Contact-resistance controlled electrical response of conductive-proppant-supported coal fractures for coalbed methane reservoir monitoring

Abstract

Conductive-proppant-assisted electrical monitoring provided a potential method for identifying the propped state of hydraulic fractures in coalbed methane reservoirs. To reduce the interference caused by natural coal heterogeneity, coal-like analog materials were prepared from coal powder, cement, gypsum, and graphene. The tests were performed under controlled fracture geometry and proppant-placement conditions. The effects of Fe 3 O 4 conductive proppant mass fraction, effective stress, fracture inclination, and fracture number on the resistivity response of propped fractures were investigated. The results showed that the specimen resistivity decreased nonlinearly as the Fe 3 O 4 mass fraction increased under a total proppant areal concentration of 0.5 kg/m 2 . Within the effective-stress range of 0–5.5 MPa, resistivity showed a rapid decrease followed by gradual stabilization. This indicated that stress reduced interfacial contact resistance mainly by increasing the real particle contact area and improving the stability of the conductive network. A larger fracture inclination may have improved current-path continuity. In contrast, more fractures dispersed conductive particles and accumulated interfaces when the total proppant amount was fixed. This increased the overall resistivity. Based on Holm contact-resistance theory, a semi-empirical normalized contact-resistance model was established. The model included proppant content, stress, and fracture-geometry factors. This study provided a physical basis for conductive-proppant-assisted identification of the propped state of hydraulic fractures in coalbed methane reservoirs.