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High-resolution seismic detection of shallow natural gas beneath Hutchinson, Kansas

Environmental Geosciences

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Abstract

Two high-resolution seismic reflection surveys were conducted to identify shallow natural gas that had caused explosions in Hutchinson, Kansas, in January 2001. Gas presence is associated with both a bright spot and a dim-out on the seismic reflection profiles. Core and log data from wells drilled to vent the gas indicate that the gas-bearing interval corresponds to thin dolomite layers, which have higher P-wave velocities than the surrounding shales. Gas in fractures can reduce the velocity of the dolomite interval to that of the shales (or lower). Depending on the magnitude of the velocity change, either a dim-out or bright spot is produced. Sonic logs from gas-bearing vent wells, recorded after venting of gas, show no anomalous velocity, indicating that as gas dissipates, any associated seismic anomaly will be reduced. Lateral variations in the seismic properties of the gas-bearing interval and adjacent strata (namely, variations in dolomite and shale content) also have a significant effect on the seismic signature of the interval, mimicking the effect of a small amount of gas. Only where the gas zone is relatively thick (2-3 m; 7-10 ft), creating a high-amplitude negative seismic reflection, is the seismic signature diagnostic of gas. Therefore, whereas the dim-outs observed on the seismic reflection profiles may be the result of gas presence, they are equally well explained by lateral variations in lithology. Dim-outs should not be used in the Hutchinson area as an indicator of gas. The observed bright spot, however, is most likely a unique gas response. Copyright ?? 2004. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
High-resolution seismic detection of shallow natural gas beneath Hutchinson, Kansas
Series title:
Environmental Geosciences
Volume
11
Issue:
3
Year Published:
2004
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Environmental Geosciences
First page:
129
Last page:
142
Number of Pages:
14