Predicting changes in seismic response within thermally produced reservoirs provides an important tool for time-lapse seismic survey interpretation. In terms of reservoir management this has three important benefits: (1) reservoirs with small seismic changes resulting from production can be monitored, (2) reservoirs with large seismic changes can be monitored more frequently, and (3) monitoring data can be used more quantitatively. Reducing the degree of nonrepeatability to as low as 6% to 12% allows monitoring of smaller reflectivity changes. After corrections by deterministic tidal time shifts and spatial interpolation of the irregularly sampled streamer data, relative rms difference amplitude levels are as low as 12% for a deep, structurally complex field and as low as 6% for a shallow, structurally simple field. Results from two controlled zero time lag monitoring experiments in the North Sea demonstrate high sensitivity to changing water level and variations in lateral positions. In this paper we show that towing many streamers with narrow separation, combined with cross‐line interpolation of data onto predefined sail lines, can give highly repeatable marine seismic data. A lack of repeatability limits how frequently reservoir changes can be monitored or the applicability of seismic monitoring at all. Monitoring subtle changes in the seismic properties of a reservoir caused by production places strong demands on seismic repeatability. Seismic reservoir monitoring has become an important tool in the management of many fields. The results show that repeated 3-D VSP surveys (preferably using permanently installed geo-phone arrays) might be an efficient tool for detailed and precise monitoring of fluid and pressure changes within a hydrocarbon reservoir. Horizontal geophone components show approximately the same degree of re-peatability compared to the vertical component, but hor-izontal geophone data is slightly more sensitive to posi-tioning errors. Repeatability variation with increasing shot separation distances is analyzed, showing a rapid de-crease in repeatability as the accuracy of the position-ing of the repeat survey decreases. This fact shows that there is a po-tential for acquiring very accurate time-lapse seismic data by using a permanently installed downhole geo-phone array. It is found that for a frequency range between 3.5 and 50 Hz, the difference root-mean-square (rms) level be-tween two recorded traces belonging to two different shots is about 8%. A 3-D vertical seis-mic profiling (VSP) data set, acquired over a period of two days, is used to analyze how repeatable a perma-nent installed geophone array can be and how repeata-bility changes with inaccuracies in source positioning. Increased repeatability is recognized as one major issue for improving the time-lapse seismic technology as a reservoir management tool.
0 kommentar(er)
