An important mechanism of seismic amplitude decay in fractured environments is related to energy conversion of the propagating wavefield into reflected and transmitted waves at the fracture interfaces. Based on this mechanism, we propose and test a method to estimate an effective compliance of a set of fractures from full-waveform sonic (FWS) log data. The method uses the time delays and amplitude differences in the critically refracted P-wave when comparing its propagation in intact and fractured sections of the borehole. For validation, we consider synthetic FWS logs obtained from numerical simulations that emulate a borehole penetrating a series of fractures embedded in low-permeability hard rock. Under the assumption that the geometrical spreading characteristics of the critically refracted P-wave in intact and fractured rocks are similar, the existent amplitude and time differences can be mainly attributed to the transmission losses across the fractured section. Once transmission losses are quantified as a Pwave transmission coefficient associated with a fractured section, we compute an effective mechanical normal compliance of the fracture set on the basis of the linear slip theory.
Presentation Date: Tuesday, October 13, 2020
Session Start Time: 9:20 AM
Presentation Time: 11:00 AM
Location: Poster Station 2
Presentation Type: Poster
