Seismic Imaging And Characterization Of Fractured Oil Reservoirs By Focusing Gaussian Beams

Most of global oil is from carbonate reservoirs and fractures of different length scales are ubiquitous in such reservoirs. Presence of natural fractures creates major problems for oil production since fractures can influence fluid flow. A prior knowledge about fractures, their orientation, spatial density, fracture compliances, and geometrical connectivity is essential for stimulation and enhanced oil recovery. An existing fracture scaling relation shows that large fractures (10s of m) are more compliant than smaller ones. We have developed a new method, which can invert for spatially dependent fracture orientation, spacing/density, and compliance using surface seismic data in exploration acquisition. In contrast to most methods that use singly scattered waves by fractures, our method uses multiply scattered waves between fractures. The direction information of the fracture multiply scattered waves contains fracture orientation and spacing information, and the amplitude of these waves gives the compliance. Our algorithm makes use of the interference of two true-amplitude 3D Gaussian beams emitted from surface source and receiver arrays that are extrapolated downward and focused on fractured reservoir targets. The double beam interference pattern provides information about the fractures. We performed a blind test on our methodology. A 3D model with two sets of orthogonal fractures was built, and a 3D staggered finite-difference method using the Schoenberg linear-slip boundary condition for fractures was used to generate the synthetic surface seismic data set. The test results showed that we were able to not only invert for the fracture orientation and spacing, but also the compliance field.