water flow dynamics at depth

37

Concluding remarks

Generalized geothermal model

?

38

Thank you for your attention

39

Some of the waters show a Na vs. Cl linear correlation, suggesting the role of seawater or

dissolution of marine salts

On this ground, the contribution of the marine component can be removed

0.1

1

10

100

1000

10000

100000

0.1 1 10 100 1000 10000 100000

Cl (

mg

/L)

Na (mg/L)

40

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 500 1000 1500 2000 2500 3000

Na (mg/L)

HC

O3 (

mg

/L) After correction a more clear correlation in observed, following the equimolar

distribution of Na and HCO3 ions (solid line)

This is consistent with the (incongruent) silicate dissolution to generate the Na-HCO3 waters:

2452232283 4)(22232 SiOOHOSiAlHCONaCOOHONaAlSi

as an example

41