Decision and risk management of geothermal assets requires a
thorough quantitative
understanding of the effects of techno-economic
uncertainties on geothermal energy
performance. These uncertainties can be considerably large
especially in the initial
stages of exploration and design. Optimum design under such
uncertainties can benefit
considerably from best practice and probabilistic decision
and risk management tools
which are have been developed in the Oil and gas industry.
In this presentation we
give a description of best practices for probabilistic
techno-economic integration of
uncertainties all along the workflow. Combined with use of
decision trees and
parameters sensitivity analysis, this allows to find
critical uncertainties in
parameters and optimum scenarios for design.
The practical implementation of such best practices, is
illustrated through an
application in performance assesment of re-use of deep
boreholes drilled by oil and
gas industry for a deep Borehole Heat Exchanger (DBHE). A
DBHE is based on the
principle of a fluid migrating through a coaxial pipe in the
subsurface, heated
gradually by migrating downwards in the outer pipe, whereas
the inner pipe acts as
the return path for the heated fluid. The inner tube is
isolated for the total length
of the DBHE, in order to prevent the producing water from
cooling down. The upper
part of the injection tube can be isolated from the
surrounding rock up till the
depth at which the geotherm equals the temperature of the
injected fluid.
The energy performance of the DBHE is proportional to the
temperature difference
between injected and produced water multiplied by the
injection rate (m3/h). In this
study we focus on the effects of various natural
uncertainties in the subsurface
geology (heat flow, sediment conductivity), preceding use of
the well (e.g.
production heating the surrounding of the well) and specific
design parameters for
geothermal energy production.
Preceding production can have a significant effect at the
heating of the surrounding
of a well, resulting in substantial increase in geothermal
energy, especially when
production has taken place over a long period of time.
|
Overview
support
Slides