Tracer techniques for the characterisation of geothermal reservoirs

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Tracer techniques for the characterisation of
geothermal reservoirs
Georg-August-UniversitätGöttingen
Angewandte GeologieGeowissenschaftliches Zentrum
I. Ghergut, M. Lodemann, M. Sauter
Angewandte Geologie, Geowissenschaftliches
Zentrum, Universität Göttingen
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Overview

• General concepts for determination of volumes and
  surface areas
• Single-well method dual-tracer push-pull
• Application in three crystalline reservoirs in
  Germany (Urach, Lindau, KTB)
• A special flow path tracing application using a
  single well - example from the sedimentary
  reservoir near Hannover

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Tracer techniques to determine

• travel times (residence times, contact times)
  reservoir volume or porosity
• temporal changes in reservoir properties from
  cooling (deformation) (e.g., coupled
  thermo-hydro-mechanical changes)
• contact surface between fractures and rock
  matrix (heat exchange surface)
• reservoir temperature (volume averaged)

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Motivation

• Assessing equivalent
• VOLUMES
• or
• SURFACES
• of a (geothermal) reservoir

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Contact surface between fractures and rock matrix
Hydraulically equivalent reservoirs can be
distinguished
(fracture-dominated reservoir)
(pore-space dominated reservoir)
same void-space volume
( Area / Vol ) is high
( Area / Vol ) is low
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Push-pull tracer experimental concept
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Tracer candidates (soluble)

• traced water molecules (HTO, D and 18O less
  suitable)
• fluorescent dyes (e.g. Uranine)
• food dyes / additives (e.g. Tartracine, E...)
• Naphthaline-Sulphonates (z.B. 1,5-NDS)
• sulphonated Naphthalene
• Formaldehyde condensates (SNFC)

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Colouring our food in the last and the next
millennium (Downham Collins, 1999)
Some well characterised food additivesfurther
criteria Analytics Price EU-admission etc
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Determination of diffusion coefficients
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Tracer method to assess contact surfaces in a
hybrid (fractured-porous) system
influence of surface- non-related processes
(advection-dispersion, large-scale fracture
heterogeneity) on measured tracer signals
single-well method push-pull (single-well,
injection-withdrawal)
No direct determination of contact surfaces use
tracers with different diffusion and/or sorption
properties)
dual-tracer ...... multi-tracer
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Push-pull tracer experimental concept
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Forward model concentration evolution in the
fracture
Tracer separation by diffusion/sorption
coefficients reverts monotonicity upon transition
from peak to tailing phases it is advisable to
use the latter in fitting the surface area
parameter.
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Forward model concentration evolution in the
fracture
note concentrations can be measured only during
the WITHDRAWAL phase (unless some in-situ
detector available)
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mid-late slopes of tracer BTCs from a push-pull
test are independent upon early transport
details, and they contain the desired contact
surface information
At mid-late tailing times when advection-dispersio
n effects becomes negligible, the surface-area
estimation from tracer BTCs reduces to fitting
the parameter ?m for the simple integral equation
(in which f represents the first time-derivative
of tracer conc.)
with
with numeric coefficients an and ?n (having known
analytical expressions) in the approximation for
g(?) describing the geometry and size of matrix
blocks.
The contact surface parameter (specific area ?m
A/V) multiplies different tracer parameter
combinations (Dm/Rm, Dm/Rf), thus its ambiguity
of determination can be reduced using several
tracers with (known) different sorption and
diffusion properties.
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Stimulation / Push-Pull-Test (Horstberg)
Photo BGR
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Push-pull test in hydrothermally-altered granite
formation (Southern Black Forest)
100-300 m2/m3
( free outflow phase)
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Push-pull test in 4-km deep crystalline
geothermal reservoir at Bad Urach
( free outflow phase)
1-10 m2/m3
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Push-pull test in 4-km deep crystalline formation
at the KTB-pilot hole
30 100 m2/m3
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(details of KTB production phase)
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KTB-2005, after injection of 100000m³ of water
? Change in volume and contact surface
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some experiences in crystalline reservoirs, a
review (1)
0.0001 - 0.001
0.0001 - 0.001
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some experiences in crystalline reservoirs, a
review (2)
100-300/m
1-10/m
10-30/m
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some experiences in crystalline reservoirs, a
review (3)
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Flow path tracing application using a single
well sedimentary reservoir (Horstberg)
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Single-well flow-path tracing in sedimentary
reservoir
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Single-well flow-path tracing in sedimentary
reservoir tracer recovery
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single-well flow-path tracing in sedimentary
reservoir around Hannover details of hydraulic
test design and physico-chemical parameters
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Heat transport experiments
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Longterm cooling in an HDR-Reservoir Temperature
development in the matrix
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Temperature push-pull tracertest KTB-pilot hole
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(No Transcript)
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Flow path tracing at KTB-boreholes circulation
test experimental design
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Thermal Degradation
nach Arrhenius Gesetz erwartet
Rose et al. (2001)
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Flow path tracing at KTB-boreholes test design,
and thermal / flow-path scenarios
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Flow path tracing at KTB-boreholes test design,
and thermal / flow-path scenarios
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Overview tracers used
(final selection pending) tritiated water,
inert gases, naphthalene-sulfonic, further
tracer candidates under evaluation
uranine tritiated waterNDS
flow-path tracing (as of 2005) uranineNDS
uranine NDS
push-pull tests (2004, 2005) heat (injected
cold water)uraninetritiated waterkryptonNDS,
PTS (Behrens)
naphthionate Lithiumuranine Bromide NDS
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Acknowlegements
The German Research Foundation (DFG) H.
Behrens P. Rose (EGI Utah) J. Orzol (Hannover) R.
Jung (Hannover) O. Kolditz (Tübingen) C.
McDermott M. Herfort (ETH)

• S. Fischer,
• J. Brinkmann,
• O. Stückrad,
• M. Armenat
• M. Lambert (Karlsruhe),
• KTB and Urach personnel (GFZ)

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(assumptions regarding void-space structures that
control hydraulics, geomechanics and fluid
transport in the KTB reservoir)
W. Kessels
nf 2 x 10-4
C. McDermott
ehy 7 x10-5 m
(following Y. Tsang up to 100 x) 10-4 m / (200 m)
5 x 10-5