Theoretical studies of the geophone coupling influence in the limestone outcrops area
灰岩裸露区检波器三自由度耦合系统理论的研究

There are extremely abundant oil and gas resources in the sedimentary basins of marine carbonate in vast areas of South China. However, it is very difficult to make a good geophone coupling with the outcrop of hard limestone. And then the qualities of the seismic data are reduced. Now, geophone coupling test is largely blind due to lack of appropriate theoretical guidance. In this paper, in order to understand fully the transmission mechanism of the geophone-limestone coupling system, considering that the coupling mediums such as gesso, clay and so on are used in field seismic data acquisition, we bring forward the theory of geophone-limestone 3-DOF (degree of freedom) coupling system based on vibration dynamic concept. The geophone-limestone coupling system responses are computed when the parameters of coupling medium, geophone spikes and damping are changed. And we find that the geophone-limestone coupling system is a resonance system which has three resonance frequencies. The results show that the resonance frequency can be increased through increasing the elastic modulus of the coupling medium, decreasing the area of the underside and the height of the coupling medium, using spikes with lower material density, reducing the height of the spike and increasing the area of the spike′s underside. The results also show that the impact of the narrow frequency bands “band pass filtering” can be decreased by increasing the damping of the coupling system properly. Finally, we preliminarily validate the theoretical results of the geophone-limestone 3-DOF coupling system using shake table experiments.