Image Enhancement Below the pre-Khuff Unconformity Using Pre and Post-Stack Multiple Attenuation

By

 Michael A. Zinger¹, Khalid I. Hassan¹, Richard G. Jerskey¹

(1) Saudi Aramco, Dhahran, Saudi Arabia

 One of the primary processing challenges within Saudi Arabia is the attenuation of multiples. One source of multiples is the pegleg multiples generated between the Jilh and the Khuff formations. This paper discusses several techniques used to minimize this energy, the effect on the final stack and ultimately, the interpretation.

The attenuation of this energy is accomplished through several means: 1.) The optimization of the velocity analysis by using demultipled input. 2.) CDP based pre-stack demultiple algorithms. 3.) An inner trace mute. 4.) An interpretation-driven post-stack demult.

No one process is adequate, but each provides incremental improvements in the attenuation of multiples. Taken together, the first three provide an optimized stack through data processing alone. The last step, a post-stack demult, requires multi-discipline cooperation between processing and interpreting explorationists. This step flattens the data on the Jilh horizon, making the assumption that the pegleg multiples will be parallel to this event. A very narrow, surgically applied FK reject filter is applied to the data below the Khuff, with the intent of removing only flat-lying energy.

The interpretation of the pre-Khuff data becomes crucial in the final process, as primary energy is also removed if it is parallel to the Jilh. This process works best where there is a difference between the dip of the primary energy and the multiple energy. Two examples are shown in this paper: first, a dramatic subcrop beneath the pre-Khuff unconformity, and second, the image of a deep pre-Cambrian graben that is barely visible on the non-demultipled data.