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Improved Imaging of the Darby Thrust Fault using Multi-Component Seismic Receivers

Shuki Ronen, VeritasDGC, 10300 Town Park Drive, Houston, TX 77071, phone: 832-351-8554, [email protected], Mark Wagaman, Veritas, Denver, CO, and Chris Ansorger, Veritas, Calgary, AB.

Seismic imaging in rough terrain where Paleozoic rocks are thrusted to the surface over Cretaceous sediments, can be a challenge using conventional methods. Advances in acquisition technology include multi-component (3C) receivers. Conventional single- component (1C) systems consist of coiled geophones which record only the vertical component of the seismic wavefield whereas new 3C digital sensors utilize Micro-Electro-Mechanical Systems accelerometers to record all three components of the full wavefield. To evaluate the applicability of such new 3C sensors in rough terrain we conducted a test over the Darby thrust fault in southwest Wyoming. Over the thrust, near the center of the line, the elevation varied 200m vertically over a horizontal distance of 400m. The source was 5kg Pentolite at 18m hole depth, with 50m shot interval. The wavefield was recorded by both 12-element linear and 36-element areal geophone group arrays at 50m interval as well as by 3C sensors at 25m interval. The processing sequence included tomographic refraction statics, coherent and random noise attenuation, surface consistent deconvolution, two iterations of velocity analysis and residual statics, and pre-stack migration. We applied polarization filters to the 3C data to separate signal and noise. No such polarization filtering is possible with any 1C data. All types of receivers provided good data away from the more complex, thrusted area. However, the 3C sensors provided much better resolution and imaging of the complex structure of the Darby thrust. We thank Marvin Johnson and Vinny Buffenmeyer of ExxonMobil for initiating, funding, designing, and supervising the data acquisition.