Debugging And Experiments Of Low Frequency Rock Physics Measurement System

Petrophysics is a new subject composed of traditional petrophysics and seismic exploration.It provides an important basis for seismic interpretation technology from qualitative to quantitative,single rock physical model to a variety of complex rock physical models.In order to make the results of petrophysical data measured in the laboratory used to guide the seismic exploration,it is necessary to measure the seismic elastic characteristics in a specific frequency band,especially the petrophysical data measured in the laboratory within the seismic frequency band.In this paper,a low-frequency rock physics measurement system using stress-strain method is debugged.The system can simulate the complex situation of core under confining pressure,temperature and fluid,and it is a micro-scale laboratory application.This system has complex structure,including core low frequency oscillator,pressure control and fluid displacement system,signal excitation and signal acquisition and processing system,etc.It covers electronics,machinery,computer software programming and other disciplines.The core module was debugged and several improvements were made to improve the quality and reliability of the data.Then,the effects of porosity,permeability,water saturation,confining pressure and frequency on the elastic properties of core are studied by using pulse transmission technology and low frequency rock physics measurement technology.Based on the analysis of rock physical model,it is shown that confining pressure,water saturation and frequency have great influence on the elastic properties of rock.On the one hand,it is caused by the micro-pore structure of rock,on the other hand,it is caused by pore fluid.The relationship between P-wave and S-wave velocity and saturation is complex.In high frequency band,P-wave velocity increases with the increase of saturation;in low frequency band,there exists a critical saturation,which is lower than the critical saturation,and P-wave velocity decreases with the increase of saturation;above the critical saturation,P-wave velocity increases with the increase of saturation,which indicates that the critical saturation is related to frequency.The higher the effective pressure is,the closer the pore is and the greater the velocity is.The higher the fluidity of pore fluid is,the higher the frequency of dispersion characteristic band is;the frequency of dispersion characteristic band is positively correlated with permeability and negatively correlated with the viscosity of pore fluid.