Quantitative prediction of fracture scale based on frequency-dependent shear wave splitting

The development of natural fractures has a significant impact on underground reservoirs and leads to seismic anisotropy. Furthermore, the scale of natural fractures directly affects the oil and gas preservation, hydraulic fracture construction, and production development of shale reservoirs. Shear-wave anisotropy is a frequency dependent parameter and the change in shear-wave anisotropy with frequency is a function of the fracture scale. We propose an innovative method for predicting the fracture scale quantitatively using frequency-dependent shear-wave anisotropy. The quantitative relationship between different fracture scales and the frequency-dependent response of the shear-wave splitting (SWS) anisotropy can be obtained using a dynamic rock physics model. The frequency-dependent shear-wave anisotropy was calculated via SWS analysis in the frequency domain, after which this quantitative relationship and the calculated frequency-dependent response was used to establish an objective function for inversion of fracture scale at different depths using the least-squares algorithm. We synthesized data under ideal conditions, tested the proposed method, applied our method to field data, and found that the quantitative prediction method of the fracture scale yielded reasonable prediction results. The shear-wave anisotropy was calculated based on the SWS analysis from the horizontal components of the upgoing wavefields of the field vertical seismic profile. We compared the fracture scale calculated from logging data using the proposed method, and the results obtained indicated that this method can successfully predict the fracture scale quantitatively.