Cost modelling of electricity-producing hotdry rock (HDR) geothermal systems in the United Kingdom

Directorate-General For Research And Innovation European Commission

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Energy research
Electricity

Sujets

• Sciences et techniques

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION-EUROPEAN-COMMISSION
• Nombre de lectures: 22
• Langue: English
• Poids de l'ouvrage: 8 Mo

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ISSN 1018-5593
* *
European Commission
Cost modelling of electricity-producing
hot dry rock (HDR) geothermal systems
in the United Kingdom European Commission
ly^ i ï
Cost modelling of electricity-producing
hot dry rock (HDR) geothermal systems
in the United Kingdom
P. Doherty, R. Harrison
University of Sunderland
Langham Tower
Ryhope Road
Sunderland SR2 7EE
United Kingdom
Contract No EN3G-0090
Final report
Directorate-General
Science, Research and Development
1995 EUR 15388 EN Published by the
EUROPEAN COMMISSION
Directorate-General XIII
Telecommunications, Information Market and Exploitation of Research
L-2920 Luxembourg
LEGAL NOTICE
Neither the European Commission nor any person acting on behalf of
the Commission 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, 1995
ISBN 92-826-9582-4
© ECSC-EC-EAEC, Brussels · Luxembourg, 1995
Printed in Spain COST MODELLING OF ELECTRICITY PRODUCING HOT DRY ROCK (HDR)
GEOTHERMAL SYSTEMS IN THE UK
ABSTRACT
A detailed and comprehensive cost model for Hot Dry Rock (HDR) electricity producing
systems has been developed in this study. The model takes account of the major aspects of
the HDR system, parameterized in terms of the main physical and cost parameters of the
resource and the utilization system. A doublet configuration is assumed, and the conceptual
HDR system which is defined in the study is based upon the UK Department of Energy
(DEn) HDR geothermal R&D programme.
The model has been used to calculate the costs of HDR electricity for a UK defined base case
which represents a consensus view of what might be achieved in Cornwall in the long tenn.
At 14.2 p/kWh (1988 costs) this cost appears to be unacceptably high. A wide-ranging,
sensitivity study has also been carried out on the main resource, geometrical, and operational
parameters of the HDR system centred around the UK base case. The sensitivity study shows
the most important parameters to be thermal gradient and depth.
The geometrical arrangement and the shape of the reservoir constitute major uncertainties in
HDR systems. Their effect on temperature has a major influence on system performance, and
therefore a range of theoretically possible geometries have been studied and the importance
of geometrical effects on HDR electricity costs assessed.
The most cost effective HDR arrangement in terms of optimized volumes and flow rates has
been investigated for a world-wide range of thermal settings. The main conclusions from this
study suggests that for HDR electricity to be economic, thermal gradients of 55 °C/km and
above, well depths of 5 km or less, and production fluid temperatures of 210 °C and above
are required. TABLE OF CONTENTS
ABSTRACT ΙΠ
TABLE OF CONTENTS V
LIST OF FIGURES IN TEXT X
LIST OFS IN APPENDIX XII
LIST OF TABLES IN TEXT ΧΠΙ
LIST OFS IN APPENDIX
Chapter 1
INTRODUCTION 1
1.1 Introduction 3
1.2 The nature and exploitation of geothermal energy resources 5
1.3e HDR heat extraction concept 6
1.4 Potential HDR resource size 9
1.5 HDR research and development programmes 12
1.5.1 The USA HDR research and development programme
1.5.2 The UK HDRh andte3
1.5.2.1 The UK HDR resource5 2 The UK HDR technology
1.5.2.3 The UK HDR programme costs 20
1.6 Major uncertainties of commercial HDR schemes
1.6.1 Measurement of resource and rock properties
1.6.2 Drilling the HDR wells3
1.6.3 Reservoir stimulation and heat extraction
1.7 Previous cost studies of HDR electricity production4
1.8 Aim and scope of this study 26
1.8.1 Sheffield work7
1.8.2 Scope of this work
Chapter 2
MODELLING THE HDR RESERVOIR BEHAVIOUR 29
Nomenclature
2.1 Introduction 31
2.2 Thermal performance modelling
2.2.1 Modelling approaches
2.2.2 Thermal performance modelling - Gringarten approach 34
2.3 Hydraulice modelling8
2.3.1 Impedance
2.'3.2 Water loss9
2.4 . Flow distribution 40
2.5 Chapter summary
V-Chapter 3
THE HDR MODEL 43
Nomenclature
3.1 Introduction5
3.2 The HDR surface system8
3.2.1 Power plant performance and costs 4
3.3 The HDR subsurface system 51
3.3.1 The geometry of the HDR subsurface system
3.3.1.1 Definition of reservoir geometry4
3.3.2 Fluid temperature at the production wellhead7
3.3.3 Water pressures in the subsurface system 60
3.3.3.1 Injection pump power and costs2 2 Highest subsurface water pressures
3.3.4 Heat extraction efficiency and electricity production
3.3.5 HDR subsurface costs 66
3.3.5.1 Drilling costs2 Stimulation costs7
3.4 Cost allowances for catastrophic subsurface losses8
3.5 Economic Appraisal of HDR systems
3.5.1 The HDR system costs 72
3.5.1.1 Capital costs2 Operating costs
3.5.2 The HDR system performance
3.5.3 HDR discounted unit costs3
3.6 Chapter summary
Chapter 4
VALIDITY OF THE MODEL APPROACH AND PROCEDURES 75
4.1 Introduction 77
4.2 Drilling
4.3 Reservoir creation8
4.4r geometry 80
4.5r size and thermal performance
4.6 Surface plant
4.7 Choice of base case parameters1
4.8 Chapter summary
Chapter 5
RESULTS AND SENSITIVITIES FOR UK BASE CASE 83
Nomenclature 8
5.1 Introduction5
5.1.1 The base case (case I)6
5.2 Results from the sensitivity study
5.2.1 Reservoir geometry
5.2.1.1 Unit costs versus total vertical depth 90 2 Unit costss well separation
5.2.1.3 Unit costs versus well deviation2 4 Unit costss zone separation4
5.2.2 Unit costs versus thermal gradient
5.2.3 Water losses 98
VI 5.2.4 Heat extraction efficiency 104
5.2.4.1 Unit costs versus reservoir joint spacing2 Fracture sweep efficiency, flow splitting, and flow channelling.. 106
5.2.4.3 Rate of heat extraction 110
5.2.5 The effect of reservoir size on unit costs3
5.2.6 Thet of impedance on unit costs6
5.3 Sensitivities relative to the base case I9
5.4 Use of the sensitivities - Speculative long term case 122
5.5 The effect of discount rate on unit costs4
5.6 Comparison of the base case I results with the Shock base case
5.7 Chapter summary 131
Chapter 6
A CONDENSED HDR COST MODEL3
Nomenclature
6.1 Introduction5
6.2 Stimulation zone geometrical arrangement
6.2.1 RTZ/CSM geometry (RTZ/CSM) 136
6.2.2 Horizontal Axis Complete Disc geometry (HACD) 13
6.2.3l Axis Partial Discy (HASCD)
6.2.4 Slant Axis Partial Disc geometry (SAG)8
6.2.5 Vertical Axis Cylindery (VAG)
6.3 Producer wellhead temperature
6.4 Reservoir lifetimes 140
6.4.1 Percentagee drawdown of the production fluid 14
6.4.2 Average joint spacing1
6.4.3 Effective area-flow ratio
6.5 Drilling costs2
6.6 Stimulation costs5
6.7 Comparison of the condensed model with the main HDR cost model 149
6.7.1 Output results
6.8 Chapter summary 153
Chapter 7
PROCEDURE FOR IDENTIFYING OPTIMIZED HDR VOLUMES AND FLOW
RATES FOR A WIDE RANGE OF OPTIONS
7.1 Introduction7
7.2 The optimization procedure
7.2.1 Fixed and variable parameters and options 15
7.2.2 Drilling and stimulation costs uncertainties 160
7.2.3 The optimization algorithm
7.3 The optimization output and results1
7.3.1 The process of optimizing the injection flow 16
7.3.2 Thes ofg the reservoir volume
7.3.3 Changes in the optimal conditions with increasing sweep efficiency9
7.4 The effect of impedance on the optimization 174
7.5et of water loss on then
7.6 Chapter summary 17
VII Chapter 8
ECONOMICS OF HDR SYSTEMS IN DIFFERENT GEOLOGICAL SETTINGS ... 179
8.1 Introduction 181
8.1.1Reservoirstimulation zone shapes, stimulation fluid type,and
representative sweep efficiencies 181
8.2Discussionoftheoptimizedresultsandconclusions183
Chapter9
CONCLUSIONS201
9.1Aimsofthisstudy203
9.2 Conclusions from this study203
9.2.1 HDR electricity costs at Cornwall 203
9.2.2 Results from the sensitivitiesstudy203
9.2.2.1 The most importantparameters2042 The effect ofuncertaintyinthechoice of the basecase
parameters204
9.2.2.3 Use of the sensitivitiesindefiningaspeculative long termcase..204
9.2.3 The prospects for HDR developments for a world-wide range ofthermal
settings 204
9.3Suggestionsforfurther work205
REFERENCES207
APPENDICES 215
APPENDDCA
Heatbalanceanalysis on a volumetric element of an HDR fracture217
APPENDIXΒ
Solutionofthewatertemperature at the outlet of an HDR fracture 221
APPENDDCC
Numericalinversionof the laplace equation for the watertemperature exiting a
fracturedHDRreservoir using the Stehfest algorithm 233
APPENDIX D
Performance and costs of flash steampowerplants243
APPENDIX E
Performance and costs of binary cycle powerplants265
APPENDLX F
Specification of the wells and reservoir arrangement 283
APPENDDÍ G
Calculating the flow splitting betweenthereservoirzones291
APPENDLX H
Determining the water temperature enteringtheproductionwell 297
VIII