A Theoretical Study on the 3‐Degree Freedom Geophone Coupling System for Areas with Limestone Outcrops

Abstract

AbstractThere is a great potential of extremely abundant oil and gas resources in sedimentary basins of marine carbonate in vast areas of South China. However, it is very difficult to make a good geophone coupling in the field work because of large‐area outcrops of hard limestone, which lead to decline of quality of seismic data and serious limit on hydrocarbon exploration there. Now, geophone coupling test is largely blind due to lack of appropriate theoretical guidance. In this paper, in order to understand the transmission mechanism of the geophone‐limestone coupling system, considering that the coupling media such as gesso, clay and so on involved in field seismic data acquisition, we propose a theory of geophone‐limestone 3‐DOF (degrees of freedom) coupling system based on the vibration dynamic concept. The geophone‐limestone coupling system responses are computed with varying parameters of coupling media, geophone spikes and damping. 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, reducing 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 model of the geophone‐limestone 3‐DOF coupling system through experiments on a shake table.