Successful application of spectral decomposition technique to map deep gas reservoirs

Abstract

The spectral decomposition of seismic data is the process that transforms seismic amplitudes as a function of space and time to spectral amplitudes as a function of frequency, space and time. Various spectral decomposition methods are commercially available. We apply the high resolution discrete Wigner‐Ville transform for finding previously undrilled gas reservoirs but also for investigating the geological setting for possible connections to producing gas wells. We present a case study in a newly‐evaluated tight gas reservoir area with some wells that we can utilize as control points. The largest challenge lies in mapping reservoirs that have not been drilled and are not connected to previously discovered gas wells. We have been successfully applying our high resolution spectral decomposition technique to map the distribution of newly discovered tight gas reservoirs. In addition we can provide important and critical information for updating the field development plan in Daqing. We successfully applied the high resolution spectral decomposition technique to map the gas distribution along a 7 km arbitrary 2‐D seismic line that was extracted from a larger regional 3D data set. The reservoir level has a discontinuous appearance with small hydrocarbon accumulations at various levels within the reservoir zone. The pilot study indicates that the spectral amplitudes are anomalous over gas zones especially at higher frequencies. This indication can be used to predict gas pockets away from known well locations. We suggest performing the Wigner‐Ville spectral decomposition method on the whole 3D data volume. The most obvious advantage for calculating spectral amplitudes on 3D data is the ability to generate horizon maps and time slices at key frequencies for map the reservoir in 3D domain.