ASCII & Computed Curve Definitions


HEF's standard Ascii and LAS format files are:
  • .bed -Structural Bedding
  • .fra -Large and Regular Fractures
  • .red -Bedding Averaged on a 5 metre/foot interval
  • .r10 -Bedding Averaged on a 10 metre/foot interval
  • .all -All interpreted surfaces including structural bedding, cross-bedding, fractures, large fractures,
      healed fractures, drilling induced fractures, borehole breakouts, erosional truncations, and
      shear features.
  • .afr –All fracture types

These files contain the following data types:
  • Dip (DIP)
  • Dip Azimuth (AZIM)
  • Hole Deviation (DEVI)
  • Hole Azimuth (HAZI)
  • Quality (QUAL).
  • Apparent Azimuth (AAZI)
  • Apparent Dip (ADIP)
  • Dip Type
  • (Quality is an arbitrary value that is automatically generated. All dips are hand selected and so should be
      considered as being of equally good quality.)

Additionally, LAS files contain the following data types:
  • Depth difference between top and bottom of the dip (HEIGHT)
  • Length of the feature trace (TRALEN)

HEF's oilsands analysis files are:
  • .xbd –Cross-bedding and lateral accretion
  • _bioturb_codes.las –Bioturbation index
  • _facies_codes.las –Facies identification
  • _hires_image_vsh.las –Shale volume
  • _effective_perm.las –Effective permeability
  • _hires_image_sw.las –Porosity and fluid saturation percentages)
  • _layer.las –Determination of which pads are in the mud layer

 HEF's fracture analysis files are:
  • _fracden.las -Fracture Density
  • _avg_aper.las -Fracture Aperture
  • _avg_res.las –Average Resistivity of the image
  • _frac-with-aper.las –Fracture Aperture of individual fractures

The regular fracture density file contains the following curves:
  • Fracture Intersections (FDEN_RAW) - intersections/m
  • Stochastically Corrected Fracture Density (FDEN_C) – m2/m3
  • Large Fracture Intersections (LFDEN_RAW) - intersections/m
  • Stochastically Corrected Large Fracture Density (LFDEN_C) – m2/m
  • Open Shear Feature Intersections (OS_RAW) - intersections/m
  • Stochastically Corrected Open Shear Feature Density (OSDEN_C) – m2/m3
  • Healed Fracture Intersections (H_RAW) - intersections/m
  • Stochastically Corrected Large Fracture Density (LFDEN_C) – m2/m
  • Sealed Shear Feature Intersections (SS_RAW) - intersections/m
  • Sealed Shear Feature Density (SSDEN_C) – m2/m3


The wellbore generally intersects fractures at an oblique angle. As a result, the fracture spacing (and therefore density) is not simply the distance between fracture intersections along the wellbore. Commonly, the “true fracture spacing” is calculated from the intersection distance using a simple trigonometric function (known as the Terzaghi correction, or some variant). This is what is called Geometry-Corrected Fracture Density above, producing densities: FDEN and LG_FDEN.

We find, however, that this approach falters because of three issues: (1) the image log is sampling a cylindrical volume of rock rather than line, (2) most natural fractures do not cut entirely across the wellbore and (3) fractures that cross only a minor portion of the wellbore and/or intersect the wellbore at very low angles are difficult to detect on the image logs.

We have developed an alternative density correction procedure based on stochastic models of various fracture populations intersected by the wellbore and which considers only those fractures that intersect at least 50% of the wellbore. The resultant density values are called FDEN_C and LFDEN_C above.

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