Online Journal for E&P Geoscientists

Aqrawi, Ahmed A.^*1; Boe, Trond Hellem ¹
(1) Schlumberger Information Solutions, Stavanger, Norway.

We present an improved method of dip estimation as a seismic attribute, and visualize this in 2 components; dip and directional dip. This method proves to be very efficient in highlighting geologic structures. According to Marfurt and Chopra (1) there are several methods to estimate dip and they fall into three main categories; spatial and temporal derivatives, dip scan of most coherent reflector and eigenvectors of gradient structure tensors. The method for dip and directional dip calculation looks at local weighted correlation between neighboring traces and their amplitudes, searching to maximize correlation, and therefore falls in the Martfurt et al “dip scan” category. Using trace to trace dip, it is possible to estimate either the maximal dip, or the dip in a specific direction.

Our approach, uses a gradient decent (aka hill climbing) in order to efficiently find the maximal trace to trace cross correlation. When calculating the directional dip, a fourth order estimate is used in both the inline and cross-line directions and a weighted sum of five estimates. When summing the five dip estimates in a given direction, different weightings are given to them depending on their distance from the center trace. This adds a smoothing effect and can be interpreted to less noisy results. This approach is used to calculate the dip in two main directions, and then this information is used to calculate the directional dip given an angel or the maximal dip, e.g. dip. The results prove to be very useful in detecting structural geology. Data from the Gulf of Mexico has been used to prove the methodology of the dip and directional dip calculations and shows clearly discernible salt domes, faults, and fluvial systems.

References

(1)Marfurt and Chopra (2007). Seismic attributes for prospect identification and reservoir characterization. Tulsa, OK U.S.A: Society of Exploration Geophysicists. p27-p43.