Attributes

Seismic Attributes are any computations with seismic data made to ease visualization and enhance features quantification.

Purposes

Attributes calculations are motivated by three main objectives:

  • Seismic interpretation (picking process) and subsequently prospects definition,
  • Tectonic and depositional history reconstruction (i.e. structural and stratigraphic history),
  • Petrophysical parameters extrapolation (reservoir thickness, permeability, porosity, water saturation, water/oil contact,…) into geomodels.

Kinds/Classification

Attributes could be gathered in three kinds corresponding to three different domains of applications:

  • Structural attributes to highlight tectonic and structural features. Among them, amplitudes maps, dip/azimuth, curvatures, coherency…
  • Stratigraphic attributes to identify prospects geometries and to distinguish several different geological patterns. Among them, amplitudes maps, instantaneous attributes,…
  • Reservoir attributes are attributes helpful to characterize reservoirs and define their lateral extensions. Among them, amplitudes maps, AVO-related attributes…

Volume Vs Surface Attributes

  • Attributes computed on volume are independent from the picking process, these cubes can be computed without picked horizons,
  • Attributes computed around an horizon are dependent on the picking process, they need at least one interpreted horizon,
  • Attributes computed within an interval are dependent on the number of  available interpreted surfaces, these maps are calculated between two interpreted horizons,
  • Unsupervised and supervised classifications techniques.

Need of care/QC/objectivity

Attributes try to characterize signal properties. Interpretation is a translation of observations in term of geological geometries, lithology and fluids content. But some attributes need inputs from the interpreter to be computed. Hence interpreters must keep in mind, that need of input parameters could make their objectivity somehow questionable. Trying to assess petrophysical parameters, quantitative interpretation must be handled with care. It often requires QC and/or modeling.

In the session, we give the fundamentals on the main seismic attributes. We show how signal processing tools are used to create the attributes. Through examples, we illustrate the applications of seismic attributes to seismic processing and interpretation:

Envelope
RMS Amplitude
Instantaneous Phase
Instantaneous Frequency
Dip & Azimuth
Coherency

Special thanks to Ludovic Peignard for his advice and invaluable help in creating these lessons and in providing the field examples. The different data set have been processed thanks to EarthQuick software (www.earth-quick.com)