Title: Geothermal resource assessment through well testing and production response modelling

Abstract

Assessment of the properties and capacity of geothermal resources involves various kinds of tests, data
interpretation, monitoring and modelling. This ranges from the analysis of data collected during
testing of single wells to the simulation of the response of geothermal reservoirs to utilization for years
or even decades. This work presents a comprehensive review of the theoretical background and
methodology used in analysing well-test, temperature- and pressure logging data from geothermal
wells as well as a review of methods used for geothermal reservoir pressure response modelling. These
methods are, consequently, applied to data from the Hellisheidi and Nesjavellir fields in the Hengill
volcanic region of SW-Iceland. The purpose of well test analysis is to identify the type of reservoir
involved and to determine the parameters of the reservoir quantitatively. Data from two Hellisheidi
wells, HE-06 and HE-20, have been analyzed by applications of modern well-test analysis techniques
such as derivative analysis and computer software simulation. Wellbore simulator analysis of
discharge test data from the wells was used to estimate the productivity index (PI) for each well and
the results compared with the injectivity indices (II) obtained from injection tests. The results were
compared with results from three other high-temperature geothermal fields, one in Iceland and two in
Japan. The production capacity of geothermal reservoirs can be assessed most accurately by modelling
the long-term production response of the reservoir. This is demonstrated by the simulation of a 17-year
(1989-2006) long pressure-decline data series from the Nesjavellir field. Both the lumped parameter
modelling (LPM) and continuous time stochastic modelling (CTSM) methods are used and their
results compared.