New stimulation methods for more efficient EGS treatment
There is essentially one barrier that separates conventional techniques from enhanced geothermal systems (EGSs): the ability to produce affordable energy by pumping high-pressure water into a hot rock with low permeability. This process known as hydraulic stimulation would open a whole new world for society. Geothermal resources that have not been economically viable to exploit so far would suddenly become a no-brainer. We are not exactly there yet. EGS still has some way to go to prove its worth and attract investors, and efforts under the DESTRESS project are meant to clear the path. Since 2016, the project has been building upon advances in the oil and gas sector to develop new stimulation methods with a view to reducing cost, increasing reservoir transmissivity and minimising environmental impact. This notably involves preventing seismic events and pollution of groundwater reservoirs. “Inspiration came from hydrocarbon reservoir development, with one main difference: geothermal stimulation targets an environmental safe treatment of the reservoir,” says Ernst Huenges, Head of the International Centre for Geothermal Research (GFZ) at Helmholtz Centre Potsdam, Germany, and coordinator of DESTRESS. The project consortium also base their concepts on extended risk assessment and recent scientific progress in fluid-rock interaction, enabling a soft stimulation approach, more accurate determination of the stress field and the analysis of induced seismicity. The DESTRESS concept is being applied at several sites. “Our stimulation treatments are being demonstrated in different geological environments and under different site-specific circumstances such as specific states of the well and various distances to cities. In each case, the required adaptations are related to the types of pathways for fluids. Pore space-type reservoirs require more chemical treatments to dissolve obstacles with acids, while fracture-type reservoirs react more to hydraulic-mechanical stimulation,” Huenges explains. DESTRESS was divided into seven work packages, two of which aimed to provide a demonstrator for innovative stimulation treatment: one for combined hydraulic-acidisation treatments in sandstones and other rocks; and one for cyclic hydraulic and multi-stage stimulation in granites and tight sandstones.
A source of inspiration for new sites
Although the project is due for completion at the end of November 2020, Huenges is confident that any stakeholder looking for similar treatments to solve productivity or injectivity problems at their own site could take DESTRESS as an example. “Surely, lessons learnt from DESTRESS operations, especially with regard to applied risk assessment and workflows, will positively influence treatments to be performed later at other sites (for example United Downs in the UK),” he says. The potential for geothermal heat supply in Europe is huge and increasing demand for renewable energy supply makes EGS a tempting solution as long as potential environmental issues can be managed positively. The DESTRESS team will be focusing on a multi-stage stimulation over the next few months, which has yet to be demonstrated for geothermal systems with a sufficient reliability level, in order to keep closing the remaining gaps. From that stage onwards, commercialisation should not be too far into the future. “We think we are close to commercialisation in newly developed wells,” says Huenges. “However, we recently learned that there is still additional development required in older wells because of integrity issues. Several stakeholders involved in DESTRESS, along with a follow-up EU project, will continue to develop new treatment solutions.”
Keywords
DESTRESS, geothermal, EGS, hydraulic stimulation, fluid-rock interaction, demonstrator, environmental impact