Abstract:

Petrophysical modeling of fractures and its seismic response characterisitics serve as an important fundation for the fractured reservoir prediction using seismic data, for which we may propose effective seismic inversion and reservoir characterizing methods.With regard to the horizontal bedding-parallel fractures in unconventional shale oil and gas reservoirs, we conducted a study on the petrophysical modeling and its seismic response characteristics.We obtained the rock background media by integrating non-clay and clay minerals, pores and fluids, using actual sample testing and well-logging data, also adopting both the Voigt-Reuss-Hill (VRH) method and self-consistent approximation (SCA) theory.Combined with the information of actual fracture occurence and growth patterns, we estalished the petrophysical modeling of horizontal bedding-parallel fractures based on the Chapman's petrophysical modeling of multi-scale fractures.Finally, the seismic responses were generated using propogator matrix modeling.In combining the above-mentioned test data and the field data, we proposed a workflow of petrophysical modeling of horizontal bedding-parallel fractures based on the petrophysical model of multi-scale fractures, and applied it to the shale reservoirs in the Jianghan oilfield.The forward modeling results show that the horizontal bedding-parallel fractures were well developed in the shale reservoirs, and the seismic responses are significantly frequency-dependent.Meanwhile, the fracture length and density, major target parameters for seismic prediction of horizontal bedding-parallel fractures, are the most important parameters inducing seismic anisotropy.

Key words: Chapman's model, frequency-dependent characteristic, seismic anisotropy, horizontal bedding-parallel fracture, petrophysical modeling