Dynamics of fluid-triggered fracturing in the models of a geological medium

Abstract

Implications of infusion of small (compared to the pore space) amounts of water for the dynamics of fracturing are studied in the laboratory experiments on the models of a heterogeneous geological medium. Variations in the acoustic emission that precede macrofracture are analyzed, including as candidate precursors. In all experiments, the macrofracture had occurred not immediately after the mechanical loading or water infusion but with a time-delay after a period of acoustic quiescence and subsequent activation. The enhancement in acoustic activity preceding macrofracture is well reproduced by the exponential law; the correlation between the actual number of events (or the released energy) and the exponential approximation exceeds the 95% confidence level. The power law is slightly worse although also a confident approximation of the acoustic emission process. The facts of subsequent occurrence of quiescence and activation suggest that, in principle, this phenomenon can be used as a precursory signature in the prediction of macrofracturing.