Comparison of Single Sensor 3C MEMS And Conventional Geophone Arrays For Deep Target Exploration

Stotter, Christian (OMV E&P GmbH) | Angerer, Erika (OMV E&P GmbH) | Herndler, Erwin (OMV E&P GmbH)

OnePetro 

Summary OMV acquired a 2D vibroseis line in the Vienna Basin /Lower Austria with the purpose of comparing digital multi-component single sensors (MEMS) and conventional geophone arrays. The primary exploration target for this line is below 3 km depth. For such deep targets efficient noise reduction is a key element of processing, since signals from these depths are weak and may be totally obscured by the noise cone. All source points were recorded in single sweep mode, i.e. no vertical stacking has been performed in the field. This results in a dense sampling of coherent noise in the common receiver domain, which is consequently used for coherent noise reduction using FK filters for both the conventional geophone and the MEMS sensor line. Additionally, further noise reduction techniques like digital group forming in both source and receiver domain, and polarization filters were tested. The results show that with the use of single sweep recording and polarization filter techniques it is possible to produce seismic sections for the single receiver MEMS line that are comparable to the conventional geophone array line in signal to noise ratio but with an increased frequency content both on the high and the low end of the seismic spectrum. It is subsequently demonstrated that coherent noise rejection with polarization filtering gives similar or even superior results compared to FK filtering of densely sampled data. This may have consequences for the application of 3C single sensors in a possible 3D seismic survey, since a polarization filter is a single trace processes that does not require dense spatial sampling. Introduction In recent years targets for hydrocarbon exploration have become more challenging as explorationists are looking into deeper and more complex reservoirs. In addition to this many processes like acoustic impedance inversion depend on the low frequency content of the seismic signal. Thus the increased demands of exploration require continuous advances in methods for seismic imaging but also in acquisition. A possible way forward on the receiver instrumentation side are single sensor, multi-component digital geophones, based on micro-machined electromechanical sensors (MEMS). These MEMS are accelerometers with a broadband linear amplitude and phase response together with a large dynamic range. On the down side single sensors lack the noise rejection power of conventional geophone arrays both for coherent and random noise rejection. The use of MEMS-based digital sensors has been promoted by several authors during the last few years (Tessman et al.;,2001; Mougenot, 2004; Mougenot and Thorburn, 2004) and some field examples of different MEMS-based systems in comparison with conventional geophone arrays have been presented (Ronen et al., 2005; Gibson et al., 2005; Lansley et al., 2007). Despite the fact that most of the mentioned comparisons gave positive results for the MEMS systems, all those surveys investigated shallow targets between 0 and 2 s TWT and were aimed at increasing the vertical resolution with high frequencies. In this study we have tested the use of digital MEMS sensors for recording signals with a 2D line designed for relatively deep targets from 2 to 4 s TW.

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