Olivier Winter

Over 40,000 vibrator points per day with real‐time quality control: opportunities and challenges

To evaluate high-density source and receiver land seismic acquisition designs, two sets of simultaneous highproductivity vibroseis field tests were performed in a relatively flat terrain area with good signal-to-noise ratio. These included distance separated simultaneous sweeping (DSSS) (Bouska, 2009), slip-sweep (Rozemond, 1996), distance separated simultaneous slip-sweep (dynamic slipsweep) and independent simultaneous sources (ISS) (Howe et al., 2008) with unique sweeps. The second dynamic slipsweep field test used a 29 km active fixed super-spread (12 receiver lines separated by 300 m) with 20 point vibrator fleets on a 25 m x 25 m source grid. A group of 10 point vibrators were oriented orthogonal to the receiver spread in the North and 10 in the South direction with a lateral separation distance of 14.5 km. This method achieved 30,346 vibrator points (VPs) in a 24 hour period. The same fixed active receiver spread was reduced to continuously record two unconstrained simultaneous sources (microseismic mode) in 18 sectors (3x6). Each sector was 1.8 km x 1.8 km with 4,320 VPs on a 25 m x 25 m source grid (77,760 total VPs) with 18 unique 12 s pseudorandom sweeps (Sallas et al., 2008) and repeated with 18 unique linear upsweeps (14.5 s average sweep length) from 5 to 110 Hz. We achieved optimum productivity rates of 45,501 and 44,793 VPs per 24 hours, respectively, with real-time quality control (QC) – we were not sweeping blind. Seventy two drivers were organized in three eight-hour shifts along with four vibrator pushers per shift. Three helped with fleet management and one for TDMA real-time communication between the vibrators and the recorder. Even higher productivity rates could have been achieved with stakeless guidance training of the vibrator drivers and pushers.

Broadband Vibroseis using simultaneous pseudorandom sweeps

Simultaneous pseudorandom sweep technology (SPST) is a new method of Vibroseis acquisition. Carefully designed long pseudorandom sweeps that are mutually weakly correlated over a time window of interest permit source contributions to be separated. An advantage of random sweeps is the ability to create low-dwell sweeps without running the risk of overtaxing the vibrator hydraulic system. Since the sources tend to act independently, conventional correlation can be used for initial separation thereby permitting field QC of the process. A second separation using measured signals further suppresses crosstalk. We conducted a field test in Oklahoma using conventional, SPST and HFVS methods to develop subsurface images allowing a comparison of data quality and frequency content.