The distribution and orientation of faults, fracture intensity and seismic-reflection characteristics of the Mesaverde Group (Williams Fork and Iles formations) at Mamm Creek Field vary stratigraphically, and with lithology and depositional setting. For the Mesaverde Group, the occurrence of faults and natural fractures is important as they provide conduits for gas migration, and enhance the permeability and productivity of the tight-gas sandstones. The Upper Cretaceous Mesaverde Group represents fluvial, alluvial-plain, coastal-plain and shallow-marine depositional environments. Structural interpretations based on three-dimensional (3D) seismic-amplitude data, ant-track (algorithm that enhances seismic discontinuities) seismic attributes and curvature attributes are utilized jointly to understand the complex fault characteristics of the Williams Fork Formation. This study reveals that the lowermost lower Williams Fork Formation is characterized by NNW- and east–west-trending small-scale thrust and normal faults. Study suggests that the uppermost lower Williams Fork Formation, and the middle and upper Williams Fork formations, exhibit NNE- and east–west-trending arrays of fault splays that terminate upwards and do not appear to displace the upper Williams Fork Formation. In the uppermost Williams Fork Formation and Ohio Creek Member, NNE-trending discontinuities are displaced by east–west-trending events and the east–west-trending events dominate. Fracture analysis, based on borehole-image logs, together with ant-track and attenuation-related seismic attributes, illustrates the spatial variability of fracture intensity and lithological controls on fracture distribution. In general, higher fracture intensity occurs within the southern, southwestern and western portions of the field, and fracture intensity is greater within the fluvial sandstone deposits of the middle and upper Williams Fork formations. More than 90% of natural fractures occur in sandstones and siltstones. In situ stress analysis, based on induced-tensile fractures and borehole breakouts, indicates a NNW orientation of present-day maximum horizontal stress ( S H max ), an approximate 20° rotation (in a clockwise direction) in the orientation of S H max with depth and an abrupt stress shift below the Williams Fork Formation within the Rollins Sandstone Member.

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The Thrace Basin of Turkey has sandstone and carbonate reservoirs of Eocene and Oligocene age. Mapping undrained sweet spots from seismic data is currently a challenge, especially because there is no water drive after production. Time-lapse (4D) land seismic data was used to investigate undrained liquid gas pockets and to help with the planning of gas storage into the depleted reservoirs. Two vibroseis 3D baseline and monitor surveys were acquired in 2002 and 2011, respectively. The 4D seismic data has low repeatability and required conditioning to reduce the nonrepeatable 4D noise that is not related to production. Cross-equalization is applied to the base and the monitor data to bring out similarities (noise cancellation by subtracting seismic volumes), and the inverted rock properties primarily show changes due to production. We cross-equalized the corresponding angle-band stack cubes prior to prestack inversion as the available cross-equalization software was implemented for poststack seismic data. The cross-equalized angle-band stacks from the base and the monitor surveys were separately inverted to acoustic impedance (Zp), shear impedance, and density. The differences of inverted rock properties and other pore-fill indicators like Zp, P-wave velocity over S-wave velocity, and BulkRho cubes were created to map possible undrained zones after 10 years of production. A poststudy well that was drilled following the 4D analysis penetrated an undrained gas pocket.

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