Discrimination and Enhancement of Fracture Signals on Surface Seismic Data
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Fracture patterns control flow and transport properties in a tight gas reservoir and therefore play a great role in siting the production wells. Hence, it is very important that the exact location and orientation of fractures or fracture swarms is known. Numerical models show that the fractures may be manifested on seismograms as discrete events.A number of data processing workflows were designed and examined to enhance these fracture signals and to suppress the reflections in seismic data. The workflows were first tested on a 2D synthetic data set, and then applied to 3D field data from the San Juan Basin in New Mexico. All these workflows combine conventional processing tools which makes them easily applicable. Use of conventional P-wave data may also make this approach to locate fractures more economical than other currently available technology which often requires S-wave survey or computationally intensive inversion of data. Diode filtering and dip-filtering in the common-offset domain yield good results and work very well in the presence of flat reflectors. NMO-Dip filter depends on the NMO velocity of the subsurface, but removes both flat and slightly dipping reflectors without affecting the fracture signals. Prior application of dip-moveout correction (DMO) did not make any difference on reflections, but included some incoherent noise to the data. The Eigenvector filter performed very well on flat or near-flat reflectors and left the fracture signals almost intact, but introduced some incoherent noise in the presence of steeply dipping reflectors. Harlanâ s scheme and Radon filtering are very sensitive with regard to parameters selection, but perform exceptionally well on flat or near-flat reflectors. Dip-filter, Eigenvector filter, and Radon filter were also tested on 3D land data. Dip-filter and Eigenvector filter suppressed strong reflections with slight perturbations to the fracture signals. Radon filter did not produce satisfactory result due to small residual moveout difference between reflectors and fracture signals.
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