UNCONVENTIONAL RESERVOIR CHARACTERIZATION BASED ON SPECTRALLY CORRECTED SEISMIC ATTENUATION ESTIMATION

Fracture characterization is critical in exploration and development in unconventional resource plays. Fluid-filled fractures and cracks directly alter the effective impedance of rocks, attenuate amplitude and distort seismic spectrum, all of which make the seismic attenuation estimation a promising tool for characterizing fracture system. However, existing methods for estimating seismic attenuation are usually based on "Constant Q" model, which ignores the interference from reflectivity anomalies. For unconventional reservoirs, the spectrum of the reflected wave may be affected by the presence of thin (shales) beds in the formation, which makes Q estimates less reliable. We employ a non-stationary Q model to characterize attenuation, and correct the reflected spectrum by using inverted reflectivity sequence based on well logs to remove local thin-bed effects from seismic reflection data. In synthetic examples, variance in the estimated values and unphysical negative Q values are reduced sgnificantly. Following the workflow, we also applied attenuation estimation on a seismic survey acquired over the Barnett Shale. The recovered Q estimates have a good correspondence with the production data. Though, the attribute is the average over a target formation, this may be sufficient to find evidence of fluid-filled fractures, or variation in lithology.