Reliable estimation of seismic and geomechanical properties of organic-rich shale provides important constraints to guide production by identifying sweet spots and locations for effective hydraulic fracturing. We investigate the feasibility of amplitude variation with offset (AVO) inversion based on the full Zoeppritz solutions for reflection amplitudes and the ability of the inversion to constrain important properties. By theoretical analysis and inversion tests, we determine behaviors of the AVO inversion solutions developed for isotropic media when the target shale formation instead has seismic anisotropy related to organic content. The anisotropy of the model shale is related to the kerogen volume fraction values using published laboratory data. Both theoretical results and inversion tests show that the inversion accurately determines normal incidence impedance, but that the velocity value corresponds to the horizontal P-wave velocity in the shale so that density is typically underestimated. Analysis of simple reflection coefficient solutions based on linearized approximations helps to explain why the inversion obtains the horizontal velocity of the shale. Though the linearized results are only applicable for lower values of kerogen volume fraction, the nonlinear inversion based on the full Zoeppritz results obtains reliable results even for strong anisotropy. The results also allow the estimation of Young’s modulus and the Poisson ratio. Based on the results and the analysis, we propose a workflow using this approach for shale reservoir characterization to define geophysical and geomechanical properties in both horizontal and vertical directions.
Presentation Date: Monday, September 25, 2017
Start Time: 2:15 PM
Location: Exhibit Hall C, E-P Station 3
Presentation Type: EPOSTER