Colchester Northern Gateway

The Geothermal industry is one of the fastest growing sectors of the energy industry in the UK, and is 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 specialities!

WJ were engaged in 2019 by Colchester Amphora Energy ltd, a company formed by Colchester Borough 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 Heat Network project, a district heat system with a open loop ground source heat pump as the primary heat source which is supported by the Department of Business, Energy Industrial Strategy Heat Network Investment Project.

The works consists of the construction and testing of a deep boreholes, in to the underlying Chalk aquifer, with associated development and testing to create a system of abstraction and re-injection boreholes to give the maximum thermal capacity for the geothermal network.

The site is 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 135 metres below ground level were proposed, comprising of a 500 mm 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 wells are developed by airlift and acidisation techniques to remove fines prior to the pumping testing to see the flow rates that can be achieved. Due to the results obtained from the testing, two of 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 tests are undertaken based upon a specification provided by the client, comprising:

• Step tests, 12 hours duration
• Constant rate tests, 12 hours duration
• Hydraulic balance step tests, abstraction and recharge test, 12 hours duration
• Multi-well tests, 12 hours duration
• Hydraulic balance constant rate test, Abstracting from one well and recharging to another, 168 hours duration

When complete a system of five boreholes will have been installed with an 800kW heat pump, which is planned to deliver 5.5 GW of low carbon heat a year to homes, offices and health care facilities across the area. This will be the largest system of its type (using a chalk aquifer) in the UK. A truly ground breaking project!

• LOCATION: Colchester

• CLIENT: Colchester Amphora Energy Limited