S1.1: Laboratory Study of the Dynamics of Stick-Slip Sliding in Large Sand-stone Block Induced by Fluid InjectionsSafe geologic sequestration of CO₂ is essential to decrease the concentration of greenhouse gases in the atmosphere. However, the injection could raise the underground pore pressure and potentially induce sliding of critically stressed faults. We report results of laboratory tests, where different fluid injections were implemented close to the stressed artificial interface of a ~1m length with the intention to induce an activation of interface sliding. We have found that increases of pore pressure in the interface up to ~1 MPa did not cause any acceleration in the interface sliding, nei-ther in case of a locked nor sliding interface. Injection of fluid under elevated pore pressure created hydraulic frac-turing in the vicinity of the interface, causing an increase of pore pressure in the interface up to ~ 6.2 MPa, and after injection shut-in, pore pressure dropped to almost zero. However, about 10 minutes later, a sudden sliding of the interface (stick-slip motion) was recorded. This kind of stick-slip event could be considered analogical to the natural earthquakes in the Earth. Two types of Acoustic Emission (AE) signals were detected: short bursts and long-lasting oscillations (tremors). The analysis of the spatial distribution of the AE energy was applied to monitor the evolution of the hydraulic fracture and thereafter – the dynamics of stick-slip. It was found that at first, the nucleation of the sliding near one edge of the interface occurred, then sliding propagated along the whole ~ 1 m long interface with an average speed of a few m/s. The speed and the energy radiated during this event were approximately 6 orders of magnitude larger than observed during quasi-static sliding preceding the stick-slip. Occurrence of this powerful sudden event in the stressed artificial interface is to be related to the injection of fluid under elevated pore pressure completed 10 minutes before the stick-slip event, creating hydraulic fracturing in the rock and causing significant increase of pore pressure in the interface. Such a suddenly occurring event could be considered a laboratory analogy to the fluid-induced seismicity, for example, earthquakes induced by wastewater disposal.
|Title of host publication
|Rock fracturing and fault activation: Experiments and models 13th EURO-CONFERENCE ON ROCK PHYSICS AND GEOMECHANICS THE GUÉGUEN CONFERENCE
|Published - 2019