It has been demonstrated in both numerical modeling and lab experiments that a fluid-filled fracture can be a subsurface pressure amplifier to a weak driving force such as an incident seismic wave. We refer this phenomenon to as the transient pressure surge (PS) effect. PS is frequency dependent and can be a very useful for enhancing fracture systems because it may transiently enhance pore pressure and alter fluid flow patterns. In this paper, we use PS to infer fluid-filled fracture parameters. We develop a three-dimensional boundary element (BEM) method to study the seismic/geomechanical response of fluid-filled fractures with different sizes and apertures. We first review the previous modeling and lab evidence of the PS phenomenon and then present our new BEM modeling results. The PS effect could be used for imaging subsurface fracture systems and inverting for discrete fracture parameters for fracture characterization.
Knowing locations and geometries of discrete fractures is crucial for reservoir modeling and production prediction in both unconventional oil/gas and enhanced geothermal systems. Here we distinguish between individual fractures and statistic parameters for a group of fractures. For the latter case, many approaches have been developed to indirectly infer fracture parameters in fractured media. When the scale of a microfracture network is much smaller than the seismic wavelength, the rock matrix within the fracture network can be treated as an effective anisotropic medium. Amplitude variation with offset and azimuth (AVOAz) can then be used to characterize the velocity anisotropy and fracture orientation (Far et al., 2014). When the scale of a fracture network is comparable to the seismic wavelength, seismic- wave scattering-based methods can be used to determine the fracture orientation, spacing, and compliance (Willis et al., 2006; Zheng et al., 2013; Kang et al., 2016; Hu et al., 2018). Sonic waves of kHz recorded in boreholes can also be used to image the fracture (Cheng et al., 1995; Kostek et al., 1998a; Kostek et al., 1998b; Bokov and Ionov, 2002; Henry, 2004; Bakku et al., 2013; Minato and Ghose, 2017).
