Martin Bayly

Marine seismic acquisition: efficiency and environment, new technologies applied in Australia

The design of successful marine seismic surveys is driven by many factors, two prime issues being efficiency and environmental impact. Efficiency is primarily driven by reduction of non-productive time and creating the largest sub-surface illumination area possible in the shortest time. In addition, public opinion and governmental regulations are requiring the industry to minimise their environmental impact. One aspect is reducing the overall sound exposure level (SEL) of the source into the marine environment. Using recent Australian examples, we will discuss and demonstrate the use of two new technology groups that address these concerns. The first is the use of a new type of seismic air-gun with optimal output over the range of frequencies commonly used in seismic exploration, while limiting potential environmental effects from unnecessary high-frequency emissions. The second is continuous data acquisition along the entire boat traverse, including the turns, thereby reducing non-productive vessel time. Both are described with examples from a recent survey acquired offshore north-west Australia.

High Resolution Anisotropic Earth Model Building on Conventional Seismic Data Using Full Waveform Inversion: A Case Study Offshore

We present a case study from the North West Shelf of Australia where the complexity of the overburden consists of several thin multi-level channel systems filled with a combination of anomalously high or low velocity sediments. Not accounting for these strong velocity variations accurately, can lead to subtle image distortions affecting the underlying section down to and including the reservoir level. This can have significant impact on the volumetric estimates of reserves in place. To resolve these complexities in the overburden, full waveform inversion (FWI) was utilized to generate an updated earth model exploiting both early arrivals and reflection events. One caveat to using full waveform inversion is the need for low frequencies to be present in the seismic data, or, the initial starting velocity model must contain the correct low wavenumber components. However, conventional seismic data acquired at shallow tow depths are usually band limited particularly at the very low frequencies. Our case study will discuss these issues along with other limitations that this “conventional data” presented along with the workflows and quality control methods adapted to this data in order to converge to a plausible, high resolution earth model.

Depth Imaging Coil Data: Multi Azimuthal Tomography Earth Model Building And Depth Imaging the Full Azimuth Tulip Coil Project

Summary The Tulip 3D is a full azimuth single vessel Coil shooting survey in Indonesia. Coil geometry acquisition records a dataset with a wide range of source to detector azimuths. Amongst the numerous benefits of extended azimuth sampling methods is the advantage of illumination diversity. This has a desirable impact with tomographic velocity model building for depth imaging. The broad range of source to detector azimuth information allows an additional constraint on the travel time tomography by providing a network of intersecting rays not available with narrow azimuth geometries.

Seismic imaging of the fault that caused the great Indian Ocean earthquake of 26 December 2004, and the resulting catastrophic tsunami

WesternGeco and Schlumberger, as part of the Sumatran Andaman Great Earthquake Research (SAGER) team, contributed to the effort to image the Sumatran seismogenic zone that ruptured on 26 December 2004. Resulting reflection images allow interpretation of the rupture point down to 40 km of depth, providing arguably the best seismic reflection images of a deep subduction zone to date. Early images, generated on the vessel, showed that the subducting mechanism (oceanic crust plus Moho) can be seen down to 12 s two-way traveltime (TWTT). Additional interpretation has shown seismic reflections as deep as 18 s TWTT (50–60 km of depth). This is a rare example of a complete subduction zone system being directly imaged with reflection seismic technology to over 40 km of depth.