Experimental Study of Sensitivity of Multifrequency (MF) Dielectric Measurements to Hydraulic Fractures in Sandstone and Carbonate Formations

Multifrequency (MF) dielectric is one of the most powerful petrophysical techniques for determining water saturation. It can also be used to study the formation structure and characterize natural or induced fractures. Most of the previous studies in this area have focused on numerical models or synthetic systems. This study presents an experimental investigation into the sensitivity of MF dielectric measurements to fracture presence,orientation, and proximity in sandstone and carbonate formations under dry and brine-saturated conditions. In this study, the rock samples were subjected to routine core analysis to determine porosity, permeability, and mineralogy. Also, nuclear magnetic resonance (NMR)was employed to assess the pore systems and porosity distribution. Thereafter, an open-ended coaxial dielectric probe was used to measure relative permittivity and electrical conductivity before and after inducing hydraulic fractures. The dielectric probe operates at frequencies between 1 MHz and 3 GHz, and fractures were induced and controlled in vertical and horizontal orientations. Measurements were taken at various distances from the fracture (near and far) and under dry and brine-saturated states using 3 wt% KCl brine. The results demonstrate that dielectric dispersion is highly sensitive to fracture presence and geometry. The permittivity was increased by 22 units on average, from around 45 (dimensionless)to more than 60 for carbonate rocks, while the increase varied between 15 and 35 units for sandstone rocks. Also, measurements taken near the fracture showed higher dielectric responses due to enhanced fluid connectivity and polarization effects close to the fracture points. Moreover, the conductivity increased by approximately 12 to 34% in the fractured carbonate and sandstone samples, espectively. The fracture orientation showed a notable impact, with vertical fractures producing relatively higher conductivity and permittivity compared to horizontal fractures. In contrast, NMR was unable to distinguish fracture orientation due to its bulk measurement nature. This study demonstrates the sensitivity of MF dielectric measurements to hydraulically induced fractures. The dielectric approach enhances the resolution of fracture orientation, connectivity, and localization, with significant implications for both conventional and unconventional reservoir development.