High Fidelity Vibratory Seismic Research Articles

Vibroseis productivity: shake and go

ABSTRACTWe use both model and field data to compare three methods for increasing vibroseis productivity and decreasing acquisition costs. The first method, HFVS (high‐fidelity vibratory seismic), allows us to separate the responses from individual vibrators when multiple vibrators are operating simultaneously. The data quality of the separated records is superior to that of conventional correlated data because they are processed with measured ground‐force signals, but the number of sweeps must be greater than or equal to the number of vibrators. The second method, cascaded sweep, eliminates the listening time between multiple sweeps and partially mitigates harmonic noise observed at later times on near‐offset traces. Finally, a combined method, continuous‐HFVS (C‐HFVS), allows source separation with a single, long, segmented sweep. Separation is as good as with HFVS and interference noise is limited to times near the end of a sweep‐segment length. All three methods produce acceptable seismic images for post‐stack and prestack amplitude interpretation.The choice of which option to use depends upon the area being investigated. HFVS has numerous benefits, especially when fine sampling is required to mitigate static problems and elevation changes. Due to the ability to separate individual responses, fine sampling can be achieved without sacrificing productivity. For deeper targets, cascaded sweep can be more efficient but data quality suffers from harmonic noise. C‐HFVS, which combines features of HFVS and cascaded sweep, has the potential to result in the highest productivity, without sacrificing either fine sampling or data quality.

HFVS™: Enhanced data quality through technology integration

Known problems with vibroseis data include difficult-to-pick and inaccurate first-arrival times, poor well ties, correlation side lobes, harmonic ghosts, and coupling differences. Also, to reduce acquisition costs, various methods are used to record and then separate data from different source locations using vibrators sweeping simultaneously, but these methods suffer from poor data separation and harmonic contamination. A novel combination of heritage Mobil High Fidelity Vibratory Seismic (HFVS) and heritage Exxon vibrator technologies solves these problems with vibroseis data. The method involves vibrator separation combined with vibrator signature deconvolution in such a manner that the output is minimum phase and matches impulsive data. Vibrator signatures are calculated from the vibrator accelerometer measurements. The signatures from multiple vibrators and multiple sweeps are used to design a filter that optimally separates the data from each vibrator and replaces the signatures with a specially designed impulse response. Specific procedures are included to reduce the effects of inversion noise, which can distort the phase. HFVS recording can be used to increase production rates and reduce acquisition costs or to increase spatial sampling and improve data quality. Data recorded from multiple vibrators sweeping simultaneously can be separated by at least 60 dB. After separation, the data from each vibrator can be processed as unique source points. Compared with traditional vibrator arrays, individually processing each source point can result in better data quality by reducing intra-array effects and improving the mitigation of ground-roll noise.

Sweeping changes for Vibroseis operations

This paper reviews current slip-sweep and High Fidelity Vibratory Seismic (HFVS) operations and tracks their evolution over the past 3-5 years. Projecting the technological advances and operational experience over this period, high-productivity and high-resolution vibroseis surveys may become a future standard in the oil industry. Such surveys utilising simultaneous sweep technology are designed to use increased vibroseis production to explore large areas with suitable fold and resolution, or improved seismic data quality through increased fold and denser surface sampling. Further improvement in seismic data quality in all forms of vibroseis acquisition is achievable by real-time processing of actual vibrator ground motion with the uncorrelated field record. Perhaps vibroseis signal correlation with a synthetic pilot sweep will become anoutdated standard?