Evaluation of the slip-sweep technique near southwest Ghawar field, Saudi Arabia

A 14-swath seismic acquisition experiment was conducted in November 2006 over a prospect area southwest of Ghawar field. The objective of this experiment was to compare four source designs with various numbers of vibrators in flip-flop or slip-sweep modes. The receiver geometry (4,400 receivers, interval 50 m) and sweep frequency range [4–94 Hertz]) were kept constant throughout the test. For each array, the parameters were as follows: (1) number of vibrators/fleet 5 3 2 1; number of fleets 2 4 4 12; (3) Sweep length (second) 15 15 15 42; (4) Slip time (second) Flip-flop 11 9 5; (5) Source density (VP/km) 200 400 800 800; (6) Actual productivity (km/ hour) 0.51 0.54 0.32 0.8. It is clear that the slip-sweep method can provide a very significant improvement in productivity compared to flip-flop acquisition. Two questions remain: (1) is vibroseis source-generated noise or ambient noise the limiting factor? (2) How will the additional noise associated with the slip-sweep method affect the seismic image? The conventional fivevibrator 0source array design has proven to improve the initial signal-to-ground roll and ambient noise ratio. These source arrays can be decomposed into single-vibrator, point-source efforts, maintaining the same source density per area while increasing the sampling density. This improved source sampling optimizes source-generated scattered noise attenuation methods. Preliminary analysis of stack data showed equal quality for the fivevibrator and the three-vibrator data; but the single-vibrator achieved better quality although the square-root theory predicted a signal-to-noise ratio of 3.5 decibels lower. This seems to indicate that source-generated direct and scattered noise is indeed the problem in this area and that it is serious enough to mask the additional noise associated with the slip-sweep method.