Application of electrical and electromagnetic geophysical methods for detecting hydraulically-active fractured zones
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Copyright 2016 ARMA, American Rock Mechanics Association. We perform coupled flow-geomechanics-electrical/electromagnetic (EM) modeling and examine the feasibility of surface-based electrical/EM methods for detecting hydraulically-active fractured zones in depth. We employ the finite element methods for geomechanics and electrical/EM modeling, while the finite volume method is used for flow modeling. After converting flow-geomechanics models to conductivity models via a rock physics relationship, we show that anomalous distribution of electrical conductivity is directly related to injected water saturation, implying that EM responses are directly sensitive to hydraulically-active fractured zones. In our modeling experiments, we inject saline water that has high concentration of NaCl, to enhance EM signals associated with the hydraulically-active fractured zones. By using a steel-cased injection well though which surface electrical sources directly charge saline-water-saturated fracture zones, we demonstrate that surface electrical/EM methods can identify the difference in the electric fields between with and without the hydraulic fracture. Thus, this measurable difference implies that the electrical and EM methods can be an important complementary tool to detect and image propagation of a large hydraulic fracture.
