dipmeter data, borehole image logs and interpretation
TRANSCRIPT
Dipmeter data, borehole image logs and interpretation
Kris VickermanMay 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 InterpretationStep 1: Processed Image
Borehole Image InterpretationStep 2: Beds
Borehole Image InterpretationStep 3: Large Fractures
Borehole Image InterpretationStep 4: Fine Fractures
Image interpretationDip “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
Outline
Basics of borehole image interpretation Bedding and structural dip analysis Natural fractures Stress features
Basic Structural Dip Analysis
Tadpole Plots Stereonet Plots Stick Plots True Stratigraphic Thickness Plots
Tadpole Plot
Stereonet
Stick Plot (cross-section)
Interpreted Stick Plot
True Stratigraphic Thickness Plot
True Stratigraphic Thickness Plot
Interpreted Stick 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 stereonetsUncluttered 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
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
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
Outline
Basics of borehole image interpretation Bedding and structural dip analysis Natural fractures Stress features
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
50 cm
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
Open Fractures
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
50 cm
*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
Healed Fractures
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
Shear features
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
50 cm
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
Outline
Basics of borehole image interpretation Bedding and structural dip analysis Natural fractures Stress features
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
s hm ax
s hm in
After: Mossop, Shetsen, 1994
Low Pf
Stress direction from breakout
s hm a x
s h m in
Breakout visible as paired vertical conductive smears
Can pick the centre of the breakouts to get shmin
Stress direction from breakout
s hm a x
s h m in
Breakout visible as paired vertical conductive smears
Can pick the centre 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
Un-natural fractures Stress direction from borehole breakout Stress direction from induced fractures
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
s hm ax
s hm in
High Pf
Stress direction – Induced fractures Induced fracs. visible
as paired thin vertical conductive cracks
Can pick the centre of the induced fractures to get shmax
s hm ax
s hm in
Stress direction – Induced fractures Induced fracs. visible
as paired thin vertical conductive cracks
Can pick the centre of the induced fractures to get shmax
s hm ax
s hm in
shmaxshmax
Stress direction – Both types
shminshmaxshmax shmin
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