Seismic attributes and structural interpretation—it takes two to tango...

Abstract

In this paper, different 3D seismic attributes calculated to improve the accuracy and robustness of structural interpretations in several energy-rich Australian basins are compared. Detailed and precise fault and fracture maps are crucial not only for initial petroleum play assessment, but also for fault seal analysis and reservoir integrity studies. Robust fault and fracture models are also needed to improve the design of reservoir simulation programs and to manage the long-term containment of gas in geological formations. Different attributes (including coherency, dip-steered similarity, dip-steered median filter, dip-steered variance, apparent dip, and dip-steered most-positive and most-negative curvatures) from an array of 3D seismic datasets to better image structural fabrics, such as normal and different fractures patterns, in the North Perth, Cooper, Ceduna, Otway and Gippsland basins have been calculated. The results provide a remarkable improvement in the quality and precision of structural maps using this multi-attribute mapping workflow by comparison with more conventional maps produced, solely using seismic amplitude data. The key to the successful application of multi-attribute structural analysis, however, remains with the ability of the interpreter to identify meaningful structural information from a large volume of data. Thus, the structural expertise of the interpreter remains as the cornerstone to making geological sense of the various seismic processing techniques available.

Remote sensing of subsurface fractures in the Otway Basin, South Australia

“…Using several different seismic attributes (Figure ), a pervasive natural fabric is identified on attribute mapped horizons, namely, the Top Pretty Hill Formation at approximately 1900 ms two‐way time. The most positive and most negative curvature attributes are most likely to indicate structural fabrics present within the data set due to the established relationship between high curvature values and structural features [ Lisle , ; Roberts , ; Backé et al ., , ]. The lineations preserved in the curvature fabric share similar orientations throughout the seismically mapped area and are also consistent with the orientations identified on image logs (Figures and ).…”

“…Faults and fractures are often very poorly expressed on seismic amplitude data because the majority of faults and fractures lie below seismic amplitude resolution [ Roberts , ; Backé et al ., , ]. This poses a challenge when interpreting seismic data when regional information on small‐scale features is desired.…”

“…Fault trend definitions are enhanced for a much clearer and more well‐defined view of structures, highlighting fractures and fractured zones. Both faults and fractures show up as distinct lineations on the attribute‐draped surfaces [ Roberts , ; Chopra and Marfurt , , ; Backé et al ., , ]. The calculation of seismic attributes relies on the methodology outlined in Al‐Dossary and Marfurt [].…”

“…Several methods exist for identifying natural fractures in the subsurface, most notably various wellbore geophysical and image logs, recovered core, and surface analogues [ Barton et al ., ]. Both 2‐D and 3‐D seismic amplitude data are also commonly used to identify geological structures, which are likely to be fractured; and recently, 3‐D seismic attribute analysis has been applied to identify zones of fractured rock [ Roberts , ; Backé et al ., , ]. However, while identifying natural fractures can often be relatively simple with basic oilfield data such as wellbore image logs, accurately characterizing the transport properties of fractures within rock is another matter entirely and is one fraught with uncertainty.…”