Fig. 2
From: Laboratory investigation of coupled electrical interaction of fracturing rock with gases
a Current signals for combination of quartz diorite/CO2 at ~ 25 °C with electrode bias of + 77 V and S = 1.6 × 10–4 m2, where black curve is the signal at the gas current electrodes, orange curve is the signal at the reference electrode, and light grey curve is the vibration signal; b electric currents for combination of quartz diorite/CO2 at ~ 25 °C with electrode bias of ± 77 V (left) and electric currents for combination of gabbro/CO2 at ~ 160 °C with electrode bias of ± 77 V and without bias (0 V) (right) (in all tests, S = 1.2 × 10–4 m2), where blue curves are at electrode bias of − 77 V, orange ones are at + 77 V and grey one is at 0 V; c electric currents for combination of gabbro/CH4 at ~ 160 °C without electrode bias at S = 1.2 × 10–4 m2 and S = 2.4 × 10–4 m2; d electric currents for combination of gabbro/CO2 at ~ 25 °C and ~ 160 °C (two signals for each temperature overlap because two tests were performed at each temperature to check the reproducibility) and e electric signals for combination of gabbro/CO2, water vapour, N2, and CH4 at ~ 160 °C and combination of basalt/N2 at ~ 160 °C. Arrows in a–e show the final rupture point when the gas started to flow in the crack gap. f Relationship between the peak current Ip and rock/gas interaction area S for the various test conditions listed in the plot legend. The data for quartz diorite/CO2 for + 77 V and ~ 25 °C were taken from one author’s previous work (Enomoto et al. 2017). The dotted line in f is an approximated relation: Ip (μA) = 1069 × S (m2), where the coefficient of determination is R2 = 0.83