by Eva Schill, Denis . Voskov

We propose a 3-day workshop to develop a borehole science plan for a multi-use exploration and monitoring well of 3-4.5 km depth that will be part of a unique research infrastructure on the TU Delft campus. This so-called urban energy laboratory will include a well-instrumented geothermal well doublet (reaching to a depth of 2.5 km), an ultra-sensitive portable seismic monitoring array, the scientific monitoring components of a high temperature aquifer heat storage system (HT-ATES) and a borehole array to monitor and protect groundwater supplies. The addition of the multi-use well to the urban energy laboratory will allow us to tackle problems and better understand processes related to multiple/competing subsurface uses in densely populated areas, and their interference with natural processes and the deep biospehre. The monitoring aspects target fluid/flux movement in 3D with unprecedented precision, aiming to understand the propagation of the geothermal cold front and reservoir pressures away from the well. In addition, access to the test sites and the data will enable the international research community to develop and optimise novel downhole and cross-hole imaging and measurement methods and techniques in this unique environment under challenging (for geophysical monitoring: noisy) conditions. Through the workshop and the broad expertise of the participants, we want to explore key science directions and opportunities even beyond the geothermal aspects. We also consider the workshop as our first platform to (i) bring together the international research community from academia and industry to plan research projects and tests of novel methods and equipment in the urban energy laboratory and (ii) think about ways for public/stakeholder engagement, as social acceptance of a drilling project is a crucial step for successful implementation, especially in an urban environment.

• The workshop is organized to discuss and identify key and innovative monitoring technologies and methods for the observation of downhole processes resulting from human activities and their interference with potential other subsurface utilization plans. The expected outcome will be project ideas, suggestions for well layout and completion that allows advanced monitoring methods, and a list of potential installations and downhole tools to monitor heat and mass transfer processes and their potential interference with the multiple usage of subsurface space at different depths. These outcomes will be used to plan the implementation of the deep multi-use well that will aid in achieving the following scientific objectives:
• (1) improve monitoring capabilities of an operating geothermal system to better understand fluxes, pressures, and fluid distribution at depths,
• (2) to improve predictions of reservoir properties via the petrophysical log response and geological understanding,
• (3) enable risk assessment of induced seismicity during long term geothermal operations. Another scientific objective for drilling the multi-use well is of more regional importance and is related to the exploration of geothermal reservoirs at greater depth. All of the other objectives are of global importance when it comes to low-enthalpy geothermal heat production from sedimentary aquifers and are especially relevant for such systems in the urban environment where the subsurface is used for multiple/competing purposes.

Geothermal Heat, Multiple Subsurface Use, Urban Energy

Latitude: 52.00104, Longitude: 4.37016