Dipmeter Data, Borehole Image Logs and Interpretation

Dipmeter data, borehole image
logs and interpretation
Kris Vickerman
May 25, 2016

 Dipmeter refers to the bedding data (depth, dip, azimuth,
quality, etc.). The small plot on top is a dipmeter plot.
 Dipmeter also refers to an older tool with 4, 6 or 8 buttons
 Borehole image logs refer to any tool that samples an array
of measurements in the borehole:
 Resistivity – FMI, CMI, XRMI, etc.
 Ultrasonic images – UBI, CBIL, CAST
 LWD images – (GR, Density, Resistivity and so on.)
Introduction

 Data comes from the logging truck typically via satellite or
FTP transmission:
 File types such as DLIS, TIF, LIS, XTF, AFF, LAS, CSV
 Large files, often 100’s of MB
 Data is also found in digital archives:
 Corporate archives as digital or paper well files
 Government archives (BCOGC), as scans, paper logs, and digital
 Service company archives (HEF for example has more than 10,000
wells in our Recall Database dating back to the early 90’s)
 Log data vendor archives as rasters, etc.
 Digitized data such as ASCII bed dip files from above sources
 Data can also be sourced from physical media:
 Magnetic tapes, CD/DVD, scanning old paper prints and so on…
Introduction – input data sources

Outline
 Basics of borehole image interpretation
 Bedding and structural dip analysis
 Natural fractures
 Stress features

Basics of borehole image logs
 Wireline or MWD tool is positioned in the
borehole (resistivity, sonic, density, gr)
 Inclined surfaces intersect the measurement
buttons at different depths, unrolling to a sinusoid
in the standard display

Basics of borehole image logs
 Wireline or MWD tool is positioned in the
borehole (resistivity, sonic, density)
 Inclined surfaces intersect the measurement
buttons at different depths, unrolling to a sinusoid
in the standard display

 Typical Conductivity Image plot
is shown as an unrolled view
of the inside of the borehole
 Conductive features are dark;
resistive are light
 Planes that intersect the
borehole become sine waves
in this view
 Bedding (orange-yellow) and
fractures (black) visible in this
section
Borehole Image Example (FMI)

Image normalization
 Image colour is statically normalized with
conductive as black and resistive as white
 To enhance local contrast, colours are
renormalized in a sliding 1m window making a
“Dynamically Normalized” image
Dynamically NormalizedStatic

Image logs and core
 Conductive shale is
black, resistive
bitumen sand is
white/yellow
 We can often see
resistivity contrast
features that are hard
to see in core
DynamicStatic

Oil-Based horizontal field imager
 Horizontal field
electric images see
fractures better but
also see bit marks
 Acoustic images are
lower resolution
 Bedding is clear
 Some fracturing is
visible
 Some induced
features are visible

Borehole Image Interpretation
Step 1: Processed Image

Step 2: Beds

Step 3: Large Fractures

Step 4: Fine Fractures

Image interpretation
Dip “Tadpoles”
Hand-picked
sinusoidsLithology zoning

“Basics” products
 Plot of the interpreted image at various scales
(Paper / PDF / TIFF)
 Output of the interpreted image in DLIS
 Output/backup of the interpreted image in DB
format like Recall or Geoframe, etc.
 Output of the interpreted features (Beds,
fractures, etc.) in LAS

Basic Structural Dip Analysis
 Tadpole Plots
 Stereonet Plots
 Stick Plots
 True Stratigraphic Thickness Plots

True Stratigraphic Thickness Plot

Example of structural interpretaion
 Each domain is taken to
have consistent average
dip
 The boundaries between
the domains are oriented
on the bisectors of the
dip domains

Interpreted Stick Plot
Simple stereonets
Uncluttered bed dips and
subtle frac. den. curve
GR and tops markers
Depth tracks visible
but not in the way
Projected bedding
Anything else you
might like to add
FDEN, tadpoles,
openhole data

Interpreted stick plot (Lithotect)

Stratigraphic beds
 Describing bedforms and lithology
 Sand count and facies plots
 Vuggy porosity analysis

Sandy IHS
 Moderate GR,
moderate resistivity
 Inclined alternating
sand/mud beds
 Consistent bedding
dip direction
towards channel
centre
 Vsh 10-40%

Trough crossbedded sand
 Very clean GR,
high resistivity
 >10° crossbeds
 Inclined truncations
 Vsh < 10%
 Dip Downstream

Planar-tabular crossbedded sand
 Clean GR, high
resistivity
 >10° flow
crossbeds, often
alternating direction
 Flat truncations
 Vsh < 10%
 Dip down-current

Mud Breccia
 Moderate to high
GR, low resistivity
 Often crossbedded
 Clast supported
conductive (dark)
mud clasts
 Petrophysically
indistinguishable
from laminated
mud beds below
 Vsh > 10%

Sand count plot
 Sand count / facies plots can take many forms
 This one shows:
 Openhole data on the right
 High-res resistivity curve for thin bed petrophysics (red, on the right)
 Facies track (Green/yellow/black)
 Sand count track (brown and yellow to the right of image)
 Sand bed thickness and percentage curves (yellow and grey to the right of image)

Secondary porosity plot
 Image thresholding produces an estimate of irregular (secondary)
porosity as a percentage of the whole
 Plot shows limestone / dolostone flag on left, thresholded black and
white image on right followed by secondary porosity curves in red, green
and grey

Bed Interpretation products
 Stereonet, Tadpole, Stick, TST, etc. (Paper / PDF)
 Lithology zonation file (LAS) and plots
 Bed dip types on plots and in LAS / ASCII

Natural fracture interpretation
 Fracture types (open, closed, shear)
 Fracture properties (geometry, density, aperture)

Open Fractures
 Open fractures are filled
with conductive drilling
mud (dark on borehole
images)
 Fractures are not infinite
in length so partial
intersections are
common
 Direct measurements
include dip, azimuth,
trace length, minimum
radius, type (LAS)

Open Fracture Exaggeration
50cm
 This fracture is probably on the
order of .5 mm, not 5 cm as it is
seen here
 Tool current “seeks” the conductive
fracture before and after it, making
it appear much larger
*From Cheung, 1999

 Mineralized fractures
might be filled with
calcite, quartz or
dolomite, all resistive
 Often fracture traces are
invisible
 See artificial halo inside
fracture plane
Healed Fractures

Healed Fracture Haloing
50cm
*From Cheung, 1999
 The resistive fracture itself is
invisible, see halo instead
 Tool current “piles up” inside of
resistive fracture plane and is
dispersed outside of it

Shear feature in Borehole Images
 Visible as a bedding offset
 Can be healed or open
 Can be mm-scale to km-
scale in throw
 Geologists would call these
faults but some managers
might not be so keen

Natural fracture interpretation
 Fracture types, (open, closed, shear)
 Fracture properties (geometry, density, aperture)

Fracture Density
 Fracture density can be calculated a few ways:
 As line-density 1-D
 As tracelength density 2-D
 As a modelled volumetric density 3D

Fracture Density Comparison
2 metres of image

Fracture Density Comparison
9 m2/m3 5 m2/m3
2 metres of image

Fracture Density Plot
 Gives an at-a-glance
curve to tell fracture
intensity but no indication
of aperture, permeability
or connection to porosity
 If drilling induced
fractures or foliation is
included, it gives false
results

Fracture aperture estimation
50cm
 Open fractures are invaded by conductive
drilling mud
 The amount of invaded mud is somehow
proportional to aperture

MUD
Fracture aperture estimation
*U.S. Patent No: 52435211
Aperture = A * Rt 0.1505 * Rm 0.8495
A = Excess conductance
Rt = Formation resistivity
Rm = Mud resistivity

Fracture aperture plot
 Apertures are calculated two
ways:
 As an average for each
fracture
(red dots, second to right)
 …And as a rolling mean
(blue-red cuve on right)

Fracture Interpretation products
 Fracture types on tadpole, image and stereonet
plots and in LAS / ASCII
 Fracture density plot and LAS file
 Fracture aperture plot and LAS file
 Fracture statistics like trace length, minimum
radius, height and so on in LAS file

Un-natural fractures
 Stress direction from borehole breakout
 Stress direction from induced fractures

Stress direction from breakout
 Measure shmin by
observing where
breakouts occur in
the wellbore
 Vertical and oriented
in the plane of shmin
 Borehole sloughs in
when the drilling fluid
pressure is less than
formation pressure
shmax
shmin
After: Mossop, Shetsen,
1994
Low Pf

shmax
shmin
 Breakout visible as
paired vertical
conductive smears
 Can pick the centre
of the breakouts to
get shmin

shmax
shmin
 Breakout visible as
paired vertical
conductive smears
of the breakouts to
get shmin
shmin shmin

Stress Magnitude from breakout
 Width of the breakout
is proportional to the
magnitude of shmin
 Width of the breakout
is also proportional to
the rock strength
 Need a database of
the strengths of
various formations to
measure shmin
Width

Stress direction - Induced fractures
 Measure shmax by
observing where
drilling induced
fractures occur
 Vertical and oriented
in the plane of shmax
 Borehole wall cracks
when drilling fluid
pressure is more
than formation
pressure
shmax
shmin
High Pf

Stress direction – Induced fractures
 Induced fracs. visible
as paired thin vertical
conductive cracks
of the induced
fractures to get shmax
shmax
shmin

Stress direction – Induced fractures
 Induced fracs. visible
as paired thin vertical
conductive cracks
of the induced
fractures to get shmax
shmax
shmin
shmaxshmax

Stress direction – Both types
shminshmaxshmax shmin

Stress Interpretation products
 Horizontal maximum stress direction on stereonet
 Stress features on tadpole plots and in LAS files
 Further analysis can be done for more in depth
geomechanical understanding

 Interpreted borehole image data should always be
distributed as digital files (Downloaded via FTP/website or
on DVD)
 Can be printed on paper
 Can be supplied in a format that can be loaded into other
software packages (a DLIS array of the processed image)
 Should be stored by the interpreter and logging contractor (if
different) in some permanent database (Recall, etc.)
 Ideally should become part of government databases once
off confidential
Outtroduction – data outputs

 The words Dipmeter and Borehole image log are pretty
loaded and can mean a lot of things
 Depending on the questions, these logs can provide a large
suite of answers about the nature and textures of bedding
and fracturing in the subsurface
 The products come in a wide and challenging variety of
plots, files and media
Conclusion

Dipmeter Data, Borehole Image Logs and Interpretation

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