Diptype Glossary

While we are open to specialized dip type classifications and definitions based on your needs, HEF does apply a consistent set of bedform and fracture fabric definitions when we manually interpret borehole image features with the following typical designations:

Dip Types (Standard Structural and Fracture Interpretations)

Bed (formerly referred to as COMPUTED)
  • Bedding features that are laid down horizontally, or close to it
  • The main guide for interpreting primary structural features (faults and folds)
  • In well bedded zones the bedding surfaces are usually very distinct features on the image log

  • Lower confidence bedding where the image is poor quality, is distinct or shattered by fractures,
     or otherwise obscured by other textures

  • Bedding surfaces with stratigraphic dip relative to surrounding structural bedding
  • Wispy texture like brush strokes on the image log
  • Good indicators of paleocurrent, energy and depositional environment

  • Irregular contact such as from a concretion
  • Features that are lens or irregularly shaped and should not be included as structural or
     stratigraphic bedding, or truncations of any significance
  • Nodular events are included only in the HEF image plot, so that the orientation of these features
     can be known at a glance, but do not pollute other data sets

  • Contacts between different rock types, or a significant stratigraphic break
  • Well defined surfaces that are oblique to the bedding (BED) above or below (or both) 
  • Questionable or unclear structural breaks, such as possible faults that have no associated fracturing
  • HEF avoids using the term TRUNCATION for the many bed-set boundaries within a cross-bedded
     sandstone sequence

  • Open, dark, conductive (or acoustically non-reflective) feature (dark because the mud almost always
     has a lower resistivity than the surrounding rock)
  • Intersects more than 50% of borehole circumfrence
  • Note: The fracture aperture on an image log appears orders of magnitude larger than the actual
     aperture (HEF can estimate the aperture using mud and formation resistivities along with the trace

  • Same characteristics as an open fracture 
  • Intersects less than 50% of the borehole circumfrence 
  • Lower confidence feature
  • Usually only picked in acoustic and oil-based images

  • Open fractures that appear over the full circumfrence of the borehole
  • Have an appreciable thickness (aperture) on the image

  • Fractures with no open aperture space
  • Electric image logs: light-colored traces or traces that are dark on one side and light on the other
  • Acoustic image logs: often cannot be imaged or appear as light colored (acoustically reflective)
  • Filling material is generally mineral cements or sometimes low-porosity gouge developing along the
     fracture, particularly common along small offset shear fractures that occur in high-porosity
  • Fractures infilled with clay cements will appear dark, and are nearly impossible to distinguish from
     open fractures

  • Normally as a result of under balanced drilling, the sides of the wellbore that are in the direction
     of the minimum horzontal stress may spall away
  • Breakout, or spalling appears as dark, parallel vertical features on opposite sides of the borehole
  • Good indicator of present-day principal horizontal stress direction

  • As a result of over balanced drilling, tensile fractures (drilling induced fractures) can form and
     propagate in the direction of the maximum horizontal stress
  • They appear as a pair of borehole-parallel straight conductive cracks (vertical, en echelon or
     otherwise stress-delimited) that are non-sinusoidal
  • Good indicator of present-day principal horizontal stress direction

  • Open fracture that appears to have some amount of fault displacement
  • This term is reserved for features that have direct or indirect indications of shear offset
  • Generally shear fractures or small faults, though sometimes they may be the surfaces of
     larger faults or fault zones
  • May appear as a) an offset or mismatch of the bedding across a fracture-type trace or b) the
     appearance of a "breccia" texture along a zone. Open shears are often associated with significant
     flow zones

  • Closed or resistive-material-filled fracture that appears to have fault displacement
  • Similar to OPEN SHEAR, but filled with fault gouge and/or healed with resistive minerals (similar

Dip Types (Oilsands)

Scour Surface
  • Truncational surfaces where the overlying sand is different in dip magnitude and/or direction from
      the underlying bedding
  • Bedding surfaces with “pebbly” rip-up clast features (uneven surfaces) in the sands
  • Muddy units with an overlying sand body. Contact is generally clear
  • Lower and upper contacts of Mud Breccias

Erosional Surface
  • The contact between sand and overlying thick mud (> 0.5m), signifying a flooding event
  • Boundaries within an IHS (Inclined Heterolithic Strata) unit where there is a clear, abrupt change in
     the lateral accretion direction

Unconformable Bed Boundary
  • Only at the top of the Carbonate/McMurray boundary

Lateral Accretion
  • Packages of alternating thin sand/shale beds (cm’s thick) which are inclined (3-15 deg) with similar
     dip magnitude and direction
  • Generally occur in IHS and mudstone, but can carry on into marginal sands and mudstones
  • Units can be several metres thick

Cross Bedding
  • Very thin, sometimes faint, wispy beds in clean sands (<10% VSH)
  • Bedding inclined between 10-35 degrees
  • Good paleocurrent cross-beds occur generally between 15-35 deg
  • Cross-beds commonly bounded by scour surfaces

  • Any other bedding surface that doesn’t fit the above definitions
  • Stratigraphically flat bedding contrast

Convoluted (Bedding)
  • High-angled bedding (>10 deg)

Nodular Event
  • Discontinuous lenses or concentrations of harder sediment which disrupt the surrounding bedding
  • Generally occur in siderite bands in the caprock

Large Fracture
  • Open fractures that appear over the full diameter of the borehole and have an appreciable
     thickness (aperture) on the image (see above)

  • Open conductive fracture that occurs across more than 25% of the borehole
  • Fractures appear darker than the surrounding lithologys
  • In rare cases, the resistivity of the mud filtrate (RMF) value is higher than the openhole resistivity
     curve, resulting in a fracture that is lighter than the surrounding lithology (see above)

Healed Fracture
  • Sealed or mostly sealed fracture filled with resistive material
  • Healed fractures appear lighter than the surrounding lithology (see above)

Open Shear
  • Open fracture that appears to have some amount of fault displacement (see above)

Sealed Shear 
  • Closed or resistive-material-filled fracture that appears to have fault displacement (see above)

  • Parallel vertical cracks in the plane of horizontal principal stress (see above)

  • Parallel vertical features where the borehole wall is enlarged perpendicular to the principal
     horizontal stress direction (see above)

·         The main guide for interpreting primary structural features (faults and folds)

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