Independent simultaneous sweeping in Libya‐full scale implementation and new developments

Abstract

At the 2008 SEG convention in Las Vegas (Howe, Allen, Jack et al SEG 2008) we reported on a proof of concept of a new acquisition technique called ISS (Independent Simultaneous Sweeping). This paper describes a full scale implementation of this method in Libya, where it is being used to acquire a very large exploration land 3D survey in excess of 13,000 sq.kms Recent developments in recording systems allow for a recording spread to be continually active, which we refer to as continuous recording, although it may be more accurately described as recording of a set of contiguous records. This removes the necessity for real time synchronization of sources and recording systems. As long as the continuously recorded data and the source initiation can both be linked to the same time standard, (e.g. GPS time) the traditional shot records can be combed from the continuous dataset at any later stage. We have used the benefit of continuous recording to operate a large number of sources simultaneously on a large recording spread thereby greatly improving the productivity of land acquisition. In this method all vibrators work independently without any attempt to synchronize their activity, and the underlying principle is that all interference between sources can be treated as ‘noise’. The noise is randomized as much as possible, and a standard suite of noise removal tools is used during processing. The standard noise removal techniques are very effective, however, we recommend the paper by Abma et al which reports inversion techniques that remove the noise in a more deterministic manner, and which may be beneficial for development quality surveys. In our simple and robust approach, there is no apparent limit to the number of sources that can be operated simultaneously, there is no waiting time for any vibrator and very little central control or communication is required. It is very well suited for work in many environments including difficult terrain, where vibrator manoeuvering is slow, or where radio communication is challenged. We demonstrate that this technique can deliver very high fold data at high efficiencies, such that it enables land 3D to be acquired for exploration purposes at costs comparable to marine exploration surveys. We also report the initial results from a field trial of a cable‐less node recording system which, when combined with the efficiency of ISS, has the potential to change the way land seismic crews are configured and operated.