Hindcasting injection-induced aseismic slip and microseismicity at the Cooper Basin Enhanced Geothermal Systems...

Area of Science:

• Geophysics
• Earthquake Science
• Geothermal Energy

Background:

• Subsurface fluid injection is increasingly linked to both seismic and aseismic fault slip.
• Identifying field-scale aseismic slip is challenging due to limited monitoring capabilities, often relying solely on seismic arrays.

Purpose of the Study:

• To develop and apply a modeling workflow for detecting aseismic slip during fluid injection.
• To investigate the interplay between aseismic slip, microseismicity, and pore pressure changes in a granitic reservoir.

Main Methods:

• A numerical model simulating discrete microseismic events and aseismic slip concurrently with fluid injection.
• Application of the workflow to a 2012 Enhanced Geothermal System injection case study in Cooper Basin, Australia.
• Analysis of observational constraints including microseismicity, injection rate, and wellhead pressure.

Main Results:

• Aseismic slip likely accounted for approximately 50% of the total moment release during the injection episode.
• Pore pressure changes, leading to fault weakening, were the primary drivers of microseismicity, rather than elastic stress transfer from aseismic slip.
• A theoretical model was developed to estimate the spatiotemporal extent of seismicity induced by pore pressure increases.

Conclusions:

• This study provides the first inference of injection-induced aseismic slip in a granitic reservoir.
• Aseismic slip may be a common phenomenon across various geological lithologies during fluid injection operations.
• Understanding aseismic slip is crucial for managing risks associated with fluid injection projects, including geothermal energy and wastewater disposal.