Time slices

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Seismic Data Analysis
Seismic-data-analysis.jpg
Series Investigations in Geophysics
Author Öz Yilmaz
DOI http://dx.doi.org/10.1190/1.9781560801580
ISBN ISBN 978-1-56080-094-1
Store SEG Online Store


A time slice contains events from more than one reflection horizon at the same time level. A spatially high-frequency event on a time slices is either a steeply dipping event or a high-frequency event in time. Thus, from the time slices in Figure 7.5-1, we can infer steep dip at location H from the high-frequency character of the event, and gentle dip at location L from the low-frequency character. Additionally, contours associated with a reflection horizon can be traced from time slices. If contours narrow between a shallow and a deeper time slice, then the feature is a structural low (Figure 7.5-1). Conversely, if contours widen between a shallow and a deeper time slice, then the feature is a structural high (Figure 7.5-2).

Time slices can be used to generate structural contour maps. Some 2-D smoothing can be applied to time slices to ease contouring (Figure 7.5-3b). Edge enhancement can be used to better delineate zero crossings (Figure 7.5-3c). Some image processing tools also can be used to detect and enhance subtle structural features on time slices. Illumination of a time slice by a pseudosun is an example of such a technique (Figure 7.5-3d). The angle of illumination and its direction can be manipulated for optimum detection. The main structure in Figure 7.5-3d is a salt dome. Note the presence of tensional faults associated with salt diapirism. Bone [1], Brown [2], and Brown [3] have made pioneering use of of time slices in 3-D interpretation.

One common artifact that is observable on time slices is the presence of horizontal striations. The pseudo-sun illumination has enhanced the streaks in Figure 7.5-3d. These striations typically are oriented along the shooting direction. Although there are several causes for time-slice striations, one cause is the positioning errors present in the navigation data. Schultz and Lau [4] identify these striations as time shifts from one inline to another (crossline statics). They also suggest a poststack procedure to estimate and eliminate these time shifts in the inline-crossline wavenumber domain.

  • Figure 7.5-1  Part 1: Selected time slices from a land 3-D survey starting at 580 ms and moving down to 1740 ms at 40-ms intervals. The northeast-southwest extending feature is a small basin between two salt domes. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

    Figure 7.5-1  Part 1: Selected time slices from a land 3-D survey starting at 580 ms and moving down to 1740 ms at 40-ms intervals. The northeast-southwest extending feature is a small basin between two salt domes. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

  • Figure 7.5-1  Part 2: Selected time slices from a land 3-D survey starting at 580 ms and moving down to 1740 ms at 40-ms intervals. The northeast-southwest extending feature is a small basin between two salt domes. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

    Figure 7.5-1  Part 2: Selected time slices from a land 3-D survey starting at 580 ms and moving down to 1740 ms at 40-ms intervals. The northeast-southwest extending feature is a small basin between two salt domes. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

  • Figure 7.5-2  Part 1: Selected time slices from a land 3-D survey starting at 1000 ms and moving down to 1660 ms at 60-ms intervals. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

    Figure 7.5-2  Part 1: Selected time slices from a land 3-D survey starting at 1000 ms and moving down to 1660 ms at 60-ms intervals. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

  • Figure 7.5-2  Part 2: Selected time slices from a land 3-D survey starting at 1000 ms and moving down to 1660 ms at 60-ms intervals. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

    Figure 7.5-2  Part 2: Selected time slices from a land 3-D survey starting at 1000 ms and moving down to 1660 ms at 60-ms intervals. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

Besides contouring, time slices also are useful in quality control. Figure 7.5-4 is a time slice before and after residual statics corrections were applied to the data. Note the improvement in the signal-to-noise ratio and the continuity of events in Figure 7.5-4b.

Time slices can be used to check for consistency in picking time horizons along inlines and crosslines. Actually, in some areas with very complex structures, time slices can sometimes be used to trace faults and horizon contours. Figure 7.5-5a shows a time slice that exhibits a major fault from left to right across the survey area and a series of oblique fault blocks adjoining the major fault zone. A time slice contributes one contour level for a horizon as illustrated in Figure 7.5-5b. Such a display can be used for the quality control of structural interpretation.

  • Figure 7.5-3  Processing time-slice data for improved interpretation: (a) A time slice, (b) after 2-D smoothing, and (c) edge enhancement; (d) another time slice with pseudo-sun illumination applied to enhance the intensive fracturing associated with salt diapirism. (Data in (a) courtesy Shell Oil Company and Esso, and data in (d) BP Amoco.)

    Figure 7.5-3  Processing time-slice data for improved interpretation: (a) A time slice, (b) after 2-D smoothing, and (c) edge enhancement; (d) another time slice with pseudo-sun illumination applied to enhance the intensive fracturing associated with salt diapirism. (Data in (a) courtesy Shell Oil Company and Esso, and data in (d) BP Amoco.)

  • Figure 7.5-4  A time slice (a) before and (b) after residual statics corrections. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

    Figure 7.5-4  A time slice (a) before and (b) after residual statics corrections. (Data courtesy Nederlandse Aardolie Maatschappij B.V.)

  • Figure 7.5-5  (a) A time slice from the time-migrated volume of data that exhibits intensive faulting, and (b) another time slice intersected by a time structure surface derived from interpretation of the time-migrated volume of data.

    Figure 7.5-5  (a) A time slice from the time-migrated volume of data that exhibits intensive faulting, and (b) another time slice intersected by a time structure surface derived from interpretation of the time-migrated volume of data.

References

  1. ↑ Bone et al. (1975), Bone, M. R., Giles, B. F., and Tegland, E. R., 1975, Analysis of seismic data using horizontal cross-sections: Presented at the 45th Ann. Internat. Mtg., Soc. Expl. Geophys.
  2. ↑ Brown (1978), Brown, A. R., 1978, 3-D seismic interpretation methods: Presented at the 48th Ann. Internat. Soc. Expl. Geophys. Mtg.
  3. ↑ Brown et al. (1982), Brown, A. R., Graebner, R. J., and Dahm, C. G., 1982, Use of horizontal seismic sections to identify subtle traps, in The Deliberate Search for the Subtle Trap: Am. Assoc. Petr. Geol. Memoir, 32, 47–56.
  4. ↑ Schultz and Lau (1984), Schultz, P. S. and Lau, A., 1984, Poststack estimation of three-dimensional crossline statics: Geophysics, 49, 227–236.

See also

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