A Feasibility Study to Determine if the Surface Seismic Method Can Detect Thin Channels in the Presence of Statics and Noise

By

Mark S. Egan¹, Subhashis Mallick¹

(1) WesternGeco, Gatwick, United Kingdom

 Exploratory wells found oil-bearing sand channels in a field in Oman. Despite the fact that these reservoirs were less than 5 meters thick, they were still considered to be economic. Conventional 2D and 3D surface seismic programs were conducted, but they were unsuccessful in detecting the locations of the reservoirs. Consequently interest waned in further seismic attempts until the development of high channel count systems was announced.

The mission of this study was to predict if such high channel count systems could detect the sands. The chief tool used was modeling. In addition to handling signal, all major noise components were comprehended. These included multiples, scattered ground roll, air waves and ambient noise. The effects of inelastic attenuation and intra-array statics were also considered.

Although results showed that high channel count systems could indeed provide significantly better signal-to-noise ratios than conventional systems, the bandwidth inherent in vibrator surveys was found to be too restrictive for direct detection of the reservoir sands in conventional wiggle trace sections.

However, prestack inversion was also executed using the modeled records and those results were found to be quite promising.