Insights from Subsurface Monitoring for Engineering of the Stimulation Pattern in Fractured Reservoirs

Area of Science:

• Geosciences
• Geothermal Energy Engineering
• Rock Mechanics

Background:

• Stimulation operations are key to enhancing geothermal reservoir performance by improving fluid flow and heat transfer.
• Predicting stimulation outcomes is difficult due to reservoir complexity and limited operational data.
• Reservoir stress state, natural structures, pressure, and injection methods are critical factors.

Purpose of the Study:

• To provide detailed observations from a large-scale stimulation experiment.
• To analyze the influence of geological and geomechanical factors on stimulation outcomes.
• To identify key parameters for optimizing geothermal reservoir stimulation.

Main Methods:

• Conducted a hectometer-scale stimulation experiment at the Bedretto Underground Laboratory.
• Utilized dense monitoring within a crystalline rock volume with significant overburden.
• Analyzed seismic event propagation patterns in relation to hydraulic connectivity, pressure compartments, and geomechanics.

Main Results:

• Hydraulic connectivity, pressure compartments, and geomechanics of existing structures significantly influence seismic event propagation.
• Seismicity initiation and distribution are strongly affected by zonal pressure isolation and pressure diffusion.
• Distinct activation patterns between injection cycles demonstrate the impact of stimulation strategy adaptation.

Conclusions:

• Adapting stimulation strategies to specific reservoir geomechanical and geological characteristics is essential.
• The spatial extent of stimulation can be influenced by the number of cycles and injection pressure.
• The interplay between hydraulic pressures and stress states is critical for optimizing fractured reservoir stimulation.