<p>In this study, we investigated the source parameters of microseismicity detected during laboratory hydraulic fracturing (HF) of granite conducted with high- (gear oil/1000 cP) and low- (water/1 cP) viscosity injection fluids. These HF experiments were monitored with real-time acoustic emission (AE) setup which consisted of 16 calibrated sensors. The spectral parameters (corner-frequency and low-frequency spectral plateau) were determined for each AE event by fitting Omega-models with variable high-frequency fall-off exponents to the detected AE signals. Seismic parameters such as seismic moment, source radius, stress drop, and seismic energy were determined after incorporating the focal-mechanism information determined through moment-tensor inversion. Higher breakdown pressures and fracture propagation times along with greater number and strength of microseismicity were observed for experiment conducted with higher-viscosity fluid. For both experiments, an inverse relationship was observed between corner frequency and seismic moment, similar to those observed for large-scale induced-earthquakes. The corner-frequency, seismic moment, stress drop, and seismic energy were noticeably higher for the higher-viscosity injection fluid. However, the seismic source radius was slightly larger for the lower-viscosity fluid. Varied spectral and seismic parameters (16–29%) were obtained based on the adopted Omega model; however, these variations did not affect the observed relationships between seismic parameters in high- and low-viscosity experiments. The seismic efficiency was << 1% (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40948_2025_948_Article_IEq1.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="99" /> </InlineMediaObject> <EquationSource Format="TEX">${10}^{-6}-{10}^{-4}\%$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>-</mo> <mn>6</mn> </mrow> </msup> <mo>-</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>-</mo> <mn>4</mn> </mrow> </msup> <mo>%</mo> </mrow> </math></EquationSource> </InlineEquation>) for both experiments but it was much lower for experiment conducted with lower-viscosity injection fluid, implying a more pronounced aseismic response. Comparing the seismic source parameters determined in this study with those derived from large-scale induced earthquakes suggests potentially similar scaling relationships.</p>

Energy budgeting of laboratory hydraulic fracturing in granite with different viscosity injection fluids

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2025年7月2日

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A. Butt,
A. Hedayat,
O. Moradian

摘要

In this study, we investigated the source parameters of microseismicity detected during laboratory hydraulic fracturing (HF) of granite conducted with high- (gear oil/1000 cP) and low- (water/1 cP) viscosity injection fluids. These HF experiments were monitored with real-time acoustic emission (AE) setup which consisted of 16 calibrated sensors. The spectral parameters (corner-frequency and low-frequency spectral plateau) were determined for each AE event by fitting Omega-models with variable high-frequency fall-off exponents to the detected AE signals. Seismic parameters such as seismic moment, source radius, stress drop, and seismic energy were determined after incorporating the focal-mechanism information determined through moment-tensor inversion. Higher breakdown pressures and fracture propagation times along with greater number and strength of microseismicity were observed for experiment conducted with higher-viscosity fluid. For both experiments, an inverse relationship was observed between corner frequency and seismic moment, similar to those observed for large-scale induced-earthquakes. The corner-frequency, seismic moment, stress drop, and seismic energy were noticeably higher for the higher-viscosity injection fluid. However, the seismic source radius was slightly larger for the lower-viscosity fluid. Varied spectral and seismic parameters (16–29%) were obtained based on the adopted Omega model; however, these variations did not affect the observed relationships between seismic parameters in high- and low-viscosity experiments. The seismic efficiency was << 1% ( ${10}^{-6}-{10}^{-4}\%$ $10^{- 6} - 10^{- 4} %$ ) for both experiments but it was much lower for experiment conducted with lower-viscosity injection fluid, implying a more pronounced aseismic response. Comparing the seismic source parameters determined in this study with those derived from large-scale induced earthquakes suggests potentially similar scaling relationships.