Theoretical studies of the geophone coupling influence in the bare carbonate rock area

Abstract

Extremely abundant oil and gas resources in the sedimentary basins of marine carbonate which are of vast areas exist in South China. However, it is very difficult to make a wonderful geophone coupling with the outcrop of hard limestone. And then the qualities of the seismic data are reduced. Now, geophone coupling test is of great blindness 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, I bring forward the theory of geophonelimestone 3-DOF (degree of freedom) coupling system based on vibration dynamic concept. The geophonelimestone coupling system responses are computed when the parameters of coupling medium, geophone spikes and damping are changed. And we find that the geophonelimestone 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 and reducing the height of the spike. 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 preliminary validate the theoretical results of the geophone-limestone 3-DOF coupling system using shake table experiments.