География, геология
УДК 550.836:551.247.1
SALT DOMES OF THE PRIPYAT
TROUGH AS HEAT ACCUMULATORS
V. I. ZUI a, M. A. DUBANEVICH a, E. A. VASILIONAK a
a
Belarusian State University, Nezavisimosti avenue, 4,
220030, Minsk, Republic of Belarus
Geothermal field of salt domes was considered in the paper. Salt domes are widely developed within the Pripyat Trough territory
within southeastern Belarus. It was shown that high values of heat conductivity and volumetric heat capacity of rock salt against
adjoining terrigenous rocks produce a focusing effect of heat. Heat flow density within them has increased values as compared to
terrigenous deposits surrounding domes. Analysis shows that its maximal values were observed within the dome crests. According
to observations heat flow could reach as high as 80–100 mW/m2. Temperature of sediments above domes is always higher than its
background values at comparable depths. In result a specific feature of salt domes is an elevated density of recoverable geothermal
resources. It was concluded that from this point of view they could be considered as «accumulators» of geothermal energy.
The recovery of this energy is possible only by means of borehole heat exchangers with circulating circuit of fresh water through
them.
Key words: salt domes; heat flow; geothermal field; geothermal energy; borehole heat exchangers; recovery of geothermal energy.
СОЛЯНЫЕ КУПОЛА ПРИПЯТСКОГО ПРОГИБА
КАК АККУМУЛЯТОРЫ ТЕПЛА
В. И. ЗУЙ 1), М. А. ДУБАНЕВИЧ 1), Е. А. ВАСИЛЁНОК 1)
1)
Белорусский государственный университет,
пр. Независимости, 4, 220030, г. Минск, Республика Беларусь
Рассматривается геотермическое поле соляных куполов, которые широко распространены в пределах Припятского прогиба в юго-восточной части Беларуси. Показано, что высокие значения теплопроводности и объемной теплоемкости создают
эффект фокусировки тепла в соли. Тепловой поток в их пределах имеет повышенные значения по сравнению с окружающими
купола терригенными отложениями. Анализ показывает, что его максимальные значения наблюдаются в верхней части куполов и могут достигать 80–100 мВт/м2. Температура отложений над куполами также выше ее фоновых значений на сопоставимых глубинах. В результате специфической особенностью соляных куполов является повышенная плотность извлекаемых
геотермальных ресурсов. Сделано заключение о том, что с этой точки зрения соляные купола можно рассматривать в качестве
аккумуляторов геотермальной энергии. Извлечение геотермальной энергии возможно только посредством скважинных теплообменников с циркуляцией пресной воды через них.
Ключевые слова: соляные купола; тепловой поток; геотермическое поле; геотермальная энергия; скважинные теплообменники; извлечение геотермальной энергии.
О б р а з е ц ц и т и р о в а н и я:
Зуй В. И., Дубаневич М. А., Василёнок Е. А. Соляные купола
Припятского прогиба как аккумуляторы тепла // Вестн. БГУ.
Сер. 2, Химия. Биология. География. 2016. № 2. С. 85–90.
F o r c i t a t i o n:
Zui V. I., Dubanevich M. A., Vasilionak E. A. Salt domes of
the Pripyat Trough as heat accumulators. Vestnik BGU. Ser. 2,
Khimiya. Biol. Geogr. 2016. No. 2. P. 85–90 (in Engl.).
А в т о р ы:
Владимир Игнатьевич Зуй – доктор геолого-минералогических наук; профессор кафедры инженерной геологии и
геофизики географического факультета.
Маргарита Алексеевна Дубаневич – магистрант кафедры
инженерной геологии и геофизики географического факультета. Научный руководитель – В. И. Зуй.
Елена Анатольевна Василёнок – студентка географического факультета.
A u t h o r s:
Vladimir Zui, doctor of science (geology and mineralogy);
professor at the department of engineering geology and geophysics, faculty of geography.
[email protected]
Margarita Dubanevich, undergraduate student at the department of engineering geology and geophysics, faculty of
geography.
Elena Vasilionak, student at the faculty of geography.
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Evaporites within platform covers, in particular rock salt layers, were revealed in many of deep sedimentary
basins of the World including ones within the East European Platform, for instance within the Cis-Caspian
Basin, Dnieper-Donets Depression, the Pripyat Trough, etc. Thick layers of rock salt were accumulated in
the process of their evolution in marine conditions subjected to evaporation of marine waters within shallow
lagoons.
Later thick terrigenous sediments overlaid salts. Growing accumulation of sediments created pressure for
salt layers and resulted in their subsidence. Under the influence of tectonic stresses and due to salt plasticity
under elevated temperature and increased pressure from overlying rocks, a gradual flow of salt was originated
(fig. 1). In many localities it formed salt domes of the squeezed salt penetrated through the overlying sediments.
Roofs of such domes were revealed at different depths. Sometimes, they reach the ground surface. Cryptodiapirs
were frequently formed above salt domes. Sometimes oil deposits adjoining domes were observed as well.
Fig. 1. Buildup scheme of a salt dome [1] (modified):
– permeable rock;
– caprock;
– argillaceous-marl rock;
– oil deposit;
– sandstones;
– dolomites;
– rock salt;
– salt flow from horizontal layer into salt dome
Rock salt shows plastic properties under high pressure and temperature existing within deep horizons of the
platform cover. The thermal expansion coefficient for rock salt is higher than for other sediments. Therefore
the salt is squeezed upwards.
A great pressure developed under the weight of accumulating strata overlaid the salt layer will allow the
salt to intrude accumulating above sediments and overcome the weight of sedimentary strata, their strength,
and the gravity force.
Two salt layers exist within the platform cover of the Pripyat Trough. They are so-called Upper Salt and
Lower Salt. These thicknesses are spread actually within the whole trough area.
Salt tectonics is widely developed within the Pripyat Trough [2]. Columns of salt here pierced through
overlying sediment units and form salt domes. Overburden load of younger sediments comprising hundreds
and thousands of meters of terrigenous rocks place enormous pressure on the salt layers and cause them to
flow. Salt tectonics developed within the Pripyat Trough formed salt folds, swells, domes and pillows. Such
domes are frequently accompanied by cryptodiapirs in their upper parts.
Geothermal field of salt domes
The Pripyat Trough belongs to good studied geologic structures of Belarus. Geothermal logging was
fulfilled in a number of boreholes. At present hundreds of temperature-depth profiles, recorded in the process of
standard logging, are available. Many holes were drilled into salt domes and their vicinity as well. Frequently
the time elapsed after finishing of holes and recording of temperature-depth profiles was only 5–15 days.
For deep boreholes it is not enough the thermal field, disturbed by the drilling process, returned to its natural
condition. Nevertheless these thermograms gave a possibility to learn the temperature distribution pattern in
salt domes and surrounding rocks as well as to estimate heat flow density (HFD) distribution within them [3].
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Salt structures have contrast geothermal field parameters. These features were pointed out earlier mostly on
the qualitative level. Field measurements, undertaken from fifties of the last century, showed that in general
the geothermal gradient within salt domes is 2,4 or even 2,8 times higher than for surrounded rocks [4, 5]. Heat
flow density was studied for a number of salt domes in the Pripyat Trough. It was considered in [6] at the background of their low to normal values within local inter-synclinal structures. The highest heat flow corresponds
to caprock sediments in upper parts of salt domes.
A thickness of the Lower Salt and Upper Salt bodies has a considerable differentiation in lateral directions
within the Pripyat Trough. It influences the distribution both the temperature and observed heat flow density.
Their contrast variations in sediments overlaid the Upper Salt are explained mainly due to groundwater
filtration. In the vertical cross-section variations of interval heat flow values within salt domes were observed
due to the contrast of heat conductivity coefficients of rock salt and terrigenous deposits surrounding domes.
The coefficient of heat conductivity for rock salt is around 5–7 W/(m ∙ K) depending on the admixture of
terrigenous material. At the same time this coefficient ranges for surrounding the dome sediments from 1,2 till
2,0–2,5 W/(m ∙ K). Such a heat conductivity contrast leads both to heat gain within the salt column and to the
deflection of heat flow vectors from vertical directions, as shown in fig. 2.
Fig. 2. Redistribution of heat flow within a salt dome area [7] (modified):
– permeable rock;
– marl and argillite;
– sandstones;
– dolomites;
– rock salt;
– caprock.
Arrows show heat flow paths at the contact of salt and surrounding sediments
The concentration of heat in the salt dome results in a complex temperature distribution both inside the
dome itself and in adjoining sedimentary rocks. As an example a profile through the Tishkovka salt dome of
the Pripyat Trough, located in its northern zone, and the temperature distribution along it, is shown in fig. 3. In
the uppermost part the dome has a developed caprock at a burial depth around 200 m formed in the process of
the dome growing. 10 themograms of boreholes, shown in this figure, were recorded and used to produce the
temperature distribution pattern along the considered geologic profile. An interpolation of data and drawing of
isotherms were fulfilled using the program package Generic Mapping Tools (GMT) [8, 9].
A contrast pattern of isotherms distribution is clearly visible along the whole profile. At a general background
of the temperature increasing with the depth, their variation in the vicinity of the salt dome represents some
kind of the temperature field «distortion» when approaching to the salt dome. It is possible to indicate that
isotherms are located closer to the ground surface above the nucleus of the dome. On the contrary, the dome has
a negative impact on regionally depressed isotherms before and after the salt dome at distances of 0,5–1,0 km.
This general tendency is not in an agreement concerning the borehole No. 67 (33) where it shows higher
temperature at shallow depths and its lower values at greater depth intervals when comparing to adjacent row
of wells. It could be explained by the absence of thermal equilibrium of rocks disturbed by the drilling mud
circulation at the moment of this thermogram was recorded. It typically happens when temperature-depth
profile was recorded in a few days after a mud circulation through the wellbore was stoped.
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Fig. 3. Temperature-depth profile through the Tishkovka salt dome located in the northern part of the Pripyat Trough:
– caprock;
– rock salt;
– boreholes. Isotherms in grey are given in ºC.
Dotted lines represent stratigraphic surfaces. Circles show depths where temperature readings were recorded or extrapolated
Heat flow density distribution in the vicinity of the Tishkovka salt dome, which acts as a thermal «lens», has
similar contrast pattern for the same profile (fig. 4). To construct it heat flow densities were calculated for several
intervals for each borehole and used as an input data for the profile using the GMT program package to fulfill
the interpolation and construct the pattern of heat flow isolines. A concentration of heat in the salt dome body
results here in a complex heat flow density distribution along the whole profile. The most contrast heat flow
variation is observed within crests of domes with their caprocks where it increases to 50–60 mW/m2 at shallow
depths around 100 m as shown in the fig. 4. At the same time its background value is around 40 mW/m2 for left
and right distant parts of the profile.
The maximal value of heat flow density exists in the salt dome crest and the caprock where it reaches
80–100 mW/m2. Heat flow decreases to 70–80 mW/m2 below the salt dome. A distinct vertical heat flow
variation exists within the whole thickness of the platform cover. The general tendency is the increasing heat
flow with depth.
Review of results for other salt domes
Heat flow density variations were calculated not only for described Tishkovka salt dome but for a number
of other salt bodies existing within the Pripyat Trough [6, 10]. The limited size of the paper doesn’t permit
to describe them in details. For instance, we observe HFD 88 mW/m2 for the interval of 1100–1200 m and
82 mW/m2 for the interval of 2000–2100 m for the Smaglovskaya-2R hole. Within the interval of 800–900 m,
corresponding to the caprock of the dome the HFD is 77 mW/m2 and it drops to 72 mW/m2 within the interval of
1900–2000 m for the Nikulinskaya-6R drillhole. It in general increases with the depth until it reaches 72 mW/m2
within the interval of 800–1600 m in the Zolotukhinskaya-2R hole. Similar situation concerning the HFD
distribution exists in salt domes and salt diapirs developed within the Ostashkovichi, Pervomaisk, Rechitsa and
other geological structures of the Pripyat Trough [11, 12]. The HFD maximum of 76–80 mW/m2 was observed
within the interval of 760–1052 m in the Rechitsa salt dome. Its maximal value reaches here 107 mW/m2 (interval
450–530 m) in the well 17 and even 120 mW/m2 in the interval of 500–535 m (caprock) in the well 128, its normal
values outside the dome are: 69–80 mW/m2 (well 93), 45–92 mW/m2 (well 4) and 65–87 mW/m2 (well 12).
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Fig. 4. Heat flow-depth profile through the Tishkovka salt dome located in the northern part of the Pripyat Trough:
– caprock;
– rock salt layer;
– boreholes.
2
Isolines in grey are given in mW/m . Dotted lines represent stratigraphic surfaces
Discussion
A contrast pattern of the HFD distribution exists within deposits overlying a number of domes within the
Pripyat Trough. In particular, within Cretaceous, Jurassic, Triassic, Permian, Carboniferous and overlying
the salt Devonian sediments of the Zolotukha Structute it ranges from 27 to 100 mW/m2 (well 3-R), from 46
to 103 mW/m2 (well 2-R). Within deposits overlying the Smaglovskaya Brachianticlinal it ranges from 13
to 92 mW/m2. The main factors influencing a scatter of values in this part of the geologic cross-section are
pronounced groundwater filtration within loose sediments existing in overlying the salt sediments, as well
as heat redistribution due to the developed salt tectonics. A growing dome weakens integrities of caprocks
terrigenous deposits, overlying the salt dome, increases their decompaction and permeability for underground
fluids, resulting in origination of convective heat flow component. Hence, higher geothermal gradients and
interval HFD values are observed within cracked zones in strata above salt domes. The decompaction zone
and its hydrodynamic connection to a zone of active water exchange within the Meso-Cenozoic deposits were
confirmed by investigations conducted within the South-Kazanskaya Syncline of the Pripyat Trough [13].
Similar situation exists in other parts of the East European Platform with dominating evaporates, where
the heat conductivity of rock salt is 2,0–2,5 times higher the conductivity of typical terrigenous rocks. The
creep capability of rock salt due to the tectonic stress and vertical movements creates different forms of salt
structures. Detailed investigations of these effects were conducted [14] for salt domes Kenkiyak, Mortuk,
Shengelshi, Alibekmola, Karatyube located in the Cis-Caspian Depression.
Conclusions
The maximal value of heat flow density exists within crests of salt domes and caprocks where it could reach
up to 80–100 mW/m2. It sufficiently decreases at the base of the salt domes. Due to heat concentration in salt
domes, heat flow vectors deflect of their vertical orientation and horizontal HFD components range from 4 to
20 mW/m2 within salt domes and from 4 to 10 mW/m2 at their contact with terrigenous sediments. Such HFD
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distortion was observed up to the lateral distances of 1 km off the dome axis [14]. Similar situation concerns
the temperature distribution pattern both within the dome and adjoining rocks. Variations of main parameters
of the geothermal field shown in fig. 3 and 4 are typical for other salt domes and diapirs, penetrating the
overlying strata of sediments. In all situations, the maximal distortion of geothermal field parameters (both the
temperature and HFD) corresponds to crests of salt domes.
Due to increased temperature values at same depths as compared with their background values outside
salt domes, as well as increased heat flow densities in crests of domes and their caprocks, these salt structures
actually represent accumulators of geothermal energy. As there is no porosity and fluids in these salt bodies,
the heat withdrawal from them is possible by means of heat exchangers.
REFERENCES
1. What is a Salt Dome? 2016 [Electronic resource]. URL: http://geology.com/stories/13/salt-domes/ (date of access: 20.02.2016).
2. Конищев В. С. Соляная тектоника Припятского прогиба. Минск, 1975.
3. Богомолов Г. В., Цыбуля Л. А., Атрощенко П. П. Геотермическая зональность территории БССР. Минск, 1972.
4. Van-Orstrand C. E. Normal geothermal gradient in the United States // Bull. Am. Assoc. Petrol. Geol. 1935. Vol. 19, № 1.
P. 21–34 [Van-Orstrand C. E. Normal geothermal gradient in the United States. Bull. Am. Assoc. Petrol. Geol. 1935. Vol. 19, No. 1.
P. 21–34 (in Engl.)].
5. Hawtorf E. Results of deep well temperature measurements in Texas // Bull. Am. Petrol. Inst. Prob. 1930. № 205. P. 333–339
[Hawtorf E. Results of deep well temperature measurements in Texas. Bull. Am. Petrol. Inst. Prob. 1930. No. 205. P. 333–339
(in Engl.)].
6. Zhuk M. S., Tsalko P. B., Zui V. I. Heat flow of the Pripyat Trough // Літасфера. 2004. № 1 (20). С. 122–130 [Zhuk M. S., Tsalko P. B., Zui V. I. Heat flow of the Pripyat Trough. Litasfera. 2004. No. 1 (20). Р. 122–130 (in Engl.)].
7. Горы под землей. 2016 [Electronic resource]. URL: http://prokameshki.ru/gory-pod-zemlej.html/ (date of access: 20.02.2016).
8. Smith W. H. F., Wessel P. Gridding with continuous curvature splines in tension // Geophysics. 1990. Vol. 55. Р. 293–305
[Smith W. H. F., Wessel P. Gridding with continuous curvature splines in tension. Geophysics. 1990. Vol. 55. Р. 293–305 (in Engl.)].
9. Wessel P., Smith W. H. F. Free software helps map and display data // EOS Trans. Am. Geophys. U. 1991. Vol. 72 (41).
Р. 445– 446 [Wessel P., Smith W. H. F. Free software helps map and display data. EOS Trans. Am. Geophys. U. 1991. Vol. 72 (41).
Р. 445– 446 (in Engl.)].
10. Зуй В. И. Тепловое поле платформенного чехла Беларуси. Минск, 2013.
11. Цыбуля Л. А., Левашкевич В. Г. Тепловой поток Припятского прогиба и причины его неоднородности // Геол. журн.
1990. № 11. С. 19–26 [Tsybulya L. A., Levashkevich V. G. Teplovoi potok Pripyatskogo progiba i prichiny ego neodnorodnosti.
Geol. J. 1990. No. 11. P. 19–26 (in Russ.)].
12. Жук М. С., Макаренко В. М., Цалко П. Б. Геотермические условия южной части Припятского прогиба // Докл. АН БССР.
1993. Т. 37, № 4. С. 109–113 [Zhuk M. S., Makarenko V. M., Tsalko P. B. Geotermicheskie usloviya yuzhnoi chasti Pripyatskogo
progiba. Dokl. AN BSSR. 1993. Vol. 37, No. 4. P. 109–113 (in Russ.)].
13. Гарецкий Р. Г., Монкевич К. Н., Толстошеев В. И., Цалко П. Б. Структуры Припятского прогиба как потенциальные
подземные хранилища газа // Геология нефти и газа. 1998. № 11. С. 2–7 [Garetsky R. G., Monkevich K. N., Tolstosheev V. I.,
Tsalko P. B. Struktury Pripyatskogo progiba kak potentsial’nye podzemnye khranilishcha gaza. Geologiya nefti i gaza. 1998. No. 11.
P. 2–7 (in Russ.)].
14. Хуторской М. Д. Тепловой поток в районах структурно-геологических неоднородностей. М., 1982.
Received by editorial board 01.03.2016.
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