Patent ID: 9733372
Date: 2017-08-15
CPC Classifications: G01V

Claim:
1. A method for identifying gas hydrate saturation and associated free gas comprising: receiving, at a processor, well log data of a well captured from within the well; receiving, at the processor, a field seismic data set of and adjacent to the well captured from above the well; constructing a velocity-density-thickness model of background clays and target sand based on the well log data, initially setting the target sand as saturated with water; generating two sets of synthetic seismograms, a first set based on varying the sand thicknesses and hydrate saturation in the target sand of the model, and a second set based on varying the sand thickness, hydrate saturation, and an amount of free gas under the hydrate, in the target sand of the model; applying spectral decomposition to the field seismic data set of the target sand, whereby the seismic data set is narrow-band-limited by the application of spectral decomposition; applying spectral decomposition to the first set of synthetic seismograms, whereby the first set of synthetic seismograms is narrow-band-limited by the application of spectral decomposition; applying spectral decomposition to the second set of synthetic seismograms to narrow-band-limit the second set of synthetic seismograms, whereby the second set of synthetic seismograms is narrow-band-limited by the application of spectral decomposition; identifying locations of the target sand in the narrow-band-limited seismic data, extracting a positive amplitude followed by a negative amplitude of the narrow-band-limit seismic data at the identified locations, the polarity convention relative to zero phase data, positive indicating increasing impedance; classifying the extracted amplitudes based on whether the positive amplitude or the negative amplitude is dominant; for extracted amplitudes where the positive amplitude is dominant, comparing the extracted amplitudes with the first set of narrow-band-limited synthetic seismograms, and selecting the synthetic seismogram having the best match in thickness and amplitude to the extracted amplitude, whereby gas hydrate saturation is identified; for extracted amplitudes where the negative amplitude is dominant, comparing the extracted amplitudes with the second set of narrow-band-limited synthetic seismograms, and selecting the synthetic seismogram having the best match in thickness and amplitude to the extracted amplitude, whereby gas hydrate saturation and associated free gas is identified.