Finite-Element Forward Modeling of Electromagnetic Response of Hydraulic Fractures in Layered Medium

For better understanding of response characteristics of electromagnetic logging instruments in fractures in multi-layer medium, based on the low-frequency electromagnetic field theory, fracture models of a single-layer medium formation and a five-layer medium formation were built with finite-element software, respectively. On this basis, forward modeling of the induced electromotive force in the receiving coil in hydraulic fractures in the layered medium was carried out. The results showed that the induced electromotive force curve changed significantly at the fracture position. When the fracture is symmetrical and the angle between the fracture and the borehole is from 25° to 90°, the smaller the angle, the more tortuous the fracture response signal, which was exactly opposite to the case when the angle was between 90° and 155°. If the fracture was asymmetrical, the larger the widening angle, the more obvious the asymmetry of fracture response signal under the condition of multi-layer medium when the widening angle was in the range of 30–150°. The research shows that a multi-layer medium has influence on the fracture response curve, and the research results provide a theoretical basis for the detection and evaluation of hydraulic fractures in horizontal wells.