Experimental study of relationship among acoustic wave, resistivity and fluid saturation in coalbed methane reservoir

Experimental study of logging petrophysical parameters is very important for the establishment of logging evaluation model of coalbed methane reservoir. The acoustic and resistivity measurements of coal rock samples taken from the southern Qinshui Basin in China were measured under dry and saturated conditions of different salinity solutions. The variation laws of acoustic velocity and waveform with saturated salinity were analyzed. The changes of resistivity with temperature and pressure conditions were also analyzed. With the increase in salinity, acoustic velocity showed parabolic attenuation characteristics. The fluid content of coal samples can be judged by the acoustic wave. The waveform of dry coal sample presented multiple excitation state, and the waveform had larger fluctuation and smaller amplitude. The waveform of saturated salinity coal sample presented stable and smooth fluctuation characteristics. The resistivity of coal rock decreased exponentially with the increase in pressure. The property of fluid in pores can be judged by the sensitivity of resistivity of coal rock to temperature.