Susan E. Nissen

Debris flow outrunner blocks, glide tracks, and pressure ridges identified on the Nigerian continental slope using 3-D seismic coherency

The Nigerian continental slope, approximately 100 km offshore from the northwestern flank of the Niger Delta, is in the earliest phases of exploration; therefore, no well control is available to aid in the interpretation of the paleodepositional setting of this area. However, a 500-km2 portion of the area is covered by a 3-D seismic survey, and in the absence of well control, 3-D seismic coherency images have played an important role in the interpretation and confirmation of the paleoenvironment and depositional systems of the area.

3-D seismic attributes applied to carbonates

Coherency mapping has become a widely used tool within Amoco and is being applied in both frontier exploration and exploitation areas. Coherency and other 3-D seismic attributes have been successfully used to identify and delineate features in clastic depositional environments, including reworked deltaic sand bodies, deltaic channels with associated point bars, slump features, debris flow outrunner blocks, and various geologic drilling hazards including faults, salt diapirs, buried channels, and shallow gas pockets.

Delineation of geologic drilling hazards using 3-D seismic attributes

Historically, geologic hazards have been primarily identified using high‐resolution 2-D single‐channel seismic (e.g., 3.5 kHz and minisparker records), side‐scan sonar surveys, geotechnical data from selected borings and in‐situ measurements, and drop cores. However, effective use of coherency and other seismic attributes on standard 3-D seismic data can allow early detection and delineation of both surface and subsurface geologic drilling hazards prior to the acquisition of high‐resolution “hazard” surveys.

3-D dip filtering and coherence applied to GPR data; a study

Three‐dimensional seismic data are now used routinely in hydrocarbon exploration and reservoir exploitation. Poststack processing of 3-D seismic data often includes the application of 2-D filters to the stacked data one line at a time (so‐called 2-D by 2-D filtering). In this application, 2-D filtered data are sorted into cross line ensembles before a second pass of 2-D filtering. Alternatively, local three‐dimensional filters may be applied to a volume of seismic data, true 3-D filtering.

3-D Seismic Coherency And the Imaging of Sedimentological Features

A coherency time slice at 1250 ms, corresponding to a Pleistocene surface at approximately 4000 ft. below sea level, from the South Marsh Island area of the Gulf of Mexico displays a complex system of channels which in part are similar to the channel system of the present Mississippi Delta. A comparison of Pleistocene channel geometries with the modem delta suggests the presence of a main Mississippi trunk channel and its associated distributary channels. Apparent lateral accretion and point bar development are observed on the coherency slice where a distributary channel crosses a fault. This interpretation is confirmed using seismic and log data. Complex linear zones of relatively low coherency were also observed on the coherency slice. Seismic and log data from these areas suggest these features are reworked deltaic sands overlying a complex system of channels.

3‐D seismic coherency techniques applied to the identification and delineation of slump features

3-D seismic coherency techniques and associated calculations of dip and azimuth of the coherent seismic reflections have been used successfully to aid in the identification and delineation of slump blocks with both high and low seismic amplitudes within a submarine canyon in the South Marsh Island area of the Gulf of Mexico. Block faces with low amplitude, but relatively high coherence, which are not evident on standard seismic time slices, can be seen on coherency time slices and dip/azimuth plots. These slump blocks produce a distinctive mottled pattern on coherency time slices and correspond to areas of high dip and varied azimuth on dip/azimuth plots. Similar coherency and dip/azimuth patterns are found elsewhere in the world, associated with slumping in areas of faulting, dewatering, and mass wasting.

Stratigraphic and structural interpretation with 3‐D coherence

3-D seismic coherence is useful for identifying faults, stratigraphic features and the relationship between them (Bahorich, and Farmer, 1994). This paper documents the use of this technology in three basins; the Gulf of Mexico, the North Sea, and the Ardmore Basin of Oklahoma.

Visualization and characterization of structural deformation fabric and velocity anisotropy

Fractures develop with different intensity and preferred orientations in response to changing stress regimes throughout geologic time. Fractures with preferred orientations are often interpreted as the cause of seismic P-wave velocity (Vp) anisotropy as well as linear features seen in seismic attribute volumes. Field experiments show that stress orientation can often be directly measured by P-wave anisotropy while the lineaments seen in the volumetric curvature attributes are related to deformation.

Improving Geologic and Engineering Models of Midcontinent Fracture and Karst-Modified Reservoirs Using New 3-D Seismic Attributes

Our project goal was to develop innovative seismic-based workflows for the incremental recovery of oil from karst-modified reservoirs within the onshore continental United States. Specific project objectives were: (1) to calibrate new multi-trace seismic attributes (volumetric curvature, in particular) for improved imaging of karst-modified reservoirs, (2) to develop attribute-based, cost-effective workflows to better characterize karst-modified carbonate reservoirs and fracture systems, and (3) to improve accuracy and predictiveness of resulting geomodels and reservoir simulations. In order to develop our workflows and validate our techniques, we conducted integrated studies of five karst-modified reservoirs in west Texas, Colorado, and Kansas. Our studies show that 3-D seismic volumetric curvature attributes have the ability to re-veal previously unknown features or provide enhanced visibility of karst and fracture features compared with other seismic analysis methods. Using these attributes, we recognize collapse features, solution-enlarged fractures, and geomorphologies that appear to be related to mature, cockpit landscapes. In four of our reservoir studies, volumetric curvature attributes appear to delineate reservoir compartment boundaries that impact production. The presence of these compartment boundaries was corroborated by reservoir simulations in two of the study areas. Based on our study results, we conclude that volumetric curvature attributes are valuable tools for mapping compartment boundaries in fracture- and karst-modified reservoirs, and we propose a best practices workflow for incorporating these attributes into reservoir characterization. When properly calibrated with geological and production data, these attributes can be used to predict the locations and sizes of undrained reservoir compartments. Technology transfer of our project work has been accomplished through presentations at professional society meetings, peer-reviewed publications, Kansas Geological Survey Open-file reports, Masters theses, and postings on the project website: http://www.kgs.ku.edu/SEISKARST.

Seismic detection of shallow natural gas beneath Hutchinson, Kansas

A high-resolution seismic reflection survey was conducted in order to identify shallow natural gas that had leaked from a gas storage facility near Hutchinson, Kansas. Gas presence produced both bright spots and dim spots on the seismic reflection profiles. Core and well 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 within fractures in these dolomites appears to reduce the velocity of the dolomite interval down to or below that of the shales. Depending upon the magnitude of the gas effect, a dim out or bright spot is produced. As gas dissipates from a given location, the associated seismic anomaly is reduced.