project

Reliable and affordable backfilling of boreholes in closed thermal energy systems

Expert(s):
Martin Bloemendal MSc PhD, Martin van der Schans MSc, Marette Zwamborn

  • Start date
    01 Jan 2019
  • End date
    30 Jun 2020
  • Principal
    TKI Watertechnologie, BodemenergieNL en BTO
  • collaborating partners
    BodemenergieNL, Remon, Nathan, Duratherm, GroenHolland, KWR, SIKB, Deltares

Thermal energy is an important technique in the heat transition. The use of these systems can therefore be expected to increase very rapidly in the decades ahead. The installation of closed thermal energy systems involves penetrating semi-permeable layers in the subsurface. The sealing integrity of these layers must be restored after the drilling to prevent exposing groundwater quality to any risks. Because the installation involves deep wells (>100m) of relatively small diameter (<20cm), backfilling them is not easy. There is thus an urgent need for a boost in innovation and efficiency to make techniques available that effectively and efficiently backfill boreholes in closed thermal energy systems. In this research project we will search for techniques and methods to enable a subsequent verification of the sealing integrity, which should also make controlling it easier.

Saving energy with thermal sources too

To limit climate change, the Dutch government has signed agreements to cut the country’s CO2 emissions. One of the techniques that should play an important part in CO2 emission reduction is thermal energy. Closed thermal energy systems are suitable for small, individual buildings, of which there are very many in the Netherlands (>6 million). In places where the building density is low, collective heat networks can’t be installed, so that a closed thermal energy system is the only option to obtain sustainable heating and cooling. It is expected that by 2050, about 25% of this kind of building will be equipped with a closed thermal energy system. We are therefore talking about the installation of a huge number of such systems. The producers are already under a great demand pressure, so that this can only be expected to increase.

Improvement needed in methods to backfill boreholes

The installation of closed thermal energy systems involves penetrating semi-permeable layers in the subsurface. The sealing integrity of these layers must be restored after the drilling, to prevent exposing groundwater quality to any risks. Since groundwater is a key raw material for drinking water production, it is important, for a start, to backfill the boreholes properly. Moreover, it is also important, in view of the huge anticipated growth in the use of the systems, that this be done efficiently.

Because the installation involves deep wells (>100m) of relatively small diameter (<20cm), backfilling them is not easy. The currently common techniques are laborious, which leads to problems in practice. This is why it is important that the sector and the competent authorities boost the effectiveness and efficiency of the process, and clearly define which techniques, work methods and materials are suitable.

Innovation and efficiency boost for backfilling boreholes

There is an urgent need for a boost in innovation and efficiency to make techniques available that effectively and efficiently backfill boreholes in closed thermal energy systems. The objective of this research is to:

  1. optimise existing techniques and develop new techniques, work methods and backfill material;
  2. develop a method to enable the verification of the integrity of the backfilled borehole after the system’s installation;
  3. develop a framework within which the control can be conducted in an efficient and straightforward manner.

Since it is expected that the demand for the drilling of holes for closed thermal energy systems will increase significantly, the drilling companies are faced with the need to decide on major investments regarding the backfilling or sealing of boreholes. To avoid investments being made in the wrong materials, it is important, in the short term, to make it clear which techniques can be invested in responsibly.

Schematic representation of a closed thermal energy system, highlighting the required restoration of the sealing integrity of the penetrated clay layer.