A significant reduction in harmonic noise was achieved using the new harmonic noise removal approach. That is allows the implementation of slip sweep method properly without any data quality deterioration. Therefore, we can consider the data obtained using slip sweep technique after noise removal equivalent to conventional data. We conclude that the slip sweep method offers the advantages to reduce the cost per km² with the same parameters, or to improve the seismic image resolution by acquiring a higher source density data with no extra cost.

In recent years, the demand of large 3D data volume, such as the high-density and wide-azimuth, leads the seismic companies to improve the productivity of their seismic crews. A significant increase of Vibroseis productivity, in 3D land survey, can be obtained by using more than one group of vibrators shooting at the same time. The Slip Sweep technique offers a high productivity by enabling the recording of overlapping sweeps from different groups of vibrators. Unfortunately, this technique often suffers from data quality deterioration associated to the harmonic noise distortion, generated by the adjacent vibrators (caused by non-linear phenomena and vibrator-earth coupling problems).The time between two consecutive sweeps, called slip-time, controls the productivity. A short slip-time allows obtaining a high productivity. However, if the slip-time was taken too short the more harmonic noise increased.

Because the quality of data should not be significantly affected by the technique used to speed up acquisition, several methods have been developed for reducing this harmonic noise. These methods are based on harmonic prediction operator for all harmonics calculated using Ground Force (GF) measurements (weighted sum the base plate and mass accelerations) and/or uncorrelated traces.
It is important to note that the estimation of harmonics using the Ground Force measurements is not entirely representative of the far field signature and the estimation by an operator calculated from several uncorrelated traces (range of offsets), is only representative of the signature of the selected range of offsets. Indeed, the evaluation of harmonics using a unique operator is found to be inaccurate. In this paper, we present a new method for the reduction of harmonic noise in slip-sweep data. The method consists of estimating each harmonic component of a seismic trace, at first, by applying  a prediction operator of considered harmonic. The prediction operator is calculated using the representative emitted signal (GF) measured by the vibrator. The prediction operator can be calculated in frequency domain by a ratio of the cross-correlation of the considered harmonic and the fundamental components and the auto-correlation of the fundamental component of the Ground Force signal.

Field application :
ENAGEO conducted a 3D field tests survey recorded in slip sweep and conventional mode, in Hassi Messaoud (south of Algeria). For the case illustrated here, the production source configuration consisted of two fleets of four vibrators operating in flip-flop mode, whilst the slip-sweep configuration was four fleets of three vibrators. Data was acquired with both configurations using the same receiver spread (50 m group interval and 300 m line spacing). With three sweep/VP of 12s the two fleets conventional crew achieved 52 VP/hr with a 56 m VP interval on 200 m spaced lines. The slip-sweep operation used a 14s single sweep, and achieved 162 VP/hr with the same VP interval and source spaced lines. Another test, in conventional mode, has been conducted in the same area using the same configuration as slip-sweep (the same fleet number and the same sweep length), and achieved 120 VP/hr.