Abstract: Disclosed are methods, systems, and computer-readable medium to perform operations including: spectrally decomposing seismic data associated with a target subsurface area into a plurality of iso-frequency volumes; selecting a low-frequency volume and a high-frequency volume from the plurality of iso-frequency volumes; dividing the low-frequency volume by the high-frequency volume to generate a frequency ratio volume for the target subsurface area; establishing a time-depth relationship in the target subsurface area; extracting, based on the time-depth relationship and the frequency ratio volume, an iso-frequency ratio log in the target subsurface area; and using the iso-frequency ratio log to identify a subsurface gas reservoir in the target subsurface area.

Abstract: Examples of methods and systems are disclosed. The methods include, obtaining a seismic dataset regarding a subsurface region of interest, wherein the seismic dataset comprises a plurality of time-domain seismic traces. The methods also include determining a plurality of single-frequency volumes from the plurality of time-domain seismic traces. The methods further include determining a frequency ratio volume based, at least in part, on the plurality of single-frequency volumes. The methods still further include extracting a three-dimensional (3D) geological body based, at least in part, on the frequency ratio volume. The methods further include determining a drilling target in the subsurface region based on the 3D geological body.

Abstract: A method that includes transforming a relative amplitude preserved 3D seismic volume acquired in the time-domain into a plurality of isofrequency volumes, extracting from the plurality of isofrequency volumes a first isofrequency spectral amplitude volume and a second isofrequency spectral amplitude volume. The method further includes determining an attribute volume from the two isofrequency spectral amplitude volumes, and determining a presence of gas in a subterranean region of interest based on the attribute volume.

Abstract: Methods and systems for determining a spectral ratio log using a time domain seismic image and a seismic velocity model are disclosed. The method includes determining a first mono-spectral seismic image and a second mono-spectral seismic image from the time domain seismic image. The method further includes determining a time domain spectral ratio image from the first mono-spectral seismic image and the second mono-spectral seismic image and transforming the time domain spectral ratio image into a depth domain spectral ratio image using the seismic velocity model. The method still further includes defining a wellbore path through the depth domain spectral ratio image and determining a spectral ratio log along the wellbore path from the depth domain spectral ratio.

Abstract: Disclosed are methods, systems, and computer-readable medium to perform operations including: spectrally decomposing seismic data associated with a target subsurface area into a plurality of iso-frequency volumes; selecting a low-frequency volume and a high-frequency volume from the plurality of iso-frequency volumes; dividing the low-frequency volume by the high-frequency volume to generate a frequency ratio volume for the target subsurface area; establishing a time-depth relationship in the target subsurface area; extracting, based on the time-depth relationship and the frequency ratio volume, an iso-frequency ratio log in the target subsurface area; and using the iso-frequency ratio log to identify a subsurface gas reservoir in the target subsurface area.

Abstract: Methods and systems for determining a spectral ratio log using a time domain seismic image and a seismic velocity model are disclosed. The method includes determining a first mono-spectral seismic image and a second mono-spectral seismic image from the time domain seismic image. The method further includes determining a time domain spectral ratio image from the first mono-spectral seismic image and the second mono-spectral seismic image and transforming the time domain spectral ratio image into a depth domain spectral ratio image using the seismic velocity model. The method still further includes defining a wellbore path through the depth domain spectral ratio image and determining a spectral ratio log along the wellbore path from the depth domain spectral ratio.

Abstract: A method of obtaining a relative amplitude preserved seismic volume acquired in a time-domain for a subterranean region of interest and transforming it into a low-frequency monospectral amplitude volume. The method further determines a seismic attenuation volume from the relative amplitude preserved seismic volume acquired in the time-domain. Furthermore, the method generates a low-frequency monospectral amplitude map for a surface of interest by averaging the low-frequency monospectral amplitude volume over a depth-window around the surface of interest, and generates a seismic attenuation map for a surface of interest by averaging the seismic attenuation volume over a depth-window around the surface of interest. The method further determines an attribute map based on the seismic attenuation map and the low-frequency monospectral amplitude map for the surface of interest, and determines a presence of gas in the subterranean region of interest based on the attribute map.

Abstract: A method of obtaining a relative amplitude preserved seismic volume acquired in a time-domain for a subterranean region of interest and transforming it into a low-frequency monospectral amplitude volume. The method further determines a seismic attenuation volume from the relative amplitude preserved seismic volume acquired in the time-domain. Furthermore, the method generates a low-frequency monospectral amplitude map for a surface of interest by averaging the low-frequency monospectral amplitude volume over a depth-window around the surface of interest, and generates a seismic attenuation map for a surface of interest by averaging the seismic attenuation volume over a depth-window around the surface of interest. The method further determines an attribute map based on the seismic attenuation map and the low-frequency monospectral amplitude map for the surface of interest, and determines a presence of gas in the subterranean region of interest based on the attribute map.

Abstract: A method of processing a three-dimensional (3D) seismic dataset includes: producing a relative amplitude preserved (RAP) processed seismic volume that includes a reservoir from the 3D seismic dataset; decomposing the RAP processed seismic volume into a first iso-frequency volume; generating a first overburden sediment interval map and a first reservoir interval zone map for the first iso-frequency volume; generating and outputting a first ratio map for the first iso-frequency volume by dividing the first overburden sediment interval map by the first reservoir interval zone map; and characterizing a fluid content of the reservoir based on the first ratio map.

Abstract: A method of processing a three-dimensional (3D) seismic dataset includes: producing a relative amplitude preserved (RAP) processed seismic volume that includes a reservoir from the 3D seismic dataset; decomposing the RAP processed seismic volume into a first iso-frequency volume; generating a first overburden sediment interval map and a first reservoir interval zone map for the first iso-frequency volume; generating and outputting a first ratio map for the first iso-frequency volume by dividing the first overburden sediment interval map by the first reservoir interval zone map; and characterizing a fluid content of the reservoir based on the first ratio map.

Abstract: A method that includes transforming a relative amplitude preserved 3D seismic volume acquired in the time-domain into a plurality of isofrequency volumes, extracting from the plurality of isofrequency volumes a first isofrequency spectral amplitude volume and a second isofrequency spectral amplitude volume. The method further includes determining an attribute volume from the two isofrequency spectral amplitude volumes, and determining a presence of gas in a subterranean region of interest based on the attribute volume.