Changes

Single tomographic images, however, are often difficult to interpret. Changes in the observed seismic velocity field across the reservoir may be due to the combined effects of lithology, pore fluids, and the physical state of the reservoir. Often geological stratification is easily discernible (Figure 4) due to the contrast in seismic velocities characteristic of different types of rocks The results of faulting and other structural features in the reservoir can also sometimes be seen, when associated with a sufficient contrast in seismic velocities.

Single tomographic images, however, are often difficult to interpret. Changes in the observed seismic velocity field across the reservoir may be due to the combined effects of lithology, pore fluids, and the physical state of the reservoir. Often geological stratification is easily discernible (Figure 4) due to the contrast in seismic velocities characteristic of different types of rocks The results of faulting and other structural features in the reservoir can also sometimes be seen, when associated with a sufficient contrast in seismic velocities.

[[file:cross-borehole-tomography-in-development-geology_fig4.png|thumb|{{figure number|4}}Single image tomograms documenting stratigraphy and reservoir zones. Heterogeneity of the lower reservoir is documented by the contrast in log curves and the corresponding change in the tomographic velocity fields. (After Justice et al., 1990.)]]

[[file:cross-borehole-tomography-in-development-geology_fig4.jpg|thumb|{{figure number|4}}Single image tomograms documenting stratigraphy and reservoir zones. Heterogeneity of the lower reservoir is documented by the contrast in log curves and the corresponding change in the tomographic velocity fields. (After Justice et al., 1990.)]]

==Applications==

==Applications==

Tomography display parameters are one of the more important factors governing the ease of interpretation and acceptance of results. To facilitate correlations with cross-borehole geology, tomogram velocity fields should be scaled to match major stratigraphic and reservoir units (Figure 4). The definition of smaller velocity fields may be appropriate to show details such as reservoir heterogeneity within selected major velocity fields. Stratigraphic units such as formation tops and sedimentary facies should also be delineated. In addition to defining velocity fields that match geological units, the use of standard colors and/or graphic symbols for rock units is important. Cold colors (blues) should be used for high velocity fields with a transition to hot colors (reds) for low velocities. Using these guidelines for display should result in tomograms that closely resemble geological cross sections and are more readily understood and utilized by geologists, engineers, and management. Analysis of tomograms with reference to reservoir models and any available surface seismic should provide the basis for interpretations that can be summarized with integrated data displays, as illustrated in Figure 5. Most important are the well data to velocity field correlations and the log to tomography correlations documenting lithology, porosity, fluid saturation, and temperature. The resulting log and tomography display should provide the data needed to qualitatively document cross-borehole structure, especially dip and faults, reservoir heterogeneity and homogeneity, fluid contacts and any EOR flood fronts.

Tomography display parameters are one of the more important factors governing the ease of interpretation and acceptance of results. To facilitate correlations with cross-borehole geology, tomogram velocity fields should be scaled to match major stratigraphic and reservoir units (Figure 4). The definition of smaller velocity fields may be appropriate to show details such as reservoir heterogeneity within selected major velocity fields. Stratigraphic units such as formation tops and sedimentary facies should also be delineated. In addition to defining velocity fields that match geological units, the use of standard colors and/or graphic symbols for rock units is important. Cold colors (blues) should be used for high velocity fields with a transition to hot colors (reds) for low velocities. Using these guidelines for display should result in tomograms that closely resemble geological cross sections and are more readily understood and utilized by geologists, engineers, and management. Analysis of tomograms with reference to reservoir models and any available surface seismic should provide the basis for interpretations that can be summarized with integrated data displays, as illustrated in Figure 5. Most important are the well data to velocity field correlations and the log to tomography correlations documenting lithology, porosity, fluid saturation, and temperature. The resulting log and tomography display should provide the data needed to qualitatively document cross-borehole structure, especially dip and faults, reservoir heterogeneity and homogeneity, fluid contacts and any EOR flood fronts.

[[file:cross-borehole-tomography-in-development-geology_fig5.png|thumb|{{figure number|5}}Integrated data display documenting cross-borehole tomography interpretation across thermal EOR project. Log-defined stratigraphic units and fluid saturation zones correlate with tomographic velocity fields and provide the basis for interpretation of reservoir and fluid properties. (From Justice et ai., 1990.)]]

[[file:cross-borehole-tomography-in-development-geology_fig5.jpg|thumb|{{figure number|5}}Integrated data display documenting cross-borehole tomography interpretation across thermal EOR project. Log-defined stratigraphic units and fluid saturation zones correlate with tomographic velocity fields and provide the basis for interpretation of reservoir and fluid properties. (From Justice et ai., 1990.)]]

==See also==

==See also==