Integrated simulation of vertical fracture propagation induced by water injection and its borehole electromagnetic responses in shale gas systems

Abstract

We analyze fracture propagation induced by hydraulic fracturing with water injection and examine their detectability with crosswell electromagnetic (EM) geophysical methods. For rigorous 3D coupled flow-geomechanical modeling, we employ a numerical method that can model failure by tensile and shear stresses, dynamic nonlinear permeability, dual continuum approach, and thermo-poro-mechanical effects. From numerical simulation, we find that the fracture propagation is not the same as propagation of the water front, because fracturing is governed by geomechanics whereas water saturation is determined by multiphase flow. At early times, the water front is almost identical to the fracture tip, suggesting that the fracture is mostly filled with the injected water. However, at late times, movement of the water front is retarded compared to fracture propagation, yielding a significant gap between the water front and the fracture top, filled with reservoir gas. During fracture propagation, the coupled flow-geomechnical models are transformed via a rock-physics model into electrical conductivity models. We employ a full 3D finite-element EM geophysical simulator to evaluate the sensitivity of the crosswell EM method to fracture propagation. It is shown that anomalous distribution of electrical conductivity is closely related to the injected water saturation, but not closely related to newly created unsaturated fractures. Our numerical modeling experiments demonstrate that the crosswell EM method can be highly sensitive to electrical conductivity changes that directly indicate the migration pathways of the injected fluid. Accordingly, the EM method can serve as an effective monitoring tool for monitoring the injected fluids during hydraulic fracturing operations.

A New Modeling Framework for Multi-Scale Simulation of Hydraulic Fracturing and Production from Unconventional Reservoirs

“…An example of the TOUGH+ mesh before and after coupling the GEOS aperture is shown in Figure 2. (6) As the pressures and stresses change in the course of production, the macro-scale properties of the matrix (porosity and permeability) are continuously adjusted using either the simplified of the full geomechanical capabilities built into TOUGH+ [5,35,36]. (7) Property changes due to micro-scale processes with fractures and at the fracturematrix interfaces are incorporated based on the imaging, testing, and modeling work described in Section 5.…”

Integration of Electromagnetic Geophysics Forward Simulation in Coupled Flow and Geomechanics for Monitoring a Gas Hydrate Deposit Located in the Ulleung Basin, East Sea, Korea

“…Particularly for the gas hydrate exploration, dense hydrates are found to have direct relations to the amount of electrical resistivity [9][10][11]. Moreover, the EM geophysical method has the potential to complement the (micro-)seismic methods to detect subsurface geometry or dynamics (e.g., fracture propagation) [12], because they are highly sensitive to fluids in pores and fractures and can provide independent information about fluid flow coupled with geomechanics [13,14].…”

“…Regarding the EM simulation that follows, we employ the diffusion model [14,25] to calculate the electric field. Hydrological and petrophysical parameters (i.e., change in saturations of fluids and in pore volume while gas is extracted from the hydrates) computed by the coupled flow-geomechanical simulation are first transformed into electrical conductivity via Archie's law based on the rock physics model.…”

Research on cross‐well pseudorandom electromagnetic detection method and extraction of response characteristics

“…As an important means of geophysical survey, the cross-well electromagnetic method can be used to detect the distribution of remaining oil and find oil and gas enrichment zones, to improve the success rate of drilling and enhance recovery efficiency. [1][2][3][4] In the past 20 years, cross-well detection technology has gradually developed into two kinds of detection methods with different physical mechanisms: cross-well seismic and cross-well electromagnetic detection. [5][6][7][8][9] The results show that, compared with the cross-well seismic method, the cross-well electromagnetic detection method is more sensitive to the changes in cross-well formation characteristics and fluid properties, and can directly provide the resistivity distribution information describe the reservoir cross-well fluid spatial distribution.…”

“…As an important means of geophysical survey, the cross‐well electromagnetic method can be used to detect the distribution of remaining oil and find oil and gas enrichment zones, to improve the success rate of drilling and enhance recovery efficiency 1‐4 . In the past 20 years, cross‐well detection technology has gradually developed into two kinds of detection methods with different physical mechanisms: cross‐well seismic and cross‐well electromagnetic detection 5‐9 .…”