The Lesueur formation has several distinctive features that complicate conventional seismic characterisation of the subsurface: the Yalgorup member consists of finely layered shaley lenses and not continuous impermeable layers; the Wonnerup member, has no seismic reflections inside; intense faulting in the area causes lateral variations of the subsurface properties and further complicates seismic imaging conditions.
Advanced methods of seismic quantitative interpretation and joint analysis of a broad range of available geophysical/geological data may provide a refined model of the Lesueur formation and its properties. The project uses the large commercial seismic and high resolution nested seismic survey around Harvey-4 to resolve a shallow part of the subsurface. To constrain static geomodelling, all available 3D surface seismic data, VSP data from Harvey-1, -2, -3 and -4, well log data and the results of the core analysis performed in a preceding study was dedicated to geological data integration.
To date, a conventional quantitative interpretation (QI) approach has been set up and applied to both seismic data sets. The principal goal of the study was the mapping of the concentration of potential fluid baffles – paleosols. The workflow developed consisted of the following steps:
- True-amplitde seismic processing to allow for adequate interpretation of the intensity of seismic events on the seismograms
- Application of some conventional seismic attribute analysis,
- Sparse-spike acoustic impedance inversion of the commercial seismic
- Well-logs quality control and conditioning for seismic inversion
- Feasibility study/correcation analysis between acoustic and petrophysical properties within the Yalgorup and Wonnerup formations,
- Matching commercial seismic to all four Harvey wells, wavelet extraction using reliable wells;
- Model-based acoustic inversion of the commercial seismic;
- Paleosol bodies mapping in the acousitic impedance cubes;
- Modelling test of AVO-effect in the nested survey, selection of the most reliable range of offsets; model-based elastic impedance inversion of the nested survey data, and
- Mapping of the paleosol facies and determination of its characteristic lateral sizes.