--> Seismic Exploration for Fractured Lower Dakota Alluvial Gas Sands, San Juan Basin, New Mexico, by Reeves, James J. and W. Hoxie Smith; #90030(2004)
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Previous HitSeismicNext Hit Exploration for Fractured Lower Dakota Alluvial Gas Sands, San Juan Basin, New Mexico

Reeves, James J. and W. Hoxie Smith
GeoSpectrum, Inc, Midland, TX

Reservoir fractures are predicted using multiple azimuth Previous HitseismicNext Hit lineament mapping in the Lower Dakota reservoir section. A Previous HitseismicNext Hit lineament is defined as a linear feature seen in a time slice or horizon slice through the Previous HitseismicNext Hit volume. For lineament mapping, each lineament must be recognizable in more than one Previous HitseismicNext Hit attribute volume. Previous HitSeismicNext Hit attributes investigated include: coherency, amplitude, frequency, phase, and acoustic impedance. We interpret that areas having high Previous HitseismicNext Hit lineament density with multi-directional lineaments are associated with high fracture density in the reservoir.

Lead areas defined by regions of “swarming” multi-directional lineaments are further screened by additional geologic attributes. These attributes include reservoir isopach thickness, indicating thicker reservoir section; Previous HitseismicNext Hit horizon slices, imaging potentially productive reservoir stratigraphy; and a collocated cokriged clay volume map for the reservoir zone computed from near trace Previous HitseismicNext Hit amplitude (an AVO attribute) and a comprehensive petrophysical analysis of the well data to determine discrete values of clay volume at each well. This map indicates where good/clean reservoir rock is located. We interpret that clean/low clay reservoir rock is brittle and likely to be highly fractured when Previous HitseismicNext Hit lineaments are present.

A gas sensitive AVO Previous HitseismicNext Hit attribute, near trace stacked phase minus far trace stacked phase, phase gradient, is used to further define drill locations having potential high gas saturation. The importance of this attribute cannot be understated, as reservoir fractures enhance reservoir permeability and volume, they may also penetrate water saturated zones in the Dakota and/or Morrison intervals and be responsible for the reservoir being water saturated and ruined.

Previous HitSeismicNext Hit interval velocity Previous HitanisotropyNext Hit is used to investigate reservoir potential in tight sands of the Upper Dakota up hole from the main reservoir target. We interpret that large interval velocity Previous HitanisotropyNext Hit is associated with fracture related Previous HitanisotropyTop in these tight sands.