Fractured Formation Evaluation by Seismic Attenuation Derived from Array Acoustic Log Waves Based on Modified Spectral Ratio Method and an Extended Biot's Poroelastic Model

A comprehensive application of the seismic attenuation deduced from the array acoustic log waves by using modified spectral ratio method together with an extended Biot's poroelastic model has been developed for detection and evaluation of fractures in carbonate and sandstone formations. First, profile of amplitude ratio based on deconvolution interferometry (DCI) and modified spectral ratio method (MSRM) are introduced and applied on array acoustic waveforms to derive the seismic attenuation factors. Second, an extended Biot's poroelastic model with consideration of fracture parameters is described and derived for its expression of attenuation. Both the computational method and the theoretical model are tested on simulated sonic data and meaningful results are obtained which are connected with analysis of application on field data in final section. Finally, the MSRM and extended Biot's poroelastic model are applied to field waveforms acquired from carbonate and sandstone formation in oilfields of Petro China. In the present study, we mainly focused on the subject of fracture identification and evaluation in both carbonate and sandstone formation. Field application results show that within frequency range of 1-40 kHz, attenuation derived from sonic log waves by using MSRM has close relationship with fracture development. Meanwhile, the simulation responses based on the extended Biot's poroelastic model verify the fact that the attenuation magnitude is mainly sensitive to fracture porosity. Our results also suggest that profile of amplitude ratio can be a potentially useful indicator of fracture identification and evaluation, and, maybe also an interpreting toll of radial heterogeneity.