17:15 〜 19:15
[SSS09-P05] Acoustic measurement of viscosity change in functional fluid
Efficient subsurface fluid resource development, including geothermal energy, requires precise control over invisible underground flow. Functional fluids, whose viscosity changes with shear rate, offer a potential solution by selectively opening or sealing complex flow pathways. If their behavior can be linked to geophysical observations, predicting their movement upon injection into reservoirs becomes feasible. This study aims to experimentally and theoretically link the behavior of functional fluids to seismic velocity changes, facilitating their real-world application.
Functional fluids are known to change their properties based on variations in particle packing density during shear. According to rock physics models, seismic wave velocity depends on material porosity. Since porosity in this context corresponds to the packing density of functional fluid particles, it is hypothesized that changes in packing density (i.e., viscosity variations) during shear can be detected through seismic velocity measurements. This study develops a method to measure seismic velocity changes due to functional fluid behavior within a reservoir-mimicking sample.
A simple flow channel model was designed, and initial flow blockage experiments using functional fluids were conducted in the laboratory. Simultaneously, seismic velocity measurements were performed. The preliminary results indicated that measurement frequency effects must be examined in detail based on the channel model's dimensions. Consequently, a smaller channel model was redesigned using a 3D printer, and multiple preliminary experiments were conducted in our laboratory to analyze the effects of measurement frequency.
A measurement system was first constructed for preliminary experiments. The pulse transmission method was employed, where the pulse input trigger was generated using a function generator (WF1974), and the transmitted waveforms were amplified via a preamplifier (NF9913) before being recorded by an oscilloscope (DLM5034). Seismic P-wave velocities were calculated based on the arrival time of the first pulse and the distance between the transmitter and receiver transducers. Fuji Ceramics transducers were used as sensors. The input pulse was a 10 V amplitude sine wave, and measurement frequencies were varied at 0.1, 1, 3, and 5 MHz. To enhance the signal-to-noise ratio (S/N), over 1000 waveform stacks were analyzed. Seismic waves were measured in three different conditions: (1) air-filled, (2) water-filled, and (3) standard viscous fluid-filled channels.
The results showed that as the fluid in the channel transitioned from air to water to a standard viscous fluid, the arrival time of transmitted waves decreased. This suggests that seismic wave velocity can detect changes in the viscosity state of the functional fluid. Analysis of P-wave velocities revealed the most significant variations at 5 MHz: 2960 m/s for air, 3370 m/s for water, and 3750 m/s for the standard viscous fluid. Furthermore, theoretical calculations using Voigt averaging indicated that solidified functional fluids could exhibit an additional 170% velocity increase.
To detect seismic velocity changes due to functional fluid solidification, we constructed a velocity measurement system capable of analyzing fluid substitution effects within a channel model. Frequency analysis showed that increasing fluid viscosity led to higher seismic velocities, with the most significant variations at 5 MHz. Voigt averaging calculations predicted a 170% velocity increase upon fluid solidification. Based on these findings, our next step is to experimentally measure seismic velocity changes when functional fluids solidify in a controlled environment. This research provides a fundamental step towards utilizing functional fluids for precise subsurface flow control in geothermal and other underground resource developments.
Functional fluids are known to change their properties based on variations in particle packing density during shear. According to rock physics models, seismic wave velocity depends on material porosity. Since porosity in this context corresponds to the packing density of functional fluid particles, it is hypothesized that changes in packing density (i.e., viscosity variations) during shear can be detected through seismic velocity measurements. This study develops a method to measure seismic velocity changes due to functional fluid behavior within a reservoir-mimicking sample.
A simple flow channel model was designed, and initial flow blockage experiments using functional fluids were conducted in the laboratory. Simultaneously, seismic velocity measurements were performed. The preliminary results indicated that measurement frequency effects must be examined in detail based on the channel model's dimensions. Consequently, a smaller channel model was redesigned using a 3D printer, and multiple preliminary experiments were conducted in our laboratory to analyze the effects of measurement frequency.
A measurement system was first constructed for preliminary experiments. The pulse transmission method was employed, where the pulse input trigger was generated using a function generator (WF1974), and the transmitted waveforms were amplified via a preamplifier (NF9913) before being recorded by an oscilloscope (DLM5034). Seismic P-wave velocities were calculated based on the arrival time of the first pulse and the distance between the transmitter and receiver transducers. Fuji Ceramics transducers were used as sensors. The input pulse was a 10 V amplitude sine wave, and measurement frequencies were varied at 0.1, 1, 3, and 5 MHz. To enhance the signal-to-noise ratio (S/N), over 1000 waveform stacks were analyzed. Seismic waves were measured in three different conditions: (1) air-filled, (2) water-filled, and (3) standard viscous fluid-filled channels.
The results showed that as the fluid in the channel transitioned from air to water to a standard viscous fluid, the arrival time of transmitted waves decreased. This suggests that seismic wave velocity can detect changes in the viscosity state of the functional fluid. Analysis of P-wave velocities revealed the most significant variations at 5 MHz: 2960 m/s for air, 3370 m/s for water, and 3750 m/s for the standard viscous fluid. Furthermore, theoretical calculations using Voigt averaging indicated that solidified functional fluids could exhibit an additional 170% velocity increase.
To detect seismic velocity changes due to functional fluid solidification, we constructed a velocity measurement system capable of analyzing fluid substitution effects within a channel model. Frequency analysis showed that increasing fluid viscosity led to higher seismic velocities, with the most significant variations at 5 MHz. Voigt averaging calculations predicted a 170% velocity increase upon fluid solidification. Based on these findings, our next step is to experimentally measure seismic velocity changes when functional fluids solidify in a controlled environment. This research provides a fundamental step towards utilizing functional fluids for precise subsurface flow control in geothermal and other underground resource developments.