Hydraulic fracturing has been widely used to increase reservoir productivity in unconventional resources such as tight and shale oil/gas reservoirs. Estimating fracture geometry is important for optimizing development design, including the well allocation and completion. However, hydraulic fracturing is operated in the field at depths of 2,000 - 4,000 m below the surface, and direct observation is impossible. To address these challenges, we conducted a small-scale field experiment to visualize the spatial distribution and propagation characteristics of hydraulic fractures using coagulable fluorescence resin and analyzed the correlation with the distribution of Acoustic Emission (AE) hypocenters. A hydraulic fracturing experiment using the coagulable fluorescence resin (resin fracturing) was conducted against metamorphic bedrocks in the Kamioka mine, Japan, from 2022 to 2023. Following the resin fracturing in a 76 mm diameter vertical hole, a 205 mm diameter core was recovered through coaxial overcoring, aligned with the original resin-fracturing borehole. Then, the fractures filled with resin were visible on the surface of the recovered hollow core under black light (Takeuchi et al., 2025, Geosciences 15, 103). To investigate the feature of the extension of the fractures, six 205 mm diameter vertical cores were newly recovered continuously from the resin-fracturing hole towards the horizontal direction, where hydraulic fractures propagate based on the distribution of AE hypocenters in 2025. The vertical fractures with NE-SW trend created by resin fracturing were observed on the overcoring core. The extensions of NE-SW vertical fractures were also confirmed on the two cores drilled adjacent to the resin-fracturing hole. It was revealed that the vertical fracture did not reach the further northeastern region, where the AE hypocenters were not distributed. On the other hand, we observed the resin-filled fractures in the eastern region, where AE hypocenters were concentrated. Low dip angle fractures formed at a depth of 2.8 m, shallower than the injected section of resin fracturing at a depth of 3.3 m, were confirmed by the fluorescent resin filling. The extensions of these low dip angle fractures were confirmed by the presence of fluorescent resin seen in two cores drilled at the eastern area from the resin-fracturing hole, where AE hypocenters were intensively distributed. Our experiment of resin fracturing in the Kamioka mine successfully distinguished the fractures generated by hydraulic fracturing from the existing natural fractures. We revealed that the distribution of AE hypocenters around the resin-fracturing hole corresponds to the formation of vertical fractures. We also found that AE didn't always occur when resin filled pre-existing geological weak surfaces. However, AE was observed intensively in certain regions, such as the eastern area. This analogue study will contribute to improving the accuracy of hydraulic fracture evaluation using AE monitoring, that is, microsiesmic monitoring in field application.
This paper presents a numerical study of multimode evanescent-wave fiber sensors for midinfrared detection of H2O–CO2 mixture response over 1–6 ìm wavelengths. The wavelength-dependent effective absorption coefficient and the corresponding normalized transmission are computed using complex refractive indices of the surrounding analytes for a high-numerical-aperture chalcogenide fiber baseline. We show, for the first time, that tapering deepens the transmission minimum at the characteristic ~3.0 μm (H2O) and ~4.26 μm (CO2) wavelengths while maintaining the separability of both signatures in the mixture spectrum. In addition, reducing the waist radius strengthens absorption at both bands. Specifically, decreasing the waist radius from 150 to 110 μm yields at least a fourfold increase in the peak effective absorption near ~3.0 μm and ~4.26 μm. To assess thermal effects, temperature-dependent simulations were performed for water only. The effective absorption peak near the water bands at ~3.0 and ~4.7 μm decreased as temperature increased from approximately -2 to 38 °C. Finally, a room-temperature fluoride fiber measurement was used as experimental reference and reproduced the dominant water-induced dip near ~3.0 μm, with a weaker feature near ~4.7 μm, being consistent with the modeled spectral locations.
Using box-type pilot-scale bioreactors installed at an abandoned mine site, we investigated the influence of pH, hydraulic retention time (HRT), and ethanol concentration on reactor performance and microbial community during acid mine drainage (AMD) treatment. Bioreactors with 25 h of HRT that were fed 1.04 mM of ethanol at both pH near-neutral and acidic conditions showed sulfate reduction, predominantly by Desulfosporosius- and Desulfovibrio-related sulfate-reducing bacteria (SRB), that decreased zinc concentrations to less than the Japanese national effluent standard. Under acidic conditions at 12.5 h HRT, the bioreactor showed reducing conditions and effective treatment with a high dominance of Desulfosporosius-related SRB (relative abundance: more than 25
