SEGJ Technical Conference

Repeatability estimation of ACROSS in Al Wasse field, Saudi Arabia

Abstract We carried out the seismic time-lapse experiment in water pumping field in the Kingdom of Saudi Arabia using ACROSS with an ultra-stable seismic source. By the present study, we identified huge temporal changes of waveforms. It is, however, necessary to understand the nature of seismic arrivals and their travel paths, and magnitude of repeatability. We carried out refraction study using the ACROSS seismic source and found that the first arrivals disappear around 700 m offset distance due to the presence of the shadow zone. A strong arrival appears at the distance further than 1500 m refracted at 900 m depth. In this paper, we discuss the NRMS repeatability of the ACROSS seismic source. Because the first arrivals disappear around 700 m distance, we used those shorter than 700 m and found that the NRMS repeatability was better than 5% during 2 month periods. The travel-time drift was 0.2 ms during 2 months at the best two stations. The source itself might have roughly 2% NRMS repeatability. The present result supports that the ACROSS source has excellent repeatability well enough to discuss the time lapse of the subsurface.