Geothermal potential evaluation
Reserve estimation
In this study, geothermal-reserve estimation will be carried out
for evaluating the possible geothermal capacities of the geothermal
waters of the studied thermal collectives and hot springs using the
volumetric and the probability method (Monte Carlo simulation).
The volumetric analysis concerns mainly with determining the
total heat energy stored in a volume of rock as compared to certain
reference temperature. This necessitates estimating the thermal
energy stored in the rock matrix and the thermal energy of the fluid
occupied in the rock pore spaces. The probability method, on the
other hand, is based mainly on constructing a multi-array matrix
(X1,..n * X2,..n) using the RAND function. This depends on the
number of iterations and parameters necessary for computing the
thermal reservoir reserves in the different studied geothermal areas.
It is much often to use two common randomness methods in such
analyses.
The first is the square distribution (normal) which is used to
describe the possible distribution of a certain parameter within
defined limits. Meanwhile, the second is the triangular distribution
which describes the distribution within a range or limits (high and
low). However, the Z-rand software will be used to conduct the
randomness functions and the Monte Carlo simulation module
which is a part of the freely distributed risk analysis and decisionmaking software of U.S. Department of Energy (DOE software,
2002), will be used to perform the necessary probability
calculations. Only, the most likely range of the reserve will be
taken into account.
In general, the reservoir parameters necessary for geothermalreserve estimation are gathered from the analyses of the
temperature data and from other geophysical and geochemical
interpretations. A computer programme (RESPAR, ICEBOX
software) is used to estimate the different reservoir properties
providing that, the temperature, porosity and the reservoir thickness
parameters are known. Porosity can be calculated form the
available velocity data given form the shallow seismic refraction
surveys. The initial temperature of the reservoir is taken as 80 °C,
while the reference temperature is suggested in this study to be 45
°C due to the higher average annual surface temperature in Saudi
Arabia. The total stored energy of the geothermal reservoir can be
regarded as the sum of energy stored in the rock (Er) and the
energy represented by the fluid stored in the pore spaces (Ef). It can
be estimated using the following equation:
Et  Er  Ef  V 1-  ρr Cr  Ti  To   V  ρw Cw  Ti  To 
where: Et is the total thermal energy (J) in the rock (Er) and fluid
(Ef);  is the reservoir porosity (%); V is the reservoir volume
(m3); r ,w are the densities of rock and water (kg/m3); Cr,w are
the heat capacities of rock and water (J/kg°C) and Ti , To are the
initial reservoir and the reference temperatures (°C).
This stored thermal energy can be converted into power potential
using the following equation:
Power Potential (MWt) 
Et x R F x C E
PL x LF
where: RF is the recovery factor, CE is the conversion efficiency,
PL is the geothermal plant life in years and LF is the load factor.
Construction of power plants (Kalina Cycle)
Kalina power plants was developed in the 1990s and utilizes a
water-ammonia mixture as a working fluid. It can be designed in a
small-sized mobile plants which, can help in meeting the energy
requirements of isolated areas. The convenience of these small
mobile plants is most evident for areas and communities, which
have no high voltage transmission lines in the vicinity and that
would be too expensive to connect to the national electric grid. By
selecting suitable secondary fluids and by obtaining the minimum
temperature limit, binary systems can be designed to utilize
geothermal fluids in the temperature range below 170°C.
Most of the geothermal collectives and hot springs to be studied
are categorized as low-grade geothermal resources (To<150 oC).
The average surface temperature reaches more than 80 oC. A
much higher temperature range up to 120 oC can be accessible at
shallow depth range of 50 m-100 m. Then it will be possible to
make use of such higher range of temperature by inserting a steel
pipe down the opened hot springs and/or thermal water wells. The
fluid usually used in Kalina cycle is a mixture of the ammonium
and water with a boiling point around 70 oC. Having higher
temperature range than needed to get the Kalina fluid to boil, the
thermal waters coming from the studied hot springs can be
economically used in Kalina power plants (Fig. 3) for possible
electricity production. Nowadays, the technology of these
machines is well known, and they are readily available on the
geothermal market.
Figure 1. The design of a simple Kalina power plant.
Regarding the geographic distribution of studied thermal
collective and hot spring, the possibility of installing such types of
power plants is actually available. The occurrence of these hot
springs near the coastal parts of the Red Sea, provides a
continuous source for water supply and enable fast recharging for
the geothermal reservoirs through the structurally controlled
subsurface feed zones.
Low grade utilization of geothermal energy
The most common forms of utilization are; district heating, fish
farming, agricultural
applications
and green houses.
Constructing a number of swimming pools for touristic purposes is
also another important application. Some of these applications are
now in use like those in Al Laeith-Maka area, where a number of
geothermal-based natural therapy, medical and tourstic purposes
are already constructed. In other places of active geothermal
aspects, the investment of geothermal energy will enhance the
infra-structure of these communities and will have direct feed back
both economically and socially on the inhabitants of these areas.