The Study Of The Technology Of The Two-dimensional Ultrasonic Imaging Of Hydrate Bearing Unconsolidated Sediments

Natural gas hydrate is a kind of new efficient and clean energy that has attracted more and more attention of the world.Due to the unique advantages of ultrasonic,to study the acoustic characteristics of natural gas hydrate becomes a kind of effective means for the geophysical exploration of natural gas hydrate.In this paper,we introduced tomography technology into the acoustic test,dynamically measured the hydrate formation conditions by the bend elements technology,and obtained the two-dimensional acoustic velocity profile distribution images of hydrate formation in loose sediments.Combined with the hydrate saturation data obtained by time domain reflection technology,we analyzed the changes of the two-dimensional sound velocity profile of sedimentary layer in the process of hydrate formation.This method could provide some basic geophysical parameters for the hydrate reservoir exploration and resource evaluation.In this paper,we used the finite element analysis technology,analyzed the wave propagation in sedimentary layers,and discharged the influence of phenomena like polarization to received signals.We discussed the application of the traditional FIR filter and the new adaptive filter,designed the adaptive noise canceller to eliminate the signal noise,and obtained the information of the first wave of acoustic wave using the FFT-WT method.At the same time,we calibrated the bender element testing probes and time domain reflectometry probes,implementing pre-processing of experimental data.In this paper,we used the straight ray tracing method to construct the travel time and ray path,realizing the forward modeling of ultrasonic tomography.We used the iterative reconstruction method based on improved SIRT algorithm to realize the inversion of ultrasonic tomography,and we reconstructed the two-dimensional acoustic profile images of hydrate bearing unconsolidated sediments.Experimental results showed that the two-dimensional sound velocity profile structures of hydrate bearing sediments obtained by using ultrasonic tomography technology could accurately reflect the distribution of hydrate in sediments at different time and saturation,and P-wave velocity profile structures fit in well with S-wave velocity profile structures.Besides,with the experimental data,several velocity models were used to validate the relationship between the sonic velocity and the saturation of hydrate.