Search

Recently there has been renewed interest in the hydrocarbon potential of the Perth Basin in Western Australia. Recent discoveries of gas have shown that there is a working hydrocarbon system within at least the northern and central parts of the basin. In most parts of the basin, modern seismic data is relatively scarce. In the current low oil price environment, explorers are looking for cost-effective ways of exploring and targeting seismic acquisition. Airborne gravity gradiometry is such a technique. It has been widely used in frontier basins to understand the basin architecture, sedimentary structure and planning of seismic acquisition.

We demonstrate how we unlocked the potential of one of the last underexplored regions of the South Atlantic margin through smart seismic acquisition, processing technology and close collaboration.

In seismic processing and reservoir characterization we often need to measure relative displacements between different realizations of data. Over the years many methods have been developed utilizing different similarity measuring techniques. Such alignment or warping methods are often effective signal or image processing tools. However, a survey of available methods shows that none are directly driven by the physics of seismic imaging. We show that a seismic image can be considered a field governed by the wave equation. We visualize different image realizations as snapshots of the wavefield at different times, and these give us the required displacements or time-shifts. By formulating the problem in a physical context, displacement vectors are obtained that honor the directionality of the wave propagation. For example, 4D time-shifts are obtained in a direction normal to the reflectors. We compute these shifts in an inverted finite-difference scheme. To overcome limitations of the two-way wave equation, we factorize it to its one-way counterparts. The method is demonstrated on synthetic and real datasets.

Initial imaging results are deeper and clearer than have been seen in this area before, with enhanced imaging of the Triassic to Lower Cretaceous reservoir units. In addition to demonstrating that there is at least 20km of sediment in this area, clear faulting and structure of the deep layers can be seen, demonstrating the exceptional penetration power of broadband low-frequency seismic data.

For seismic exploration (i.e. reservoir geophysics), retrieval of body waves appears promising, especially at low frequencies (below 3 Hz) where seismic vibrators reach a limit. These low frequencies are of interest for velocity model building (Baeten et al. 2013) and for broadband seismic inversion (Kneller et al. 2014). Here we demonstrate an example of body wave retrieval using ambient noise correlation in the context of seismic monitoring. The result of the ambient noise correlation is correctly arranged to produce noise-induced shot point gathers at each sensor positions. The noise-induced migrated image is compared and then combined with the image obtained by migrating the conventional active shot point gathers generated by vibroseismic sources (Cotton et al, 2014). In so doing, we considerably broaden the image spectrum toward the low frequencies.

Combined with recent receiver deghosting strategies, the use of multi-level sources can provide further uplift to the ever broadening bandwidth of seismic data. While multi-level sources help mitigate source notches in the output spectrum, the resulting emitted wavelet still exhibits residual ghosts, directivity, and bubble energy which must be handled in processing. We highlight the compatibility of Ziolkowski’s notional source method with multi-level source acquisition. We continue by showing how the directional signatures may be used for 3D directional designature and deghosting on shallow water towed streamer data. The results show a significant improvement in the level of ringing relating to source wavelet directivity effects.

Recently, a lot of efforts has been done in seismology and geophysics to track and monitor sub-surface property variations such as velocity, fluid pressure or saturation. In 4D monitoring, the two main observables are velocity and amplitude variations. For a given reflection, variations are classically monitored using wavelet travel time and amplitude. Today, combined travel time and amplitude variations measures are possible. In this paper, we present an array processing method to measure new observables linked with the velocity variations in 4D monitoring such as the slowness at both the source and the receiver sides.

The use of broadband data in reservoir characterization has proven advantages. However, the whole workflow should be reviewed and renewed in order to get all the advantages of broadband data.

Reliable low frequency content and phase alignment are critical for broadband seismic inversion and the prediction of reservoir properties. However, currently there is a lack of tools for ultra-low frequency (less than 5 Hz) quality and phase assessment. A focusing metric in the impedance domain is proposed to assess the ultra-low frequency phase alignment. The method has been applied on a real broadband dataset for the assessment of the residual phase correction process and the conclusion is validated by using well information.