Abstract
As an emerging geophysical exploration method, complex resistivity method is a potential non-invasive one for evaluating hydrofracturing effect. Reactance X is an important parameter of complex resistivity method. Compared with the traditional parameter resistance R, reactance has advantages such as distinct dispersion characteristics, clear conduction mechanism and rich information. In this paper, reactance X of four kinds of coal sample with different water saturation was tested, their dispersion characteristics were analyzed, and their conductive mechanism was studied. The results show that, (1) the characteristic curve of reactance dispersion presents a three-stage law when the water saturation is low, and a two-stage law when the water saturation is high,to some extent, the water content of coal body and the effect of hydraulic fracturing are distinguished;(2) polarization is the cause of dispersion, in which low frequency is induced polarization, high frequency is dielectric polarization, and electromagnetic induction is the interference phenomenon in the frequency band of induced polarization; (3) spectrum extremum frequency point is sensitive to changed water saturation. Extremum points of different coal rank are concentrated in 100-1000Hz. This frequency band can serve as the dominant frequency band for evaluating coal seam water saturation. This paper gives new insight into the evaluation of coal seam hydrofracturing effect by complex resistivity method.
Experimental Study on Characteristics of Reactance Dispersion of Water Bearing Coal