An Experimental Study on rock properties through the change of velocity measurement of high porosity in red sandstone

Abstract:

The main research focus is to understand the effect of deformation on rock properties through the change of velocity measurement of high porosity in red sandstone. We have carried out the numerical simulation and laboratory experiments. We studied pulse compression of numerical simulation, which is based on the basic coded excitation principle. From the simulation results, in order to achieve the best effect to pulse compression of incentive transducer, cycle number of carrier frequencies of unit code element need to be chosen according to close degree of the specific signal band width and bandwidth transducer. For single frequency characteristics of piezoelectric ceramic transducer, we have compared to the performance of various transducers in our lab. When the transducer matching combines with coded excitation signal matching, experimental system platform of coded excitation was established. In this project, we analyzed the influence on different excitation signal with different modulation and its pulse compression result by transducer.

To improve the resolution of detection of changes of wave velocity in rocks and solve the problem of attenuation in high porous rocks, different high porosity of red sandstones were used, which were processed into different size of rock samples. Coded excitation under uniaxial loading of rock experiments were used to test the variation of wave velocity in rock media under coded excitation conditions. This research detected the changes of wave velocity with the single pulse and coded excitation signal in rocks during dynamic loading, and the result shown that wave velocity of coded excitation signal was stable and reliable. With the ultrasound imaging experimental system set before, imaging experiments under uniaxial loading were performed on rock samples. In the loading process, four transmission methods of observation were used in the rock sample. Four sides of rock sample were respectively arranged a plurality of transducer and the ultrasonic signal was collected. By reading the P wave travel time, we reconstructed velocity and ultrasonic P wave velocity tomography. By comparing the P wave velocity from four different stresses, the result indicated the velocity variation with stress increase, showing a P wave velocity variation tendency of the localization.