Abstract

We have developed deeply-towed mechanical driven marine seismic vibrator (MSV) for the use in time-lapse seismic reflection survey to monitor offshore hydrocarbon reservoirs, in which interstitial fluids move with the production, for the optimization of recovery. For this objective, we evaluate the survey performance using MSV and revisited the data processing.

A downsized MSV was manufactured to conduct a sea trial to evaluate the performance as a seismic source in a real 2D seismic line survey off the coast of the Japan Sea. We compare the processed results (a) for the data acquired by a downsized MSV and (b) for that acquired by a 480 cu-inch airgun array. We then tried to improve the data processing for data acquired by the downsized MSV that was towed at a water depth which any conventional airgun could not be fired to see if the signal-to-noise ratio is improved.

We verified the survey performance using deeply-towed MSV and our data processing approach could be equivalent to it of airgun array the maximum seismic emission power of which is about 40 dB larger than that of the downsized MSV. Downsized MSV which was towed 50 m below the sea surface could acquire a conventional 2D seismic survey data with a conventional streamer cable. The superposition of long-leg surface multiples was observed in the data acquired by deeply towed MSV as anticipated. Our MSV showed the high stability in the source signature over the entire survey period, which is favorable for the use in time-lapse surveys. We also confirmed that the surface multiples could be suppressed in the processing we have introduced to exploit the utilization of multichannel signal processing to improve the SNR of acquired data. Moreover, we noticed that the surface multiples removed in the processing may also be used as signal to be superimposed with the processing data to enhance further the SNR.

Since the MSV does not sacrifice the power of signal generation against the towing depth and generated signal has high repeatability, the combination of deeply-towed MSV and our processing method could realize precise time-lapse survey which keeps the quality of survey data without large-volume amplitude.

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