MODELLING, CHARACTERISATION AND OPTIMISATION OF DEEP GEOTHERMAL ENERGY IN THE CHESHIRE BASIN by CHRISTOPHER SIMON BROWN A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Department of Civil Engineering University of Birmingham October 2019 i University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ii Abstract Despite the significant geothermal resource in the UK, only one small scale scheme in Southampton is presently operating. Few wells have been drilled to target deep resources, particularly in the Cheshire Basin where only two wells have penetrated depths approaching 3 km. As a result, the knowledge of aquifer quality in the more central parts of the basin is limited, meaning there is a high geological risk associated to any geothermal development. To investigate this, a single well model was designed to simulate the extraction of fluid from the Collyhurst Sandstone Formation. Simulations of a range of geological and engineering parameters highlighted hydraulic conductivity could be the most significant obstacle to production, however, it could be minimised by altering engineering parameters (i.e., production rate, length and position of the well screen). A key issue with conventional extraction only methods is the disposal of waste water. To circumvent this issue, innovative deep borehole heat exchangers and standing column wells were modelled. Results indicated that both methods can produce heat loads up to 3.7 MW for short periods. Further analysis was also undertaken on heat exchangers, highlighting significant savings could be made from switching to a geothermal run heat network (>£49 million). iii iv Dedication To my parents and grandparents: Rachel, Andrew, Pam, Betty and the two Alans. Without whom none of this would have been possible. ‘Audere est Facere’ v vi Acknowledgments I would like to thank my academic and industrial supervisors, Professor Nigel Cassidy, Dr Stuart Egan and Mr Dan Griffiths, for their continued support and feedback throughout this PhD. I would also like to thank the Natural Environment Research Council (NERC grant reference number NE/M00998X/1) and Cheshire East Council for funding my research. I am extremely grateful to Keele University for allowing the use of facilities during my transition to the University of Birmingham and to everyone who made this possible, in particular Richard Burgess and my supervisors. I also appreciate all the support I have received from fellow PhD candidates in Keele University and co-workers in the council, including Diane Spivey and Matt O’Neil. I would like to thank my family for their unwavering support throughout my PhD and giving me a great foundation to achieve my goals. I would also like to thank my other family the ‘Smithies’ for their support and at times daily calls (from Janet)! A special mention must also be given to two people: my brother Richard Brown and partner Lucy Smith. Thank you Rich for our weekly motivational calls and general advice! Thank you Lucy for putting up with the late working periods and all the support you have provided throughout my PhD! I am extremely grateful for your help proof reading manuscript/thesis drafts and am eternally indebted. vii viii Contents CHAPTER 1 - INTRODUCTION......................................................................................................... 1 1.1 Introduction ............................................................................................................................ 1 1.2 Aims and Objectives ................................................................................................................ 7 1.3 Thesis overview ...................................................................................................................... 8 CHAPTER 2 - AN OVERVIEW OF THE GEOTHERMAL DEVELOPMENTS IN THE UK AND THE GEOLOGY OF THE CHESHIRE BASIN ............................................................................................................. 10 2.1 Introduction .......................................................................................................................... 10 2.2 Geothermal developments in the UK ..................................................................................... 11 2.2.1 Types of deep geothermal resources in the UK ....................................................................... 11 2.2.2 Overview of current UK schemes ............................................................................................. 15 2.2.3 Heat flow of the UK .................................................................................................................. 17 2.2.4 Data from existing deep boreholes in the Cheshire Basin ....................................................... 20 2.3 Geological history of the Cheshire Basin ................................................................................ 24 2.3.1 Caledonian Orogeny ................................................................................................................. 25 2.3.2 Variscan Orogeny ..................................................................................................................... 26 2.3.3 Permo-Triassic extension ......................................................................................................... 27 2.4 Present structure of the Cheshire Basin ................................................................................. 29 2.5 Pre-Permian strata ................................................................................................................ 33 2.6 Permo-Triassic stratigraphy of the Cheshire Basin .................................................................. 36 2.6.1 Permian Appleby and Cumbrian Coast Groups ........................................................................ 36 2.6.1.1 Collyhurst Sandstone Formation ....................................................................................... 36 2.6.1.2 Manchester Marl Formation ............................................................................................. 38 2.6.2 Triassic Sherwood Sandstone Group........................................................................................ 40 2.6.2.1 Kinnerton Sandstone Formation ....................................................................................... 40 2.6.2.2 Chester Formation............................................................................................................. 40 2.6.2.3 Wilmslow Sandstone Formation ....................................................................................... 42 2.6.2.4 Helsby Sandstone Formation ............................................................................................ 43 2.6.3 Triassic Mercia Mudstone Group ............................................................................................. 45 2.6.3.1 Tarporley Formation ......................................................................................................... 45 2.6.3.2 Sidmouth Formation ......................................................................................................... 45 ix 2.6.4 Triassic Penarth and Jurassic Lias Groups ................................................................................ 46 Summary .................................................................................................................................... 47 CHAPTER 3 - NUMERICAL METHODS AND GOVERNING EQUATIONS ............................................. 48 3.1 Introduction .......................................................................................................................... 48 3.2 Key governing equations for heat and fluid fluxes in a geothermal system .............................. 49 3.3 Numerical methods for solving heat and fluid fluxes .............................................................. 51 3.4 The finite-difference method ................................................................................................. 53 3.5 Solution methods .................................................................................................................. 56 Summary .................................................................................................................................... 57 CHAPTER 4 - MODELLING GEOTHERMAL SINGLE WELLS: INSIGHTS FROM THE GEOTHERMAL WELLS IN SOUTHAMPTON, UK ............................................................................................................... 59 4.1 Introduction .......................................................................................................................... 59 4.2 Method of numerical modelling ............................................................................................. 62 4.2.1 Governing equations for modelling reservoir interactions ...................................................... 64 4.2.2 Governing equations for modelling thermal borehole