Experiments and simulations of a prototype triaxial electromagnetic induction logging tool for open-hole hydraulic fracture diagnostics

The monitoring and diagnostics of induced fractures are important for the real-time performance evaluation of hydraulic fracturing operations. Previous electromagnetic-based studies show that single backbone triaxial induction logging tools are promising candidates for real-time monitoring and diagnosis of fractures in noncased wells. With a fast-forward solver and reliable parametric inversion techniques, it may be possible to estimate many features of the propped fracture geometry (e.g., area, dip, conductivity) from the measured induced voltages. To support the development of field deployable tools, the concept must be tested in experiments, in a controllable environment, before it is tested under field-like conditions. To this end, we have designed and built a prototype induction tool and performed two sets of tests to compare with numerical simulation results. The experimental setup consists of triaxial transmitter and receiver coils in coaxial, coplanar, and cross-polarized configurations. Thin (highly conductive) metallic targets of various sizes, shapes, and orientations are used to emulate various fracture geometries. The laboratory and shallow earth measurements are shown to be in good agreement with simulations for all examined cases. The average relative and maximum discrepancies of the measured signals from the simulated ones are lower than 3% and 10%, respectively. With the prototype tool, strong signals sensitive to the fracture's surface area and dip are measured in a coaxial coil configuration, whereas weaker signals sensitive to the fracture's aspect ratio are observed in a coplanar configuration. Cross-polarized signals are also shown to be strong and sensitive to the fracture's dip. The results suggest that a tool of similar specifications can be used for the detection and extraction of the parameters of fractures propped with sufficiently electrically conductive proppant.