3d Simulation of Seismic Wave Propagation in Fractured Media Using an Integral Method Accommodating Irregular Geometries

Fractures play an important role in most carbonate and unconventional reservoirs. Precise identification of fractures and their associated properties from seismic data have significant impact on reservoir management and hydrocarbon recovery. Traditional seismic methods for fracture identification and characterization, such as shear birefringence and amplitude variations with offset and azimuth, are based on equivalent medium theory with the assumption that fracture dimensions and spacing are small relative to the seismic wavelength. Hence, the overall population of fractures is equivalent to a homogeneous anisotropic medium. Large fractures with spacing on the order of the seismic wavelength are more interesting because they are crucial for enhanced oil recovery, and they scatter seismic waves. Instead of equivalent medium theory, characterizing discrete fractures based on seismic modeling and scattered seismic energy can aid in the understanding of wave patterns observed on seismograms and can provide crucial guidance for seismic interpretation. We model seismic wave propagation in a fractured medium using an integral method with tetrahedral grid cells. The integral approach is derived from the finite element and finite difference methods in heterogeneous media. It is flexible in modeling irregular interface and surface topography. It also has low computational cost and memory requirements, which is essential in 3D simulation. The fractures are explicitly treated as interfaces with displacement discontinuity using linear slip model. We implemented the 3D explicit interface scheme on an irregular mesh. Arbitrary fractures can be accurately modeled in the numerical discretization. This approach can provide detailed wave propagation phenomena resulting from spatially heterogeneous fractures. Comparisons of seismic signatures induced by various fracture length, fracture spacing, and fracture density show obvious differences in terms of scattering patterns. Shot records acquired parallel and normal to fractures. The model used is a 3D model contains three layers. The first and the third layers are isotropic and homogeneous. The second layer is inserted with 2D vertical fractures. The fracture density in the second layer varies laterally.