Fracture detection and characterization are challenging aspects of completion plans for unconventional tight carbonate and shale reservoirs. Current industry methods, such as high resolution resistivity imaging, mitigate uncertainties in fracture characterization, but are not cost effective or always available. Conventional well logs (e.g., induction logs) can be better solutions for the industry for reliable fracture characterization. However, these measurements do not provide significant sensitivity to fracture location and geometry. An improved evaluation of thickness and near-wellbore geometry of induced fractures using conventional well logging tools could significantly enhance operational decisions and increase production during field development.
We propose the use of surface gas readings and downhole measurements in combination with numerical simulations of electromagnetic induction log responses to define and high-grade natural fracture corridors. We performed numerical simulations to model the effects of hydraulic fractures on induction log response, within the fractured zones. These simulations consisted of placing resistive fractures, with variable parameters, inside a layered formation, and modeling the apparent resistivity using an induction logging simulator. The fractured zones were represented using a geologic roughening parameter, β, while the simulator is based on the finite element method. The simulator, Seatem, solves the diffusive Maxwell equations, and plots the resulting apparent resistivity distributions within an unstructured tetrahedral mesh. This provides us with a good understanding of how the targeted zone interacts with different stimulation factors.
We successfully performed numerical simulations along a multi-zoned reservoir interval for three synthetic cases: a sandstone formation, a carbonate formation, and an organic shale formation. We quantified the effects of hydraulic fracturing on induction logs and optimized placement of fracture treatments on synthetic cases. The results of this paper indicate fractured zones with beta values larger than 0.3, viable for fracture corridor depletion and geologic targeting, can be identified from induction log responses.