Imaging three-dimensional hydraulic fractures in horizontal wells using functionally-graded electromagnetic contrasting proppants

Hydraulic fracturing has been the main completion technique to enhance production from unconventional shale reservoirs. Determination of the hydraulic fracture geometry is of great significance to obtain a reliable assessment of the treatment, production prediction, and validation of fracture models. In this study, we investigate the idea of using an electromagnetic induction logging tool to diagnose hydraulic fractures using functionally-graded conductive proppants as contrasting agents to enhance the tool response. A finite element method is utilized to solve Maxwell's equations to simulate the impact of different hydraulic fracture geometries on the tool response. To minimize the application of special type of proppant and better estimate fracture length, we propose using a functionally-graded configuration for proppant placement, in which the density of proppant particles can be adjusted by tuning the volume of the inner void space to assure about their placement locations. Hence, fractures are imaged by detecting the distribution of highly conductive particles around fracture edges. The tool consists of a transmitter and a set of receiver coils that measure the time-harmonic electric and magnetic fields as the logger sonde travels along the wellbore. Different transmitter-receiver spacings of induction tools are considered to obtain optimal parameters that can be used for field operations. Results show it is possible to qualitatively use the tool to determine length, and width of hydraulic fractures. Utilization of special placement of conductive particles at the top and bottom fractures gives a stronger relationship of tool responses to hydraulic fracture geometries. Relationships of logging results for different hydraulic fracture geometries, as well as electromagnetic properties, are established. Results also show the tool can identify fractures' length up to 200 ft long in horizontal wells. A larger transmitter-receiver spacing of 16 m gives a deep reading for fractures with larger length. A smaller transmitter-receiver spacing of 1.2 m enables more accurate determination of the location of hydraulic fractures along the wellbore.