Contractors' meeting and workshop on geochemistry

Directorate-General For Research And Innovation European Commission Directorate-General For The Information Society And Media

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Energy research
Energy policy

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION-EUROPEAN-COMMISSION-DIRECTORATE
• Nombre de lectures: 5
• Langue: English
• Poids de l'ouvrage: 2 Mo

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Commission of the European Communities
energy
Contractors' meeting
and workshop on geochemistry
Antwerp, 5 November 1986
Report
EUR 11362 EN Commission of the European Communities
energy
Contractors' meeting
and workshop on geochemistry
Antwerp, 5 November 1986
Edited by:
K. Louwrier, J. Garnish
Commission of the European Communities
Rue de la Loi 200
B-1049 Brussels
Directorate-General
Science, Research and Development
|988 C E 1 EUR 136 2 N Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on
behalf of then is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1988
ISBN 92-825-8287-6 Catalogue number: CD-NA-11362-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1988
Printed in Belgium CONTENTS
Page
INTRODUCTION 1
ROCK CORROSION AND MINERAL DEPOSITION IN HDR SYSTEMS 3
E. Tirtadinata, E. Althaus
ION MICROANALYSIS OF TRACE ELEMENTS IN MINERALS FROM THE
CARNMENELLIS GRANITE 19
D. Goossens, L. Van *t dack, F. Michiels, R. Gijbels
GEOCHEMISTRY OF THE CARNMENELLIS GRANITE HOT DRY ROCK RESERVOIR
SYSTEM 31
W.M. Edmunds, R.L.F. Kay, D. Savage, A.E. Milodowski, M.R. Cave,
J.N. Andrews, N. Hussain, A.V. BromLey, L. Thomas
WATER-ROCK INTERACTIONS AT HIGH TEMPERATURE 45
H. Pauwels, G. Michard
WATER-ROCK REACTIONS IN A TRIASSIC SANDSTONE AQUIFER. DETAILED
STUDY OF A LOW TEMPERATURE GEOTHERMAL SYSTEM, MELLERAY, FRANCE 51
C. Fouillac, F.D. Vuataz, M. Brach, A. Criaud
CHEMICAL EVOLUTION OF THE FLUIDS FROM THE DOGGER AQUIFER 63
A. Criaud, C. FouiLLac, M. Brach
3 4He/ He MEASUREMENTS IN GEOTHERMAL SYSTEMS : A PRELIMINARY
EVALUATION 75
E.R. Oxburgh, R.K. O'Nions
BEHAVIOUR OF UNCONSOLIDATED SANDSTONE SUBJECTED TO PERCOLATION
WITH NaCL and CaCL SOLUTIONS AT DIFFERENT TEMPERATURES 83 2
J. Baudracco, Y. Tardy
THERMODYNAMICAL MODELLING OF GEOCHEMICAL PHENOMENA ARISING
FROM GEOTHERMAL INJECTION IN AN AQUIFER 99
A. Coudrain-Ribstein, A. Vinsot
DEVELOPMENT OF A METHODOLOGY FOR MEASURING CO AND ITS GEOTHER-
MOMETRIC APPLICATIONS. Part I : MODEL DEVELOPMENT 107
F. D'Amore, R. Fancelli, L. Saracco
III -Introduction
The Commission of the European Communities has been involved in research,
development and demonstration of geothermal energy since 1975. Chemistry
is an important aspect of this research. It enters at many levels in the
process of extracting heat from the sub-soil. Water-rock interaction is
important in the Hot Dry Rock technology where water is pumped through a
man-made fracture system in a rock that has otherwise virtually no water
circulation.
Natural deep ground waters that are of interest for geothermal
developments often contain considerable amounts of salts that may
precipitate at lower temperature or pressure. This leads to scaling
during the production of hot water or steam.
The abatement of scales is of the utmost importance. Proper pressure
control and inhibitors can control the precipitation of calcium
carbonate. Sulphides and silica however still pose serious problems
during the exploitation of geothermal energy, and research on the control
of these scales should continue.
Certain clastic sediments consist of sandstone containing clay particles.
Producing water from or injecting water into such formations may cause
these particles to move. This can lead to plugging of the pores and
formation of a significant "skin". Study of the behaviour of these
sediments, consolidated or unconsolidated, and of its clays is an
important aspect of water-rock interaction.
4
Water circulating through granite picks up He produced by spontaneous
fission of uranium and Thorium. The study of He and Rn concentrations
gives information on, the development of a Hot Dry Rock reservoir.
Measurements of the He/ He ratio in geothermal fluids gives important
information on the outgassing of the mantle and therefore on the
development of fault systems and geothermal reservoirs.
This workshop brings together the scientists who work on these problems
under contract to the Commission of the European Communities. Meetings
like this are important for the mutual information of the participants
and for the strengthening of international cooperation.
- 1 ROCK CORROSION AND MINERAL DEPOSITION IN HDR SYSTEMS
Editha Tirtadinata and Egon Althaus
Mineralogisches Institut der Universität Karlsruhe
Contracts EN3G/0002/01 and EN3G/0076/00
Summary
Experiments with natural mineral phases likely to be formed as alteration
products of HDR reservoir rocks by interaction with heat exchange fluids
have shown that these solids will continue to react, giving rise to
hydrous, voluminous newly formed minerals. Natural HDR fluids (Urach)
show the same type of interaction, causing scaling on natural rock
surfaces as well as on tubing and surface installations. During rock
corrosion, trace elements follow a different reaction scheme compared to
major constituents.
1. Introduction
The response of HDR reservoir rocks to chemical attack from aqueous heat
exchange fluids has been the subject of many experimental investigations
(e.g. Althaus, 1984, Althaus & Gijbels, 1985, and others). From these
and other experiments the basic scheme of reaction is rather well known.
Mineral and rock surfaces are subject to distinct erosion processes
depending both on mineral and fluid compositions and on physical para­
meters like temperature, flow rate, etc. Two basically different types
of reaction have been found to occur: complete and congruent dissolution
of the minerals of the reservoir rock and selective leaching of indivi­
dual components leading to incongruent dissolution with secondary solids
left behind. The former case occurs when the minerals are far from
equilibrium with the fluids, while the latter is typical for
near-equilibrium conditions.
Different minerals are decomposed in different ways, both with respect to
3 -reaction rate and reaction mechanisms. Usually reaction rates are the
higher the more unstable a mineral is with respect to a given fluid com­
position (cf. Althaus & Gijbels, 1985). If minerals of different disso­
lution behaviour are present in a rock, the one with the highest reaction
rate dominates the rock dissolution by depressing the composition of all
other minerals until it has disappeared and the next solid takes over.
If, however, phases with comparable reaction rates are present, they
influence each other to about the same extent.
Since most reactions of minerals with neutral or acid solutions are of
the "hydrolysis" type, pH i* a very important parameter in rock corro­
sion. As the typical reactions follow the scheme
+ +Mineral I + H ­ Me + Mineral II
+ +or Mineral I + H ­ Me + H,Si0 (aq) > Si0 · aq(s) 4 2
formation of secondary phases is a common phenomenon in rock­water­
interaction. Only if pH is very low (pH ■ 1 to 2) is complete
dissolution of the rock likely to occur, and this will lead to very
strongly corroded surfaces and solutions heavily loaded with dissolved
species.
Secondary minerals that formed in­situ have been found to be mostly
amorphous silica, glbbsite, and clay minerals like kaolinite or
montmorillonite. Since rock corrosion procceeds like a reaction front,
the composition of the solution is likely to change on its way through
the rock. Constituents dissolved at on« place are at disequilibrium with
secondary minerals at a place encountered later; they have, therefore, a
distinct potential of being converted by reaction with secondary ­ or
sometimes even primary minerals ­ into newly formed minerals. The net
effect will be an increase in volume of secondary phases because these
usually are hydrous minerals with loosely packed crystal lattices. This
will result in a change in both surface properties and permeability if no
measures are taken against it by tailoring injection fluids according to
the prerequisites of the individual rock­fluid system. Although diffe­
rent rocks will show a different characteristic behaviour, some common
features can be envisaged which should be investigated experimentally.
4 ­