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Exploring High Temperature reservoirs: new challenges for geothermal energy - Volterra, Italy, Workshop2
Exploring High Temperature reservoirs: new challenges for geothermal energy - Volterra, Italy, Workshop2
1-4 April 2007 Volterra, Tuscany, Italy
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Continuous Measurement of Gases for Effective Geothermal Reservoir Management
Efficient and sustainable production of geothermal energy requires constant 
monitoring of changes occurring in the reservoir.  These changes, which may 
result from mass extraction for production, waste fluid injection for disposal and 
pressure support, and from natural geologic processes, are usually manifested 
in the chemistry and physical characteristics of the wells.  Experience has also 
shown that these changes are related to the structure of the reservoir—the 
faults that transect the field as well as smaller fractures contained in the 
reservoir rocks.  Identification and evaluation of chemical changes, and their 
correlation with the structural features, require among others the constant 
analysis of hot brine and gases discharged by the wells.  

Changes in water and  gas chemistry, for example, can indicate:  1) lowering in 
the water level of the reservoir, 2) invasion of cold and degassed re-injection 
fluids, 3) entry of shallow acidic steam condensates and deep corrosive volcanic-
related fluids, 4) precursor of an earthquake, etc.  Any of these changes can 
significantly alter the short- and long-term viability of the geothermal 
operation.  Hence, it is critical that up-to-date collection and analysis of water 
and gases be undertaken.  However, since almost all of the production wells 
are connected to the power plant, it is rarely possible to disconnect the wells in 
order to collect samples for analysis because such disconnection will result to 
shortfall in power generation.  In addition, the process is time-consuming and 
significant lapse is achieved from sample collection to the availability of the 
information.  There is therefore a pressing need for a continuous and on-line 
system of measuring chemical parameters in the field.

A progress in this field is presented in this paper with the development of a 
new versatile measuring system called MEDAS (MEDAS – Modular Environmental 
Data Acquisition System) based on experiences and recent results from 
different research groups. MEDAS is an innovative multi-parameter station, 
which can continuously record as a function of time up to more than 100 
geochemical and physical parameters suitable to earthquake research and 
other applications. A microcomputer system inside the MEDAS handles data 
exchange, data management and control and it is connected to a modular 
sensor system. The number of sensors and modules can be selected according 
to the needs at the measuring sites.
A MEDAS has been installed in four production wells in the Mahanagdong 
production sector of the  Leyte Geothermal Production Field located in the 
island of Leyte, central Philippines.  This field is chosen because:  1) it is the 
largest geothermal field in the Philippines with five separate power plants with 
total installed capacity of about 700 MW, and 2) the area is bisected by the 
Philippine Fault, a major left-lateral transcurrent fault similar to the San Andreas 

The preliminary results of the three years measurement on radon and CO2 
concentrations; gas flow, temperature and humidity; water temperature and 
pH; Cl-concentration the Redox potential and conductivity will be presented. 
These parameters will be correlated with the historical and current data from 
the PNOC EDC established monitoring set-up for seismicity, micro-gravity and 
precise levelling surveys, wellhead pressure trends and wellbore chemistry 
changes from monthly production sampling.
Id: 10
Place: Volterra, Tuscany, Italy
Campus SIAF, SP del Monte Volterrano
Localita' Il Cipresso
Volterra, Italy
Starting date:
02-Apr-2007   11:47
Duration: 03'
Primary Authors: Dr. STREIL, Thomas (SARAD GmbH)
Co-Authors: OESER, Veikko (SARAD GmbH)
Presenters: Dr. STREIL, Thomas
Material: slides Slides
poster Poster

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