The broad bandwidths provided by BroadSeis enhance interpretation since the higher frequencies provide more detail about the geology, such as thin stratigraphic features and subtle rock structures, and the low frequencies contribute to better imaging of deep targets and large scale facies variations as well as providing better stability for pre- and post-stack seismic inversions.
The low frequencies give an envelope to the seismic signal that shapes the larger scale impedance variations or, in geological terms, the major lithology variations. This increases confidence in correlating seismic interpretation across faults and other major structural features and allows layers to be easily differentiated. The phase control of the low-frequencies is very good, so BroadSeis data have a characteristic 'texture' which brings a new appearance to seismic stratigraphy.
In this example from northwest Australia the broader bandwidths provided by BroadSeis
give better lateral resolution and clear layer definition
The increased resolution provided by wavelets without side lobes produces events that are single peaks or troughs, corresponding to genuine geological layers. This clarifies impedance contrasts and creates sharp images of small features, as well as providing clear differentiation between different sedimentary packages. Examples from northwest Australia show unprecedented clarity of deeper targets, with resolution our clients tell us they have never before seen in this area.
Rock Property Differentiation
BroadSeis allows the direct inference of rock or fluid properties. In the example below, the top of the uplifted fault block is distinctly differentiated as a dark body or layer above a lighter layer. This indicates differences in rock and/or fluid properties.
The top of the uplifted fault block is distinctly differentiated as a dark body or layer above a lighter layer, indicating variations in rock or fluid properties
The broader bandwidth provides greater correlation between traces for faster and more reliable interpretation by auto-tracking tools. In the North Sea example below tests demonstrated that it is five times faster to interpret the top chalk horizon on BroadSeis data than on conventional data.
In this example from the North Sea BroadSeis demonstrates the additional value gained from the broader bandwidth. The sharp peak and lack of sidelobes enabled clear identification of thin layers andt erminations in the Dornoch coals. Deeper in the stratigraphy, at the prospective Tertiary turbidite systems, there is a thick, low acoustic impedance shale sequence in the Paleocene Lista formation. The seismic correlates very well with well log data showing top and base of these soft shales. The strong amplitude low frequencies bring in the true envelope signature of this formation revealing a major impedance contrast.
Central North Sea example. BroadSeis data help to interpret as yet unseen details of the geology
to identify new prospects and better define existing plays
Away from the well calibration point, in the central part of the section, there is a prominent relief structure corresponding to a channel compactional feature with fill deposits having a different lithology, i.e. composed of less compactable sediments, including the desirable reservoir channel sands. The top of these sands appears very clearly on the BroadSeis data although it could hardly be identified on conventional data. Channel levee sands, overbank deposits and sand body pinch-outs are also easier to identify.