The geothermal industry is one of the fastest growing sectors of the energy industry in the UK and becoming an increasingly common option for new council developments. Fortunately for WJ, these geothermal systems require the construction and testing of deep boreholes which are one of WJ’s specialties!
WJ were engaged in 2019 by Colchester Amphora Energy Ltd, a company formed by Colchester council to promote the use of more low carbon sources of heat and power in and around Colchester, to provide our expert services for the innovative Colchester Northern Gateway project.
The initial works consisted of the construction and testing of a new deep borehole, toed in to the underlying Chalk, with associated development and testing. Based upon the results of these tests further wells were commissioned, to provide additional capacity for the geothermal network.
Due to the location of the site, whilst the installation and testing of the wells was vital, so was maintaining the public condition of the site. Therefore, it was necessary for WJ to provide protection to the greenfield site in the form of protective matting for the drilling rig and all other plant and equipment to utilize.
The site was underlain by a typical geological sequence for the area comprising made ground/topsoil overlying sand and gravel deposits, the London Clay, the Woolwich and Reading Beds, all underlain at depth by the Chalk. Due to this sequence, wells to approximately 140m below ground level were proposed, comprising of a 500mm section of casing installed in to the London Clay, advanced via Open Hole techniques in to the Chalk, with 340mm permanent steel casing, before the well is extended, via open hole techniques to the proposed finish depths. Upon completion the well was developed by airlift and acidisation techniques to remove air fines prior to the pumping commencing. Due to the results obtained from the testing, the wells were extended to 200m in depth – some of the deepest wells WJ have drilled in the UK, but perfectly suited to our extensive drilling fleet!
Upon completion of installation and development a pumping test was undertaken based upon a specification provided by the client, comprising:
- Step tests, 12 hours duration, up to 20 l/s
- Constant rate tests, 12 hours duration, up to 20 l/s
- Hydraulic balance step tests, abstraction and recharge test, 12 hours duration
- Multi-well tests, 12 hours duration
- Hydraulic balance constant rate test, Abstracting from multiple wells and recharging to multiple wells, 168 hours duration
Due to the success of the initial wells, as of the end of August 2019 a total of three number boreholes have been installed and tested to the above specification!
- LOCATION: Colchester
- CLIENT: Colchester Amphora Energy Limited