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ORIGINAL ARTICLE
Technologies of geothermal resources development in Southof Russia
A. B. Alkhasov . D. A. Alkhasova . A. Sh. Ramazanov
Received: 20 July 2019 / Accepted: 25 October 2019 / Published online: 5 November 2019
� Springer Nature Switzerland AG 2019
Abstract A technology has been proposed for the
integrated development of low-temperature geother-
mal resources for using their thermal and water
potentials for various purposes. The possibility is
substantiated for efficient development of geothermal
resources by construction of binary geothermal power
plants (GeoPP) using idle oil and gas wells that will
significantly reduce capital investments for their
building. The East Ciscaucasian artesian basin situated
in the South European part of Russia has a number of
fields with idle wells that can be converted to thermal
water production. Involving the entire fund of idle
wells will make it possible to obtain up to 300 MW of
summary net capacity at a geothermal power plant.
This work proposes a deployment of hybrid technol-
ogy of geothermal power plant coupled with combined
cycle plant of gas turbine type (further GCP) for the
effective utilization of medium-temperature thermal
waters (80–100 �C). These technologies are shown to
be promising for using such water for electricity
generating with high efficiency. A comparative anal-
ysis was carried out for GeoPP and GCP operating on
medium-temperature water, which has shown the
advantage of the latter. According to the calculations,
the implementation of hybrid technology at the
Thernair field in Makhachkala town will make it
possible to get a power plant capacity of up to 60 MW.
The prospects of integrated processing of high-
temperature geothermal brines are shown. The tech-
nological diagrams are presented where the electricity
generated at a binary GeoPP is used in the unit for the
chemical components extraction. The estimated
parameters for the Berikey geothermal field are given.
The proven reserves of the Berikey field thermal
brines are shown to be promising for output more than
2000 tons of lithium carbonate annually. The pro-
spects of integrated processing of high-temperature
geothermal brines in the Tarumovka geothermal field
have been presented. The thermal energy of the
geothermal brine can be converted into electricity in a
binary geothermal power plant using a low-boiling
working agent. The Rankine thermodynamic cycles
have been considered realized in the secondary circuit
of the GeoPP at different temperatures of evaporation
of the working agent isobutane. The most effective in
terms of maximum power generation is a supercritical
cycle, close to the so-called ‘‘triangular’’ cycle with an
evaporation pressure pe = 5.0 MPa. The spent brine
with a low temperature from the GeoPP will go to a
A. B. Alkhasov (&) � D. A. Alkhasova �A. Sh. Ramazanov
Institute for Geothermal Research, DSC RAS,
Makhachkala, Russia
e-mail: [email protected]
D. A. Alkhasova
e-mail: [email protected]
A. Sh. Ramazanov
e-mail: [email protected]
A. B. Alkhasov
Branch of the Joint Institute for High Temperatures, RAS,
Makhachkala, Russia
123
Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
https://doi.org/10.1007/s40948-019-00129-w(0123456789().,-volV)(0123456789().,-volV)
chemical plant, where the main chemical components,
namely, lithium carbonate, magnesia, calcium car-
bonate and sodium chloride will be extracted accord-
ing to the developed by us technology for the
integrated utilization of hydrothermal brines. For the
production of valuable inorganic materials, the elec-
tricity generated at the GeoPP may be applied. The
need is shown in the priority integrated processing the
associated highly saline brines of the Yuzhno-
Sukhokumsk group of oil and gas wells in Northern
Dagestan. At present, the associated brines with a
radioactive background exceeding permissible stan-
dards are dumped onto surface filtration fields. Tech-
nological solutions for their decontamination and
development have been proposed.
Keywords Geothermal energy � Efficienttechnologies � Integrated development � Binarygeothermal power plants � Hybrid geothermal and
combined cycle power plants
1 Introduction
Energy-saving technologies based on geothermal
energy are an important component in the develop-
ment of renewable energy. The increase in the volume
and expansion of geothermal resources application is
characteristic for industry of recent years. In a number
of countries, geothermal technologies are becoming
dominant, and the share of geothermal power in the
global energy balance is steadily growing. A number
of following publications present the results of studies
on the efficient development of geothermal energy
resources (Bertani 2010; Falcone et al. 2018; Gharibi
et al. 2018; Jiang et al. 2016; Kaya et al. 2011;
Ozdemir et al. 2017; Ramazanov et al. 2016; Rybach
2010; Shortall et al. 2015; Song et al. 2018; Tomarov
et al. 2012).
The economic potential of geothermal resources in
the Russian Federation is estimated of 115million tons
of reference fuel/year, the use of which can be up to
10% in the overall balance of the energy supply. The
total installed electrical capacity of GeoPP in Russia is
82 MW, and the thermal capacity of power plants
using geothermal heat directly is 310 MW. One of the
reasons for such a low level of geothermal energy
development is the lack of advanced technologies.The
development of a specific geothermal field or site
should be accompanied by the selection of the most
efficient technological scheme taking into account
many factors: geological and hydrogeological,
geothermal characteristics of the field, physical and
chemical parameters of the geothermal heat carrier, as
well as environmental, landscape and climatic, con-
struction, social, etc. (Alkhasov 2008).
Promising for large-scale geothermal energy
deployment is the North Caucasus region (South of
Russia), where the East-Ciscaucasian artesian basin
(ECAB) covers the area of more than 200 thousand
km2. It represents a huge ‘‘bowl’’ filled with Mesozoic
and Cenozoic sedimentary strata. In the vertical
section of the basin, there are three stages of low,
medium, and high-temperature water, isolated from
each other by waterproof clay rock.
Figure 1 shows the geothermal map of ECAB
(Kurbanov 2001).
In the upper horizon, the water temperature,
depending on the depth, ranges from 25 to 60 �C,and the salinity varies between 0.5 and 1.5 g/dm3.
Wells are gushing with an overpressure of
0.1–0.3 MPa. The expected operational resources
with an average temperature of 40 �C are more than
1.5 mln m3/day. The depths of thermal aquifer in the
upper horizon range from 300 to 700 m.
In the middle horizon, the reservoirs contain a
powerful water drive system of thermal water with the
salinity of 5–35 g/dm3, temperature of 70–130 �C, andwell flow rate of 500–5000 m3/day at overpressures of
0.3–1.5 MPa. The potential operational resources
make up 1 million m3/day.The maximum depth of
the roof of the middle horizon is up to 3500–4000 m.
The lower horizon is composed of rocks of the
Cretaceous, Jurassic, and Triassic periods. High salt
thermae of sodium chloride and calcium composition
are confined to it with the salinity of 60–210 g/dm3
and temperatures of 130–220 �C. Gas factor in such
water is more 10 m3/m3. The maximum depth of the
lower horizon is up to 10–12 km. This thermal water is
an industrial hydromineral raw material with a high
content of lithium, rubidium, cesium, iodine, bromine,
boron, potassium, magnesium, and strontium. The
potential resources of geothermal waters and brines of
the lower stage are 2.6 million m3/day (Kurbanov
2001).
Geothermal deposits occurring at depths from 300
to 3500 m are quite investigated in this region. The
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7 Page 2 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
temperature in deep reservoirs reaches 180 �C and
higher. About 500,000 people use geothermal energy
for heat supply in the household sector, agriculture,
and industry. However, the share of geothermal power
in the overall balance of energy consumption is less
than 1%. The operation of most geothermal deposits is
low. Only one-fifth of the heat potential of geothermal
water is used. A producing volume of water is
significantly lower than proved reserves. Only 15%
of the water resource potential and 19% of thermal
potential are used in North Caucasus. The large-scale
development of geothermal reserves can raise elec-
tricity generation and heat supply in the region up to
the level of 50% from the total energy consumption.
2 Integrated development of low-temperature
thermal water
The low-temperature water is promising for heating,
as well for household and technological water supply.
The task is to utilize such water efficiently using heat
pump heating technologies. High commercial return
of the low-enthalpy geothermal reserves may be
achieved when using thermal potential both for power
generation, and all sorts of water consumption.
The direct use of geothermal resources for heat
supply in most cases is associated with the seasonal
operation of wells producing thermal water, which
results in a reduction of deposits heat extraction and a
deterioration in the economic parameters of geother-
mal production. It is necessary to strive for the most
efficient development of thermal water intakes with
the continuous operation of wells with flow rates
corresponding to the operational reserves and bringing
the temperature drop of used water to the lowest
possible value.
According to various estimates, the number of wells
in the region for the extraction of low-temperature
water ranges from 7000 to 10,000. The water salinity
of most wells does not exceed 1–3 g/l. But, many of
Fig. 1 Geothermal map of
East-Ciscaucasian Artesian
Basin Values of heat flow,
mW/m2: 1-\ 30 are the
negative anomalies on heat
flow; 2-30–50; 3-50–75; 4-75 -100; 5-[ 100; 6-thermo-anomalies of the
bedding
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Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 3 of 17 7
them have been decommissioned by now for various
reasons (Alkhasov et al. 2012).
We have proposed a number of technologies for the
efficient utilization of the low-temperature thermal
water. In one of them (Fig. 2), the heat of water can be
used for heating and for increasing water temperature
in the system of hot water supply (Alkhasov 2018).
The water cooled in the heat exchangers goes to the
water treatment unit, where it is brought to the
drinking water standard, and then to consumers. In
the inter-heating period, part of the thermal water from
the well, used in the heating system, flows into vertical
down-hole heat exchangers 100–300 m deep to restore
the thermal field around them, and the water cooled in
the wells goes to water treatment. During the heating
period, the heat regenerated in the formation is used in
a separate heating system with a heat pump. The
proposed technology will make it possible to transfer
wells to the year-round operation mode, fully utilize
their water and thermal potential with maximum
benefit.
3 Electricity generation using hydro-thermal
resources of East-Ciscaucasian artesian basin
The most promising kind of geothermal energy
utilization is its conversion into electrical power with
year-round operation of geothermal wells. The
expected thermal capacity of hydro-geothermal
resources of ECAB is estimated up to 10,000 MW
and electrical capacity up to1000 MW. The hydro-
geothermal reserves of the region with temperatures
above 100 �C are suitable for electricity generation.
However, the characteristic features of such water
include high salinity, large gas content, tendency to
scaling when changing temperature and pressure
conditions, and high corrosiveness. Besides, for the
maximum their extraction, it is necessary to build
high-production wells of large diameter involving
huge capital investment, which is not realistic at the
present state of affairs in the regional economy.
In the short term, the reconstruction of existing idle
wells in the depleted gas and oil fields is the most
optimal. In Northern Dagestan only there are more
than 1000 idle wells drilled to the depths of
2000–5000 m. Most of them are applicable to output
thermal water for power generation.
Expenses for geothermal wells construction make
up a significant part of the geothermal energy system
cost. The capital investments in the geothermal
circulation system (GCS) consisting of two wells can
reach up to 90% of the total value. Reconstruction of
the idle wells for the thermal water production will
significantly reduce the investments in the construc-
tion of geothermal power plants.
3.1 Power generation with binary geothermal
power plant
Electric power, based on discussed sort of resources, is
usually generated at a binary GeoPP. The primary heat
carrier circulating in the GCS loop with idle oil–gas
wells is used for heating and evaporating a low-boiling
working agent circulating in the secondary circuit of a
steam-turbine unit (STU), where the Rankine cycle is
implemented.
The main goal in creating any binary GeoPP is to
obtain the maximum useful capacity with optimal
performance of the plant. It can be achieved by
optimizing the design and operating parameters of the
Fig. 2 Outline of integrated utilization of low-temperature
thermal water. 1 Geothermal well, 2 heat consumer, 3 water
treatment unit, 4 clean water tank, 5 pump, 6 heat exchanger, 7
to hot water supply, 8 to cold water supply, 9 low-temperature
heating system with a heat pump, 10 heat-accumulating wells
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7 Page 4 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
primary (GCS) and secondary (STU) circuits (Alkha-
sov 2008).
The factor limiting the increase in net power is that
oil and gas wells have, as a rule, small diameters of
production strings (0.104–0.124 m).The use of such
wells for the extraction of thermal water reduces
sharply the optimal flow rate of heat carrier circulating
in the GCS loop and, accordingly, the net power of the
plant.
Earlier, we had performed estimates of binary
GeoPP construction for a number of fields. The
methodology and equations to determine the optimal
characteristics of the binary geothermal power plant
were considered in detail in previous works (Alkhasov
2008, 2010, 2012; Alkhasov and Alkhasova 2011).
The computations were conducted for a GCS
consisting of one production and one injection wells.
There is an optimal flow rate of the GCS correspond-
ing to the maximum net power of the GeoPP. A further
increase in the flow rate of the primary heat carrier in
the loop of the GCS results in a growth of the electrical
system total capacity. However, simultaneously the
useful capacity reduces, since the energy costs for
circulating the heat carrier increase sharply. Depend-
ing on the temperature of thermal water, the useful
capacity of a GeoPP with a GCS of two wells is from
365 to 2000 kW. With using the entire number of idle
wells we will obtain up to 300 MW of the summary
net power for the plant.
The technological parameters of the GeoPP are
collected in Table 1, calculated for the hydrogeolog-
ical and geothermal conditions of the Thernair
geothermal field (in the vicinity of Makhachkala
town, Dagestan).
It follows that the use of medium enthalpy thermal
water is ineffective for generating electricity in the
GeoPP with reverse injection. With an increase in the
discharge in the GCS, the power consumption of the
injection pumping station grows faster than the
capacity of the GeoPP and begins to exceed the latter
from a certain small value of flow rate. From the
tabular data it can be seen that, depending on the initial
temperature of geothermal water, the maximum net
power of a binary GeoPPwith a GCS loop may be only
39–163 kW.
To increase the useful capacity of the plant, it is
necessary to reduce costs of power for pumping the
used coolant back into the reservoir. This can be
achieved by increasing the borehole diameters and by
improving the filtration parameters in surrounding
formation.
3.2 Hybrid geothermal and combined cycle power
plant
The significant resources of medium-temperature
thermal water in the region are used extremely
inefficiently, only for heating some objects during
the cold season. To overcome such state of affairs, one
needs to look for other approaches.
For all-year-round utilizing the medium enthalpy
geothermal water, the hybrid geothermal and com-
bined cycle plants (GCP) can be proposed collecting
advantages both renewable energy and fossil fuel
(Alkhasov and Alkhasova 2018). In such a plant
(Fig. 3), exhausted gas of gas turbine engine (GTE)
serve for evaporation and overheating of the working
medium, circulating in the circuit of GeoPP. Heating
of the heat carrier at the plant occurs with geothermal
water.
Table 2 compares the parameters of the hybrid
GCP and the binary GeoPP and demonstrates the
advantage of the first one.
Thermal water with a temperature of 100 �C in the
GCP system makes it possible to heat 1.6 kg of
isobutene up to the evaporation temperature Te-= 89 �C corresponding to the pressure Pe = 1.6 MPa.
At the same time, the temperature of the used water is
Tu = 40� C. The consumption of thermal water in the
GCS loop is 21 kg/s with the STU capacity of
1.5 MW.
The use of thermal water with the same temperature
for heating and evaporation in the system of binary
GeoPP helps to evaporate of 0.4 kg of isobutane at the
optimum evaporation temperature Te = 62 �C (Pe-
= 1.6 MPa) and waste water temperature Tu = 64 �C.The mass flow rate of thermal water for a 1.5 MW
GeoPP is 144 kg/s. To achieve such a flow, it is
necessary to increase the number of wells, which
increases the cost of GeoPP construction itself.
Temperature reducing the used thermal water to the
value of 40 �C in a hybrid PP with a capacity of
1.5 MW results in saving of 2870 tons of reference
fuel/year.
The deployment of the hybrid GCP at the Thernair
field, where there are geothermal wells ready for
operation, will promote producing up to 60 MW of
capacity. It will solve the problems of power supply as
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Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 5 of 17 7
Table 1 Technological parameters of GeoPP
Flow rate of GCS
(kg/s)
Wells spacing
(m)
Pumping pressure
(MPa)
Total capacity of
GeoPP (kW)
Power of injection
pump (kW)
Net power of GeoPP
(kW)
Thermal water temperature Tt = 80 �C4 343 SCS regime 16.4 0 16.4
5 384 0.063 20.5 3.2 17.3
10 542 0.6 40.9 6.2 34.7
14 641 1.25 57.3 17.9 39.4
20 767 2.59 81.8 53.0 28.8
24 840 3.73 98.2 91.7 6.5
25 857 4.05 102.3 103. 6 0
Thermal water temperature Tt = 100 �C7 455 SCS regime 72.6 0 72.6
8 487 0.087 83.0 0.7 82.3
23 826 3.18 238.5 75.5 163.0
35 1018 7.77 363.0 280.2 82.8
39 1075 9.73 404.4 391.4 13.0
40 1089 10.3 414.8 423.2 0
GTE
GeoPP
1 2
Fig. 3 Geothermal power
plant coupled with
combined cycle plant. 1
Production well 2 Injection
well
Table 2 Parameters of
power plants
aGas turbine engine
produced in Russia
Parameters GCP GeoPP
Capacity of the unit GTU-4Pa (MW) 4.3(e); 8.3(t) –
Capacity of the unit on low-boiling working medium (MW) 1.5 1.5
Thermal water consumption in the loop of GCS (kg/s) 21 144
Specific consumption of the working agent (isobutane) (kg/s) 1.6 0.4
Consumption of the working agent (isobutane) (kg/s) 33.6 57.6
Temperature of thermal water (�C) 100 100
Temperature of used water (�C) 40 64
Temperature of working agent evaporation (�C) 89 62
Pressure of working agent evaporation (MPa) 1.6 0.9
Capacity of pumping house (MW) 0.065 20.84
Distance between wells (m) 790 2065
123
7 Page 6 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
well as some environmental and social tasks for the
Makhachkala town.
4 Prospects for integrated development of high-
temperature brines
The most promising for mastering are the currently
unused high-temperature brines of the lower stage,
although there are more than 2000 idle wells in the
depleted oil and gas fields that can be converted to
production. There is a need in integrated development
of these resources that could solve the very complex of
economic, environmental and social problems of the
Ciscaucasia. Under the integrated development of
high-temperature brines, we mean the use of their
thermal potential for electricity generation using the
technology of binary GeoPP on low-boiling working
agents and the subsequent extraction of chemical
components from the geothermal brine. The high-
temperature brines contain rare elements in quantities
sufficient for long-term production. A number of
technologies have been proposed by us for the
combined development of such resources (Alkhasov
et al. 2015, 2016, 2017).
Figure 4 shows the schemes for the integrated
development of high-temperature geothermal brines.
In the diagram (Fig. 4a), the thermal potential of high-
temperature water is used to generate electricity in a
binary GeoPP. The used low temperature brine from
the GeoPP enters the plant, where after complete
removal of the chemical components the water at the
outlet is desalinated. Further, this water is distributed
for various water needs. The advantage of this
scheme is the full realization of the thermal and
chemical potentials of highly parametric geothermal
resources. There is no need in re-injection, which
excludes the significant capital investments on the
injection wells and pumping stations construction, and
operating costs for their maintenance. In addition, the
use of desalinated water for various purposes saves
fresh surface water, which is a scarce raw material in
the arid North Caucasus region. The disadvantages of
this technology are in a drop of stratal pressure without
re-injection in the exploited reservoir with time and a
gradual decrease in the volume of recoverable hydro-
thermae, which will result in a reduction of the
capacity of both GeoPP and the brine processing plant.
In Fig. 4b, the brine used at the GeoPP is divided
into two streams, one of which enters the plant for
chemical components recovery, and the other is
pumped through the injection well back into the
exploited reservoir. The demineralized water after
separation of chemical components is consumed for
the needs of the plant itself and other consumers. Such
complex development scheme is preferable for high-
production wells producing highly saline brines, but
the extraction of chemical components from all the
raised water entails the problem of storing and selling
large quantities of food salt, which is the main
component of brine compounds.
In the diagram (Fig. 4c) the flow of a high-
parametric geothermal heat carrier passes through
GeoPP and a chemical plant, where one or several
rare-metal elements demanded in the industry are
selectively extracted, and then the brine with the bulk
of the salt is pumped into the maternal reservoir.
In the above technologies, the production of
valuable inorganic materials is supplied with electric
power generated by the GeoPP, which ensures com-
plete production autonomy and independence from
external conditions. It should be noted that in all
development options for high-temperature geothermal
brines, it is necessary to provide a water treatment
stage for the subsequent treatment of valuable com-
ponents and/or injection into the operated reservoir
waste brines in order to maintain reservoir pressure.
This is due to the fact that some of the physico-
chemical properties of geothermal brines change as a
result of the thermal potential utilization. For example,
the bicarbonate equilibrium is disturbed, with which
undesirable processes occurring in wells and surface
technological equipment such as scaling and corrosion
can be associated.
The salinity parameters of brines and the content of
rare elements in them in some fields of ECAB with
industrial geothermal water are given in Table 3. The
data of that Table shows that in the indicated areas
there are two or more rare elements in industrial
concentrations. It is necessary to say that in two-
component brines, the conditional content of each of
them can be 75% of its content in a one-component
system, with three components it is 60%, with four
ones it may be 50%, and with five or more approx-
imately 45%.
The most prepared for industrial integrated devel-
opment are geothermal brines of the Berikey and
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Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 7 of 17 7
Tarumovka fields and associated high-salt waters of
the Yuzhno-Sukhokumsk group of gas and oil wells in
Northern Dagestan. A number of products that can be
obtained from 1 m3 of brines of these deposits are
collected in the Table 4.
4.1 Berikey geothermal field
The priority for development is the Berikey geother-
mal field, located 100 km south of Makhachkala town
and 3 km of the Caspian coastal line. This field causes
irreparable environmental damage due to uncontrolled
Fig. 4 Flowcharts (a, b,c) of complex processing of
high-temperature
geothermal brines. 1
operating reservoir; 2
production well; 3 binary
GeoPP; 4 plant for chemical
components recovery; 5
economic application of
used water; 6 pump station;
7 injection well
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7 Page 8 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
Table 3 Content of rare elements in thermal brines of the ECAB
Well no Area Perfora-tion interval (m) Content of rare elements (mg/l) Mineral content (mg/l)
Li Rb Cs Sr
The Republic of Dagestan
18 Russkiy Khutor 3179–3185 37.5 2.25 0.43 750 125.0
44 3473–3483 44.9 4.40 3.20 1035 121.0
4 Sukhokumsk 3255–3257 44.3 3.36 0.61 756 104.8
4 Vostochno-Sukhokumsk 3367–3371 63.7 5.46 559 133.8
3691–3695 72.4 3.99 0.18 137.0
14 Yuzhno-Sukhokumsk 3291–3295 53.6 3.59 0.69 1169 132.0
20 3392–3398 50.0 2.10 0.70 550 127.0
2 Oktyabr’skiy 3383–3390 44.0 4.30 0.70 243 109.0
4 Talovka 3443–3455 53.8 5.50 0.90 596 112.4
1 Emirovskiy 3590–3603 75.4 4.24 1.50 134.4
1 Kumukh 4778–4811 53.9 1.70 0.55 110.5
2 Yubileynyy 3909–3911 93.0 5.54 0.86 125.0
2 Severo-Kochubey 3436–3446 86.8 5.40 0.91 540 119.0
1 Komsomol’skiy 5078–5084 166.0 10.40 3.00 1607 203.0
1 Tarumovka 5429 210.0 9.30 5.60 1400 210.0
6 Dakhadayevskiy 3636–3642 70.3 4.10 0.40 741 131.0
14 Solonchakovyy 3640–3646 122.5 5.00 0.94 625 124.0
1 Nogayskiy 3580–3585 66.7 4.60 739 136.4
21 Mayskiy 3627–3635 80.0 6.03 1.88 790 129.1
6 Ravninnyy 3716–3720 63.7 529 132.0
8 Kapiyevskiy 3830–3840 55.0 3.20 2.10 700 130.3
20 Berikey 42.0 3.40 0.85 520 70.0
Stavropol Krai
116 Zimnyaya Stavka 20.0 0.10 0.49 106.0
96 Ozek-Suat 21.3 1.70 0.10 312 79.0
27 Achikulak 26.3 3.02 0.57
Chechen Republic
167 Karabulak-Achaluki 21.0 31.2 7.70
11 Datykhskiy 160.0 18.3 3.30
Table 4 Production
quantity (kg) from 1 m3 of
brine
Product Geothermal field
Tarumovka Yuzhno-Sukhokumsk Berikey
Lithium carbonate (Li2CO3) 1.0 0.2 0.2
Magnesia (MgO) 1.3 1.1 0.4
Calcium carbonate (CaCO3) 23.7 18.2 2.6
Sodium chloride (salt) (NaCl) 133.1 77.4 58.2
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Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 9 of 17 7
accidental release of highly saline geothermal fluids
containing a significant amount of toxic components.
In 1954, as a result of an accident at the well and its
collapse, a flow-through lake of rare-metal hydro-
thermae was formed, into which more than a hundred
gryphons were discharged. About 10 million tons of
mineral salts and toxic components have been deliv-
ered to the water of the Caspian Sea. Currently, the
flow rate of the overflowing well is 1500–1600 m3/day
with mineral content of 70 kg/m3 and up to 0.044 kg/
m3 of lithium content (Table 3). The extraction of
geothermal brines can be increased to 10 million m3/
year with 40 years of exploitation, which will ensure
the production of 2000 tons/year of lithium carbonate
that meets the needs of Russia. For this, it is necessary
to restore 17 previously drilled wells, equip them with
deep well pumps and water intake.
Taking into account a certain risk associated with
the lack of experience in creating such a production
based on hydro-mineral raw materials, as well as the
need to identify in practice the possibilities to reduce
the cost of the processing technology itself, it seems
appropriate to divide the construction of the plant into
two stages. At the first stage it is proposed to organize
the production based on overflowing resources. After
improving the technology and finding reserves for its
cost reduction, one can proceed to the second stage,
namely the construction of a plant with full utilization
of all resources of the deposit. The estimated flow rate
of overflowing brines is 1500 m3/day. The annual
output of lithium carbonate is 111 tons, and magnesia
is 250 tons.
The Fig. 5 shows the schematic diagram of the
second stage for the integrated processing of the
Berikey geothermal brines with the complete extrac-
tion of all the resources available there.
In the proposed scheme, the geothermal brine of the
production wells enters the collector and then with a
temperature of up to 70 �C is sent to the heat
exchangers of the geothermal power plant coupled
with combined cycle gas turbine plant, where the low-
boiling working agent is heated to a temperature of
60 �C. Further, heating to a higher temperature,
evaporation and overheating of the working agent
are carried out by exhaust gas of a gas-turbine engine.
The overheated working agent is sent to the electricity
generator. The brine spent in the heat exchangers of
the GCP is fed to the plant for the extraction of
chemical components. The resulting desalinated water
is used for various needs, and can also be pumped
through injection wells to maintain reservoir pressure.
The characteristics of one power unit of the GCP
based on GTU-4P (gas-turbine engine) for the thermal
water of the Berikey field are given below:
Capacity of the unit GTU-4P (MW)
Electric 4.3
Thermal 9.63
Capacity of the unit at low-boiling
Agent (MW) 1.5
Thermal water consumption (kg/s) 18.2
Consumption of working agent (isobutane) (kg/s) 28
Water temperature (�C)Thermal 70
Waste 40
Evaporation temperature of the working agent (�C) 89
Evaporation pressure of the working agent (MPa) 1.6
Fig. 5 Scheme of geothermal brines integrated development in
the Berikey deposit. 1 production wells 2 collection point 3
geothermal–combined cycle power plant (GCP) 4 plant for
chemical components extraction 5 pumping station 6 injection
wells 7 waste water for household needs 8 gas turbine engine 9
exhaust gas disposal
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By adding such modular units, it is possible to
utilize the thermal potential of all recoverable
geothermal resources.
4.2 Tarumovka geothermal field
This section considers a possibility of the comprehen-
sive development of multi-parameter resources of the
Tarumovka geothermal field situated near the epony-
mous village (Tarumovka) in Northern Dagestan.
When the well no. 1 issued the emergency fountain
and was eliminated, it was decided to explore the
Tarumovka field for the purpose of studying the
feasibilities to build a GeoPP and a chemical plant for
utilization of superheated brines with a high content of
rare elements. Early in the 1980s, the Dagneft’
association drilled five wells (nos. 2–6), from which
wells nos. 3 and 5 were eliminated for technical
reasons. Wells nos. 2, 4, and 6 are the world deepest
(5500 m) wells, drilled specially for thermal waters.
The Cretaceous and Jurassic sediments were explored
and water-bearing horizons at depths of 5385–5479,
5382–5388, and 5421–5427 m were tested, from
which the fountains were obtained of steam-thermal
water of the same type with high content of valuable
elements. The parameters characterizing the Taru-
movka field of multi-parameter waters are listed in
Table 5.
The aquifer VI of the middle Jurassic is the most
water abundant; the permeable part of it is represented
by the sand reservoir with a thickness of 2.5–3.5 m
according to the data of geophysical studies. The
mineral and gas compositions of thermal brines of the
productive thickness are of the same type and similar
to the composition of waters of well No. 1. Total
salinity is 176–198 g/dm3. In the saline composition,
ions of chlorine and sodium dominate. Amount of
dissolved gas is 4.5 m3/m3. A main component of
dissolved gases is hydrocarbons: 87% (by volume).
Well tests of No. 2, 4, and 6 are confirmed that the
reservoir VI of the middle Jurassic contains highly
saline steam-thermal waters. Water density is
1118–1123 kg/m3, and temperature at a depth of
5500 m reaches 198 �C, which corresponds to a
temperature gradient of 0.034 �C/m. The field is
characterized by the anomalously high stratal pressure
of 71 MPa. A discharge of wells through the nozzle
42 mm in diameter is equal to 1000–1600 m3/day.
The results of investigations of the well No. 6 have
shown that, when operating through a production
string (PS) and pump-compressor pipes (PCP), the
flow rate with overflow at the dynamical pressure at
the mouth of pdyn = 7 MPa reaches 7000 m3/day. In
this case, the mouth temperature of water for the time
of the well operation during 2 h reached 170 �Cindicating that the well products can be efficiently
used for obtaining electric power. By calculation
studies, it was found that, with a reduction in the
dynamical pressure at the mouth of well No. 6 down to
1 MPa, discharge of high-temperature brine
Table 5 Parameters of Tarumovka field of multi-parameter thermal waters
Parameter No. of well
2 4 6
Effective thickness of the reservoir (m) 2.5 3.0 3.5
Water density at atmospheric pressure and temperature of 20 �C (kg/m3) 1222 1123 1118
Reservoir permeability (md) 1250 685 1560
Reservoir porosity (%) 25 25 25
Water salinity (g/dm3) 191 180 176
Reservoir temperature (�C) 198 198 198
Reservoir pressure (MPa) 71.5 71.9 70.9
Gas factor (m3/m3) 1.2 4.5 1.7
Injectivity index (m3/(MPa day)) – – 130
Maximum discharge when operating through PCP (m3/day) 1067 1123 1587
Calculated maximum discharge at pdyn = 1 MPa and with operation through PS (m3/day) – – 12,000
123
Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 11 of 17 7
overflowing from the production string increases up to
12 000 m3/day, and the brine temperature rises and is
stabilized at the level of 195 �C.Thermal energy of geothermal brine can be con-
verted to the electric power at a binary GeoPP based on
low-boiling working substance. The thermodynamic
Rankine cycles implemented in the secondary loop of
the binary GeoPP are considered at different evapo-
ration temperatures of the low boiling working
substance—isobutane. A supercritical cycle that is
close to the so-called triangular cycle at an evapora-
tion pressure of pe = 5.0 MPa (whose t–s diagram is
given in Fig. 6) is most efficient from the viewpointof
obtaining the maximum power.
With this cycle, due to a minimal difference in
temperatures between the heat carrier and working
medium, the temperature potential of thermal water is
utilized most efficiently. A comparison of the super-
critical cycle with a subcritical one (pe = 3.4 MPa)
shows that the power generated by the turbine with the
supercritical cycle increases by 11%, while density of
the substance flow entering the turbine is 1.7 times
higher than in the cycle with pe = 3.4 MPa, which
leads to the improvement of transport properties of the
heat carrier and to the reduction in sizes of equipment
(intake pipes and the turbine) of the steam-turbine
unit. In addition, in the cycle with pe = 5.0 MPa,
temperature ti of the used thermal water, which is
injected back into the reservoir, is 42 �C, whereas thetemperature ti = 55 �C in the subcritical cycle with
pe = 3.4 MPa.
At the same time, an increase in the initial pressure
up to 5.0 MPa in the supercritical cycle has an
influence on the equipment cost, in particular on the
turbine cost. With a growth in pressure, sizes of a
steam path of the turbine reduce, the number of its
stages increases, a more developed end seal is
required, and, above all, thickness of the casing walls
and other elements grows. However, such factors as an
increase in the power, a reduction in sizes of the intake
pipelines and turbine, and a more complete utilization
of the temperature potential of thermal water speak in
favor of a supercritical cycle.
Figure 7 presents a technological scheme of
geothermal brines processing of Tarumovka field.
The production of valuable inorganic materials is
ensured by the electric power generated at the GeoPP,
owing to which the full autonomy of production and
independence from external conditions is achieved.
The estimated parameters of integrated processing
of high-temperature brine from well no. 6 are given in
Fig. 6 View of t–s diagram
of supercritical cycle. Points
1, 2, and 3 correspond to
temperatures of the working
substance at the inlet of heat
exchanger, at the inlet of the
turbine, and at the outlet of
the turbine, respectively.
Point 4 corresponds to the
temperature of
condensation. A
temperature of thermal
water is denoted with tt, pc,
tc are the pressure and
temperature of condensation
123
7 Page 12 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
Table 6, which implies a high efficiency of the
proposed technology.
The waters of the field are complex minerals
mixture for output of sodium chloride, bromine,
iodine, boron, lithium, rubidium, cesium, strontium,
potassium, not to mention dissolved gases and heat
potential. The explored reserves of the Tarumovka
thermal water field will allow producing annually
Fig. 7 Technological scheme of geothermal brines processing for the Tarumovka field
123
Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 13 of 17 7
more than 4000 tons of lithium carbonate and thus not
only fully meet the needs of Russia, but also export it,
improving significantly the economic structure of the
region.
4.3 Yuzhno-Sukhokumsk field
Figure 8 shows a schematic flowchart of complex
processing of geothermal brines of the Yuzhno-
Sukhokumsk gas and oil field, where, along with oil,
up to 1.5 million m3 of thermal (100–110� C) brinesare produced annually. The associated brines contain
big amount of mechanical impurities (740 mg/dm3),
organic substances (2275 mg O2/dm3) and a signifi-
cant amount of iron, calcium, magnesium and bicar-
bonate ions. At present, these brines with a gamma
background of 28–32 lR/h are discharged onto
filtration fields without any prior deactivation, which
causes great damage to the environment. Drainage of
untreated waters with a high radioactive background
leads to salinization and radioactive contamination of
areas adjacent to the oil field for many centuries. In
this regard, the need to work out an integrated,
economical and environmentally friendly technology
for the disposal of brines, which are produced
simultaneously with oil, is absolutely obvious.
The brine deactivation can be accomplished in
different ways: by physico–chemical (distillation,
precipitation, coagulation, flotation, filtration, sorp-
tion, ion exchange, extraction, and evaporation),
electrolytic (electrolysis, electrodialysis, and elec-
troionization), as well biological methods or by their
joint application. The choice of the method of water
decontamination depends on whether radioactive
substances in it are suspended or dissolved, on their
half-life and chemical properties, the degree of water
pollution, the amount of water, etc.
The associated with oil brines are collected into a
united collector and fed into the heat exchanger of the
binary GeoPP with a capacity of 0.5 MW. The
temperature of the brine in GeoPP decreases to
60 �C. Next, the brine enters the unit by removing
the residual heat, where in the double-pipe heat
exchangers its temperature decreases to 30 �C. Tocool the brine, fresh artesian water with a temperature
of up to 20 �C flowing at shallow depths in the
Pliocene–Quaternary sediments is directed counter-
current to the heat exchangers. The cooled brine enters
the decontamination unit and then goes to the chem-
ical plant, where lithium carbonate, caustic magnesite,
and sodium chloride are extracted. The desalinated
water from the chemical plant is directed to household
needs, including oasis irrigation of agricultural crops.
The artesian water heated in heat exchangers up to
Table 6 Parameters and processing data of high-temperature
brine for the well No. 6 of the Tarumovka field
Name of parameter and products Amount
Well flow rate (m3/day) 12,000
GeoPP capacity on supercritical cycle (mW) 15.4
Annual electric power production (kW h) 135 9 106
Lithium carbonate (Li2CO3) (t/year) 4380
Magnesia (MgO) (t/year) 5690
Food salt (NaCl) (t/year) 583,000
Calcium carbonate (CaCO3) (t/year) 103,806
Fig. 8 Diagram of complex processing of associated brines of
the Yuzhno-Sukhokumsk oil field. 1 wells 2 binary GeoPP 3residual heat removal unit 4 decontamination unit 5 plant for the
extraction of chemical components 6 desalinated water 7artesian wells 8 energy–biological complex 9 sediment to
disposal
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7 Page 14 of 17 Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7
53 �C is used in various units of the energy–biological
complex.
As the raw material for the chemical and rare-metal
industries, brines of ECAB are attractive due to their
inexhaustible reserves and the relatively low cost of
extracting actually all valuable chemical components
from them. With the integrated processing the
geothermal brines, the expenses for environmental
problems solving are also significantly reduced. It
should be noted that the extraction of chemical
elements from the formation through the construction
of mining enterprises is much more expensive and
entails catastrophic environmental changes.
5 Conclusions
1. Energy technologies based on geothermal
resources should become an important component
of the strategic development of the North Cauca-
sus region of the Russian Federation.
2. The prospects for the mastering the hydro-
geothermal resources of East Ciscaucasia is
proven to be promising. These resources are
estimated at 10,000 MW on thermal power and
1000 MW on electric capacity.
3. The high economic efficiency of low-temperature
geothermal waters can be achieved by their
integrated development using the thermal poten-
tial for energy needs, and the water itself for
various water management purposes. The tech-
nology of such integrated developing the low-
temperature geothermal resources is presented.
4. The possibility of effective geothermal resources
utilization through the construction of binary
GeoPPs using idle oil and gas wells is substanti-
ated. There is a fair amount of idle well fields in
this region that can be converted to thermal water
production. Estimations were carried out for these
fields meaning the construction of binary GeoPP.
The calculations were made for a geothermal
circulation system (GCS) consisting of one pro-
duction and one injection wells. There is an
optimal GCS flow rate corresponding to the
maximum useful capacity of the GeoPP. Further
increase in the flow rate of the primary heat carrier
in the GCS loop results in an increment of the total
power of the energy system. But simultaneously
reducing the net power occurs since the energy
consumption for heat carrier circulating rises
sharply. Using the entire reserve of idle wells will
make it possible to generate up to 300 MW of net
capacity at the GeoPP in total.
5. There are significant resources of medium- tem-
perature thermal water within the boundaries of
the ECAB, which are used extremely inefficiently.
In the geothermal fields, the wells producing such
water are operated only in the cold season to heat
various facilities. Effective development of med-
ium- temperature waters is feasible in hybrid
geothermal–combined cycle power plants. The
use of hydro-geothermal resources with a temper-
ature of 80–100 �C for the production of electric
energy in the hybrid power plants is proposed. The
implementation of combined technologies at the
Thernair field, where geothermal wells are ready
for operation, will make it possible to achieve a
power plant capacity of up to 60 MW, which will
solve significant energy, economic and socio-
environmental problems in the Makhachkala
town.
6. The prospects are shown of complex processing
the high-temperature geothermal brines using
their thermal potential for various usable heat
and power needs and the subsequent extraction of
valuable chemical components. The technological
diagrams are presented where the electricity
generated at the binary GeoPP is used in the unit
for chemical components extraction. The priority
areas for development are indicated, estimated
parameters are given for the Berikey geothermal
field. The explored reserves of the Berikey thermal
water deposit alone can produce more than 2000
tons of lithium carbonate annually and thereby
fully satisfy the requirements of the Russian
industry in it. The efficiency of complex process-
ing of high-temperature geothermal brine of the
Tarumovka geothermal field is shown. The ther-
mal energy of the geothermal brine can be
converted into electricity in a binary geothermal
power plant using a low-boiling working agent.
The Rankine thermodynamic cycles have been
considered realized in the secondary circuit of the
GeoPP at different temperatures of the working
agent isobutene evaporation. The most effective
from the point of view of obtaining maximum
capacity is a supercritical cycle, close to the so-
123
Geomech. Geophys. Geo-energ. Geo-resour. (2020) 6:7 Page 15 of 17 7
called ‘‘triangular’’ cycle with an evaporation
pressure pe = 5.0 MPa. The spent brine with a low
temperature will pass from the GeoPP to a
chemical plant, where the main chemical compo-
nents will be extracted: lithium carbonate, burnt
magnesia, calcium carbonate and sodium chlo-
ride. The developed by us technology is applicable
for the integrated utilization of sodium chloride-
type hydrothermal brines. The characteristic of the
current state of the Tarumovka field and estimated
parameters of the integrated processing of high-
temperature brine of well No. 6 are given, from
which it follows that the proposed technology is
highly efficient. The explored reserves of the
Tarumovka thermal water deposit will make it
possible to produce more than 4000 tons of lithium
carbonate annually. Recommendations are given
on a priority integrated development of associated
highly saline brines of the Yuzhno-Sukhokumsk
group of gas and oil wells in Northern Dagestan.
At present, the associated brines with a radioactive
background exceeding permissible norms are
dumped onto surface filtration fields. The work
offers technological solutions on their decontam-
ination and integrated processing in order to
eliminate the serious environmental problems.
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