Limitations on the performance of field arrays and FK filters: models, case histories and remedies

Not generally appreciated at first glance, but nonetheless crucial to understanding the recording and imaging of reflections, is the linkage between acquisition arrays and fk filters. Over the past decade several pioneering studies. ^1,2,3 have shifted the basic focus of array design from area-dependent deployments to "generic" patterns involving the matching of array lengths to the station spacing. By controlling the passage of coherent noise in the shot gather, and by decomposition into other domains, it has been argued that multichannel filters such as the stack and fk filter work more effectively. ^1,2,3,4,5 However, geophysicists have become wary of claims attributed to theoretically optimal array designs and the use of fk filters because results often vary unpredictably and include undesired artifacts 6 This paper examines these concerns by addressing how distorted reflections and linear noise, whether caused by variations in amplitude or static shifts, and superimposed random noise are recorded by arrays and mapped into the fk domain (Magazine Cover, Figures I and 2). From these model studies:

1. methods are suggested to reduce the leakage of signal and linear noise across the fk spectrum so that the effectiveness of fk filters may be enhanced (Figure 3), and
2. limits are established for accuracy in positioning stations and arrays and for acceptable geophone sensitivity/coupling variations so that in the fk domain separation of reflections and aliased linear noise is maintained.

Case histories from Alberta indicate that the application of reversible scaling and static shift corrections prior to pre-stack fk filtering may increase reflection bandwidth and relative signal strength resulting in improved ties to well control and increased resolution of stratigraphic plays.

Acknowledgments

We would like to thank Dr. Easton Wren for drawing our attention to the possibilities of designing arrays on the signal and for suggesting some of the approaches presented here.