| CPC G01N 29/07 (2013.01) [G01N 29/14 (2013.01); G01N 29/2437 (2013.01); G01N 33/24 (2013.01); G01N 2291/011 (2013.01); G01N 2291/023 (2013.01); G01N 2291/0289 (2013.01); G01N 2291/106 (2013.01)] | 10 Claims |
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1. A method for monitoring structural deterioration of a reservoir rock mass under a long-time high-temperature condition, comprising:
arranging ultrasonic transducers and fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors oppositely in a loading briquette, wherein the fiber optic EFPI sensors each are in contact with a rock mass sample in the loading briquette through a sensor channel in the loading briquette; the ultrasonic transducers comprise longitudinal (P)-wave ultrasonic transducers and transverse(S) ultrasonic transducers; and the P-wave ultrasonic transducer and the S-wave ultrasonic transducer are arranged in a same direction of the loading briquette;
loading ultrasonic waves on the rock mass sample with the ultrasonic transducers;
monitoring ultrasonic and acoustic emission signals at the rock mass sample with the fiber optic EFPI sensors;
inverting, by fast marching acoustic emission tomography using standard optimization (FaATSO) and according to the ultrasonic and acoustic emission signals, a velocity model indicating a change of a wave velocity inside the rock mass sample over time; and
conducting joint inversion by a fast-marching method according to the velocity model, the acoustic emission signals, and observation data to determine a position of rock mass fracturing in the rock mass sample, wherein the observation data comprises coordinates of the fiber optic EFPI sensors and an active/passive arrival time;
wherein the conducting joint inversion by a fast-marching method according to the velocity model, the acoustic emission signals, and observation data to determine a position of rock mass fracturing in the rock mass sample specifically comprises:
conducting the joint inversion by the fast-marching method according to the velocity model, the acoustic emission signals, and the observation data to determine a theoretical arrival time;
determining an arrival time residual between the theoretical arrival time and a signal arrival time obtained according to the ultrasonic and acoustic emission signals, and determining a minimum arrival time residual within a detection range, wherein the minimum arrival time residual refers to the position of the rock mass fracturing in the rock mass sample;
determining whether the minimum arrival time residual meets an error;
if the minimum arrival time residual meets the error, taking the position of the rock mass fracturing in the rock mass sample determined after the active and passive joint inversion; and
if the minimum arrival time residual does not meet the error, inverting the velocity model by a quasi-Newton method in combination with the minimum arrival time residual, and with an inverted velocity model instead of the current velocity model, repeating the step of conducting the joint inversion by the fast-marching method according to the velocity model, the acoustic emission signals, and the observation data to determine a theoretical arrival time until a final minimum arrival time residual meets the error, wherein
a vibration demodulation technology with a sampled-grating distributed-Bragg-reflector tunable laser as a light source is adopted; the sampled-grating distributed-Bragg-reflector tunable laser emits a scanning laser beam with a fixed step size according to signal requirements of a control module, and the scanning laser beam is modulated by a laser output module and then enters a fiber optic splitter; the control module of the sampled-grating distributed-Bragg-reflector tunable laser sends a pulse signal to a counting output module while sending a control signal, and the counting output module outputs a counting signal to a sampling circuit after receiving the pulse signal; after receiving a laser beam output by the sampled-grating distributed-Bragg-reflector tunable laser, the fiber optic splitter divides the laser beam output by the sampled-grating distributed-Bragg-reflector tunable laser into laser beams for n channels, the laser beams for n channels enter three-port fiber optic couplers of the n channels, respectively, and the three-port fiber optic couplers output the laser beams for n channels to the corresponding fiber optic EFPI sensors; when a vibration signal acts on a diaphragm of a sensor, a length of a Fabry-Perot (FP) cavity changes to generate an interference spectrum; a reflected laser beam is returned along the original optical path and enters a corresponding photodetector through a fiber optic coupler, and the photodetector converts a received reflected laser beam into an electrical signal and inputs the electrical signal into an amplification circuit; the amplification circuit amplifies the received electrical signal and outputs an amplified electrical signal to the sampling circuit, and the sampling circuit conducts data sampling for the amplified electrical signal with the counting signal; sampling data is transmitted to the communication module to allow information transmission with a monitoring host, and software of the monitoring host conducts restoration of a waveform spectrum through computing; the ultrasonic and acoustic emission signals are restored through a vibration signal of an environment in which a sensor reflecting a waveform spectrum is located.
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