Georg-August-UniversitätGöttingen

Tracer techniques for the characterisation of geothermal

reservoirs

I. Ghergut, M. Lodemann, M. Sauter

Angewandte Geologie,

Geowissenschaftliches Zentrum,

Universität Göttingen

Angewandte GeologieGeowissenschaftliches Zentrum

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

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)

Contact surface between fractures and rock matrix

same void-space volume

( Area / Vol ) is high ( Area / Vol ) is low

(fracture-dominated reservoir)

(pore-space dominated reservoir)

Hydraulically equivalent reservoirs can be distinguished

Push-pull tracer experimental concept

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)

‚Colouring our food in the last and the next millennium‘ (Downham & Collins, 1999)

Some well characterised food additives

further criteria : Analytics Price EU-admission etc

Determination of diffusion coefficients

Push-pull tracer experimental concept

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.

note: concentrations can be measured only during the WITHDRAWAL phase (unless some in-situ detector available)

Forward model: concentration evolution in the fracture

Stimulation / Push-Pull-Test (Horstberg)

Photo: BGR

Push-pull test in hydrothermally-altered granite formation (Southern Black Forest)

(~ free outflow phase)100-300 m2/m3

Push-pull test in 4-km deep crystalline geothermal reservoir at Bad Urach

(~ free outflow phase) 1-10 m2/m3

Push-pull test in 4-km deep crystalline formation at the KTB-pilot hole

30 – 100 m2/m3

KTB-2005, after injection of 100000m³ of water Change in volume and contact surface

Flow path tracing application using a single well: sedimentary reservoir (Horstberg)

Single-well flow-path tracing in sedimentary reservoir

Heat transport experiments

Longterm cooling in an HDR-Reservoir: Temperature development in the matrix

Temperature push-pull tracertest KTB-pilot hole

Flow path tracing at KTB-boreholes: circulation test – experimental design

Thermal Degradationnach

Arrhenius‘ Gesetz

erwartet:

Rose et al. (2001)

Flow path tracing at KTB-boreholes: test design, and thermal / flow-path scenarios

Acknowlegements

S. Fischer,

J. Brinkmann,

O. Stückrad,

M. Armenat

M. Lambert (Karlsruhe),

KTB and Urach personnel (GFZ)

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)